Principles and Technologies of Flotation Machines [1 ed.] 9789811603310, 9789811603327, 9787502487638

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Springer Tracts in Mechanical Engineering

Zhengchang Shen

Principles and Technologies of Flotation Machines

Springer Tracts in Mechanical Engineering Series Editors Seung-Bok Choi, College of Engineering, Inha University, Incheon, Korea (Republic of) Haibin Duan, Beijing University of Aeronautics and Astronautics, Beijing, China Yili Fu, Harbin Institute of Technology, Harbin, China Carlos Guardiola, CMT-Motores Termicos, Polytechnic University of Valencia, Valencia, Spain Jian-Qiao Sun, University of California, Merced, CA, USA Young W. Kwon, Naval Postgraduate School, Monterey, CA, USA Francisco Cavas-Martínez, Departamento de Estructuras, Universidad Politécnica de Cartagena, Cartagena, Murcia, Spain Fakher Chaari, National School of Engineers of Sfax, Sfax, Tunisia

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Zhengchang Shen

Principles and Technologies of Flotation Machines

Zhengchang Shen Beijing General Research Institute of Mining and Metallurgy (BGRIMM) Beijing, China

ISSN 2195-9862 ISSN 2195-9870 (electronic) Springer Tracts in Mechanical Engineering ISBN 978-981-16-0331-0 ISBN 978-981-16-0332-7 (eBook) https://doi.org/10.1007/978-981-16-0332-7 Jointly published with Metallurgical Industry Press The print edition is not for sale in China (Mainland). Customers from China (Mainland) please order the print book from: Metallurgical Industry Press. ISBN of the Co-Publisher’s edition: 978-7-5024-8763-8 © Metallurgical Industry Press 2021 This work is subject to copyright. All rights are reserved by the Publishers, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publishers, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publishers nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publishers remain neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Preface

The history of mineral processing over the recent one hundred years has shown that the froth flotation is a predominant technology of mineral beneficiation, and nowadays it is widely used for materials separation, valuables recovery and wastes treatment in the industries of mining, petroleum, chemical engineering, etc. Flotation equipment plays vital roles in the practices of flotation processing. The development of flotation equipment made it possible for more and more traditional and nontraditional ores and materials to be treated by flotation process with high efficiency. Many books on flotation principles and flotation reagents have been published in the past century, however very few of them emphasizes on flotation equipment and the principles behind. The innovation on flotation machines should be brought to the forefront for the further improvement of flotation technology. The author of this book started the investigation of flotation equipment since the 1980s. This book has summarized the research findings achieved by the author, his research group as well as researchers around the world in the past decades. It starts with the fundamental principles of the physic phenomena such as hydrodynamics of slurry, aeration mechanism, bubble-particle interaction and so on helping readers to understand how a flotation machine works. The principles and approaches of flotation equipment design are then described and discussed in details. An emphasis is put on the scale-up design methods since it has been a trend to design more and more massive flotation machines. The critical structures, key components, typical applications and histories of the equipment from the major suppliers are introduced to provide readers with a whole picture. This book is suitable for teachers, researchers, R&D engineers, graduate students and professionals in the area of mineral processing and extractive metallurgy who wish to study flotation process knowledge and explore innovative technologies.

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Preface

At the time of publishing this book, I would like to express my gratitude to my group members and graduate students who have spent hundreds of days and nights verifying data, plotting charts, and editing contents. A special acknowledgment is given to Ms. Yinhe Xu who encouraged me on writing this book and undertook the proposal for the publication. Thanks also to all my colleagues who helped to complete this project. Beijing, China 2020

Zhengchang Shen

Contents

1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Brief Introduction of the Evolution History of Flotation Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.1 Flotation in Ancient Times . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.2 Flotation in Ancient Times . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Development Trend of Flotation Equipment . . . . . . . . . . . . . . . . . . 1.2.1 Classification of Flotation Machines . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 1 2 28 29 31

2

Basic Study of Flotation Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Collision Between Mineral Particles and Bubbles . . . . . . . . . . . . . 2.1.1 Collision Process Mechanism of Coarse Minerals . . . . . 2.1.2 Collision Process Mechanism of Fine Minerals . . . . . . . . 2.2 Adhesion Between Mineral Particles and Bubbles . . . . . . . . . . . . . 2.2.1 Adhesion of Coarse Minerals . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 Adhesion of Fine Minerals . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Detachment of Mineral Particles and Bubbles . . . . . . . . . . . . . . . . 2.4 Influence of Size on Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.1 Influence of Coarse Particles on Flotation . . . . . . . . . . . . 2.4.2 Influence of Fine Particles on Flotation . . . . . . . . . . . . . . 2.5 Dynamic Zoning of Flotation Machine . . . . . . . . . . . . . . . . . . . . . . 2.5.1 Agitating and Mixing Zone . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.2 Transport Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.3 Separation Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.4 Froth Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

33 33 37 37 39 41 41 42 45 45 47 49 49 50 53 56 57

3

Dynamic Characteristics and Evaluation of Flotation Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Characteristic Parameters and Evaluation of Flotation Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.1 Aeration (Suction) Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.2 Dispersion Degree of Air . . . . . . . . . . . . . . . . . . . . . . . . . .

59 59 59 65 vii

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3.1.3 Diameter and Distribution of Bubbles . . . . . . . . . . . . . . . . 3.1.4 Bubble Surface Area Flux . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.5 Gas Holdup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.6 Bubble-Loading Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.7 Pulp Resident Time Distribution . . . . . . . . . . . . . . . . . . . . 3.1.8 Short Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.9 Volume Utilization Coefficient . . . . . . . . . . . . . . . . . . . . . . 3.1.10 Pulp Suspension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.11 Critical Speed of Impeller . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.12 Spindle Power Consumption . . . . . . . . . . . . . . . . . . . . . . . 3.2 Performance Evaluation of Flotation Machines . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

67 68 68 70 71 74 75 76 77 79 81 82

4

Research on Fluid Dynamics Test of Flotation Machines . . . . . . . . . . 4.1 Flow State Test of Flotation Machines . . . . . . . . . . . . . . . . . . . . . . . 4.1.1 LDV Testing Technology . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.2 PIV Testing Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Pulp Flow Test Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Residence Time Distribution Test . . . . . . . . . . . . . . . . . . . 4.2.2 Circulation Volume and Flow Velocity Test . . . . . . . . . . . 4.2.3 Suspension Capacity Test . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Bubbles and Particles Testing Technology . . . . . . . . . . . . . . . . . . . 4.4 PEPT Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Spindle Force Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

85 85 86 87 95 95 102 108 110 117 122 126

5

CFD Simulation Research on Fluid Dynamics of Flotation Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Summary of CFD Simulation Research of Flotation Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1 Significance of CFD Simulation of Flotation Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.2 Research Objective of CFD Simulation of Flotation Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.3 Problems Existing in CFD Simulation of Flotation Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.4 Prospect on CFD Simulation of Flotation Machines . . . . 5.2 CFD Simulation Research of Flotation Machines . . . . . . . . . . . . . 5.2.1 CFD Mathematical Model of Flotation Machines . . . . . . 5.2.2 CFD Simulation Research of Flotation Machines Under the Single-Phase Condition . . . . . . . . . . . . . . . . . . . 5.2.3 Flow Field of the Flotation Machine Under the Two-Phase System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.4 Flow Field of the Flotation Machine Under the Two-Phase System . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

127 127 127 128 132 133 135 135 145 154 161

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5.2.5

Optimization of Flotation Machines Based on CFD Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 6

7

8

Flotation Machine Upsizing Method and Technology . . . . . . . . . . . . . 6.1 Flotation Machine Upsizing Process . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Flotation Machine Upsizing Technology . . . . . . . . . . . . . . . . . . . . . 6.2.1 TankCell Flotation Machine . . . . . . . . . . . . . . . . . . . . . . . . 6.2.2 Wemco Flotation Machine . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 BGRIMM Flotation Machine Upsizing Technology . . . . . . . . . . . 6.3.1 Difficulties of Flotation Machine Upsizing Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.2 BGRIMM Flotation Machine Upsizing Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.3 Key Structure Design of BGRIMM Large Flotation Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.4 Rapid BGRIMM Flotation Machine Upsizing Driven by CFD Technology . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

179 180 181 182 185 188

BGRIMM Mechanical Agitation Flotation Machine . . . . . . . . . . . . . . 7.1 SF, BF and GF Mechanical Agitation Flotation Machines . . . . . . 7.1.1 SF Flotation Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1.2 BF Flotation Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1.3 GF Flotation Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 JJF Mechanical Agitation Flotation Machine . . . . . . . . . . . . . . . . . 7.2.1 Working Principle and Key Structures . . . . . . . . . . . . . . . 7.2.2 Analysis of Dynamic Performance of the JJF Flotation Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

213 214 214 216 226 238 238

BGRIMM Pneumatic Mechanical Agitation Flotation Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 KYF Pneumatic Mechanical Agitation Flotation Machine . . . . . . 8.1.1 Working Principle and Key Structures of KYF Flotation Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1.2 Fluid Dynamics Research in KYF Flotation Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1.3 Performance and Application of the KYF Flotation Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 XCF Automatic Suction Pneumatic Mechanical Agitation Flotation Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.1 Working Principle and Key Structures of XCF Flotation Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.2 Fluid Dynamics Research in XCF Flotation Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

190 191 201 206 210

242 262 263 264 264 270 276 300 301 305

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8.2.3

Performance and Application of the XCF Flotation Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 9

BGRIMM Wide-Size-Fraction Flotation Machine . . . . . . . . . . . . . . . . 9.1 Technology of Wide-Size-Fraction Flotation Machine . . . . . . . . . 9.1.1 Design Principle of Wide-Size-Fraction Flotation Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1.2 Working Principle and Structure of Wide-Size-Fraction Flotation Machine . . . . . . . . . . . . 9.2 CLF Air-Forced Wide-Size-Fraction Flotation Machine . . . . . . . . 9.2.1 Working Principle and Key Structures . . . . . . . . . . . . . . . 9.2.2 Performance of CLF-8 Flotation Machine . . . . . . . . . . . . 9.2.3 Performance of CLF-40 Flotation Machine . . . . . . . . . . . 9.3 CGF Automatic Suction Wide-Size-Fraction Flotation Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3.1 Key Structure and Working Principle . . . . . . . . . . . . . . . . 9.3.2 Dynamic Performance of CGF Flotation Machine . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10 Process Control System of Flotation Machines . . . . . . . . . . . . . . . . . . . 10.1 Development and Current Situation of Flotation Machine Control System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1.1 Early Development of Flotation Machine Process Control Technology at Home and Abroad . . . . . . . . . . . . 10.1.2 Process Control Situation of Flotation Machines at Home and Abroad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2 Pulp Level Control of Flotation Machines . . . . . . . . . . . . . . . . . . . . 10.2.1 Level Detection Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2.2 Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2.3 Pulp Level Control Strategies . . . . . . . . . . . . . . . . . . . . . . . 10.2.4 Industrial Application of the Level Control System of BFLC Flotation Machine . . . . . . . . . . . . . . . . . 10.3 Aeration Rate Control of Flotation Machines . . . . . . . . . . . . . . . . . 10.3.1 Aeration Rate Detection Device and Control Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3.2 Automatic Control Strategy for Aeration Rate . . . . . . . . . 10.3.3 Industrial Application of the Aeration Rate Control System of BFLC Flotation Machine . . . . . . . . . . 10.4 Froth Image Analysis of Flotation Machines . . . . . . . . . . . . . . . . . 10.4.1 Flotation Froth Image Equipment and Implementation Method . . . . . . . . . . . . . . . . . . . . . . . . 10.4.2 Static and Dynamic Characteristic Detection Technology of Flotation Froth . . . . . . . . . . . . . . . . . . . . . . 10.4.3 Application of Froth Image Analysis in the Flotation Process Control System . . . . . . . . . . . . . .

317 319 319 321 325 326 330 332 337 337 341 349 351 351 352 354 355 357 359 361 366 371 371 374 375 376 377 378 388

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10.5 Process Control Problems and Development Trend of Flotation Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.5.1 Process Control Problems of Flotation Machines . . . . . . 10.5.2 Development Trend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Model Selection and Design of Flotation Machines . . . . . . . . . . . . . . . 11.1 Technical Characteristics of Flotation Machines . . . . . . . . . . . . . . 11.2 Preliminary Determination of Flotation Machine Type and Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Selection for the Specification of Flotation Machines . . . . . . . . . . 11.3.1 Calculation of Flotation Pulp Volume . . . . . . . . . . . . . . . . 11.3.2 Determination of Flotation Time of Operations . . . . . . . . 11.3.3 Calculation and Determination of Tank Quantity of Flotation Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3.4 Calculation Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.4 Configuration of Flotation Machines . . . . . . . . . . . . . . . . . . . . . . . . 11.4.1 Horizontal Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . 11.4.2 Stepwise Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.4.3 Selection of Two Configuration Methods . . . . . . . . . . . . . 11.4.4 Selection Cases of Configuration Methods . . . . . . . . . . . . 11.5 Selection of Supporting Equipment . . . . . . . . . . . . . . . . . . . . . . . . . 11.5.1 Flotation Process Control System . . . . . . . . . . . . . . . . . . . 11.5.2 Supporting Equipment for Process . . . . . . . . . . . . . . . . . . 11.6 Fuzzy Comprehensive Evaluation of Flotation Machine Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.6.1 Process of Fuzzy Comprehensive Evaluation . . . . . . . . . . 11.6.2 Factor Sets and Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.6.3 Determination of Weight Coefficient . . . . . . . . . . . . . . . . . 11.6.4 Fuzzy Conclusion Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.7 Model Selection of Flotation Machines of CBR . . . . . . . . . . . . . . . 11.7.1 Design and Selection of CBR . . . . . . . . . . . . . . . . . . . . . . . 11.7.2 Example Expression and Example Retrieval . . . . . . . . . . 11.8 Model Selection of Flotation Machines Based on JK Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.8.1 Flotation Process Simulation Software of JKSimFloat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.8.2 Flotation Process Simulation Software of HSC Sim . . . . 11.8.3 Flotation Process Simulation Software of USIM PAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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390 390 391 393 395 395 397 398 398 398 399 401 404 404 409 413 414 414 414 416 418 419 419 419 420 423 423 424 428 428 430 431 433

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12 Application Examples of Flotation Machines . . . . . . . . . . . . . . . . . . . . . 12.1 Applications of Flotation Machines for Non-Ferrous Metal Ores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1.1 Application of Flotation Machines for Bauxite . . . . . . . . 12.1.2 Application of Flotation Machines for Copper Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1.3 Application of Flotation Machines for Lead–zinc Ore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1.4 Application of Flotation Machines for Nickel Ore . . . . . 12.1.5 Application of Flotation Machines for Molybdenum Ore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.2 Applications of Flotation Machines for Ferrous Metal Ores . . . . . 12.2.1 Application of Flotation Machines in JISCO’s Concentrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.2.2 Application of Flotation Machines in the Concentrator of Daye Iron Mine . . . . . . . . . . . . . . . 12.2.3 Application of Flotation Machines in Baotou Iron and Steel Company’s Concentrator . . . . . . . . . . . . . . . . . . 12.2.4 Application of Flotation Machines in Jianshan Iron Ore Mine of Taiyuan Iron & Steel (Group) Co., Ltd. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.2.5 Application of Flotation Machines in Anshan Iron and Steel Group Corporation . . . . . . . . . . . . . . . . . . . . . . . 12.2.6 Application of Flotation Machines in Shougang Peru S.A.A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3 Application of Flotation Machines in the Separation of Rare and Precious Metal Ores . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3.1 Application of Flotation Machines for Gold Ore Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3.2 Application of Flotation Machines in Lithium Ore Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.4 Applications of Flotation Machines for Non-Metal Ores . . . . . . . 12.4.1 Application of Flotation Machines for Potassic Salt Ore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.4.2 Application of Flotation Machines in Phosphorite Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.4.3 Application of Flotation Machines in the 4.5 Million t/a Project of Kunyang Phosphate Mine . . . . . . . 12.4.4 Application of Flotation Machines in Silica Sand Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.4.5 Application of Flotation Machines in Fluorite Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.4.6 Application of Flotation Machines in Graphite Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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12.5 Application of Flotation Machines in Reconcentration of Tailings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.5.1 Application of Flotation Machines in Tailings Concentrator of Dexing Copper Mine . . . . . . . . . . . . . . . . 12.5.2 Application of Flotation Machines at Sizhou Concentrator of Dexing Copper Mine . . . . . . . . . . . . . . . . 12.5.3 Application of Flotation Machines in Chengde Shuangluan Jianlong Mining Co., Ltd . . . . . . . . . . . . . . . . 12.6 Application of Flotation Machines in Copper Smelting Slag . . . . 12.6.1 Application of Flotation Machines at Guixi Smelter of Jiangxi Copper Corporation Limited . . . . . . . 12.6.2 Application of Flotation Machines in PASAR . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Chapter 1

Introduction

Earth contains abundant mineral resources that normally need to be mined and extracted before further refining. Mineral processing, also known as mineral dressing or ore dressing, is a process that separates useful minerals from gangue materials by means of various kinds of technology and equipment to achieve relative enriched valuable minerals. Flotation was explicitly proposed as a mineral processing method at the end of the nineteenth century. In 1904, the first type of flotation equipment was invented and adopted by industrial application in Australia [1]. The first flotation plant in China, Qingchengzi Lead–Zinc Flotation Plant in Liaoning Province, was built in 1917. Over the past 100 years, numerous efforts have been made by academia and industry to improve the technology of flotation equipment which has gradually become diversified, serialized, enlarged and automated. At present, flotation equipment has been widely applied in mining, pulp and paper, agriculture, food, medicine, environmental protection and other industries. The evolution history, development trend and classification of flotation machine technology is briefly reviewed in this chapter.

1.1 Brief Introduction of the Evolution History of Flotation Machine 1.1.1 Flotation in Ancient Times Flotation was applied in the medical and mining industries as early as the Ming Dynasty. In the medical field, the natural hydrophobicity of mineral surface is used to purify mineral drugs such as cinnabar and talc so that fine mineral mixture floats on the water surface and is separated from sinking gangue. As recorded in the Compendium of Materia Medica written by Li Shizhen in the Ming Dynasty © Metallurgical Industry Press 2021 Z. Shen, Principles and Technologies of Flotation Machines, Springer Tracts in Mechanical Engineering, https://doi.org/10.1007/978-981-16-0332-7_1

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1 Introduction

and other classical ancient medical books: The course of processing of red ocher, mica, etc., (i.e. hematite) is as follows: “Porphyrize the hematite, wash with the wax water for several times, and remove the red things like the thin cloud on the water surface”; the processing method of realgar is as follows: “grind the realgar, liquorice, gynura bicolor, elephantopus scaber, and blue-edge flowers, put them in the crucible and heat for some time, filter out, smash into powder, grind while adding water, remove the black, dry and grind for use”; and the processing method of mica is as follows: “mix 0.5 kg of mica with 1 kg of elephantopus scaber, gynura bicolor, raw licorice, and rehmannia juice, place them in the porcelain crucible, add two kilograms of water and heat for seven days and nights, add water continuously and agitate. Remove the floating things useless and harmful, and repeat for three times” [2]. In the course of washing and processing of gold and silver, the natural hydrophobicity and lipophilicity of gold powder are used to scrape gold powder floating on the water surface with a goose feather dipped in oil so that the gold powder is separated from hydrophilic impurities such as dust. As recorded in the book Tiangong Kaiwu, a process of recovery of gold and silver is that “scrape and incinerate the gold foil sticks, drip a few drops of boiled oil into the ash, and then burn in the stove after washing, to gain all the gold” [2]. Agricola Georgius (1494–1555), a German mineralogist known as the father of mineralogy, discussed the process of mining and metal smelting in his book De Re Metallica in detail. There were also evidences about mineral collection with oil and asphalt in Ancient Greece and Europe: The phenomenon of the rise of gas adhering to solid particles to water surface had been known in the eighteenth century. Early in the nineteenth century, people used air bubbles generated by reaction with carbonate minerals through gasification (boiled pulp) or acidification for graphite flotation. Special flotation equipment was not available until the mid-nineteenth century.

1.1.2 Flotation in Ancient Times In the late nineteenth century, the resources of coarse lead, zinc, copper and sulfide ores that could be treated by gravity separation gradually decreased due to the increasing demand for metals. Flotation was explicitly proposed as a mineral separation method for the purpose of separating fine ores. In 1903, Elmore proposed a mixed oil flotation process deemed as the starting point of modern flotation. Subsequently, rapid development of the flotation technology was achieved, and the flotation equipment was developed intensively. In 1909, GooverT made the first multi-tank impeller agitator for froth flotation. In 1913, John Callow invented a pneumatic flotation machine and Robert Towne and Frederick Flinn invented a pneumatic flotation column. In 1914, Callow G obtained a patent for flotation equipment that sprayed air from a porous false bottom of a tank. In 1915, Durrel made a prototype of jet flotation machine [3]. In the 1920s, various types of mechanical agitation flotation machines and pneumatic mechanical agitation flotation machines were developed and applied for industrial production in order to meet the copper demand of the

1.1 Brief Introduction of the Evolution History of Flotation Machine

3

booming power industry at that time. Since 1930, the development of new flotation machines had been stagnated for a time as the market demand for copper metal was significantly reduced. At the end of World War II in 1945, the mechanical agitation flotation machine became the most widely used flotation machine at that time while the pneumatic flotation machines were still in use. At that time, hundreds of flotation tanks with a volume of about 2 m3 were used in a large concentrator at high costs of construction, management and operation. For example, the Morenci concentrator in the United States was the largest concentrator in 1942, with a processing capacity of 40,800 tons/day. The number of Fagergren flotation machines in this plant with the single tank volume of 1.7 m3 reached up to 432. In 1960, the price of copper metal rose again, the shadow from economic depression and wars was gradually dispersed and flotation equipment began to develop towards upsizing. A few years later, the successful application of the first largescale mechanical agitation flotation machine in Bougainville Island announced the commencement of upsizing of flotation machines. Since the 1970s, in addition to mechanical agitation flotation machines, pneumatic flotation machines, flotation columns and other equipment have also been constantly innovating in structures and materials, gradually recognized by the market, and industrially applied on a large scale. China started late in the research of flotation equipment and did not begin to develop flotation machines until the mid-1950s. In the 1970s, flotation machines with independent intellectual property rights emerged, and the pneumatic mechanical agitation flotation machine, coarse-size-fraction flotation machine, skim-air flotation machine and other types of flotation machines were developed successively, which could meet the production requirements of different concentrators. Since 1980, despite the continuous deterioration of ore properties, the sustained and rapid growth of the world economy and domestic economy has promoted the continuous progress of theoretical research on flotation and flotation equipment technology, and significant progress has been made, especially in the research on upsizing, diversification, automation, etc., of flotation equipment. The characteristics of flotation machines at home and abroad are described herein by two stages with flotation machines flourishing again in 1960 as the cut-off point according to the development history of flotation equipment.

1.1.2.1

Before 1960

From 1903 (when the concept of modern flotation was proposed) to 1960, the development of flotation process achieved remarkable progress, while the flotation equipment was also developed rapidly, and various types of flotation equipment constantly emerged. However, many kinds of flotation equipment were quickly eliminated by the market since the understanding of flotation process and flotation equipment was not deep enough at that time. Most of the flotation equipment in this period were small mechanical agitation flotation machines and pneumatic flotation machines, and the flotation machines most widely used at that time were Minerals Separation flotation

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1 Introduction

machine, Callow flotation machine, Fahrenwald Denver flotation machine, Fagergren WEMCO flotation machine, Galigher Agitair flotation machine, MexaHoop flotation machine, etc. (1)

Minerals separation flotation machine

Minerals Separation, the earliest flotation equipment manufacturer, became a technology leader in the flotation industry in 1910. So far, Minerals Separation has produced three types of flotation machines [4], including the first generation of flotation machine for which a patent application was filed by Hebbard in 1913 is shown in Fig. 1.1. The sub-A flotation machine for which a patent application was filed by Wilkinson and Littleford in 1926 is shown in Fig. 1.2. The design of the tank body of this flotation machine has become the standard design for subsequent tank bodies of flotation machines; the countercurrent flotation machine invented by Taggart is shown in Fig. 1.3. The design of this flotation machine is similar to that of the Denver flotation machine. The difference lies in that the froth tanks are separated by upper open baffles to facilitate countercurrent flow of pulp at this point and circulation of downstream pulp through the gap in the false bottom. The design theory of this Fig. 1.1 The standard flotation machine of the Minerals Separation Company

1.1 Brief Introduction of the Evolution History of Flotation Machine

Fig. 1.2 The sub-A flotation machine of the Mienrals Separation Company

Fig. 1.3 Countcurrent flotation machine of the Minerals Separation Company

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1 Introduction

machine is that the suction capacity of the impeller is much greater than the ore feeding speed, which ensures that at least a part of the excess suction capacity of the impeller is effectively used as the motive power for the pulp countercurrent. The Minerals Separation flotation machine was still applied to major concentrators until the 1960s. For example, it was used for sulphur removal at the concentrator of Bancroft Mines’ Konkola in 1963 [5] and for concentration at the Silver Summit concentrator in North Edward in 1966 [6]. This is enough to prove the superiority of this type of flotation machine at that time. (2)

Callow flotation machine

The Callow flotation machine is a kind of pneumatic flotation machine invented by John Callow. The first Callow flotation machine was successfully put into service at the Morning concentrator in 1914 and patented in 1915. Its prototype is shown in Fig. 1.4 [7, 8]. A perforated distributor at the bottom of the tank body generates pressurized air. The material of the perforated distributor may be perforated brick or even cocoa matting. The ore feeding speed must be moderate so that solid particles remain suspended in the tank body. This flotation machine has the disadvantage that the bottom perforated distributor is easily plugged, which makes the operation and maintenance of the Callow flotation machine very complicated. Interestingly, a tailing container with the cone valve and a level control mechanism are described in the patent, which is amazingly consistent with the characteristics of modern flotation machines.

Fig. 1.4 Callow’s forced-air flotation machine

1.1 Brief Introduction of the Evolution History of Flotation Machine

(3)

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Fahrenwald Denver flotation machine

Founded in 1927, Denver Equipment Co., Ltd. produced Sub-A flotation machine, the first flotation machine. The equipment was designed based on Arthur W Fahrenwald’s patent in 1922 [9], so the Denver flotation machine was also called Fahrenwald Denver flotation machine in the early stage and was improved several times later [10, 11]. The structural principle of Denver Sub-A flotation machine is shown in Fig. 1.5, which is characterized in that: (1) As the impeller rotates, air is sucked into the impeller through a vertical pipe sheathed on the impeller shaft, and current is stabilized via a four-blade stator after being mixed with the pulp; (2) Greater circulation rate is realized by punching a hole in the hollow spindle; (3) The froth area is separated from the mixing area of air and pulp through a baffle plate. The machine is equipped with three different types of impellers: Conical disc-shaped impeller, retracted disc-shaped impeller and multi-wing disc-shaped impeller, which are available for the treatment of coarse high-concentration pulp, general operation and roughing and scavenging, respectively.

Fig. 1.5 Denver flotation machine

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(4)

1 Introduction

Fagergren WEMCO flotation machine

The Fagergren WEMCO flotation machine invented in 1920 is a mechanical agitation flotation machine. At that time, the agitation mechanism of this flotation machine was transverse, with its structure shown in Fig. 1.6. The machine is equipped with a transverse rotation mechanism with a speed of 200 r/min. Air is sucked into the spindle mechanism via an air supply duct 31 through rotation of the impellers on the agitation mechanism, and forced to pass through the space between transverse baffle plates. Pulp entering a feed pipe 35, is mixed with air in a cavity inside the spindle mechanism, and then mineralized froth floats to the tank surface and overflows into froth tank 37 [12]. In 1934, the agitation structure of the machine was changed into a vertically placed structure as shown in Fig. 1.7, with metal impellers and stators. Annular discs were arranged at the upper and lower ends of each impeller, vertical round bars or tubes were installed at the edges between two discs, and their sizes had a great influence on the performance of the flotation machine. The stator was also surrounded by round

Fig. 1.6 Fagergren flotation machine in the 1920s

Fig. 1.7 Fagergren flotation machine in the 1930s

1.1 Brief Introduction of the Evolution History of Flotation Machine

9

bars or tubes. The bending direction of the disc-shaped blade on the impeller shall ensure that air is sucked in when the impeller rotates, while the lower disc-shaped blade can suck the pulp from the central hole at the tank bottom into the impeller. After being mixed in the impellers, air and pulp are sprayed outward after current stabilization through the clearance between the stator and the round bar so that mineral-laden bubbles are dispersed into the tank body. This design is also known as “squirrel cage” [13]. The Fagergren WEMCO flotation machine is characterized in that (1) Because of the special design of stators and impellers, the machine has high bubble mineralization rate and large circulation rate of pulp, as well as higher flotation efficiency. This flotation machine has a higher flotation rate and larger processing capacity than other flotation machines of equal volume. (2) The high flotation performance of this flotation machine brings the low energy consumption for processing every ton of ores. The shallow froth tank of the flotation machine also makes production energy consumption much lower. (3) The operation and maintenance costs are lower. In view of its high flotation performance and low energy consumption, the operation and maintenance costs of this flotation machine are very low. Also, all the wearable parts of this flotation machine are covered with high-quality wear-resistant rubber, making their service life longer. (4) Simple structure and convenient installation. This flotation machine is a spindle component which can be lifted out as a whole. The disadvantage of the machine lies in that it needs to be strictly operated to maintain the stability of the liquid level in the tank body because the aeration rate will be reduced by two-thirds once the pulp level rises by 100 mm, thus affecting production. (5)

Agitair flotation machine

The Agitair flotation machine is a kind of pneumatic mechanical agitation flotation machine invented by Lionel Booth, and the structure of the first generation of Agitair flotation machine is shown in Fig. 1.8. As air is taken from the bottom of the tank body into the machine, the air intake pipe is easily plugged, which is inconvenient for operation [14]. The design was improved in the early 1940s, a hollow shaft was added to the upper part of the impeller mechanism, and the air intake position was arranged on the upper part of the flotation machine. Compared with other types of flotation machines at that time, this flotation machine has separate air intake for each tank body, separate froth overflow and little mutual influence between tanks, thus meeting the flotation requirements for various ores, mineral particles with high lime contents or viscous pulp. This flotation machine has higher recovery rate and less power consumption. (6)

MexaHoop flotation machine

The MexaHoop flotation machine was designed by the Mineral separation, Design & Research Institute of the Soviet Union, with its structure similar to that of the Fagergren WEMCO flotation machine. As the impellers rotate, air is sucked through a conduit and mixed with the pulp between the impellers and the cover plate and then the mixture is thrown to the tank body. A feeding pipe and a middling pipe

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1 Introduction

Fig. 1.8 Agitair flotation machine

may be installed at the lower part of the air intake pipe. The pulp passes through circulation holes and small holes in the cover plate to form the internal circulation. Compared with the Fagergren WEMCO flotation machine, the MexaHoop flotation machine is improved in the following aspects: (1) Due to the installation of guide vane on the cover plate, pulp is thrown out in a more stable manner, the head loss is low, and the suction rate of the impellers is improved; (2) A steady flow plate is installed circumferentially at the lower part of the tank body to prevent eddy current generated by the pulp. This machine has the disadvantages that: The impeller rotates at a high speed, the impeller stator is seriously worn, and the power consumption is high; Meanwhile, as the wear clearance of impeller stator is enlarged, the suction rate is decreased obviously, and uneven wear may lead to fluctuation of the pulp level.

1.1.2.2

After 1960

As the price of copper metal rose again and the shadow of economic depression and wars was gradually dispersed in 1960, the research and development of flotation equipment were revived, established manufacturers of flotation equipment launched the research on the new structure and upsizing of flotation machines in succession, and the representative flotation machines included the Denver DR flotation machine developed by Denver, WEMCO1+1 flotation machine developed by WEMCO, etc. New flotation equipment manufacturers such as OUTUKUMPUM and Beijing General Research Institute of Mining & Metallurgy (BGRIMM), etc. have also been gradually recognized by the market for their unique designs.

1.1 Brief Introduction of the Evolution History of Flotation Machine

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Fig. 1.9 Denver DR flotation machine

(1)

Denver

In the early 1960s, Arthur Daman Jr and Leland Logue designed the Denver DR flotation machine in order to increase the circulation rate of tank body and the bubble mineralization rate [15]. Figure 1.9 is a drawing attached to the patent. The most distinguishing characteristic of the DR flotation machine in contrast with the previous Denver flotation machine lies in that a pulp circulating pipe extending from the impeller to the top of the tank body is designed so that the pulp is led into the circulating pipe rather than flowing directly to the impeller area, making the pulp and air mix in the circulating pipe before entering the impeller area. The machine has the characteristics that (1) The pulp is circulated vertically, even in an unclosed tank body. This can effectively prevent sediment in the tank; (2) Bubbles and pulp are mixed vertically; (3) High suspension of mineral particles and effective bubble mineralization are still maintained under the conditions of low power motor drive and low impeller speed. The first DR flotation machine was installed and applied in Endako Group’s concentrators in Colombia and Canada in 1964. Since then, Denver has carefully expanded its original flotation tank to design a large flotation machine. The main consideration from the very beginning of design is whether the spindle mechanism can produce enough kinetic energy to work with the expanded tank body. Denver originally designed the large flotation machine by connecting two small tank bodies

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1 Introduction

together and removing the intermediate spacer. The company’s first generation of large flotation machine was named Denver DR 600 (17 m3 ), which was made by splicing two Denver DR 300 tank bodies back to back, so there were two spindle mechanisms in one tank body. In 1967, a new molybdenum concentrator of DR 600 s was installed in the Endako mining area, Columbia. In 1972, 108 Denver DR 600 flotation machines were installed on Bougainville Island as the coarse particle concentration equipment. The processing capacity of the flotation production line reached up to 90,000 t/d. Denver was highly appreciated in the industry as a flotation machine manufacturer as a result of the two successful applications. A few years later, Denver was acquired by JOY, and its flotation machine production business moved towards recession. Most of the mineral separation technologies developed by Denver, including flotation machine technology, were sold to Sala by JOY and Sala was renamed Svedala after reorganization. The Sub-A flotation machine and DR flotation machine in Svedala’s product catalog in 1996 were almost entirely the same as those designed by Denver in those years without any change. During the next few mergers and acquisitions, Svedala transferred these flotation technologies to Metso. Currently, the Metso flotation machine is the successor of Denver flotation machine. (2)

Metso

Metso’s RSCTM (Reactor Cell System) flotation machine is a kind of pneumatic agitation flotation machine with the maximum single tank volume of up to 200 m3 , and its structure is shown in Fig. 1.10. Equipped with a deep blade mechanism, it Fig. 1.10 Metso’s RCS flotation machine

1.1 Brief Introduction of the Evolution History of Flotation Machine

13

can not only forcefully throw the pulp radially towards the tank wall, but also can produce a strong pulp flow that can flow back to a portion below the impeller, thus reducing the sediment in tank. This flotation machine is characterized in that (1) The solid mineral particles in the lower area of the tank body are well suspended and transported, resulting in multiple contacts and collisions between mineral particles and bubbles and high recovery probability; (2) The turbulence at the upper part of the tank body is small to prevent coarser particles from falling off; (3) The liquid level is stable, and the probability of particle entrainment is low. (3)

FLSmidth

FLSmidth has two types of machines, namely WEMCO and Dorr-Oliver. In 1964, WEMCO was acquired by Arthur G McKee; Envirotech acquired WEMCO and EIMOCO Mining Equipment Co. Envirotech was subsequently acquired by Baker Hughes which transferred WEMCO’s production line of mineral processing equipment to EIMCO, Salt Lake City. In 2007, EIMCO was indirectly acquired by FLSmidth. The representative products of WEMCO flotation machine include WEMCO1+1 flotation machine and WEMCO SmartCell™ flotation machine. 1.

WEMCO1+1 flotation machine

After 1960, WEMCO improved its technology due to decreasing market share of WEMCO Fagergren flotation machines. In 1969, WEMCO successfully developed the WEMCO1+1 flotation machine, as shown in Fig. 1.11. Compared with the Fagergren WEMCO flotation machine, this equipment: (1) retains the false bottom, the tube for guiding airflow into the impellers and the slope of the Fagergren WEMCO flotation machine; and (2) changes the squirrel cage impellers and stators of the Fagergren WEMCO flotation machine to blade impellers with star-shaped sections. The stators have elliptical holes. The steel structure surfaces of both impellers and stators are covered with rubber or similar materials. An optional protective cover is arranged above the stator for reinforcing the mineralized froth flow of the flotation machine. 2.

WEMCO Smart Cell™ flotation machine

The Smart Cell flotation machine is a kind of mechanical agitation flotation machine improved on the basis of WEMCO1+1 flotation machine. As the impeller rotates, ambient air is sucked in via the vertical pipe, dispersed into fine bubbles through the disperser cover and uniformly distributed throughout the pulp. The rotation mechanism is located in the middle of the tank body so that the wear of the impeller and the disperser cover is reduced, and the machine can be started immediately after shutdown. The impeller of symmetrical structure can run clockwise or counterclockwise, or run upside down, having a long service life [16–19]. In 1996, WEMCO Smart Cell™ flotation machine was tested in a copper mine, and then Kennecott Copper Corp. purchased the copyright of this flotation machine. The flotation machine is characterized by a cylindrical tank body with a volume of

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1 Introduction

Fig. 1.11 WEMCO1+1 flotation machine

125 m3 . The design of the spindle mechanism is a typical 1+1-type spindle design, but the tube line at the bottom of the spindle mechanism is expanded to increase the suction volume of pulp. In 2003, FLSmidth installed the first Smart Cell™ flotation machine with a capacity of 257 m3 . The design of this flotation machine was based on fluid dynamics analysis and Computational Fluid Dynamics (CFD). Since 2004, FL Smidth has cooperated with the Center for Advanced Spatial Technologies (CAST) in in-depth research on CFD. Based on the results of CFD model analysis, FL Smidth designed the large Super Cell™ flotation machine whose volume reached up to 300 m3 . In 2009, two Super Cell™ flotation machines were tested in the copper concentrator of Rio Tinto [20]. In 2012, FLSmidth produced Supercell, a larger flotation machine with a volume of 660 m3 . 3.

Dorr-Oliver pneumatic flotation machine

The Dorr-Oliver flotation machine is a kind of pneumatic mechanical agitation flotation machine which has been developed rapidly in FLSmidth in the last few years. The maximum single tank volume currently has reached 660 m3 . The structure diagram is shown in Fig. 1.12. The blade properties of the impellers of this machine are generally similar to the blade properties of the Outokumpu flotation machine. Therefore,

1.1 Brief Introduction of the Evolution History of Flotation Machine

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Fig. 1.12 Dorr-Oliver flotation machine

its pulp circulation form is basically the same as that of the Outokumpu flotation machine. Its impeller is surrounded by short stator blades that are suspended radially from the circular top to the ground. The air released from the hollow shaft is directly supplied into the pumping guideway between the rotor blades, the pulp flows in from below and the mixture is directly ejected from the upper part of the rotor. (4)

Outotec

Outotec was separated from its parent company Outokumpu in 2016. Outokumpu was not engaged in the research of flotation equipment until 1958. In 1959, 1.5 and 3 m3 OKKO flotation machines were first put into service in the Kolatahti concentrator [21]. Flotation has always been the research priority of Outokumpu whose Technical Department has been developing a mechanism that can effectively mix air and pulp and designing new tank bodies and froth treatment systems. Outokumpu has successfully applied its flotation technology to its concentrators all over the world and met the needs of various mineral processing applications. They focused on the characteristics of each flotation operation, and developed the flash flotation machine for grinding circuit, OF flotation machine for roughing and scavenging and HG flotation machine for concentration [22]. The characteristics of various flotation machines developed by the company are described as follows: 1.

Skim-air flash flotation machine

The flash flotation machine applies to grinding-classification circuit: Cyclone grit is fed. The flotation concentrates are of high grade and mixed into the final concentrate, and flotation tailings are returned to the ball mill. The flash flotation machine is characterized in that: (1) Liberated coarse minerals are recovered in time so that overgrinding of useful minerals is reduced, and the cost of ore grinding is decreased; (2) The particles of concentrates are coarse, which facilitates subsequent dewatering operation.

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1 Introduction

OF flotation machine

As the result of Outokumpu’s long-term research, the OF flotation machine has the advantages of small floor area, small equipment foundation, etc., as compared with conventional flotation machines. It is characterized in that (1) The tank body is shaped like a funnel without dead angle, which is conducive to froth flow to the froth tank; (2) The tank body is light in weight to allow self-support; (3) With different impeller stator systems, it can be used for separation of coarse or fine particles; (4) The conical tank body reduces the surface area of the pulp, allowing the formation of a thick froth layer and easy adjustment of thickness. 3.

HG flotation machine

In 1987, Outokumpu developed the HG flotation machine in order to improve the grade of concentrates [23]. Froth directly flows into the froth tank so that high-grade froth is collected quickly with a high rate of recovery. This flotation machine has the characteristics as follows: (1) Concentrates are not only high in grade but also are clean; (2) The effective mixing of flocculates is broken to achieve effective recovery; (3) The circulating load is small, and the process is simple. 4.

Tank Cell flotation machine

Due to more and more frequent use of the flotation column, Outokumpu simulated the structure of the flotation column and added a mechanical injection device (Tank Cell flotation machine) to it. In 1983, the first Tank Cell flotation machine with a capacity of 60 m3 was installed and used in the Pyhasalmi Concentrator. In 1995, the first Tank Cell flotation machine with a capacity of 100 m3 was installed and used in the Los Colorados Concentrator of Chile’s Escondida Mine. In 1997, Tank Cell flotation machine with a capacity of 160 m3 was firstly applied in Chuquicamada Concentrator in Chile. In 2002, the first Tank Cell-200 flotation machine was installed and used in the Century mine in Australia. In 2007, Outokumpu developed the world’s largest flotation machine with a single tank volume of 300 m3 , and this flotation machine was installed and used in the Macaes Gold Mine in New Zealand. In January 2014, the first TankCell e500 flotation machine was applied in the First Quantum Minerals’ Kevitsa mine in Finland. The Tank Cell flotation machine is the most successful and widely applied flotation machine developed by Outokumpu. At present, it is widely used by concentrating mills around the world in roughing, scavenging and concentration operations [24, 25]. TankCell e630, a flotation machine with a maximum volume of 630 m3 , was successfully developed in October 2014. The Tank Cell flotation machine is a kind of pneumatic mechanical agitation flotation machine. Its structure is shown in Fig. 1.13. The tank body is cylindrical. The air enters the impeller chamber through the hollow shaft. The pulp enters the tank body from the lateral pulp circulation hole in the lower part of the tank body, and the froth flows out of the overflow weir above the tank body. The Tank Cell flotation machine has the features of both flotation column and mechanical agitation flotation

1.1 Brief Introduction of the Evolution History of Flotation Machine

17

Fig. 1.13 TankCell flotation machine

machine. It not only enables coarse particles to be fully suspended, but also makes it possible to obtain concentrates of a higher grade. (5)

Beijing General Research Institute of Mining and Metallurgy

Since the 1960s, Beijing General Research Institute of Mining & Metallurgy (BGRIMM) has devoted itself to the research, promotion and application of BGRIMM series of flotation equipment technologies, and has developed into a sound flotation machine system. There are more than ten types such as CHF-X, JJF, KYF, SF, XJZ, XCF, LCH-X, CLF, YX and BF, and nearly 100 specifications of flotation machines and flotation machine integral units [26, 27]. By aeration mode, there are pneumatic mechanical agitation flotation machine and mechanical agitation flotation machine; From the perspective of the sorted minerals, they can not only meet the needs of non-ferrous metals, ferrous metals and other metallic minerals but also meet the needs of non-metals, sewage treatment, etc. From the perspective of processing capacity, they can not only meet the demand for a processing capacity of 10 t/d but also of a 100,000 t/d concentrator. From the perspective of the size of minerals, both conventional and coarse minerals can be sorted. From the perspective of applications, they can be used not only in roughing, scavenging, concentration and other operations but also in grinding circuits. From the perspective of flotation machine configuration, both stepwise configuration and planar configuration are allowed, and its creative planar configuration mode is more suitable for equipment upgrading in old plants. Its representative products include KYF flotation machine, XCF flotation machine and XCF/KYF integral unit, GF flotation machine, BF flotation machine, CLF flotation machine and flash flotation machine.

18

1.

1 Introduction

KYF flotation machine

The KYF flotation machine, as a pneumatic mechanical agitation flotation machine, is an excellent example of the upsizing of BGRIMM flotation machines. In 2000, a flotation machine with a single tank volume of 50 m3 was successfully developed [28, 29], and nearly 1000 such flotation machines were quickly promoted and used at home and abroad. In 2005, a flotation machine with a single tank volume of 160 m3 was successfully developed and used in the 34,000 t/d project of Wunugetushan Cu–Mo deposit of China National Gold Group Co., Ltd. [30, 31]; In early 2008, a 200 m3 of pneumatic mechanical agitation flotation machine was successfully developed and used in the 90,000 t/d project of Dashan Concentrator of Jiangxi Copper Corporation Limited [32, 33]. At the end of 2008, BGRIMM successfully developed the KYF-320 pneumatic mechanical agitation flotation machine, which is one of the flotation machines with the largest single tank volume industrially applied in the world, whose enrichment ratio of copper reaches up to 20.62 for a single flotation machine, enrichment ratio of sulfur is 71.44, and single-unit power consumption is 160 kW. The Toromoch project of Aluminum Corporation of China in Peru finally adopted 28 flotation machines (320 m3 ) [34]. In 2017, BGRIMM newly developed the KYF-680 pneumatic mechanical agitation flotation machine with the largest single tank volume in the world and organized industrial tests in Dexing Copper Mine, the largest copper mine in Asia. The test results showed that its unique structure form is beneficial to the separation of coarse minerals. The structure diagram of KYF flotation machine is shown in Fig. 1.14. This machine features the inverted-cone impeller with a backward-inclined blade and the suspended stator, and a porous cylindrical air distributor is designed in the middle of the impeller chamber. The working principle of the machine is that the low-pressure air supplied by the blower enters the air distributor via the hollow spindle along with the rotation of the impeller and enters the spaces between impeller blades through the holes in the sidewall of the distributor. Meanwhile, the pulp in the tank is sucked into the spaces between impeller blades from the lower end of the impeller, fully mixed with air, discharged from the upper part of the impeller, stabilized by the stator and supplied into the tank. Mineralized bubbles rise to the tank surface and form froth, and the pulp returns to the impeller area for recirculation. 2.

XCF flotation machine and XCF/KYF integral unit

The XCF flotation machine is developed to solve the following problems existing in general pneumatic mechanical agitation flotation machines: the capability of automatic pulp suction is unavailable, the flotation machine must be configured in a stepwise way, middlings need to be returned through a pump, resulting in complex process of the concentrator, high cost of capital construction or upgrading, etc. The equipment not only has the advantages of general pneumatic flotation machines but also allows automatic pulp suction [35], and its structure is shown in Fig. 1.15. The machine has the characteristics as follows: The impeller consists of upper and lower blades and a spacing disc. The upper blades are radial blades forming a pulp

1.1 Brief Introduction of the Evolution History of Flotation Machine Fig. 1.14 KYF flotation machine

Fig. 1.15 XCF flotation machine

19

20

1 Introduction

suction area together with the cover plate, whose function is to suck the pulp from outside the tank; The lower blades are backward leaning blades for circulating pulp and dispersing air, and this is the aeration area; The diameter of the spacing disc is greater than or equal to the outer circle diameter of the blade, and the spacing disc has the function of distinguishing the aeration area from the pulp suction area. The working principle of the machine is that: The low-pressure air supplied by the blower enters the air distributor via the hollow spindle with the rotation of the impeller and enters the spaces between impeller blades through the holes in the sidewall of the distributor. Meanwhile, the upper blade of the impeller sucks the external pulp into the tank, the pulp in the tank is sucked into the spaces between lower impeller blades from the lower end of the impeller, fully mixed with air, and supplied into the pulp in the tank after current stabilization and orientation by the stator installed above the impeller. Mineralized bubbles rise to the tank surface and form froth, and the pulp returns to the impeller area for recirculation. The XCF flotation machine and the KYF flotation machine can form an integral unit to realize the planar configuration, both of which have been widely applied to non-ferrous metals, ferrous metals and chemical industries and produced remarkable economic and social benefits. Compared with the original 6A flotation machine, XCF-8 flotation machine in Yinshan Pb–Zn Deposit increases the lead recovery rate and the zinc recovery rate by 0.67 and 1.94%, reduces the power consumption by 23.1% and saves the floor area by 40% [36]. 3.

GF flotation machine

At present, there are many types of flotation machines which can represent BGRIMM’s high-efficiency and low-consumption automatic suction mechanical agitation flotation machine, among which the GF flotation machine has the relatively excellent technical performance. The structure of GF flotation machine is shown in Fig. 1.16. This machine also has automatic suction of pulp and air, whose working principle is that as the impeller rotates, negative pressure is formed in the centre area of the upper blades of the impeller to suck air, feed and middlings. Meanwhile, the lower blades of the impeller suck pulp from inside the tank, the upper and lower streams of pulp flow are merged in the middle part of the blade, flow to the periphery of the impeller and enter the pulp in the tank. Mineralized bubbles rise to the tank surface and form froth, and the pulp returns to the impeller area for recirculation [37]. This machine has the characteristics as follows: (1) Automatic air suction, with automatic air suction volume up to 1.2 m3 /m2 min−1 ; (2) Automatic pulp suction, allowing automatic suction of feed and froth middlings from outside the tank and planar configuration of the flotation machine workshop; (3) Small impeller diameter, low circumferential speed and low power consumption; (4) Long service life of wearing parts. The GF flotation machine applies to medium- and small-sized enterprises for the separation of metallic and non-metallic minerals. The production practice of the GF flotation machine in a gold mine in Shandong Province showed that the cold grade

1.1 Brief Introduction of the Evolution History of Flotation Machine

21

Fig. 1.16 GF flotation machine

of concentrates is 43.46 g/t, and the gold recovery rate is 94.3% with grind fineness of –74 µm accounting for 75% and gold grade of raw ore of 3.07 g/t. 4.

BF flotation machine

The BF flotation machine is an efficient separation plant developed by Beijing General Research Institute of Mining & Metallurgy, having the characteristics of planar configuration, automatic air suction, automatic pulp suction, automatic return of middlings froth, etc., without the need of any auxiliary equipment. Compared with A-type flotation machine, it has the advantages of saving power consumption per unit volume by 15–25%, adjustable suction rate, stable pulp level, high separation efficiency, long service cycle of wearing parts, convenient operation, maintenance and management, etc. It is a kind of fuel-efficient separation equipment. As shown in Fig. 1.17, the BF flotation machine mainly consists of a motor device, tank body components, a spindle mechanism, a froth scraper and other components. The spindle mechanism comprises a big pulley, a bearing block, a central cylinder, a spindle, a suction pipe, an impeller, a stator and other parts and components. The spindle mechanism is fixed to the main beam of the tank body. The working principle of this machine is similar to that of the GF flotation machine, allowing automatic pulp suction from outside of the tank. The No. 2 Concentrator of Gongchangling Mining Company of Ansteel adopts 39 BF-20 flotation machines developed by Beijing General Research Institute of Mining & Metallurgy. The grade of iron concentrates is increased from 65.55%

22

1 Introduction

Fig. 1.17 BF flotation machine

before upgrading to 68.89%, and that of iron concentrates is increased by 3.34%; The content of SiO2 is decreased by 4.41% from the previous 8.31 to 3.90% [38]. 5.

CLF flotation machine

The CLF flotation machine is a kind of wide-size-fraction mechanical agitation flotation machine capable of separating conventional and coarse minerals with relatively high density and concentration and is especially suitable for separation of quartz sand, refining furnace slag and others containing coarse non-ferrous metals, ferrous metals and non-metallic minerals [39]. The CLF flotation machine is shown in Fig. 1.18, whose working principle is that as the impeller rotates, the low-pressure air supplied from the blower enters the spaces between impeller blades via the hollow spindle through the distributor. Meanwhile, the pulp below the false bottom is sucked into the spaces between impeller blades from the lower part of the impeller, fully mixed with air and discharged from the upper part of the impeller. Then, the pulp passes through the grid plate after stator current stabilization and enters the upper area in the tank. At this time, a large number of bubbles are contained in the flotation machine, while no bubbles or very few bubbles are contained in the outer circulation channel so that a pressure difference is formed. Under the action of this pressure difference and impeller suction, the internal pulp and bubbles rise, pass through the grid plate and bring coarse minerals to the part above the grid plate, forming a suspended layer. The mineralized bubbles and the pulp containing fine mineral particles continue to rise. The mineralized bubbles rise to the liquid surface so that a froth layer is formed, while the pulp containing fine mineral particles is returned to the impeller area via the circulation channel for reseparation [40, 41]. This machine has the characteristics as follows: (1) It adopts the impeller with backward leaning blades featuring the high specific speed, the blade shape is consistent with the flow line of pulp passing through the impeller, and it has the characteristics of a large pulp circulation rate and low power consumption; (2) The grid plate shortens the rising distance of coarse minerals and lowers the falloff probability; (3) The circulation channel makes fine minerals pass through the impeller area many times so that the collision probability is increased, which is beneficial to fine particles flotation [42].

1.1 Brief Introduction of the Evolution History of Flotation Machine

23

Fig. 1.18 CLF flotation machine

6.

YX flash flotation equipment

The YX flash flotation machine is a kind of single tank pneumatic flotation machine used in a grinding-classification circuit, as shown in Fig. 1.19, and used for separation of grit from a spiral classifier or cyclone to obtain the liberated coarse minerals in advance. This machine has the characteristics as follows: (1) A pulp circulating cylinder is installed under the impeller stator for promoting pulp circulation and suspension of mineral particles under the impeller, enabling floatable minerals to enter the impeller area many times, and increasing the collection probability; (2) An upper circulation channel is arranged at the upper part of the impeller to generate the upper circulation, increase the agitation strength and uniformity, and make the chemicals come into sufficient contact with the mineral particles; (3) The tank body has a conical bottom for eliminating any dead angle in the tank to avoid plugging and playing the role of densification so that tailings are discharged densely and evenly through the lower cone [43]. The application of this machine in Sizhou Concentrator of Dexing Copper Mine showed that the gold content in concentrates is 8.348, 1.384 g/t higher than that of the total gold ores of the Concentrator and +74 µm accounts for 68.89% in gold ores, much higher than 27.79% for the conventional flotation concentrates, with the underflow concentration up to 70–75%.

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1 Introduction

Fig. 1.19 YX flash flotation machine

(6)

China Coal Research Institute

The China Coal Research Institute is one of the units firstly engaged in flotation machine research in China. It mainly studies flotation machines for coal preparation, and its representative devices include XJM flotation machine and XJM-S flotation machine. The XJM flotation machine is a mechanical agitation flotation machine, which is characterized in that: (1) Three-layer umbrella impellers are adopted. There are six straight blades in the first layer, whose function is to suck pulp and air; an umbrellashaped baffle plate is in the second layer, forming a suction chamber together with the first layer; the third layer is an umbrella-shaped plate with an opening in the centre, forming a pulp suction chamber together with the baffle plate in the second layer for sucking the pulp; (2) The stator is also shaped like an umbrella and installed above the impeller. It consists of cylindrical surfaces and circular cone surfaces where pulp circulating holes are formed separately. There are stator guide plates at an angle of 60° at the lower end of the conical surface of the stator, and the direction of the stator guide plates is consistent with the rotating direction of the impeller. This machine is widely applied to coal slime flotation, but it has poor selectivity for coal slime with poor floatability, unsatisfactory flotation effect for coarse coal slime and great loss in tailings. The XJM-S flotation machine was successfully developed on the basis of XJM flotation machine, and the structure is shown in Fig. 1.20. It is also a mechanical agitation flotation machine. The biggest difference between this flotation machine

1.1 Brief Introduction of the Evolution History of Flotation Machine

25

Fig. 1.20 XJM-S flotation machine (1—Tank body; 2—Impeller; 3—Stator; 4—Steady flow plate; 5—False bottom; 6—Bubble scraping mechanism; 7—Suction tube; 8—Middling container)

and XJM flotation machine lies in that the number of impeller layers is changed from three to two, the umbrella-shaped baffle plate on the second layer of the XJM flotation machine is replaced by other mechanisms and the design heights of blades and impeller chambers are optimized. This machine has the characteristics as follows: (1) The upper and lower circulation rates of the impellers are adjustable, and the section of the circulating channel may be changed through the adjusting device on the stator cover plate, thus adjusting the upper circulation rate. The lower circulation rate is adjusted by changing the adjusting plate at the lower suction opening, with adaptability to the separation of coal slime varying in floatability; (2) In the mixed feeding mode, most of feeds are sucked into the impeller through the suction tube, and the rest of the materials enter the agitation area through the gap between the periphery of the false bottom and the tank wall; (3) The stator is a separated structure of stator cover plate and guide blade, and the pulp suction pipe on the stator is directly opposite to the lower suction opening of the impeller; the lower suction opening of the impeller extends into the pulp suction pipe at a certain distance to ensure the suction of enough new pulp. (7)

Other flotation machines

In addition to the flotation machines mentioned above, there were also some other flotation machines that met the demands for some time then. However, with the development of the mineral processing industry, these flotation machines were either not adapted to the requirements of the flotation process, or failed to successfully achieve upsizing. There were relatively few market demands for these flotation machines which were gradually withdrawn from the market. But this part of flotation machines has made certain contributions to the development of flotation equipment, and these flotation machines are mainly:

26

1.

1 Introduction

KHD Humboldt Wedag flotation machine

The mechanical agitation flotation machine manufactured by KHD Humboldt Wedag International AG (KHD), with disc-shaped, single-runout, double-runout, multirunout and various other types of impellers. With the runout increase, the suction rate of the flotation machine is also increased, and the processing capacity per unit volume is enhanced, while the energy consumption is reduced. However, this machine failed to achieve upsizing, and was gradually withdrawn from the flotation machine market. 2.

Krupp flotation machine

Both KR and TR flotation machines manufactured by Krupp are automatic suction mechanical agitation flotation machines with a minimum volume of 0.5m3 and a maximum volume of 5m3 . Such machines feature that pulp and air are, respectively, sucked from the feeding pipe and the hollow spindle when the impellers are rotating. There are three types of impellers: (1) Ordinary impeller, wherein the pump blades are of closed type, and the pulp inlet is arranged at the upper end of the impeller; (2) The pulp inlet can be located at the upper or lower end of the impeller; (3) Straight-flow impeller. These types may be selected according to the process requirements. 3.

Warman flotation machine

The Warman flotation machine manufactured by Warman Equipment Company of Australia was developed on the basis of Fagergren flotation machine. This machine is mainly used in such countries as Australia, Japan, and those in Southeast Asia and South America. The greatest features of the machine are the impeller and diversion plate: The impeller is installed at the lower end of the hollow shaft and consists of round bars and a disc, wherein the round bars are arranged at an inclination angle of 45° with the reverse direction of the impeller while extending outward, configured symmetrically with the axis as the centre at equal intervals and fixed to the disc. The advantage of such design lies in that the impeller will not be completely depressed when the machine is shut down with less wear. The diversion plate consists of curved plates with different curvature radii so that the upper part of the sorting area is kept stable while violent agitation is occurring in the flotation machine. 4.

AS flotation machine

The AS flotation machine was developed by Sala International (Sweden). This flotation machine with a maximum volume of 44 m3 features a distinctive design. It is mainly devoted to minimizing the circulating pulp flow. It is believed that the natural stratification of pulp is beneficial to flotation. The impeller of this machine is a flat disc with vertically radial blades on both sides, the upper blades are used for dispersing air, and the lower blades are used for sucking pulp. This machine is suitable for fine particle separation.

1.1 Brief Introduction of the Evolution History of Flotation Machine

5.

27

LM flotation machine

The LM flotation machine is a pneumatic mechanical agitation flotation machine manufactured in the former Soviet Union. This machine has a maximum volume of 25 m3 . It is reported that this machine as a substitute for MexaHoop flotation machine has increased the production capacity per unit by more than 50% and reduced the power consumption for processing pulp per unit by more than 26%. 6.

XJN flotation machine

The XJN flotation machine is a flotation machine for coal preparation in early stages in China. It consists of a feed box, an agitator, a tank body, a tailings box, froth scrapers, etc. The feed box is a pulp preparation device, which makes coal slurry enter the flotation tank smoothly. The agitator mainly consists of an impeller, a stator, a stator cover plate and a transmission device. A false bottom and a suction pipe that can help pulp circulation are designed at the bottom of the tank body, and an adjusting ring is arranged on the suction pipe to allow adjustment of the centre height of the suction pipe. The tailing box is a device for tailing disposal. A manual gate valve in the box body is used for controlling the liquid level and tailings discharge capacity. The froth scrapers are arranged on both sides of the flotation tank, and concentrate froth at the upper part of the tank body is scraped into the froth tank when driven by the motor. 7.

XPM jet flotation machine

The XPM jet flotation machine, also a kind of flotation machine for coal preparation developed in China, has the working principle that: Coal slurry is injected from the nozzle at 15–20 m/s, forming a negative pressure and air is sucked in via the suction pipe. Meanwhile, the air is evenly dispersed in the coal slurry under the actions of “roll wraps” and “cutting emulsification” of jet stream, and then evenly distributed into the flotation tank after passing through the venturi and the umbrella-shaped disperser. When the pulp collides with the bubbles, the hydrophobic coal particles adhere to the bubbles to form mineralized bubbles, the bubbles float upward to form a froth layer, and then the froth layer is scraped out by the scrapers; coal particles not adhering to the bubbles are supplied into the pneumatic agitation device after pressurized by the circulating pump. Tailings are discharged from the tail end of the flotation machine. This machine has the characteristics as follows: (1) A large number of microbubbles are separated out of the flotation machine, which can intensify coal flotation. The mixing chamber is a negative pressure area where the air dissolved in coal is supersaturated and selectively separated out on the surface of hydrophobic coal particles in the form of microbubbles, thus intensifying the flotation process; (2) The pneumatic agitation device is a kind of emulsification device, which creates good conditions for the mineralization of bubbles. Currently, this type of flotation machine is seldom used, but it has fairly widespread influences.

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1 Introduction

In addition, there are some other flotation equipment, such as fluidization flotation machine of the former Soviet Union, Japanese V-flow flotation machine, BSX flotation machine of the General Research Institute for Nonferrous Metals in Beijing, China, and ring efflux flotation machine of the Central South University of Technology, etc.

1.2 Development Trend of Flotation Equipment With the development and application of flotation equipment for over a hundred years, the flotation technology has been greatly developed, the flotation machines have gradually become diversified, serialized, upsized and automated, the application fields keep expanding, and the application requirements in non-ferrous metals, ferrous metals, water treatment, biological separation and other aspects are basically met. However, with the depletion, refinement and hybridization of primary mineral resources, the mineral separation process is becoming increasingly complex, the production costs are rising, and new and higher requirements are put forward for the development of flotation equipment. (1)

(2)

Intelligence: With the development of microelectronics technology, great progress has been made in the automatic control technology of flotation equipment. At present, automation of the process control of mineral pulp level, aeration rate, pulp density, chemical addition, froth imaging analysis, etc. of flotation equipment has been realized, and intelligence is the development trend of flotation equipment. One sign of intelligence is the deep learning function. A flotation machine can learn the key historical data that affect the process indicators, deeply understand its own capabilities and attributes, automatically adjust the operation parameters such as velocity, liquid level, aeration rate and chemical addition of the flotation machine according to feeding changes, analyze the whole system, and automatically optimize the process to achieve the flotation objectives set by the concentrator; Another sign is the powerful self-diagnosis function. Each flotation machine stores and analyses its own mechanical performance data in real time, pushes diagnosis reports and maintenance suggestions to customers regularly and makes customers know the changes in equipment performance initiatively to achieve preventive maintenance. Specialization and upsizing: In terms of the sorting of conventional metallic and non-metallic minerals, the current flotation equipment can basically meet the demands. However, with the demands for mineral resources on the increase, the scale of concentrators is increasing, and the mineral resource endowments are continuously deteriorating. To improve the comprehensive utilization of resources, the requirements for equipment specialization and upsizing are higher, and the upsizing and serialization of special equipment needs to be continuously advanced to meet the requirements of different mineral species and different processing capacities. The research of differentiated solutions

1.2 Development Trend of Flotation Equipment

(3)

(4)

(5)

29

such as coarse flotation, high efficiency and energy saving flotation and flotation equipment for fine and micro-fine particles in compound force fields for the floatability and size distribution characteristics of different ores is still the research direction of flotation machines in the future. Diversification of configuration: Flotation is a systematic process, and there are many factors affecting the flotation indicators, involving mineral properties, reagent system, equipment performance, personnel operations, etc. The mode of operation configuration is also an important influencing factor. Flotation equipment having different features is selected according to different characteristics of roughing and scavenging operations to achieve the optimal configuration of the whole flotation process. For example, the combined use of mechanical agitation flotation machine, pneumatic mechanical agitation flotation machine and column flotation equipment, and the rational selection of grinding circuit flash flotation machine, special flotation machine for tailings recovery and other systems. Enrichment of research techniques: Flotation is a complex gas–liquid–solid three-phase physicochemical reaction process, the flotation machine flow field cannot be accurately measured and calculated, and the mineralization mechanism and coupling relationship are complex. The existing theories such as fluid dynamics and flotation dynamics cannot support the research of flotation machines well, especially the research of flotation machine upsizing, thus resulting in high R&D expenditures and long R&D cycle. The development of computer technology has promoted the development of Computational Fluid Dynamics (CFD) in recent years, making large-scale complex computing possible. Profound research on the fluid dynamics properties of flotation machines is made using the Computational Fluid Dynamics to achieve the effect of “virtual test”. It can also reduce the cost of equipment development and development cycle and improve the performance of newly developed flotation machines, and the application of CFD plays an irreplaceable role. New flotation equipment shows up prominently: Flotation equipment has been developed for more than one century, and there are three types of mainstream equipment: Mechanical agitation flotation machine, pneumatic mechanical agitation flotation machine and column flotation equipment. However, with further research on mineralization modes, several new types of flotation equipment have been developed, and mineralization and separation are realized by new methods or means, such as SFR, cascade flotation, etc.

1.2.1 Classification of Flotation Machines There are a great variety of flotation machines, and the main difference is reflected in the aeration method and agitator structure. According to the most commonly used classification method, the flotation machines are divided into two categories,

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1 Introduction

i.e. mechanical agitation type and non-mechanical agitation type (also known as flotation column) depending on aeration and agitation methods. Mechanical agitation flotation machines are divided into two categories depending on air supply methods: Pneumatic mechanical agitation flotation machine and mechanical agitation flotation machine. The pneumatic mechanical agitation flotation machine is a kind of flotation machine with gas fed under the action of external force, and the impeller only acts as an agitator and mixer without air suction. Its main advantages lie in that the aeration rate can be accurately adjusted as required, gas is sucked in without vacuum production by the impeller, the velocity requirement is low, and the energy consumption is less. The pneumatic mechanical agitation flotation machine is currently the most widely applied flotation machine. It is widely applicable to the sorting of nonferrous, ferrous and non-metallic ores such as copper, lead, zinc, nickel, molybdenum, sulphur, iron, gold, bauxite, apatite and leopoldite, especially to minerals with low requirement for gas volume and precise control, such as bauxite and phosphate rocks, etc. The mechanical agitation flotation machine is a kind of flotation machine which realizes vacuum air suction by mechanical agitation. Its main advantage lies in that air can be automatically sucked without the addition of any inflator; Its main advantage lies in that the adjustment range of suction rate is narrow, and accurate control is impossible. It mainly applies to the sorting of metallic and non-metallic minerals with wider requirements for the gas volume range. It is divided into two types, i.e. free-flow tank and pulp suction tank according to the configuration method. The flotation machine with the free-flow tank cannot suck pulp, and has the characteristics of less wear and low electricity consumption; the flotation machine with the pulp suction tank is capable of sucking the pulp, and it can be used with the flotation machine with the free-flow tank to achieve a horizontal configuration. Middlings are returned without froth pump so that the concentrator process is simplified. The classification of flotation machines is varied, and the specific classification is shown in Table 1.1. Table 1.1 List of flotation machine classification Classification basis

Type of flotation machine

With or without mechanical agitator

Flotation column/flotation machine

Flow direction of froth and pulp

Downdraft/reflux

Air intake method

Automatic suction/pneumatic/pressure saturation

Tank body size

Deep tank/shallow tank

Froth discharge method

Unilateral froth discharge/bilateral froth discharge/peripheral froth discharge (continued)

References

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Table 1.1 (continued) Classification basis

Type of flotation machine

Tank body shape

Quadrilateral/polygonal/circular

Usage occasion

Flash flotation machine/concentration flotation machine/roughing and scavenging flotation machine

According to the range of sorted size fraction

Fine-size-fraction flotation machine/coarse-size-fraction flotation machine/conventional flotation machine/wide-size-fraction flotation machine

Sorting material

Special for oxidized ore/water treatment/etc.

References 1. Albitel N (2000) Scale-up theory and technology of flotation cell. Met Ore Dress Abroad (7):2–7 2. Wang D, Yao G (2009) Mining and oredressing technique in ancient China. Strateg Study CAE (4):9–13 3. Zhao Y (2007) The application and development of flotation machines. Min Process Equip (7):65–68 4. Taggart AF (1945) Handbook of mineral dressing. Wiley, New York, Sections 12–53 5. Barlin B, Keys NJ (1963) Concentration at Bancroft. Min Eng 15(9):47–53 6. Beall JV (1966) Coeur D’Alene profile-1966-introduction. Miner Eng 28:164–178 7. Callow J (1915) Ore-flotation apparatus: US Patent, 1124856, 12 Jan 1915 8. Callow JM (1916) Notes on flotation, AIME Transactions, pp 3–24 9. Fahrenwald AW (1992) Flotation apparatus, US Patent 1417895, 30 May 1922 10. Fahrenwald AW (1928) Flotation practice in the Coeur d’Alene district. AIME Transactions, Idaho, pp 107–132 11. Fahrenwald AW (1934) Machine for flotation of ores, US Patent 1984366, 18 Dec 1934 12. Fagergren W (1929) Apparatus for circulating and distributing flotation pulp, US Patent 1736073, 19 Nov 1929 13. Fagergren W (1934) Aerating machine, US Patent 1963122, 19 June 1934 14. Booth LE (1936) Aerating machine, US Patent 2055065, 22 Sept 1936 15. Logue LH, Daman Jr AC (1968) Aerating assembly for froth flotation cells, US Patent 3393802,23 July 1968 16. Vibeer A (2002) Scale-up design of large flotation cells. Met Ore Dress Abroad (4):24–27 17. Nilson MG (1998) Power measurement of large flotation machines. Met Ore Dressing Abroad (10):22–25 18. Nelson MG, Lelinski D (2000) Hydrodynamic design of self-aerating flotation machines. Miner Eng 10–11:991–998 19. Lelinski D, Allen J, Redden L, Weber A (2000) Analysis of the residence time distribution in large flotation machines. Miner Eng 15:499–505 20. Lelinski D, Gordon I, Weber A, Dabrowski B, Traczyk F, Dunn M, Newman R (2008) Commissioning of the Supercells™ World’s largest flotation machines, VI International Mineral Processing Seminar, Santiago, GECAMINE 21. Olawajan X (2002) Research and development of Outokumpu flotation machines. Metallic Ore Dressing Abroad (4):13, 32–34 22. Mintee O (1994) Study and practice of Outokumpu flotation theory. Nonferrous Mines 5:31–35 23. Jonaitis AJ (2001) Advancement of the Outokumpu 100 m3 Tank Cell. Met Ore Dressing Abroad (5):30–34

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24. Burgess FL (1997) OK100 tank cell operation at Pasminco—broken hill. Miner Eng 7:723–741 25. Zheng X, Knopjes L (1994) Modelling of froth transportation in industrial flotation cells Part II: Modelling of froth transportation in an Outokumpu tank flotation cell at the Anglo Platinum Bafokeng—Rasimone PlatinumMine (BRPM) concentrator. Miner Eng 17:989–1000 26. Shen Z, Liu G, Lu S (1999) Features and applications of BGRIMM flotation machines. Nonferrous Metals (Mineral Process Section) (6):31–33 27. Liu G, Shen Z, Lu S (1999) The modern technology of BGRIMM flotation machines. Nonferrous Metals (Miner Process Section)(2):17–20 28. Shen Z, Liu Z, Lu S (1994) Research and design of the KYF-50 force-air flotation machine. In: The proceedings of the 4th mineral processing equipment conference of China 29. Shen Z, Liu Z, Lu S (2001) Research and development of the KYF-50 flotation machine. Min Metall 3:31–36 30. Shen Z (2005) Study of flotation dynamics of the 160 m3 flotation machine. Nonferrous Metals (Miner Process Section) (5):33–35 31. Shen Z (2006) Industrial test of the KYF-160 flotation machine. Nonferrous Metals (Miner Process Section) (3):37–41 32. Shen Z (2006) 200 m3 research and design of the super larger forced-air flotation machines. Nonferrous Metals (Miner Process Section) (5):100–103 33. Xie W (2010) Research and applications of the 200 m3 0forced-air flotation machine. Nonferous Metall Equip 2:5–8 34. Shen Z (2009) Research and development of the 320 m3 forced-air flotation machine. In: Proceedings of the 7th academy conference of chemical, metallurgy and material Engineering Department of CAE, Beijing, pp 788–793 35. Shen Z, Liu Z (1996) XCF flotation mechine. Min Metall 4:41–45 36. Li L (2000) Characteristics and applications of the combined flotation machines. Nonferrous Metals (Miner Process Section) (2):20–22 37. Lu S (2008) Research and development of the GF flotation machine. In: Proceeding of the 6th mining and metallurgical science and technology conference of Beijing Young Scholars, p 173 38. Dong G (2005) Application of the BF-T flotation machine to updrading iron concentrate. Min Metall 4:20–22 39. Shen Z, Yang L, Chen D (2007) Development and application of special flotation equipment for refining slag. Nonferous Metall Equip 2007(3):14–16 40. Shen Z, Liu Z, Wu Y (1996) Design principle of the coarse particle flotation machine. Nonferrous Metals (Miner Process Section) (3):23–27 41. Shen Z, Liu Z (1997) Rotor design of the coarse particle flotation machine. Nonferrous Met (Miner Process Section) (1):8–13 42. Liu H (1998) Research and application of the coarse particle flotation machine. Min Metall 2:58–62 43. Xia X (1993) Research and development of the YX flotation machine. Gold Silver Indus 2:42–47

Chapter 2

Basic Study of Flotation Dynamics

The main factors affecting the flotation process include ore properties (mineral composition, size distribution, particle shape, floatability of minerals, etc.), flotation process (workflow configuration, reagent system, pulp density and temperature, etc.), operating factors, characteristics of flotation machine, etc. The technical indicators of flotation mainly depend on the performance of the flotation machine provided that other flotation conditions are determined. Therefore, the fluid dynamics state of the flotation machine tank should meet the requirements of the flotation process for different mineral particles in order to improve the mineral flotation efficiency. To realize the flotation process for mineral particles, the primary conditions are contact and adhesion of mineral particles to bubbles. After adhesion of mineral particles to bubbles, the particle-bubble aggregate rises in the flotation machine, forming mineralized froth. In this process, the particle-bubble aggregate will undergo the exchange process of detachment, re-collision and re-adhesion. According to the basic theory of flotation dynamics, the flotation process of mineral particles is divided into three stages: Collision between mineral particles and bubbles, adhesion of mineral particles to bubbles and detachment of mineral particles from bubbles. The acquisition of ideal flotation indicators requires a higher adhesion probability and lower detachment probability of target minerals on bubbles, and lower adhesion probability and higher detachment probability of non-target minerals on bubbles. In addition to the influences of reagent system, a flotation machine with excellent performance must be capable of being matched with the flotation process of mineral particles in terms of flotation dynamics properties.

2.1 Collision Between Mineral Particles and Bubbles There are mainly two mechanisms of contact between minerals and bubbles [1]: Inertia mechanism and inertia-free mechanism for the force field on bubble surfaces. The inertia mechanism is that the collision between inertial particles and bubbles is © Metallurgical Industry Press 2021 Z. Shen, Principles and Technologies of Flotation Machines, Springer Tracts in Mechanical Engineering, https://doi.org/10.1007/978-981-16-0332-7_2

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2 Basic Study of Flotation Dynamics

generated by the inertia force. The greater the mass of minerals is, the higher the relative velocity of minerals and bubbles is and the more opportunities for collision and contact between mineral particles and bubbles are; the inertia-free mechanism for the force field on bubble surfaces is that inertia-free particles are attracted by the diffusion and electrostatic force of action at a distance generated by moving bubbles. When the mineral size is smaller than a critical value, it is difficult for mineral particles to collide with bubbles inertially. The contact with the bubbles is reflected as the sliding contact (poor selectivity) in most cases, which is also one of the reasons why fine minerals are difficult to separate. When the bubbles and water are relatively static, all the mineral particles in the water columns whose radius above the bubbles is Rb + Rp (Rb is the radius of bubbles, and Rp denotes the radius of mineral particles) can come into contact with the bubbles under the action of gravity settlement; when bubbles move relative to water, the flow line bends when water passes over bubbles, the trajectory of mineral particles in water deviates from bubbles under the influence of viscous force of the medium, and only the mineral particles in the pitot tube with radius B may come into contact with the bubbles, with b < Rb + Rp . The value of b depends on the equilibrium state of the viscous force of medium and inertial force acting on mineral particles. The viscous force bends the trajectory of mineral particles along with the flow line, and the inertial force makes the trajectory of mineral particles deviate from the flow line, as shown in Fig. 2.1. When the inertial force plays a leading role, the trajectory of mineral particles deviates from the flow line, enabling the inertial collision with the bubbles; when the viscous force plays a leading role, the trajectory of mineral particles follows the flow line, mostly in sliding contact (viscous contact) with the bubbles [2]. The above process of contact between minerals and bubbles is a prerequisite for the completion of inertial contact mineralization and non-inertial contact mineralization. Fig. 2.1 Trajectory of mineral particles

R

R b

b

2.1 Collision Between Mineral Particles and Bubbles

35

The success probability of collision between minerals and bubbles determines the probability of mineral recovery in the whole flotation process. The collision probability is determined by the fluid dynamics factors of the system and is affected by the mineral size, bubble size and turbulence degree. Yoon and Kuttrell believed that the collision probability depended largely on the collision section, and the collision probability (Pc ) between mineral particles and bubbles is [3] Pc ∝ 3rp /rb2

(2.1)

where rp rb

Radius of mineral particles; Radius of bubbles.

As seen from Formula (2.1), collision is affected by the mineral size and the bubble size and is proportional to the mineral size. The larger the mineral size is, the greater the inertia force is and the greater the contact probability is; collision is in inverse proportion to the square of the bubble size. The smaller the bubble size is, the higher the collision efficiency is. In addition to the mineral size and the bubble size, the collision probability is also affected by the relative velocity between mineral particles and bubbles, gas holdup, thickness of hydration shell on the mineral surface and other factors. Formula (2.2) is derived from the collision theory: Pc = σ · u ∞ · N

(2.2)

where u∞ σ N

Relative velocity of mineral particles and bubbles; Collision section; Number of bubbles in the pulp.

The above formula showed that the collision probability is proportional to the relative velocity of mineral particles and bubbles and the gas holdup in the flotation tank. Schulze believed that the collision probability depended on the thickness of the hydration shell on the mineral surface [4, 5], as shown in Formula (2.3): Pc = 1.78

rp (Hcr )1/8 rb

where Hcr

Dimensionless critical thickness of the hydration shell;

(2.3)

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2 Basic Study of Flotation Dynamics

Hcr =

h cr Rp

h cr is the critical thickness of the hydration shell on the mineral surface, Rp is related to the wettability of the mineral surface. The more hydrophobic the mineral particles are and the larger the h cr is, the higher the collision probability is. Therefore, the collision between mineral particles and bubbles is mainly related to the mineral size, the thickness of the hydration shell on the mineral surface, the bubble size, the relative velocity between the bubbles and mineral particles and the gas holdup. It can be known from the above analysis that the mineral size is closely related to the particle-bubble collision process and is the main factor affecting the flotation effect. Flotation requires not only the liberation of mineral monomers, but also satisfactory mineral sizes. The optimum size range of froth flotation varies with the flotation process parameters and flotation machine types. Too coarse or fine sizes are not suitable for flotation, that is to say, a suitable flotation size is subject to upper and lower limits. The optimum size range for froth flotation has the lower limit of about 3–7 μm based on a large number of experiments and analysis of production data. Generally, it is lower, i.e. 3–5 μm, for sulphides; It is higher, i.e. 5–7 μm, for oxidized minerals; For the froth flotation process, the division of the range of mineral size recommended by Lu Shouci is shown in Table 2.1: Hu et al. [6] believed that coarse particles above 74–100 μm are excellent objects of the physical multi-separation method, and on the contrary, it is difficult for froth flotation to work; The typical size of colloidal particles is less than 0.1 μm; With the size range of 5–0.1 μm, the particles having some properties of colloids are difficult to be processed by the conventional froth separation method, this size range is exactly the main size of silt carrying pulp, and such particles are called micro-particles; The optimum size range suitable for the conventional froth flotation is 100–7 μm or 74–3 μm, i.e. the so-called fine particles. The key to understand the flotation law and solve flotation problems is to research the flotation dynamic properties of minerals with different size fractions and grasp the influencing factors and characteristics of collision, adhesion and detachment processes of coarse and fine minerals and bubbles. Table 2.1 Division of the range of mineral size

Size fraction

Range of size fraction (μm)

Coarse particles

>150

Fine particles

100~7

Micro-particles

3~0.1

Colloidal particles

1, which is represented by the inertial collision; with K < 1, the inertial force becomes less important, the movement of mineral particles is mainly affected by the viscous resistance of the medium and the contact with bubbles is dominated by the sliding contact. K value is related to the size and the Reynolds number of bubbles. The coarser the size is, the greater the mass (K value) is, the greater the relative velocity of minerals to bubbles is and the more collision opportunities between minerals and bubbles are. Thus, the inertial collision mechanism plays a dominant role in the flotation process in terms of coarse particles. The inertial collision efficiency E c (the ratio of the number of mineral particles in actual contact with bubbles to the total number of mineral particles within the trajectory of bubbles in the forward direction of bubbles) may be approximated by Formula (2.4): Ec =

K (K + 0.5)

(2.4)

This formula is applicable to the case of K > 1/12, Re ≥ 1.  Ec =

1 + 3 ln 2K 4(K − 1.214)

−2 (2.5)

Formula (2.5) is applicable to the case of K > 1.24, Re ≤ 1.

2.1.2 Collision Process Mechanism of Fine Minerals Compared with coarse minerals, fine minerals have different processes of mineral collision, adhesion and detachment. For fine minerals, the collision process is mainly reflected as the non-inertial mechanism of the force field on bubble surfaces, that is to say, the mineral particles are in the state of sliding contact with bubbles mainly subject to the viscous force action of the medium. Two additional factors, i.e. nearfluid mechanics effect and surface force effect, shall also be considered in the collision process of fine particles. The near-fluid mechanics effect refers to the fluid resistance suffered by two objects when they are infinitely close to each other to push back the interstitial water. The trajectory of mineral particles subject to the near-fluid mechanics effect near the

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2 Basic Study of Flotation Dynamics

equator of bubbles will shift outward by H, and the contact probability between two objects will be further reduced. Surface forces mainly refer to the molecular force and the electrostatic force generated by the overlapping of electric double layers. When the mineral particles and bubbles are so closed that the surface force works, the trajectory of the mineral particles will shift accordingly based on the nature of the surface force. The operating distance of the near-hydrodynamic force is equivalent to the radius of mineral particles. Generally, the operating distance of surface forces does not exceed tens of nanometers, and there is nearly one order of magnitude between them. The non-inertial collision probability is extremely low, generally not more than 0.2%, but the contact efficiency can be significantly improved under some conditions. When the Re value of bubbles is greater than 20, the water stream separated by the bubbles begins to escape at the tail of the bubbles to form a whirlpool, the mineral particles may be entrained by the backflow whirlpool and come into contact with the tail of the bubbles, and such contact is called turbulent diffusion contact. Test results showed that the size of the mineral particles enabling this contact is not greater than 3 μm for the bubbles with a radius of 1 mm. For example, the determined contact efficiency E c between particles with a radius of 0.25 μm and paraffin spheres (taken as bubble) with a radius of 2 mm in a turbulence field is 1–2%. When the mineral particles reach the colloidal size (RP < 1 μm), the mineral particles obviously exhibit the characteristics of Brownian movement, and the trajectory of mineral particles can be separated from the flow line to achieve diffusion contact with the bubbles. The contact efficiency E c can be expressed by Formula (2.6): Ec ∝

1 2/3

Rb2 RP

(2.6)

At this time, E c increases with the decrease of the size. The fine mineral particles dominated by non-inertial collision have small mass, slow movement and long time (sliding time) from sliding along the bubble walls to entrainment. According to theoretical calculation results, the sliding contact time of mineral particles (RP is 5 μm) and bubbles (Rb is about 1 mm) can reach 440 ms. Yang et al. [7] believed that fine particles came into contact with the bubble surfaces by means of Brownian movement and were captured by rising bubbles through interception. In the theoretical research, Stokes and potential flow functions can be used to calculate the recovery efficiency of bubbles and particles. They summarized the relational expression of Marangoni effect and fluid mechanics. The Ma (Marangoni Number) is expressed by Formula (2.7). Ma =

E0 α R b ηf

(2.7)

In the above formula, α represents the particle adsorption parameter in the equilibrium state, E 0 represents the Gibbs elasticity of surface active particles and the

2.1 Collision Between Mineral Particles and Bubbles

39

Marangoni number represents the ratio of tension gradient force to the viscous force at the interface. In summary, the contact mode and contact efficiency of mineral particles and bubbles are closely related to the size of mineral particles. The contact efficiency has the minimum value with Rp of 1–10 μm.

2.2 Adhesion Between Mineral Particles and Bubbles In fact, the contact between mineral particles and bubbles does not necessarily result in adhesion. When hydrophilic mineral particles collide with bubbles inertially, they are likely to be rebounded finally although they can come into contact with the bubbles and deform the bubbles. The processes from collision to adhesion include: The hydration shell between mineral particles and bubbles is thinned and fractured, forming a long enough three-phase contact periphery, and a solid–gas interface between mineral particles and bubbles appears. The time spent on completion of the whole process is called induction time. Therefore, the necessary condition for realizing adhesion after the mineral particles come into contact with the bubbles is that: The required induction time must be less than the actual contact time when the mineral particles collide with the bubbles. Only in this case can the mineral particles adhere to the bubbles, otherwise they will fall off since there’s no enough time to adhere. The relational expression between induction time and size is as shown by Formula (2.8) [8–10]: t = kd n

(2.8)

where t k d n

Induction time; Coefficient; Size; Related to the movement state of the pulp, n = 0 for the laminar flow, n = 1.5 for the turbulence, n = 0–1.5 for the transition state.

The relationship between induction time and size is shown in Fig. 2.2. As the movement state of the pulp changes from laminar flow to turbulence, the induction time increases correspondingly. Due to the large size and great inertia, the contact time of coarse minerals with bubbles is generally short, only a few milliseconds, particularly in the turbulent condition, the time of contact between mineral particles and bubbles is much shorter than the induction time, which is one of the reasons why coarse minerals are difficult to float. The turbulence degree (agitation intensity) must be reduced to enable the contact between the mineral particles and bubbles in a stable environment in order to achieve the adhesion of coarse particles.

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2 Basic Study of Flotation Dynamics

Fig. 2.2 Relationship between induction time and particle size

Recent researches by Zongfu Dai et al. showed that the induction time is also related to the contact angle with particles, bubble size, etc. [11]. The induction time increases with the increase of size, contact angle and bubbles. The contact time between mineral particles and bubbles depends on the final velocity of mineral particles, so the movement velocity of mineral particles may be reduced by reducing the agitation intensity, and then the contact time between mineral particles and bubbles is increased, which is favourable for the adhesion of mineral particles to bubbles. In consideration of the influences of induction time, particle diameter, bubble diameter, turbulence intensity and other factors, the particle-bubble adhesion probability can be expressed by Formula (2.9):  Pa = sin2 2ar ctg exp



 −(45+8Re0.72 b Vb ·ti ) R 30Rb ( b +1) Rp

(2.9)

where Reb Vb ti Rb Rp

Reynolds number of bubbles Reb < 100; Average movement velocity of bubbles; Induction time; Radius of bubbles; Radius of mineral particles.

Therefore, the adhesion of mineral particles to bubbles depends not only on the properties of the mineral particles and those of the pulp, but also on the turbulence degree in the flotation machine, the bubble size and other factors. The high turbulence degree in the flotation machine is favourable for the adhesion of fine minerals, but not for the adhesion of coarse minerals.

2.2 Adhesion Between Mineral Particles and Bubbles

41

2.2.1 Adhesion of Coarse Minerals The adhesion of coarse minerals to bubbles is mainly caused by inertial collision, and the contact between mineral particles and bubbles does not necessarily result in adhesion. The necessary conditions for particles to adhere to bubbles are as follows: (1) The hydration shell between mineral particles and bubbles is fractured; (2) A three-phase contact periphery is formed and expanded to a sufficient length. This necessary condition is particularly important for coarse minerals in the inertial collision state. Otherwise, the coarse minerals might fall off from the bubbles due to the excessive inertial force caused by greater mass of the mineral particles even if adhesion occurs. The fracture of the hydration shell depends on the correlation of various surface forces. Depgin l.B. et al. put forward the concept of shell fracture pressure (the additional energy for thinning the hydration shell until it is fractured) based on the analysis of various surface forces during the action between minerals and bubbles, and argued that the shell fracture pressure consisted of electrostatic components, molecular components and structural components. The changes in the structure components mainly include the energy changes caused by the hydrophobic interaction. Although the distance of the hydrophobic interaction is less than the interaction distance of the other two components, the hydrophobic interaction becomes a decisive factor as long as the hydrophobic particles approach the bubbles to the interaction distance with the help of external energy, and as a result, the hydration shell is fractured. After the hydration shell is fractured, the three-phase periphery must be formed and gradually expanded to finally achieve equilibrium so that the mineral particles can adhere to the bubbles. The research results showed that the expansion of the threephase periphery is affected by the factors such as surface water viscosity, surface roughness and surface inhomogeneity of mineral particles and the diffusion effect of reagents at the particle-bubble interface.

2.2.2 Adhesion of Fine Minerals With regard to the non-inertial collision of fine minerals, there may be two cases in which the adhesion process is realized: One is the fracture of the hydration shell, forming the three-phase contact periphery; The other kind of adhesion does not necessarily accompany the fracture of the hydration shell, and the mineral particles can also “adhere” to the bubble phase as long as the distance between mineral particles and bubbles reaches the energy valley of their surface-effect potential energy. Two conditions are required for realizing the latter: (1) the mineral particles and bubbles shall approach the distance where the surface force starts to work; (2) the interaction potential energy of them is negative, with the minimal value on the potential energy curve.

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2 Basic Study of Flotation Dynamics

Note that: the fracture of the hydration shell and the generation of the solid–gas interface are the necessary conditions for ensuring the flotation selectivity of mineral particles; the “adhesion” in the energy valley state is in lack of selectivity, which is exactly one of the reasons for non-selective floatation of slime.

2.3 Detachment of Mineral Particles and Bubbles After the mineral particles collide with and adhere to the bubbles, detachment may occur under the action of the turbulence force field, and the detachment probability may be expressed by Formulas (2.10) and (2.11): When dp < dmax , d

p Pd = ( dmax )1/2

(2.10)

Pd = 1

(2.11)

When dp ≥ dmax ,

where d max —Maximum size of mineral particles stably adhering to the bubbles. The smaller the size is, the smaller the detachment probability is. The greater the maximum size of mineral particles adhering to bubbles is, the smaller the detachment probability is. The diameter of the maximum size adhering to the bubbles can be calculated according to Schultz’s derived Formula (2.12) [12]:  dmax =

1 1 3γg sin(180− θ)(180+ θ) 2 2 2[(ρp −ρl )g+ρp ·bm ]

(2.12)

where γg θ bm

Liquid–gas surface tension; Contact angle; Turbulent acceleration.

It can be seen from Formula (2.12) that the maximum size that can float decreases with the increase of turbulent acceleration, and the detachment probability of mineral particles will increase; the smaller the contact angle is, the faster the detachment probability increases. Not only the coarse minerals do not float, but also the fine minerals may not float. The firmness of particles adhesion to bubbles and the influencing factors causing the detachment of particles may be evaluated through force analysis under static conditions and energy balance calculation under dynamic conditions.

2.3 Detachment of Mineral Particles and Bubbles

43

The forces acting on spherical mineral particles at the gas–liquid interface include adhesive force, buoyant force, hydrostatic pressure, gravity, capillary pressure and additional inertia force. Under statics conditions, the total resultant force acting on mineral particles F is expressed by Formula (2.13):

F=

2ρP 3h 3 − 1 + cos3 ω − sin ω + sin ω sin(ω + θ ) 2 ρl 2RP a R2p

(2.13)

where ρP ρl h RP ω θ

Particle density; Liquid density; Immersion depth of mineral particles; Particle diameter; Central angle; Wetting angle.

It can be seen from the above formula that when the mineral particles are given, ρ , P RP and θ are also given. The resultant force acting on the mineral particles F = 0 when the mineral particles is in an adhesive equilibrium state at the gas– liquid interface under static conditions. At this time, the immersion depth of mineral particles is hl (Fig. 2.3a). The mineral particles continue to sink due to a great enough external force exerted on the mineral particles or great dead weight of the mineral particles. As the h increases, F is accordingly changed ([ F = f (h)]), and the mineral particles will fall off by themselves until they reach the critical immersion depth hcr (Fig. 2.3b). Therefore, the detachment work E cr shall be represented as Formula (2.14): hcr (ω)



E cr =

Fdh(ω)

(2.14)

h l (ω

Under the turbulent pulp flow state, the necessary condition for the mineral particles to fall off is that the movement of the pulp enables the mineral particles to obtain

T

(a)

N (b)

Fig. 2.3 Immersion depth of mineral particles: a immersion depth is h1 where the particles are in equilibrium state; b immersion depth is hcr where the particles will lose their force equilibrium

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2 Basic Study of Flotation Dynamics

the kinetic energy quantitatively greater than the detachment work. Both velocity and pressure of any point in the turbulent motion of a fluid fluctuate continuously over time, and its actual movement speed ν is manifested as the sum of the average velocity of the fluid and the additional fluctuating velocity v  , namely, v = (v + v  ). Set vt = v 2 0 to be the mean square value of the additional fluctuating velocity, which represents the intensity of turbulence. For the locally isotropic turbulence, Formula 2.15 can be used to calculate vt :

ε1/9 (2Ragr )7/9 ρ 2/3 vt = 0.33 ν 1/3 ρL

(2.15)

where υ Ragr

Kinematic viscosity, Pa s; Radius of mineralized bubbles, cm;

ρ = ρs − ρl , g/cm3 ; ε

Average energy dissipation.

The mineral particles will fall off from the bubble surface once the kinetic energy E min obtained by the mineral particles is greater than or equal to the detachment work E det , i.e. E min ≥ E det , and Formula (2.16) can be obtained: 2 2 π RP3 ρvl2 ≥ π RP3 ρl g 3 3

hcr

heq

2ρp 3h sin3 ω − 1 + cos3 ω − ρl 2R

 3 + 2 sin ω sin(ω + θ ) dh a RP

(2.16)

According to the above discussion and calculation, it can be known that the influencing factors of the adhesion firmness and detachment of particles include: Density of mineral particles ρ P , particle size RP , wettability θ, liquid density ρ l , gas–liquid interface tension γ gl and average fluctuating velocity of the pulp vt . For the given mineral particle and liquid system, the wettability θ and gas–liquid interface tension γ gl of mineral particles can be changed by adding different surfactants to control the detachment probability of mineral particles to a certain degree. In addition, the adhesion firmness decreases accordingly with the increase of the density and size of mineral particles. Under statics conditions, the detachment of mineral particles is due to the increase of gravity as a detachment force; under turbulence conditions, either the increase of particle mass or the increase of average fluctuating velocity v leads to the increase of inertial detachment force of mineral particles.

2.4 Influence of Size on Flotation

45

2.4 Influence of Size on Flotation The size fraction distribution of suspended particles is one of the important factors affecting the flotation recovery. Fine particles and coarse particles have different flotation rate constants. Very coarse particles cannot be recovered largely due to easy detachment; Very fine particles have a small adhesion probability, and fine particles that cannot adhere to bubbles will also consume a large number of reagents, which limits the recovery of useful minerals in conventional size fraction. Therefore, both too coarse and too fine mineral particles can affect the flotation effect in different ways.

2.4.1 Influence of Coarse Particles on Flotation Coarse minerals have the characteristics of large size and great mass. A large number of production data and laboratory observations showed that both too coarse and too fine sizes of flotation minerals will cause obvious decrease of the flotation efficiency and deterioration of the flotation effect. As seen from the force analysis of particles under static conditions and the calculation of energy balance under dynamic conditions in Sect. 2.3, there are two main reasons for the adverse effects of too large mineral particles on the flotation process: (1)

The increase of particle–bubble induction time makes it difficult for particles to adhere to bubbles. The contact between mineral particles and bubbles does not necessarily result in adhesion. The necessary conditions for realizing the adhesion of particles to bubbles are that the hydration shell between mineral particles and bubbles is fractured, and the collision time is longer than or equal to the induction time.

Through high-speed photography observation of the bubble mineralization process of coarse minerals, it is found that when 0.5 mm galena particles collide with 2 mm bubbles, the bubbles are significantly deformed, the contact portion is flattened, and the bubbles change from spheres to 1.5 mm × 3 mm elliptical spheres. The deformation occurs in 2–3 ms and recovers within 2–3 ms later, and the mineral particles can even be thrown out due to such elastic vibration. The observation results also showed that the bubbles can be deformed when the coarse particles collide with the bubbles. Since the contact area is too large, water in the central zone of the contact area cannot be discharged, and a sandwich water zone is formed so that the mineral particles cannot really come into contact with the bubbles. Base on theoretical analysis of the floatability of sulphide minerals with different size fractions, Jowett pointed out that the main reason for deterioration of coarse flotation was that the induction time increased accordingly with the increase of particle size, and presented the relationship between particle-bubble induction time and mineral size. When the time of contact between mineral particles and bubbles

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is less than the induction time, the adhesion process is impossible and the mineralization cannot be realized. The coarser the size is, the longer the induction time accordingly becomes as the movement state of the pulp transits from laminar flow to turbulent flow, while the contact time is only a few milliseconds, which is much shorter than the induction time, and adhesion is obviously unachievable. (2)

(1)

Coarse minerals are easy to fall off from the bubbles. Since the dead weight of mineral particles with too coarse sizes exceed the load capacity of bubbles, these mineral particles are difficult to float even if they adhere to the bubbles; under static conditions, the main detachment force of coarse and heavy mineral particles is gravity, with a higher probability of detachment; under turbulence conditions, the increase of particle mass or the increase of average fluctuating velocity v may lead to the increase of the inertial detachment force of mineral particles [13]. For a series of characteristics of the coarse minerals causing flotation deterioration, the measures may be taken to improve the flotation of coarse minerals from the aspects of flotation process and flotation equipment. In the flotation process aspect. 1.

2. 3. (2)

Make appropriate changes to the reagent system. Strengthen the hydrophobicity of the coarse particle surface, and enhance the adhesion firmness of mineralized bubbles; adjust the bubble strength, and control the bubble diameter and the speed of bubble coalescence and fracture to a certain extent. Introduce the regrinding process of middlings. Regrind middlings to effectively reduce the mineral size. Strengthen the particle size separation. Discard coarse gangue in advance to avoid the short cut of coarse mineral particle in size seperation.

In the flotation equipment aspect. 1.

2.

Change the structure of the tank body of the flotation machine and create a suitable circulation mode for coarse minerals separation. From the above analysis, it can be seen that the intense turbulent movement of the pulp in the mechanical agitation flotation machine increase detachment possibility of coarse minerals. Create a circulation mode suitable for the sorting of coarse-fraction minerals, reduce the average fluctuating velocity of the pulp so that the relative velocity of mineral particles and bubbles is reduced, slow down the collision of mineral particles with bubbles, prevent the elastic vibration of bubbles generated by intense collision, thus prolonging the contact time between mineral particles and bubbles, and improve the probability of adhesion of mineral particles to bubbles. Change the agitation mode of flotation machines. To reduce the influence of intense turbulence in the flotation machine on the adhesion of coarse minerals, grid plates may be added above the impeller area of the mechanical agitation flotation machine to reduce the turbulence intensity, inhibit the rising speed of the mineralized bubble and ensure that the hydrophobic

2.4 Influence of Size on Flotation

3.

4.

47

mineral particles have higher stability at the gas–liquid interface so that they can directly bring the mineral particles into the froth layer. Reasonably design the froth tank and froth scrapers. Effectively extend the length of the froth overflow weir, and discharge the floating products as quickly as possible to avoid detachment of the mineral particles. Optimize the aeration mode. A high aeration rate and even air dispersion degree shall be provided to create favourable conditions for carrying coarse particles jointly by multiple bubbles.

2.4.2 Influence of Fine Particles on Flotation The physical and chemical properties of fine minerals often have a negative impact on the flotation process. Too fine mineral particles will not only obviously reduce the recovery rate, but also significantly affect the grade of flotation concentrates. (1)

Influence of physical properties 1.

2.

3.

(2)

The collision and adhesion between mineral particles and bubbles are influenced. Fine minerals have the small diameter, small mass and low momentum. The probability of collision and adhesion between particles and bubbles decreases with the reduction of size. Therefore, the probability of collision and adhesion between particles and bubbles is low, resulting in poor mineralization and low recovery; once adhering to the surface of the bubbles, the fine particles are not easy to fall off, which causes excessive stability and tackiness of the froth in the flotation process, makes the selectivity of the flotation process worse and affects the improvement of concentrate quality. Reduce the flotation rate. Due to the low probability of collision between fine minerals and bubbles, the flotation rate of fine minerals will decrease with the reduction of the mineral size. Increase the hydraulic entrainment. The research showed that: the finer the mineral particles are, the smaller the mass is and the higher the degree of hydraulic entrainment is. The entrainment of fine particles will also destroy the selectivity of the flotation process and affect the grade of flotation concentrates.

Influence of chemical properties 1.

2.

Slime coating. Due to the electrostatic interactions under different conditions, fine particles will cover the surface of coarse particles, which will inhibit the flotation of target mineral and deteriorate the flotation indicators Coagulation of fine particles. Fine particles with different charges will coagulate with each other because of the same reason of electrostatic interaction. Non-selective coagulation can also deteriorate the flotation indicators.

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3.

4.

Reagent consumption. The fine minerals have large specific surface area and specific surface energy so that they have higher reagent adsorption capacity. Poor selectivity of reagent adsorption is unfavourable for the flotation process. Solubility. The fine minerals have large specific surface areas, higher oxidation rate and increased solubility, the ionic components in the pulp will be increased, and the mutual activation between minerals will be strengthened, causing difficulties in flotation separation. The dissolved components will react with the mineral surfaces, causing transformation of the mineral surfaces. The mutual transformation of mineral surfaces will have an important impact on the electrical properties and flotation behaviours of the mineral surfaces so that different mineral surfaces may represent similar surface electrical properties and flotation behaviours in the pulp, thus further deteriorating the flotation separation effect.

For a series of characteristics of the fine minerals causing flotation deterioration, the measures may be taken to improve the flotation of fine minerals from the aspects of flotation process and flotation equipment: (1)

Flotation process 1. 2. 3. 4.

(2)

Use the desliming process (removal of fine minerals that deteriorate the flotation effect) before the flotation process; Prevent non-selective coagulation of fine minerals to ensure full dispersion of the pulp; Use a flotation reagent suitable for fine particles to selectively hydrophobize the target mineral surface; Selectively agglomerate the fine mineral particles to increase their flotation size;

Flotation equipment 1.

Particle size separation. Fine minerals can be extracted by adding an auxiliary device having the sizing function into the flotation machine. An apatite concentrator added a double-outlet device to an independent 5 m3 flotation machine in the production flow. The semi-industrial research on the separation efficiency of phosphorus ores by this flotation machine has achieved ideal results. The feed of the flotation machine is cyclone underflow, with the dry ore flowrate of 50 t/h. The device draws a third product flow accounting for 5–15% of the feed from the flotation machine, with relatively fine suspended particles. The product analysis results showed that the recovery rate of particles less than 74 μm is more than 31% for the double-outlet device with an obvious enrichment effect on the fine particles. The device makes it possible to remove a part of the fine mineral particles that failed to adhere to bubble from the flotation machine, these particles are fed to the next flow for further treatment and recovery, and

2.4 Influence of Size on Flotation

2.

3.

4. 5.

49

the recovery of coarse particles in the flotation concentrates will also be improved [14]. Froth spray water device design. The thinner the mineral particles are, the higher the degree of hydraulic entrainment is. The froth spray device is added into the flotation equipment to make full use of the secondary enrichment of the froth in the flotation process. Aeration way optimization. The research on the flotation dynamics of fine particles showed that the flotation rate constant is K ∝ d p /d b for fine particles (where d p and d b are the diameters of mineral particles and bubbles, respectively, n = 2, m = 2.67–3). Therefore, reduction of the bubble diameter is one of the main ways to improve the flotation of fine minerals. Agitation way optimization. Optimize the agitation way to prevent nonselective flocculation of fine minerals. Tank structure improvement. Change the structure of the tank body of the flotation machine to create a suitable circulation mode for the flotation of fine minerals.

2.5 Dynamic Zoning of Flotation Machine There is actually no strict and clear boundary between dynamic zones in the flotation machine, and the dynamic zones of different flotation machines are also different. Generally, the conventional flotation machine may involve four dynamic areas: agitating and mixing zone, transport zone, separation zone and froth zone. The properties of different dynamic zones in air force flotation cell are elaborated as an example combined with the flotation process of mineral particles, as shown in Fig. 2.4.

2.5.1 Agitating and Mixing Zone The agitating and mixing zone is an essential zone in the flotation machine. Most of the processes, such as pulp suspension and circulation, bubble dispersion, collision and adhesion between mineral particles and bubbles, occur in this zone. The pulp suspends in the tank through impeller rotation. The suspension state and circulation rate of the pulp mainly depend on impeller geometric structural and rotation speed. In a definite flotation machine, an appropriate impeller rotation speed is required by a dynamic environment that is suitable for flotation process. The pulp cannot be sufficiently suspended at a too low impeller speed, which not only affects the collision between mineral particles and bubbles, but also easily produces dead zones or even sediment; a too high impeller speed will affect the effective adhesion

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Fig. 2.4 Flotation dynamic zones in flotation cell

between mineral particles and bubbles and increase the detachment probability, which is unfavourable for the flotation. Bubble dispersion mainly depends on the impeller structure and its operating parameters (such as impeller speed, clearance between impeller and stator and air speed) will significantly affect air dispersion. The impeller agitation force needs to satisfy smooth circulation of the pulp, ensure that coarser mineral particles can be fully suspended without obvious sediment at the tank bottom and ensure that the turbulence generated by impeller agitation has moderate intensity in order to avoid detachment of the mineral particles adhering to the bubbles.

2.5.2 Transport Zone The main function of the transport zone is to form an ascending pulp flow so that the mineralized bubbles are transported to the upper part of the flotation machine tank body under the action of fluid dynamics and their own velocity. According to the observations of researchers, the particle-bubble aggregates are almost disintegrated due to the strong agitation force when leaving the agitating and mixing zone, and all

2.5 Dynamic Zoning of Flotation Machine

51

the bubbles have a weak degree of mineralization. In the transport zone, the collision and adhesion between mineral particles and bubbles occur again, and this kind of phenomenon is called secondary collision and adhesion. Therefore, this zone requires not only the formation of an ascending flow to transport the mineralized bubbles to the separation zone, but also an appropriate ascending speed, which can increase the probability of secondary collision between mineral particles and bubbles while reducing the detachment probability of mineral particles. Figures 2.5, 2.6 and 2.7 shows the overall flow field of the flotation machine measured by PIV under three-speed conditions. It can be seen that two kinds of flow, i.e. obviously oblique upward and oblique downward are formed after fluid being deflected from the stator blade. The oblique upward flow gradually forms a clockwise upper circulating flow field under the action of sidewalls, top free surface, etc. The oblique downward flow also gradually forms a counterclockwise lower circulating flow field which is finally sucked into the impeller zone at the bottom of the impeller. Base on the analysis of the ascending stream in the flow field under three-speed conditions, it can be seen that the transport zone is located in a vortex field with zero-point energy (singular point) in the centre. Later, the zone near the tank wall is dominated by vertical ascending flow which is deflected gradually to the centre of the tank body, and a vortex flowing downward is slowly formed. The fluid returns

Fig. 2.5 Overall flow field of the flotation machine measured by PIV at impeller speed of 195 r/min

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Fig. 2.6 Overall flow field of the flotation machine measured by PIV at impeller speed of 256 r/min

to the zone above the impeller stator and converges with the fluid transported by the impeller pumping function, and then continues to flow upward. Based on the above analysis, it can be deduced that the contour shape of the transport zone along the impeller centreline section presents a near-trapezoidal structure with one side at the singular point, as shown in Fig. 2.8. The height of the transport zone on this section jet-flows is from the port of stator to the boundary with the upward velocity of zero (H = Te − Ts). The width of the transport zone is from the tank wall to the liquid stream boundary where the direction keeps 45° angle with horizontal line (; W = Bt − Te), K is the velocity zero point of the section vortex, and the lower width of the transport zone is the constant velocity line of the vortex whirled from the impeller zone at an angle of 45° with the horizontal direction. According to the flotation dynamics theory and the structural features of the transport zone, it can be deduced that on the one hand, if the height of the transport zone is increased, i.e. the upper boundary Te − Bt or the lower boundary Ts − To of the transport zone, the ascending liquid flow will transport the particles to a location closer to the overflow weir, or the length of the transport zone is reduced, thus reducing the detachment probability of coarse particles; on the other hand, if the width of the transport zone is increased, the receiving zone of particles detached

2.5 Dynamic Zoning of Flotation Machine

53

Fig. 2.7 Overall flow field of the flotation machine measured by PIV at impeller speed of 318 r/min

from the froth phase can be enlarged, thus increasing the probability of secondary collision of coarse particles.

2.5.3 Separation Zone The key function of the separation zone is to form a clear pulp-froth interface. To achieve this dynamic condition for the flotation machine, the bubble diameter shall be within a certain range, and the gas velocity at the cross section shall not be too high but must be lower than a certain critical value [16]. With the bubble size d b = 0.8–1.2 mm, the upper limit of the gas velocity at the cross section can be adjusted to 2.7 cm/s. When the bubble size is small (3 mm), the bubble load capacity is small and the froth stability is poor.

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Fig. 2.8 Structural features of transportation zone in cross section

The separation zone also requires a relatively stable pulp flow, while the relationship between particle movement speed and particle-bubble collision in a suspended state is considered. Zeng et al. [17] measured the particle velocity in all dynamics zones in the XFD-12 8L flotation machine with the world’s advanced Particle Dynamics Analyzer (PDA). The test points were radially distributed outside the axial wall with the central axis as the datum line and with 7.8 mm as the step length. A total of 9 points were measured in the separation zone. Figures 2.9 and 2.10 showed that the distribution of the time mean velocity V X (tangential velocity of the cross section of the flotation machine tank body) in the separation zone is similar to that in the mixing zone, and the time mean velocity V X of radial distribution changes from large to small until becomes zero, and then changes to negative. The absolute value of the time mean velocity of mineral particles in the separation zone is just less than that in the mixing zone. The test results showed that reflux is encountered at a point 40–50 mm away from the axis centre, which is unfavourable to flotation, and the intensity is just less than that in the mixing zone. The radial distribution rule of the time mean velocity V Y (the velocity in the axial direction of the flotation tank

2.5 Dynamic Zoning of Flotation Machine

55

Fig. 2.9 Tangential time mean velocity and fluctuating velocity distribution along radial direction in transportation zone in cross section of flotation cell (1—Tangential fluctuating velocity V X ’ in the separation zone; 2—Tangential time mean velocity V X in the separation zone)

Fig. 2.10 Axial time mean velocity and fluctuating velocity distribution along radial direction in transportation zone in cross section of flotation cell (1—Axial time mean velocity V Y in the separation zone; 2—Axial fluctuating velocity V Y ’ in the separation zone)

body) is changing from small to large, and then getting smaller gradually. This is unfavourable to the suspension of mineral particles near the tank wall, but beneficial to the suspension of mineral particles near the axis. Mineral particles that have not adhered to the bubbles can be better suspended near the axis, and re-collide with the bubbles for adhesion. The fluctuating velocity V X ’ of the particles is not high and is relatively uniform; however, the radial attenuation of fluctuating velocity V Y ’ is great, which is unfavourable to the particle suspension. This will reduce the opportunities of collision between mineral particles and bubbles and affect the flotation effect. Therefore, the gangue particles can be fully separated from the mineralized bubbles by mastering and making good use of the dynamic properties of the separation zone, the probability of detachment of the target mineral particles from

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the bubbles is reduced, and then the product recovery and concentrate quality are improved.

2.5.4 Froth Zone The function of the froth zone is to further enrich the minerals. A steady froth layer can ensure that the mineral particles adhering to the bubbles do not fall off, and the mineral particles are collected by froth flowing smoothly into the froth tank. This zone focuses on investigating the thickness of the froth layer and the residence time of the froth. The thickness of the froth layer is a key operating parameter, which has a direct effect on the concentrate recovery and grade. For the flotation operation, the thickness of the froth layer is indirectly controlled by adjusting the pulp liquid level through the pulp valve of the middling box or tailing box. Besides, the reagent systems, pulp properties and other factors can also affect the thickness of the froth layer. The general conditions in the flotation machine are that: The thicker the froth layer is, the better the capacity of mineral enrichment is; the thinner the froth layer is, the worse the capacity of mineral enrichment is; ensuring a reasonable thickness of the froth layer is favourable for the secondary enrichment of the froth layer on the mineral particles and the improvement of the concentrate grade. But too thick froth layer should be prevented because if the froth layer is too thick, bubbles in the upper layer will become larger, the total surface area of the bubbles will decrease, and some coarse particles that have floated up or mineral particles that are more difficult to float will fall off from the bubbles; too thin froth layer is also unfavourable because it will not only weaken the secondary enrichment, but also cause “pulp spring” phenomena, i.e. fluctuation of the pulp level, which will affect the concentrate quality. In the practical operation of the flotation process, there is often a thick froth layer in the concentration operation to ensure that high quality concentrates are obtained, that is, focusing on the concentrate grade; there is a thin froth layer for the rougher and scavenger operations to ensure that minerals with poor floatability and part of coenobiums are recovered as much as possible, that is, focusing on the mineral recovery rate. The ultimate aim of the flotation machine is to discharge the enriched froth from the overflow weir for recovery. The quicker and more complete the froth is discharged, the better the effect is. The mineral recovery in froth is reduced exponentially with the increase of the froth residence time [18]. Therefore, the froth residence time is one of the important indicators for evaluating the recovery rate. Shortening of the froth residence time in the design process of the flotation machine will be very helpful to improve the recovery rate. The relationship between recovery rate and froth residence time is shown in Formula (2.17). ε(t) = exp(−kt)

(2.17)

2.5 Dynamic Zoning of Flotation Machine

57

where ε(t) t k

Recovery rate at moment t; Froth residence time; Coefficient;

In consideration of the velocity of particles in both vertical and horizontal directions in the froth layer, the froth residence time t can be expressed as Formula 2.18 [19]. R 2h f εf Hf εf + ln t(r ) = Jg Jg r

(2.18)

where Hf hf Jg R r εf

Distance from the gas–liquid interface to the overflow weir; Distance from the overflow weir to the froth top; Surface gas velocity rate; Equivalent radius of the flotation tank; Radius of the position where mineralized bubbles enter the froth layer; Gas holdup in the froth layer.

It can be seen from the above formula that the froth residence time is related to the operating conditions (the thickness of the froth layer and the surface gas velocity rate) of the flotation machine, the distance of froth movement (equivalent radius of flotation tank) and the position where mineralized bubbles enter the froth phase. The froth residence time will be increased by extending the thickness of the froth layer and the gas holdup in the froth, and the froth residence time will be reduced by increasing the surface gas velocity rate of the froth phase.

References 1. Shen Z, Lu S (2004) Comments on large scale flotation machines. China Min (2):229–233 2. Massinaei M, Kolahdoozan M, Noaparast M etc (2007) Mixing characteristics of industrial columns in rougher circuit. Miner Eng (20):1360–1367 3. Yoon (1993) Hydrodynamics and surface forces in particle-bubble interaction. Translated by Dai Zongfu. Met Ore Dress Abroad (6):5–11 4. Schulze HJ (1983) Physicochemical elementary processes in flotation. Elsevier Science Publishers, p 348 5. Hu QiuGuanzhou WD Yuehua 1993 Interaction between particles and flotation of fine particles Technology Press of central south university Changsha 6. Hu X, Huang H, Mao J et al (1991) Flotation theory and technology. Technology Press of Central South University, Changsha 7. Yang SM, Han SP, Hong JJ (1995) Capture of small particles on bubble collector by Brownian diffusion and interception. J Colloid Interface Sci 125–134 8. Miller JD, Ye Y (1987) The significance of bubble/particle contact time in the analysis of flotation phenomena-the effect of bubble size and motion, presented at 114th Ann. SME/AIME Meeting, Denver, CO

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9. Schulze HJ, Gottschalk G (1981) Investigations of thehydrodynamic interaction between a gas bubble and mineral particles in flotation. In: Laskowski J (ed) Proceedings of 13th international mineral processing congress. Elsevier, Warsaw, Poland, N.Y., pp 63–84 10. Jowett A (1980) Formation and distribution of particle-bubble aggregates in flotation. In: Somasundaran P (ed), Fine particles processing, Proceedings of international symposium on fine particles, LasVegsa, Nev. AIME, N.Y., pp 720–754 11. Dai Z, Fornasiero D, Ralston J (2000) Particle-bubble collision models-a review. Adv Colloid Interface Sci 85:231–256 12. Lu S, Weng D (1992) Interface separation principle and application. Metallurgical Industry Press, Beijing 13. Zheng X, Franzidis JP, Manlaping E Modeling of froth transportation in industrial flotation cells Part I: development of froth transportation models for attached particles 14. Wierink GA, Heiskanen K, Niitti T et al (2008) The dual outlet device—key to size-selective flotation. Miner Eng 21:894–898 15. Ji SB (1984) Current situation and prospect of flotation theory. Translated by Liu Enhong. Metallurgical Industry Press, Beijing 16. Anatos B (2004) design, modeling and control of flotation equipment. Met Ore Dress Abroad 4:19–24 17. Zeng K, Xue Y, Yu Y (2001) Particle velocity in solid-liquid-gas three phase flow in flotation cell. Metal Min 2001(5) 18. Gorain BK, Harris MC, Franzidis JP et al (1998) The effect of froth residence time on the kinetics of flotation. Miner Process 11(7):627–638 19. Zheng X, Franzidis JP, Manlaping E (2004) Modeling of froth transportation in industrial flotation cells Part I: Development of froth transportation models for attached particles. Miner Eng (9–10):981–988

Chapter 3

Dynamic Characteristics and Evaluation of Flotation Machines

The dynamic characteristic of flotation machines is a key factor to evaluate the performance of flotation machines, and also an important link to improve the flotation indicators. The characteristic parameters of dynamics performance of flotation machines are discussed in this chapter, including aeration (suction) rate, dispersion degree of air, diameter and distribution of bubbles, bubble surface area flux, gas holdup, bubble-loading rate, distribution of pulp resident time, definition and measurement method of pulp suspension capacity and critical impeller speed, etc.

3.1 Characteristic Parameters and Evaluation of Flotation Machines 3.1.1 Aeration (Suction) Rate The aeration (suction) rate refers to the volume of air overflowing out of each square meter of the liquid surface of a flotation machine every minute, which represents the aeration (suction) capacity of the flotation machine. For the froth flotation, bubbles are used as carriers which capture mineral particles with good hydrophobicity and float up to the liquid level in the flotation machine. The aeration (suction) rate will directly affect the flotation rate, which is one of the most commonly used dynamics parameters of flotation machines for industrial production. In academic researches, the aeration (suction) capacity of a flotation machine is usually expressed by the incoming air volume flow rate, i.e. superficial gas velocity, per unit of cross-sectional area of the flotation machine. That is to say, the superficial gas velocity is actually another expression of the aeration (suction) rate of a flotation machine, and their influencing factors and determination methods are described below.

© Metallurgical Industry Press 2021 Z. Shen, Principles and Technologies of Flotation Machines, Springer Tracts in Mechanical Engineering, https://doi.org/10.1007/978-981-16-0332-7_3

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3.1.1.1

Influencing Factors of Aeration (Suction) Rate

For air-forced flotation machine, the aeration (suction) rate depends on the fan performance and its operating parameters; for the mechanical agitation flotation machine, the suction rate is also affected by the structure of the flotation machine itself and its operating parameters: (1)

(2)

(3)

(4)

Clearance between the impeller and the stator. If the clearance is large, the aeration rate will decrease, but a too small clearance will cause impact and friction between the impeller and the stator and reduce the suction rate. The suitable clearance is 5 ~ 15 mm. Revolution of the impeller. If the impeller rotates at a high speed within a certain range, the suction rate will also be high, but a too high speed will accelerate impeller wear, increase the power consumption and make the liquid level unstable. In addition, argillation is easy to occur to some brittle ores. Circulation rate. When the pulp volume entering the centre of the impeller is the most appropriate, the suction rate reaches the maximum value. But when the pulp feeding volume exceeds the production capacity of the impeller, the pulp will block the air cylinder so that the suction rate decreases. In addition, if the circulation rate of internal pulp is large (i.e. the pulp volume returning from the circulation holes in the stator into the impeller chamber), the suction rate will be high, but the power consumption will increase accordingly. Pulp density at the upper part of the impeller. The greater the value is, the greater the static pressure acting on the impeller is, the impeller rotating resistance is increased, and the suction rate is reduced.

3.1.1.2

Measurement Methods of Aeration (Suction) Rate

The measurement methods of aeration (suction) rate mainly include (1)

Water drainage and gas collection. The suction rate of a flotation machine is measured by water drainage and gas collection, as shown in Fig. 3.1. Select several representative measurement points in the flotation machine, take a PMMA tube with height marks and one end closed, fill up PMMA tube with water, then vertically invert and insert the tube into clear water or pulp, and ensure that the tube opening is below the liquid level. Start timing when the liquid level drops to the mark 1, stop timing when the liquid level drops to the mark 2, and record the time spent. Measure the next point in the same way until all the measurement points are measured. To ensure the accuracy of measurements, each measurement point is repeatedly measured twice. If the time interval between two measurements is large, the third measurement shall be conducted. Then calculate the aeration rate at each point, and calculate the dispersion degree of air in the flotation machine.

The aeration (suction) rate of the flotation machine is expressed by the air volume passing through the 1 m2 cross section of the tank body within 1 min, and the air

3.1 Characteristic Parameters and Evaluation of Flotation Machines

61

Fig. 3.1 Air dispersion measurement

volume is represented by the volume of drained water in the measurement. Q=

S×L L L V 60 × L = = = t = T ×S T ×S T t 60

(3.1)

where Q V T S L t

Aeration (suction) rate at the measurement point, m3 /(m2 ·min); Volume of clear water drained from PMMA tube, m3 ; Measurement time, min; Cross-sectional area of the PMMA tube, m2 ; Length of effective measuring section, m; Measurement time, s.

To improve the accuracy of measurement, the length of effective measuring section L is generally taken as 150 mm. Q = 1 m3 /(m2 ·min) when t=9 s. Calculation process: Firstly, calculate the average value of water drainage time at each measurement point, substitute into the formula Q = 9/t to calculate the average aeration rate Q of all the points, and then calculate the average value Q of all the measurement points. This value is the aeration (suction) rate of the flotation machine. (2)

Pitot tube method. Install a pitot tube with a micromanometer to the intake tube of the flotation machine (Fig. 3.2), and calculate the result of the measured intake volume Q (m3 /s) according to Formula 3.2:  Q = F 2 giρ L K (h − h 0 )/ρa

(3.2)

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Fig. 3.2 Aeration rate measured by pitot tube. 1—Intake tube; 2—Pitot tube; 3—Micromanometer

1

2 3

where Cross-sectional area of the intake tube, m2 ; Acceleration of gravity; Sine of the manometer to the horizontal inclination angle; Correction coefficient of the pitot tube; Liquid level of the piezometer tube before and after measurement, respectively, m; Density of liquid (usually alcohol) in the manometer, kg/m3 ; Air density under measurement conditions, kg/m3 .

F g i K h0 ,h ρL ρa (3)

Anemometer method. Install an anemometer to the aeration (suction) tube of the flotation machine, and calculate the air intake volume by Formula 3.3:

Q = KVF

(3.3)

where V F K (4)

Wind velocity indicated by the anemometer, m/s; Effective area of the anemometer ring, m2 ; Head loss correction factor. Flowmeter method. Vertically install a gas rotor flowmeter to the air induced or air-forced flotation machine, and directly measure the air flow rate.

The water drainage and gas collection method is the most commonly used method since the error is substantial in the last three methods of the above four aeration (suction) rate measurement methods. In addition, according to the relationship between the superficial gas velocity and the aeration rate, it can be considered that the superficial gas velocity is the velocity at which the gas drains the liquid phase, thus the superficial gas velocity can be

3.1 Characteristic Parameters and Evaluation of Flotation Machines

63

determined by water drainage and gas collection which is the same as the aeration rate, and is calculated by Formula 3.4. Jg =

Qc Qm V 60LS 5L = = = Sc S TS 100tS 3 t

(3.4)

where Jg Qc Sc Qm V T S L t

Superficial gas velocity in the flotation machine, cm/min; Volume flow rate of air coming into the tank body of the flotation machine, m3 /min; Cross-sectional area of the tank body of the flotation machine, m2 ; Flow rate of air coming into the PMMA tube, m3 /min; Volume of clear water drained from the PMMA tube, m3 ; Measurement time, min; Cross-sectional area of the PMMA tube, m2 ; Length of effective measuring section, m; Measurement time, s.

Substitute Formula 3.4 into Formula 3.1, and it can be seen that Q=

5 Jg 3

(3.5)

Therefore, the flow rate of air induced or forced can also be indirectly measured by measuring the superficial gas velocity in the flotation machine, as shown in Fig. 3.3. Use a PMMA tube with one end closed and one end open, insert the opening end into

Fig. 3.3 Superficial air velocity measurement

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3 Dynamic Characteristics and Evaluation of Flotation Machines

the pulp of the flotation machine, and connect the closed end with the air flowmeter. Then Jg = Qg/Ac

(3.6)

where Qg Ac

Volume flow rate of air entering the PMMA tube per unit time, m3 /s; Cross-sectional area of PMMA tube, cm2 .

Based on Formula 3.5, the flow rate of air induced or forced can also be measured by two other methods. (5)

McGill valve open/close reactor [1].

This sensor consists of two tubes (generally 10 cm in diameter), an inductor and a diffuser. The top may be closed, and the outer wall is connected with a valve and a pressure sensor, see Fig. 3.4. The pressure sensor is connected by an electronic board to obtain signals and provide them to the computer for further analysis. The marked sensor is used to collect bubbles and record the increased pressure when the valve is closed. The J g value depends on the gradient change of pressure increased with time, as shown in calculation formula 3.7.

Fig. 3.4 McGill switching valve measuring device and its pressure signal

3.1 Characteristic Parameters and Evaluation of Flotation Machines

 Jg =

 dP Patm + ρb · HL · (cm/s) ρb · [Patm + ρb · (HL − H0 )] dt

65

(3.7)

where Represents the atmospheric pressure at that time, expressed in the water column height cm; Total length of sensor tube; Distance between the sensor top and the overflow weir of the flotation machine; Density of aerated pulp calculated according to the pressure difference when the sensor and the diffuser tubes are filled with air, as shown in Formula 3.8.

Patm HL H0 ρb

ρb =

P2 − P1 (g/cm2 ) HBD

(3.8)

where P1 , P2 H BD (6)

Pressure calculated by water column height, cm; Distance between the bottoms of two tubes, cm.

McGill continuous reactor

The top of the inductive electronic tube used is equipped with one pressure sensor and one orifice with scale marks, see Fig. 3.5. Bubbles enter the tube, and air overflows through the orifice with scale marks. The liquid level in the tube drops until reaching a steady state. J g is estimated by the pressure drop P of the orifice with scale marks on the cross section, and the calculation formula is as shown in 3.9.  Jg = α ·

P +b ρα

(3.9)

where a, b ρa

Empirical constant; Air density.

3.1.2 Dispersion Degree of Air The dispersion degree of air is both a parameter that represents the uniformity of air dispersion in the flotation machine and an important evaluation parameter for the gas

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3 Dynamic Characteristics and Evaluation of Flotation Machines

Fig. 3.5 McGill continuous reactor and its pressure signal

dispersion function of the impeller stator of the flotation machine. The uniform air distribution in the flotation machine is favourable for fuller contact between bubbles and mineral particles and effectively increases the probability of bubble–particle collision, thus improving the flotation efficiency. The dispersion degree of air is mainly affected by the aeration performance, agitation mode and geometrical structure of the flotation machine itself. The more uniform and stable the aeration of the flotation machine is, the higher the dispersion degree of air in flotation is. Generally, the dispersion degree of air can be improved by adding an air distributor to the impeller stator system, increasing the impeller speed and designing a symmetrical tank structure. According to the calculation method of aeration (suction) rate described in Sect. 3.1.1.2, the calculation formula 3.10 of the dispersion degree of air is η=

Q Q max − Q min

(3.10)

where Q Qmax , Qmin

Average value of aeration (suction) rates at all measurement points; The maximum and minimum aeration rates in all measurement points.

3.1 Characteristic Parameters and Evaluation of Flotation Machines

67

3.1.3 Diameter and Distribution of Bubbles The diameter and distribution of bubbles is an important parameter in the flotation process. The fluid dynamics characteristics and the flotation effects are affected to a certain extent by the air velocity and dispersion mode in the flotation machine. Coalescence and fracture between bubbles in different diameters occur in the process of bubble ascending, thus affecting the fluid dynamics environment in the flotation machine.

3.1.3.1

Influencing Factors of Diameter and Distribution of Bubbles

An increase in the froth concentration will result in a decrease in the froth surface mobility, thus reducing the ascending velocity of the bubbles. Also, the reduction of surface tension can significantly reduce the bubble coalescence intensity, thus significantly reducing the average bubble size. If the tank body of the flotation machine is infinitely high, the bubble size distribution at the upper part of the tank body will tend to be constant. After the bubbles rise to a large distance, the average size of the bubbles depends not on the positions where the bubbles are generated, but on the potential energy in the positions of the bubbles. To simulate the flotation behaviour, the decreased hydrostatic pressure and increased bubble diameter in the process of bubble ascending should be considered. The gas holdup is high at the high velocity gradient of the near-wall surface course (with the thickness of several centimeters) of the flotation machine and near the agitator shaft, which results in bubble coalescence, and the average size of bubbles in these areas is larger than that in other areas. It takes time to form a constant state of bubble size distribution, and this time depends on the aeration rate, surfactant and solid concentration and characteristics. When the gas and liquid velocity on the surface increases and the surfactant concentration decreases, coalescence is the primary cause that affects the bubble diameter. Bubble coalescence easily leads to the formation of big bubbles, and the fluctuating velocities of gas and liquid phases in the tank body of the flotation machine cut the initial bubbles into bubbles with smaller diameters. In the case of low surfactant concentration and moderate pulp velocity, the influence of the final bubble velocity on the surface migration and deformation of the bubbles becomes greater as the bubble diameter increases. Two types of bubbles will be generated in the froth layer: big bubbles and fine bubbles. The experimental research on the froth layer by the segregation process showed that most of the gases exist in the big bubbles, and about 80 ~ 90% of gas– liquid interfaces in the flotation machine consist of 0.5 ~ 2 mm bubbles under normal conditions. Due to different ascending velocities of coarse and minute bubbles, they have different resident times in the flotation machine. In the flotation machine, the bubble size distribution at different heights is different from the average bubble distribution

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3 Dynamic Characteristics and Evaluation of Flotation Machines

in the tank body of the flotation machine even if bubble coalescence, fracture and bubble growth due to different hydrostatic pressures are not considered.

3.1.4 Bubble Surface Area Flux Gas dispersion should generate minute bubbles with a large enough surface area. The bubble interface generated per unit surface area of the flotation machine per unit time is called the bubble surface area flux (S b ). The gas surface area flux having the same effect as the dispersion degree of air is both a commonly used variable which indicates the degree of gas dispersion. Generally, the dispersion degree of air is used for actual production, while the gas surface area flux is mainly used for academic research. The latter is characterized by the combination of the gas surface velocity and bubble size into a single variable. For a group of bubbles with the average size of db at the gas surface velocity of Jg , the bubble surface area flux can be derived from geometry [2]: Sb = 6 ∗ Jg /db

(3.11)

It can be seen from this formula that the gas surface area flux is proportional to the superficial gas velocity and inversely proportional to the average diameter of bubbles. To calculate the value S b , the first step is to determine the average diameter of bubbles, then determine the superficial gas velocity according to the method described in Sect. 3.1.1.2, substitute them into Formula 3.11 and calculate.

3.1.5 Gas Holdup The gas holdup in the flotation machine refers to the volume fraction of air in all mixtures (pulp and air). The gas holdup affects not only the bubble size distribution, but also the flotation and selectivity. The flotation dynamics can be improved by increasing the gas holdup to a certain value because the number of bubbles per unit volume increases; however, excessive air holdup will have negative impacts on the flotation effect because this will significantly reduce the resident time of the pulp in the tank body of the flotation machine. Thus, different types of flotation machine operations need to correspond to different gas holdups. The air holdup is determined by the phase velocity and bubble size. Assuming that the bubble sizes are the same and the phase velocities are also the same, the volume occupied by gas on a section of the flotation machine is the gas holdup δ in this case; the gas holdup is determined by the following method (Fig. 3.6). Firstly, add the pulp into the tank of the flotation machine until it approaches the overflow weir (height H1 ). Secondly, fill the flotation machine with air, and start

3.1 Characteristic Parameters and Evaluation of Flotation Machines

69

Fig. 3.6 GAS holdup measurement. a—Initial pulp liquid level; b—Pulp liquid level with aeration, c—Pulp liquid level without aeration

the motor of the flotation machine. At this time, the pulp will overflow from the overflow weir (if the pulp does not overflow, continue to fill the tank body of the flotation machine with the pulp). Stop supplying air after the aeration state becomes stable, and then the pulp in the flotation machine will drop to a new height. Record this new height H2 , and then the air holdup of the flotation machine is δ=

H1 − H2 H1

(3.12)

In fact, the air holdup in the flotation machine varies from place to place, and the local air holdups should be tested if necessary. The test tool consists of a handle, a PMMA tube with openings at both ends, an elastic band and a sealing ball. Put the PMMA tube into the measuring point with a certain air holdup in the flotation machine with the handle, and keep the sealing ball in the a) state by external force. When the pulp in the measuring point fills the PMMA tube up, remove the external force, and then the sealing ball is changed into state B under the elastic force of the elastic band. Seal the pulp in the PMMA tube, remove the PMMA tube from the flotation machine with the handle, pour the pulp in the PMMA tube into a measuring cylinder, refer to Fig. 3.7, then δlocal = Vb /Va ∗ 100% where δ local Va Vb

Local air holdup, %; Spatial volume of the PMMA tube closed by the sealing ball, L; Pulp volume measured by the measuring cylinder, L.

(3.13)

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3 Dynamic Characteristics and Evaluation of Flotation Machines

Fig. 3.7 Measuring device for local air holdup. a sealing balls controlled by external force b sealing balls controlled by elastic band

3.1.6 Bubble-Loading Rate The bubble-loading rate L refers to the mass of mineral particles carried per unit area of mineralized bubbles in the pulp phase, generally in g/m2 . It can also be expressed by the mass g/L of mineral particles carried per unit volume of bubbles, i.e. the ratio of the total mass m of minerals carried by bubbles to the total volume V of bubbles, L = m/V. The bubble-loading rate is mainly used to represent the loading capacity of bubbles on mineral particles in the pulp phase. On the one hand, it can reflect the effect of reagents on the mineralization process; on the other hand, it can reveal the influence of fluid dynamic environment in the flotation machine on mineralization. Figure 3.8 shows a bubble load measuring device, which consists of a sampling pipe, a collecting chamber, a diversion cone, an exhaust valve and an ore-drawing valve. Firstly, fill the measuring device with clean water. Secondly, close the exhaust valve and the ore-drawing valve, insert the sampling pipe to a location below the liquid level of the flotation machine (i.e. in the pulp) so that the mineralized bubbles can enter the collecting chamber through the sampling pipe orifice. The bubbles are fractured when rising to the gas–liquid interface in the collection chamber, and the mineral particles adhering to the bubbles will be separated from the bubbles and deposited to the bottom of the collecting chamber. Open the exhaust valve (connected with a peristaltic pump for sucking air, with measurable air volume), adjust the frequency of the peristaltic pump to balance the volumes of incoming air and discharged air. If the air generated by the fractured bubbles is timely eliminated, the liquid level in the collecting chamber will remain unchanged. The diversion cone arranged at the upper

3.1 Characteristic Parameters and Evaluation of Flotation Machines Fig. 3.8 Bubble load measuring device

71

Collecng chamber

Diversion cone

Ore-drawing ball valve

Sampling pipe

end of the sampling pipe can avoid falling particles falling back into the sampling pipe. After the completion of testing, the minerals in the collecting chamber are taken out from the ore-drawing hole. The mass of the mineral particles taken out is m, and the volume of air drawn out by the peristaltic pump is V.

3.1.7 Pulp Resident Time Distribution Resident Time Distribution (RTD) refers to the distribution of time consumed from the moment the materials enter the flotation machine to the moment the materials leave the flotation machine, which is the best representation method of material flow in the flotation machine. It is directly related to the flotation efficiency of flotation machines. The most commonly used method for determining the RTD is using watersoluble substances as pulse tracer particles after a stream of solid substance is injected, and determine the RTD by testing the concentration of such tracers appearing at the outlet of the flotation machine and the time. To conduct a full analysis on the degree of continuity of pulp flow in the flotation machine, it is necessary to clarify the duration of mineral particles from the inlet to the outlet of the flotation machine. The flow pattern of the pulp can be judged by injecting

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3 Dynamic Characteristics and Evaluation of Flotation Machines

the pulse tracer particles made of monitorable materials into the flotation machine and observing the effluent state of these particles at the outlet of the flotation machine. Another method is to suddenly change the feed concentration, and then observe the change of the effluent concentration at the outlet. The flow pattern of the pulp inside the flotation machine is usually considered in two ideal types: plug flow and ideal mixing. The simplest flow pattern in the flotation process is that all the components of the pulp in the flotation machine have the same resident time τ, i.e. plug flow. τ is obtained from the following formula: τ = volume of flotation cell/pulp volumetric flow rate

(3.14)

In this case, the resident times of all the units in the flotation machine are equal, and the mixing action occurs in the lateral direction rather than in the movement direction. If a pulse tracer is introduced into the feed, the tracer will be immersed in the pulp after t = τ (Fig. 3.9). In the ideal mixing state, the feed component will be evenly mixed in the whole flotation machine immediately, the tracer particles are injected at the moment of t = 0, and the outlet concentration C at the moment t is calculated as follows: C = C1 exp(−

Iν t) V

(3.15)

C1 : The initial concentration at t = 0 is shown in Fig. 3.10. As can be seen from Fig. 3.10, some tracers immediately flow out of the tank body, while others Fig. 3.9 Residence time distribution (pulse tracer)

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73

Fig. 3.10 Residence time distribution in ideal mixing state of multiple flotation machines predicted by formula 3.17

theoretically do not leave the tank body, thus RTD is equal to zero or infinitely great, so the greatest significance of the RTD test lies in obtaining the average RTD [3]. If the nominal resident time still uses the definition in Formula 3.15, then Formula 3.16 can be written as t C = C1 exp(− ) τ

(3.16)

Formula 3.16 can be extended to the mixing process of N flotation machines in a series, then CN (t/τ ) N −1 exp(−t/τ ) = C1 (N − 1)!

(3.17)

where CN τ

Concentration of products discharged from the Nth tank body of the flotation machine at the moment t; Nominal resident time of each tank body of the flotation machine.

The theoretical curve derived from Formula 3.17 is shown in Fig. 3.10. It is significant to compare the ideal mixing state with plug flow state in this series. Figure 3.10 indicates that the pulp will be dispersed in time when flowing through a series of tank bodies of the flotation machine, and the total nominal resident time τ remains the same constant even though the number of tank bodies is changing. It follows such a law that a small number of continuous flotation equipment is less

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3 Dynamic Characteristics and Evaluation of Flotation Machines

effective in the ideal mixing state than in the plug flow state because the resident time of some materials is too short, while that of others is too long.

3.1.8 Short Circuit The short circuit in the flotation process refers to the pulp that flow out directly and the direct flow of pulp without full circulation in the flotation machine. This case means that there is a dead zone in the flotation equipment, and the flotation time is shorter than the design requirement, resulting in a poor flotation effect. The occurrence of a short circuit to the pulp in the flotation machine is related to the process parameters, reagent system and flotation machine characteristics. In the previously conventional design of flotation circuits, the method of increasing the number of flotation machines is often used for the flotation machine operations to increase the resident time of minerals in the operations, that is, to prevent the “short circuit” in order to avoid the loss of useful minerals, so as to increase the opportunities of useful minerals recovery, such as rougher and scavenger operations, which usually have 4 ~ 8 tanks or more per row. This mode has changed with improvements in the technical level of flotation equipment, equipment upsizing and control level of concentrators. Firstly, the short circuit of pulp can be avoided to a certain extent by adjusting the reagent system and control strategy in the actual production; secondly, the determination of the resident time of pulp showed that the nominal resident time of pulp is a constant (refer to Sect. 3.1.7) when the pulp mixing flow state in the flotation machine is the plug flow. In this case, adding the number of flotation machines will not have a significant impact on the dynamic properties of the flotation machine; thirdly, different flotation dynamics and geometric structure characteristics of flotation machines also provide the ideas to solve and avoid the short circuit of pulp. From the perspective of flotation dynamics, the flotation of useful mineral particles is the result of competition with gangue mineral particles in bubble adhesion. When medium and small flotation machines are used, the flotation machines have small volumes, short pulp resident time, small pulp depth and great influence of impact force of pulp flow on the adhesion of particles to bubbles. After falling off in the adhesion competition with the gangue mineral particles, the useful mineral particles always move a certain distance horizontally in the direction of pulp flow under the action of gravity, centrifugal force and transverse impact force. In this case, the probability of adhesion of useful mineral particles to bubbles again is always less than 100%; when large flotation machines are used, the flotation machines have large volumes, long pulp resident times and large pulp depths. Especially, because of different internal structures and agitator principles of the flotation machines, the influence of pulp flow impact force in the flotation system on the adhesion of particles to bubbles is almost negligible. After useful mineral particles fall off from the bubbles to which they adhere, the probability of adhesion of useful mineral particles to bubbles

3.1 Characteristic Parameters and Evaluation of Flotation Machines

75

again is close to 100% due to a long descending distance when influenced only by gravity and centrifugal force; at present, cylindrical tanks are used in all large mechanical agitation flotation equipment worldwide. Their symmetry can improve the degree of air dispersion and pulp surface stability, and improve the efficiency of flotation machines. The tank bottom is designed into the shape of a conical bottom to facilitate the movement of coarse and heavy mineral particles to the tank centre so as to return to the impeller area for recirculation and reduce the phenomenon of pulp short circuit. Therefore, the “short-circuit” phenomenon which is easy to appear in the conventional configuration is not easy to occur in the configuration circuit of the short column flotation machine [4].

3.1.9 Volume Utilization Coefficient The volume utilization coefficient refers to the ratio of the pulp volume in the tank body of the flotation machine to the geometric volume of the tank body. Flotation time is an extremely important basic data for concentrators in the expanding test and engineering design. The determination of flotation time involves the utilization characteristic of the flotation machine volume. This characteristic is usually described by the volume utilization coefficient, i.e. K value. The selection of K value has a great influence on the calculation results of the flotation time.

3.1.9.1

Influencing Factors of Volume Utilization Coefficient

The geometric volume of the flotation machine can be divided into four parts, i.e. pulp volume, froth layer volume, volume of air dissolved in the pulp, and volume of other parts and components in the tank body of the flotation machine. The volume utilization coefficient is related to the proportion of the last three volumes to the geometric volume of the flotation machine. In actual production, the above three volumes are related to the flotation process (froth layer thickness), reagent system (air dissolved in the pulp) and flotation machine structure (parts contained in the tank).

3.1.9.2

Calculation of Volume Coefficient

In general, the volume utilization coefficient can be calculated by the following formula: K = (v − v1 − v2 − v3 )/v

(3.18)

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3 Dynamic Characteristics and Evaluation of Flotation Machines

where v v1

v2 v3

Geometric volume of the tank body of the flotation machine; Froth layer volume, which is calculated from the froth thickness actually measured in the production of the flotation machine. When the froth is below the overflow weir, v1 also contains the volume of the “depressed” froth part; Volume of air bubbles contained in the pulp during flotation; Volume of flotation machine parts and components immersed in the pulp during production.

3.1.10 Pulp Suspension Pulp suspension refers to a suspended state of mineral particles in the pulp. It directly affects the mixing effect of pulp and reagent and the collision probability between particles and bubbles. Sufficient mineral suspension in the flotation machine is the prerequisite for obtaining good flotation indicators. The suspended state of mineral particles in the flotation machine is related to the mechanical structure of the flotation machine (structure of the tank body of the flotation machine, structure of the impeller stator), operating parameters of the flotation machine (impeller speed, aeration rate) and the properties of mineral particles themselves (particle size, particle density). Flotation machine is in different model and specification, but there are mainly two agitation states of flotation machine when divided from the characteristics of solid–liquid suspension [5]: The mineral particles are completely suspended away from the tank bottom, i.e. complete off-bottom suspension; the mineral particles are suspended and evenly distributed in the tank, i.e. uniform suspension. For the two different states of solid–liquid suspension, two bases for judging two solid–liquid suspended states are put forward. (1)

(2)

The unsuspended solid volume at the tank bottom is regarded as the judgment basis. If the resident time of solid particles at the tank bottom is no more than 1 ~ 2 s, it is believed that the solid particles are completely off-bottom suspended. When the solid particles are completely suspended away from the bottom, the solid contents in all positions in the tank are not completely uniform. Accordingly, a qualitative analysis of the suspended state of mineral particles in the flotation machine can be made. Figure 3.11 indicates the change of the suspended state of particles in the tank as the speed of the agitating mechanism gradually increases. The movement velocity of mineral particles is regarded as the judgement basis. Since the solid particles in the centre of the tank bottom are the finally suspended portions, the investigation on the velocity variation of the solid particles in this position at different agitation speeds may also be regarded as the basis for judging whether the particles are completely suspended or not. When the particles are not completely suspended, the movement speed of

3.1 Characteristic Parameters and Evaluation of Flotation Machines

complete suspension

77

uniform suspension

Fig. 3.11 The particle suspension state changes when the stirring speed increases gradually

particles in the centre of tank bottom changes very little; when the particles are completely suspended, the movement speed of particles varies significantly with the agitation speed.

3.1.11 Critical Speed of Impeller The critical speed of the impeller of a flotation machine refers to the minimum speed of the impeller when the air in the flotation machine is completely dispersed or the pulp is completely off-bottom suspended.

3.1.11.1

Critical Dispersion Speed of Air

In the gas–liquid agitation equipment, the gas is dispersed in the liquid in the form of minute bubbles, and the dispersed state will change with the changes in agitation speed and aeration rate. Figure 3.12 describes the changes in the gas–liquid dispersion state when the agitation speed gradually increases at a certain aeration rate, which may be divided into three states:

(a)

(b)

Fig. 3.12 Bubbles distributed in flotation cell

(c)

(d)

(e)

78

(1)

(2)

(3)

3 Dynamic Characteristics and Evaluation of Flotation Machines

Flooding state. At this time, most of the gas is not dispersed, the bubble diameter is also relatively large, and the bubbles rise directly to the liquid level along the agitator shaft, which is equivalent to a bubble kettle (Fig. 3.12a, b). Loading state. The gas is basically dispersed, the bubbles have already been close to the wall surface of the tank body of the flotation machine, but the gas is not well dispersed in the area below the impeller, and the bubbles can only circulate with the liquid flow in a limited way (Fig. 3.12c). There is a critical speed in the mutual transformation between this state and the flooding state, which is called the flooding point speed Nf . It usually increases with the increase of aeration rate. Completely dispersed state. The gas is well dispersed in the equipment, and the bubbles are small and often recirculated with the liquid (Fig. 3.12d, e). There is also a critical speed in the transition between this state and the loading state, which is called the full dispersion speed N cd . N f and N cd are not so far different from each other due to the narrow operating conditions of the loading state, and these two critical speeds are generally not strictly distinguished in engineering.

3.1.11.2

Critical Pulp Suspension Speed

The critical pulp suspension speed refers to the minimum speed for suspending all mineral particles in the flotation machine, which is expressed in Nc and usually used as the criterion for judging the suspension effect of flotation machines. The critical suspension speed of impellers is very important for the design of flotation machines [6]. A.

Influencing factors of critical pulp suspension speed

The critical impeller speed can be visually considered as the result of two opposite mechanisms. The first kind of mechanism is the particle suspension mechanism, which is mainly influenced by the impeller performance and geometry. The particle suspension mechanism is related to the flow state of the overall pulp flow, which depends on the suction capacity of impellers and the turbulence vortex caused by local energy dispersion. The second mechanism is opposite to the first one, i.e. the settlement mechanism of particles. The driving force of the settling process is the well-known critical settling velocity of particles. This will result in phase separation, which is mainly influenced by particle properties (particle size, solid concentration and relative solid density) and pulp properties (liquid phase viscosity and superficial gas velocity). O.A. Lima, D.A. Deglon b and L.S. Leal Filho performed the comparative test on the critical impeller speed using 6L Denver and Wemco flotation machines [7]. Three kinds of minerals were used in the test: Apatite, quartz and mica. The research showed that the critical impeller speed mainly depends on the particle size, particle density and air volume (superficial gas velocity), while the solid concentration has only subtle effects on it, and the influence of liquid viscosity on it is negligible. For the three kinds of flotation machines, the influence indices of

3.1 Characteristic Parameters and Evaluation of Flotation Machines

79

particle size, solid concentration and liquid viscosity are equal. The influence index of solid density on the critical impeller speed is not as great as that observed by previous researchers, and it is consistent with the result measured by testing in the agitation tanks as reported in the general literature. B.

Determination of critical pulp suspension speed

The mineral particles contained in the pulp treated by the flotation machine do not have the same size. Generally, their sizes are normally distributed, so it shall be ensured that large minerals in the pulp can be completely off-bottom suspended when determining the impeller speed. At this time, particles smaller than this size can be generally off-bottom suspended, that is to say, the impeller speed must be greater than the speed for the largest particles in the pulp to achieve the completely off-bottom suspended state. A large number of flotation tests and theoretical researches showed that the critical speed calculation formula of solid complete off-bottom suspension for mechanical agitation flotation machines design is 0.13 0.10 0.45 υ g Nc = K s T −0.85 d 0.20 p B

(ρs − ρl ) 0.45 ρl

(3.19)

where Nc Ks T dp B υ g ρs ρl

Critical speed, r/min; Geometry factor of the tank body; Diameter of the tank body of flotation machine, m; Diameter of large particles in the pulp, mm; Ratio of solid mass to liquid mass in the pulp of flotation machine; Kinematic viscosity of pulp, MPa·s; Gravity acceleration, m/s2 ; Density of solid particles, g/cm3 ; Liquid density, g/cm3 .

3.1.12 Spindle Power Consumption The spindle power consumption refers to the actual power consumption generated by the flotation machine in the working process, and the motor power consumption may be regarded as the spindle power consumption without considering the transmission loss. For concentrators, the energy consumption of the flotation operation is second only to that of the grinding operation, so the energy consumption of the flotation machine naturally becomes an important technical indicator that indicates the performance of the flotation machine [8].

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3 Dynamic Characteristics and Evaluation of Flotation Machines

3.1.12.1

Influencing Factors of Spindle Power Consumption

Without considering the influence of the flotation process on flotation machine energy consumption, the energy consumption of a mechanical flotation machine is mainly influenced by the structure parameters of the flotation machine, including the dimensions of the flotation tank (depth of the tank body), impeller structure form (impeller diameter, impeller speed, number of blades, blade height), operating parameters of the flotation machine (impeller speed). Therefore, analysis must be conducted from these aspects in order to reduce the energy consumption of the flotation machine, with the emphasis on the form and structure parameters of the impeller. When the impeller of the flotation machine rotates, the power consumption is used to overcome the resistance of the pulp, suck the pulp and throw the pulp out of the impeller area. When the impeller rotates, the power can be expressed by the formula below: N = N1 + N2

(3.20)

where N

N1 N2

Total power consumed by the rotating impellers of the flotation machine, excluding energy consumption of bubble scraping in the flotation machine and that of the blowing system of the pneumatic agitation flotation machine, kW; Power consumed in sucking the pulp by the impeller, overcoming the static pressure head of the pulp and throwing the pulp out of the impeller area, kW; Power consumed for overcoming pulp resistance when the impeller rotates, kW.

N1 =

γ QH 102η1 η2

(3.21)

where γ Q H’ η1 , η2

Pulp density, kg/m3 ; Pulp volume sucked by the impeller (including feed and circulating pulp), m3 /s; Pressure head generated by impeller rotation (its value is equal to the static pressure head of the pulp in the tank body), m; Hydraulic and mechanical efficiency of impellers.

N2 =

Ψ π Z D 2 n H Sγ 102 × 102

(3.22)

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81

where

Z D n H S γ

Positive drag coefficient of impeller blades; Number of blades, piece; Impeller diameter, m; Impeller rotating speed,r/min; Static pressure head of pulp in the tank body (H = H’), m; Impeller height, m; Pulp volume-weight, kg/m3 .

Where, N 1 is much smaller than N 2 , which often accounts for only about 10% of the total impeller rotating power, while N 2 accounts for about 90%, that is to say, power consumption is mainly used to overcome the pulp resistance. From Formula 3.22, we can see the influence of the parameters related to the tank body, impeller and pulp on the spindle power of the flotation machine.

3.1.12.2

Calculation and Measurement of Spindle Power Consumption

The flotation power can be expressed in the following expression: P = N p ρn 3 D 5

(3.23)

where P Np ρ n D

Spindle power, kW; Power number; Pulp density, g/cm3 ; Impeller speed, r/min; Impeller diameter, m.

The formula above is generally used to calculate the installed power design of flotation machines. In actual production, we pay more attention to the real power consumption of the flotation machine spindle, and this power can be measured directly by a power meter or calculated from the measured current.

3.2 Performance Evaluation of Flotation Machines The separation process of the flotation machine is the result of interaction of multiple variables. Klimpel et al. [9] considered the flotation process as a system in which chemical, operational and mechanical factors influenced each other. The balance research on the three factors has changed for a long time, and factor researches on machinery have begun to flourish. The work presently carried out focuses on the researches on the dimensionless number related to the dynamic performance

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of flotation machines [10]. These researches showed that single mechanical factors (such as impeller speed, aeration rate and tank body design) will not significantly affect the dynamic performance of flotation machines, but the dynamic conditions of flotation—flow state, strength of mixture, suspension state of particles, degree of air dispersion, bubble–particle interaction—formed by them will in turn control the dynamic performance. Therefore, the flotation performance evaluation of the flotation equipment itself depends on the flotation dynamics and operating parameters during its operation. As mentioned above, there are many dynamic and operating parameters of flotation machines. In the actual production process, the froth loading rate, pulp resident time and operating speed of the prototype equipment for certain pulp properties and reagent system are unchangeable, so these parameters of flotation machines are generally not used for the investigation on the dynamic performance of flotation machines in the actual production. The performance evaluation parameters of flotation machines commonly used in engineering practices need to have the following characteristics: (1)

(2)

(3)

They will have a significant impact on the flotation effect, such as degree of air dispersion, which directly affects the collision and adhesion probabilities between bubbles and particles. They are closely linked to the process operations, affected by the process conditions or may be adjusted according to the process requirements, such as aeration rate. They are important parameters that represent the aeration capacity of flotation machines, and can be adjusted according to different pulp properties at any time. They are easy to measure. For example, gas holdup, pulp suspension capacity and spindle power consumption. The measurement process is simple and accurate.

Therefore, the most commonly used parameters for evaluating the performance of flotation machines are aeration rate, degree of air dispersion, gas holdup, pulp suspension capacity and spindle power consumption, which are also used to evaluate the performance of the flotation machines in engineering practices.

References 1. Ledezma RA (2009) Gas distribution in industrial flotation machines: a proposed measurement method[D]. McGill University 2. Colmetz CO et al (2003) Measurement of gas dispersion in flotation machine [J]. Metallic Ore Dressing Abroad, (4) 3. Lelinsky D et al (2003) Analysis of pulp retention time distribution in a large scale flotation machine [J]. Metallic Ore Dressing Abroad, (3) 4. Songrong Y, Wu Z (2000) Several issues in flotation circuit [J]. Nonferrous Mines 29(5) 5. Flotation machine manual [R]. Beijing general research institute of mining and metallurgy

References

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6. Shen Z, Lu S, C Dong et al (2009) Study on the solid suspension in the tank of a large-scale mechanical agitation flotation machine. Nonferrous Met (mineral processing section) (4) 7. Lima OA, Deglonb DA, Leal Filho LS (2009) A comparision of the critical impeller speed for solids suspension in a bench-scale and a pilot-scale mechanical flotation cell. Miner Eng 22:1147–1153 8. Yang F (2004) Energy consumption analysis of mechanical agitation flotation machine. Nonferrous Met (mineral processing section). (5) 9. Klimpel RR, Dhansen R, Fee BS (1986) Selection of flotation reagents for mineral flotation. In: Mular AL, Anderson MA (eds) Design and installation of concentration and dewatering circuit, pp 384–404 10. Harris CC (1976) In Fuerstenau MC (ed) Flotation machines, in Flotation A.M. Gaudin Memorial Volume, vol 2, ALME, pp 753–815

Chapter 4

Research on Fluid Dynamics Test of Flotation Machines

Computational fluid dynamics simulation and experimental fluid dynamics testing are two main means for the research of flotation machines [1–3]. The test data of experimental fluid dynamics supports the improvement in computational fluid dynamics simulation. The computational fluid dynamics simulation technology well solves the problems of high experiment cost, long cycle and difficult comprehensive acquisition of a large number of microscopic flow field information. The combination of the two promotes the efficient development of flotation machines. This chapter mainly introduces the current researches on experimental fluid mechanics of flotation machines [4]. Over the past few decades, the means of experimental fluid mechanics have developed rapidly, which helps researchers to better understand the essence of flow and related laws and promote the emergence of more efficient equipment [5]. It mainly introduces the experimental fluid mechanics methods used for experimental flotation machines and industrial flotation machines. These methods can be not only used for the research of flotation equipment, but also can be applied for other fluid mechanics researches.

4.1 Flow State Test of Flotation Machines The flow state is an important aspect in the research of the flow field of flotation machines, and the key to the flow state research is the flow velocity measurement. The flow velocity measurement is divided into contact and non-contact measurements. A very rapid progress has been made in the non-contact measurement technologies, mainly including laser Doppler velocimetry (LDV), particle dynamics analyzer system (PDA), particle image velocimetry (PIV), etc. [6]. These methods have the advantages of no interference to flow field, high measurement accuracy, fast dynamic response, high resolution, etc. They realize real-time collection and analysis, display of particle images, velocity vector maps, etc. They are the first choices for flow

© Metallurgical Industry Press 2021 Z. Shen, Principles and Technologies of Flotation Machines, Springer Tracts in Mechanical Engineering, https://doi.org/10.1007/978-981-16-0332-7_4

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velocity measurement. The new generation of contact velocity measurement technology, represented by the electromagnetic current metre and the mechanical agitation propeller current metre, has also developed rapidly in measurement precision, accuracy and portability.

4.1.1 LDV Testing Technology The laser Doppler velocimetry (LDV) began to be widely applied in the 1960 s. LDV is a non-contact measurement method. Different from a hot-wire anemometer which disturbs the flow field to a certain extent by insertion of a sensitive element into the flow field, LDV has a wide range of measurement and high spatial resolution. Since the 1990 s, LDV has been widely applied in various branches of fluid mechanics with the LDV integration, utilization of optical fibres, intelligence and the development of modern digital signal processing technology. LDV measurement is performed at a certain measuring point over a period of time, so the measured velocity is a time-averaged quantitative value, and the whole velocity field can be obtained by measuring every point in the agitation tanks [7, 8]. The principle of laser Doppler velocimetry is to measure the velocity of particles by the Doppler effect of scattered light from moving particles. TSI’s threedimensional LDV system of a five-beam single-lens backscattering mode has the major components as follows (Fig. 4.1): (1) (2)

A laser: INNOVA70C Series 2 W Hydrogen Ion Laser manufactured by COHERENT. A multicolor beam splitter with six optical fibre couplers, which divides a laser beam into three pairs of parallel emitted light, whose wavelengths are 514.5 nm (green), 488 nm (blue) and 476.5 nm (purple), respectively. In each

Fig. 4.1 Three-dimensional LDV test system (TSI company)

4.1 Flow State Test of Flotation Machines

(3)

(4)

(5)

(6)

87

pair of beams, there is one beam to which a 40 MHz frequency-shift signal is added. A PDM 100 photoelectric receiver which receives, separates and converts scattered light into an electrical signal and extracts a frequency-shift signal for analysis and processing by software TSI’s Flowsizer. An FSA3500 signal processor which distinguishes signal pulse from noise according to the signal-noise ratio and extracts velocity information from the signal. A five-beam three-dimensional optical fibre probe. Five beams focus on a measuring point in parallel through a convertible lens, and the scattered light is received and transmitted into the multicolor beam splitter by the receiving optical fibre so that an optical signal with three velocity components is separated out. A three-dimensional moving coordinate frame on which an optical fibre probe is arranged to allow movement in three directions, with the minimum moving distance up to 0.001 mm.

The signal source of LDV measurement comes from scattering particles. The rational selection of particles can improve the signal-noise ratio of Doppler signals. With the three-dimensional moving coordinate frame, the laser can measure the fluid flow at any point in the agitation tank.

4.1.2 PIV Testing Technology (1)

PIV principle

Particle image velocimetry, referred to as PIV technology, is an advanced full-field measurement technology suitable for measuring typical transient flow fields such as combustion flame fields, flow conditions near the moving surface of the horizontal wing of a helicopter and flow fields in agitation tanks. The PIV technology enables both measurements of a velocity field in a large enough area with coherent structures and access to the flow field information of a flowing small-scale structure due to its high enough spatial resolution. With the development of technologies in the computer, optics, infographics and other related fields, the PIV technology has achieved important results in the experimental researches of turbulence, separation vortex, jet flow, etc. All the main turbulence data measured, such as velocity field, turbulence intensity, wave number spectrum, Reynolds stress, root mean square velocity value, total shear stress and other structures, are in good agreement with the results of hot-wire anemometer, LDV and Direct Numerical Simulation (DNS). At present, TSI’s PIV technology has enabled the measurement of 12,000 instantaneous velocity vectors in a flow field with the area of 10 × 13 cm, and its accuracy is about 0.1 ~ 1% [9].

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Fig. 4.2 Schematic diagram of PIV system

During velocity measurement by the PIV technology, tracer particles with good following performance, good reflection and equivalent specific gravity to that of fluids need to be uniformly dispersed in the flow field. A light sheet formed by scattering the light beam generated by a laser through a lens is incident on the area to be measured in the flow field, and the CCD camera is aimed at the area in the direction of the vertical light sheet. Images of the particles during two pulse laser exposures are recorded by the light scattering of tracer particles, two PIV negatives (i.e. a pair of pictures of the same measurement area and different moments) are formed, and the contents recorded on the negatives are the particle images in the whole area to be measured [10–13]. Figure 4.2 is a schematic diagram of the PIV system. Since the whole area to be measured contains a large number of tracer particles, it is difficult to distinguish the same particle from the two images, thus the required displacement vector is unavailable. The images are divided into many small interrogation areas by image processing technology, and the magnitude and direction of particle displacement in the interrogation areas are obtained by auto-correlation or cross-correlation analysis. The velocity vector of particles can be calculated since the interpulse time has been set, as shown in Fig. 4.3. The velocity vector in a certain interrogation area can be obtained by calculating the data of all the particles in the interrogation area, and the whole velocity vector field can be obtained by counting and calculating all the interrogation areas. In the actual measurement, many pairs of exposure pictures can be taken in the same position so that the flow state inside the whole flow field can be reflected much more comprehensively and accurately. Unlike the point measurement of LDV, PIV is a planar measurement technology which is advantageous to research the unsteady characteristics of flow, and the

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Fig. 4.3 Basic test principle diagram of PIV

particle image velocimetry (PIV) is essentially the development of flow field visualization technology. Flow visualization is an important component of experimental fluid dynamics. The traditional flow field visualization technology can only be used to qualitatively analyse the measured flow field, but quantitative results are difficult to obtain. The PIV technology is a measurement instrument developed by the image processing technology on the basis of flow visualization. The whole structure of the flow field can be obtained by the PIV technology, especially the detailed understanding of transient flow. BGRIMM has made many meaningful exploration efforts in the measurement of the flow field in flotation tanks by the PIV technology. Figure 4.4 is the PIV test

Fig. 4.4 PIV test system of flotation machine

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Fig. 4.5 Whole flow field in the tank measured by PIV

system of flotation machines. Figure 4.5 is the whole flow field in the tank measured by PIV. The laser velocimetry technology has the characteristics of non-contact, no disturbance, fast response, high spatial resolution, wide measurement range, etc., which enables the PIV technology to have many advantages in measuring the flow field of flotation equipment, so that the overall flow field structure in the tank can be well measured. However, there are still many problems worth profound research on the visibility of the flow field, the shielding of the scattered light from tracer particles by bubbles, etc. in terms of the measurement of the flow field structure in the rotor area, gas-liquid two-phase flow field and even multiphase flow field. No matter it is LDV or PIV, all these non-contact optical measurement systems obtain the velocity of the flow field by measuring the velocity of tracer particles moving with the fluid rather than by direct measurement. How to select and add appropriate tracer particles is a very important subject in laser velocimetry. Generally, the tracer particles need to meet the following requirements: (1)

Good following performance: They can follow the fluid motion well, and the relative motion between particles and fluid flow is as small as possible so as to ensure that the movement speed and direction of the tracer particles can

4.1 Flow State Test of Flotation Machines

(2)

(3)

(4)

91

represent the velocity and direction of the fluid. The following performance of tracer particles to fluid mainly depends on the diameter and density of particles, the viscosity and density of fluid and other parameters. Good light scattering performance: They have high scattering efficiency, which is conducive to low-noise scattering light and convenient for signal processing, with higher measurement accuracy. When the optics system is determined, the scattering characteristics of the tracer particles are closely related to the wavelength of incident light, the diameter of particles, the physical properties of the particles (such as refractive index), etc. Good physical and chemical properties: The added scattering particles should be non-toxic, non-irritating, non-corrosive or non-abrasive to flow pipelines, and stable in chemical properties and so on. The tracer particles should be easily generated, clean and hygienic, without pollution to the environment. For open experiments, the tracer particles should be cheap, with a wide adjustable extent of concentration. There are many types of materials for the tracer particles, such as glass micro-particles and melamine particles coated with rhodamine dye.

Figures 4.6 and 4.7 shows the conditions photographed by PIV when the tracer particles perform well and poorly, respectively. It can be seen that when the tracer

Fig. 4.6 PIV photograph when the tracer particles perform well

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Fig. 4.7 PIV photograph when the tracer particles perform poorly

particles perform well, the particles in the whole flow field are uniformly dispersed, and the brightness of the tracer particles is obviously higher than that of the background colour. In the principle of tracer particle selection, good light scattering and following performance are the basic requirements for tracer particle selection. But sometimes the two requirements contradict each other. The scattering property of tracer particles usually increases with the increase of their sizes, and the larger the sizes of tracer particles are, the worse their flow following performance is. Therefore, the influences of the two requirements must be weighed in practical experiments. Relatively speaking, LDV can be relatively convenient to ensure the concentration of tracer particles because it is a point measurement method so that data acquisition has a suitable sampling rate. But PIV is a planar measurement method by which the velocity of each interrogation area is obtained by image processing calculation. For related processing technologies, it would be best to ensure 3–8 tracer particles per interrogation area to ensure the accuracy of measurement. PIV receives scattered light in the 90° direction where the scattered intensity is relatively weak and fluctuates greatly, so the particle size should be relatively small to ensure the scattering intensity in the 90° direction.

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(2)

93

PIV measurement of the flow field of flotation machines

We obtain a velocity vector map of the whole flow field with a single liquid phase of KYF-0.2 flotation machine by the PIV method, as shown in Fig. 4.8a. The fluid has two kinds of flow, i.e. obviously oblique upward and oblique downward after being deflected from the stator blade. The oblique upward flow forms a clockwise upper circulating flow field under the action of sidewalls, top free surface, etc. The oblique downward flow forms a counterclockwise lower circulating flow field which is sucked into the rotor area at the bottom of the rotor. This intuitively shows the upper and lower circulation flow field structure in the design theory of flotation machines. Figure 4.8b is the flow field of the flotation machine predicted by CFD. CFD and PIV have the same structure of the whole circulating flow field, which indicates that their joint research on the flow of flotation machines is very effective. Figures 4.9 and 4.10 reflects the comparison of CFD predictions and PIV measurements of radial and axial velocities on a vertical line with the longitudinal section r/R = 0.56. From an overall point of view, the CFD predictions and PIV measurements fit well in the variation trends of radial and axial velocities, velocity values, etc., which indicates that the CFD predictions are more correct to reflect the internal flow field state of the flotation machine. The vertical line where r/R = 0.56 is located is just at the stator blade outlet. From the curves, it is seen that both the radial and axial flow velocities in the tank body bottom area upward along the tank bottom are smaller, and the peak velocity occurs outside the upper part of the stator blade about 220–240 mm away from the tank bottom height, which is consistent with the actual condition. The velocity vector map of the rotor bottom flow field of the experimental KYF0.2 flotation machine based on the PIV method is shown in Fig. 4.11. It can be seen that the flow tends to be inclined upward and downward after the fluid is diverted from the stator blades, and the flow velocity in the inclined upward direction is obviously greater than the flow in the inclined downward direction. That is because the flow inclined upward is mainly due to the lifting effect provided by the special rotor blade design, while the flow inclined downward which is mainly powered by the suction effect at the rotor bottom is weaker in intensity. The suction effect of the rotor is remarkable at the rotor bottom. The closer the fluid is to the rotor, the higher the upward velocity is and the upward flow is also obvious at the tank bottom below the rotor. However, the velocity at the tank bottom far from the rotor is small, especially at the edge of the tank body at the lower left corner of the vector map, which is less than 0.2 m/s. According to the PIV test results, the actual fluid velocity in this area is very small and easy to cause mineral deposition. The velocity vector map between stator blades of the flotation machine based on the PIV method is shown in Fig. 4.12. Figure 4.13 shows the flow field position of the stator blades in the PIV test. As seen from the figure that the fluid thrown out of the rotor enters the spaces between stator blades where the flow is smooth and free of vortex, and the flow velocity in the inclined upward direction is high, which indicates the remarkable effects of diversion and current stabilization of the stator blades.

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(a) PIV

(b) CFD Fig. 4.8 Velocity vector map of the whole flow field by the PIV at impeller speed of 195 rpm in KYF-0.2 flotation machine

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Fig. 4.9 Comparison between CFD predictions and PIV measurements of radial velocities on a vertical line of r/R = 0.56 in the longitudinal section

4.2 Pulp Flow Test Technology 4.2.1 Residence Time Distribution Test Generally, residence time distribution (RTD) means that if fluids flow in a chemical reactor at a constant flow rate, these fluids may be regarded as a combination consisting of many fluid elements, then the time spent by them in the reactor between inlet and outlet is the residence time of the fluids [14–17]. For the flotation, when the pulp flows through the flotation machine at a steady flow rate, the routes of all the pulp elements flowing through the tank body are not exactly the same although the overall residence time is predictable, thus the residence times in the tank body are also different. The residence time distribution laws of the pulp in the flotation tank, i.e. the residence time distributions of the pulp, are not exactly the same. The residence time distribution tracer test is usually such a process that a few tracers are fed at the equipment inlet by pulse (in a very short time), the concentration changes of the tracers are monitored at the outlet. Thus, the residence time distribution curve is drawn. There are many kinds of test methods, such as conductivity method, turbidity method, fluorescence method and radioactive tracer method. The conductivity method is simple and practicable for the RTD test of aqueous phase in a laboratory. It is difficult to apply in the industrial flotation process due to the

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Fig. 4.10 Comparison between CFD predictions and PIV measurements of axial velocities on a vertical line of r/R = 0.56 in the longitudinal section

Fig. 4.11 The velocity vector map of the rotor bottom flow field of KYF-0.2 flotation machine by PIV

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Fig. 4.12 The velocity vector map between stator blades of the flotation machine by PIV

problems of complexity of the industrial system, high pulp conductivity, etc. The fluorescent trace method which can avoid the above problems is widely applied in the RTD tests of the industrial flotation process. Its main limitation is that it can only evaluate the overall characteristics of pulp flow but cannot reveal the RTD of solid phase or gas phase particles separately. The radioactive tracer technique can realize the RTD of the solid phase, liquid phase and even gas phase in the flotation machine. Its main disadvantages are the harmfulness of radioactivity and high requirement for safety protection.

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Fig. 4.13 The flow field between the stator blades by PIV

(1)

Conductivity method

The core instrument of the conductivity tracer method is the conductivity metre, which requires high precision and high sampling frequency. It can sample once in 1 s while realizing the on-line test. Conductivity metre parameters and pictures: The tracers of the conductivity tracer method are relatively easy to acquire. All solvents such as KCL and NaCl are permissible. Figure 4.14 and 4.15 is the test systems for residence time distribution of flotation machines based on the conductivity method. Clean water is circulated through a pump in the tank, the KCL solution is pulseinjected at the inlet, with clean water or pulp (with very low conductivity) in the tank, and the changes in conductivity are monitored at the outlet. Figure 4.16 and 4.17 gives the RTD curves of water for single-tank and continuous-tank 30L flotation machines. After the pulse injection of the tracers, the peak concentration appears after a short period, followed by fast attenuation. This type of curve is very similar to that of the ideal agitated reactor. (2)

Fluorescent trace method

The test method of the fluorescent trace method is consistent with that of the conductivity tracer method, that is, the fluorescence tracer solution is injected at the inlet by pulse, monitoring and sampling are conducted at the outlet, followed by a discrete test

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Fig. 4.14 Test systems for residence time distribution of single flotation machine

of the fluorescence intensity, thus obtaining the RTD curve. The fluorescent tracing instrument is the core instrument of this method, as shown in Figs. 4.18 and 4.19. Table 4.1 gives the basic parameters of some commonly used fluorescent tracing instruments. The fluorescein sodium powder is generally the choice for the fluorescent tracers. This reagent is red and soluble in water easily. The fluorescent trace method allows tests to be carried out at the site of the industrial flotation machine to obtain the RTD distribution of the pulp. Due to the high turbidity of the pulp from the industrial flotation machine after sampling, discrete sampling is usually adopted to test the fluorescence intensity by taking the supernatant of a clear solution. Because of the long residence time of the industrial flotation machine, the precision of obtaining the RTD curve by discrete sampling is reliable.

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Fig. 4.15 Test systems for residence time distribution of united flotation machines

Fig. 4.16 RTD curves of water for single-tank

(3)

Radioactive tracer method

The radioactive tracer method is a method of tracer testing with radioactive nuclides as tracers. It has been widely applied in all scenarios in the industrial field due to its advantages of non-intervention, etc. Its main disadvantages lie in the high safety and environmental protection requirements, strict control of dosage of radioactive substances, highly professional and technical natures of testers, etc. The radioactive

4.2 Pulp Flow Test Technology

Fig. 4.17 RTD curves of water for united tanks Fig. 4.18 FluoroQuik fluorescent tracing instrument

Fig. 4.19 AquaFluor fluorescent tracing instrument

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Table 4.1 Basic parameters commonly used for fluorescent tracing instrument

Equipment name Company

Main parameter

FluoroQuik

Ami science, USA

Range: 0–15000 ppb Precision: 1 ppb Portable

AquaFluor

Turner Designs,USA Range: 0–1000 ppb Range of linearity 0–400 ppb Precision: 0.4 ppb Portable

tracer method is a crucial step in the experimental research for the selection of radioactive tracers. Table 4.2 gives the radioactive tracers applied in industry. Flotation is a gas–liquid–solid three-phase system. The RTD of each phase can be separately obtained by the radioactive tracer method. Br-82 is often selected and used as a radioactive tracer for the pulp liquid phase test. Figure 4.20 gives the RTD curves of liquid phase and solid phase particles in the flotation machine. There is a significant difference between the two kinds of particles, that is, the average residence time of solid phase mineral particles is shorter than that of liquid phase mineral particles. Na 24 is often used as a tracer of solid mineral particles and can be used as a mark on mineral particles with different particle sizes so as to research the RTD differences between mineral particles with different particle sizes, as shown in Fig. 4.21. It can be concluded that the coarse mineral particles have the shortest coarse mineral particles among the three kinds of size fractions, which explains the reason why the separation of coarse minerals is more difficult from the perspective of RTD. For the gas tracer method, some scholars use Kripton-85 and Freon-131 as the gas tracers.

4.2.2 Circulation Volume and Flow Velocity Test The pulp circulation capacity of rotors is an important performance indicator for flotation machines [18, 19]. The key to acquire the circulating capacity of the flotation machine is to measure the flow velocity of the fluid entering the rotor. The main instruments for measuring the flow velocity of the flotation machine fluid include the pitot tube velocimeter, vane current metre velocimeter, electromagnetic flowmeter velocimeter, etc. (1)

Electromagnetic current metre

The electromagnetic flowmeter velocimeter is designed based on Faraday’s law of electromagnetic induction. When moving along a plane where an alternating magnetic field of a flow velocity sensor is perpendicular to the central axis of electrodes, the conductive fluid cuts the line of magnetic force and generates the induced potential which is collected by the signal electrode and is proportional to the flow

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Table 4.2 Radioactive tracers for marking different substances Isotope

Chemical composition of the recommended marker Gas

Aqueous solution

Solid inorganic matter

Organic matter

3H

Gas

3H O 2

–

Various organic compounds

14 C

CO2

–

–

Various organic compounds

Na

–

Water soluble ions

Na2 CO3 (Carboxy acrylic Naphthenate, salicylate ball)

S

H2 S

–

–

Various organic compounds

Cl

–

–

–

Various organic compounds, chlorobenzene

Ar

Gas

–

–

–

Se

–

Water soluble ions

SeO2

–

Cr

–

–

Adsorb on quartz surface

–

Fe

–

–

Metal

Co

–

–

Metal

Naphthenate

Ca

–

Water soluble ions

CaO

Naphthenate

Zn

–

–

ZnO

–

Ni

–

–

–

Stearates, oxalate

As

AsH3

–

–

–

Ge

–

–

–

Various organic compounds

Br

CH3 Br

Water soluble ions

CaBr2

p-Dibromobenzene, bromobenzene

Kr

Gas

–

–

–

Rb

–

–

–

Ag

–

–

Adsorb on solid surface

–

Sb

–

–

Metal

Triphenyl stibine

I

–

Water soluble ions

–

Solution of kerosene with iodine, iodobenzene

Xe

–

–

–

–

La

–

–

La2 O3 (Polypropylene ball)

–

Ce

–

–

Ce2 O3

–

Ta

–

–

Ta2 O5

–

Au

–

–

AuCl3 absorb on powder surface

Amine salt, colloidal gold,

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Fig. 4.20 The RTD curves of liquid phase and solid phase in the flotation machine

Fig. 4.21 The RTD curves differences between mineral particles with different particle sizes

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velocity; the converter calculates the flow velocity of the conductive fluid flowing through the profile of the flow velocity sensor through the induced potential, and this velocity signal is amplified by the flow indicator and converted into a digital quantity signal proportional to the flow velocity signal, thus realizing the measurement of the flow velocity. Table 4.3 lists the main technical parameters of the technical parameters of the electromagnetic current metre. Figure 4.22 is the electromagnetic current metre. Figure 4.23 gives a schematic diagram of internal circulation volume measurement of flotation machines. Test the flow velocities at different radii in the diversion cylinder by moving the test bar, and calculate the volume flow rate of the pulp in the diversion cylinder by means of integral average calculation. Figure 4.24 shows the speeds along different positions from the axle centre to the edge of the diversion cylinder 500 mm below the rotor of a flotation machine. It can be seen that there is a peak velocity in a certain position off the axle centre. Figure 4.25 is the relationship between different speeds and circulation volumes of a flotation machine. The circulation volume increases gradually with the increase of rotating speed. The main advantage of measurement of the internal flow velocity of the flotation machine by Table 4.3 Technical parameters of electromagnetic current metre Equipment name

Company

Main parameter

Accessories

FH950 Portable Electromagnetic Current Metre

Hach, USA

0-10 m/s ±2% Portable

Sensor, mainframe, 30 m long line

MGG/KL-DCB(II) Portable Electromagnetic Current Metre

Henan HongDaer Instrument Co., Ltd.

0-10 m/s ±1% Portable

Sensor, mainframe, 30 m long line

LDX-2012 Portable Electromagnetic Current Metre

Shandong Lidaxin Instrument Equipment Co., Ltd.

0-10 m/s ±1% Portable

Sensor, mainframe, 30 m long line

FH950 Fig. 4.22 The electromagnetic current metre

MGG/KL-DCB(II)

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Fig. 4.23 Schematic diagram of circulating volume measurement

Fig. 4.24 Velocity distribution in different location below the rotor

the electromagnetic current metre lies in that measurements can be performed in the pulp environment of the flotation machine without being affected. (2)

Vane current metre

The mechanical propeller-type current metre is a kind of river and canal monitor commonly used in the hydrological monitoring industry. The flow velocity sensor is placed in the water flow, the pulp at the front end rotates under the action of the water flow and the velocity of the water flow is determined by the speed of propeller rotation, as shown in Fig. 4.26. The measuring range of the current metre

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Fig. 4.25 The relationship between speeds and circulation volumes of a flotation machine

Fig. 4.26 Mechanical paddle type current metre

is generally 0.1–4.0 m/s, and the propeller diameter is 60–80 mm. The current metre is also used for the testing research of the internal velocity and rotor circulation capacity of flotation machines, and the test schematic diagram is shown in Fig. 4.23. This method is mainly used to measure the internal velocity of the flotation machine under the condition of clean water. Since there are too many foreign substances, the problem of propeller winding is easy to occur in the pulp environment, resulting in distortion of measurement results.

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Fig. 4.27 Slurry suspension capacity measurement by siphon method

4.2.3 Suspension Capacity Test The circulation capacity test of the flotation machine can reveal the dispersed state of internal mineral particles and evaluate the agitation and mixing capacities of the equipment. For the suspension capacity test, the pulp at different depths in the tank is generally obtained by means of sampling, thus analysing the concentration, size fraction distribution, etc. There are many sampling ways and means, and those commonly used include the siphon method, submersible pump suction method, specially made sampling tools, etc. The siphon method is the simplest method, and the materials are easy to obtain, as shown in Fig. 4.27. A hose is used to siphon the pulp in different section positions using the principle of communicating vessels. At present, various deep tank samplers are manufactured at many industrial sites to facilitate the acquisition of pulp at different liquid levels, as shown in Fig. 4.28. Although the siphon method is convenient, the sampling may be impossible due to the great flow resistance of the pulp in the pipeline when the pulp in the superficial coat is drawn. The above problem can be avoided by sampling with the sampler, but there are also problems such as sampling speed, equipment tightness, etc. Figures 4.29 and 4.30 gives the test results of the internal suspension capacity of the flotation machine in a concentrator. On the whole, the concentrations at all sections in the flotation machine are equal, the mineral particles are evenly distributed, and the suspension effect is good. The size fraction distribution can be obtained by screening the samples at all depths with 100-mesh, 200-mesh and 400-mesh sieves, respectively. Figure 4.31 shows the size data of deep tank sampling in the first roughing tank of XCF-16.

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Fig. 4.28 Sample collector for deep cell

Fig. 4.29 Suspension capacity measuring points of 16m3 KYF-XCF flotation cell

The distribution rules of all the size fractions in different positions in the flotation machine are identical. The mineral content with +100 mesh size fraction is the lowest, and the mineral content with −400 mesh size fraction is the highest. As the height from the overflow weir decreases, the mineral content with the size fraction of +200 slightly decreases, the mineral content with the size fraction of −200 ~+400 gradually increases, and the distribution of the contents of −400 mesh minerals is relatively uniform at different heights of the flotation machine.

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Fig. 4.30 Slurry concentration changing with the distance to overflow weir

Fig. 4.31 The particle size of sample at different distance to overflow weir of XCF-16 flotation cell

4.3 Bubbles and Particles Testing Technology It is very important to research the bubble feature parameters. From the research on theoretical modelling of the flotation column, it is not hard to see that getting the local bubble feature parameters such as bubble size, distribution, velocity and phase

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holdup is the basis of researching the local feature flow and phase interactions. In recent years, the experimental fluid technical means have been developed rapidly, and the testing methods and technologies of local bubble feature parameters have also been well developed. Table 4.4 summarizes the characteristics of the testing method of bubble feature parameters. It should be noted that the optical method in the table has the advantage of noncontact measurement in acquiring the bubble feature parameters, but its application in three-phase opaque media and industrial opaque equipment is subjected to considerable restrictions. The application of advanced optical testing methods, such as particle image velocimetry (PIV) and laser Doppler velocimetry (LDV), is also limited by the testing environment and fluid properties. Generally, only the tank wall can be tested, or measurements can only be conducted at low gas holdup (generally 30%) due to the intense reflection and scattering of the bubble surfaces to the light. (1)

Test principle of conducting probe method

A thin insulating wire, i.e. probe, is introduced into the test of the conducting probe method. When the medium conducts electricity and a voltage is applied to the probe, the electric current will be interrupted and drop to the zero point (i.e. the electric current will decrease rapidly due to insulation with the probe in the gas phase) in the process of bubbles impacting the probe. In other words, the test principle of the conducting probe method is that the probe has different potential features in the continuous fluid phase and the dispersed bubble phase. The dynamic properties of local gases and fluids of the flotation column can be well studied by the conducting probe method. Figure 4.32 is a schematic diagram of acquisition of local bubble feature parameters by conducting probe method. The local details of the conducting probe are shown in Fig. 4.33. The ordinary probe is an insulating wire end with the diameter of 0–1.2 mm, one probe is arranged over the other, and the two probes are 3–5 mm apart from each other. Only the lower probe is enough for measuring the local gas holdup and bubble diameter, while both the upper and lower probes are needed for measuring the bubble velocity parameters. Figure 4.34 shows a bubble feature parameter tester developed by the Chinese Academy of Sciences. The equipment converts the test signal into a rectangular wave and amplifies it. The conducting probe method can be mainly applied in two aspects, one is the evaluation of the bubble diameter and velocity, and the other is the evaluation of the local gas holdup. For the evaluation of the bubble diameter and velocity, when a bubble comes into contact with the lower probe, the control circuit of the lower probe opens, and the measurement begins. When the bubble leaves the upper probe, the upper probe circuit is interrupted, and the measurement stops. The velocity of bubbles can be estimated from the known spacing between the two probes, plus the obtained time for the bubble to pass through the space between the two probes. The time for the bubble to pass through one probe can be used to estimate the bubble diameter parameter. For the calculation of the local gas holdup, simply speaking, the local gas holdup can be estimated by measuring the total time when the circuit

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Table 4.4 Introduction of the testing method of bubble feature parameters Method

Measurement Advantage of parameter/Measurement method rule

Disadvantage of method

Photography

Image analysis

Simple and easy, non-contact

The tank wall and liquid must be transparent; it is impossible to measure the total volume of the equipment, and it is more difficult to measure when the bubbles vary in size

Tracer method

Evaluation and analysis of RTD

Simple and easy, non-contact

No local feature is available; the results are difficult to handle

Vacuum method

Local sampling and electron microscope measurement

Local parameter measurement

To be calibrated, it is difficult to execute when the value is great; sampling will cause flow turbulence

Degassing method

Dynamic changes in the Non-contact; upper and lower applied to high air boundaries of the bubble current layer after sudden degassing

Evaluate the even distribution of the tank bodies; a priori hypothesis is required for calculation

Chemical method

Achieve the mass Non-contact absorption of gas components by changing the local pressure of the gas

Evaluate the average value of the tank bodies; the gas absorption kinetics and bubble residence time should be known

Pressure gauge method

Pressure gradient along the spindle of the flotation column

Evaluate the section range value

Radiation method

Absorption and Ditto scattering measurements of X-ray or neutron radiation

Sound, visible light The measurement and ultraviolet method is just like its radiation absorption name measurements

Ditto

Non-contact

Calculate the average value at the optical channel by radiation The radiation energy cannot be absorbed by the medium; not available for high value measurement; only one kind of parameter can be assessed with other parameters known (continued)

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Table 4.4 (continued) Method

Measurement Advantage of parameter/Measurement method rule

Disadvantage of method

Point conductivity method

The resistance changes abruptly during vaporization and liquefaction

Local measurement, small detector size and convenient transportation

The dispersion and high turbulence state of minute bubbles cannot be measured; to be calibrated and demarcated in use; not available for aspherical bubbles and insulating liquid (non-conductive)

Optical fibre method

Ditto

Ditto (except the latter item); in addition, it cannot be used in a three-phase flow system

Pressure gauge/pitot tube

Local measurement

It cannot be used for turbulence, and the test instrument will cause flow distortion

Determination of vortex wind force

Speed of micro-vortex

Local measurement, in which the velocity evaluation can be performed and can be used in a high-speed phase

No pulsating component can be measured; to be calibrated

Wind speed measurement based on temperature difference

Thermal resistance measurement Thermoelectric-EDP

Local measurement, in which the direction and pulse of the velocity are measured

Calibration is required, and the measurement and recognition of the results are complicated; flow distortion, which is sensitive to medium temperature changes and other interferences; have the same disadvantages as those of the point conducting probe method during measurement

Measurement of laser Doppler wind force

Evaluate the reflection frequency and light wave frequency through the local non-uniform optical density of bubbles or fluids

Local measurement, non-contact, allowing evaluation of the direction of instantaneous velocity

When coarse bubbles exist, it cannot be used for a large-diameter column body (but only close to the column body wall), or opaque liquid (continued)

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Table 4.4 (continued) Method

Measurement Advantage of parameter/Measurement method rule

Disadvantage of method

Acoustic resonance

Evaluation of the range of acoustic wave absorption

Non-contact

Evaluate the uniform distribution of the cross sections; sensitivity to turbulence

Acoustic measurement of wind force

Evaluate the reflection frequency of ultrasonic waves through the local inhomogeneity of bubbles or fluids

The same as the wind speed measurement method based on temperature difference

The signal can be obtained and processed

Simple and easy

Measurement of average values between electrodes

Measurement of conductivity or capacitance (electrical impedance) Electrochemical method

Electrochemical reaction generated by electric current flowing through the electrodes

Local measurement, allowing evaluation of the velocity vector

Calibration is required during measurement. The following phenomena often occur in the liquid: Distortion, entry of fluid into the electrodes

Automatic generation method

Measure the phase The bubble size transition in the solenoid distribution will not when the research area affect it or the whole equipment serves as the core

Calibration is required, and the solid phase will affect the measurement results

remains open and the number of pulses generated by the collision between the bubble and the probe. Figure 4.35 shows the test points where the bubble diameters and velocity distribution at different points in the flotation machine based on the conducting probe method. Figure 4.36 gives the test results of bubble feature parameters at test point 2 and quantifies the condition of the bubbles in the flotation machine. (2)

Bubble feature parameter analyzer

The purpose of the bubble diameter test is to acquire the diameter sizes and their distribution rule of the bubbles in the flotation machine. The principle of a general bubble diameter tester is to measure and analyse the bubble diameters by photography. In the traditional method, a scale is set at the view window, and the diameters and sizes of the bubbles are manually analysed, as shown in Fig. 4.37. It is difficult to quantify the roundness of the bubbles well by this method, and manual measurement has the problems of heavy workload and low efficiency. With the development of

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Fig. 4.32 Schematic diagram of bubble feature parameters measurement by conducting probe

Fig. 4.33 The conducting probe

machine vision technology and computer technology, the modern bubble diameter analyzers are basically automated (Fig. 4.38). Figures 4.39 and 4.40 shows the size of bubbles obtained from the tank, and the diameter parameters of bubbles can be obtained by software analysis.

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Fig. 4.34 The bubble feature parameter tester

Fig. 4.35 Measuring points of bubble feature parameter

Table 4.5 shows the bubble diameter parameters of a flotation machine. The acquisition of bubble feature parameters by the conductivity method is the analysis of bubble velocity, diameter and other parameters by identifying electric signals, i.e. indirect measurement. The bubble feature parameter analyzer is an image identification technology, which is more accurate in the identification of bubble shapes, but the requirements for the computer algorithm are very high for the problem of overlapping of a large number of bubbles.

4.4 PEPT Technology

(a) bubble velocity distribution at measuring point 2

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(b) bubble diameter distribution at measuring point 2

Fig. 4.36 Bubble feature parameter

Fig. 4.37 Bubble size measuring device

4.4 PEPT Technology Positron Emission Particle Tracking (PEPT) is an advanced technology for determining the particle trajectories by testing the tracer radioactivity so as to research the flotation process. Quite a few explorations have been made by this technology in mineral separation equipment, such as flotation machines, spiral chutes, hydrocyclones, etc. In the flotation equipment, it has been used in the experimental researches

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Fig. 4.38 Bubble diameter analyzer Fig. 4.39 Bubbles in the measurement

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4.4 PEPT Technology

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Fig. 4.40 Bubble for analysis

Table 4.5 Bubble diameter parameters of a flotation machine

Bubble test result 1

Bubble test result 2

D10

D32

D10

D32

0.77

2.2

0.83

2.47

of the movement trajectories of particles in the pulp phase and the movement trajectories of particles in the froth area for a profound understanding of the processes of flotation mineralization and desorption, and exploratory studies in the optimal design of froth tanks and the performance improvement of flotation machines have been conducted. The PEPT technology equipment is complex and expensive. There are not many universities and research institutes equipped with the equipment, including The University of Cape Town, McGill University, etc. Prof. J.J. Cilliers from Imperial College London has done a great deal of work in the application of PEPT to flotation machines. Figure 4.41 shows the flotation machine test system developed by Prof. J.J. Cilliers with the PEPT equipment of The University of Cape Town. Using the radioactive tracer technique, PEPT marks the minerals with radioactive substances so that they become the tracers, such as 18F and 68 Ga. The emitted positron collides with the electron, with a pair of γ rays emitted in the annihilation process (as shown

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Fig. 4.41 PEPT equipment developed by the University of Cape Town

on the left of Fig. 4.42). Many detection units (right figure) are arranged in the PEPT equipment, and a pair of colinear γ rays detected by the detection units can locate the position of the tracer. Figure 4.43 shows the test equipment used by Prof. J. J. Cilliers, and Fig. 4.44 shows the test result data. Figure 4.45 shows the obtained

Fig. 4.42 Technical principle of PEPT

4.4 PEPT Technology

Fig. 4.43 The test equipment of Prof. J.J. Cilliers

Fig. 4.44 PEPT measuring data obtained by Prof. J .J. Cilliers

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(a) hydrophobic particles

(b) hydrophilic particles

Fig. 4.45 The obtained flow state of hydrophobic and hydrophilic particles (superficial air flow rate Jg is 1.31 cm/s, the height of slurry-froth layer interface is 80 mm, the height of overflow weir is 120 mm)

flow of hydrophobic and hydrophilic particles. It can be seen intuitively that the hydrophobic particles can flow out of the overflow weir so as to be recovered.

4.5 Spindle Force Test The spindle power consumption is a very important performance indicator for flotation machines. In projects, the power consumption is generally calculated through current and voltage, or the power consumption of the flotation machine is directly read by a power metre, but this test method is not accurate enough. The spindle torque of the flotation machine can be acquired through a strain gauge, then the power consumption is calculated, and the axial force, bending moment and other spindle force conditions of the flotation machine can also be acquired, as shown in Fig. 4.46. According to the stress–strain test method, the strain gauge is attached to the spindle by the Wheatstone Bridge principle, and the data is transmitted by means of wireless transmission so as to solve the problem of spindle rotation. Different bridge circuit connections are to be designed for different force conditions. Figure 4.47 shows a strain gauge bridge circuit connection method for testing the spindle torque when testing the presence of the bending moment action. Figure 4.48 shows the strain gauge bridge circuit connection of the bending moment.

4.5 Spindle Force Test

Fig. 4.46 Torque telemetry system developed by Binsfeld company

Fig. 4.47 Bridge connection of shaft torque measuring

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Fig. 4.48 Bridge connection of bending moment measuring

Figures 4.49 and 4.50 shows the strain gauge test conditions of a flotation machine. Table 4.6 shows the results of the spindle force analysis of a flotation machine. It can be seen that the forces acting on the flotation machine are relatively complicated and subjected to the combined action of torque, bending moment, etc. Relevant data is of great significance to the spindle design of flotation machines, the model selection of reducers, etc. Remarks: The radial force 1 is staggered with the radial force in the 90° direction. Advances in experimental fluid dynamics provide new tools and means for the R&D of flotation machines. In recent years, PIV, PEPT and other technologies are developed so that people can have a deeper understanding of the flotation process. The development of advanced sensor technology promotes the measurement of the threephase dynamic complex system of flotation machines and quantifies the key parameters of flotation machines. The comprehensive utilization of the fluid dynamics simulation of flotation machines and the advanced experimental fluid dynamics method has become one of the most important technical means for the R&D of flotation machines.

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Fig. 4.49 Force measuring of flotation machine shaft

Fig. 4.50 Strain gauge patch Table 4.6 Results of the spindle force analysis of a flotation machine Air volume/cm/s

Speed/rpm

Strain power/kw

Radial force 1/N

Radial force 2/N

0

86.2

7

3,183

2,251

0

86.2

356.5

6,661

6,863

1.88

86.2

210

3,700

4,575

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References 1. Wang F (2004) Computational fluid dynamics analysis-CFD software principle and application[M]. Tsinghua Univercity Press 2. Jiang F, Huang P (2008) Advanced applications and case analysis of Fluent[M]. Tsinghua Univercity Press 3. Zhao Y (2004) Study on the performance of tracer particles in PIV measurement[D]. Dalian University of Technology 4. Wang Q, Zhao X, Shi H (2003) PIV (Particle Image Velocimetry) measurements of particle movement in a circulating fluidized bed[j]. J Eng Therm Energy Power 7:18(4) 5. Liu D, Yang M, Gao B (2008) PIV measurement of flow with Salt-out in centrifugal pump[J]. Trans Chinese Soc Agric Mach 139(11):55–58 6. Feng X, Zheng S (2003) Technology development of PIV (particle image velocimetry)[J]. Electron Instrument Customer 10(6) 7. Kilander J, Rasmuson A (2005) ENERGY dissipation and macro instabilities in a stirred square tankinvestigated using an LE PIV approach and LDV measurements. Chem Eng Sci 60(24):6844–6856 8. Kang Q (1997) Technical progress of full-field velocity measuremen. Adv Mech 31(11):46–50 9. Service manual of particle image analysis system Microvec V2.3. Beijing Lifang Tiandi Technology Development LLC 10. Xu X (2004) Principle and application of PIV testing technology[D]. Xihua University 11. Aubin J, Sauze NL, Bertrand J, Fletcher DF, Xuereb C PIV measurements of flow in an aerated tank stirred by a down—and an up pumping axial flow rotor[J]. Exp Thermal Fluid Sci 28:447–456 12. Wei C (2010) The flow field of XJM-S flotation machine studied by PIV technique[D]. China Coal Research Institute(CCRI) 13. Sun S (2003) Experimental study on flow field in semi-open centrifugal pump by PIV[D]. Yangzhou University 14. Lilin Lilinsky D (2003) Analysis of residence time distribution of slurry in large volume flotation machine[J]. Metallic ore Dressing Abroad 3:38–41 15. Lin C (1993) The three-parameter flow model describing residence time distribution[J]. J Fuzhou Univ (Natural Science Edition) 6:81–85 16. Bi X, Li H, Liu G (2010) Numerical simulation of design optimization of a continuous casting tundish based on RTD curve[J]. J Wuhan Univ Sci Techno (Natural Science Edition) 33(4):343– 346 17. Yianatos JB, Bergh LG (1992) RTD studies in an industrial flotation column: use of the radioactive tracer technique. Int J Min Process 36(1–2):81–91. https://doi.org/10.1016/03017516(92)90065-5 18. Zeng K (2001) Theoretical and applied research on the effect of slurry turbulence intensity on flotation[D]. Central South University 19. Zeng K, Yu Y, Xue Y (2002) Effect of flow velocity of particlesin flotation cell on flotation[J]. Indus Min Process 31(6)

Chapter 5

CFD Simulation Research on Fluid Dynamics of Flotation Machines

5.1 Summary of CFD Simulation Research of Flotation Machines 5.1.1 Significance of CFD Simulation of Flotation Equipment With the rapid progress of computer science and technology, the computational fluid dynamics (CFD) simulation technology, which has gradually emerged and developed since 1960s, makes it possible to research the flotation equipment, a kind of complex three-phase mixing equipment, by the computational fluid dynamics method, and provides a new approach and platform for the research and development of flotation equipment [1–4]. The flotation equipment is essentially a kind of fluid machinery. Researchers make great efforts to form a flow field state in the tank that meets the requirements of mineral separation through specific rotor–stator and tank body design. However, most kinds of the flotation equipment are currently designed on the basis of engineering experiences and empirical formulas, while it is hard to clearly explain the flow field state in the tank, which we are most concerned about. With the emergence and development of computational fluid dynamics, this key problem is just solved. The research on the flotation equipment using the computational fluid dynamics allows visual display of the flow field pattern in the flotation tank, reveals relatively abstract concepts such as upper and lower circulations of the rotor, zoning of the flow field in the tank, etc. in theory in a more clear manner, quantifies the traditional design methods such as circulation volume design and the empirical design methods such as rotor off-bottom height, and forms a set of design and optimization methods for flotation equipment, which are not entirely dependent on empirical design [5, 6]. On the other hand, the computational fluid dynamics simulation is a more efficient and cheaper design method and concept than the design method based on small laboratory exploratory tests, large equipment industrial tests and the technology of flow field © Metallurgical Industry Press 2021 Z. Shen, Principles and Technologies of Flotation Machines, Springer Tracts in Mechanical Engineering, https://doi.org/10.1007/978-981-16-0332-7_5

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display and measurement. Taking BGRIMM Technology Group as an example, its direct cost for industrial tests is up to over 20 million yuan in order to develop the largest individual 320 m3 flotation equipment in the world [7, 8]. Throughout the R&D focuses of well-known flotation equipment suppliers and research institutes at home and abroad on the flotation equipment in recent years, it has become an inevitable choice for the development of flotation equipment to further interpret the principle of the flotation equipment by the CFD simulation of fluid dynamics, optimize the equipment structure and improve the equipment performance in consideration of the deficiencies of traditional methods for the flotation equipment in the fields of theoretical research and equipment optimization.

5.1.2 Research Objective of CFD Simulation of Flotation Machines The research and optimization of the flotation equipment cannot be separated from the computational fluid dynamics, so it is necessary to clarify the role of fluid dynamics simulation technology in the research work of the flotation equipment. Judging from the current research status, the fluid dynamics simulation analysis has advantages in the following aspects. (1)

Interpretation of the internal flow field of flotation equipment

The key to realize the process of mineral enrichment by the flotation equipment lies in the formation of stable separation areas in the tanks, namely, the mixing area, transport area, separation area and froth area as we often say. The existing flotation theory clearly describes the function of each area and the flow field characteristics, and the flotation equipment structure is designed to generate a specific flow field structure. However, it’s hard to deny that the flow field structure of each area theoretically described is too absolute, and the real flow field state in the tank remains unknown, especially the microscopic details of the flow field. Taking the mixing area as an example, the flotation theory requires that stable upper and lower circulations shall be formed in the area, the upper circulation should not be too large to affect the transport area, and the lower circulation should not be too small in case of deposition in the tank. But whether the real equipment only forms two entirely different circulations (i.e. upper and lower circulations), and whether big and small turbulence eddies will be formed therein. In other words, which rotor structure design can better form the upper and lower circulations that meet the flotation theory requirements. This series of problems are neglected to some extent in the original flotation equipment design theory, and even cannot be interpreted clearly. The advantage of the computational fluid dynamics simulation technology is that it can visually reflect the flow field pattern of the research target, especially the microscopic state in the flow field. The simulation analysis of the whole flow field of the flotation equipment can clarify the detailed flow field pattern of each separation

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area, give explanatory notes on the requirements of the flotation theory for the flow field in the tank, scientifically and reasonably explain the problems and phenomena occurring in the production practices, find the basis for the optimization design and performance improvement of the equipment and define the direction for the development of flotation equipment. (2)

Interpretation of the traditional design method of flotation equipment

After decades of development of flotation equipment, especially in the process of upsizing of flotation equipment, a set of effective design methods and experiences have been formed, and the flotation equipment designed on this basis has been fully verified in the mineral separation practice. Admittedly, the original design method of flotation equipment has passed the test of practice and achieved great commercial success. However, the deficiencies of the design method of flotation equipment based on empirical formulas and engineering experiences are also obvious. The structural design method based on empirical formulas is essentially a kind of engineering simplification which cannot visually interpret the specific influence of design details on the flotation equipment. Taking the rotor design as an example, the outer edge of the rotor is often designed as an “inverted cone” in order to form stable upper and lower circulations after the rotor rotates. In this way, different velocity fields can be formed along the edge of the rotor, the fluid in the low-velocity zone moves to the high velocity zone, thus forming a circulating flow. The traditional design method theoretically analyses the causes of formation of the circulating flow and summarizes the empirical design formulas on this basis to guide the engineering design. However, we cannot visually display or reveal the specific details of the circulating flow, such as size and intensity of the circulating flow. The design method based on engineering experiences is a valuable asset. It is sometimes difficult to clearly explain why is it designed like this, but the actual effect fully verifies the correctness of the design. Taking the rotor off-bottom height as an example, an appropriate rotor off-bottom height often needs to be determined to achieve the optimal separation effect in view of different mineral properties and separation requirements. However, this key parameter is often determined by the designer’s personal experiences. The problems existing in such design method which lacks accurate computation can be seen from this. While for new designers, this is an insurmountable challenge which is adverse to inheritance and development. The weakness of the traditional design method which lacks visual analysis and phenomenon disclosure in design is just the advantage of the simulation research on computational fluid dynamics. The computational fluid dynamics simulation can interpret the intention and rationality of the traditional design methods by simulating different design parameters to form specific flow field states. For example, the circulating flow field patterned by the “inverted cone” blade design is visually displayed by simulating the flow field patterned by rotor rotation, which also shows the scientific nature of the traditional design method. The rationality of the empirical design is interpreted by comparing the forms and sizes of the lower flow fields of the rotor formed by different rotor off-bottom heights. The computational fluid dynamics

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simulation provides the possibility for quantifying the traditional design method and theory by interpreting the scientific nature and rationality of the traditional design method of flotation equipment. (3)

Quantification of the key structure design method of flotation equipment

The structure design of flotation equipment mainly includes the three aspects of rotor design, stator design and tank body design, wherein the design of the rotor–stator system is the most critical and the core of the formation of specific flow field patterns in the tank. The rotor design has formed a design method based on the parameters such as circulation volume, diameter, speed and power. Specific rotor forms and specific rotor structure parameters are designed by empirical formulas to meet the process requirements. It is difficult for the method to reveal the detailed features of the flow field generated by rotor rotation, so it is impossible to visually show the influence of subtle changes in the rotor structure parameters on the overall performance of the flotation equipment. Similarly, the stator structure parameters designed on the basis of the empirical stator design method should achieve the current stabilization and diversion effects but cannot display the actual effects of current stabilization and diversion, so it is difficult to clarify the influence of subtle changes in the stator structure parameters. Sloping bottoms and other feature structures are designed in the tank to prevent dead zones. Froth push plates and froth push cones are designed to accelerate froth overflow. But the determination of the specific parameters of these structures often lacks scientific argumentation. The CFD simulation technology can refine the details of the flow field in the flotation tank, and the influence of the changes in key structural parameters on the flow field in the flotation tank can be characterized through the changes in flow field details or changes in the flow field feature parameters, that is to say, the advantages and disadvantages of the changes in the structural parameters can be evaluated. The CFD simulation technology can reveal the influence of changes in the design parameters through the changes in the flow field feature parameters, thus summarizing the influence of the changes in the structural parameters on the performance of the flotation equipment. Then, it supplements and improves the empirical formulas and achieves the purpose of quantifying the key structural design method of the flotation equipment. (4)

Quantification of the empirical design method for flotation equipment

Flotation is a very complicated physicochemical phenomenon, and the flotation principle has not been fully clarified from a certain point of view. Similarly, no appropriate design method has been found for many key parameters in the process of flotation equipment design, and we can only rely on the experiences summarized from longterm production practices. The design of the rotor off-bottom height as mentioned before is mainly determined by depending on the designer’s experiences. Although the traditional design methods failed to summarize the calculation method of some key parameters such as rotor off-bottom height of the flotation equipment, the flotation theory explains the effect to be achieved by these design parameters to meet

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the requirements of mineral flotation. In other words, we can summarize the design rules of these design parameters from the flow field pattern and give approximate calculation methods in engineering to those design parameters which can only be determined by experience in the past, that is, quantify the design method of flotation equipment based on engineering experiences as long as we can reveal the flow field pattern generated by the specific design parameters. (5)

Structural optimization of flotation equipment

The R&D process of the flotation equipment is usually subjected to the small prototype testing in the laboratory, and the better and optimized structural design will be determined by comparison by changing the key structural parameters of the small prototype. A large industrial prototype is designed based on the structural form of the small prototype testing according to the scale-up theory and engineering practice experiences. The actual operational effect of the large industrial prototype is verified through industrial tests, and the design is finalized. It’s not hard to see that it’s hard for the performance of the industrial flotation equipment finalized by the above method to guarantee that the property is optimality. Based on cost factors, comparative tests on the structural design of the industrial prototype are almost impossible, especially in the R&D process of the large flotation equipment. Even the comparative testing of small test prototypes is very complicated and time-consuming. That’s why the key structural forms and design parameters of the flotation equipment cannot be optimized and perfected for a long time once finalized. The application of the CFD simulation technology solves the problems in the traditional design, research and development well in both time and cost. More importantly, it allows direct optimization research on the large industrial prototypes. By establishing different flotation equipment simulation models, or different key structure forms and parameters, the CFD simulation simulates the flow field pattern in the flotation tank so as to evaluate the advantages and disadvantages of the structural design and specific parameter design, thus realizing the structural optimization of the flotation equipment in a more scientific manner. (6)

Simulation and optimization of flotation equipment process parameters

Flotation is a continuous process, which involves process-related parameters such as feeding quantity, residence time and pulp short circuit, and these parameters will have an important impact on the performance of the flotation equipment. The current design method of flotation equipment mainly considers the structure design of individual equipment, with imperfect consideration about the process parameters, the design of process-related parameters gives priority to the engineering experience or influence coefficient, and many aspects have not been clearly interpreted yet. The CFD simulation can truly simulate the influences of feeding quantity, pulp residence time, pulp short circuit and other process parameters on the flotation equipment by simulating the dynamic flow process of the flotation equipment and optimize the flotation equipment under dynamic conditions in many ways such as equipment structure design and operating parameters design.

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Research on the adaptability of flotation equipment application in new fields

The flotation equipment has been widely applied in the field of mineral separation, but it does not mean that the flotation equipment can only be applied in the field of mineral separation. It also has its application space and application prospect in other fields such as sewage treatment, paper deinking and oil–water separation. The application of the flotation equipment in new technical fields inevitably requires the research on the adaptability of the flotation equipment itself in the hope of producing satisfactory application effects in the new fields. Therefore, it is valuable to optimize the equipment design by the computational fluid dynamics simulation technology to meet its application in new fields.

5.1.3 Problems Existing in CFD Simulation of Flotation Machines Over the past few decades, all the research institutes and suppliers of flotation equipment all over the world have put the stress of the R&D of equipment on the upsizing of equipment, developed and put large flotation equipment with the scale of 300 m3 into service within a short time. The R&D and optimization of the flotation equipment will certainly focus on the improvement of equipment performance and efficient and stable work in the future. For this reason, the computational fluid dynamics has been favoured by a vast number of researchers in order to solve or break through the bottleneck existing in the traditional design methods of flotation equipment. Well-known research institutes and suppliers have carried out research work for nearly 20 years in CFD numerical simulation of the flotation equipment, many research outcomes have been integrated into equipment R&D, but there are still many problems that need to be addressed as a matter of urgency. (1)

Reliability of simulation results

The flotation process is a very complex gas–liquid-solid three-phase system. Whether it is two-phase flow or three-phase flow, the reliability of the results has been controversial. It is generally believed that the convergence residual of numerical simulation completely satisfies the requirements of engineering application when it is 1e−5 . The simulated residual of the current flotation equipment can only reach the level of 1e−3 , whether it is two-phase flow or three-phase flow, so how to improve the convergence of numerical simulation and make the numerical simulation results further recognized by the engineering community is very important. (2)

Adaptability of multiple reference frame (MRF)

It is a more common practice to select the steady-state multiple reference frame (MRF) method in order to simplify the simulation difficulty and calculation time of flotation equipment. The MRF has been well applied and verified in equipment

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with a long distance between the rotor and stator of the agitation mechanism, but its applicability still needs to be verified in the case of small spacing between the rotor and stator of the flotation equipment. In addition, the role of the rotor and stator is essentially a transient process, and the simplification into a steady-state process is also open to question. Therefore, it deserves further attention to explore the application of the dynamic grid and sliding grid in the CFD simulation of flotation equipment. (3)

Simplification and gridding of models

The first step of numerical simulation is the issue of model simplification. The structure of the flotation equipment is relatively complex, and it is very important to simplify the equipment structure scientifically and reasonably without affecting the simulation results. The multiphase flow analysis work needs to be performed on the flotation equipment. Traditionally, the hexahedral grid is considered to have great advantages in the field of multiphase flow, while it is very difficult to realize the gridding of a hexahedron in a complex structure. Therefore, grid division in a more skillful manner will greatly reduce the difficulty of subsequent simulation and improve the reliability of simulation results through reasonable model simplification. (4)

Selection of computational fluid dynamics models and parameters thereof

The computational fluid dynamics describes the flow phenomenon through various mathematical models, each of which has certain applicability and limitations. Therefore, it is essential for simulation to select an appropriate mathematical model and related parameters to describe the flow field in the flotation tank. More importantly, the flotation equipment has been serialized, and the efficiency of numerical simulation will be greatly improved if a set of model parameters of a type or a series of equipment can be found. (5)

Integration of the CFD simulation method into the fields of equipment design and optimization

The first task of CFD simulation of flotation equipment is to clarify the details of the flow field in the tank, interpret the flotation process in the equipment from the perspective of flow field distribution, and evaluate the equipment performance. The application of CFD numerical simulation results to the equipment development and optimization process will be the ultimate aim of numerical research. Therefore, it is a new challenge to combine the traditional design means with the CFD numerical simulation method for technological innovation of the equipment.

5.1.4 Prospect on CFD Simulation of Flotation Machines Comparing with the traditional design means, the research and optimization of the flotation equipment by the CFD simulation method are still in the starting stage,

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especially for the domestic research institutes. In view of the current situation of the flotation equipment in the CFD numerical simulation research, researches need to be further carried out in the following aspects. (1)

Development towards a three-phase system

The flotation process is a three-phase complex system, while the CFD numerical simulation begins with a single-phase system and gradually goes deep into the gas– liquid two-phase flow. Some scholars have explored the flow field state under the three-phase system. The simulation research on the multiphase system is closer to the real operative state of the flotation equipment, so further development of the CFD numerical simulation work under the multiphase system is one of the important directions of the CFD simulation of flotation equipment. (2)

Simulation of dynamic parameters and performance of equipment

The influences of dynamic performance or parameters such as pulp inflow and outflow, short circuit phenomenon and residence time on the equipment are very important but difficult to measure and visually embodied. The original design method is designed mainly based on experience parameters and engineering experiences, so the simulation of the dynamic parameters and performance of equipment by the CFD technology is one of the important directions of equipment R&D and optimization. (3)

Simulation of various types of flotation equipment

The flotation equipment has achieved its serialized development. Taking BGRIMM as an example, it includes 11 types, such as KYF, XCF, GF, CLF and BF, and the same type is further divided into different models by volume. So to speak, the flotation equipment has developed into a big family. Therefore, it will help to improve the performance of the flotation equipment as a whole by carrying out the simulation research on different types of flotation equipment, researching the flow field condition of the same type of equipment with different specifications and optimizing the equipment structure in a targeted way. (4)

Combination of the CFD simulation method with the latest testing technology

The CFD simulation has many advantages such as low cost and high efficiency, but the reliability of simulation results is still controversial in the engineering community, so it is very important to verify the correctness of CFD simulation results. But sometimes relevant data is difficult to detect by the traditional testing means. Therefore, the research on the flow field state of the equipment by the latest testing means, and technologies such as PIV and LDV and the combination of both will be one of the new directions of flotation equipment studies.

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5.2 CFD Simulation Research of Flotation Machines The computational fluid dynamics simulation method of flotation machines has become one of the main means for flotation equipment studies. It has obvious advantages in the R&D of large flotation machines and optimization of details in the flotation machines. All the main research institutes of flotation equipment in the world have applied the CFD simulation method in the research process of flotation machines, which enables people to have a deeper understanding of the internal flow of flotation machines, the collision, adhesion and desorption of minerals and bubbles and other processes.

5.2.1 CFD Mathematical Model of Flotation Machines 5.2.1.1

Basic Theory of the Multiphase Flow in Flotation Machines

With the continuous development of computational fluid dynamics, the flow field system has been gradually expanded from the initial single-phase system to the flow field analysis and calculation under the multiphase system. The flotation process is a very complex physical–chemical change. In essence, it is a kind of gas–liquid–solid three-phase mixed flow field patterned by the flotation equipment. Therefore, the development and breakthrough of the computational fluid dynamics under the multiphase system bring opportunities to the CFD numerical simulation of the multiphase flow in the flotation equipment. The CFD is becoming more and more mature in the field of two-phase flow and has been recognized by the engineering to a considerable extent, which lays a good foundation for the simulation of the two-phase flow in flotation equipment. The CFD has made many achievements in the field of threephase flow and has also been recognized by technicians to a certain extent. But it still needs further development and perfection in the reliability, stability and other aspects of the calculation results. Therefore, the three-phase flow simulation of the flotation equipment is still in an exploration stage in consideration of the existing theoretical level and technical level of computational fluid dynamics. (1)

Euler Method and Lagrange Method [9]

The research on the two-phase flow in flotation equipment focuses on the gas–liquid two-phase system, so this book mainly introduces the related theoretical basis of computational fluid dynamics in the two-phase flow. At present, there are mainly two methods for processing the gas–liquid two-phase flow in the computational fluid dynamics: The Euler–Lagrange method and the Euler–Euler method. In the Euler–Lagrange method, the fluid is regarded as a continuous medium, bubbles as regarded as discrete systems, the trajectories of the bubbles are obtained through the orbit model under the Lagrange coordinate system, and then the law of bubble motion is studied. Such model is also called the discrete orbit model. This

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method assumes that the fluid phase affects the bubble motion, but in turn the bubbles do not affect the movement of the liquid phase. The treatment of the bubble phase by the Lagrange method can give more detailed information on the bubble motion, but since it is difficult to completely consider all kinds of turbulent transport of the bubbles, it is only suitable for the motion of sparse bubbles in turbulent motion. The calculation cost is very heavy, which is not suitable for the analog computation of an industrial reactor. At present, all the Euler–Lagrange methods reported in the literatures use the hypothesis of a single spherical bubble, and it is very difficult to characterize the force acting on the bubbles when there is a certain distribution of bubble sizes and deformation occurs. The Euler–Euler method treats both the gas phase and the fluid phase as quasicontinuous media and considers the bubble phase as a pseudo-fluid interpenetrated with the fluid, which is described in the Euler coordinate system by the conservation equations for mass, momentum and energy similar to those of the continuous fluid. The coupling between the bubble phase and the fluid phase is obtained through the interphase transfer term in two conservation equations. Such model is also called the two-fluid model. Such models have experienced all the stages of the no-slip model, small-slip two-fluid model and two-fluid model with slip-diffusion, as well as the processes such as particle dynamics two-fluid model based on inter-particle collision developed in recent years. The governing equations of the particle phase, gas phase and fluid phase in the two-fluid model have the same form and relatively low requirements for the computing power consumption, and the method is currently the most promising method for making a breakthrough in the simulation of the industrial reactor. The Euler–Euler method can simulate both single bubble size flow and bubble flow with size changes. For example, the simplified MUSIG model based on PBM (Population Balance Model) is a model for calculating the size changes in the bubble diameters under the Euler–Euler method. It allows analog computation of the bubbles according to the bubble grouping by defining the maximum and minimum diameters of the bubbles to obtain the size distribution of the bubbles, the fraction of each group of bubbles, etc. This method which improves the analog computation of the gas phase to a certain extent as compared with the method of hypothesis of a single bubble is currently an ideal method for calculating the size distribution of bubbles. The fluid flow in the flotation tank is an intense turbulent motion, so there is the question about how to describe the turbulence modelling of phases under the twophase system. For this problem, there are mainly three kinds of models: Mixture Turbulent Model, Turbulence Model for Each Phase and Dispersed Turbulence Model. The dispersed turbulence model is suitable for the case where the concentration of the second phase is thinner, the inter-particle collision at this time is negligible, and it is the influence of the principal phase turbulence that dominates the random motion of the second phase, so the fluctuating quantity of the second phase can be given according to the average features of the principal phase, the relaxation time of particles and the time of interaction between particles and turbulent eddies. Therefore, the current CFD numerical simulation of flotation machines mainly uses the dispersed turbulence model form.

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(2)

137

Basic Equations Based on Euler Method [10]

For the time being, the Euler method is most widely applied in the simulation of flotation machines, etc., so this section will briefly introduce the basic knowledge of models and equations commonly used by the Euler method in the simulation of flotation machines. In a practical context, there is a transfer of mass, momentum and energy between gas and liquid. The Euler gas–liquid two-fluid model can establish the conservation equations of mass, momentum and energy of each phase separately and make equations coupled by the action (transfer) of the phase interface. But since there are many unknown aspects with regard to the interphase interaction mechanism and most of the split-phase turbulence dispersion models have more experiential elements and poor universality, concrete problems must be analysed on a case-bycase basis. The following assumptions are made in this chapter in order to simplify the problem [11]: (1) (2) (3) (4)

Both the continuous phase (liquid phase) and the dispersed phase (gas phase) are incompressible Newtonian fluids; The whole simulation process is isothermal flow without heat transfer; Two-phase fluids follow their respective governing equations; Both fluids are regarded as continuous media and interpenetrated with each other, with their respective velocities and volume fractions in the same spatial location. According to the above-assumed conditions, the fluid governing equation is The mass-conservation equation is ∂(rα ρα ) + ∇ · (rα ρα Uα ) = S M Sα ∂t

(5.1)

The momentum-conservation equation is    ∂(rα ρα Uα ) + ∇ · [rα (ρα Uα ⊗ Uα )] = −rα ∇ pα + ∇ · rα μα ∇Uα + (∇Uα )T ∂t 2    + + αβ Uβ − βα Uα + S Mα + Mα rα ρα g + β=1

(5.2) The subscript here, α, β, represents different fluid phases, i.e. gas phase and liquid phase, respectively. r denotes the phase volume fraction, ρ denotes the density, t denotes the time and U denotes the mean velocity vector. In the mass-conservation equation, S M Sα denotes the mass source term. The momentum-conservation equation S Mα denotes the momentum source term and other momentum source terms generated by the applied volume force, Mα denotes the interphase interface force acting on the + + Uβ − βα Uα denotes the interphase momentum transfer generated by phase α, αβ mass transfer. By applying the theory of eddy viscosity hypothesis, the Reynolds

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stress can be linearly correlated to the mean velocity gradient, which is similar to the relationship between stress and tension tensor in Newtonian laminar flow,   so the equivalent turbulent stress tensor can be written as rα μα ∇Uα + (∇Uα )T . In the momentum-conservation formula, μα is the turbulent viscosity, which can be written as the sum of laminar viscosity and turbulent viscosity: μα = μ L + μT

(5.3)

The turbulent viscosity in each phase is calculated using the most commonly used standard k −ε model. The turbulent viscosity is calculated according to the following formula: μT = C μ ρ

k2 ε

(5.4)

Here, Cμ is a constant with the value of 0.09. In the source term of the momentum-conservation equation, S Mα the applied volume force (denoted by Bα ) can be denoted by the sum of Coriolis force and centrifugal force: Bα = SCor + Sc f g

(5.5)

SCor = −2ρω × U

(5.6)

x=

−b ±

√ b2 − 4ac 2a

(5.7)

where r is the position vector, and U is the related velocity vector. The interphase interface term can be written in the form of the sum of several forces: Mα = Fα + Aα + L α + Tα

(5.8)

where Fα denotes the drag force, Aα denotes the virtual mass force, L α denotes the lift force and Tα denotes the turbulence dispersion force. Under steady-state conditions, the balance of drag force and buoyancy force results in a slip velocity obtained specific to the bubbles relative to the liquid phase. The slip velocity has an important influence on the gas holdup obtained. When the bubbles pass through the flotation tank under the influence of liquid phase circulation, the slip velocity of the bubbles essentially determines the gas ascending rate and the ratio of recirculation. Therefore, the drag force is often correlated with the slip velocity. The drag force can be expressed as CD 3 |U2 − U1 |(U2 − U1 ) F2 = −F1 = − r2 ρ1 4 d

(5.9)

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C D denotes the drag coefficient. Different scholars give different expressions of the drag coefficient, and the Grace model is used here to calculate the drag coefficient. 4 gd ρ 3 UT2 ρc

(5.10)

μc M −0.149 (J − 0.857) ρc d p

(5.11)

μ4c g ρ ρ2σ 3

(5.12)

CD = UT =

M=

0.94H 0.751 2 < H ≤ 59.3 3.42H 0.441 H > 59.3

 4 μc −0.14 −0.149 H = EoM 3 μref

J=

EO =

(5.13)

(5.14)

g ρd 2p

(5.15)

σ

where UT denotes the endpoint velocity, M denotes the Morton number, μef = 0.0009 kgm−2 s−1 , denotes the molecular viscosity of water at certain temperatures and pressures, EO, the Eotvos number, denotes the ratio of gravity to surface tension, ρ in the formula ρ denotes the interphase density difference σ and σ denotes the surface tension coefficient. When the bubbles are accelerated relative to the continuous phase fluid, not only the bubbles are accelerated, the fluid flow field around the bubbles will also change with them. The force driving the bubbles to move increases the kinetic energy of both the bubbles and the fluid. It is also used to overcome the energy dissipation of liquid circumfluence around the bubbles. This force is greater than the force accelerating the bubbles, and the effect is equivalent to the mass addition of the bubbles. The added force is called the virtual mass force (or apparent mass force, additional mass force), and the virtual mass force and lift force are, respectively, expressed as

A2 = −A1 = r2 ρ1 CA

DU2 DU1 − Dt Dt



L 2 = −L 1 = r2 ρ1 CL (U2 − U1 ) × (∇ × U1 )

(5.16) (5.17)

here, CA denotes the additional mass force coefficient, CL denotes the lift coefficient. The turbulence dispersion force is given by the following formula: T2 = −T1 = −Ctd ρ1 k1 ∇ρ2

(5.18)

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The turbulence dispersion force coefficient Ctd here has the value of 0.1, because Ctd is a quantity that varies depending on the particle content and turbulence degree in turbulence, and the values of different turbulent dissipation coefficients are also applied in different literatures. The jury is still out as to how effective is the application, so it is only set to a constant and assigned the value of 0.1. In a word, with the rapid development of computational fluid dynamics in theory and numerical algorithms, the conditions for a scientific and systematic research on the details of the flow field of the flotation equipment are available, and researchers at home and abroad have also carried out a lot of fruitful work in the computational fluid dynamics simulation of the flotation equipment. All the well-known equipment suppliers and research institutes such as OUTOTEC, CSIRO (Commonwealth Scientific and Industrial Research Organization) and BGRIMM (Beijing General Research Institute of Mining and Metallurgy) have applied the CFD simulation technology to the fields of equipment development and optimization [12–16].

5.2.1.2

CFD Simulation Pre-processing of Flotation Machines

The R&D of the flotation equipment assisted by the computational fluid dynamics simulation has become a consensus in the industry. Overseas research institutes and suppliers have carried out hard exploration for more than 20 years. OUTOTEC, FLSmidth and BGRIMM have begun to comprehensively popularize the research and design of flotation machines based on CFD design. The numerical simulation method is generally divided into three stages: pre-processing, numerical solution and post-processing, wherein the pre-processing process is the part with the highest manual controllability. Scientific and reasonable pre-processing settings have a decisive influence on the numerical simulation results to a certain extent. In a broad sense, pre-processing includes several parts, such as simplification of physical structures, gridding of physical models and boundary conditions. The gridding of physical models is the most time-consuming and most difficult part. Especially for the gridding of complex physical models, the high quality grid generation can often obtain better simulation results, while poor quality grid generation may lead to convergence failure in the calculation. (1)

Grid generation technology. 1.

2.

Tetrahedral grid technology. The tetrahedral grid technology is highly adapted to complex physical structures, and any physical structure can basically be mesh by the tetrahedral grid. Moreover, the mainstream commercial grid generation software provides the function of automatic tetrahedral grid generation so that the time for grid generation is greatly saved. Hexahedral grid technology. The hexahedral grid is very regular and has many advantages in the required time, resource, etc. for calculation. In some fields, the hexahedral grid is the only choice because calculation is

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3.

141

impossible due to the poor quality of the tetrahedral grid. More importantly, the simulation results based on the hexahedral grid technology are preferred by academic circles. However, the hexahedral grid is very difficult to generate, the user’s personal experiences and skills are very important, and some complex structures cannot generate the hexahedral grid. Hybrid grid technology. The hybrid grid technology refers to the use of a hexahedral grid in an area where the hexahedral grid can be generated, while the tetrahedral grid is used in areas where the hexahedral grid is difficult to generate, or even in areas where the hexahedral grid cannot be generated in order to obtain as high computational efficiency and low computational resources as possible.

The special rotor–stator structure of the flotation equipment makes grid generation very difficult. Most researchers use the hybrid grid for processing. Adaptive tetrahedral grid separation is adopted in the rotor–stator area due to its complex structure, while the hexahedral grid is adopted in the tank body area. The combination of the hybrid grid with the split grid is applied so that the problem of grid generation in the flotation equipment is solved to a certain extent, and the requirement of numerical simulation for the grid quality is basically met. Figure 5.1 shows the BGRIMM’s KYF-320 m3 flotation machine grid condition generated by the tetrahedral and hexahedral grid methods. Figure 5.2 shows the conditions of tetrahedral and hexahedral grid separation, respectively, performed on the BGRIMM’s KYF-0.2 m3 flotation machine. There are always disputes on the advantages and disadvantages of tetrahedral and hexahedral grid separation. It is generally recognized that the calculations obtained by the hexahedral grid are the best relative to those obtained by the tetrahedral grid

Fig. 5.1 The BGRIMM’s KYF-320 m3 flotation machine grid condition

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Fig. 5.2 The comparsion between tetrahedral and hexahedral grid separation in flotation cell

or hybrid grid in the simulation of three-dimensional incompressible flow. However, the tetrahedral grid becomes the best choice in view of the fact that it is too difficult for many complex structures to generate the hexahedral grid. Many scholars have carried out comparative studies. Scientific and reasonable settings of tetrahedral grid parameters, grid smoothing, etc. enable the tetrahedral grid to meet the same computational accuracy as that of the hexahedral grid. Juha TIITINEN carried out a comparative research on the OUTOTEC industrial OK flotation machine [17], and the results prove that the predicted velocity values of the structured and unstructured grids in the same position of the same section of the flotation machine are basically the same. But it has to be pointed out that the conclusion of comparative results was obtained when the flotation equipment was simulated under the single-phase system. Studies showed that the tetrahedral grid is prone to generate the problem of numerical dissipation in multiphase flow analysis. For the flotation equipment, the tetrahedral grid and hexahedral grid have their own advantages and disadvantages, which can be simply summarized as follows: 1.

Time cost

The rotor and stator in the flotation tank belong to comparatively complex geometric structures. Generally speaking, it is extremely time-consuming to build a structured or hybrid grid for such a problem. Therefore, for the problem of complex geometry, the short time for setting a grid is the main reason for using the unstructured grid (triangular or tetrahedral element). However, if the geometry is relatively simple, there may be no significant savings in the setting time no matter which grid is used. 2.

Computation cost

In some cases, it is comparatively economic to use the quadrilateral/hexahedral elements because the quadrilateral/hexahedral elements allow a greater aspect ratio than that of triangular/tetrahedral elements. A great aspect ratio in the triangular

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and tetrahedral elements always affects the skewness of the elements, thus affecting the accuracy and convergence of the calculations. As a result, if the geometry of the simulation equipment is relatively simple and the flow therein agrees well with the geometry, for example, a long and thin pipeline, a high aspect ratio grid with quadrilateral/hexahedral elements may be utilized. This grid may have much fewer elements than triangular and tetrahedral elements, with lower computational costs. (2)

Boundary conditions

For numerical simulation workers, the importance and significance of researching boundary conditions correctly are beyond all doubts. The boundary conditions, which is essentially a correct understanding and interpretation of physical phenomena, is the scientific and reasonable simplification of introducing physical phenomena from the real world into the simulated virtual environment. The flotation equipment, more precisely the requirement of the flotation process, makes the setting of boundary conditions quite difficult. It often results in difficult convergence of the boundary constrain computation that is the closest to the reality, while the appropriately simplified boundary conditions are in certain conflicts with the reality although they are more likely to converge. In view of the key role of scientific and reasonable boundary conditions for the numerical simulation, it is also a very important work to research and analyse the reasonable simplification of the boundary conditions and its influence on the calculation results. It is a three-phase system in the flotation tank, the air inlet is at the air intake pipe, the outlet is at the free froth surface and the rotor rotation drives the fluid to move, forming a specific flow field. For the outlet boundary conditions of the flotation equipment, the boundary condition of gas overflow only without liquid overflow is very severe in the case of simulation in the gas–liquid two-phase system. Under the three-phase system, how to define the problem of overflow at the froth surface is more difficult. For the inlet boundary of the flotation equipment, especially for the self areated flotation equipment, there is a shortage of relevant researches on how to embody the automatic suction of the flotation equipment. For the special rotor– stator structure of the flotation equipment with a tiny clearance between the rotor and stator, the problem of applicability of the multiple reference frame (MRF) is also worth discussing. In particular, the problem of how to define the dynamic and static interface of the air distributor flow circulation hole for the flotation equipment with the air distributor structure, the problem of how to define the interface where the air enters the three-dimensional domain of revolution for the automatic suction flotation equipment and so on bring many challenges to the setting and reasonable simplification of the boundary conditions. FLUENT and CFX are the most widely used software in the field of commercial CFD software, they are similar in function, and each has its advantages, disadvantages and unique features. At present, the CFX software is used much more frequently in the field of CFD simulation of flotation equipment, so the settings of the boundary conditions in the simulation of flotation equipment are described in this section based on CFX.

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➀

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Inlet boundary condition:

For the air forced flotation equipment, the inlet boundary condition is generally set to the velocity inlet, and the whole process of air intake at the inlet is considered as the full extension of gas turbulence by default. For the automatic suction flotation equipment, the inlet boundary condition is generally set to the Static Pressure inlet, and the pressure value is set to the atmospheric pressure. ➁

Outlet boundary condition:

Generally, the pressure outlet, Degassing Condition outlet and Opening Condition outlet are selected depending on the actual situation of the flotation equipment and the simulated phase system. The Degassing Condition outlet only allows gas phase outflow and does not allow liquid phase outflow. Notwithstanding strict constraints and relatively difficult convergence of the calculations, it is more realistic. The Opening Condition outlet which allows free access of both gas and liquid is a kind of less restrictive boundary condition which allows relatively easy convergence in simulation but is still different from the reality to a certain extent. ➂

Boundary condition for gas phase entry into the liquid phase domain of revolution:

In the simulation of the flotation equipment with the air distributor, the gas phase needs to enter the rotating liquid phase area through the circulation hole of the air distributor, thus forming the gas–liquid two-phase flow or three-phase flow. An appropriate outlet boundary condition must be selected in order to make the numerical simulation practically close to this process. Commonly used conditions include: Average Pressure Condition and Opening Condition. The Average Pressure Condition is a common pressure outlet, with standard atmospheric pressure at the outlet. The Opening Condition is an interface allowing free access of both gas and liquid in both directions. In the self-aerated flotation equipment, the process of suction of the gas phase into the liquid phase also needs to be simulated through reasonable strategy for the gas phase. Generally, the General Interface boundary condition is used to simulate the process of entry of the gas phase into the liquid phase. ➃

Boundary condition of the wall surface:

The wall surface condition is one of the most common boundary conditions in numerical simulation. Generally, the No Slip boundary condition is used for liquid phase fluids. At this time, the liquid phase velocity at the wall surface will be the same as the wall surface velocity. When the wall surface is stationary, the liquid phase velocity is zero. Since the multiphase flow is often encountered in the simulation of the flotation equipment, the Free Slip boundary condition is generally selected for the gas phase component therein. At this time, the shear stress at the wall surface is zero (τ = 0), and the gas phase fluid close to the wall surface has no obvious friction

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145

effect [9]. Additionally, in the case of multiphase flow, if a fluid uses a free sliding boundary, other boundary settings can significantly affect the fluid state [10]. ➄

iInterface

The Multiple reference frame (MRF) method is generally used in order to simulate the rotor–stator system of the flotation equipment. CFD software provides three kinds of different multiple reference frame algorithms to deal with the problem in the rotor and stator. The solidified rotor model is suitable for solving the problem in the compact machinery with very small calculated spacing between the rotor and stator. It is widely used in agitation machinery and conforms to the simulation requirements of the flotation equipment. The frozen rotor belongs to the Cauchysteady state algorithm, with relatively fixed positions between the rotor and stator. All the rotating areas are set to rotation, that is, the transient effect is ignored [11]. After the flow field area is divided into an rotor rotating area and a static area of the tank body and stator, a rotor–stator interface exists between the two areas. To solve the flow field information transfer on the interface, CFD software provides the feature of Generalized Grid Interface (GGI), which allows bonding of different types of grid blocks, and greatly reduces the difficulty of grid generation for complex models. This algorithm can guarantee strict conservation on the interface for all flow equations. The interface is processed as a fully implicit scheme, which will not affect the convergence of the solutions. When passing through the interface, the fluid is automatically enlarged or reduced to fit in with the difference in grid sizes. The multiple reference frame method is based on the Generalized Grid Interface (GGI) algorithm. At present, the frozen rotor model is generally selected in the simulation of the flotation equipment in order to solve the rotor/stator problem in the rotor–stator.

5.2.2 CFD Simulation Research of Flotation Machines Under the Single-Phase Condition The flotation equipment is a complex three-phase system. At present, the simulation research of the three-phase flow field is not very mature in both theory and technology. The computational fluid simulation research of the flotation equipment begins with the simulation research under the single-phase system, and gradually goes deep into the simulation of the gas–liquid two-phase system. Many researchers have also explored the flow field condition under the three-phase system, which lays a foundation for the design and optimization of the flotation equipment.

146

5.2.2.1

5 CFD Simulation Research on Fluid Dynamics of Flotation Machines

Influence of the Turbulence Model on the Flow Field of Flotation Machine

The flotation equipment produces an intense turbulent flow in the tank due to the effect of rotor rotation, and the high nonlinearity of turbulent motion brings many challenges to the development of computational fluid dynamics. Therefore, one of the major achievements of computational fluid dynamics in recent decades is that many turbulence models for different turbulent flows are proposed. The CFD simulation research of the flotation equipment was started a little later than other equipment, and the industry has not put forward a special turbulence model for the flotation equipment yet. Therefore, it is a basic research work to explore the applicability of currently general turbulence models such as standard k − ε model to the flotation equipment. In this regard, domestic and foreign researchers have carried out many active explorations. In the simulation research of the flotation equipment, the standard k − ε model is mainly used as the turbulence model, but there are fewer relevant studies in contrast to the adaptability of, for example, RNG k − ε model, K-W model, RSM model, etc. in the simulation of flotation equipment. The influences of the turbulence models on the flow field of flotation equipment under the single-phase system are described in this section based on the studies conducted by Jiliang Xia, Antti Rinne et al. [12] of OUTOTEC. Figures 5.3, 5.4 and 5.5 reflect the influences of the standard k−ε model, realizable k − ε model and RSM model on the predicted turbulent kinetic energy, dissipation rate and vortex intensity. The flow patterns predicted by the three kinds of turbulence models are very similar, but the local properties of the flow fields, especially the predictions of turbulent kinetic energy k, dissipation rate ε, etc., are different. The turbulent kinetic energy predicted by the standard k − ε model and that predicted by the realizable k − ε model are higher than that predicted by the RSM model, and a jet flow is formed in the rotor–stator area. Similarly, the maximum dissipation rate predicted by the RSM model is also lower than the corresponding values predicted by the standard k − ε model and realizable k − ε model. For the prediction comparison of the vortex intensity, all the three models predict a vortex generated on the leeward side of each rotor blade, and the RSM model predicts a larger range

Fig. 5.3 The influences of the turbulence models

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147

Fig. 5.4 The influences of the turbulence models on turbulence dissipation

Fig. 5.5 The influences of the turbulence models on vortex

of vortex circulation area. Table 5.1 gives the predictions of the power consumption of flotation equipment by the three models, and the RSM model predicts relatively higher power consumption of the equipment. Compared with the other two models, the RSM model predicts more accurately in comparison with the actual measurements. Therefore, we can believe that the values predicted by the RSM model are more accurate, while viscosity models such as standard k − ε model and realizable k − ε model are more suitable in the simulation for the purposes of engineering design and optimization. Table 5.1 Prediction of equipment power consumption by three turbulence models

P/P1

Np/Np1

k−ε

1.02

1.02

Realizable k − ε

1.0

1.0

RSM

1.12

1.12

Note: P Power; Np Power number

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5.2.2.2

5 CFD Simulation Research on Fluid Dynamics of Flotation Machines

Circulation Capacity

The rotor circulation volume is a key parameter in the design of flotation machines, and the accurate determination of the rotor circulation volume is of great significance for evaluating the performance of flotation machines, determining the flotation time much more reasonably and even improving the separation index. But no reliable access to the circulation volume of the equipment is available now. FLSmdith performed a testing research on the rotor circulation volume of the WEMCO flotation machine and measured the circulation volume by arranging the sensors at multiple points at the bottom of the rotor. But this method is based on the design of the diversion cylinder of the WEMCO flotation machine, and the accurate rotor circulation volume can be calculated only by acquiring the velocity field at the section of the diversion cylinder. Therefore, this method is difficult to apply in flotation machines without the draft tube, and its test difficulty and cost are higher. Select the section at the stator disk as the tested section and predict the axial velocity field in the section by the CFD method so as to calculate the rotor circulation volume, as shown in Fig. 5.6. This method can be adapted to most flotation machines, and the errors in the characterization of the planar velocity field by multipoint measurement are also avoided by predicting the velocity of the whole section. Figure 5.7 Shows the relationship between the circulation volumes of backward inclined, forward inclined and radial rotors and their speeds. As the rotor speed increases, the circulation volumes of all the groups of rotors increase. At the same

Fig. 5.6 The test section of the rotor circulation volume

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Fig. 5.7 The comparsion of the three rotors

speed, the circulation volumes of the backward inclined rotor and radial rotor are equal, both of which are 7% greater than that of the forward inclined rotor. Table 5.2 gives the circulation volumes of KYF series flotation machines with bottom and central rotors under the clean water condition. The topic defines that the circulating density QF is the ratio of equipment circulation volume to equipment volume. It can be seen that the experimental flotation equipment has a high circulating density, while the industrial flotation machine has a relatively small circulating capacity. The circulating density tends to decrease with the increase of the equipment volume. For the large-scale flotation machines, the circulating density is less than 1. Table 5.2 Flotation machine with bottom and middle positioned rotors (Clean water condition) Equipment

Bottom positioned rotor

Middle positioned rotor

N

V

Q

QF

Speed/rpm

Volume/m3

Circulation volume/m3 min−1

Circulation volume/volume

KYF-160

105

200

207

1.04

KYF-320

107

320

264

0.83

KYP-560

93

560

359.5

0.64

KYP-680

90

680

539

0.79

KYP-70

140

70

135

1.93

KYP160

105

200

265

1.04

KYP-320

107

320

314

0.98

Remarks KYP-160 is the equipment with the special design of the spindle of a 200 m3 flotation machine

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5.2.2.3

RTD Simulation of Flotation Machines

It is very difficult to detect and evaluate the pulp short circuit according to the traditional test method. It is basically impossible to conduct relevant experimental researches on large industrial flotation equipment, and it is difficult to reflect the residence time distribution of the pulp efficiently and visually. The advantage of the CFD numerical simulation technology in cost and time is an excellent choice for characterizing and evaluating the pulp short circuit of the flotation equipment and is of great significance for the equipment design and performance optimization. The research on the pulp residence time of the flotation equipment by the CFD numerical simulation technology is of great significance to the research on the flow properties of flotation machines. (1)

Residence time distribution curve

The residence time distribution curve is studied by tracer testing. The process of gradual dispersion of tracers from the inlet in the tank body can represent the process of aqueous phase movement. Therefore, the movement of the tracers can be discussed by predicting the flow field of the aqueous phase in the tank body from the side and making a judgment on the areas where any dead zone and short circuit exist in the spatial area. When the rotor speed of the flotation machine is 200 r/min, it can be seen from Fig. 5.8 that the flow of the tracers in the flotation tank can be divided into the following processes: The tracers are injected into the rotor area from the inlet, thrown out from a portion above the rotor due to rotor agitation, and split into the upper and lower circulations. Since the outlet is in the lower circulation area, a small part of the tracers will directly flow out of the outlet in the process of lower circulation. The parts not flowing out return to the rotor area to continue with the next process of agitation and throw-out. In comparison with the upper circulation, the lower circulation is faster in circulation and shorter in the residence time of tracers. The upper circulation is lower in speed and longer in the residence time in some areas (e.g. above the rotor, near the barrel wall at the top). The tracer concentration in the whole tank body decreases slowly over time. The residence time distribution model is introduced to research the short circuit and dead zone in flotation machines. As shown in Fig. 5.9, the injected tracers are regarded as two parts, one part directly flows out of the outlet without being well mixed, i.e. being short-circuited. It accounts for f of the total. The other part is supplied into the mixing area and fully mixed with water before flowing out. The proportion of this part is (1 − f ). But the mixing area contains a complete mixing area and a part of the dead zone. It is difficult for the tracers to enter the dead zone, or the residence time is extremely long after their entry. The ratio of the mixing area is w, and that of the dead zone is (1 − w). According to the above model, the complete mixing flow model of the short circuit and dead zone obtained after correction is

5.2 CFD Simulation Research of Flotation Machines

Fig. 5.8 The tracers distribution at the centre section at 1 s, 2 s, 4 s, 6 s, 8 s, 10 s, 20 s, 40 s

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Fig. 5.9 The residence time distribution model

 1 (1 − f ) 1 (1 − f )2 exp t E(t) = t ω t w

(5.19)

According to E(t) = CC0i(t) under this condition, the tracer concentration Ci = 1 ti at the time of entry, with the injection time ti = 1 s. The data of tracer concentration at the outlet is processed, and the obtained residence time distribution curve is shown in Fig. 5.10. The whole residence time distribution is close to exponential distribution. The tracers with the residence time of less than 200 s account for more than half of the total quantity, followed by the phenomenon of long smearing, with the mean residence time of 178 s. This residence time distribution approaches the ideal complete mixing flow time distribution, but there are some deviations, which may be due to the complex flow properties and the existence of short circuit and dead zone. According to the above model, the short circuit ratio is about 7.7%, the dead zone ratio is about 2.1% and the mean residence time is about 178 s. E(t) = 0.0048 exp(−0.0052t)

Fig. 5.10 The residence time distribution (200 rpm)

(5.20)

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Table 5.3 Residence time distribution, short circuit ratio and dead zone ratio at different rotor speeds Rotor speed (rpm)

Expected mean residence time (s)

Mean residence time (s)

200

200

Short circuit ratio (%)

Dead zone ratio (%)

178

7.7

2.1

250

170

10.7

6.3

300

174

9.2

3.2

Fig. 5.11 The residence time distribution of different speeds

(2)

The influence of rotor speed on residence time

The speed plays a vital role in the whole flotation process. Table 5.3 and Fig. 5.11 give the residence time distribution, short circuit ratio and dead zone ratio at different rotor speeds. In the process of speed increase from 200 to 300 rpm, the mean residence time of the liquid phase was not increased significantly, and all remained around 170 s. The mean residence time even decreased from 200 to 250 rpm. That’s the case when it corresponds to the short circuit ratio and the dead zone ratio, the differences between the three are not obvious, the short circuit ratio is about 8%, and the dead zone ratio does not change much either. The short circuit ratio and dead zone ratio of the liquid phase are also slightly increased from 200 to 250 rpm, and then slightly decreased when it reaches 300 rpm. (3)

The influences of pulp flow rate on residence time distribution

The flow rate at the inlet and outlet also influences the residence time of the liquid phase. The flow rate at the inlet and outlet is reduced from 1 to 0.5 m3 /s and the residence time distribution at the speed of 200 rpm is shown in Fig. 5.12. Similar to the distribution curve of the original flow rate, no significant changes have taken place. The calculated short circuit ratio is about 14.2%, the dead zone ratio is about 8% and the mean residence time is about 343 s.

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Fig. 5.12 The residence time distribution of inlet 0.386 m/s

Table 5.4 Residence time distribution, short circuit ratio and dead zone ratio at different flow speeds Flow rate (m/s)

Speed (rpm)

Expected mean residence time (s)

Mean residence time (s)

Dimensionless mean residence time

Short circuit area (%)

0.77

200

200

178

0.89

7.7

0.38

200

400

343

0.85

14.2

E(t) = 0.0023 exp(−0.0027t)

Dead zone (%)

2.1 8

(5.21)

The dimensionless mean residence time is the ratio of the mean residence time to the expected mean residence time. By comparing Table 5.4 “Residence Time Distribution” of both of them, it can be seen that the dimensionless mean residence time decreased from 0.89 to 0.85 after the flow rate at the inlet and outlet was reduced and both the short circuit ratio and dead zone ratio were increased to some extent.

5.2.3 Flow Field of the Flotation Machine Under the Two-Phase System The simulation of the gas–liquid two-phase flow field is closer to the real state of the flotation equipment and is more valuable for guiding the R&D and design work. But the CFD simulation of the gas–liquid two-phase system faces many new challenges, for example, how to correctly simulate the process of gas phase entry into the liquid phase, are the gas phase understood as a continuous fluid or a discrete fluid, is the gas studied by the Euler method or the Lagrange method and so on. Therefore, in the simulation research of the gas–liquid two-phase flow, not only the flotation equipment model is simplified, the theoretical basis of computational fluid dynamics for gas–liquid two-phase flow simulation is yet to be developed.

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Fig. 5.13 The air holdup distribution at the centre section (195 rpm, 0.1 m3 /m2 min−1 )

(1)

Gas–liquid two-phase dispersion feature of flotation machines

Figure 5.13 shows the distribution characteristics of gas holdup in the longitudinal section of KYF-0.2 flotation machine. The air enters the rotor and stator areas from the air distributor, and then dispersed by rotor agitation. Since the bubbles have an upward escape velocity, the gas holdup distribution is an inclined upward and gradually diffusing trend. In the main area of the tank body of the flotation machine, a higher gas holdup area is shown at the stator blade outlet, which coincides with the result of relatively great gas holdup in the area tested by the bubble feature parameter measuring instrument. From the distribution of gas holdup in the section, the distribution of gas holdup in the upper area of the tank body is uniform, and the gas diffusion effect is quite good. But the gas holdup is very low in the bottom area of the tank body. Figure 5.14 shows the gas holdup distribution characteristics in a section of the flotation machine 30 mm away from the rotor disk. A high gas holdup area appeared on the back side of the rotor blade of the flotation machine, that is, the phenomenon of bubbles accumulation at the rotor blade occurs. That is because a negative pressure zone is formed due to the high velocity of the back side of the rotor blade, where the air phase is easily accumulated. (2)

Gas–liquid two-phase CFD correction

The problem of simulation distortion at a high air volume will be encountered in the CFD research on the two-phase flow in the flotation machine. The movement

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5 CFD Simulation Research on Fluid Dynamics of Flotation Machines

Fig. 5.14 The air holdup distribution at the centre section (315 rpm, 0.5 m3 /m2 min−1 )

of bubbles in the flotation machine is mainly subjected to buoyant force, gravity force, drag force, lift force, virtual mass force, etc. in which the drag force and lift force having a great influence on the dispersion of bubbles should be emphasized. Generally speaking, the residence time of gas in the pulp can be extended with the increase of the drag coefficient Cd. The following formula is the empirical formula of the drag coefficient. Cd =

4gdg ρg − ρl 3ρl UT2

(5.19)

where g—Gravity acceleration, m/s2 ; ρ g denotes the bubble density, kg/m3 ; ρ 1 denotes the bubble density, kg/m3 ; d g denotes the bubble diameter, mm; U T denotes the turbulent fluctuation velocity, m/s; The simulation of gas–liquid two-phase characteristics may be seriously distorted as a result of the improper selection of the drag model, as shown in Fig. 5.15 and Fig. 5.16. The effect of gas–liquid dispersion in the flotation machine can be improved by analysing the influence of drag coefficient Cd. Figure 5.17 shows the influences of different drag coefficients Cd on the dispersion characteristics of gas–liquid twophase at the aeration rate of 0.6 m3 /m2 ·min−1 . It can be seen that the residence time

5.2 CFD Simulation Research of Flotation Machines

Fig. 5.15 The air accumulation in the rotor

Fig. 5.16 The bubbles flood

157

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5 CFD Simulation Research on Fluid Dynamics of Flotation Machines

Cd=0.44

Cd=1

Cd=2

Cd=5

Fig. 5.17 The influence of differecnt drag coeifficent Cd. Figure 5.18 gives the bubble dispersion in the flotation machine under different aeration rate conditions. It can be seen that the gas holdup in the tank is high under a large gas superficial velocity, but the overall distributions are uniform, which better solves the problem of simulation distortion under a large gas volume

of the bubbles in the tank increases with the increase of the drag coefficient, which is manifested by the more advantageous dispersion. Figure 5.18 gives the bubble dispersion in the flotation machine under different aeration rate conditions. Figure 5.19 is the liquid phase velocity cloud picture of the

0.1 m3/ m2 min

0.5 m3/ m2 min

Fig. 5.18 The air dispersion of different air superficial velocity

1.1 m3/ m2 min

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159

Fig. 5.19 The water velocity in the KYF-320 flotation cell

320 m3 flotation equipment, and Fig. 5.20 is the liquid phase velocity vector map of the rotor and stator areas. As the main body of fluid motion in the tank of the flotation machine, the high liquid phase velocity in the mixing area is favourable for the mixing of pulp and bubbles, while the low liquid phase velocity in the transport area enables the mineralized bubbles to ascend steadily without falling off due to excessive disturbance. After leaving the stator blade, the liquid phase becomes a radial jet and develops to the tank wall. It is split into two strands near the wall surface of the tank body of the flotation machine, one moves upward, and the other moves downward. The downward flow forms the lower circulation in the mixing area. The lower circulation is small, and the appropriate flow rate can prevent mineral sediment in the tank, allowing re-participation in the pulp circulation. The upward jet forms the upper circulation in the mixing area. The upper circulation is large, and the flow velocity is slow. It provides reasonable motive power for the bubbles to transport Fig. 5.20 The vector diagram of rotor and stator region

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5 CFD Simulation Research on Fluid Dynamics of Flotation Machines

the mineral particles without affecting the adhesion between air bubbles and mineral particles. It is difficult, and even impossible, to acquire the relative flow states of the gas in the flotation tank accurately by the traditional measurement technology. Figure 5.21 is the gas phase velocity cloud picture in the flotation tank. A higher gas superficial velocity in the rotor and stator areas is favourable for the full mixing of the pulp and bubbles and increases the probability of collision and adhesion between the mineral particles and bubbles. The smaller velocity at the upper part of the tank body ensures the stability of the ascending area and the froth layer, which is favourable for the flotation process. Gas holdup is an important criterion for evaluating the performance of the flotation equipment. Figure 5.22 is the predicted air holdup in the tank. The air distribution in the flotation tank is mainly concentrated in the rotor and stator areas where the air holdup decreases gradually with the increase of the height. The predicted result of the gas holdup can coincide with the actual flotation equipment well. Fig. 5.21 The air superficial velocity in the KYF-320 flotation cell

Fig. 5.22 The air holdup in the KYF-320 flotation cell

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161

At present, the Euler two-fluid flow model is generally used in the gas–liquid two-phase flow. The gas phase is generally considered as a discrete phase under the low concentration condition, and the collision between particles is neglected. It is considered that the gas phase flow is affected by the main phase turbulence. The gas and liquid phases follow their governing equations, respectively. The commonly used turbulence models such as standard k − ε turbulence model and its corrected model, etc. are generally selected for the liquid phase, while the Dispersed Phase Zero Equation model is mainly used for the gas phase. Generally speaking, the simulation research on the gas–liquid two-phase flow of the flotation equipment gradually becomes mature. Many research findings have been recognized by the engineering and applied to the equipment development and optimization.

5.2.4 Flow Field of the Flotation Machine Under the Two-Phase System In the early application of the flotation equipment, the CFD method is dominated by the single-phase pure water condition, the key parameters such as flow pattern and velocity of the liquid phase in the equipment are accessible without considering the gas and solid phases. Moreover, the accuracy and reliability can be guaranteed when supplemented by PIV, LDV and other advanced experimental fluid dynamics testing instruments. Although there are a lot of simplifications in single-phase simulation, it is still one of the main means in the optimization research of the flotation equipment. To make up for the deficiencies of the single-phase CFD research on the flotation equipment, engineers and technicians have carried out research work on the gas– liquid two-phase system. Air is essential for the froth flotation. The research on the gas–liquid two-phase flow in the flotation equipment can optimize the gas phase distribution in the equipment and make the equipment have a good air dispersion state. Some research institutes such as CSIRO and the CAST Group have carried out in-depth and systematic researches on the two-phase flow. As a result, TankCell, SuperCell and other series of flotation machines have been well optimized [18, 19]. Currently, the CFD simulation research of flotation machines with gas–liquid– solid three-phase systems is a relatively frontier field, and relevant scholars have carried out meaningful explorations. The difficulty existing in the research of the three-phase system lies not only in the complex interaction among three phases and the higher difficulty in the convergence of CFD numerical simulation itself, but also in the great limitations and imperfections in the basic mathematical model of the three-phase system. At present, neither the traditional design method nor the testing instrument can accurately describe the real three-phase flow state in the tank of the flotation equipment. Therefore, the research on the three-phase flow of the flotation machine by the CFD simulation method is still a relatively effective means.

162

(1)

5 CFD Simulation Research on Fluid Dynamics of Flotation Machines

Solid phase flow characteristics of KYF flotation machine

The solid phase flow and distribution characteristics under the three-phase system of the flotation machine are explored with BGRIMM’s large-scale air forced mechanical agitation flotation machine KYF-160 as the object of research. The Euler two-fluid control model is used in the CFD simulation research to avoid the limitation of the Lagrange method that the phase holdup shall generally not be higher than 12%. Air and ore particles are regarded as discrete phases, and water is regarded as the continuous fluid phase. The drag force (Grace drag model), surface tension and turbulence dispersion force (using the Lopez de Bertodano model) are considered between the continuous main phase, i.e. the water, and the discrete fluid phase, i.e. the air. The drag model Schiller Naumann is considered between the continuous main phase, i.e. the water, and the discrete solid phase, i.e. the ore particles, and Sato Enhanced Eddy Viscosity is selected for the turbulence transmission model. In terms of the turbulence models, the standard K-E model with good universality is selected for liquid phase water, and the zero equation model with good stability is selected for air and ore particles. Apatite is chosen as the object of research, its density is 3200 kg/m3 , molecular weight is 300 kg/kmol, pulp viscosity is taken as 3cp and pulp volume concentration is 12% (with the mass concentration of 30%). In actual industrial production, the grinding size of apatite varies greatly depending on the production conditions. For example, the grinding fineness of a phosphorus concentrator in Yunnan reaches -200 meshes, accounting for more than 90%. The particle sizes of phosphorus ores are firstly set to a single particle size 0.074 mm (200 meshes) in consideration of the problems brought to the computational convergence by the CFD method after solid phase addition. Figures 5.23 and 5.24 is velocity vector maps of the liquid phase water and solid phase ore particles in the KYF-160 flotation machine, respectively. The velocity vector maps of liquid and solid phases are very similar, which indicates that the ore particles can be agitated and mixed well with the main fluid, i.e. water, in the flotation machine. The rotor has the obvious effects of agitation and discharge, forming a very significant lower circulation flow in the lower area of the tank body. A vortex centre of upper circulation appears near the tank body wall surface slightly higher than the rotor, but the overall velocity of the upper circulation is not high. Therefore, it can be considered that an agitation and mixing area of the flotation machine is formed in the periphery of the rotor. In the upper-middle part of the tank body, the upward flow is not intense, the flow is smooth without obvious vortex features, which indicates that the KYF-160 flotation machine provides a relatively stable transport area where the ore particles can be lifted to the upper area of the tank body. In the upper area of the tank body, there is a stable flow field area, i.e. separation area, which is dominated by horizontal flow. The existence of this area is very critical because it provides a fluid dynamics environment that can satisfy the separation of target minerals from gangue minerals. Figure 5.25 is the solid holdup (volume holdup, the same below) distribution in the KYF-160 flotation machine. A cone-shaped high solid holdup area appears below

5.2 CFD Simulation Research of Flotation Machines

Fig. 5.23 The water velocity in the KYF-160 flotation cell

Fig. 5.24 The solid velocity in the KYF-160 flotation cell

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Fig. 5.25 The solid holdup distribution in the KYF-160 flotation cell (single particle diameter 0.074 mm)

the rotor, which coincides with the high solid holdup at the lower part of the rotor in the engineering practice. The existence of the cone-shaped high solid holdup area explains the reason for the occurrence of a cone-shaped ore particle accumulation area at the bottom in the production practice. Therefore, a diversion cone is often designed at the bottom of the rotor in flotation machines, especially in large flotation machines. On the one hand, the diversion cone can increase the pulp flow velocity at the bottom and avoid the formation of the dead zone below the rotor. No serious high solid holdup area appears on the bottom wall surface of the tank body, which indicates that the design of the cone bottom of the tank body is reasonable and no dead zone will appear in the production. In the lower area of the tank body, the distribution characteristics of the solid holdup are very similar to those of the lower circulating flow field structure where the solid holdup in the vortex centre is low, but the solid holdup is increased obviously in the circulation area in the periphery of the vortex centre. This shows that the ore particles follow the fluid for circulation flow well. The gas holdup distribution in the upper-middle part of the tank body is uniform, with a slightly decreasing trend, which indicates that the flow in the upper-middle part does not change dramatically, most of the solid phases in the tank body area are distributed uniformly, accounting for about 11%, with good agitation and fixing effects (theoretically, the proportion for full and uniform mixing in the tank body is 12%). In the top area near the liquid level, the solid holdup is lower, about 8%. The solid holdup distribution gradually decreases from bottom to top in the whole tank

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165

body, which coincides with the actual situation that medium and fine particles are easy to float up and coarse particle ore deposits are easy to occur at the bottom of the tank body in the actual production. Therefore, we should start from many aspects such as optimal design of key structures of flotation machines and adjustment of operating parameters in order to improve the ore recovery ratio of coarse particles. (2)

Influences of the ore size on solid phase holdup

The feed size of ores is very critical for the separation effect of flotation operation. Generally, the flotation machines can only separate medium and fine sized ore particles, and coarser particles are difficult to recover because they are difficult to adhere to the bubbles and easy to fall off after adhesion and so on. Therefore, it is generally easier to recover the ores by grinding them to a finer state. The power consumption in the grinding section generally accounts for more than 60% of that in the whole grinding-flotation section. Therefore, reduction of the grinding cost plays an important role in improving the running benefit of concentrators. Based on this, it is very valuable to research the separation performance of the flotation machine for different particle sizes, improve the separation performance of the flotation machine and reduce the grinding consumption. (3)

Influences of a single particle size on solid phase holdup

Figures 5.26 and 5.27 shows the distribution of solid phase holdups in the KYF-160 flotation machine with the particle sizes of 0.1 and 0.25 mm. It is not hard to see that with the increase of particle sizes, the phenomenon of accumulation of ore particles at the bottom of the tank body becomes more and more serious, and the range of low solid holdup area at the top is getting larger. This indicates that the deposition of coarse particles at the bottom becomes more serious after the particle size increases, and it is more difficult for coarse particles to be lifted to the upper part of the tank body, making the recovery effect of coarse particles worse. On the whole, all the solid phase holdup distributions near the rotor area with different particle sizes coincide well with the circulation flow of the rotor, and the solid holdup distribution in the upper-middle area is still relatively uniform. In Fig. 5.28, the coordinate values of the solid holdup are adjusted to the solid holdup results of 100% (max.) and 0% (min.) based on Fig. 5.27, which is a more visual reflection of the deposition condition of the coarse particles. Coarse particle deposition areas with the solid phase holdup of nearly 100% begin to appear at the bottom of the tank body and below the rotor, an area with a very low solid holdup has appeared in the top area, which shows that the grind fineness of the particle size 0.25 mm has approached the separation limit of the flotation machine without changing the operating parameters and optimizing the design, and it is not easy to further coarsen the grinding. This coincides with the generally considered feed fineness of below 0.3 mm in the engineering practice. (4)

Influences of multiple particle sizes on solid phase holdup

Ore grinding products cannot be of a single particle size. Generally, the grind fineness is evaluated by the proportion of −200 mesh products. In many concentrators, the

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Fig. 5.26 The solid holdup distribution of 0.1 mmin the KYF-160 flotation cell

Fig. 5.27 The solid holdup distribution of 0.25 mm in the KYF-160 flotation cell

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167

Fig. 5.28 The solid holdup distribution of 0.25 mmin the KYF-160 flotation cell (the maximum in the coordinates 100%, minimum 0%)

proportion of −200 mesh products needs to be up to more than 90%, such as Cu–Mo deposits. On other occasions, −200 mesh products can be liberated as long as the proportion reaches 45%, and the −200 mesh products only account for less than 30% even in some comprehensive tailing recovery projects. Therefore, it is of great significance to explore the distribution of all the size fractions in the tank under the condition of multiple particle sizes for the research of the size fraction separation performance of flotation machines. With the comprehensive recovery of apatite tailings as the research background, the grind fineness of apatite tailings is coarse, and sediment in the tank occasionally occurs in the production of the flotation equipment due to the coarse particle size in industrial production. Therefore, the project group carried out the researches on the distribution characteristics of different size fractions in the flotation machine under the two conditions: 9% 0.1 mm particle size and 3% 0.25 mm particle size; 9% 0.1 mm particle size and 3% 1 mm particle size. And the project group investigated the maximum floating size (with the total solid phase volume holdup of 12%, which is converted into the mass concentration of about 30%) of the equipment. Figures 5.29 and 5.30 is the solid phase holdup distribution diagrams of particle sizes 0.1 mm and 0.25 mm under the condition of combination of double particle size 0.1 mm and 0.25 mm, respectively. The solid phase holdup distribution of mineral particles with the particle size of 0.1 mm is similar to that in Fig. 5.26 (with the single particle size of 0.1 mm). The distribution of solid phase holdups of mineral particles

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Fig. 5.29 The solid holdup distribution of 0.1 mmin the KYF-160 flotation cell in the two kinds of particles 0.1 and 0.25 mm

with the particle size of 0.25 mm has a higher solid holdup below the rotor, but the particles can be raised to the upper-middle area of the tank body with the circulation flow of water. It shows that the KYF-160 flotation machine can basically achieve the effective mixing of the combination of double particle size 0.1 and 0.25 mm. Figures 5.31 and 5.32 is the solid phase holdup distribution diagrams of particle sizes 0.1 mm and 1 mm under the condition of combination of double particle size 0.1 mm and 1 mm, respectively. The main difference between the distribution of solid phase holdups of ore particles with the particle size of 0.1 mm and that in Fig. 5.26 (with the single particle size of 0.1 mm) lies in that the solid holdups at the bottom of the tank body and that directly below the rotor are very low because the above areas are occupied by deposited particles with the particle size of 1 mm. Solid particles with the particle size of 1 mm are mainly concentrated at the bottom of the tank body and directly below the rotor, and the solid holdups in both positions are above 90%. In consideration of the overall volume fraction of 1 mm particles which only accounts for 3% of the tank body volume, it can be concluded that almost all 1 mm particles are deposited at the bottom of the tank body, and the KYF-160 flotation machine cannot realize the suspension of 1 mm ore particles, which further shows that the size of the floating particles of the flotation machine is limited.

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169

Fig. 5.30 The solid holdup distribution of 0.25 mmin the KYF-160 flotation cell in the two kinds of particles 0.1 and 0.25 mm

(5)

Influences of the ore density on solid phase holdup

There are a great variety of ores. As general equipment, the flotation equipment needs to adapt to the separation requirements of different kinds of ores. Therefore, it is very important to research the influences of different kinds of ores on the flow of the flotation machine. In the differences among the ore types, the most critical difference is their difference in density in the case of CFD numerical simulation. Apatite, chalcopyrite and quartz are selected for comparative research which focuses on the influence of changes in the ore density on the solid phase holdup. Table 5.5 shows the physical parameters of different ores. Figures 5.33, 5.34 and 5.35 is solid phase holdup distributions of quartz, apatite and chalcopyrite, respectively. With the increase of density, the solid phase holdup at the bottom of the tank body continuously increases, and the low solid holdup area at the top is continuously enlarged. With the increase of ore density, the deposition of ore particles will become more serious. On the whole, the distribution of solid phase holdups is relatively uniform in most areas of the tank body, and all the high solid holdup areas are small. Therefore, this flotation machine can fully agitate and mix quartz, apatite and chalcopyrite, with good ore adaptability.

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Fig. 5.31 The solid holdup distribution of 0.1 mmin the KYF-160 flotation cell in the two kinds of particles 0.1 and 1 mm

(6)

Influences of the pulp viscosity on solid phase holdup

The pulp viscosity is an important process parameter for the flotation process. Therefore, the project group studied the influence of the pulp viscosity on the solid phase holdup of ore particles. Figure 5.36, 5.37 and 5.38 is the diagrams of the distribution of solid holdups with the pulp viscosities of 3 mpa.s, 8 mpa.s and 13 mp.s, respectively. With the increase of pulp viscosity, the average solid holdups in the upper and middle areas of the tank body decrease significantly, which indicate that the ores deposited in the tank body are increased. Due to the introduction of the solid phase medium, the simulation of the flotation equipment in the three-phase system can simulate and research the phase distribution of the gas–solid two-phase system, the influence of solid properties on the original flow field, the wear in the rotor–stator caused by solid particles and other research work full of practical significance, so the research on the flow field of the flotation equipment under the three-phase system is of extraordinary significance for guiding practice. However, from the prediction results of the simulation, we can see that the continuous homogeneous phase assumption of solid and liquid phases leads to similar prediction results of the solid and liquid phase flow fields and convergence of variation laws, the actual phenomena such as solid phase separation and diffusion in the flotation tank are difficult to reflect, so the simulation research of the threephase system still has much room for improvement in the fundamental theory of computational fluid dynamics and specific model settings.

5.2 CFD Simulation Research of Flotation Machines

171

Fig. 5.32 The solid holdup distribution of 1 mmin the KYF-160 flotation cell in the two kinds of particles 0.1 and 1 mm

Table 5.5 Physical parameters of ores Ore

Density (kg/m3 )

Quartz

2650

Molecular weight (kg/kmol) 60

Viscosity (cp)

Volumetric concentration (%)

Mass concentration (%)

3

14

30

Apatite

3200

300

3

12

30

Chalcopyrite

4100

119

3

9.5

30

5.2.5 Optimization of Flotation Machines Based on CFD Simulation The influence research on the rotor off-bottom height based on the CFD method introduces the application of the CFD method in the optimization and design of flotation machines. The key to the design of the middle positioned rotor is the design of the false bottom, circulating cylinder structure, off-bottom height, etc. Figure 5.39 is the velocity vector diagram of the flotation machine after the rotor is raised. The flotation machine still has obvious upper and lower circulation flow fields. The lower circulating flow field has a wide range of action, with a significant rotor suction effect. The upper circulation is located near the top. It is worth noting that there is

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5 CFD Simulation Research on Fluid Dynamics of Flotation Machines

Fig. 5.33 The solid holdup distribution of the quartz with 2650 kg/m3

Fig. 5.34 The solid holdup distribution of the apatite with 3200 kg/m3

5.2 CFD Simulation Research of Flotation Machines

Fig. 5.35 The solid holdup distribution of the copper pyrites with 4100 kg/m3

Fig. 5.36 The solid holdup distribution of the viscosity with 3 mPa.s

173

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5 CFD Simulation Research on Fluid Dynamics of Flotation Machines

Fig. 5.37 The solid holdup distribution of the viscosity with 8 mPa.s

Fig. 5.38 The solid holdup distribution of the viscosity with 13 mPa.s

5.2 CFD Simulation Research of Flotation Machines

175

Fig. 5.39 The water velocity in the KYP-160 flotation cell

an obvious effect of horizontally projected jet after the fluid is discharged from the rotor area. Figure 5.40 is the velocity vector diagram of the KYP160 flotation machine after the draft tube is added. After the diversion cylinder is added, the velocity in the diversion cylinder at the lower part of the rotor area obviously increases. Compared with the flow field without the diversion cylinder, the lower circulation has changed greatly. Figure 5.41 is the velocity vector diagram of the KYP160 flotation machine after the draft tube and the false bottom structure are added. After the draft tube and the false bottom structure are added, the structure of upper and lower circulating flow fields is still obvious. The influence of the false bottom structure on the flow field is mainly embodied near the lower circulation wall surface. Since the false bottom reduces the flow area at the bottom edge, most of the circulating fluid at the lower part is forced to pass through the flow section between the false bottom and the tank body, where the flow velocity is reinforced. Therefore, the diversion cylinder plays a role in reinforcing the lower circulation.

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5 CFD Simulation Research on Fluid Dynamics of Flotation Machines

Fig. 5.40 The vector of water velocity in the KYP-160 flotation cell with draft tube

Fig. 5.41 The vector of water velocity in the KYP-160 flotation cell with draft tube and false bottom

References

177

References 1. Wang F (2004) Computational fluid dynamic analysis-CFD Software principles and applications. Tsinghua University Press 2. Shen Z, Lu S, Shi S (2013) Single-phase flow field measurement and analysis based on PIV for KYF flotation machine—flow field measurement and simulation research on KYF flotation machine I. Nonferrous Metals 01:59–64 3. Han L (2005) Numerical simulation of fluid flow in stirred tank reactors using CFD method. Xiangtan University 4. Grau. An investigation of the effect of physical an d chemical variables on bubble generation and coalescence in laboratory scale flotation. Helsinki University of Technology, TKK-ME-DT-4, Espoo 5. ANSYS CFX Tutorials,ANSYS. Inc (2010) 6. Han W (2009) Numerical study of multi-phase flow characteristics and flotation dynamics performance in flotation machine. Lanzhou University of Technology 7. Shen Z, Chen D, Yang L et al. (2010) Numerical simulation of gas-liquid two-phase flow in 320 m3 air-forced mechanical agitated flotation machine. Non-ferrous Metall Equip (06):14–17 8. Song T (2010) Numerical simulation of gas-liquid flow in gold leaching reactors. BGRIMM Technology Group 9. ANSYS CFX-Solver, Release 10.0: Theory, Computational Fluid Dynamics Services, ANSYS. Inc (2005) 10. ANSYS FLUENT 12.0 User’s Guide, ANSYS. Inc (2009) 11. Jiang F, Huang P (2008) Fluent advanced application and case analysis. Tsinghua University Press 12. Xia J, Rinne A, Grönstrand S (2009) Effect of turbulence models on prediction of fluid flow in an Outotec flotation cell. Miner Eng 22:880–885 13. Koh PTL, Schwarz MP (2003) CFD modelling of bubble–particle collision rates and efficiencies in a flotation cell. Miner Eng 16:1055–1059 14. Koh PTL, Schwarz MP (2006) CFD modelling of bubble–particle attachments in flotation cells. Miner Eng 19:619–626 15. Koh PTL, Schwarz MP (2007) CFD model of a self-aerating flotation cell. Int J Miner Process 85:16–24 16. Xia J, Rinne A, Gronstrand S (2009) Effect of turbulence models on prediction of fluid flow in an Outotec flotation cell. Min Eng 22:880–885 17. Tiininen J, Vaarnno J, Gronstrand S (2003) Numerical modeling of an Outokumpu flotation device. In: Third international conference on CFD in the minerals and process industries, Melbourne, Australia, 10–12 December 18. Rodrigo G, Martta N, Alejandro Y (2014) Gas dispersion measurements in three Outotec flotation cells: Tankcell 1, e300 and e500, 27th International Mineral Processing Congress, IMPC 2014. Santiago, Chile, p 197 19. Salem-Said A, Fayed H, Ragab S (2011) CFD simulation of a Dorr-Oliver flotation cell. In: Proceedings of the SME annual meeting and exhibit, Denver, CO, USA

Chapter 6

Flotation Machine Upsizing Method and Technology

With the social development, there has been increasing demand for mineral resources, and mineral resources have gradually become poor and complex due to the continuous development. It is necessary to improve the processing capacity of flotation equipment greatly in order to process more and more poor ores and refractory ores [1]. In addition, the large flotation equipment has outstanding advantages [2] such as a small number of machines to be installed, small foot, easy implementation of automatic control, low capital investment in infrastructure and low power. The flotation machine upsizing has always been the focus of research in the recent 30 years. Flotation is a complex physicochemical reaction process involving the three phases of gas, liquid and solid. The scale-up process of the flotation machine does not mean to increase geometric dimensions of key components (such as the tank cell, rotor and stator) of the flotation machine simply in proportion, but it requires the full consideration of internal flotation dynamics feature of the flotation machine so that the hydrodynamic environment meets the requirements for the separation of minerals particles with different size fractions. Compared with small and medium flotation machines, the large flotation machine has significantly different flotation dynamics process and micro-flotation behaviours. For the large flotation machine, due to its high tank cell and long rising distance of mineralized bubbles, coarse minerals are prone to fall off from mineralized bubbles, which will reduce the recovery. In addition, the Reynolds number is low due to the low specific power (kW/m3 ), relatively small rotor circulation flow rate and high short-circuit probability, which reduces the collision probability between fine mineral particles and bubbles. Therefore, during flotation machine upsizing, besides the scale-up by a certain method based on the original design of small and medium flotation machines, the impact of factors mentioned above on the separation performance shall be fully considered. In addition, when the large flotation machine is amplified in proportion, the relation between the volume of the large flotation machine and the number of tanks for a group of flotation machines must be considered carefully. The number of tanks for a group of flotation machines depends primarily on the volume of the flotation machine tank, the processing capacity of the flotation circuit and the flotation time © Metallurgical Industry Press 2021 Z. Shen, Principles and Technologies of Flotation Machines, Springer Tracts in Mechanical Engineering, https://doi.org/10.1007/978-981-16-0332-7_6

179

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6 Flotation Machine Upsizing Method and Technology

sufficient to achieve the desired recovery rate. For the minimum number of tanks for a group of flotation machines, an appropriate margin shall be reserved in order to avoid the adverse impact of the pulp flow short circuit on the recovery rate [3].

6.1 Flotation Machine Upsizing Process Since the 1940s, the flotation machine has been developed towards upsizing. Since the 1990s, the use of the large-volume flotation machine has attracted much attention. The production practice has shown that the cost per unit may be reduced by improving the production capacity per unit of the flotation equipment, and the design work of the flotation machine should follow the principles of the large single tank volume, strong production capacity, low power consumption, simple structure and good automatic control. The volume of the flotation machine has been increased by 10 times at least in the recent 30 years, and increased by 100 times compared with that in the 1940s. The flotation equipment with the single tank volume greater than 100 m3 has been applied in the industry substantially [4]. At present, the volume of the largest flotation machine for the industrial application has reached 680 m3 . Figure 6.1 shows changes in the volume of the flotation machine over about 50 years. The single tank volume of the flotation equipment reflects the level of research and technology for the flotation equipment to a certain extent. At present, companies that can represent the internationally highest level research, development and application of the flotation equipment mainly include Outotec, FLSmidth, Metso and Beijing General Research Institute of Mining and Metallurgy (BGRIMM). Particularly, representative products include OK-TankCell flotation machine, Wemco flotation machine, Dorr-Oliver flotation machine, XCELL flotation machine, RCSTM (reactor cell system) flotation machine, KYF flotation machine, JJF flotation machine, etc.

Fig. 6.1 Scale-up of flotation machine process

6.1 Flotation Machine Upsizing Process

181

Table 6.1 Statistical table of flotation equipment with the largest volume developed and applied by different manufacturers Flotation equipment brand

Developed flotation machine with the largest volume/m3

Applied flotation machine with the largest volume/m3

Air inflation method

R&D launched year

Country

KYF flotation 680 machine

680

Air-forced

2017

China

JJF flotation machine

320

320

Air-induced

2015

China

TankCell flotation machine

630

630

Air-forced

2014

Finland

Wemco flotation machine

660

300

Air-induced

2014

USA

Dorr-Oliver flotation machine

660

660

Asir-forced

2014

USA

XCELL flotation machine

350

50

Air-forced

2009

USA

Table 6.1 lists the flotation equipment with the largest volume that is successfully developed by flotation equipment developers. Due to the complexity of the flotation process, it is difficult to measure and calculate the three-phase flow field. The theoretical results of original fluid dynamics and flotation dynamics are far from supporting the research on flotation machine upsizing. At present, although researchers have made a lot of efforts and made great contributions to the research on flotation machine upsizing, the speed of increasing the volume of the flotation machine is much faster than that of theoretical research. Currently, all kinds of upsizing methods are mainly based on empirical formulas and supplemented by experience in engineering practice. It is difficult to find a uniform and accurate scale-up method for the large flotation machines.

6.2 Flotation Machine Upsizing Technology The flotation machine upsizing technology is the core secret of flotation machine manufacturers. This section will briefly introduce the upsizing technology of typical pneumatic mechanical agitation flotation machines, such as the TankCell flotation machine, BGRIMM mechanical agitation flotation machine and Wemco flotation machine.

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6 Flotation Machine Upsizing Method and Technology

6.2.1 TankCell Flotation Machine Since the first batch of OK-1.5 and OK-3 flotation machines developed by Outotec was put into operation at the Kolatahti mineral processing plant in 1959, Outotec has always focused on the development of the flotation equipment. As a pneumatic mechanical agitation flotation machine, it utilizes the characteristics of the height-todiameter ratio of the flotation column and combines with the mechanical agitator of the flotation machine; therefore, with the characteristics of both the flotation column and the mechanical agitation flotation machine, it can not only make coarse particles fully suspended, but also obtain relatively high-grade concentrates.

6.2.1.1

Development History

In 1983, the OK-TankCell flotation machine with the specification of OK-60-TC and the volume of 60 m3 was firstly installed and used at Pyhasalmi Concentrator. Since then, the OK-TankCell flotation machine has been amplified in proportion, achieving the good separation effect in many mines. In 1996, 6 set of 100 m3 OK-TankCell flotation machines were deployed in the copper roughing and flotation circuit in a 2-2-2 layout at the Morenci-Metcalf copper ore concentrator of Phelps Dodge in USA. In view of the space, the tanks were arranged in a “U” shape in the circuit design, achieving the excellent separation effect and significantly reducing the power consumption. In 1999, 80 set of 100 m3 OKTankCell flotation machines were installed at the Escandeda copper ore concentrator of BHP/RTZ in Chile. Compared with the flotation machine used previously, due to the successful installation and industrial application of the TankCell flotation machine, the copper grade and recovery rate of BHP’s copper concentrates were greatly improved [5–10]. In 1999, the TankCell-200 flotation machine was applied at the Zinifex Century zinc concentrator in Queensland and the Cowal gold concentrator in Australia. In 2007, the first 300 m3 TankCell flotation machine was applied at the Macraes gold mine in New Zealand. It was used together with the original TankCell-150 of this concentrator to replace the old line composed of two flotation columns and the traditional flotation machine, increasing the recovery rate by 4%. In 2009, the TankCell-300 flotation machine was successfully tested and certified to achieve the desired effect at Chuquicamata Branch of CODELCO in Chile, as shown in Fig. 6.2. Compared with two TankCell-160 machines installed in parallel, the recovery rate was increased by 5% and the concentrate grade was increased by 1%; moreover, the power consumption of the TankCell-300 was reduced to 0.58 kW/m3 . A single Outotec TankCell-300 flotation cell was installed at Codelco’s Chuquicamata copper mine in Chile outperformed two TankCell-160 cells, for this flotation machine, the air supply flow rate was about 16–31 m3 /min and the shaft inlet air pressure was 71 kPa.

6.2 Flotation Machine Upsizing Technology

183

In 2012, Outotec developed the TankCell e500 flotation machine with larger volume than before (as shown in Fig. 6.3) by using the FloatForce agitation mechanism and gearbox transmission technology, in which low-pressure air was forced into the rotor chamber directly from the hollow part of the gearbox output shaft. The flotation machine had a diameter of 10 m, an overflow weir height of 6.8 m and Fig. 6.2 A single Outotec TankCell-300 flotation cell was installed at Codelco’s Chuquicamata copper mine in Chile outperformed two TankCell-160 cells, providing higher recovery with copper grade equal to the two smaller machines. As featured in Womp 09 Vol 05—www.womp-int.com

Fig. 6.3 TankCell e500 flotation cell. Picture from https://www.e-mj.com

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6 Flotation Machine Upsizing Method and Technology

Fig. 6.4 e630 flotation cell (picture from https://www. outotec.com)

a rotor diameter of 2200 mm; its installed power varied within the range of 400– 500 kW under different working conditions and its absorbed power varied within the range of 260–430 kW; its aeration pressure was 66 kPa and its aeration rate was 30–80 m3 /min. In 2014, the company launched the research program of the world’s largest e630 flotation machine, which was designed with a diameter of 11 m, an overflow weir height of 7 m and a geometric volume up to 700 m3 , as shown in Fig. 6.4. By means of the FloatForce agitating technology, its installed power reached 500 kW. The flotation machine was intended for roughing and scavenging operations of gold ores and base metals. Compared with concentrators using the TankCell-300, it was expected that the operation cost might be reduced by 10–20%.

6.2.1.2

TankCell Upsizing Technology

In 2001, Outotec successfully developed the 160 m3 flotation machine by amplifying the 16 m3 TankCell flotation machine in proportion, for which the following parameters were mainly considered: (1) (2) (3)

Structure of rotor/stator. Geometry of tank cell. Suspension capacity of mineral particles. Flotation feed generally contains coarse, medium and fine particles. The behaviour for different size particles is

6.2 Flotation Machine Upsizing Technology

(4)

185

different in the flotation process. All flotation machines with different volumes should have the ability to mix the pulp effectively and disperse air thoroughly. Froth characteristics. The mineral recovery may be influenced by the froth stability, froth depth, froth stability and the method for scraping froth out effectively.

During the scale-up in proportion for tank bodies of flotation machines with different volumes, the dynamic head should be similar to the hydrostatic pressure head, which means that the Froude number should be equal. The equations of scaleup in proportion for a series of flotation machines are obtained according to the Froude number [11].    23  Impeller diameter to tank width ratio: DD = LL . 

Pulp volume ratio: Power ratio:



P P

=

Q Q

=

   73 L L

   53

=

L L

=





D D

 27





D D

 25

.

.

where D, Q, P and L refer to the rotor diameter, pulp flow rate, power and tank width of the flotation machine. Upon the determination of the primary parameters above, the three-phase flow state of the flotation machine is simulated and optimized by use of the computational fluid dynamics, which accelerates the research process of flotation machine upsizing.

6.2.2 Wemco Flotation Machine FLSmidth is one of the world’s largest flotation cell manufacturers; its representative products are WEMCO and Dorr-Oliver flotation machines. In recent years, over 400 flotation machines with the volumes of 130 and 160 m3 have been installed in South America [12–19].

6.2.2.1

Wemco Development History

In 2003, the SmartCell-250 flotation machine with the single tank volume of 257 m3 was developed successfully. The industrial test of the machine was conducted at Minera Los-Pelambres in Chile. The SmartCell-250 flotation machine was used in the roughing circuit of the copper sulphide concentrator to replace the SmartCell-160 flotation machine. The test result showed that the installed power was reduced by 15%, the energy cost was decreased by 7%, the spare part cost was saved and the downtime for maintenance was shortened. The pilot machine was shown in Fig. 6.5 [13]. After the successful test, Minera Los Pelambres used 10 set of 257 m3 flotation machines to increase its throughput from 120,000 to 140,000 t/d.

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6 Flotation Machine Upsizing Method and Technology

Fig. 6.5 Test location of SmartCell-250 (https://www. mining-technology.com/con tractors/crushers/ffe_min erals/pressreleases/pre ss5-16/)

In 2004, FLSmidth Mining Company designed the SuperCells (super flotation machine) with the world’s largest volume from 300 to 350 m3 . In 2009, the industrial test of two SuperCells™—300 machines was launched at the Kennecott Copperton concentrator in Utah, USA. The machines were successfully applied in the copper and molybdenum bulk flotation process of the concentrator, shown in Fig. 6.6. In 2012, FLSmidth launched the development program for the SuperCell™ 600 flotation machine with the volume of 600–650 m3 in three types, i.e. WEMCO, Dorr-Oliver and Xcell. Fig. 6.6 Test location of SuperCell-300 (https://www. directindustry.com/prod/fls midth-dorr-oliver-eimco/pro duct-62016-554816.html)

6.2 Flotation Machine Upsizing Technology

187

Fig. 6.7 SuperCell™ 660 flotation cell test location (https://www.at-minerals.com/imgs/101314 984_167b4c4489.jpg)

In 2015, one SuperCell™ 660 flotation machine was installed for test in Rougher and Scavenger of Robinson Mining Company in Nevada, as shown in Fig. 6.7.

6.2.2.2

Wemco Flotation Machine Upsizing Technology

The Wemco flotation machine was scaled up in proportion by use of the fluid dynamics parameters. Such parameters are as follows [14]: (a)

(b)

Superficial gas velocity: It depends on the amount of gas entering the unit cross-sectional area of the flotation tank. Due to the low gas flow rate per unit section of the flotation machine, the recovery rate of hydrophobic minerals is reduced; however, as the gas flow rate per unit froth surface is too large, the pulp surface is disturbed or tumbled. In order to prevent the pulp surface from being excessively disturbed, generally for the flotation, the maximum allowable gas flow rate is 1.5–2.5 cm/s. Downtime of the gas and pulp in the disperser: It represents the time of contact between bubbles and mineral particles, which depends on the total volume of the pulp and gas in the disperser area per unit time. The volume of the disperser of the flotation machine refers to the volume of the disperser covering chamber.

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6 Flotation Machine Upsizing Method and Technology

(c)

Power intensity of the disperser covering: It represents the power of the disperser volume per cubic foot, which is another parameter that depends on the disperser cover area. Circulation intensity of the flotation tank: The circulation intensity represents the number of times the pulp passes through the aeration mechanism before discharging from the flotation tank. The greater the circulation intensity is, the more times the particles contact with air bubbles in the disperser cover area. Pulp velocity in upward tube: The pulp flow velocity refers to the pulp flow rate per unit cross-sectional area of the tube. In order to improve the solid suspension characteristics of the large-volume flotation machine, the pulp flow velocity should be increased with the increase in the size of the flotation machine. Therefore, this parameter can quantify the solid suspension characteristics of the flotation machine. Number of gas flow (Q/DN 3 , Q—gas flow, N—rotor speed and D—rotor diameter). It represents the suction capacity of the agitation mechanism, which directly determines the aeration velocity of the mechanical agitation flotation machine which is an important determinant in the flotation process.

(d)

(e)

(f)

6.3 BGRIMM Flotation Machine Upsizing Technology The research on flotation machine upsizing started late in China, and was commenced in 1990s. In order to meet China’s demand for the large flotation machine, BGRIMM has made a lot of efforts to figure out the technical difficulties and key points in the process of amplifying the flotation machine, and thus has formed the key flotation machine upsizing technology. In 2000, the flotation machine with the single tank volume of 50 m3 was developed successfully, and nearly 1000 flotation machines were promoted and applied rapidly in China. In 2005, the flotation machine with the single tank volume of 160 m3 was successfully developed; in 2007, it was applied in the 34,000 t/d project of Wunugetushan copper-molybdenum mine of China Gold Group. In early 2008, one 200 m3 pneumatic flotation machine was successfully developed and used in the 90,000 t/d project of Dashan Concentrator of Jiangxi Copper Corporation Limited. At the end of 2008, BGRIMM successfully developed the KYF-320 pneumatic flotation machine; the industrial test data of Dexing Copper Mine showed that the copper enrichment ratio can reach 20.62, the sulphur enrichment ratio can reach 71.44 and the power consumption of a single machine is 160 kW. The test site of KYF-320 is shown in Fig. 6.8. In 2009, 28 sets of 320 m3 flotation machines were finally applied in the Toromoch project of Aluminum Corporation of China (Chinalco) in Peru. In 2011, 16 sets of 320 m3 flotation machines were applied in the phase II upgrade project.

6.3 BGRIMM Flotation Machine Upsizing Technology

189

Fig. 6.8 KYF-320 test in Dexing copper mine in China in 2008

In 2015, BGRIMM had completed the design of the 680 m3 flotation machine, with 500 kW installed power, 65 kPa air pressure and the control system for the slurry level, aeration rate and froth image. In 2018, the industrial test was completed and the operation power consumption was about 350–400 kW. The test site of 680 m3 flotation machine is shown in Fig. 6.9.

Fig. 6.9 680 m3 flotation machine test in Dexing copper mine in Jiangxi Province in China

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6 Flotation Machine Upsizing Method and Technology

6.3.1 Difficulties of Flotation Machine Upsizing Technology The scale-up technology of the flotation machine relies on the analysis and verification of the flotation process, which actually is a process of mixing three phases of gas, liquid and solid and having complicated physical and chemical interactions between each other. Those processes cannot be directly observed. Therefore, the flotation machine upsizing technology has the following difficulties. (1)

Similar scale-up of the flotation machine

As the geometry of the flotation machine becomes larger, the characteristics of the internal fluid dynamics of the flotation machine with different specifications should be similar in order to ensure the kinetic environment required for bubble–particle collision, adhesion and mineralized bubble transport. However, the characteristics of the fluid dynamics for the rotor mixing zone, transport zone, separation zone and froth zone in the flotation machine are quite different; in addition, the requirements of the flotation dynamics for the air bubbles, particles and liquid are different too. Therefore, it is very difficult to make the three-phase separation environment in the flotation machine with different specifications similar. (2)

Difficult recovery of flotation froth recovery

In terms of mechanical structure, compared with the medium and small flotation machines, the large flotation machine has a larger cross-sectional area and a deeper tank cell. In terms of process, compared with the medium and small flotation machines, a single large flotation machine has a larger froth output and thicker froth. Therefore, the froth transport distance of a large flotation machine becomes relatively long; if the froth cannot be recovered as soon as possible, the targeted mineral particles that have attached on the mineralized bubble will be dropped, so that the recovery rate of the flotation will be reduced. (3)

Difficulty to overcome the shortcut in the flotation machine

Compared with the small flotation machine, the large flotation machine has a deeper tank cell, larger diameter and more processing capacity, in which the dead zone and shortcut turn seriously. In this case, the actual retention time of the pulp in the flotation tank will be less than the flotation time that is calculated based on the effective volume of the flotation machine, i.e. a shortcut, which will also reduce the recovery rate of the flotation. Therefore, it is a key and difficult point for the flotation machine upsizing technology to eliminate the dead zone of the flotation machine and avoid the phenomenon of a shortcut.

6.3 BGRIMM Flotation Machine Upsizing Technology

191

6.3.2 BGRIMM Flotation Machine Upsizing Technology As the largest flotation machine research institute and flotation equipment supplier in China, Beijing General Research Institute of Mining & Metallurgy (BGRIMM) has carried out a series of researches on key technologies and gradually formed the key technologies of BGRIMM flotation machine upsizing with independent intellectual property rights, including similar scale-up technology of the flotation machine, froth transport technology, pulp direction and selection circulation technology and dynamic calculation technology of the pulp retention time.

6.3.2.1

Similar Scale-Up Technology of the Flotation Machine

The key of the flotation machine scale-up is the scale-up principle and the selection of the scale-up factor. Due to different work principles, operating parameters and scope of applications, different flotation machines adopt different scale-up factors and principles. The fluid movement states in different sizes of flotation tanks are different, which results in different flotation effects. The similar scale-up criteria of flotation machine provide a certain guiding significance in the design of the large flotation machine. There are some similar scale-up criteria in the design of the flotation machine, such as the power number, Froude number, air flow number, Weber number, Reynolds number and suspension similarity [14–16]. (1)

(2)

(3)

(4)

(5)

Power number, N P = ρ NP3 D5 (in the formula: N P —power number; P—power; ρ—pulp density; N—rotor speed; D—rotor diameter): It represents the power in the tank of the flotation machine and reflects the relation between the geometrical characteristics of the components in the tank and the working parameters. 2 Froude number, Fr = N g D (in the formula: Fr—Froude number; N—rotor speed; D—rotor diameter): It is defined as the ratio between the centrifugal or inertial forces due to the pumping action of the rotor and the gravitational forces due to hydrostatic head in the flotation cell. Air flow number, N A = NQDA3 (in the formula: N A —air flow number; Q A —air flow; N—rotor speed; D—rotor diameter): It represents the suction capacity of the agitation mechanism, which directly determines the aeration rate of the flotation machine. 2 2 Weber number, We = NγgtD (in the formula: We—Weber number; γgt —tension at the gas–liquid interface; N—rotor speed; D—rotor diameter): It is the ratio of the inertial force to the surface force and describes the similarity of the bubble size in the flotation tank. 2 Reynolds number, Re = ρ NηD (in the formula: Re—Reynolds number; η— dynamic viscosity; ρ—pulp density; N—rotor speed; D—rotor diameter): It is a dimensionless number to determine the fluid flow character and is the ratio of the inertial force to the viscous force.

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6 Flotation Machine Upsizing Method and Technology

(6)

Suspension similarity: In order to make the flotation tank operate normally, it is necessary to maintain sufficient suspension state in the tank. The mineral particles can be attached to the bubble and the flotation process can be processed only on the premise of suspension state. The suspension similarity is based on the principle of kinetic similarity.

All criteria above are equal. However, in fact, they are not equal in the same model of the flotation machine with different specifications. It is impossible to apply all those criteria in the design of the flotation machine. Different types of flotation machines require different scale-up criteria. For the flotation equipment, in addition to mechanical structural parameters, main factors affecting the flotation process are kinetic factors: turbulence intensity, particle suspension, air dispersion, bubble–particle collision, bubble size and quantity, liquid level stability (such as aeration velocity), etc. Therefore, under the premise of ensuring the similarity of the mechanical structure at the time of amplifying the flotation machine, it requires the suspension similarity in the flotation tank and the fluid dynamics similarity of the flotation machine. A.

Similar scale-up of the mechanical structure

Similarity of the mechanical structure means to maintain the geometrical similarity of key components of the flotation machine, including the tank cell similarity and geometrical similarity of the rotor agitation mechanism. The tank cell similarity and the rotor similarity are the premise of suspension similarity in the flotation tank and the similarity of fluid dynamics parameters. The scale-up factors and rules of the tank cell and rotor may be found by the regression method. a.

Tank cell similarity

According to the required volume of the flotation machine, it is not necessary to make the scale-up mechanically based on the geometrical method when simulating the tank cell scale-up; it is necessary to fully consider hydrodynamics in the largescale flotation tank. First, it is necessary to find the parameters to represent the correlation of key components in the tank and their relationship to the volume of the flotation tank. Generally, the flotation machine is amplified by the method for maintaining the ratio of the rotor diameter to the section characteristic dimensions of the tank cell unchanged; moreover, the section characteristic dimension of the tank cell is characterized as the width of tank. Such scale-up method has following problems: (1)

(2)

First, the tank cell dimensions should include the tank depth, which cannot be replaced with the section dimension of the tank cell; moreover, the section dimensions of the tank cell include the tank width, tank length and section area of the tank, which cannot be replaced with the tank width simply, either. Researches show that the ratio of the rotor diameter to the tank width of the same type of flotation machines with different size is not fixed [20].

Fig. 6.10 The relationship between the volume of tank and the ratio of cross-sectional area and rotor diameter

Ratio between cross-sectioin area and rotor diameter

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193

30 28 26 24 22 20 18 16 14 12

Air-forced flotation machine

10

Air-induced flotation machine

8 6 4 0

20

40

60

80

Volume/m

3

100

120

140

Through researches on the same type of flotation machines with different size, the relationship between tank cell dimensions, rotor diameter ratio and tank volume can be obtained, as shown in Fig. 6.10. It can be seen from Fig. 6.10 that the ratio of the cross-sectional area of the tank to the rotor diameter shows a power function relationship with the tank cell volume; therefore, the ratio of the sectional area to the rotor diameter is used as the scale-up factor for amplifying the tank cell of the flotation machine, and its scale-up formula is given as follows: S = a1 V b1 D

(6.1)

where S D V a1 , b1

cross-sectional area of the flotation tank; rotor diameter; tank cell volume; coefficients related to the tank cell structure, which may be determined by fitting the structural data of the same series of the flotation machines.

When the section area of the tank cell is determined, it is not possible to get the tank cell depth mechanically by dividing the tank cell volume by the section area of the tank. The tank cell volume used above refers to the effective volume of the tank cell, but the geometrical volume of the flotation machine should include the rotor, stator, froth tank, dead corner at the bottom of the tank, etc. Therefore, the tank cell depth should be calculated based on the geometrical volume of the tank cell. b.

Rotor similarity

Similarly, it is also necessary to find the key parameters of the rotor and their relationship with the volume of the flotation tank for amplifying the rotor. The rotor diameter is a key parameter that can reflect the rotor properties in a best manner. The

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Rotor diameter/m

Fig. 6.11 Relationship between the tank volume and rotor diameter

1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0

Air-induced flotation machine Air-forced flotation machine

0

10 20 30 40 50 60 70 80 90 100 110 120 130 140 Volume/m 3

relationship between the rotor diameter and the tank cell volume of the same type of main flotation machines in the world is plotted in Fig. 6.11. It can be seen from Fig. 6.11 that the rotor diameters of two types of flotation machines show a power function relationship with the tank cell volume of the flotation machine, and moreover the fitting degree is high. Therefore, the rotor diameter may be used as the scale-up factor; its scale-up formula is given as follows: D = a2 V b2

(6.2)

where D V a2 , b2 B.

rotor diameter, m; tank cell volume, m3 ; coefficients related to the tank cell structure, which may be determined by fitting the rotor data of the same type of the flotation machines.

Suspension similarity scale-up

Upon the achievement of the geometrical similarity of key components of the flotation machine, it is important to keep the similar suspension of solid particles. In flotation tanks with different sizes, the absolute value and direction of the velocity of the fluid at the corresponding point should be similar. It is assumed that at any point in the flotation tank (coordinate X), the pulp velocity is u and the velocity at the corresponding point of another flotation tank (coordinate X ) is u , then 



u(X ) ∝ u (X )

(6.3a)

It can be seen from the analysis in the previous section that the cross-sectional area of the tank can reflect the characteristics of the flotation tank in a better way

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than the tank length, tank width and tank depth; therefore, the equivalent radius can be taken as the characteristic dimension of the tank R = πS and the factor analysis method is used, and it can be available from the formula above that 



u(R) ∝ u (R )

(6.3b)

The formula for calculating the velocity is derived approximately by the characteristics of the velocity field of the pulp flow pumped from the rotor. For simplicity, it is assumed that the jet flow is from a circular outlet, and symmetry plane orthogonal to the outlet centre and the axial line is taken as the coordinate, i.e. the position is determined based on the radius r and the distance to the symmetry plane z. The velocity of this point is given as follows: u = u 0 f (r )φ(z /r )

(6.4)

where u0 f (r) φ(z /r )

jet-flow velocity at the circular outlet on the symmetry plane; change rate of the velocity on the symmetry plane to value r; change rate of the velocity in the vertical direction of the symmetry plane at radius r to value z.

When the pumped fluid is injected to the surrounding fluid, it is available based on the law of conservation of momentum that ∞ 2π u 2 r dz = Constant

I =ρ −∞

According to Formula 6.4: ∞ I =

u 20

f (r )ρ

2π φ 2

2

−∞

z z d = Constant r r

If the momentum is constant, the f (r ) · r = Constant, i.e. f (r ) = C/r . The jet-flow velocity along the symmetry plane is u(r ) = u 0 f (r )  At the distance of r = σ (D 2), the jet-flow velocity is the same as the velocity in the circular disc gap of the rotor: u 0 = u 0 C/σ D2 , then: C = σ2 D.   Therefore u(r ) = u 0 (σ 2)(D r ). where

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coefficient, only related to the shape of the rotor; the σ values of geometric similarity are equal. According to Formula 6.3b: 

u D u0 D ∝ 0 R R



The jet-flow velocity at the circular outlet on the symmetry plane of the jet flow is proportional to the average velocity of the outlet, and the later is proportional to the linear velocity of the rotor, then u 0 = N D. Then 

D2 N D 2N ∝ R R



(6.5)

Therefore, the scale-up factor for the suspension similarity of the flotation machine 2 is DRN . The rotor is a key component to suspend the flotation machine; therefore, this scale-up factor is defined as the suspension number J, then J=

D2 N R

(6.6)

As shown in the formula below, the suspension number also includes two factors, namely, the rotor diameter and the rotor speed, which may reflect the impact of the rotor on the fluid dynamics state in the flotation tank. Formula (6.6) may be derived from Formulas (6.1) and (6.2) as follows: J = a3 · V b3

(6.7)

where a3 , b3 —structural parameters of the tank cell, which may be determined by fitting the rotor data of the same series of flotation machines. C.

Dynamics similarity scale-up

Flotation kinetics is mainly related to the law of the flotation rate and analyses various influencing factors in order to provide basis for improving the flotation process and flow picture, design of the flotation machine, proportional scale-up, etc. The flotation rate may be measured by the grade change or recovery rate change of targeted minerals per time. There are many factors influencing the flotation rate, which mainly include ore properties, flotation environment and characteristics of the flotation machine. Particularly, the characteristics of the flotation machine mainly include structural characteristics (tank cell structure, rotor structure, etc.), agitating characteristics (including rotor and linear velocity of the rotor, etc.), bubble characteristics (including bubble size, aeration rate, air retention amount, etc.), froth layer properties (including thickness and stability of the froth layer, froth load rate, etc.),

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197

etc. Bubble characteristics and froth layer characteristics may be indicated by the fluid characteristics in the flotation tank. Reynolds number is an important parameter to indicate the fluid characteristics. Re = ρLν/η

(6.8)

where Re ρ L η v

Reynolds number; pulp density, g/cm3 ; characteristic length of the flow field, m; dynamic viscosity, Pa s; fluid velocity, Pa s.

Generally, in order to attempt to evaluate the agitating suspension conditions with ND constant, the velocity v in Formula (6.8) can be indicated by the value of ND that is proportional to the rotor linear velocity π ND [17, 18]. In fact, for the same type of flotation machines, the fluid dynamics states in the tank cell are greatly different at the same rotor linear velocity, so it is inevitable to lead to the design error by use of this method [19]. ND cannot represent Re, because it is only the velocity in Re. If that is the case, we can not ignore the influence of another linear velocity L. 2 In addition, someone replaces the linear velocity L with N, i.e. Re = ρ NηD , which is the Reynolds number criteria mentioned above. However, in fact, based on calculation, it is not equal for the same type of flotation machines with different specifications; it cannot evaluate the fluid dynamics states in the flotation tank accurately. In order to evaluate the fluid dynamics states in the flotation tank accurately, first, it is necessary to establish a dimensionless number without missing of factors indicating the fluid state in Re, and indicating the correlation of key components in the flotation tank. Upon the analysis of the tank cell scale-up method in the previous section, S/D is used as the tank cell scale-up factor, which can show the correlation of key components in the flotation tank. Therefore, the revised Reynolds number Re is given as follows:       Re = k × S D × ρ η × N D

(6.9)

where S k

section area of the tank cell; correction factor.

In the system of Metres Kilograms Seconds (MKS), L, T and M are taken as the basic dimensions, and the derived dimensions include. Dim N = T −1 ; dim ρ = L −3 M; dim η = L −1 T −1 M. where k refers to a dimensionless number, with the results of

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dim Re =

T −1 × L 2 × L −3 × M =1 L 2 × L −1 × T −1 × M

It can be seen that the corrected Reynolds number Re is same as the physical property of Re. S/D is able to reflect the correlation of dimensions between two key components in the tank cell. For a determined system, ρ/η is unchanged. Therefore, the fluid movement state in the same type of flotation tanks with different specifications has relation to the value of k × (S/D) × N D, and particularly ND is proportional to the rotor linear velocity πND. So it can be said that the fluid movement state in the same type of flotation tanks with different specifications is related to the S/D times of the rotor linear velocity. The relationship between the S/D times of the rotor linear velocity of the same type of main flotation machines and the tank cell volume of the flotation machine is analysed in Fig. 6.12. Therefore, the S/D times of rotor linear velocity may be used as the scale-up factor; its scale-up rule is given as follows: S ν = a4 V b4 D

(6.10)

where a4 , b4

coefficient related to the tank cell structure, which may be determined by fitting the data of the same series of the flotation machines.

In summary, for amplifying the flotation machine, it is necessary to achieve the similarity of the mechanical structure, suspension similarity in the flotation tank and the fluid dynamic similarity of the flotation machine; its scale-up method is given as follows: Scale-up of the tank, the ratio of the cross-sectional area of the tank cell to the rotor diameter DS is taken as the scale-up factor; its scale-up rule is DS = a1 V b1 . 240 -1

Fig. 6.12 The relationship between the tank volume and S/D multiply linear velocity of rotor

S/D Mutiply linear velocity of rotor / m.s

(1)

220 200 180 160 140 120 100

Air-forced flotation machine

80

Air-induce flotaiton machine

60 40 20

0

20

40

60 80 3 Volume/m

100

120

140

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(2) (3) (4)

199

The rotor diameter is taken as the scale-up factor to amplify the rotor shape; its scale-up rule is given as follows: D = a2 V b2 . Suspension similarity, the suspension number is taken as the scale-up factor; its scale-up rule is given as follows: J = a3 · V b3 . Hydrodynamic similarity in the tank, the S/D times of rotor linear velocity is taken as the scale-up factor; its scale-up rule is given as follows: S ν = a4 V b4 . D

6.3.2.2

Pulp Direction and Selection Circulation Technology

Pulp direction and selection circulation technology is a material circulation technology for a single large flotation machine, which is specially developed for the difference of flotation behaviours of coarse and fine minerals with different size fractions, as shown in Fig. 6.13. The rotor structure is closely related to the pulp circulation rate and the flow direction. It is an effective method to improve the height of the transport area by strengthening the upper circulation of the pulp, which further ensures the recovery of coarse minerals and reduces the shortcut. Forced pulp circulation passages are arranged in the flotation tank to return the un-mineralized fine minerals to the rotor area again, so that it can increase the chance of fine minerals attaching to the bubbles and thus improve the separation effect of fine minerals and also reduce the probability of the shortcut.

6.3.2.3

Dynamic Calculation Technology of Pulp Retention Time

The pulp retention time is an important basis for the sizing of the flotation machine. Generally, it is recognized that the pulp retention time is approximately equal to the flotation time. The whole operation is fully considered for the calculation based on

Fig. 6.13 Sketch of pulp direction and selection circulation

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6 Flotation Machine Upsizing Method and Technology

Fig. 6.14 Traditional retention time calculation mode

the traditional pulp retention time calculation model, as shown in Fig. 6.14. In the figure, QF refers to the volume flow rate of the pulp fed into a certain operation, QC refers to the froth volume flow rate of a certain operation and QT refers to the tailing volume flow rate of a certain operation, so the retention time of the operation is given as follows: tr = Ve n/Q F

(6.11)

where tr Ve n QF

pulp retention time in a single operation, min; effective volume of a single flotation machine, m3 ; number of equipment in the flotation operation; feed flowrate, m3 /min.

For a large flotation machine, it produces a large amount of froth; the production fact that froth is produced from each flotation machine is not considered in this method, which results in that the actual flotation time is more than the calculation time, causing disadvantages of heavier circulation load, higher energy consumption, more equipment and longer process. However, in actual production, each working flotation machine produces different froth yields; the dynamic calculation model of the retention time is shown in Fig. 6.15. It is assumed that the pulp amount fed into a certain flotation machine is given as follows: Q fi = Q fi−1 − Q ci−1

(6.12)

where Qfi Qfi − 1 Qci − 1

volume flow rate of feeding into a certain flotation machine, m3 /min; volume flow rate of feeding into the previous flotation machine, m3 /min; volume flow rate of froth into the previous flotation machine, m3 /min.

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201

Fig. 6.15 Dynamic calculation model of the retention time

The actual pulp retention time for this flotation operation is calculated based on the formula which is given below: tr = Ve /Q f1 + Ve /Q f2 + · · · + Ve /Q fi

(6.13)

In this model, the production fact that the large flotation machine produces a large amount of froth and each flotation machine produces froth is fully considered; by use of the system theory method, a new dynamic calculation model of pulp retention time of a flotation machine is established to change the traditional calculation method for flotation time and achieve the flotation through a shortcut.

6.3.3 Key Structure Design of BGRIMM Large Flotation Machine 6.3.3.1

Tank Cell Design

Generally, the tank cell bottom is designed with a tapered structure in order to avoid the large particles settling, force them flow towards the tank centre to return to the rotor area for recirculation and reduce the phenomenon of pulp shortcut and ensure the uniform dispersion of the pulp. Take the pneumatic mechanical agitation flotation machine as an example. Unlike air-induced flotation machine, the air is forced into

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6 Flotation Machine Upsizing Method and Technology

the tank by a blower, in which it does not require the consideration of the impact of the static pressure of the upper part of the rotor on the air forced. Therefore, the tank cell may be deepened appropriately, which may bring the following advantages: (1)

(2)

(3) (4)

The bubble rising distance is long, the retention time of the bubble in the tank is extended; the chance of collision between the bubble and particles is increased; the sufficient bubble utilization rate is increased; the air consumption is reduced as the increase of the tank depth. The rotor diameter size of the flotation machine is directly related to the tank cell diameter of the flotation machine. When the tank cell is enlarged, the required rotor diameter should also be enlarged; when the tank cell diameter is reduced, the required rotor diameter shall also be reduced. Therefore, when the volume is constant, if the tank depth is increased, the tank cell diameter of the flotation machine may be reduced and the rotor diameter should be reduced accordingly and thus the power consumption may be reduced. It is easy for a deep tank to form a relatively stable froth area and separation area in the flotation process, which is good for improving the concentrate quality. The deep tank occupies a small area of the plant, which may reduce the infrastructure cost.

6.3.3.2

Rotor Design

The following problems are mainly considered in the rotor design: (1)

(2)

(3)

The rotor should be able to produce a large pulp flow under a relatively low head in order to ensure a smooth pulp circulation, sufficient suspension of particles and no particles settling at the bottom of the tank. The ability to disperse air should be strong. The air dispersion cannot be reduced due to the expansion of the cross-sectional area of the large flotation machine; the air dispersion degree should be maximized. The three-phase mixture pumped from the rotor should be transported to a relatively high position in order to improve the rising distance of the particle and bubble to increase the chance of collision between the particle and air bubbles and shorten the rising distance of the mineralized bubble.

Firstly, for the design of the large flotation machine rotor, the following three aspects must be considered: the height of the transport area should be maximized in order to transport the mineral particles to a relatively high position in the tank and thus reduce the rising distance of the mineralized bubble and decrease the chance of particles falling off the bubble. The comparison of different pulp circulation forms that are created by two types of rotors is shown in Fig. 6.16; compared with the former one, the later one significantly increases the transport height of the mineral particles. Secondly, it is necessary to change the shape of the rotor and expand the mineralized area of the rotor chamber in order to strengthen the recovery of fine minerals.

6.3 BGRIMM Flotation Machine Upsizing Technology

203

Fig. 6.16 Pulp circulation created by two types of rotor

6.3.3.3

Stator Design

The three-phase mixing zone in the flotation cell is a very important zone for the flotation kinetics, which requires strong agitation in order to make the pulp be in a turbulent state, and the separation area and the froth area require a relatively stable state. If the turbulence intensity is too strong, it will increase the detachment of particles from bubbles, which may affect the separation effect. Pulp will be thrown out tangentially from the rotor; it will rotate in the tank, which may affect the separation environment. Therefore, the stator must be deigned to be able to stabilize the flow in order to convert the circumferential pulp flow that is produced by the rotor into the radial pulp flow in order to prevent the pulp from spinning in the flotation machine; it is also helpful to recirculate the pulp in the tank. Secondly, a strong shearing force annular area is generated around the rotor and between the stator blades; big bubbles are shredded under the action of shearing force to promote the formation of small bubbles. The large flotation machine is designed with a suspended radial vane opening stator; it is composed of 24 blades and installed on the periphery of the rotor; it also maintains a certain radial and axial clearance with the rotor. It is fixed at the bottom of the tank with feet in order to increase the pulp flow area around the lower area of the stator, eliminate the hindrance of the lower parts against the pulp, assist the pulp to flow into the lower area of the rotor and reduce the power consumption, enhance the pulp circulation in the lower part of the circulation area of the tank cell and the suspension capacity of the solid particles.

6.3.3.4

Air Distributor Design

BGRIMM believes that the recovery of fine minerals may be improved by strengthening the pre-mineralization. BGRIMM invents the air distributor, which is used for pre-cutting the air into small airflow and then distributing it to the rotor chamber in order to improve the bubble surface area flux.

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6 Flotation Machine Upsizing Method and Technology

(a) Saline minerals

(b) Oxidized minerals

(c) Sulfide minerals

Fig. 6.17 3 types of air distributor

Due to the difference of aeration rate required in the mineral flotation process, the air distributor may be designed differently according to the types of minerals, namely, saline minerals, oxidized minerals and sulphide minerals, as shown in Fig. 6.17. Saline minerals require the least amount of air; oxidized minerals require the medium amount of air and sulphide minerals require the most amount of air.

6.3.3.5

Flow Steadying Grid (A Special Mechanism for the Large Flotation Machine in a Flotation Environment for Coarse and Heavy Minerals)

Upon the consideration of the flotation characteristics of coarse and heavy minerals that are easy to fall off from the mineralized bubbles and rest at the bottom of the tank, a suspension flow steadying grid may be designed in the large flotation machine, as shown in Fig. 6.18. The flow steadying grid is composed of multiple V-shaped structures that are arranged fully on the cross section of the tank cell; the clearance L b is designed between multiple V-shaped structures; it is installed on the above of the rotor. The pulp rising velocity is increased by reducing the cross-sectional area of the rising pulp flow and such velocity is required to be greater than the settling velocity of the high specific gravity particles of the pulp. Therefore, a suspension layer of coarse and heavy particles is formed on the grid when the pulp flows upward through the flow steadying grid in order to ensure the good suspension and efficient recovery of coarse and high specific gravity minerals.

6.3 BGRIMM Flotation Machine Upsizing Technology

205

L Lb

V2 V1

Fig. 6.18 Schematic diagram of steady flow grids

6.3.3.6

Froth Tank Design

Compared with the medium and small flotation machines, in order to design the froth launder for the large flotation machine, it is necessary to consider the movement characteristics of froth and the structural parameters of the tank in large flotation cell. Because the froth layer is relatively thick, the rapid recovery of froth must be considered. The distance to transport froth is too long, which causes the particles attached on bubbles to fall off during moving to weir. In addition, local froth stagnation is also a problem to be considered. The froth transport distance is a key factor to affect the targeted mineral recovery. Because the large flotation machine has a relatively large volume and a relatively long tank cell radius, it may be designed with double crowders, which consists of external crowder and inner crowder. Froth close to the edge of the tank cell overflows from the external froth launder; froth close to the centre overflows from the inner froth tank; in this way, froth is divided into two parts so that the froth transport distance is shortened. As shown in Fig. 6.19.

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6 Flotation Machine Upsizing Method and Technology

Fig. 6.19 Double crowders in KYF-160 flotation machine

6.3.4 Rapid BGRIMM Flotation Machine Upsizing Driven by CFD Technology In the flotation machine upsizing process, BGRIMM analyses the hydrodynamic macroscopic features and local features in the large-scale flotation machine by full use of CFD technology, which promotes the upsizing advanced. The CFD method is fully applied in the process of R&D of the flotation machines with the volume of 160, 200 and 320 m3 , even for the largest volume of 680 m3 . The velocity cloud picture and turbulent energy distribution diagram of the central section of the 680 m3 flotation machine are shown, respectively, in Figs. 6.20 and 6.21 [21–23]. It is generally recognized that the agitating and mixing areas in the flotation machine are located near the rotor and the stator areas, where it requires strong turbulence intensity. It can be seen from the velocity cloud picture that the velocity is large in the rotor and stator areas and a relatively large horizontal jet effect occurs in the middle and upper parts of the stator blades, which is good for increasing the flow intensity of the mixing area. The turbulence intensity distribution cloud picture can reflect the relatively large turbulence energy near the rotor and stator areas in a better manner. Except the area near the rotor and stator, the velocity and turbulence energies in the central and top section of the flotation machine are very small, which is essential to form the stable transport area and separation area. The velocity flow diagram and vector diagram of the central section of the 680 m3 flotation machine are shown, respectively, in Figs. 6.22 and 6.23. It can be seen clearly from the diagram that there are two significant upper and lower circulation flow field structures in the flotation. For the upper circulation flow field, its covering aera is large, but its turbulence intensity is not large, which is good for increasing

6.3 BGRIMM Flotation Machine Upsizing Technology Fig. 6.20 Velocity cloud picture in central section

Fig. 6.21 Turbulent energy distribution diagram of the central section

Fig. 6.22 Velocity flow diagram in central section

207

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6 Flotation Machine Upsizing Method and Technology

Fig. 6.23 Velocity vector diagram in central section

the transport area and improving the conveying capacity of coarse particles. For the lower circulation flow field, its action range is small, but its velocity intensity is large, which has positive significance for bottom suspension and circulation of particles. The results show the fluid dynamic environment suitable for the mineral separation can be established in the 680 m3 flotation machine. The dynamical dimensionless number analysis is a common design method and an optimization method. The relationship between the volume of the flotation machine, power number N p and power density PF is shown in Fig. 6.23. The power intensity or power density is a function criterion for evaluating the economics of the flotation equipment, which reflects the energy consumption indicator per unit volume of the equipment. In the process of developing the flotation machine from the volume of 70 m3 to the volume of 680 m3 , the power number is basically in the range of 5–6, which indicates that the scale-up of the equipment achieves a good power balance. The power density PF reflects the energy consumption for pulp per circulation unit. It can be seen that the power density is basically stable, but it has a slight increase trend with equipment upsizing. Therefore, it is necessary to pay attention to change in the circulation capacity during the process of amplifying the equipment in order to further improve the energy consumption. The relationship between the volume of the flotation machine, Froude number Fr and circulation density (QF ) is shown in Fig. 6.26. Froude number (Fr) is a very important similarity number, which reflects the ratio of the centrifugal force to the inertial force. Specifically for the flotation machine, it indicates the ratio of the pumping action of the rotor to the hydrostatic head, which is related to the suspension of solid particles in the flotation machine. It is not difficult to find that the Froude numbers of the flotation machines with different specifications are similar, which shows a good consistency. Circulation density QF reflects the relative circulation capacity of the equipment, which shows the relationship between the structural change and circulation capacity of the tank cell to a certain extent. For a large flotation machine,

6.3 BGRIMM Flotation Machine Upsizing Technology

209

the circulation density QF is basically constant, but it also shows a decreasing trend. Therefore, it is necessary to strengthen the circulation capacity of a large flotation machine (Figs. 6.24 and 6.25). Fig. 6.24 The relationship of volume, power number N p and circulation intensity

Fig. 6.25 The relationship of volume, power intensity, air flow number Na and Froude number Fr

Fig. 6.26 The relationship of volume, power intensity, air flow number Na

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6 Flotation Machine Upsizing Method and Technology

The relationship between the volume of the flotation machine, air preservation number Ca and flow rate number Na is shown in Fig. 6.26. It can be seen that the air preservation number Ca and flow rate number Na are basically consistent during the process of scale-up. The main dynamic parameters of the 680 m3 flotation machine show a good consistency with those of its same series of flotation machines, which indicates that the scale-up design of the equipment is reliable so that it can ensure the equipment with good hydrodynamic characteristics. Due to years of development and utilization of the world’s mineral resources, high-grade resources that are easy for processing have been gradually exhausted, the proportion of poor, fine and complex mineral resources is increasing, so the daily processing capacity of a new ore concentrator is also increasing, and it is even over 100,000 t/d for some concentrators. Therefore, there is an urgent demand for the large flotation equipment. The flotation equipment faces a more arduous task, which will be further developed towards the direction of upsizing, specialization, environmental protection and efficiency.

References 1. Reese P (2000) Innovation in mineral processing technology. In: New Zealand minerals & mining conference proceedings, 29–31 Oct 2000 2. Shen Z, Lu S (2004) Large scale flotation machines advanced. In: China Mining, Proceedings of the 7th national conference on comprehensive utilization of mineral data, no 2, pp 229–233 3. Arbiter M (2000) Development and scale-up of large flotation cells. Min Eng 52(3):28–33 4. Raffunek AA (2007) Application status and main development of flotation equipment. Met Ore Dressing Abroad 12:4–12 5. Jounas AJ (2001) Design, development, application and operation of 100 m3 TankCell flotation machine of Outokumpu. Met Ore Dressing Abroad (5):30–34 6. Olazuwan X (2002) Research and development of flotation machine of Outokumpu company in Finland. Met Ore Dressing Abroad 4:32–34 7. Outokumpu mintee (1994) Flotation theory research and practice of Outokumpu. Nonferrous Mine (5):31–35 8. Burgess FL (1997) OK100 tank cell operation at Pasminco—broken hill. Miner Eng 7:723–741 9. Zheng X, Knopjes L (2001) Modelling of froth transportation in industrial flotation cells Part II: modelling of froth transportation in an Outokumpu tank flotation cell at the Anglo Platinum Bafokeng –Rasimone PlatinumMine (BRPM) concentrator. Miner Eng 7:743–751 10. Fang Z (1998) New development of mineral processing equipment. Non-ferrous Metall Equipment (1):15–20 11. Guo M (1988) Disscuss on the similarity scale-up of flotation cell. Proc Large-Scale Flotation Cell 1–9 12. Caifen W, Zhendong Z (2009) Review of development and application of several key flotation cells. Mod Min 5:33–35 13. Castile K (2006) Flotation Advanced. Met Ore Dressing Abroad 4:10–13 14. Yudong Z (2007) Advances in flotation equipment of metallic minerals. Express Inf Min Ind 11(11):7–10 15. Fallenius K (1980) New equations of flotation cell scale-up. Met Ore Dressing Abroad 6:31–38 16. Cheng H (2000) The principle of flotation machine scale-up. J China Coal Soc (25):182–185 17. Sun Z (2001) Design principle of mineral processing equipment. Changsha Hunan Province in China. Central South University Press

References

211

18. Cheng H, Cai C, Zhang X et al (1998) Flotation microscopic kinetics and mathematical model. J China Coal Soc (10):545–549 19. Yang F (2004) Analyse of energy consumption in agitation flotation machine. Nonferrous Metals (5):31–36 20. Hongxin Z (2003) Series parameter models of agitation/flotation cells in coal industry. J China Unive Min Technol 3:141–144 21. Shen Z (2007) Development of large pneumatic mechanical agitation flotation machine (Ph.D. thesis). Chuanyao Sun, Guidance, Beijing University of Science and Technology 22. Zhang M, Shen Z, Fan X, Shi S (2015) Dynamic analysis of 680 m3 mechanical agitation flotation machine. Min Metal 43–47 23. Ming Z, Zhengchang S, Xuesai F, Shuaixing S (2015) Mechanical analysis of 680 m3 mechanical agitation flotation. Min Metal 11:43–47

Chapter 7

BGRIMM Mechanical Agitation Flotation Machine

The mechanical agitation flotation machine is one of the flotation machines that is invented at the earliest. The early mechanical agitation flotation machine is designed with a complicated structure, but a poor flotation effect. With the development of science and technology and the gradual revealing of the principle of flotation, the performance of the equipment has been improved continuously and a large number of mechanical agitation flotation machines with different structures have appeared [1, 2]. Chinese mining companies introduced the A-type mechanical agitation flotation machines from the Soviet at the earliest, which solved the concentrators’ urgent need for the technology of the flotation equipment after the founding of the country. With the deepening of research on the technology of the mechanical agitation flotation machine in China, research institutes, represented by Beijing General Research Institute of Mining & Metallurgy, have gradually developed China’s mechanical agitation flotation machine [3]. The mechanical agitation flotation machine has the function of automatic air suction, so it does not require a complicated air supply system; especially for a mechanical agitation flotation machine with the function of automatic pulp suction, due to this function, it does not require the process pipeline for middling return; therefore, the process is simplified and the operation is more convenient [4, 5]. Due to its simple structure and superior functions, the new mechanical agitation flotation machine has been widely used. However, it has the disadvantages of the narrow adjustable range of the suction rate and failure of accurate control. At present, the mechanical agitation flotation machine has been mainly suitable for the separation of the metal and non-metallic minerals which have a wide requirement for the air volume range.

© Metallurgical Industry Press 2021 Z. Shen, Principles and Technologies of Flotation Machines, Springer Tracts in Mechanical Engineering, https://doi.org/10.1007/978-981-16-0332-7_7

213

214

7 BGRIMM Mechanical Agitation Flotation Machine

7.1 SF, BF and GF Mechanical Agitation Flotation Machines The research on the flotation machine started late in China. Until 1970s, China has begun to independently develop the flotation machine; and in the early 1980s, the SF mechanical agitation flotation machine was developed successfully. With the change of resources and the improved requirements for equipment technology by concentrators, BF and GF mechanical agitation flotation machines have appeared successively, which have been widely used due to their excellent separation performance [6–8]. They can meet the production requirements of different concentrators.

7.1.1 SF Flotation Machine The SF flotation machine was developed successfully by the Beijing General Research Institute of Mining & Metallurgy (BGRIMM) in 1986. In the initial stage of its research and development, the SF flotation machine was generally used as the first tank in each flotation work; it was combined with the JJF flotation machine as a joint unit to play the automatic pulp suction in order to return to the middling without the use of ladder configuration and the froth pump. Due to its excellent use effect, the SF flotation machine was used along to form a horizontal configuration that is fully composed of SF flotation machines. As shown in Fig. 7.1, the structure of the SF flotation machine is mainly composed of the tank body, spindle components (including the impeller), motor, scraper and its Fig. 7.1 SF flotation machine (1–pulley; 2–suction pipe; 3–central cylinder; 4–spindle; 5–tank body; 6–stator; 7–impeller; 8–tube; 9–false bottom; 10–upper blade; 11–lower blade; 12–impeller disc)

7.1 SF, BF and GF Mechanical Agitation Flotation Machines

215

transmission device, etc.; when its volume is greater than 10 m3 , it is equipped with the tube and the false bottom structure. The SF flotation machine is mainly characterized with its rotor with the backward tilting double blades, as shown in Fig. 7.2, which can achieve the double pulp circulation in the tank. Its working principle is the spindle is driven by the motor through the V-shaped belt to rotate its lower impeller. The pulp in the upper and lower impeller chambers can produce the centrifugal force under the action of the upper and lower blades, so that the pulp is thrown to the periphery to establish a negative pressure area in the upper and lower impeller chambers. At the same time, the pulp in the upper part of the stator (as shown in Fig. 7.3) can also be sucked into the upper impeller chamber through the circulation hole on the stator to form the upper pulp circulation. The specific gravity of the pulp that is thrown out from the lower impeller chamber is larger than that of the three-phase mixture that is thrown out from the upper blade; so its centrifugal force is larger and its movement speed is attenuated slowly; moreover, it also produces additional driving force to the three-phase mixture that is thrown out from the upper blade to increase its centrifugal force; therefore, Fig. 7.2 Rotor of SF flotation cell

216

7 BGRIMM Mechanical Agitation Flotation Machine

Fig. 7.3 Stator of SF flotation cell

the vacuum degree in the upper impeller chamber is improved; and it plays a function of assisting the suction. When the pulp is thrown out to the periphery from the lower blade, the pulp from its lower part moves to the centre to form the lower pulp circulation. Air is sucked into the upper impeller chamber through the suction pipe and central cylinder, and is mixed with the sucked pulp to form a large number of fine bubbles, which are evenly dispersed in the tank after being stabilized through the stator to form mineralized bubbles. The mineralized bubbles are floated up to the froth layer and scraped off by the scraper to form a froth product.

7.1.2 BF Flotation Machine The BF flotation machine is an efficient separation plant developed by Beijing General Research Institute of Mining & Metallurgy, having the characteristics of planar configuration, automatic air suction, automatic pulp suction, automatic return of middlings froth, etc., without the need of any auxiliary equipment [9, 10]. The BF flotation machine is a brand new efficient automatic air and pulp suction flotation

7.1 SF, BF and GF Mechanical Agitation Flotation Machines

217

machine that is developed by Beijing General Research Institute of Mining & Metallurgy based on the summary of A-type and SF flotation machines. Compared with A-type flotation machine, it has the advantages of saving of power consumption per unit volume by 15–25%, adjustable suction rate, stable pulp level, high separation efficiency, long service cycle of wearing parts, convenient operation, maintenance and management, etc. It is a kind of fuel-efficient separation equipment.

7.1.2.1

Working Principle and Key Structures

As shown in Fig. 7.4, the BF flotation machine is mainly composed of the spindle mechanism, tank body components, scraper components, etc. The entire spindle mechanism is installed on the main beam of the tank body. (1)

Working principle When the spindle is driven by the motor to rotate the impeller, the pulp in the impeller chamber is thrown out to the periphery under the action of the centrifugal force, so that a negative pressure is formed in the impeller chamber and air is sucked in through the suction pipe. At the same time, the pulp in the lower part of the impeller is sucked in through the central hole of the lower cone disc of the impeller and is mixed with air in the impeller chamber; and then it is thrown out to the periphery through the passage between the stator and the impeller; the air and some pulp moves towards the upper part of the flotation tank to participate in the flotation process after leaving the stator passage. The rest pulp moves towards the bottom of the flotation tank and returns to the impeller chamber again due to the impeller pumping and suction to form the

Fig. 7.4 Working principle of BF flotation cell

218

(2)

7 BGRIMM Mechanical Agitation Flotation Machine

lower pulp circulation. The existence of the lower pulp circulation is good for the suspension of coarse particle minerals, which can minimize the deposition of coarse sand in the lower part of the flotation tank. Key structures The BF flotation machine mainly consists of a motor device, tank body components, a spindle mechanism, a froth scraper and other components. The spindle mechanism comprises a big pulley, a bearing block, a central cylinder, a spindle, a suction pipe, an impeller, a stator and other parts and components. The spindle mechanism is fixed to the main beam of the tank body. 1.

2.

Design of the tank body structure The tank body of the BF flotation machine is designed as a shallow tank structure with a trapezoidal cross section; the bottom of the tank is provided with the false bottom and the tube to promote the generation of a large forced lower pulp circulation, as shown in Fig. 7.5. Impeller and stator The impeller and stator are key components of the BF flotation machine. The superiority of the efficient flotation machine is mainly reflected in the rationalization of the structures of the impeller and stator and the optimum values of the relevant parameters. The requirements for the performance of the BF flotation machine mainly include small power consumption, sufficient suction rate, reasonable pulp circulation, no deposition of coarse particle minerals, long service life of wearing parts and stable pulp level. Impeller: According to the design theory of a centrifugal pump, the outlet installation angle β of the impeller blade includes three conditions, namely, blade forward (β > 90°), blade radial (β = 90°) and blade backward (β < 90°), as shown in Fig. 7.6. For these three types of impellers, the relationship curve between the pressure head Ht and the theoretical

Fig. 7.5 Structure of BF flotation cell (1. agitator assembly 2. tank cell 3. motor device 4. froth paddle)

7.1 SF, BF and GF Mechanical Agitation Flotation Machines

219

Fig. 7.6 Three angle forms of rotor blades. If β = 90º, it will be the radial type; if β < 90º, it will be the backward type; if β > 90º, it will be the forward type

>90¡ã =90¡ã

Ht

Nt

>90¡ã

=90¡ã 12

0.05~1.4

KYF-3

3

7.5

>14

0.05~1.4

KYF-4

4

11

>15

0.05~1.4

KYF-5

5

11

>15

0.05~1.4

KYF-6

6

11

>17

0.05~1.4

KYF-8

8

15

>19

0.05~1.4

KYF-10

10

22

>20

0.05~1.4

KYF-16

16

30

>23

0.05~1.4

KYF-20

20

37

>25

0.05~1.4

KYF-24

24

37

>27

0.05~1.4

KYF-30

30

45

>31

0.05~1.4

KYF-40

40

55

>32

0.05~1.4

KYF-50

50

75

>33

0.05~1.4

KYF-70

70

90

>41

0.05~1.4

KYF-100

100

132

>46

0.05~1.4

KYF-130

130

160

>50

0.05~1.4

KYF-160

160

160

>52

0.05~1.4

KYF-200

200

220

>56

0.05~1.4

KYF-320

320

280

>64

0.05~1.4

KYF-450

450

355

>65

0.05~1.4

KYF-560

560

400

>65

0.05~1.4

KYF-680

680

500

>70

0.05~1.4

270

8 BGRIMM Pneumatic Mechanical Agitation Flotation Machine

8.1.2 Fluid Dynamics Research in KYF Flotation Machines 8.1.2.1

Flow Field Characteristics of KYF Flotation Machines

The KYF series flotation machines have similar flow field characteristics. By taking the laboratory KYF-0.2 m3 flotation machine as an example, the flow field characteristics of KYF flotation are introduced, and the overall three-dimensional velocity vector is shown in Fig. 8.6. In the rotor area, the fluid driven by the rotor has a very high velocity, and every stator blade has an obvious diversion effect. As the fluid leaves the rotor–stator area, the fluid velocity gradually decreases, and multiple strands of upward and downward circulation structures as many as the stator blades are formed in the tank body. It should be noted that the original flotation theory points out that there are upper and lower circulating flow field structures in the tank, but when judging from the overall three-dimensional velocity vector diagram, the circulating flow field structures are greatly affected by the stator, and a stream of circulating flow will be formed at each stator blade. Figure 8.7 shows the details of circulation flow at the longitudinal section in the KYF flotation machine. Remarkable upper and lower circulating flow fields are formed in the flow field after the fluid is thrown out by the rotor blades. According to the design theory of flotation machines, one of the design intents for the special structure of the rotor is to form the circulating flow field structures to ensure that the pulp can realize the flotation process efficiently. Figure 8.8 shows the details of fluid flow at the cross section below the rotor disc. Due to the counterclockwise rotation of the rotor, the fluid is thrown out of the rotor area under the action of centrifugal force, hits the blade side towards the pulp and gets out as jet flow in the direction of the stator blades. In the velocity cloud picture, Fig. 8.6 Velocity vectors of the lab-scale KYF-0.2 flotation machine

8.1 KYF Pneumatic Mechanical Agitation Flotation Machine

(a) Velocity vector diagram

(b) Velocity cloud picture

Fig. 8.7 Flow pattern of the lab-scale KYF-0.2 flotation machine

Fig. 8.8 Velocity contour on a plan below rotor lid

271

272

8 BGRIMM Pneumatic Mechanical Agitation Flotation Machine

Fig. 8.9 Velocity vectors between rotor blades

the obvious jet flow effect of the fluid along the stator blade sides towards the pulp indicates that the stator has good current diversion and stabilization effects. Figure 8.9 further reveals the flow characteristics between the rotor blades. It should be noted that a clockwise eddy obviously opposite to the rotation direction is formed at the rotor blades near the leeward side of the pulp. The maximum velocity region in the whole field appears near the leeward side of the pulp, which is even higher than the blade tip velocity.

8.1.2.2

Research on the Rotor of KYF Flotation Machine

The rotor of the KYF flotation machine is designed with backward-inclined blades, and a backward inclination angle β = 30 is formed in the relative rotation direction (the rotor of the flotation machine rotates in the clockwise direction) of the blades, as shown in Fig. 8.10. A research was carried out by selecting a backward-inclined rotor, a radial rotor and a forward inclined rotor in order to master the dynamic performance of the rotor at a backward inclination angle. Figure 8.11 gives the tests of three kinds of rotors and the comparison of PIV power consumption. The results show that the backward-inclined rotor has the lowest power consumption among the three kinds of rotors, which verifies the advantage of the flotation machine with backward-inclined rotors in energy consumption.

8.1 KYF Pneumatic Mechanical Agitation Flotation Machine

Backward inclined rotor

Radial rotor

273

Forward inclined rotor

Fig. 8.10 Feature of KYF flotation machine rotor (top view)

(a) Test

(b) CFD

Fig. 8.11 Power consumption comparison of the three rotors

The rotors with different backward inclination angles (β = 0°, 15°, 30°, 45°, 60°, 69°, 75°) (Fig. 8.12) also have great influences on the performance of flotation machines. Figure 8.13 gives the relationship between the power consumption 315 rpm and the backward inclination angle. With the increase of the backward inclination angle, there is a law that the power consumption of the flotation machine decreases first and then increases, and the flotation machine with the rotor that is inclined backward at 69° has the smallest power consumption, and a point of inflection appears.

8.1.2.3

Research on the Stator of KYF Flotation Machine

The size of the stator of the flotation machine is enlarged with the continuous enlargement of the volume of the flotation machine, but the structure type does not change much. The continuously growing height of the stator blades causes the increase in the impact of the pulp on the stator blades, and the deformed potential at the upper end of the stator blades is bound to increase. From the mechanical point of view, a

274

8 BGRIMM Pneumatic Mechanical Agitation Flotation Machine

Fig. 8.12 Rotor blades with different inclined angles

Fig. 8.13 Power consumption versus blade inclination angle at 315 rpm

8.1 KYF Pneumatic Mechanical Agitation Flotation Machine

275

(a) Standard stator

(b) Stator with an annular reinforcing ring

(c) Stator with a vertical reinforcing ring

(d) Stator with a 45° vertical reinforcing ring

Fig. 8.14 Different stator designs

reinforcing ring needs to be added to the upper part of the stator blades of a supersized flotation machine to ensure the mechanical reliability. However, the introduction of the reinforcing ring will affect the flow field structure. Therefore, the influences of different reinforcing rings on the flow field are studied, as shown in Fig. 8.14. Figure 8.15 shows the influences of the stator structure on the flow field. The results show that the fluid flow pattern distributions of four kinds of flotation machines with stators are slightly different. The stator with an annular reinforcing ring has more obvious horizontal jet flow, and high velocity areas appear in the rotor area and the stator horizontal jet flow area. The vertical reinforcing ring results in the trend of upward flow of part of the fluid from the inside of the reinforcing ring. Therefore, a high velocity area of the fluid also appears in the upper area inside the stator. Due to the existence of the annular reinforcing ring, the original upward inclined jet flow is not very obvious, and the fluid blocked flows out of the stator area horizontally. The velocity is high at this point, and the annular reinforcing ring is impacted. On the other hand, whether this will cause the mineralized particles in the rotor area to fall off will also cause a waste of energy. Due to the existence of the vertical reinforcing ring, the original upward inclined jet flow is blocked and thrown upward, and the current stabilization and guiding effects of the stator are weakened, which is equivalent to

276

8 BGRIMM Pneumatic Mechanical Agitation Flotation Machine

(a) Standard stator

(c) Stator with a vertical reinforcing ring

(b) Stator with an annular reinforcing ring

(d) Stator with a 45° vertical reinforcing ring

Fig. 8.15 Flow patterns of different stator designs

the fact that only part of the stator blades work, a high velocity area appears at the upper part of the stator and the horizontal jet effect is obviously worsened. The 45° vertical reinforcing ring acts as a guide for the fluid which is thrown out in the upward inclined direction. To sum up, the addition of the reinforcing ring also plays a guiding role for the fluid, leading to changes in the flow field.

8.1.3 Performance and Application of the KYF Flotation Machines 8.1.3.1

Performance of the KYF-50 Flotation Machine

The KYF-50 flotation machine is the first large flotation machine independently developed by Beijing General Research Institute of Mining & Metallurgy. Industrial tests were carried out in 2000, and the product was rapidly put into industrial application. At present, it has been widely applied in large and medium-sized mining enterprises at home and abroad. A.

Dynamic performance

To investigate the performance of the KYF-50 flotation machine, the dynamic parameters of the flotation machine were measured under the clean water condition, mainly including the suction rate, the degree of air dispersion, power, air holdup, bubble diameter, etc. The test results are shown in Table 8.2.

8.1 KYF Pneumatic Mechanical Agitation Flotation Machine

277

Table 8.2 Dynamics test results of KYF-50 flotation machine Speed of flotation machine /r min−1

Average aeration rate /m3 (m2 min) −1

Air dispersion

Current of flotation machine /A

136

1.22

1.63

93

131

1.17

2.07

97

126

1.15

1.71

84

The degree of air dispersion of the KYF-50 flotation machine is greater than 2.0 at 131 r/min, which meets the requirement of air dispersion. The aeration rate reaches 1.17 m3 /(m2 .min), which meets the aeration rate required for conventional mineral separation. B.

Pulp suspension capacity

Four points were measured downward from the liquid level of the overflow weir of the flotation machine, i.e. samples were taken at four pulp layers at depths of 1 m, 1.5 m, 2 m and 2.5 m for hydraulic analysis and grade analysis. The results of detection and analysis show that the distribution of particle sizes in the pulp in the tank body of the KYF-50 flotation machine is uniform, without stratification of coarse and fine particle sizes, which indicates that the flotation machine has strong agitation force, good air dispersion and no turbulence in the ore current. C.

Process index

The industrial test of the KYF-50 flotation machines was carried out in a nickel mine in Jinchuan. Two KYF-50 flotation machines were used to replace the five 16 m3 flotation machines and one 20 m3 agitation tank before primary rougher in the original production process and the five 16 m3 flotation machines before secondary scavenger in the original production process. Under the same process conditions, the cumulative indexes in the primary rougher stage of the KYF-50 flotation machine are shown in Table 8.3, and the cumulative indexes in the secondary scavenger are shown in Table 8.4. Compared with the indexes of the 16 m3 flotation machine with 5 tanks before the primary stage of the original process, the indexes of the KYF-50 flotation machine, i.e. the grades of nickel and copper in the concentrate, are improved by 2.322% and 1.408%, respectively, the content of magnesium oxide in the concentrate decreases by 4.181%, the operational recovery rate of nickel is as high as 0.108% and the operational recovery rate of copper is as high as 2.363% in the case that the nickel grade in the run-of-mine is 0.045% higher and the copper grades are equivalent. This indicates that the KYF-50 flotation machine has certain effects on improving the concentrate grades of nickel and copper, reducing the content of magnesium oxide in concentrate and improving the recovery rate of copper. From Table 8.4, it is seen that the concentrate grade of nickel is improved by 0.06%, the concentrate grade of copper is improved by 0.06% and the concentrate

278

8 BGRIMM Pneumatic Mechanical Agitation Flotation Machine

Table 8.3 Cumulative indexes in the primary rougher stage of the industrial test on KYF-50 flotation machine (%) Item

Raw ore grade

Concentrate grade

Tailings grade

Recovery

Ni

Ni

Cu

Ni

Ni

Cu

Cu

Cu

m3

50 for primary rougher

1.499

0.848

8.963

4.881

0.646

0.387

61.343

59.043

16 m3 for primary rougher

1.454

0.850

6.646

3.473

0.655

0.456

61.235

56.680

Difference

0.045

−0.002

2.499

1.408

−0.009

−0.069

0.108

2.363

Table 8.4 Cumulative indexes in the secondary scavenger stage of the industrial test on KYF-50 flotation machine (%) Item

Raw ore grade

Concentrate grade

Tailings grade

Recovery

Ni

Cu

Ni

Cu

Ni ara>

Ni

Cu

m3

50 for secondary scavenger

0.38

0.34

1.17

0.73

0.26

0.30

40.36

29.36

16 m3 for secondary scavenger

0.35

0.34

1.11

0.67

0.29

0.31

25.58

17.06

Difference

0.03

0

0.06

0.06

−0.03

−0.01

14.78

12.3

Cu

grade of magnesium oxide is improved by 1.16% with a higher grade of selected nickel when the indexes of the KYF-50 flotation machine are compared with those of the 16 m3 flotation machine with five tanks before secondary scavenger in the original process. The operational recovery rates of nickel and copper are increased by 14.78% and 12.3%, respectively. During the industrial tests, the current of the flotation machine under different concentration working conditions was measured, and the results are shown in Table 8.5. The current of the flotation machine under the normal concentration condition is close to that measured in the clean water test.

Table 8.5 Measured currents of KYF-50 flotation machine at different pulp concentrations Pulp concentration/%

52

48

36

32

Measured current/A

100.6

96

91

90

8.1 KYF Pneumatic Mechanical Agitation Flotation Machine

8.1.3.2 A.

279

Performance of the KYF-160 Flotation Machine

Dynamic performance

To investigate the performance of the KYF-160 flotation machine, the dynamic parameters of the flotation machine were measured under the clean water condition, mainly including the suction rate, the degree of air dispersion, power, air holdup, bubble diameter, etc. The flotation dynamic test results are shown in Table 8.6. Through the above tests, we have basically determined the clean water test condition of KYF-160 and relevant laws, as shown in Figs. 8.16, 8.17, 8.18 and 8.19. The air dispersion is relatively uniform at the speed of 111 r/min. At the speed of 111 r/min, the aeration rate is 0.79 m3 /(m2 min), the maximum motor power is 123.85 kW, the aeration rate is 1.6 m3 /(m2 min) and the minimum motor power is 99.37 kW. At the speed of 111 r/min, the maximum air holdup is 0.149% and the minimum air holdup is 0.085%. At the same liquid level, the changes in the air holdup with the aeration rate are the most obvious at the speed of 111 r/min. At the speed of 111 r/min, the maximum bubble diameter is 1.5 mm and the minimum bubble diameter is 1.23 mm. At the speed of 111 r/min, the range of bubble diameter distribution is also relatively large, which meets the requirements of flotation. Therefore, we can determine that the pulp test speed of the flotation machine is 111 r/min, which conforms to the design requirement. B.

Pulp suspension capacity

To investigate the pulp suspension capacity, the distribution of mineral particles at different depths in the flotation machine was measured, i.e. hydraulic analysis and grade analysis were carried out by sampling at six pulp levels as deep as 1.2 m, 1.8 m, 2.4 m, 3.0 m, 3.6 m and 4.2 m from the lower part of the overflow weir. The results of detection and analysis show that the distribution of partial sizes in the pulp in the tank body of the KYF-160 flotation machine is uniform, without stratification of coarse and fine particle sizes, which indicates that the flotation machine has good suspension capacity that meets the design requirements. C.

Process index

The pulp of the KYF-160 flotation machine is tested in order to further verify the performance of the KYF-160 flotation machine. The following tests are mainly carried out: research on the method for comparison of process indexes, comparison of pulp test indexes, on-load start test, current measurement of flotation machine, distribution detection of mineral particles at different depths in the flotation machine, automatic control of liquid level, automatic control of aeration rate, primary rougher of original process as well as particle size distribution detection of run-of-mine, and concentrates and tailings of the KYF-160 flotation machine.

1.37

0.1

1.10

Air holdup/%

Mean bubble diameter/mm

106.57

Air dispersion

Motor power/kW

0.86

104

Aeration rate/m3 (m2 min) −1

Speed/r min−1

1.12

0.11

104.17

2.63

0.93

Table 8.6 Test data of flotation dynamics tests

1.06

0.12

99.37

1.81

1.1

1.17

0.133

93.61

1.89

1.43

1.5

0.085

123.85

2.50

0.79

111

1.39

0.096

114.73

2.64

1.05

1.37

0.122

108.97

2.85

1.27

1.23

0.149

99.37

2.33

1.6

1.03

0.105

144.01

1.21

0.68

117

1.11

0.118

131.53

2.18

1.03

1.19

0.13

123.85

3.34

1.23

0.154

112.81

1.83

1.96

280 8 BGRIMM Pneumatic Mechanical Agitation Flotation Machine

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281

Fig. 8.16 Aeration rate versus air dispersion

Fig. 8.17 Aeration rate versus power consumption

The pulp test of the KYF-160 flotation machine was carried out in a nickel mine in Jinchuan. Ten KYF-16 flotation machines in primary rougher of the original production process were replaced with one KYF-160 flotation machine, and an agitation tank with the diameter of 3000 was deleted from the pulp test process of the 160 flotation machine as compared with the original process. Under the same process conditions, the cumulative indexes and comparable cumulative indexes in the primary rougher stage of the pulp test of the KYF-160 flotation machine are shown in Table 8.7, and the comparison of total indexes of the system is shown in Table 8.8. As seen from the table above, when the cumulative total index of the KYF-160 flotation machine is compared with the comparable cumulative index, with the run-ofmine grade improved by 0.04%, the Ni concentrate grade is improved by 0.14%, the

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Fig. 8.18 Aeration rate versus air holdup

Fig. 8.19 Aeration rate versus bubble diameter

tailings grades are equal and the recovery rate is improved by 0.67%. When the total cumulative index of the KYF-160 flotation machine is compared with the cumulative index of primary rougher in the original process, the grade of Ni concentrate obtained after primary rougher is improved by 0.06%, with the run-of-mine grade reduced by 0.08%. The grade of Ni tailings is 0.08% higher than that of Ni tailings of primary rougher in the original process. The KYF-160 flotation machine realizes the efficient separation of minerals. As seen from the table above, the system grade of Ni concentrate obtained through the separation in the process of the 160 flotation machine is 8.88% with the run-ofmine grade of 1.35%, while the system grade of Ni concentrate obtained through the separation in the original process is 8.63% with the run-of-mine grade of 1.43%, and the concentrate grade obtained by the KYF-160 flotation machine is 0.25% higher

0.04

1.31

0.04

1.43

−0.08

Comparable cumulative index

Comparable index error

Cumulative index of primary rougher in the original process

Cumulative index error of primary rougher

0.83

1.35

Cumulative index of 160 flotation machine 0.05

0.82

0.87

0.87

1.34

0.85

1.40

0.06

4.13

0.14

4.05

4.19

4.11

4.51

Ni

Production stage

Concentrate grade

Ni

Cu

Raw ore grade

Debugging stage

Comparison index

Table 8.7 Comparison of primary rougher indexes of the system (%)

1.82

0.37

1.27

19.08

−0.02 2.03

18.53

20.35

20.29

20.79

MgO

2.42

2.40

2.35

2.60

Cu

0.08

0.42

0.01

0.49

0.50

0.50

0.51

Ni

Tailings grade

0.04

0.36

0.04

0.36

0.40

0.40

0.39

Cu

−6.55

78.43

0.67

71.21

71.88

71.78

72.29

Ni

Operational recovery rate

−3.12

68.87

−0.15

65.90

65.75

66.11

64.49

Cu

8.1 KYF Pneumatic Mechanical Agitation Flotation Machine 283

0.02

−0.08

System index error

0.85

1.43

Total index of the original process system

0.87

1.35

0.25

8.63

8.88

Ni

0.65

4.10

4.75

Cu

Concentrate grade of the system

Ni

Cu

Raw ore grade

Total cumulative index of the 160 flotation machine system

Item

Table 8.8 Comparison of total system indexes (%)

−0.11

6.45

6.34

MgO

−0.02

0.24

0.22

Ni

−0.02

0.31

0.29

Cu

Total tailing grade of the system

−0.05

85.73

85.68

Ni

System recovery

2.21

68.86

71.07

Cu

284 8 BGRIMM Pneumatic Mechanical Agitation Flotation Machine

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285

than that obtained in the original process; The tailings grade of the Ni system in the process of the KYF-160 flotation machine is 0.02% lower than that of the original process, while the recovery rate of the system is reduced by 0.05%. It shows that the KYF-160 flotation machine is helpful to improve the total concentrate grade of Ni to some extent, and also reduces the tailings grade. In addition, the grade of Cu concentrate is increased by 0.65%, the recovery rate is increased by 2.21%, and the grade of MgO is reduced. From these data we can see that the KYF-160 flotation machine has good separation performance, and the equipment performance meets the design requirements. a.

On-load start test

The on-load start of a large flotation machine is very important for large concentrators because it can save the mineral resources and reduce the labour intensity. During the tests, the start status of the pulp in the whole tank of the flotation machine was investigated, stop and start tests were conducted, stop tests for 8, 24, 48 and 144 h were conducted successively and the flotation machine was started successfully without any problem, which indicates that the equipment can be started normally in the case of long-term deposition after stop with the tank full of pulp. b.

Determination of power consumption of the flotation machine

The power consumption of the flotation machine is an important index to investigate the performance of the flotation machine. During the tests, the current (power) was measured under different aeration rates when the pulp concentration was 36%. The data is shown in Table 8.9, and the results are shown in Fig. 8.20. y = 106 +

20.6 1+e

(8.1)

x−0.97 0.113

where y x

motor power; aeration rate.

Throughout the test, since the pulp concentration was controlled at 36 ± 2% and the aeration rate was generally adjusted between 1.1 and 1.2, the host power consumption was 113 ~ 107 kW, the aeration power consumption was about 34 ~ 38 kW and the unit total power consumption of the flotation machine was 147 ~ 145 kW and less than 150 kW. Table 8.9 Aeration rates and current change values Aeration rate/m3 (m2 min) −1

0.67

Power/kW

132.41 126.65 122.81 117.05 113.21 112.25 105.53 104.57 104.09

0.85

0.92

1.00

1.04

1.10

1.30

1.40

1.48

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Fig. 8.20 The relationship between the aeration rate and the power can be obtained by fitting

8.1.3.3 A.

Performance of the KYF-200 Flotation Machine

Dynamic test

To investigate the performance of the KYF-200 flotation machine, the dynamic parameters of the flotation machine were measured under the clean water condition, mainly including the suction rate, the degree of air dispersion, power, air holdup, bubble diameter, etc. The results of the dynamic test of the KYF-200 flotation machine are shown in Table 8.10 and Figs. 8.21, 8.22, 8.23 and 8.24. At the speed of 109 r/min, the maximum degree of air dispersion is 3.17 and the minimum degree of air dispersion is 2.63. It can be seen that at the speed of 109 r/min, all the degrees of air dispersion are above 2.5, which are not very different from each other, and all of them are ideal with uniform changes. At the speed of 109 r/min, the aeration rate is 0.80 m3 /m2 .min−1 , the current is 325A, the aeration rate is 1.8 m3 /m2 min−1 and the current is 252A. At the speed of 109 r/min, the maximum air holdup is 0.13% and the minimum air holdup is 0.10%. At the speed of 109 r/min, the maximum bubble diameter is 1.76 mm and the minimum bubble diameter is 1.29 mm. Therefore, the speed of the flotation machine is determined as 109 r/min on the basis of quantitative data in the above four aspects combined with the overall phenomena in the test. B.

Pulp tests

To investigate the separation performance of the two KYF-200 flotation machines, the run-of-mine, concentrate and tailings of the test system and the contrast system were sampled and tested during the test. After the laboratory test, the elements were

8.1 KYF Pneumatic Mechanical Agitation Flotation Machine

287

Table 8.10 Data of dynamic test with clean water Rotor speed/r min−1

Aeration rate/m3 (m2 min) −1

Air dispersion

Current/A

Air holdup

101

0.4

4.0

300

0.08

0.69

1.32

275

0.11

0.94

3.49

255

0.12

1.22

2.24

250

0.14

0.43

2.53

340

0.10

0.67

2.63

315

0.11

2.68

0.88

3.08

310

0.11

1.0

1.15

2.80

270

0.12

1.19

1.6

2.99

260

0.13

0.98

0.80

3.17

325

0.10

1.29

1.07

2.89

280

0.13

1.63

1.13

2.67

270

0.11

1.76

1.8

2.63

252

0.11

1.47

0.8

2.72

340

0.10

0.98

0.99

2.2

330

0.11

1.61

1.23

3.27

320

0.12

1.60

1.49

2.32

280

0.09

105

109

113

Mean bubble diameter/mm

Fig. 8.21 Air dispersion versus aeration rate

Cu and S for both. Samples were taken every 0.5 h and sent for the laboratory test once per shift. The 10-day debugging stage of the pulp test was carried out on the flotation machines, and the cumulative indexes are shown in Table 8.11.

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Fig. 8.22 Power consumption versus aeration rate

Fig. 8.23 Air holdup versus aeration rate

Fig. 8.24 Bubble size versus aeration rate

8.1 KYF Pneumatic Mechanical Agitation Flotation Machine

289

Table 8.11 Comparison of copper indexes in the commissioning stage (%) Item

Raw ore grade

Concentrate grade

Tailings grade

Coarse 1 work recovery rate

Flotation efficiency

System recovery

Test process indicator

0.405

8.69

0.134

68.31

65.26

85.51

Compared process indicator

0.409

10.34

0.140

66.59

64.36

84.38

Difference

−0.004

−1.65

−0.006

1.72

0.9

1.13

The indexes fluctuate greatly in the debugging stage, for example, the highest grade of copper is 14.75% and the lowest grade of copper is 5.79%. The main reason is that the liquid level is poorly controlled. The liquid level is controlled manually in the debugging stage, resulting in failure to give immediate feedback for the fluctuation of the pulp volume. The installation precision of the overflow weir of the equipment is also one of the reasons affecting the index fluctuation. The optimal production conditions, including the thickness of froth layer, the aeration rate and the liquid level, were explored through the debugging stage, to provide the basis for the technical conditions in the production stage. The 17-day indexes in the production stage of the pulp test were counted, and the cumulative indexes are shown in Table 8.12. The statistical indexes of the production stage show that the recovery rate is 6.95 percentage points higher when the run-of-mine grade is reduced by 0.001%, which is far beyond the index of the contrast process, and all the economic indexes of this type of flotation machine meet the design requirements. C.

On-load start test

The full-load stop must be realized for supersized flotation machines in order to reduce the economic losses caused by full-load stop of the supersized flotation Table 8.12 Comparison of copper indexes in the industrial test stage (%) Item

Raw ore grade

Concentrate grade

Tailings grade

Coarse 1 work recovery rate

Flotation efficiency

System recovery

Test process indicator

0.518

10.88

0.168

68.33

65.94

85.43

Compared process indicator

0.519

11.27

0.202

61.56

58.99

84.51

Difference

−0.001

−0.39

−0.034

6.77

6.95

0.92

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8 BGRIMM Pneumatic Mechanical Agitation Flotation Machine

machines to the concentrators. Through several trial stops during the test, it can be seen that the KYF-200 flotation machine can be started normally under the full load. D.

Determination of power consumption of the flotation machine

The power consumption of the flotation machine is an important index to investigate the performance of the flotation machine. During the test, the main motor power of the KYF-200 flotation machine was measured under different aeration rates with the pulp concentration of 30%. The data is shown in Table 8.13, and the results after collation are shown in Fig. 8.25. After fitting, the relationship between aeration rate and power of the KYF-200 flotation machine is y = 129.6 +

59.5 1+e

(8.2)

(x−0.91) 0.266

where y x

motor power; aeration rate.

Table 8.13 Relationship between aeration rate and power Aeration rate/m3 (m2 min) −1

0.70

Power/kW

170.00 162.3 154.2 144.00 140.21 135.25 130.53 124.57 120.09

0.85

0.92

1.00

1.10

Fig. 8.25 The relationship between aeration rate and power

1.20

1.30

1.40

1.48

8.1 KYF Pneumatic Mechanical Agitation Flotation Machine

291

Since the pulp concentration was controlled at 30% ± 2% and the aeration rate was generally adjusted between 1.0 and 1.2 throughout the test, the power consumption of a single unit was 140 ~ 150 kW, the aeration power consumption of two flotation machines was about 110 kW in total and the total power consumption of two KYF-200 flotation machines was 390 ~ 410 kW. E.

Determination of pulp suspension capacity

To investigate the pulp suspension capacity, the distribution of mineral particles at different depths in the flotation machine was measured, i.e. samples were taken at eight pulp levels as deep as 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0 and 4.5 m from the lower part of the overflow weir, and hydraulic analysis and grade analysis were carried out. The results of detection and analysis show that the distribution of partial sizes in the pulp in the tank of the KYF-200 flotation machine is uniform, without stratification of coarse and fine particle sizes, which indicates that the flotation machine has good suspension capacity of mineral particles that meets the design requirements.

8.1.3.4 A.

Performance of the KYF-320 Flotation Machine

Dynamic performance

Statistical data of the dynamic test of the 320 m3 flotation machine is shown in Table 8.14. Through the above tests, the clean water test condition and related laws of the 320 m3 flotation machine are shown in Figs. 8.26, 8.27 and 8.28. The following conclusions can be drawn for the equipment: at the speed of 107 r/min, the maximum degree of air dispersion is 2.01 and the minimum degree of air dispersion is 1.31. It can be seen that at the speed of 107 r/min, all the degrees of air dispersion are above 1.5, which are not very different from each other, and all of them are ideal with uniform changes. The maximum current is 305A and the minimum current is 280A when the aeration rate is 0.9 ~ 1.4 m3 /(m2 min) and the speed is 107 r/min. At the speed of 107 r/min, the maximum air holdup is 12.88% and the minimum air holdup is 11.36%. At the same liquid level, the changes in the air holdup with the aeration rate are the most obvious at the speed of 107 r/min. To sum up, at the five speed levels, when the speed is greater than 107 r/min, the air in the tank can be dispersed in the tank uniformly, but with the increase of speed, the spindle power consumption of the flotation machine increases, and when the speed is 107 r/min, the changes in the air holdup with the aeration rate are the most obvious. Therefore, the pulp test speed of the flotation machine is determined as 107 r/min, which is consistent with the design requirements.

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8 BGRIMM Pneumatic Mechanical Agitation Flotation Machine

Table 8.14 Clean water test data Speed/r min−1

Aeration rate/m3 (m2 min) −1

Air dispersion

Current/A

Air holdup/%

98

0.95

1.63

242

11.14

1.07

1.47

230

11.87

1.15

1.39

223

12.43

1.27

1.27

214

12.68

0.98

1.83

269

11.43

1.08

1.61

259

11.95

1.19

1.55

250

12.67

102

107

111

115

1.31

1.29

242

12.50

0.95

2.01

300

11.36

1.06

1.8

305

12.15

1.17

1.74

295

12.73

1.36

1.31

280

12.88

0.96

1.98

340

11.49

1.08

1.75

326

12.29

1.17

1.66

318

12.05

1.26

1.45

311

12.64

0.94

2.09

384

11.24

1.07

1.85

370

11.85

1.15

1.7

361

12.67

1.27

1.55

351

12.84

Fig. 8.26 Air dispersion rate versus aeration rate

B.

Pulp tests

To investigate the separation performance of the 320 m3 flotation machine, the runof-mine, concentrate and tailings of the test system were sampled and tested during

8.1 KYF Pneumatic Mechanical Agitation Flotation Machine

293

Fig. 8.27 Power consumption versus aeration rate

Fig. 8.28 Air holdup versus aeration rate

the test. Samples were taken once an hour and sent for the laboratory test once per shift. The pulp test production stage lasted for 10 days. The cumulative indexes are shown in Table 8.15. It can be seen from Table 8.15 that at the feed copper grade of 0.060%, the copper grade of concentrate is up to 1.256%, and the copper enrichment ratio is up to 20.62. At the feed sulphur grade of 0.386%, the sulphur grade of concentrate is up to 24.83%, and the sulphur enrichment ratio is up to 71.44. C.

On-load start test

To reduce the economic loss of the concentrator caused by the failure of full-load stop of the supersized flotation machine, the supersized flotation machine must realize on-load start. The full-load start tests of the flotation machine were conducted in the last stage of the test in order not to affect the tests. The 320 m3 pneumatic mechanical agitation flotation machine was successfully started after full-load stop for 0.5, 1, 2

0.386 1.256

Cu

Cu

Cu

Productivity/g

39.73 0.64

S

Recovery rate/%

0.218 12.80

S

Tailing grade/%

24.830 0.053

S

Cu

Cu

S

Concentrate grade/%

Raw ore grade/%

Value 0.060

Item

Table 8.15 Comparison of copper indexes in the industrial test stage

Cu 0.72 12.19

S

Flotation efficiency/%

Cu 39.50 20.62

S

71.44

S

Enrichment ratio

294 8 BGRIMM Pneumatic Mechanical Agitation Flotation Machine

8.1 KYF Pneumatic Mechanical Agitation Flotation Machine

295

Fig. 8.29 Solids percentage at different depths

and 4 h, respectively, which indicates that the 320 m3 pneumatic mechanical agitation flotation machine can be started normally after on-load stop. D.

Determination of power consumption of the flotation machine

The power consumption of the flotation machine is an important index to investigate the performance of the flotation machine. During the test, the pulp concentration was 30%. When the aeration rate was 1.0 ~ 1.4 m3 /(m2 min), the host current of the flotation machine was always about 320A, and its actual power consumption was about 160 kW. E.

Determination of pulp suspension capacity

To investigate the pulp suspension capacity, the distribution of mineral particles at different depths in the flotation machine was measured, i.e. samples were taken at eight pulp levels as deep as 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 and 5.5 m from the lower part of the overflow weir, and hydraulic analysis was carried out. The results are shown in Fig. 8.29 and Fig. 8.30. It can be seen from the figure that the pulp size is distributed evenly in the tank of the 320 m3 flotation machine, without showing the stratification phenomenon between coarse and fine particles; it means that the flotation machine has a good mineral suspension capability and meets the design requirement.

8.1.3.5

Performance of the KYF-680 Flotation Machine

The inner part of the flotation machine is usually divided into four areas: rotor agitation area, transport area, separation area and froth area, each of which has its own functional features. The areas should not be simply scaled up in the process of rapid upsizing of the flotation machine volume. For the purposes of full agitation and suspension of the mineral particles and effective contact with the bubbles, the rotor agitation area is scaled up to a great extent, and enough space and time are provided

296

8 BGRIMM Pneumatic Mechanical Agitation Flotation Machine

Fig. 8.30 PSD at different depths

to enable effective bubble–particle contact for mineralization. The KYF-680 supersized flotation machine is supported by the amplification theory of the BGRIMM flotation machine, and a flotation dynamics control technique for the characteristics of target minerals has been developed so that coarse minerals can be transported to higher areas to facilitate the rapid recovery in a short distance and realize the relatively shallow tank flotation process. The bubble mineralization in the flotation machine tanks mainly occurs in the way of downstream flow, while rotor agitation and stator current stabilization are the main ways for formation of mineralization environments. For the design of the rotor stator of the KYF-680 flotation machine based on the optimal control strategy for the turbulent dissipation rate, the rotor agitation area is enabled to form a powerful circulation output and produce a uniform and stable gas–liquid–solid three-phase velocity gradient field. In the rotor chamber area with high turbulent dissipation rate and great velocity gradient, fine minerals can realize mineralization with the bubbles in advance here. Outside the rotor area, the turbulent dissipation rate is moderate subject to the regulation effect of stator current stabilization. In this state, the space area in the tank is the largest, and the coarse connate minerals mainly collide with and adhere to the bubbles here. As the mineralized bubbles carrying the coarse and fine minerals float up, the turbulent dissipation rate gradually decreases so that the mineralized bubbles can smoothly enter the froth layer for recovery. From Fig. 8.31 which shows the cumulative mean values of the aeration rate and the degree of air dispersion under the ore carrying condition, we can see that the degree of air dispersion can reach 7 at the aeration rate of about 1.0 m3 /(m2 min), showing excellent air dispersibility. From Fig. 8.32, it can be seen that the gas holdup in the whole flotation tank varies at different depths. The closer the gas holdup is to the liquid level, the higher the gas holdup is, which is consistent with the distribution characteristics of gas holdups in the tank. By calculating the comprehensive gas

8.1 KYF Pneumatic Mechanical Agitation Flotation Machine

297

Fig. 8.31 Air dispersion rate

Fig. 8.32 Air holdup at different depths

holdup of the whole flotation tank, it can be seen that the comprehensive gas holdup of a 680 m3 flotation machine was 7.06% under the test conditions at that time. The circulating capacity of the 680 m3 supersized flotation machine at the design speed can reach 500 m3 /min, and the powerful circulating capacity ensures the full suspension of coarse minerals. The relationship between different aeration rates and circulation volumes is shown in Fig. 8.33. The circulation volume decreases as the aeration rate increases. Figure 8.34 shows the change law curves of the speed and power consumption of the supersized flotation machine under different aeration rate conditions. It is obvious that the power consumption of the flotation machine shows a fast-increasing trend as the speed increases, and the input power consumption of the flotation machine can be reduced with the increase of the aeration rate. Test on the suspension capacity of the 680 m3 flotation machine. The test contents include concentration distribution and size fraction distribution at different depths. From Fig. 8.35, it can be seen that all the concentration distributions of the pulp at different depths are within the range of 30 ~ 35%. From Fig. 8.36, it can be seen that the consistency of size fraction compositions is good in the same depth position,

298

8 BGRIMM Pneumatic Mechanical Agitation Flotation Machine

Fig. 8.33 Pumping capacity versus rotor speed

Fig. 8.34 Power consumption versus rotor speed

which shows that the distribution effect of suspension of all size fractions at different depths is quite good. The flotation dynamics parameters which affect and reflect the performance of the flotation machine itself were measured in the process of dynamic tests. Under the optimal aeration rate condition, the degree of air dispersion can reach above 7, with a good dispersion effect. The mean gas holdup under ore carrying conditions is about 7%. The pulp concentrations are distributed uniformly at different depths, and the size fractions also have consistent distributions in their depths. The circulation

8.1 KYF Pneumatic Mechanical Agitation Flotation Machine

299

Fig. 8.35 Concentration distribution in open-circuit test

Fig. 8.36 Suspended particle distribution in open-circuit test

volume can reach 500 m3 /min, and the operational power consumption is 360 ~ 400 kW. The behaviour of short circuit in the pulp flow is more common in supersized flotation machines. The residence time distribution of the KYF-680 flotation machine was studied in tests. Figure 8.37 shows that the mean residence time of the KYF-680 flotation machine is 17.81 min, which is 89% of the ideal residence time (20 min). Therefore, there is no obvious short-circuit or dead zone phenomenon in the KYF-680 flotation machine.

300

8 BGRIMM Pneumatic Mechanical Agitation Flotation Machine

Fig. 8.37 Residence time distribution of the KYF-680 flotation machine

8.2 XCF Automatic Suction Pneumatic Mechanical Agitation Flotation Machine The pneumatic mechanical agitation flotation machine has the characteristics of good flotation process index, reduction of energy consumption and power consumption, simple structure, convenient operation, maintenance and management, etc. The traditional pneumatic mechanical agitation flotation machine does not have the pulp suction capability, the step configuration is adopted between floatation operations and the middlings must be returned by the froth pump. Since the froth pump is easy to wear, it is difficult to lift the sticky and non-breakable froth, which makes it difficult for the process to become unblocked, and the configuration is difficult for complex processes and cleaner bank. For the newly built concentrator, the investment of capital construction is increased due to the step configuration, as shown in Fig. 8.38. The transformation of old concentrators is difficult because both plant height and process height difference are fixed, which limits the application scope of the pneumatic mechanical agitation flotation machine. Therefore, the development of an automatic suction pneumatic mechanical agitation flotation machine having both the advantages of the pneumatic mechanical agitation flotation machine and the pulp suction capacity is good for saving the return of middlings to the pump, reducing the plant height, reducing the capital costs, etc. and is of great significance to the construction and transformation of new and old mines. The XCF automatic suction pneumatic mechanical agitation flotation machine is used either separately or formed into an aggregate unit with the conventional pneumatic mechanical agitation flotation machine so that different flotation operations are configured horizontally without the froth pump, as shown in Fig. 8.39.

8.2 XCF Automatic Suction Pneumatic Mechanical Agitation …

301

Fig. 8.38 Step configuration of flotation bank

Fig. 8.39 Horizontal configuration of flotation bank

8.2.1 Working Principle and Key Structures of XCF Flotation Machine The structure of the XCF automatic suction pneumatic mechanical agitation flotation machine is shown in Fig. 8.40. This flotation machine consists of tank bodies for accommodating the pulp, big isolation disc rotors with upper and lower blades, seattype stators with radial blades, split disc-shaped cover plates, split central cylinders, connecting pipes with exhaust holes, bearing blocks, hollow spindles, air regulating valves, etc. There are two kinds of structures, i.e. open and closed. There are seat-type and side-attached bearing blocks installed to the cross member which also serves as an air supply pipe. Figure 8.41 is an aggregate unit formed by the XCF automatic suction pneumatic mechanical agitation flotation machine and the KYF pneumatic mechanical agitation flotation machine. A.

Working principle

The motor drives the rotor to rotate through the transmission device and the hollow spindle. The pulp is sucked into the space between the lower rotor blades via the inner edge of the lower rotor blades. Meanwhile, the low-pressure air supplied from the outside enters the air distributor in the lower rotor chamber through the cross

302

8 BGRIMM Pneumatic Mechanical Agitation Flotation Machine

Fig. 8.40 Structure diagram of XCF flotation machine (1—lower rotor blade; 2—stator; 3—isolation disc; 4—lower rotor blade; 5—rotor cover plate; 6—central cylinder; 7—hollow spindle; 8—tank body; 9—middlings pipe; 10—feed pipe)

Fig. 8.41 Combined unit of XCF/KYF flotation machines

8.2 XCF Automatic Suction Pneumatic Mechanical Agitation …

303

member, the air regulating valve and the hollow spindle, and then enters the space between the lower rotor blades through the small holes around the air distributor. The pulp and air are discharged from the outer edges of the lower rotor blades after being fully mixed in the space between the lower rotor blades. A certain negative pressure is generated in the upper rotor blades due to the rotor rotation and the combined action of the cover plate and central cylinder so that the middlings froth and the feed flow into the central cylinder through the middlings pipe and the feed pipe and enter the space between the upper rotor blades, and finally they are discharged from the outer edges of the upper blades. The pulp discharged from the upper and lower blades of the rotor enters the tank after current stabilization and orientation by the stator. The mineralized bubbles ascend to the tank surface and form the froth which flows into the froth tank. Then the pulp is returned to the rotor area for recirculation, and the other part enters the next tank for re-separation through the circulation holes in the wall between the tanks. The function of the rotor isolation disc is to make the mixture of pulp and air discharged from the lower blades not affect the pulp suction of the upper rotor blades. B.

Key structures

The design of the XCF automatic suction pneumatic mechanical agitation flotation machine focuses on the structures and parameters of the tank body, rotor, stator, cover plate, connecting pipe, etc., as well as the coordination relationship among them. The main parts and components are designed as follows: a.

Tank body

The tank body of the XCF flotation machine is designed into a U shape, which is favourable for the coarse mineral particles to return to the rotor area for recirculation to avoid the accumulation of ore sand and reduce the phenomenon of pulp short circuit. To facilitate manufacturing and installation, trapezoid-shaped tanks are generally used when the tank volume is less than 3 m. When the XCF flotation machine is combined with other pneumatic mechanical agitation flotation units to form an aggregate unit, the shape of the tank body may be consistent with that of the direct current tank body for convenient connection between tank bodies. To provide the XCF flotation machine with the advantages of a general pneumatic mechanical agitation flotation machine and make it easily combined with the general pneumatic mechanical agitation flotation machine to form the aggregate unit, a deep tank structure is adopted, which creates an obstacle to automatic pulp suction and increases the difficulty in the development of the rotor–stator mechanism. b.

Spindle

Since low-pressure air is compressed into the general pneumatic mechanical agitation flotation machine, the negative pressure in the central area of the rotor is reduced, making it difficult to suck the pulp. For this reason, we have designed the spindle assembly with a pneumatic agitation area and a pulp sucking area, which are separated

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8 BGRIMM Pneumatic Mechanical Agitation Flotation Machine

by the isolation disc. The pulp sucking area consists of the upper rotor blades, discshaped cover plate, central cylinder, connecting pipe, etc. and the pneumatic agitation area consists of the lower rotor blades, air distributor, etc. c.

Rotor

The rotor is the main component of the flotation machine and one of the key points in the design of the flotation machine. The rotor is designed to have upper and lower blades separated by the isolation disc in order to separate the pneumatic agitation area from the pulp sucking area. The upper rotor blades are designed into radial straight blades which can produce suitable suction force and static pressure head, and reduce the counterflow between the blades and avoid the return of the air in the main tank into the central cylinder and connecting pipe. The lower rotor blades are backward-inclined centrifugal blades with high specific speed, low dynamic head and high flow rate. They are used only for pulp circulation and air dispersion to meet the requirements of the flotation process for the flotation machine. The range of aeration rate and the degree of air dispersion have great influences on the scope of application and process indexes of the flotation machine. The air distributor is designed in the lower blade chamber of the rotor in order to further improve the aeration rate and degree of air dispersion. The air distributor is a cylinder with small holes in the wall. It can distribute the air much more evenly in most areas of the rotor blades in advance and provide a large number of pulp–air interfaces, thus improving the air dispersion capability of the rotor. d.

Stator

In addition to making the rotating pulp flow radially and shear the air, the stator of the XCF automatic suction pneumatic mechanical agitation flotation machine must also protect the air aerated into the pulp via the lower rotor blades against the obstruction of the stator so that the air can enter the main tank smoothly without entering the pulp sucking area through the upper rotor blades. The XCF flotation machine is provided with an open stator with suspended radial short blades. The stator is installed above the periphery of the rotor and fixed to the tank bottom by support members. There is a large radial clearance between the stator and the rotor and a large area for pulp circulation around the lower area of the stator so that the unnecessary interference of the lower parts on the pulp is eliminated, which is favourable for the flow of pulp to the lower area of the rotor, reducing the power consumption and enhancing the circulation in the lower circulation area and the suspension of solid particles. Currently, the XCF flotation machine has many specifications with the volumes of 1 ~ 70 m3 , and the technical parameters are shown in Table 8.16.

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Table 8.16 Technical parameters of XCF flotation machine Aeration rate/m3 (m2 min) −1

Specification

Effective volume/m3

Installed power/kW

Minimum inlet wind pressure/kPa

XCF-1

1

4

>11

0.05~1.4

XCF-2

2

7.5

>12

0.05~1.4

XCF-3

3

11

>14

0.05~1.4

XCF-4

4

15

>15

0.05~1.4

XCF-6

6

18.5

>17

0.05~1.4

XCF-8

8

22

>19

0.05~1.4

XCF-10

10

30

>20

0.05~1.4

XCF-16

16

45

>23

0.05~1.4

XCF-20

20

45

>25

0.05~1.4

XCF-24

24

55

>27

0.05~1.4

XCF-30

30

55

>31

0.05~1.4

XCF-40

40

75

>32

0.05~1.4

XCF-50

50

90

>33

0.05~1.4

XCF-70

70

110

>33

0.05~1.4

8.2.2 Fluid Dynamics Research in XCF Flotation Machines The automatic suction pneumatic mechanical agitation flotation machine has the performance in two aspects, one is the flotation separation performance and the other is suction of middlings or feed. The suction of middlings or feed may be turned on or off according to the requirements of the flotation flow. By taking the XCF-0.2 m3 flotation machine as an example, the fluid dynamics characteristics in the automatic suction flotation machine are introduced. Figure 8.42 reveals the flow pattern of the automatic suction pneumatic mechanical agitation flotation machine without middling suction under the condition of single-phase pure water. An upper flow circulation and a lower flow circulation appear inside the flotation machine, which is the basis of ensuring the excellent separation performance. Similar to the conventional flotation machines, the pulp enters the rotor area from the area below the rotor. The fluid is separated into upward and downward flows after being discharged under the action of the rotor blades. Figure 8.43 reveals the flow pattern of the automatic suction pneumatic mechanical agitation flotation machine with middling suction under the condition of single-phase pure water. The structure of the circulating flow field is comparative to the overall flow pattern of the flotation machine, that is to say, middling suction does not destroy the fluid dynamics state in the tank, which is essential for ensuring the separation performance of the automatic suction pneumatic mechanical agitation flotation machine. The fluid is sucked from the outside into the middling pipe or feed pipe, supplied into the rotor area through the central cylinder, and then discharged by the rotor. Intense collision and mixing occur to the middling and the pulp sucked in below the rotor in the rotor discharge area. It is foreseeable that

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Fig. 8.42 Flow patten of single phase—without middling suction

this is beneficial to increasing the turbulence intensity in the agitation and mixing area of the flotation machine and improving the collision between particles and bubbles. Relative to general pneumatic flotation machines, the rotor is the key to the double function of the automatic suction pneumatic mechanical agitation flotation machine. Figure 8.44 shows the rotor structure and negative pressure distribution of the automatic suction pneumatic mechanical agitation flotation machine. The rotor consists of upper and lower blades which are separated by a baffle plate. A wide range of negative pressure is produced at the leeward side of the pulp of the blades whether they are upper blades or lower blades. Therefore, under the action of negative pressure driving force, the pulp in the tank is circulated by the lower blades, and the middlings are sucked by the upper blades, as shown in Fig. 8.45. In theory, it is contradictory that negative pressure suction is formed in a low-pressure aerated environment. The automatic suction flotation machine realizes the relative isolation of the low-pressure aeration path from the suction path through a series of engineering design, thus solving the problem of middling suction in the pneumatic flotation machine.

8.2 XCF Automatic Suction Pneumatic Mechanical Agitation …

307

Fig. 8.43 Flow patten of single phase—with middling suction

Figure 8.46 reveals the axial flow distribution in the middle section of the stator ring with or without middling suction. The flow patterns in both cases are similar, with certain differences in the local velocities only. Table 8.17 Influence of pulp suction on fluid dynamic performance Table 8.17 gives a comparative analysis of the main dynamic performance parameters with or without middling suction. It can be seen that the rotor circulation volume does not change much. This is very important to maintain the stable performance of the automatic suction pneumatic mechanical agitation flotation machine under different working conditions. From the data, it is seen that the middling pumping effect of the automatic suction pneumatic mechanical agitation flotation machine has no significant effect on the fluid dynamic flow pattern in the flotation machine, but the operational power consumption is relatively increased to a large extent by about 15%.

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Fig. 8.44 Negative pressure distribution on impeller of the automatic suction air-forced mechanical agitation flotation machine

(a) Upper blades

(b) Lower blades

8.2.3 Performance and Application of the XCF Flotation Machines 8.2.3.1 A.

Performance of XCF-8 Flotation Machine

Pulp test

With the XCF-8 flotation machine as the testing object, its flotation dynamics in clean water was tested, and the degree of air dispersion, pulp sucking capacity, power consumption gas and other related parameters were mainly tested. At the linear velocity of 7.54 m/s, the mean degree of air dispersion is 2.56 and the pulp sucking capacity is 4.5 ~ 7 m3 /min. At the linear velocity of 6.97 m/s, the degree of air dispersion is 3.68 and the pulp sucking capacity is 3.6 ~ 5.5 m3 /min.

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309

Fig. 8.45 Flow path of air and pulp in the automatic suction air-forced mechanical agitation flotation machine

According to the clean water test, it can be determined that the linear velocity of the flotation machine within 7 ~ 7.5 m/s fully meets the requirements of the pulp test. Industrial tests were conducted in order to investigate the separation performance of the flotation machine, and Table 8.18 shows the index comparison in the debugging stage. As can be seen from Table 8.19, the recovery rate of lead is increased by 0.87% according to the test results of the XCF/XCF-8 flotation machine. Subsequently, the industrial tests were conducted for 1 month, with the test indexes as given in table. As can be seen from Table 8.19, the indexes of the XCF/XCF-8 flotation machine are better than those of the 6A flotation machine. B.

Comparison of power consumptions

The power consumptions were measured in order to compare the power consumptions of individual flotation machines, as shown in Table 8.20. As seen from Table 8.20, the specific power of the XCF-8 flotation machine is 10.80 lower than that of the 6A flotation machine, which shows that the XCF-8 flotation machine has a low power consumption that meets the design requirements. C.

Comparison of losses of wearing parts

The rotor stator of the 6A flotation machine has a service life of about 3 months. The wear condition of the rotor stator was checked after the XCF-8 runs for 2000 h. It

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Fig. 8.46 Axial flow distribution in the middle section of the stator ring

(a) Without pulp suction

(b) With pulp suction Table 8.17 Influence of pulp suction on fluid dynamic performance Serial No.

Item

Without pulp suction

With pulp suction

Unit

1

Torque

26

29.7

N.m

2 3

Middling pulp suction volume

1.84

1.73

m3 /min

0

0.82

m3 /min

8.2 XCF Automatic Suction Pneumatic Mechanical Agitation …

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Table 8.18 Index comparison in the debugging stage Raw ore grade %

Raw ore grade %

Recovery rate (%)

Remarks

Pb

Zn

PbK➀

Zn/PbK➁

PbK➀

Zn/PbK➁

ZnK

1

1.305

0.995

67.63

3.53

83.38

5.71

75.76

XCF/XCF-8

2

1.208

0.936

70.00

3.54

82.51

5.39

74.51

6A

3

1.244

1.092

69.38

3.69

82.71

5.29

79.77

6A

Note ➀ Lead concentrate; ➁ Lead concentrate with zinc

Table 8.19 Index comparison in the test stage Raw ore grade/%

Tailings grade/%

Pb

Zn

Pb

Zn

Zinc concentrate grade/%

Zinc concentrate recovery rate/%

Remarks

1

1.313

1.013

0.144

0.119

49.96

81.4

XCF/XCF-8

2

1.393

1.036

0.160

0.132

49.62

79.46

6A

3

1.208

0.936

0.167

0.167

49.50

74.57

6A

Table 8.20 Comparison of power consumptions of flotation machines Item

XCF

XCF

6A

1

Tank volume/m3

8

8

2.8

2

Installed power/kW

22

15

10

3

Actual power consumption of spindle/kW

16.00

9.62

8.04

4

Aeration power/kW

4.47

4.47

0.00

5

Actual power consumption/kW

21.47

14.09

8.04

6

Specific power/kW m−3

2.56

1.76

2.87

7

Saving as compared with 6A/%

10.80

38.68

was found that the rotor stator was not worn seriously, with a minor impact on the equipment performance. It was expected to be used normally for 7000 ~ 9000 h, and the consumption of the wearing parts was reduced by about 70% compared with that of the 6A flotation machine.

8.2.3.2 A.

Performance of XCF-24 Flotation Machine

Dynamic test

The XCF-24 flotation machine is taken as the testing object and tested in terms of its flotation dynamics in clean water, mainly including the determination of related

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Table 8.21 Results of dynamic test Rotor speed/r min−1

Aeration rate/m3 (m2 min) −1

Air dispersion

Current/A

Air holdup %

Mean bubble diameter/mm

145

0.95

2.49

73

12.6

1.32

151

1.13

2.80

75

12.3

1.41

157

1.08

3.89

84

13.4

1.22

163

0.97

3.33

88

11.2

1.20

parameters such as aeration rate, degree of air dispersion, speed, power, air holdup and bubble diameter. The results of the dynamic test on the XCF-24 pneumatic mechanical agitation flotation machine are shown in Table 8.21. Through the testing and analysis of the dynamic parameters in the flotation machine, the optimal dynamic performance of the pneumatic mechanical agitation flotation machine can be determined to adapt to the separation requirements of the process and achieve the optimal application effect of the equipment. A total of four groups of tests were conducted in order to investigate the pulp sucking capacity of the XCF-24 flotation machine and the influence on the pulp sucking capacity after the rotor and cover plate are worn. The aeration rate is set to about 1.23 m3 / (m2 min). Since the transient current of the flotation machine is difficult to measure and record, only the maximum current value is determined when the power consumptions are compared. The test results are shown in Table 8.22. Table 8.22 Test on pulp sucking capacity of XCF-24 flotation machine (m3 /min) Test No.

1

Test condition

Rotor speed n = Rotor speed n = Rotor speed n = Rotor speed n = 157 r/min 157 r/min 151 r/min 151 r/min

Pulp suction height

Maximum current/A

2

3

4

8 mm for the clearance between rotor and cover plate

15 mm for the clearance between rotor and cover plate

8 mm for the clearance between rotor and cover plate

15 mm for the clearance between rotor and cover plate

750

19.17

19.92

20.70

19.45

850

18.16

15.02

19.81

15.82

950

19.19

17.42

17.71

16.22

1050

17.26

14.77

16.59

15.80

1150

16.62

13.42

15.17

13.18

1250

15.54

12.09

13.70

12.96

1350

13.36

10.59

11.50

11.51

86

74

80

70

8.2 XCF Automatic Suction Pneumatic Mechanical Agitation …

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The clean water test shows that when the peripheral speed of the rotor of the XCF-24 flotation machine is 7.5 m/s. When the aeration rate of the flotation machine reaches 1.2 ~ 1.5 m3 /(m2 min), the aeration dispersion is good, the pulp level is stable, and the power consumption is within the design scope. B.

Pulp tests

To investigate the separation performance of the flotation machine, a 4-month industrial test investigation was carried out. The first 2 months were for the debugging stage, the second 2 months were for the production stage and table gives a comparison of investigation indexes (Tables 8.23 and 8.24). The debugging index of the XCF/KYF-24 flotation machine presents an upward trend month by month. As for the indexes in the production stage, the grade of coarse ores and concentrates was improved by 3.91%, the rougher recovery rate was improved by 0.9% and the total theoretical recovery rate was improved by 1.07%. All the indexes met the design requirements. Table 8.23 Statistics of indexes of XCF/KYF-24 flotation machine Time

Raw ore grade %

Grade of coarse Raw ore grade ores and % concentrates (%)

Rougher recovery rate (%)

Concentration recovery rate (%)

April

0.131

7.55

0.0135

89.63

96.38

May

0.133

9.88

0.0137

89.72

97.76

June

0.118

9.48

0.0107

90.95

98.32

July

0.119

9.49

0.0106

91.06

98.36

Total

0.125

9.06

0.0121

90.58

97.71

Table 8.24 Statistics of indexes of A-type flotation machine Time

Raw ore grade %

Grade of coarse Raw ore grade ores and % concentrates (%)

Rougher recovery rate (%)

Concentration recovery rate (%)

April

0.133

6.37

0.0141

89.34

98.06

May

0.131

6.74

0.0137

89.59

98.25

June

0.121

6.25

0.0126

89.64

98.27

July

0.119

5.71

0.0112

90.59

98.01

Total

0.125

6.34

0.0128

89.79

98.15

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8.2.3.3 A.

Performance of the XCF-50 Flotation Machine

Dynamic test

The XCF-50 flotation machine is taken as the testing object and tested in terms of its flotation dynamics in clean water, mainly including the determination of related parameters such as aeration rate, degree of air dispersion and power. The results of the dynamic test on the XCF-50 pneumatic mechanical agitation flotation machine are shown in Table 8.25. The degree of air dispersion of the XCF-50 flotation machine is greater than 2.0 at 131 r/min, which meets the requirement of air dispersion. The aeration rate reaches 1.17 m3 /(m2 min)−1 , which meets the aeration rate required for conventional mineral separation, and the power consumption is relatively low. B.

Investigation of pulp sucking capacity

To investigate the pulp sucking capacity of the XCF-50 flotation machine, it is essential to examine and evaluate the volume of pulp sucked into the flotation machine per unit time. When continuous and stable feeding and discharging volumes are maintained, the liquid level Hf of the feed box will be lower than the liquid level Hc in the tank of the flotation machine since the XCF-50 flotation machine has certain pulp sucking capacity, so there is a height difference Hc-Hf inside the flotation machine and the feed box. If the flotation machine is connected with the feed box, the pulp in the flotation machine will flow into the feed box at a certain flow rate under the action of the pressure difference Hc-Hf. This flow rate may be manually adjusted to maintain the pulp level in the feed box to be always in a constant state, and then the pulp sucking capacity of the flotation machine is equal to the feed plus the volume returned by the flotation machine to the feed box. The pulp sucking capacity of the XCF-50 flotation machine was actually examined and evaluated according to this scheme which indicated that the pulp sucking capacity of the XCF-50 flotation machine was greater than 12.8 m3 /min. The flotation machine has a stable liquid level and the good phenomenon of bubble scraping under this condition. Table 8.25 Dynamics test results of XCF-50 flotation machine Speed of flotation machine/r min−1

Mean aeration rate/m3 (m2 min) −1

Air dispersion

Current of flotation machine/A

1

136

1.22

1.63

143

2

131

1.17

2.07

152

3

126

1.15

1.71

150

8.2 XCF Automatic Suction Pneumatic Mechanical Agitation …

315

Fig. 8.47 XCF-70 automatic suction air-forced flotation machine

8.2.3.4

Performance of XCF-70 Flotation Machine

The XCF-70 flotation machine is an automatic suction pneumatic mechanical agitation flotation machine with the largest volume in the world, which has been industrially applied in the Wunugetushan Concentrator, Phase II Project, China National Gold Group Co., Ltd., as shown in Fig. 8.47. The flotation machine runs smoothly, with stable liquid level and good air dispersion effect, and there is no fluctuation of the pulp level on the liquid surface. In addition, the flotation machine has sufficient pulp sucking capacity, which meets the requirements of concentrator transformation and realizes the smooth flotation flow and qualified process indexes on the premise of no large-scale transformation of capital construction.

References 1. Zhengchang S (1996) Development of flotation machines in China in the past 15 years. Met Ore Dressing Abroad 4:18–19 2. Zhengchang S, Shuaixing S, Shijie L, Huilin L (2004) Development survey of flotation equipments, nonferrous metallurgical equipment. Supplements 21–26

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3. Liang Dianyin Wu, Jianming SZ, Shijie Lu (2002) New development of mineral processing equipment. Min Metall 7:12–15 4. Jonettis AJ (2001) Design, development, application and operation superiority of Outokumpu 100 m3 tankcell flotation machine. Met Ore Dressing Abroad 5:30–34 5. Oravaiyinia X (2002) Research and development of Outokumpu flotation machine. Met Ore Dressing Abroad 4:32–34 6. Outokumpumintee (1994) Theory research and practice of Outokumpu flotation. Nonferrous Mines (5):31–35 7. Burgess FL (1997) OK100 tank cell operation at Pasminco—broken hill. Miner Eng 7:723–741

Chapter 9

BGRIMM Wide-Size-Fraction Flotation Machine

With the large-scale mining of mineral resources, the change of resource endowments is one of the most important challenges in the mineral processing field, wherein the size distribution and size change of ores are one of new problems [1–3]. General minerals and wide-size-fraction minerals are shown in Fig. 9.1. The size fraction distribution of general minerals basically conforms to normal distribution conditions. Conventional-size-fraction minerals have high ratio, while coarse and fine minerals have low ratio. The design idea of traditional flotation equipment is mainly for recovery of conventional-size-fraction minerals. Since the recovery of coarse and fine (especially micro-fine) minerals is difficult, and the ratio is low, the recovery effect of traditional equipment is relatively poor, but not affecting the whole flotation indicators. As the ratio of coarse and fine minerals difficult to separate is significantly increased, and the ratio of conventional-size-fraction minerals is relatively reduced, the wide-size-fraction distribution is presented. Figure 9.2 shows pyrites distributed in wide-size-fraction under the microscope, wherein both coarse pyrites and sporadically distributed fine pyrites are very obvious. In the size fraction distribution of minerals, the separation performance of traditional flotation equipment is reduced and even fails to separate when coarse and fine minerals are increased. Therefore, it is necessary to research new equipment technology according to changes of mineral size fraction composition to realize efficient separation of resources. The separation demands for wide-size-fraction minerals are increased and are also consistent with the general background for comprehensive utilization of resources around the world. For example, in the re-concentration field of tailings, their mineral size fraction composition is different from primary ores. The wide-range comprehensive utilization of artificial minerals like refining furnace slag also proposes higher technical requirements for the separation technology of wide-size-fraction minerals. The difference of separation of coarse and fine mineral particles is visually shown in Fig. 9.3. The mineralization process of coarse minerals needs lower turbulence intensity in the flotation equipment so that bubbles are difficult to puncture and then fail to adhere in the collision process. Coarse minerals easily fall off after adhesion. In the transport area, it is hoped that the ascending distance of mineralized bubbles © Metallurgical Industry Press 2021 Z. Shen, Principles and Technologies of Flotation Machines, Springer Tracts in Mechanical Engineering, https://doi.org/10.1007/978-981-16-0332-7_9

317

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Fig. 9.1 Schematic diagram of general minerals and wide-size-fraction distribution of minerals

Fig. 9.2 Wide-size-fraction distribution of pyrite (microscope X260)

is small. In the separation area, it is hoped that the flow field works stably. However, compared with coarse minerals, in many aspects, the dynamics environment required for fine minerals needs higher kinetic energy to overcome the energy barrier in the adhesion process, and the agitation intensity in the agitating and mixing area needs to be higher. Because of the difficult falloff after adhesion, in order to make gangue minerals fall off, it is hoped that the transport distance of mineralized bubbles is lengthened properly and the turbulence intensity in the separation area is higher. In a manner of speaking, the dynamics environments required for coarse and fine minerals are opposite. It is very difficult to meanwhile realize efficient recovery.

9.1 Technology of Wide-Size-Fraction Flotation Machine

319

Fig. 9.3 The separation difference of coarse and fine particles

9.1 Technology of Wide-Size-Fraction Flotation Machine 9.1.1 Design Principle of Wide-Size-Fraction Flotation Machine The design principle of general flotation machines can be summarized as follows [4, 5]: (1)

(2) (3)

(4)

Ensure enough air supply in the flotation tank, and evenly disperse the air in the tank. Acquire moderate bubble size, and increase the collision and adhesion probability between mineral particles and bubbles. Ensure sufficient suspension of pulp. The agitation intensity in the agitating area shall be high, and the pulp circulation volume shall be large properly, so that the mineral particles can be suspended and the collision probability between bubbles and mineral particles can be increased. Build a relatively stable separation area and a steady froth area to reduce the falloff probability of mineral particles.

However, for separation and flotation equipment for coarse minerals, the following design principle shall be complied with: (1)

Larger air volume is required and larger bubbles shall be formed to bear larger floatation of mineral particles.

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9 BGRIMM Wide-Size-Fraction Flotation Machine

(2)

The input power shall be low, the agitation force of rotor to pulp shall be weak and the pulp turbulence intensity shall be low, to facilitate the collision mineralization and floatation between coarse minerals and bubbles. Ensure uniform air dispersion and sufficient particle suspension under low agitation force. The flotation machine shall be designed to shallow tank type to reduce the ascending distance of the mineralized bubbles of coarse minerals, and the separation area and froth area shall be more stable to reduce falloff.

(3) (4)

As mentioned earlier, there are contradictions between design principles of the flotation machines for minerals with different size fractions. In order to solve the above problem, on the basis of researching the mineralization behaviours of minerals with different size fractions, the idea of “differentiated separation” is proposed to solve the problem of simultaneous recovery of coarse and fine minerals, namely, building different dynamic zones in the same system to satisfy the mineralization of minerals with different size fractions. The conceptual design of wide-size-fraction flotation machine is shown in Fig. 9.4. For the separation problem of coarse minerals, establishing gas–liquid–solid threephase fluidization in the flotation machine and forming a separation area for coarse minerals characterized in low turbulence have been proposed in order to improve the recovery effect of coarse minerals. The rotor passes through the steady flow grid plate after agitation, and coarse particles will not fall back at a higher flow velocity

Fig. 9.4 The design philosophy of wide-size-fraction flotation machine

9.1 Technology of Wide-Size-Fraction Flotation Machine

321

inside the clearance of the grid plate and a higher upward flow velocity of coarse minerals, based on Bernoulli’s equation. Because of the choked flow of the grid plate, the turbulence intensity above the grid plate is greatly reduced, forming a low turbulent condition, which is easy for collision and adhesion between coarse minerals and bubbles. For the separation problem of fine minerals, the density gradient in the flotation machine is established, the selective circulation of mineral particles as per size fraction and mineralization is realized and a separation area for fine minerals characterized in high turbulence is formed. Circulation flow is formed due to internal and external dual design of the tank body, low density for large internal gas content, high density for small external gas content and pumping of the rotor. For fine minerals, the collision and adhesion probability is increased through multiple circulation flow in the rotor agitating area.

9.1.2 Working Principle and Structure of Wide-Size-Fraction Flotation Machine When the rotor of the flotation machine rotates, the low-pressure air (aeration or selfaerated) enters the spaces between rotor blades via the hole around the distributor. Meanwhile, the pulp below the false bottom is sucked into the spaces between rotor blades from the lower part of the rotor, fully mixed with air between rotor blades and discharged from the upper part of the rotor. Then, the discharged pulp–air mixture passes through the steady flow grid plate after stator current stabilization and enters the upper area in the tank. At this time, a large number of bubbles are contained in the pulp in the internal area in the flotation machine, while no bubbles (or very few bubbles) are contained in the pulp in the outer circulation channel so that a density difference is formed between the internal and external pulps. Under the actions of this density difference and rotor suction, the pulp and bubbles in the internal area rise, pass through the steady flow grid plate and bring unconventional-size-fraction minerals to the part above the steady flow grid plate at the set flow velocity, forming a suspended layer of coarse and heavy minerals. The mineralized bubbles and the pulp containing fine mineral particles continue to rise. The mineralized bubbles rise to the liquid surface so that a froth layer is formed, while the pulp containing fine mineral particles enters the rotor area via the circulation channel after passing through the baffle plate for recirculation [6].

9.1.2.1 A.

Tank Body

Structure and characteristics of the tank body

The tank body design of wide-size-fraction flotation machine is shown in Fig. 9.5. The tank body consists of internal and external circulation channels, internal area and false bottom. The internal area is divided into upper and lower areas through the

322

9 BGRIMM Wide-Size-Fraction Flotation Machine

Fig. 9.5 Tank design (1. External circulation channel; 2. Small area in the tank; 3. Upper area in the tank; 4. Internal circulation channel; 5. Steady flow grid plate; 6. Short-circuit circulation hole; 7. False bottom)

grid plate. The internal and external circulation channels and the false bottom form the internal and external pulp circulation circuits, and short-circuit circulation holes are, respectively, designed between the lower area in the tank and the internal and external circulation channels. The tank body design can satisfy the requirements for wide-size-fraction flotation. (1) The tank body includes aeration area (internal area) and non-aeration area (internal and external circulation channels), wherein the density difference between such two areas can be used to increase the pulp circulation in the tank to ensure the suspension of coarse minerals and reduce the agitation intensity of rotor. (2) Larger ascending flow consistent with the ascending direction of mineralized bubbles is produced in the internal area, reducing falloff, shortening the ascending time of mineralized bubbles and ensuring fast discharge of mineralized bubbles. (3) The flow velocity passing through the steady flow grid plate is increased due to the design of the steady flow grid plate, thus forming a coarse particle fluidization above the steady flow grid plate, keeping the coarse minerals at the shallow tank state, and producing a fluid dynamics condition suitable for flotation of coarse minerals in the upper area in the tank. (4) Fine particles are returned to the rotor area through the pulp circulation circuits of the circulation channels and the false bottom. The pulp turbulence intensity in the rotor agitating area is high, and the collision probability between bubbles and particles is high, which are beneficial to the flotation of conventional-size-fraction minerals and fine minerals. (5) The design of the short-circuit circulation holes of pulp can adjust the pulp circulation volume and ascending velocity of the steady flow grid plate so that mineral particles in the suspended layer can be regulated, meanwhile preventing the ore sand from blocking off the circulation channels during driving.

9.1 Technology of Wide-Size-Fraction Flotation Machine

B.

323

Parameter design of the tank body

Design parameters of tank body mainly include volume, length of tank, width of tank, area of circulation channels, height of false bottom, etc. (1)

Length, width and depth design of tank

The length of flotation tank may be initially determined through the following formula. The width size of tank is obtained by adding the length of tank to the width of the internal and external circulation channels. The depth of tank may be easily determined through geometric volume.  L=

n

V K

(9.1)

where L V K n (2)

length of tank (m); effective volume of tank; coefficient, 1.12 generally; length index of tank, between 2 and 3 generally, taking 2.7. Sectional area of circulation channels

Sectional area of circulation channels may be determined according to the pulp flow velocity in the channels and the pulp volume passing through the channels. S=

Q V

(9.2)

where S Q V (3)

sectional area of circulation channels (m3 ); pulp volume passing through the channels (m3 ); pulp flow velocity in the circulation channels (m/s). Height of false bottom

The false bottom is a part of the whole pulp circulation circuits. The minimum flow velocity in the false bottom shall not be less than the settling velocity of maximum particles, but shall not be too large either. Otherwise, it will result in severe wear. The sum between the pulp volume passing through the false bottom and that passing through the short-circuit circulation holes is the pulp circulation volume of rotor. The height of false bottom may be calculated through the following formula: H=

Q 0+ 2 × 60L V

(9.3)

324

9 BGRIMM Wide-Size-Fraction Flotation Machine

where Q V L

circulating pulp volume of rotor, as 2–3 times as the tank body volume generally (m3 /min); pulp flow velocity in the false bottom, greater than the settling velocity of maximum particles generally, and less than 1.5 (m/s); length of tank, (m).

9.1.2.2 A.

Steady Flow Grid Plate

Function and structure of the steady flow grid plate

The structure of steady flow grid plate was adopted in the fluidization flotation machine developed by the former Soviet Union at the earliest, and its function is as follows: (1) The ascending velocity of the pulp near the steady flow grid plate is greater than the specified settling velocity of maximum particles to form a suspended layer of coarse particles. Bubbles are connected and pass through the suspended layer of coarse particles. Multiple collisions are produced between coarse minerals and bubbles. Because of the consistent ascending direction between coarse minerals and bubbles, the collision and contact time between coarse minerals and bubbles is lengthened, and the adhesion probability is increased. Since mineralized bubbles have been close to the froth area when rising to the suspended layer, the ascending distance is short and the coarse particles are at the shallow tank flotation state. (2) The steady flow grid plate can reduce the turbulence in the upper area in the tank, build a more stable separation area and froth area, and reduce the falloff probability. (3) Since coarse particles are in the suspended layer, the pulp density returned to the rotor area is low and the size is fine, the equipment wear may be reduced and the aeration performance may be improved, which creates favourable conditions for the flotation of conventional-size-fraction minerals. B.

Selection and calculation of structural parameters of the steady flow grid plate

There are mainly two structural parameters of steady flow grid plate: channel width between grid plates and total area of channels. Generally, the channel width between grid plates need to ensure no blocking of sundries such as chips and rubber during mineral separation, and the channel width is designed as 30–35 mm industrially. The total area design of steady flow grid plate is a relatively complex problem, involving industrial parameters, operation parameters, etc. If the velocity of the pulp and air mixture passing through the clearance between grid plates is V 1 , the settling velocity of coarse minerals with upper limit size in the processed minerals is V 1 , the velocity of the pulp and air mixture passing through the cross section of the upper area in the tank is V 2 and the settling velocity of lower limit particles of the coarse machine in the processed minerals is V 2 , then the condition required for forming suspended layer on the grid plate is V1 > V1

(9.4)

9.1 Technology of Wide-Size-Fraction Flotation Machine

V2 < V2

9.1.2.3

325

(9.5)

Rotor

Rotor is a core of the flotation machine. For the wide-size-fraction flotation machine, the rotor shall have larger pulp circulation capacity, stronger air dispersion capacity and appropriate agitation intensity. According to the design theory of centrifugal pump, the backward-inclined rotor of the centrifugal pump has characteristics of low head and large discharge. In aspect of rotor form, in the low specific speed, medium specific speed and high specific speed, the characteristics such as large discharge and low head of high and low specific speed rotors are suitable for wide-size-fraction flotation machine. The structure form of rotor is shown in Fig. 9.6. Rotor parameters mainly include rotor diameter, pulp inlet diameter, blade height, blade inclination, etc. Specific parameter design of the rotor is a complicated process. It may be finally determined only after going through laboratory test research, simulation research, commercial test verification and other complete set of development process. BGRIMM developed the CLF air-forced wide-size-fraction flotation equipment and CGF self-aerated and pulp-induced wide-size-fraction flotation equipment on the basis of conceptual design of wide-size-fraction flotation, and both of them have been widely applied.

9.2 CLF Air-Forced Wide-Size-Fraction Flotation Machine The CLF flotation machine is a pneumatic wide-size-fraction flotation machine developed by BGRIMM [7]. Based on the research on flotation dynamics theory, for

Fig. 9.6 The structure of rotor

326

9 BGRIMM Wide-Size-Fraction Flotation Machine

working conditions such as large ratio, high selected pulp density and easy sediment, through massive exploration about special fluid dynamics environment in the tank required for separation, this machine has performed deep research on the collision, adhesion, falloff and other process between coarse and heavy minerals in the flotation tank and bubbles and on the reasons affecting these processes, and determined the fluid dynamics environment requirement of improving the recovery rate of coarse and heavy minerals.

9.2.1 Working Principle and Key Structures The CLF flotation machine adopts the new rotor, stator system and brand new pulp circulation mode, wherein it adopts the rotor with backward leaning blades featuring the high specific speed, the lower blade shape is designed to be consistent with the flow line of pulp passing through the rotor blades, the agitation force is weak and it ensures that pulp internally circulates along the specified channel at a lower rotor speed. The upper pulp downward flows to the lower part of the false bottom via the circulation channel, enters the rotor area under the actions of the density difference produced between aeration area and non-aeration area and the rotor suction, then passes through the grid plate and forms a suspended layer above the steady flow grid plate. Coarse minerals can be suspended above the steady flow grid plate. The steady flow grid plate shortens the ascending distance of the mineralized bubbles of coarse minerals, makes coarse minerals in the shallow tank flotation state and reduces the turbulence of pulp in the upper area in the tank. A stable separation area and a froth layer are built. This kind of pulp circulation mode creates good fluid dynamic conditions for mineralized bubbles ascended and transported to the froth layer; improves the load capacity of mineralized bubbles and the size of floated fine mineral particles and ensures lower pulp density, fine size and low power consumption returned to the rotor area. For the collision, adhesion and falloff processes between coarse and heavy mineral particles and bubbles in the flotation machine, combining with the characteristics of high flotation density, large ratio and concentrated distribution at both ends of coarse and fine particles, a closed stator system with medium specific speed and high gradient rotor and lower disc is studied, a strong orientated circulating flow can be formed in the tank, the circulation volume is large, the aeration rate of the flotation machine is large and the suspension capacity of mineral particles is strong. The innovative tank body structure design with multiple circulation channels and steady flow grid plate forms a suspended layer of coarse and heavy minerals on the middle and upper parts of the flotation machine, adds the opportunity of effective adhesion of mineralized bubbles in coarse and heavy minerals, and stabilizes the froth layer without fluctuation and sediment.

9.2 CLF Air-Forced Wide-Size-Fraction Flotation Machine

327

It is characterized in that 1.

2.

3. 4. (1)

Steady flow grid plate can form a suspended layer of coarse and heavy minerals on the middle and upper parts of the flotation machine, so that coarse and heavy mineral particles are in a relatively shallow tank state. Multiple circulation channels can form strong orientated circulating flow in the tank, and the circulation volume is large, adding the opportunities of minerals adhered and mineralized to bubbles. Short-circuit circulation holes that may be adjusted according to material properties are designed, strengthening the applicability. Rotor is designed to medium specific speed, stator is lower disc closed type and the suspension capacity of mineral particles is strong. Design of tank body

The tank body design of wide-size-fraction flotation machine is shown in Fig. 9.7. This tank body consists of internal and external circulation channels and false bottom. The internal area is divided into upper and lower areas through the steady flow grid plate. The internal and external circulation channels and the false bottom form two pulp circulation circuits, short-circuit circulation holes are, respectively, designed between the lower area in the tank and the internal and external circulation channels, and short-circuit circulation holes can be adjusted. An appropriate circulation hole is arranged on the tank side plate. 1.

The tank body is divided into aeration area and non-aeration area, wherein the pressure difference produced between pulp in such two areas can be used to increase the pulp circulation volume in the tank to ensure sufficient suspension of large ratio minerals, achieve reduced agitation intensity of rotor and solve the contradiction between weak agitation intensity and easy sediment required by large ratio minerals.

Baffle Steady Circulation

Circulation

Fig. 9.7 The tank of wide-size-fraction flotation machine

328

2.

3.

4.

(2)

9 BGRIMM Wide-Size-Fraction Flotation Machine

An ascending flow consistent with the ascending direction of mineralized bubbles can be produced in the internal area to reduce the falloff force of coarse and heavy minerals adhered to bubbles and shorten the ascending time of mineralized bubbles. A part of fine particles are returned to the rotor area through multiple circulation channels. Because of the pulp circulation circuit of the false bottom, the pulp turbulence intensity in the rotor agitating area is high, and the collision probability between bubbles and mineral particles of this part of particles is high, which are beneficial to the improvement for the flotation effect of conventional minerals. The design of the short-circuit circulation holes of pulp can adjust the pulp volume and ascending velocity passing through the steady flow grid plate, so that the ratio and size range of minerals in the suspended layer can be adjusted, and the scope of application of the flotation machine can be expanded. Meanwhile, short-circuit circulation holes can prevent the ore sedimentation from blocking off the circulation channel during driving and starting. Rotor–stator system

Rotor is the most important component of mechanical agitation flotation machine; it bears the functions of pulp agitation, pulp calculation and air dispersion, and its structure is shown in Fig. 9.8. The following problems are mainly considered in the rotor design of flotation machine: 1.

2.

The agitation intensity shall be moderate, while shall not cause larger velocity head in the tank. It is because a large velocity head will result in instable separation area and fluctuated liquid level, affecting bubble mineralization, reducing recovery of useful minerals, meanwhile adding unnecessary power consumption. The rotor with backward leaning blades featuring the medium specific speed shall be adopted, with large discharge and low head. The circulation volume of

Rotor Stator Air

Fig. 9.8 The rotor and stator of the CLF wide-size-fraction flotation machine

9.2 CLF Air-Forced Wide-Size-Fraction Flotation Machine

3. 4. 5.

(3)

329

pulp passing through the rotor shall be large, which is beneficial to the suspension of mineral particles, air dispersion and improvement for separation indicator. The flow streamline of pulp in the rotor shall be reasonable, and the wear shall be slight and uniform. The structure shall be reasonable, structure shall be simple and power consumption shall be low. The velocity gradient and the combined effect between rotor and stator shall produce radial high gradient velocity field, which is beneficial to bubble dispersion and recovery of fine particles. Design of steady flow grid plate

The steady flow grid plate is used in the wide-size-fraction flotation machine. As shown in Fig. 9.9, a similar device has been adopted in the fluidization flotation machine developed by the former Soviet Union. The steady flow grid plate mainly has the following functions: 1.

2.

Increase the velocity of the ascending ore current passing through the steady flow grid plate. In other words, the ascending velocity of the pulp near the steady flow grid plate is greater than the set settling velocity of the coarsest and heaviest particles to ensure that a suspended layer of coarse and heavy minerals is formed on the steady flow grid plate. Bubbles collide against coarse and heavy minerals repeatedly when continuously passing through the suspended layer of coarse and heavy minerals. Since the ascending direction of coarse and heavy minerals is consistent with bubbles, the collision and contact time between coarse and heavy minerals and bubbles is lengthened so that it is close to the induction time, thus adding the effective adhesion probability between coarse and heavy minerals and bubbles. However, because mineralized bubbles have been close to the froth area when rising to the suspended layer, the distance of the bubbles adhered with coarse and heavy minerals ascending to the froth area is short, so that coarse and heavy minerals are at the shallow tank flotation state. Steady flow grid plate can reduce the turbulence in the upper area in the tank, form a suspended layer of coarse and heavy minerals, keep coarse and heavy

Steady flow grid plate

Fig. 9.9 The steady flow grid plate

330

3.

9 BGRIMM Wide-Size-Fraction Flotation Machine

minerals in shallow tank state, shorten the ascending distance of mineralized bubbles and build a stable separation area and froth layer, reducing the possibility of mineral particles falling off from bubbles. Since coarse and heavy minerals stay in the suspended layer, the pulp density returned to the rotor area is low and the size is fine, which does not reduce the wear of rotor and stator, reduce power consumption, but also create favourable conditions for the flotation of conventional minerals.

Steady flow grid plate of wide-size-fraction flotation machine is made of steel angles that are separated uniformly and arranged horizontally, and is detachable to facilitate maintenance and replacement of the rotor, stator and other parts and components. At present, the CLF flotation machine has many specifications such as 2, 4, 8, 16 and 40 m3 , and its technical parameters are shown in Table 9.1.

9.2.2 Performance of CLF-8 Flotation Machine The flotation kinetics test of the CLF-8 flotation machine is carried out in the pulp, in which relevant parameters such as the aeration rate, air dispersion degree, speed, power, air holdup, etc. are mainly determined. See Table 9.2 for the test results of flotation machine dynamics. In addition, because the aeration rate used for flotation machine cannot represent the maximum aeration rate of the flotation machine during production, the results of the maximum aeration rate test of the flotation machine that is performed in clean water before factory shall be listed in Table 9.3. Table 9.1 Technical parameters of CLF flotation machine Specification

Effective volume (m3 )

Installed power (kW)

Minimum inlet air pressure (kPa)

Aeration rate (m3 /m2 min−1 )

CLF-2

2

7.5/5.5

>14.7

0.05–1.4

CLF-4

4

15/11

>19.6

0.05–1.4

CLF-8

8

22/15

>23.5

0.05–1.4

CLF-16

16

45/37

>35

0.05–1.4

CLF-40

40

75/55

>42

0.05–1.4

Table 9.2 Test results of dynamics in the pulp of the flotation machine with volume of 8 m3 Flotation machine operation Aeration rate (m3 /m2 min−1 )

Concentration III—2 Concentration II—2 Concentration I—2 0.59

0.62

0.68 4.86

Air dispersion

4.14

4.53

Motor power (kW)

9.5

10

Air holdup

13.33

15.03

9.5 16.95

9.2 CLF Air-Forced Wide-Size-Fraction Flotation Machine

331

Table 9.3 Test results of flotation machine dynamics in clean water Flotation machine with volume of 8 m3

Type of flotation machine Aeration rate

(m3 /m2

min−1 )

Air dispersion

0.66

1.08

1.37

1.81

4.16

4.27

3.68

2.89

air desparsion degrade

Test results of dynamics are shown in Figs. 9.10 and 9.11, and show that with the increased aeration rate, the air dispersion is increased and then reduced. If the air dispersion of the CLF-8 flotation machine is also above 4, and the maximum aeration rate is about 1.8 m3 /m2 min−1 , it will certify that the aeration rate of this machine is large, the air dispersion is uniform and the aeration performance is superior to the common flotation machines, meeting the flotation requirement of refining furnace slag and other coarse and heavy particles. In order to investigate the suspension capacity of pulp, the distribution and density of mineral particles of different depths in the flotation machine are determined. The distance of the steady flow grid plate of the CLF-8 flotation machine from the overflow weir is 1.25 m. Take a point below and nearby the steady flow grid plate, respectively, to measure whether a suspended layer is formed above the steady flow grid plate. Therefore, the CLF-8 flotation machine shall be sampled on 4 pulp layers with 0.5, 0.8, 1.1 and 1.4 m away from the lower part of the overflow weir, and subject to screening and grade analysis. See Table 9.4 for analysis results. Most metals are distributed at two sizes, −200 to +325 and −400, up to above 70%. The content of such two sizes is less at 0.5 and 1.4 m, while is more at 0.8 and 1.1 m. However, for general flotation machines, the content of each size shall be linearly decreased from the tank bottom to the top. This certifies that a suspended layer is formed above the steady flow grid plate of flotation machine, which is beneficial 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 0.58

0.60

0.62

0.64

0.66

0.68

0.70

air flow rate( m3 /m2.min) Fig. 9.10 The relationship between air dispersion degrade and air superficial velocity in 8 m3 flotation machine

332

9 BGRIMM Wide-Size-Fraction Flotation Machine 17.0 16.5

air holdup(%)

16.0 15.5 15.0 14.5 14.0 13.5 13.0 0.58

0.60

0.62

0.64

0.66

0.68

0.70

air flow rate( m3 /m2.min) Fig. 9.11 The relationship between air holdup degrade and air superficial velocity in 8 m3 flotation machine

to the flotation of minerals with large ratio and high density. The density of different depths in the tank also reflects this point.

9.2.3 Performance of CLF-40 Flotation Machine 9.2.3.1

Dynamics Performance

The flotation kinetics test of the 40 m3 CLF flotation machine is carried out in the pulp, in which relevant parameters such as the aeration rate, air dispersion degree, speed, power, air holdup, etc. are mainly determined. See Table 9.5 for the test results of flotation machine dynamics. In addition, because the aeration rate used for flotation machine cannot represent the maximum aeration rate of the flotation machine during production, the results of the maximum aeration rate test of the flotation machine that is performed in clean water before factory shall be listed in Table 9.6. Test results of dynamics are shown in Figs. 9.12 and 9.13, and show that with the increased aeration rate, the air dispersion is increased and then reduced. When the aeration rate of the CLF-40 flotation machine with ores is up to 1.64 m3 /m2 min−1 , if the air dispersion is also 3.51 and the maximum aeration rate is about 1.8 m3 /m2 min−1 , it will certify that the aeration rate of this machine is large, the air dispersion is uniform and the aeration performance is superior to general flotation machines, meeting the flotation requirement of refining furnace slag and other coarse and heavy particles.

Density (%)

44.45

49.77

63.81

59.06

Depth (m)

0.5

0.8

1.1

1.4

16

8

6.5

5

15.13

10.61

8.44

6.21

23.5

26.5

24.5

21

Weight percent

30.42

39.1

39.55

32.74

Metal distribution rate

−200 to +325

Weight percent

Metal distribution rate

+200

Size fraction (mm)

Table 9.4 Test results of pulp suspension capacity of the flotation machine with volume of 8 m3

18

5.5

8.5

9.5

Weight percent

26.38

10.02

19.62

30.62

Metal distribution rate

−325 to +400

52.5

60

60.5

65.5

Weight percent

−400

28.07

40.27

32.38

30.43

Metal distribution rate

9.2 CLF Air-Forced Wide-Size-Fraction Flotation Machine 333

334

9 BGRIMM Wide-Size-Fraction Flotation Machine

Table 9.5 Test results of dynamics in the pulp of the flotation machine with volume of 40 m3 Flotation machine operation

Scavenging III—1

Scavenging II—1

Roughing II—1

Roughing I

Aeration rate (m3 /m2 min−1 )

1.03

1.19

1.52

1.64

Air dispersion

5.83

6.25

4.58

3.51

Motor power (kw)

45.5

51.5

51

45

Air holdup

12.40

15.20

17.13

16.35

Table 9.6 Test results of flotation machine dynamics in clean water Flotation machine with volume of 40 m3

Type of flotation machine Aeration rate (m3 /m2 min−1 )

0.61

1.04

1.31

1.76

Air dispersion

4.67

5.61

3.61

2.72

6.5

air despersion degrade

6.0 5.5 5.0 4.5 4.0 3.5 1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

air flow rate( m3 /m2.min) Fig. 9.12 The relationship between air dispersion degrade and air superficial velocity in 40 m3 flotation machine

Under different aeration rate conditions, the power consumptions of the flotation machine have no larger difference, which does not conform to the rule that the power consumption of flotation machine is reduced with the increased aeration rate in the previous clean test. The reason is that the selected densities of different flotation operations are varied. With the flotation process, all the flotation densities of the next operation are lower than the previous flotation operations, and the required aeration rate is also lower than the previous flotation operations, while the power consumption of flotation machine is reduced with the reduced flotation density.

9.2 CLF Air-Forced Wide-Size-Fraction Flotation Machine

335

18

airholdup(%)

17 16 15 14 13 12

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

air flow rate( m3 /m2.min)

Fig. 9.13 The relationship between air holdup and air superficial velocity in 40 m3 flotation machine

In order to investigate the suspension capacity of pulp, the distribution and density of mineral particles of different depths in the flotation machine are determined. The distance of the grid plate of the 40 m3 flotation machine from the overflow weir is 2.15 m. Take a point below and nearby the steady flow grid plate, respectively, to measure whether a suspended layer is formed above the steady flow grid plate. Therefore, the CLF-40 flotation machine shall be sampled on 5 pulp layers with 0.5, 1.0, 1.5, 2.0 and 2.4 m away from the lower part of the overflow weir, and subject to screening and grade analysis. See Table 9.7 for analysis results. It can be seen that most metals are distributed at two sizes, −200 to +325 and − 400, up to above 70%. The content of such two sizes is less at 0.5 and 2.4 m, while is more at 1.0, 1.5 and 2.0 m. However, for general flotation machines, the content of each size shall be slightly decreased from the tank bottom to the top. This certifies that a suspended layer is formed above the grid plate of flotation machine, which is beneficial to the flotation of minerals with large ratio and high density. The density of different depths in the tank also reflects this point.

9.2.3.2

Process Indicators

The CLF-40 flotation machine has gone into operation since November 2005 and entered the production test stage after the process debugging and equipment debugging stages. In Table 9.8, the indicators of production test stage are accumulated and compared with the expectations. Results show that the obtained concentrate is higher than 2.31%, the tailing grade is higher than 0.16% and the recovery rate is higher than 0.79% under the equivalent raw ore grade.

Density (%)

54.01

52.73

59.06

75.89

70.39

Depth (m)

0.5

1.0

1.5

2.0

2.4

17.5

7.5

6

5.5

2.5

25.98

11.83

8.04

8.58

4.26

19

24.5

25.5

20

21

22.18

35.66

37.99

32.29

29.63

Metal distribution rate

Weight percent

Weight percent

Metal distribution rate

−200 to +325

+200

Size fraction (mm)

Table 9.7 Test results of pulp suspension capacity of the flotation machine with volume of 40 m3

13

8.0

6.5

8.5

6

Weight percent

19.05

10.67

11.96

15.70

19.22

Metal distribution rate

−325 to +400

50.5

60.0

62

66

70.5

Weight percent

−400

32.80

41.84

42.02

43.43

46.88

Metal distribution rate

336 9 BGRIMM Wide-Size-Fraction Flotation Machine

9.3 CGF Automatic Suction Wide-Size-Fraction Flotation Machine

337

Table 9.8 Indicator comparison Raw ore grade (%) Concentrate grade Tailings grade (%) Recovery (%) (%) Accumulated indicators of production test

2.32

27.18

0.4

83.93

Expectations

2.04

24.87

0.37

83.14

Production 0.28 test—expectations

2.31

0.16

0.79

9.3 CGF Automatic Suction Wide-Size-Fraction Flotation Machine The CGF mechanical agitation flotation machine is a high-efficiency, energy-saving, self-aerated and pulp-induced flotation machine developed by BGRIMM, and can be widely used for separation of precious metals, non-ferrous metals, ferrous metals and non-metallic coarse and heavy minerals.

9.3.1 Key Structure and Working Principle The CGF flotation machine mainly consists of a tank body, a rotor, a stator, a central cylinder, a suction pipe, a steady flow grid plate, etc. The tank body consists of internal and external circulation channels, a steady flow grid plate and a false bottom. The multiple circulation channels allow fine minerals to collide with bubbles repeatedly, realizing the wide-size-fraction recovery. The central cylinder and suction pipe are important components which can self-suck air and pulp of the CGF wide-size-fraction flotation machine.

9.3.1.1

Working Principle

The CGF flotation machine adopts the rotor comprising a separating plate, an upper blade and a lower blade, which can ensure sufficient suspension of mineral particles and sufficient separation of bubbles in all the pulp while sucking air, meanwhile adopting the stator with angle blade. The radial clearance between the stator and the rotor is larger. The pulp circulation area around the lower area of the stator is large, which can eliminate the unnecessary interference of the parts in lower tank and reduce the power consumption. The pulp–air mixture thrown out from the rotor can smoothly enter the pulp so that the air can be dispersed well, as shown in Fig. 9.14.

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Fig. 9.14 The self-aerated CGF wide-size-fraction flotation machine

A.

Key structures

(1)

Structure of tank body

In order to meet the separation requirement of wide-size-fraction minerals, on the basis of fully researching the advantages and disadvantages of the existing flotation machine tank body, the tank body of CGF wide-size-fraction flotation machine is designed as shown in Fig. 9.15, basically consistent with the CLF flotation machine. The tank body consists of internal and external circulation channels, internal area and false bottom. The internal area is divided into upper and lower areas through the grid plate. The internal and external circulation channels and the false bottom Fig. 9.15 The tank of the CGF flotation cell (1. False bottom; 2. Lower area in the tank; 3. External circulation channel; 4. Steady flow grid plate; 5. Upper area in the tank; 6. Internal circulation channel; 7. Circulation hole; 8. Short-circuit circulation hole)

4

5

3

6 7

2

8 1

9.3 CGF Automatic Suction Wide-Size-Fraction Flotation Machine

339

form two pulp circulation circuits, short-circuit circulation holes are, respectively, designed between the lower area in the tank and the internal and external circulation channels, and short-circuit circulation holes can be adjusted. The tilting plate above the external circulation channel can play the role of pushing the froth board to drive the froth to move to the overflow weir. An appropriate circulation hole is arranged on the tank side plate. (2)

Rotor stator system

In most mechanical agitation flotation machines, the bubbles adhered with mineral particles account for 30–55% only of total, which is caused due to height turbulence of pulp in the tank. All of these directly lead to reduced unit volume production capacity of the flotation machine and difficult flotation of large-particle minerals. Therefore, the CGF wide-size-fraction flotation machine is required to suck air and circulate pump. For this purpose, the rotor comprising a separating plate, an upper blade and a lower blade is adopted, as shown in Fig. 9.16. It can ensure sufficient suspension of mineral particles and sufficient separation of bubbles in all the pulp while sucking air, so that there is higher flotation probability in the flotation tank, meeting the process requirement of wide-size-fraction flotation. The CGF wide-size-fraction flotation machine is provided with a stator with corner blades. The radial clearance between the stator and rotor is large; the pulp at the periphery of the lower part of the stator can flow over a large area in order to eliminate the unnecessary disturbance against pulp by the lower parts, reduce the power consumption and enhance the circulation and suspension of solid particles in the lower circulation area of the tank. The mixture of pulp and air that is thrown out from the rotor may enter the pulp smoothly to make the air disperse properly. The rotor–stator equipment of CGF wide-size-fraction flotation machine is shown in Fig. 9.17. (3)

Central cylinder and suction pipe

The central cylinder is a key component of the CGF wide-size-fraction flotation machine to achieve the function of self-suction and pulp suction. In the flotation process, both the feeding and middling are sucked into the upper rotor chamber Fig. 9.16 The rotor of the CGF flotation cell

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Fig. 9.17 The rotor and stator of the CGF flotation cell

Fig. 9.18 The central cylinder of the CGF flotation cell

through the feeding pipe and middling pipe on the central cylinder; diameters of the feeding pipe and middling pipe can meet the requirements for the processing capacity of the flotation machine, as shown in Fig. 9.18. The suction pipe is the passage for air to enter into the rotor of the flotation machine; the inner diameter of the suction pipe not only affects the suction rate of the flotation machine, but also affects the power consumption of the flotation machine. A variety of factors should be analysed comprehensively in order to determine the inner diameter of the suction pipe, including the vacuum degree to be achieved by the rotor of the flotation machine, air amount required in the flotation process, etc. In the serialization process of CGF wide-size-fraction flotation machine, the vacuum degree that can be achieved by the flotation machine is basically consistent; it is assumed that the velocity of the air is the same in the suction pipe and the inner diameter of the suction pipe is calculated based on the required suction rate, upon the consideration of installing a butterfly valve on the upper end of the suction pipe to control the air amount of the flotation machine in the industrial production, the

9.3 CGF Automatic Suction Wide-Size-Fraction Flotation Machine

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Fig. 9.19 The suction pipe of the CGF flotation cell

inner diameter of the suction pipe should be amplified appropriately. The suction pipe of CGF wide-size-fraction flotation machine is shown in Fig. 9.19. (4)

Steady flow grid plate

Steady flow grid plate is used in the CGF wide-size-fraction flotation machine, similar to the steady flow grid plate adopted in the CLF flotation machine. The similar device has been adopted in the fluidization flotation machine developed by the former Soviet Union. Steady flow grid plate of CGF wide-size-fraction flotation machine is made of steel angles, which are separated uniformly and arranged horizontally, and is detachable to facilitate maintenance and replacement of the rotor, stator, feeding pipe, middlings pipe and other parts and components. At present, the CGF flotation machine has many specifications of 1–40 m3 , and its technical parameters are shown in Table 9.9.

9.3.2 Dynamic Performance of CGF Flotation Machine 9.3.2.1

Dynamic Performance

To investigate the performance of the CGF-2 wide-size-fraction flotation machine, the dynamic parameters of the flotation machine were measured under the clean water condition, mainly including the suction rate, the degree of air dispersion, power, air holdup, bubble diameter, etc. See Table 9.10 for test results.

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Table 9.9 Technical parameters of CGF flotation machine Specification

Effective volume (m3 )

Installed power (kW)

Suction rate (m3 /m2 min−1 )

CGF-1

1

5.5

1.0

CGF-2

2

7.5

1.0

CGF-4

4

22

1.0

CGF-8

8

30

1.0

CGF-10

10

37

1.0

CGF-16

16

55

1.0

CGF-40

40

90/110

1.0

Table 9.10 Measurement results of dynamic parameters of CGF-2 wide-size-fraction flotation machine Serial No.

Suction rate (m3 /m2 min−1 )

Air dispersion

Motor power (kW)

Air holdup (%)

Bubble diameter (mm)

Bubble surface area flux (s−1 )

1

0.32

2.36

6.5

10.75

3.92

19.43

2

0.67

2.06

6.15

16.12

6.72

23.73

3

0.83

2.47

5.81

18.31

7.26

27.21

4

0.88

2.08

6.42

19.12

8.91

23.51

5

0.89

2.46

5.86

19.12

9.57

22.13

6

1.00

2.96

6.14

19.21

9.88

24.33

The relation between suction rate and air dispersion is shown in Fig. 9.20, the relation between suction rate and power consumption is shown in Fig. 9.21, the

Fig. 9.20 The relationship between self-aerated volume and air dispersion

9.3 CGF Automatic Suction Wide-Size-Fraction Flotation Machine

343

Fig. 9.21 The relationship between self-aerated volume and power consumption

relation between suction rate and air holdup is shown in Fig. 9.22 and the relation between suction rate and bubble diameter is shown in Fig. 9.23. As seen from Table 9.10 and Figs. 9.20, 9.21, 9.22 and 9.23, the air volume of CGF-2 wide-size-fraction flotation machine can be adjusted between 0.3 and 1.0 m3 /m2 min−1 , meeting the requirement of different flotation processes for air volume. All the air dispersion is greater than 2, which is good. The actual power consumption of the motor is about 85% and it is good. The minimum air holdup is 10.75%, meeting the requirement of flotation process for air volume. Under clean water conditions, the bubble diameter of the flotation machine is less than 10 mm,

Fig. 9.22 The relationship between self-aerated volume and air holdup

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Fig. 9.23 The relationship between self-aerated volume and air bubble diameters

and the bubble surface area flux is about 23.20/s. All the measured data show that the flotation dynamic parameters of CGF-2 wide-size-fraction flotation machine achieve the design requirement. In order to investigate the suspension capacity of pulp, the pulp density and the size distribution of different depths in the flotation machine are determined. Since the distance of the steady flow grid plate of the CGF-2 wide-size-fraction flotation machine from the overflow weir is 0.42 m, take a point below and nearby the steady flow grid plate, respectively, to measure whether a suspended layer of coarse particles is formed above the steady flow grid plate. Therefore, sample at 5 heights, i.e. 0.35, 0.50, 0.65, 0.80 and 0.95 m from the tank bottom of the flotation machine, and conduct size fraction and grade analysis. The sampling analysis results of deep tank of CGF-2 wide-size-fraction flotation machine are shown in Table 9.11, the variation curve of +0.212 mm particle content with the height from the tank bottom is shown in Fig. 9.24 and the variation curve of pump density with the height from the tank bottom is shown in Fig. 9.25. As seen from Fig. 9.24, the content of +0.212 mm particles above the steady flow grid plate has a sudden rise, the content below the steady flow grid plate is 48.58%, the content above the steady flow grid plate is increased to 51.51% and the up content is reduced to 50.30%. These characteristics show that a suspended layer of coarse particles is formed above the steady flow grid plate of CGF-2 wide-size-fraction flotation machine, which is beneficial to the flotation of coarse minerals.

Pulp concentration (%)

21.88

31.93

31.88

31.70

30.65

Height from the tank bottom (m)

0.95

0.80

0.65

0.50

0.35

14.31

15.15

14.08

14.14

3.07

28.79

27.89

27.94

26.85

10.42

34.27

36.36

36.22

35.35

25.61

44.09

45.56

46.95

46.22

50.25

Metal distribution rate

Weight percent

Weight percent

Metal distribution rate

−0.5 to +0.212

+0.5

Size fraction (mm)

42.33

41.41

37.22

32.32

59.43

Weight percent

22.84

23.26

20.40

20.45

35.34

Metal distribution rate

−0.212 to +0.1

Table 9.11 Test results of pulp suspension capacity of CGF-2 flotation machine

5.56

2.02

4.02

3.03

9.22

Weight percent

2.31

0.98

1.54

1.19

2.98

Metal distribution rate

−0.1 to +0.075

3.53

5.05

8.45

15.15

2.66

Weight percent

−0.075

1.97

2.31

3.16

5.30

1.00

Metal distribution rate

9.3 CGF Automatic Suction Wide-Size-Fraction Flotation Machine 345

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Fig. 9.24 The variation of the content of +0.212 mm with the distance away from tank bottom

Fig. 9.25 The variation of concentrator with the distance away from tank bottom

As seen from Fig. 9.25, the pump density in the flotation machine has a slight rise process above the steady flow grid plate. For the common flotation machines, the pulp density is gradually and slightly decreased from the tank bottom to the top, which further shows the existence of a suspended layer of coarse particles above the steady flow grid plate of CGF-2 wide-size-fraction flotation machine. As seen from Figs. 9.24 and 9.25, the CGF-2 wide-size-fraction flotation machine is free of sediment, most coarse particles focus on the middle part of the tank above the steady flow grid plate, while the pulp density is low and the size is fine in the rotor area. Therefore, it can be seen that the CGF-2 wide-size-fraction flotation machine adopts the steady flow grid plate, coordinates with general circulation of pulp and forms a suspended layer above the steady flow grid plate, meeting the separation of coarse and fine particles at the same time, and achieving the expected requirement of design.

9.3 CGF Automatic Suction Wide-Size-Fraction Flotation Machine

9.3.2.2

347

Process Indicators

In order to investigate the flotation indicators of CGF-2 wide-size-fraction flotation machine, statistics about production indicators of flotation operations in 4 months are conducted, as shown in Table 9.12. As seen from Table 9.12, after the flotation machine parameter and reagent system are optimized and adjusted, and after experiment, under the condition in which the raw ore grade of flotation is 1.37%, the concentrate grade of the CGF flotation cell is 3.78%, the tailing grade is 0.71% and the recovery rate of flotation operations is up to 59%. In order to investigate the separation of CGF-2 wide-size-fraction flotation machine for lepidolite better, the raw ores, concentrates and tailings of the overall process are subject to sampling analysis, and the size distribution and metal content distribution of each product are investigated. Results are shown in Table 9.13. It can be seen that the lithium in the concentrates and tailings is the same with that in the raw ore, mainly distributed in three size fractions, +0.5 mm, −0.5 to +0.212 mm and −0.212 to +0.1 mm. As seen from the recovery rate of each size fraction, all the recovery rates at size fractions of −0.5 to +0.212 mm, −0.212 to +0.1 mm and −0.1 to +0.075 mm are high, among which the recovery rate at −0.1+0.075 mm is the highest, up to 85.52%, and the total recovery rate is up to 73.61%, higher than 69.2% of the expected indicator. This shows that the CGF-2 wide-size-fraction flotation machine improves the separation of coarse minerals while ensuring the flotation of conventional size fraction. The wide-size-fraction flotation machine is developed to satisfy the change of mineral resource endowments, especially the flotation equipment technology developed with the increased ratio of coarse and fine particles. For different separation requirements for coarse and fine minerals, the wide-size-fraction flotation machine forms a unique design idea and technical solution, provides differentiated flotation dynamic environments for the recovery of coarse and fine minerals, obtains a good application effect in the engineering practice and has wide application prospects.

Table 9.12 Statistics about production indicators Month

Raw ore grade (%) Concentrate grade Tailings grade (%) Recovery (%) (%)

1 (debugging)

1.43

3.85

0.97

42.70

2 (debugging)

1.39

3.81

0.91

45.60

3 (debugging)

1.41

3.94

0.94

44.40

4 (industrial test) 1.37

3.78

0.71

59.00

Concentrate

0.65

0.53

1.39

Accumulative

0.96

−0.212 to +0.1

−0.075

1.65

−0.1 to +0.075

2.1

−0.5 to +0.212

100.00

17.07

7.03

26.10

34.14

15.66

6.92

0.45

0.23

1.25

2.81

1.64

100.00

7.07

3.57

19.59

44.04

25.72

4.34

1.3

2.58

4.56

4.94

4.47

Grade Weight Metal Metal Grade (%) (%) percent content distribution (%) (g) rate (%)

Raw ore

+0.5

Size fraction (mm)

Tailings

100.00

10.71

6.46

22.22

48.08

12.53

21.48

0.69

0.83

5.02

11.76

2.77

100.00

3.27

3.92

23.82

55.83

13.16

0.48

0.16

0.12

0.24

0.66

1.98

Weight Metal Metal Grade percent content distribution (%) (%) (g) rate (%)

Table 9.13 Size and grade analysis of raw ores, concentrates and tailings (lepidolite)

100.00

11.92

7.07

31.31

33.33

16.36

2.38

0.09

0.04

0.37

1.09

1.60

100.00

2.95

1.31

11.62

34.02

50.10

73.61

79.61

85.52

79.17

69.25

10.26

Recovery (%) Weight Metal Metal percent content distribution (%) (g) rate (%)

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References

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References 1. Zhengchang S (2012) Principle and technology of flotation machine. Metallurgical Industry Press, Beijing 2. Dianyin L, Jianming W, Zhengchang S et al (2002) New progress in mineral processing equipment. Min Metall 7:12–15 3. Zhengchang S, Shuaixing S, Shijie L et al (2004) Development survey of flotation equipment. Non-Ferrous Metall Equip S1:21–26 4. Shuaixing S, Yuejun Z, Dengfeng H et al (2013) The discuss of the sever problems of the configuration of the large flotation cell. Nonferrous Met S1:199–201 5. Qiang Z (2009) Overview of mineral processing. Metallurgical Industry Press, Beijing 6. Zhenchang S, Guizhi L, Shijie L et al (1999) The application and characteristics of the BGRIMM flotation cell. Nonferrous Met 6:31–33

Chapter 10

Process Control System of Flotation Machines

10.1 Development and Current Situation of Flotation Machine Control System The process control of flotation machines refers to a continuous monitoring and automatic control technology that is used to meet the production demands of concentrators, mainly including production safety, production benefit, product quality, environmental protection, etc. The method of implementing process control is achieved by participation and coordination of designers or field operators with suitable controllers, detection instruments and execution units as hardware basis [1]. The flotation process control is an important method used to improve the flotation efficiency. Since the 1940s, the process control technology of flotation machines has rapidly developed, substantially changing the adverse situation of traditional mineral separation technology lagging. According to the traditional mineral separation process, operators manually regulate the mineral separation variables depending on their experiences. The control on technological process is neither accurate nor timely, which causes production difficult to achieve ideal indicator and causes poor work environment [2]. The automatic detection technology can timely and effectively indicate the changes of mineral separation process parameters; it can timely, accurately and automatically adjust the flotation parameters according to the feedbacks. The application of such two technologies not only improves the mineral separation indicators, but also reduces the energy consumption, effectively improving the labour condition. According to statistics [3], the automation technology can improve equipment efficiency by 10–15% after being applied in concentrators, improve labour efficiency by 25–50% and reduce the production cost by 3–5%.

© Metallurgical Industry Press 2021 Z. Shen, Principles and Technologies of Flotation Machines, Springer Tracts in Mechanical Engineering, https://doi.org/10.1007/978-981-16-0332-7_10

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10.1.1 Early Development of Flotation Machine Process Control Technology at Home and Abroad In 1915, Professor Louis Ricketts in Princeton University has started using large mechanical equipment when designing Inspiration concentrator with daily capacity of 15,000 t/d, including feeder, belt conveyor, ball mill, flotation machine, hydrocyclone, sampler, etc. [4]. With improved technology, the adjustment to xanthates can adjust the content of copper sulphide in tailings when the amount of alkali in Inspiration concentrator is controlled within a certain range. However, when the type and grade of ores changes, the equipment cannot automatically give an alarm, they can be observed depending on field operators only. The process control system of Inspiration concentrator is conducive to stabilization of technological process and reduction of external disturbance, which is very important for the development of control system in flotation. Both detection and control levels of Inspiration concentrator were up to such a degree at that time. It seems incredible after 50 years. It brings far-reaching influence on development of automatic control technology of flotation. The process control system of flotation machines has been installed in many concentrators between 1918 and 1928, such as R&D project and laboratories in colleges and universities [5]. These projects gradually develop the flotation control performance from lagging to high efficiency, predictability and controllability. However, the on-line analyzer cannot rapidly indicate grade and recovery rate at that time, while the experienced operators can visually observe the advantages and disadvantages of flotation indicators. When indicators become poor, operators will timely change the dosage, height of liquid level or aeration rate to improve indicators. The National Mining Association, Steel Manufacturers Association and American Petroleum Institute organized a conference [6] about flotation development in Salt Lake City in 1927, and discussed this issue again in 1928. However, the economic crisis made flotation technology sluggish. For control, the immature flow detection technology was also a factor restricting its development at that time. During World War II, the development of control technology also drove the metallurgical industry, and some new sensors emerged. Such as pressure sensor, it not only can detect the liquid level of pulp, but also can calculate the density of pulp [7]. The electromagnetic flowmeter and density pressure gauge can measure the flow of pulp, and their main function is to detect the extracted ore tonnage of the mill, such as Duval Sierrita concentrator in Arizona. It is always a challenge to rapidly analyze the grade of raw ore or concentrate after sampling, until an X-ray fluorescence analyzer [8] was invented in Broken concentrator in 1956, greatly reducing the sampling analysis time. The original laboratory analysis time of 4 h is changed to half an hour, but this stage is just a transitional period for now minutes of current-carrying analysis technology. The Chinese mineral separation automation started after the late 1950s. It is also a process from simple to complicated [9]. Between the late 1950s and the mid-1970s, restricted by the on-line detection instrument and control technology at that time, the concentrators have mainly achieved single-loop and single parameter control or

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353

multi-loop control for process of flotation machines by means of analog meter. For example, in the 1960s, the feed control, pH value control and overflow concentration control developed by BGRIMM in the silver concentrator were the single-loop and single parameter control. Up to the 1970s, the emergence of large integrated circuits drove the development of flotation electrical equipment. Especially for current-carrying analyzer, large integrated circuits provide hardware help for it. The OSA system has encountered some physical and mechanical difficulties at the preliminary stage of development. However, these problems have been solved with the development of science and technology [10]. In 1970, all the on-line analyzer of concentrate, digital computer control system and other modern equipment appeared in concentrators, can control the flotation process better [11]. For design of some new concentrators, it is very common to first make an automatic control plan. Outokumpu in Finland develops rapidly in the automatic control field, and develops a current-carrying analyzer when exploiting low grade of iron pyrites in the Keretti mine [12]. The accuracy of the current-carrying analyzer is verified in Outokumpu’s other five concentrators, and then sold externally. The X-ray fluorescence current-carrying analysis system was successfully developed in Outokumpu’s laboratory in 1970, accelerating the development of the automatic control system in the flotation process. The centralized control room of concentrators emerged in the mid-1970s. Monitors can obtain the operation information of equipment in concentrators at far end, and can guide field operators remotely [13]. At that time, the computer configuration was very low with memory of 8 kB only, but it was sufficient to process the electric signal fed back from the equipment. The designers of flotation control program had a deeper understanding of flotation process while developing codes that can meet the control requirements, laying a solid foundation for the design of more efficient codes. From the late 1970s, the Chinese concentrators have started controlling some parameters of mineral separation by means of single board computers, e.g. BGRIMM cooperated with Bajiazi Lead–Zinc Ore to control the mineral separation process of flotation machines by means of TP2801 single board computer; Kunming Metallurgy Institute successfully adopted TP2801 single board computer for control in the Yimen copper mine concentrator. BGRIMM, Central South University of Technology and other units carried out direct digital control in the grinding grading process by means of domestic JS210 small computer. Anhui Tongling Dongguashan concentrator adopted Finland’s Pmscon20/200 computer control system, Jiangxi Yongping Copper Mine introduced a computer control system from U.S., and all of them played facilitation function on the development of flotation process automation [14].

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10.1.2 Process Control Situation of Flotation Machines at Home and Abroad Now the automation integration degree of concentrators also becomes higher and higher, wherein the control system of flotation machines is also divided into three different levels according to complexity, hardware requirement and performance, as shown below successively: (1) Stable control; (2) Supervisory control; (3) Optimal control. 1.

Stable control

The control loops of flotation machines mainly include pulp level control, aeration rate control and reagent addition volume control of flotation machines, etc. For each single-loop control, operators can keep automatic variables at set values as long as inputting individual set values only. All programs of control loops are executed in one process controller, and the PID control algorithm is used in each control loop [15]. The early automatic flotation control includes one or two PID control loops, while the current DCS system may include hundreds of PID loops. A good adjustable controller can stabilize the pulp at the set position. For example, the liquid level will rise when the flow of pulp is increased suddenly, at this time, the valve of this operation will open wide to keep the set liquid level, which will cause increased feeding quantity of next operation. Since this kind of interference will spread from one tank wave to the other tank, the stability adjustment of the whole system will take a while. For accurate pulp level control, now the supervisory control system or other more flexible and efficient modern control strategies can be adopted. The Century concentrator in Australia has the largest flotation process control system [16] at that time, including 79 flotation machines with the volume of 200 m3 and 45 level control systems. In view of linkage relations between operations, singleloop PID control may be insufficient. Therefore, a new control algorithm is required to achieve pulp level control. 2.

Supervisory control

The supervisory control system means that the stable control loop can automatically adjust the set values so that all control loops act simultaneously to achieve optimal flotation loop performance [17]. These set values will be adjusted after compared with some performance indexes or control objectives according to the measured flotation efficiency. The supervisory control system as a higher level of control system can reduce many repeated operations of operators. For example, operators can observe the sampling result of lower tailings every five minutes by means of X-ray fluorescence analyzer, and set the current flotation parameters based on parameters such as dosage, aeration rate and liquid level of good indicators, in order to obtain better mineral separation indicators. Although this ensures the recovery rate, low grade of concentrate may be caused. The supervisory control fails to coordinate the associated influence between such two indicators. In order to solve this problem, the control

10.1 Development and Current Situation of Flotation Machine …

355

experts have used many methods to coordinate the influence between technological processes. The typical method is optimal control. 3.

Optimal control

The optimal control system adopts the optimization technology to control the flotation condition within a suitable range according to objectives such as grade or recovery rate. One method is as follows: Record as many data as possible in the monitoring system of concentrators, and extract data with good indicators for training to find the optimal flotation process parameter combination. The directional logic and rule-based control algorithm have been used on flotation parameter setting. Such a system is like an operator with rich experiences. The parameter settings are always adjusted towards the optimal direction, and are called expert control system later. It is developed by AI experts, and can simulate experienced experts to solve some problems. Now the common flotation process control system in the industrial production includes pulp level control, aeration rate control and froth image analysis, etc. of flotation machines.

10.2 Pulp Level Control of Flotation Machines The pulp level control of flotation machines is the most important part of the process control of flotation machines. Stable pulp level in tank is not only an important precondition of normal operation of flotation equipment and technological process, but also can effectively reduce the potential safety hazards, and more it also has direct influence on improvement of production indicators. Especially for large flotation machines, the volume is large and the tank is deep. Keeping stable pulp level in the flotation tank is beneficial to stabilization of concentrate grade and improvement of recovery rate. In the flotation process, the high-quality froth includes upper, middle and lower layers. The concentrate grade of the top froth is the highest, and the lower the layer, the lower the concentrate grade. The height of liquid level directly affects the grade and recovery rate of the final product. Especially in the concentration operation, the improvement of pulp level can improve the recovery rate, while the concentrate grade will be reduced. The reduction of pulp level can improve concentrate grade, while the recovery rate will be reduced. Therefore, it is a key factor to keep the liquid level of the flotation machine at a suitable height to improve the technical and economic indicators of flotation operation. In the mineral separation production process, the height of liquid level of the flotation machine is easily affected by multi-aspect disturbance factors such as instable grinding loop, ore concentration and valve opening. The liquid control technology of the flotation machine is to combine with modern detection instruments, and keep stable height of pulp level by using timely and effective regulating measures before or after periodic and non-controllable disturbance quantity takes effect.

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At present, many flotation machine manufacturers have developed matched level control systems of the flotation machine, such as Outotec’s EXACT, FLSmidth’s ECS and BGRIMM’s BFLC. Although different manufacturers’ level control systems are slightly different in specific form and technical detail, they basically consist of three main units: level detection unit, actuator unit and control strategy unit. This section introduces the level control system of the flotation machine in detail with BGRIMM’s BFLC level control system as an example. The level control system of the flotation machine consists of three parts, namely, a level measurement device, local control cabinet and actuator. Its working principle is: First, the level measurement device converts the detected liquid level to standard current signal of 4–20 mADC, after the master controller in the local control cabinet executes A/D conversion on the incoming current signal, the D/A outputs the drive current signal to the pneumatic actuator after performing a series of operations by means of a special control algorithm for flotation level, and the pneumatic actuator linearly regulates the opening of the ore discharge valve according to the magnitude of current, in order to finally achieve the purpose of controlling the liquid level. Figure 10.1 is the schematic of level control system of BFLC flotation machine. The level control system of BFLC flotation machine can achieve automatic control of the flotation operation level of multiple tanks, ensure stable flotation process, and effectively stabilize the grade and recovery rate of concentrates in order to meet the requirements of process indicators. This system has been widely applied in China’s many concentrators and obtained the industry praise with accurate and stable control, simple operation and maintenance, and stable and reliable operation.

Fig. 10.1 BFLC pulp level control strategy of flotation machine

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10.2.1 Level Detection Device In the flotation process, the pulp in the flotation tank will generate intense agitation due to rotation of the rotor. At the same time, lots of bubbles will be generated in the flotation tank due to influence of aeration and dosage. The hydrophobic mineral particles will adhere to bubbles, and will be brought into the pulp level by bubbles and then accumulate to mineralized froth layer, and the hydrophilic gangue particles will stay in the pulp. This process is carried out on a three-phase boundary, namely solid (mineral particles), liquid (water) and air (bubbles). Thicker froth layers are accumulated above the liquid level, intense agitation is generated in the flotation tank, and the pulp has adhesion and corrosivity, which brings difficulty for the liquid level measurement of the flotation machine. It is necessary to focus on how to solve the liquid level measurement problem of the flotation machine [18]. Many liquid level detection methods of the flotation machine have once appeared, such as capacitance detection, static pressure detection, blowing detection and constant buoyancy detection. However, either the detection accuracy is poor or the maintenance quantity is large and the life is short due to a complex detection environment in the flotation tank. The level detection device of BFLC flotation machine solves this problem better, namely, using the laser-float-type level measurement instrument and applying the principle of laser ranging. This device consists of a laser sensor, an isolation tube, a level bracket and a float component, as shown in Fig. 10.2. All the level bracket, isolation tube and float component are made of stainless steel materials, and have advantages of elaborate design, durable service

Laser sensor Flushing water Reflective disk Connecting rod

Isolation tube Floating ball

Fig. 10.2 BFLC level detection device of flotation machine

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and easy removal. The laser range finder has advantages of easy installation, wide measurement range, accurate and stable signal and high level of protection. The level bracket integrates a set of flushing devices, having the function of eliminating the froth generated in the isolation tube, in order to reduce the adhesion of flotation froth to float component surface, and avoid the measurement accuracy from being affected by the adhesion of froth. In addition, the isolation tube can isolate the violent shock from the rotor of the flotation machine during agitation, and can effectively reduce the flotation froth in the tube in order to ensure the real liquid level which can be detected. The float component consists of a floating ball, a floating ball rod and a reflective disc. The floating ball is arranged inside the isolation tube; the reflective disc connected with the floating ball will make up and down movement vertically with the fluctuation of the pulp level by means of cantilever construction; and the laser range finder will constantly measure the distance with the reflective disc and then output a signal of 4– 20 mADC to the master controller, and determine the liquid level through conversion. As shown in Fig. 10.3, when the pulp level arrives at the overflow weir, the distance between the laser sensor and the reflective disc is H 0 , and the froth layer thickness is calibrated as 0 mm at this time. When the deepest liquid level is detected by the floating ball, the distance between the sensor and the reflective disc is H 2 . Calibrate the maximum froth layer thickness at this time by Hmax = H2 − H0 . Generally, 500 mm ≤ Hmax ≤ 1000 mm. The formula of froth layer thickness is Hthe maximum froth layer thickness = H1 − H0

Fig. 10.3 Liquid level measurement principle

(10.1)

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The industry practice shows that it is relatively reasonable to select laser sensor for distance measuring sensor if used indoors; however, the ultrasonic sensor shall be used outdoors in view of influence of light.

10.2.2 Actuators In the level control system, the output action of the actuators controls the opening of the ore discharge valve, and the performance of the actuators directly affects the pulp level control effects. The actuators of the level control system of BFLC flotation machine include two types, namely, electric actuator and pneumatic actuator. The pneumatic actuator receives current signal to realize automatic control, as shown in Fig. 10.4; while the electric actuator plays the function of auxiliary regulation only. It can be manually operated only. The pneumatic actuator is provided with intelligent positioner, having characteristics of good linearity, high regulation accuracy and sensitive control. It is vertically installed on the mounting bracket above the tailing box in the flotation machine,

Fig. 10.4 BFLC pneumatic actuator and dart valve of flotation machine

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connected with the valve rods in the flotation equipment and tailing box, outputs vertical displacement, and drives the valve rods and bodies to move up and down along the vertical direction, in order to change the flow area of the pulp in the middle tailing box, namely, change the ore discharge flow in the middle tailing box to achieve the purpose of regulating the liquid level of the flotation machine. The pneumatic actuator must be concentrically installed with the valve rods and bodies. In addition, it shall be provided with hand wheel mechanism, which can be used to manually regulate the cylinder stroke in case the instrument air is off. In case of air off, blackout and signal failure, the pneumatic actuator can also realize the function of locking. The key component of the pneumatic actuator is the valve positioner, with the control principle as follows: Powered by compressed air, it receives the DC electric signal of 4–20 mA given by the regulating unit or that given manually, and converts into linear displacement corresponding to the input signal to regulate the medium flow. When the positioner has input signal, its output pressure will drive the piston and piston rod to do rectilinear movement, and the piston rod will drive the sliding plate and swing arm to move, and feedback to the positioner; when the piston moves to the position corresponding to the input signal, the positioner will close the output pressure. According to different handling capacities of the flotation machine, different level control loops are provided with different quantities of pneumatic actuator. Large flotation machines are usually provided with dual pneumatic actuators, namely, both actuators participate in regulation; however, for small flotation machines with a lower processing capacity, one actuator can meet the regulation requirement. In addition, the matched electric actuator will be served as an assistant to prevent the normal production from being affected when the pneumatic actuator goes wrong. Compared with the electric actuator, the pneumatic actuator has the following advantages: 1. 2.

3. 4.

It is allowed to frequently regulate the valve within short time. Its durability is superior to the electric actuator. The tailing dart valve of the flotation machine is linearly designed, and good linearity of the pneumatic actuator is exactly an important precondition for both of them to realize stable pulp level control by coordination. The pneumatic actuator has low energy consumption. The output of the pneumatic actuator is flexibility with high safety factor. Do not worry about motor overload to the pneumatic actuator in case of excessive valve pressing or valve rod decentration.

The test certifies that the single pneumatic actuator and dual pneumatic actuator cut both ways under the condition of meeting control effects: When a single pneumatic actuator is used, due to low adjustable ore discharge, the opening variation of the valve is always about 10% to ensure a steady liquid level, while when a dual pneumatic actuator is used, due to large adjustable ore discharge, the opening variation of the valve is about 3% when the liquid level is kept steady; moreover, the regulation is more sensitive; the regulation time is short; and the overshoot is low. For the whole flotation process, the amplitude and frequency of opening change of the ore discharge

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valve decide the control effects of subsequent operation levels. The test shows that the pulp level control effect of the dual pneumatic actuator is better for large flotation machines with large handling capacity.

10.2.3 Pulp Level Control Strategies 10.2.3.1

Single-Loop PID Control Strategy

The single-loop control system usually means that all the detecting element, transmitter, controller, actuator and controlled object are a closed-loop control system that realizes control based on deviations. It is a simple control system, and also a single parameter control system. It is used widely, accounting for about 80% of total control loop quantity. The pulp level control is an important branch of industrial control, and its technology is also relatively mature. The PID control algorithm is widely applied in pulp level control with advantages of simple structure, easy realization, easy adjustment, etc. [19]. Served as a linear controller, the PID controller forms control deviations according to the given values yd (t) and the actual output values y(t): error(t) = yd (t) − y(t) The control rule of PID is ⎡ u(t) = kp ⎣error(t) +

1 ki

(10.2)

⎤

t error(t)dt +

kd derror(t) ⎦ dt

(10.3)

0

Or write the form of transfer function: G(s) =

  1 U (S) = KP 1 + + Kds E(S) Kis

(10.4)

where KP Ki Kd

proportionality coefficient; Integral time constant; Derivative time constant.

In view of stability, response speed, overshoot and steady-state accuracy, etc. of the system, the functions of K P , K i , and K d are as follows [20]: (1)

The function of proportionality coefficient K P is to quicken the response speed of the system and improve the regulation accuracy of the system. The bigger the value, the faster the response speed, and the higher the regulation accuracy,

362

(2)

(3)

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but it easily generates overshoot or instability. If the value K P is too small, the regulation accuracy will be reduced, the response speed will be slow, and the static and dynamic characteristics of the system will deteriorate. The function of integral action coefficient K i is to eliminate the steady-state error. The bigger the value K i , the faster the elimination for steady-state error. However, if the value K i is too big, the phenomenon of integral windup will be generated at the preliminary stage of response process, causing larger overshoot to response process. If the value K i is too small, it will be difficult to eliminate the steady-state error, affecting the regulation accuracy of the system. The function of differential action coefficient K d is to improve the dynamic characteristics of the system, and mainly to restrain any directional change of deviations in the response process, and predict the deviation change in advance. However, if the value K d is too big, the response process will restrain in advance, lengthening the regulation time and reducing the anti-interference performance of the system.

The general PID control technology is mature and usually used to control the liquid level of small flotation machines, while the general PID control fails to meet the actual requirement for pulp level control of large flotation machines. The main problems are as follows: 1.

2. 3.

4.

The instability of grinding loop will bring larger disturbance for liquid level of the flotation machine, the response time of general PID control is long, and the regulation is slow and easily overshoots. The phenomenon of unstable control is more obvious, especially in case of initial feeding or feeding stop due to equipment failure. The level control system of large flotation machines has large hysteresis factor due to large tank volume. It is difficult to adjust the P, I and D control parameters. The flotation machine has characteristics of large capacity, large handling capacity and short service time. By taking the Jiangtongdashan concentrator test as an example, the dual tank operation is adopted, wherein it takes 6 min only for pulp to enter a 200 m3 flotation machine to enter the next flotation operation, while its time staying in each tank is 3 min only. Therefore, the pulp level control and regulation shall be sensitive. Otherwise, the accident of ore overflow will be easy to occur. The flotation machine has large ore discharge volume. In practical application, the large flotation machines not only adopt the ore discharge valve with a larger flow area, but also discharge ore by means of dual valve. Therefore, in the liquid level regulation process, it shall also pay attention to the stabilization of ore discharge volume in addition to the stabilization of liquid level, in order to avoid causing liquid level fluctuation of this flotation tank, and meanwhile avoid influence on liquid levels in subsequent operations. The action of the ore discharge valve shall not be too frequent, and the opening variation shall not be too large.

Since the pulp level of the flotation machine has such characteristics as nonlinearity, large hysteresis and multivariable mutual coupling, it must find an improved

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algorithm specially for pulp level control in the general control algorithms. In the pulp level control experiment, various improved algorithms are subject to comparative research, and finally a special pulp level control algorithm is determined, as shown in Fig. 10.5. Served as an effective way used to solve the above problems, the adaptive fuzzy PID control combines the fuzzy theory with PID algorithm, having characteristics of quick adjustment and strong robustness. With the deviation of E and deviation change rate of EC as inputs, it self-adjusts the PID online by means of fuzzy inference rule to meet the requirements of E and EC for PID parameters at different moments. The output value can also quickly recover to the set value in case of large disturbance to the system. In the level control system, generally the liquid level can be stabilized as long as the proportionality coefficient of P and integral coefficient I are adjusted. Therefore, this fuzzy control model includes two inputs (deviation E and deviation change rate EC) and two outputs (k p and k i ). All the fuzzy language variables are divided into {NL, NM, NS, ZO, PS, PM and PL}, and the elements in subset represent {negative big, negative medium, negative small, zero, positive small, positive medium and positive large}, respectively. The fuzzy reasoning is the core of fuzzy control. Establishing fuzzy control rule base becomes a key problem [21]. It is based on control theory and practical experiences of operators generally. In the flotation level system: (1) In case the deviation of E is bigger, the value of k p shall be increased and that of k i shall be reduced to quickly restrain the deviation and improve the response speed. In case the deviation of E is smaller, the value of k p shall be reduced and that of k i shall also be reduced to continue eliminating the influence of E and prevent large overshoot and oscillation. In case the deviation of E is very small, the value of k p shall be continued to get smaller and that of k i can be slightly bigger or remain unchanged aimed to eliminate the steady-state error. (2) The deviation change of EC is the rate of deviation change. When its value is bigger, the value of k p shall be reduced and that of k i shall be increased. On the contrary, when EC becomes small, the value of k p shall be increased and that of k i shall be reduced.

Fig. 10.5 Pulp level control system strategy of flotation machine

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According to the adjustment rule of adaptive fuzzy PID parameters, combining with the actual situation of liquid level of the flotation machine, establish fuzzy rule tables about k p and k i , as shown in Tables 10.1 and 10.2. The pulp level control strategy of BFLC flotation machine focuses on fuzzy PID control, meanwhile conducts optimal design based on this algorithm, and adds peripheral programs such as filtering and dead-section. For aeration flotation machines, although the isolation tube has played the role of isolating the impact force generated from intense agitation of the rotor, the floating ball will still fluctuate slightly, so it is necessary to filtrate the liquid level signal in the software. The influence of interference is reduced through regulation for filter coefficient to keep liquid level more stable. For PID control algorithm, it is a deviation-based control. There is a control signal output as long as there is a deviation. Therefore, the fluctuation of liquid level will often cause frequent action of the actuators, which greatly reduces the life of the actuators, and meanwhile causes disturbance to the liquid levels in subsequent operations. However, the setting of dead-section not only can avoid frequent action of the actuators, protect the actuators and lengthen their service life, and meanwhile can prevent the occasional large opening of the tailing valve and adverse cases such Table 10.1 k p fuzzy rule table k p EC

E NB

NM

NS

ZO

PS

PM

PB

NB

PB

PB

PM

PM

PS

ZO

ZO

NM

PB

PB

PM

PS

PS

ZO

NS

NS

PM

PM

PM

PS

ZO

NS

NS

ZO

PM

PM

PS

ZO

NS

NM

NM

PS

PS

PS

ZO

NS

NS

NM

NM

PM

PS

ZO

NS

NM

NM

NM

NB

PB

ZO

ZO

NM

NM

NM

NB

NB

Table 10.2 k i fuzzy rule table k i EC

E NB

NM

NS

ZO

PS

PM

PB

NB

NB

NB

NM

NM

NS

ZO

ZO

NM

NB

NB

NM

NS

ZO

PS

PS

NS

NB

NM

NS

NS

ZO

PS

PS

ZO

NM

NM

NS

ZO

PS

PM

PM

PS

NM

NS

ZO

PS

PS

PM

PB

PM

ZO

ZO

PS

PS

PM

PB

PB

PB

ZO

ZO

PS

PM

PM

PB

PB

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as blocking or intensive liquid level shock caused due to external signal interference, and ensures stable liquid levels in subsequent operations.

10.2.3.2

Multi-operation Cooperative Control Strategy

According to the flotation process, each series of the flotation machine is connected with multiple pulp level controls, the pulp is delivered from one operation to the next operation, and operations couple and impact each other due to existence of multiple interference sources and distribution in series of flotation operation. If only the traditional single-loop PID is used for control, the liquid level fluctuation will become larger in the subsequent process. Since the single-loop control is used, and all liquid levels pay attention to their changes only, the PID will work only when the interferences cause a liquid level fluctuation so that the deviation between liquid level and set value exists, which is hysteretic for interference regulation. Therefore, it is difficult to control the whole flotation process macroscopically by using the singleloop PID, and the stability coefficient of the whole operation is low. The interference sources of the flotation tank are mainly from inlet flow, flow of the circulating pump and opening change of the regulating valve, while the flotation level fluctuation caused by these interferences is delivered with the flotation operation, and has an amplification trend, leading into gradual increase of the liquid level fluctuation in subsequent operations, deteriorating the control effects. The level control system of BFLC flotation machine uploads the real-time data of the liquid level to the DCS via the field bus, which provides possibility for the integral control for the whole series of flotation process, i.e. multi-operation level cooperative control of the flotation machine. See Fig. 10.6 for its functional block diagram of specific control. The multi-operation level cooperative control technology of the flotation machine manages the whole flotation process at the same time. It is capable of taking effective compensation measures before the interferences affect the flotation level in order to restrain the disturbance. In addition, this technology is based on the whole flotation process and manages the liquid level change in the whole flotation process; despite flotation machine or flotation column, the integral control idea is adopted for continuous pulp process; in case of interferences, the liquid level interferences and fluctuations can be perceived in advance through model estimation, and the interferences can be restrained in the process by regulating the valve opening before affecting the liquid level, thus ensuring a stable liquid level. Therefore, this technology can effectively prevent interferences and restrain liquid level fluctuations.

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Fig. 10.6 Multi-operation cooperative control technology of flotation machine

10.2.4 Industrial Application of the Level Control System of BFLC Flotation Machine For level control system, regardless of external aeration flotation machine or mechanical agitation flotation machine, their level detection devices, actuators and control strategies are basically same. The use and data analysis are introduced below with application of the level control system of BFLC flotation machine in the industrial tests of KYF-200 flotation machine as an example.

10.2.4.1

Analysis for Open-Loop Test Result of the System

The open-loop characteristics of the system are as shown in Fig. 10.7. The liquid level will be reduced whenever the cylinder opening rises by 5%. The transient time is 246 s and the liquid level drawdown distance is 25 mm.

10.2.4.2

Manual Pulp Level Control

At the preliminary stage of test, adopt the manual control, namely, both dual cylinders that work at manual mode, and operators set the valve opening and regulate the liquid level. The manual control effects are as shown in Fig. 10.8. It can be seen from Fig. 10.8 that the liquid level fluctuation is larger and there is a liquid level equilibrium state offset in manual control. The main reason is that the

10.2 Pulp Level Control of Flotation Machines

Fig. 10.7 Open-loop control characteristic curve

Fig. 10.8 Full manual control curve

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feeding quantity fluctuation cannot be timely and effectively regulated, namely, the manual control has no immunity from interference.

10.2.4.3

Automatic Control of Single Cylinder

For automatic control of single cylinders, namely, one cylinder is set at the set manual opening value, and the other cylinder receives the automatic control signal from the controller for automatic control. The control effect curve is shown in Fig. 10.9. As seen from the control curve, the automatic control curve of liquid level always has a small range of fluctuation near the set value, with steady-state error kept within 10 mm. It can be seen from the comparison with manual control that automatic control is capable of automatically adjusting the feeding quantity change, while manual control fails to timely and effectively adjust. This shows that automatic control has an anti-disturbance function while manual control has no disturbance resistance. During the stable operation of the system, change the set value, give a unit step input to the system, and research the dynamic following performance indicator of the system. As seen from Fig. 10.10, the delay time of the system is 1 s, the regulation time is ts = 54 s, and the maximum overshoot is 1.6%. It can be seen from the dynamic characteristic curve that the dynamic following performance of the system is good

Fig. 10.9 Automatic control curve of single cylinder

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Fig. 10.10 Level control curve of set value is up

and the accuracy is higher if the response is quick, the regulation time is short and the overshoot is low in case the set value is changed.

10.2.4.4

Automatic Control of Dual Cylinder

For automatic control of dual cylinders, namely, both cylinders receive the automatic control signal from the controller for automatic control. The control effect curve is shown in Fig. 10.11. As seen from the control curve, the automatic control curve of liquid level always has a small range of fluctuation near the set value, with steady-state error kept within 10 mm. As also seen from the control curve chart, dual cylinders have two advantages compared with automatic control of single cylinders: First, the regulation is more sensitive and the response is quicker; second, the fluctuation of valve opening is lower, having small influence on subsequent operations. It can be seen that the pulp level control of dual cylinders is stable and the control effects are good. During the stable operation of the system, change the set value, give a unit step input to the system, and research the dynamic following performance indicator of the system. As seen from Fig. 10.12, the delay time of the system is 0.5 s, the regulation time is ts = 43 s, and the maximum overshoot is 1.4%. It can be seen that the system can quickly change with the set value, the regulation time is short and the overshoot is low. Compared with the dynamic performance of single cylinders, the automatic

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Fig. 10.11 Pulp level control curve of double cylinder

Fig. 10.12 The characteristic curve of the pulp level under the set value

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371

control of dual cylinders is more sensitive, the regulation time is shorter and the overshoot is lower, namely, the dynamic performance of dual cylinders is superior to single cylinders.

10.3 Aeration Rate Control of Flotation Machines Considered as the most flexible and the most sensitive parameter in the control of the flotation machine, the aeration rate forms lots of bubbles in the process of effectively mixing pulp with flotation reagents, increases the surface tension of pulp, and brings the valuable elements captured by the collecting agent into the froth layer. The aim of controlling the aeration rate is to improve the bubble load rate so that various graded minerals can be fully recovered in different operations. When the aeration rate is excessive, the pulp level in the flotation machine will “fluctuate”, the bubble layer will be damaged, and the valuable mineral particles will fall off from the bubbles; When the aeration rate is too small, the bubble load rate will be slow, and minerals will fail to be fully recovered in different operations. Maintaining stability of aeration rate of the flotation machine not only plays an important role in the separation process of flotation, but also can effectively improve the flotation indicators. Therefore, the aeration rate control of flotation is the cost-optimal effective control method.

10.3.1 Aeration Rate Detection Device and Control Device The aeration rate of the flotation machine is characterized in low pressure, low wind speed and large air volume. Generally, the wind pressure is between 11 and 65 kPa, and the wind speed is between 0.5 and 1.7 m/s. At present, the common methods used for detecting aeration rate include three types. They have respective advantages in aspects of price, detection principle and maintenance cost, and are widely applied in many industrial fields including the flotation machine [22].

10.3.1.1

Hot Gas Mass Flowmeter

The principle of hot measurement is realized by monitoring the cooling effect of the airflow passing through the heat exchanger (thermal resistance: PT100). The airflow via the sensing area shall pass through two temperature sensors (thermal resistance: PT100). One is used for temperature measurement, and the other is used for heating. The former monitors the actual process temperature value; the later maintains the steady temperature value to keep it always higher than the actual process temperature and keep steady temperature difference with this process temperature. The larger the gas mass flow rate, the greater the cooling effect, and the larger the energy required for maintaining differential temperature. Therefore, it can obtain the mass flow rate

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of the gas to be measured by measuring the energy of the heater. It measures the gas mass flow rate in standard unit without temperature and pressure compensation. The measurable wind speed is between 0 and 163 m/s, and the measurement accuracy is ±1%FS. The hot gas flowmeter adopts plug-in mounting with negligible very low pressure loss and measurement pipe diameter between 80 and 500 mm. It is characterized in simple installation and easy maintenance, but its cost is high. The measurement schematic diagram is shown in Fig. 10.13.

10.3.1.2

Venturi Differential Pressure Gas Flowmeter

The gradually narrowed venturi plays a role of restricting the gas flow rate, and calculates the gas flow rate by measuring the pressure drop generated by the gas. Its principle is shown in Fig. 10.14. This detection method is stable and reliable with low pressure drop and accurate measurement, but it also has disadvantages of large space usage and high cost, etc.

10.3.1.3

Uniform-Velocity-Tube Differential Pressure Gas Flowmeter

Both pilot tube and uniform-velocity-tube differential pressure gas flowmeters calculate the gas flow rate by comparing the differential pressure between the internal pipe pressure and static gas pressure. Their difference is that the pilot tube differential pressure gas flowmeter has one detection point only, while the uniform-velocity-tube differential pressure gas flowmeter adopts the multi-point measurement method and regards the calculated mean as the gas rate. Such two methods have advantages of high accuracy and low pressure drop. Its principle is shown in Fig. 10.15.

Fig. 10.13 Measuring principle of hot gas mass flowmeter

10.3 Aeration Rate Control of Flotation Machines

373

Fig. 10.14 Measuring principle of venturi differential pressure gas flowmeter

Fig. 10.15 Measuring principle of uniform-velocity-tube differential pressure gas flowmeter

The problem of the differential pressure gas flowmeter is that larger space is required for installation and a very long straight pipe is required to ensure the accuracy of measurement. In such a case, the current solution is to reduce the pipe diameter to shorten the length of the required straight pipe. For aeration rate regulating valve, the automatic control butterfly valve is usually used, because the butterfly valve is low in price and can completely meet the accuracy requirement of aeration rate control of the flotation machine. It is characterized in that (1) small and light, easy to remove, install and repair, and can be installed at any position; (2) simple and compact structure, quick rotation start/stop, up to hundreds of thousands of start/stop times, and long life; (3) low flow resistance, large flow capacity, inherent flow characteristics approximate to equal percent characteristics, and good regulation performance; (4) multiple accessories can be installed, namely, they can be used as a switch and can also realize continuous regulation by installing positioner.

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10.3.2 Automatic Control Strategy for Aeration Rate The automatic control for flotation aeration rate plays a very important role in flotation process. The flotation effect is usually more sensitive to the change of aeration rate than to the froth thickness. Compared with reagent addition volume, the air can be called “the cheapest reagent”, and would not leave any residual concentrate even when the aeration rate is larger. Therefore, the aeration rate can play a more efficient regulation function. Served as an important link of flotation process control, the aeration rate control system often combines with the flotation level control and dosing control system, e.g. the cascade control of the long process flotation machine is realized by regulating the liquid level and aeration rate at the same time. In general, the automatic control for flotation aeration rate is easier compared with other process control of flotation. A simple feed-forward/feedback PI control loop is sufficient to realize the regulation for aeration rate. The automatic control schematic diagram of aeration rate is shown in Fig. 10.16. The automatic control program of aeration rate is to measure the aeration rate of the flotation machine, send aeration rate signal to the control instrument, the control instrument will receive aeration rate signal and output control signal to the aeration rate regulating valve according to the set aeration rate value, and this automatically regulates the opening of the valve to stabilize the aeration rate at the set value. The regulation for valve size has a critical influence on the control effect. If the valve caliber to be used is too large, although it can effectively reduce the pressure loss, the control accuracy is very limited, and will rapidly have great influence on flotation effect and liquid level fluctuation. If the flotation machine is horizontally arranged, and one operation is air-supplied by one pipe, the flotation machine inlet butterfly valve will be manually regulated on the field to adjust the air input of each flotation machine. The mechanical agitation flotation machine is usually provided with no automatic control system of aeration rate, because this kind of flotation machine can suck limited total air volume only, especially prominent in high altitude places. This restricts the application of flotation process control system and implementation of advanced control strategy in a way.

Fig. 10.16 Automatic control strategy for aeration rate

10.3 Aeration Rate Control of Flotation Machines

375

10.3.3 Industrial Application of the Aeration Rate Control System of BFLC Flotation Machine The application and data analysis of the aeration rate control system of BFLC flotation machine in industrial tests of KYF-200 flotation machine are introduced below.

10.3.3.1

Manual Control for Aeration Rate

Manual control means that operators set the opening of the butterfly valve for aeration rate regulation. Its control curve chart is shown in Fig. 10.17. As seen in Fig. 10.17, the aeration rate is not stable and there is steady-state offset in manual control, and the reason is that manual control has no anti-interference performance.

10.3.3.2

Automatic Control of Aeration Rate

The automatic control for aeration rate means that operators set the aeration rate value, the controller performs operation processing after acquiring air flow signal, and outputs control signal to the butterfly valve for automatic regulation for aeration rate. The automatic control effect chart is shown in Fig. 10.18.

Fig. 10.17 Manual control curve for aeration rate

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Fig. 10.18 Automatic control curve of aeration rate

As seen from the control curve chart, the aeration rate is controlled stably, the opening fluctuation of the butterfly valve is small and the maximum dynamic error is 50 m3 /h. The automatic control system of aeration rate has stable control and small fluctuation, completely meeting the requirement of flotation equipment for gas volume.

10.4 Froth Image Analysis of Flotation Machines In recent years, with the rapid development of computer technology, software technology, digital image technology and image capture equipment, the digital image technology has gradually permeated into all aspects of scientific research, industrial production and daily life, and played a more and more important role. With “computer vision” instead of human vision, strengthen the application research of digital image technology in mineral separation process, and promote the development in flotation froth image technology by means of modern latest digital image technology achievements, which has a very important significance in realization of intelligent control for concentrators. Froth image is shown in Fig. 10.19. Flotation froth consists of many different sizes, shapes and colours of mineralized bubbles, including much information related to flotation process variables and flotation results. Wherein the froth speed, size and colour are three very key parameters for flotation control strategy: movement speed of froth can represent froth scraping

10.4 Froth Image Analysis of Flotation Machines

377

Fig. 10.19 Froth image

quantity of the flotation machine; size and texture of froth can represent whether the dosage of administration is appropriate; color and brightness of froth can describe grade and recovery rate of concentrates [23]. Froth image is obtained from the HD camera fixed above the flotation machine that acquires the digital image of froth surface. The application of froth image processing technology in flotation process control significantly improves the process indicators and degree of automation. Understand the system composition of flotation froth image processing and the algorithm of froth physical parameters, and the application and characteristics of image processing technology in flotation process control, which has an important significance in mastering and use of froth image processing technology.

10.4.1 Flotation Froth Image Equipment and Implementation Method In 1998, Professor Nguyen in Australia invented the first froth image analysis system applied to industry by means of powerful computing power of computers [24]. This system uses multiple high-precision CCD cameras, and then sends pictures to computers via the optical fibre. This system can compute the froth speed, deduce the froth area, etc. The JKFrothCamera system was installed in a flotation column for coal preparation for the first time, and also successfully installed in a copper concentrator later. Since 1998, the system designed by Nguyen has been purchased and applied by many companies. The froth image capture equipment designed by BGRIMM is shown in Fig. 10.20. The image capture equipment is installed on the minimum position nearest to the froth layer where the froth fails to splash. The intensity of light is vital for the algorithm of

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Fig. 10.20 Froth image capture equipment

image analysis. Therefore, the sun shield, LED lamp and other auxiliary equipment are installed near the CCD cameras. The image capture equipment mounted above the froth layer is shown in Fig. 10.20. CCD cameras capture 25 frame of picture every minute and transfer it to computers via the optical fibre or coaxial cable. Cameras can rotate, zoom in and zoom out to capture the most valuable pictures for image analysis. There is a picture that recorded the froth located in the coordinates of X-axis and Y-axis on the upper right of the image, and the picture below delimited the outline of each piece of froth. This system has very high requirement for real-time performance in order to measure the froth speed, size, viscosity and colour. In China, the BFVS flotation froth image processing system designed by BGRIMM is at the leading level. This system consists of software and hardware platforms, wherein the hardware platform mainly consists of camera subsystem, lighting subsystem, mechanical architecture subsystem, image processing workstation, etc.; the software platform is mainly developed based on VS2005.NET platform, including image acquisition module, image characteristic parameter extraction module, optimal control module, etc. [25].

10.4.2 Static and Dynamic Characteristic Detection Technology of Flotation Froth The froth image characteristic parameters are represented in two aspects: on one hand, the froth parameters based on single frame image are known as static parameters, such as froth colour, bubble size and textural features; on the other hand, the froth image characteristic parameters based on image sequence are known as dynamic characteristics, generally including froth flow rate, stability, etc. [26]. The relation

10.4 Froth Image Analysis of Flotation Machines

379

Table 10.3 Qualitative relation between froth image features and important parameters of flotation Important parameters

Froth image features

Pulp level ↑

The faster the foam speed, the lighter the color, the more serious hydration, and easy to turn flowers

Pulp level ↓

The slower the foam flow, the darker the color, the more viscous the foam

Aeration ↑

The faster the foam velocity, the bigger the bubble, the lower mineralization degree and easy to turn flowers

Aeration ↓

The slower the bubble velocity, bubble is smaller

Foaming agent ↑

Foam fast flow, small size, surface reflection, bubble sticky, not easy to break

Foaming agent ↓

The bubble velocity is slow, the thickness is thin, the foam is large, and it is easy to crack

Pulp consistency ↑

The foam is slow in flow rate, thick in bubbles and highly mineralized

Pulp consistency ↓

Foam hydration is serious and easy to crack

between froth image features and important parameters of flotation is summarized in Table 10.3. It can be seen that the flotation froth characteristics can reflect this change in case the process parameters are changed. Therefore, it is very necessary to extract the static and dynamic characteristics of flotation froth as the original data for subsequent analytical prediction and even control.

10.4.2.1

Detection of Froth Flow Rate

The calculation of froth velocity needs to depend on at least two frames of images. It is difficult to obtain correct froth movement characteristics by means of routine movement estimation algorithms such as grey-level template matching and Fourier phase correlation method, due to froth collapse or illumination variation. However, adopting the light stream constraint equation and Kalman movement estimation based on minimum energy for calculation can effectively restrain the adverse impact on movement measurement that is caused due to froth collapse, illumination variation and other noise, and finally estimate the optimal rate. The brightness mode generated on the image will move with movement of froths. The movement information of froths can be reflected in a two-dimensional image space under uniform light conditions, and the time interval between the adjacent frames is very short. It is with regard its movement as rigid translation for processing after selecting a suitable region of interest. The schematic diagram of image movement is shown in Fig. 10.21. The points in the three-dimensional space left a movement locus in the two-dimensional image space. If it is capable of keeping the camera image plane and the movement locus plane of the measured points in parallel, then the optimal value will be obtained upon prediction and correction, by implementing pixel

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Fig. 10.21 Image motion diagram

matching on the consecutive frame of images, calculating the movement distance of the interest points in the image space and providing data for the observed value of Kalman filtering. In the image space, the grey value of the point used to define the coordinates as (x, y) is I(x, y). After a very short time, the points in the image are moved to (x + x, y + y). Since the movement time is very short, it may assume that the grey values of two points remain unchanged, namely, I (x + x, y + y, t + t) = I (x, y, t). Conduct Taylor expansion on the above formula and omit second-order errors and above. ∂ I y ∂I ∂ I x + + =0 ∂ x t ∂ y t ∂t Since it is difficult to ensure light conditions unchanged in practical application, and the movements of some points in the image region are difficult to have complete consistency, the following two constraints are added based on consideration of algorithm robustness. The image brightness gradient remains unchanged with time and position, and under ideal condition can be written as ∇ I (x + x, y + y, t + t) = ∇ I (x, y, t)

T where ∇ f = ∂∂ xf , ∂∂ yf . Finally, in view of strong consistency between pixel point movements in image, i.e. the displacement of different points in a range shall be kept as same as possible, which under ideal condition can be written as ∇(x)(x, y) = ∇(y)(x, y) = 0 Based on the above three ideal conditions, adopt the constraint energy function for minimization processing. In order to simplify the expression, specify: x =(x, y)T , v =(x, y)T , obtain:

10.4 Froth Image Analysis of Flotation Machines

381

¨

 F |I (x + v, t + t) − I (x, t)|2

 + ∂|∇ I (x + v, t + t) − ∇ I (x, t)|2 dx ¨  2

+β F |∇vx (x)|2 + ∇v y (x) dx

E(v) =

 where F(x 2 ) = (x 2 + ε2 ) and ε is a tiny positive number. The F operator is introduced in order to provide convenience in the following minimization process, ∂ and β are adjustable parameters, which can change the influence degree of three factors on the function. The state estimation of Kalman filtering can effectively reduce the noise jamming to obtain the optimal state estimation vector. Upon completion of calculation v =(x, y)T , the observation vector of translation of the interest region in time in the front and back two frames of images is obtained. The translation vector has uncertainty due to image noise. The state equation can be represented as xk = Axk−1 + wk−1 , and the observation equation can be represented as zk = Hxk + vk , where wk−1 and vk forecast process noise and observation noise, which meet the white Gaussian noise requirement of mean value as zero. The state vector is a four-dimensional column vector: xk = [xk , yk , vxk , vyk ]T , x k and yk are the centre coordinates in object region and the velocity of the centre coordinates on x and y, respectively. Since the image capture frame rate used in this text is 30 fps, and the time interval between the consecutive frames is t = 30 ms, it can be considered that the object does uniform motion ⎡ in short⎤time. Therefore, the state transition matrix of A is 1 0 t 0 ⎢ 0 1 0 t ⎥ ⎥ obtained as A = ⎢ ⎣ 0 0 1 0 ⎦. 00 0 1 T Observation vector  zk = [x, y] , thus the measurement matrix is obtained 0 0 t 0 as H = , the P(wk ) = N (0, Q) and P(vk ) = N (0, R) covariance 0 0 0 t matrix met by noise is ⎡

1 ⎢0 Q=⎢ ⎣0 0

0 1 0 0

0 0 1 0

⎤ 0   0⎥ ⎥, R = 1 0 0⎦ 01 1

The initialization of model parameter is performed below. The coordinates of the centre point in interest region in the image is selected as the initial value of position (x0 , y0 )T , then a smaller velocity component is selected as the initial velocity, and herein set as (vx0 , vy0 )T = (0, 0)T . Thus the initial value of state vector is xˆ 0 = (x0 , y0 , 0, 0)T . If the state before k moment is known, then xˆ k ∈ R 4 will be

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defined as the prior state estimation at k moment; after the observed value z k at k moment is obtained, it will be the posterior state estimation. The prior and posterior estimation errors are ek· = xk − xˆ k· , ek· = xk − xˆ k· Thus the covariance matrix of prior estimation error and that of posterior estimation error are obtained:     T T Pk· = E ek· ek , Pk· = E ek· ek· ·

The posterior state estimation, i.e. Kalman Filtering Formula, is calculated below: xˆk· = xˆ k· + K (z k· − H xˆ k· ) where K is an important parameter called Kalman gain. It is capable of weighing the weight between the predicted value and the observed value of time renewal state, and minimizing the covariance matrix of posterior estimation error. However, the later controlled part is the measurement renewal, namely, representing the difference between the measured value and the predicted value of prior state. Through calculation it can obtain: K =

Pk H T H Pk H T + R

The iteration renewal process of Kalman filtering is shown in Fig. 10.22.

10.4.2.2

Textural Features

Extraction of textural features of froths: Textural features reflect the surface roughness of froths, while the roughness will reflect the variety, dosage and other working conditions of the reagent to be added. Use the Grey-Level Co-occurrence Matrix to extract the global textural features of image as well as the energy parameter (fineness degree), inertia moment parameter and uniformity parameter of image. Textures are a representation of the grey-level correlation of the adjacent pixels. There are spatial co-occurrence matrix method, grey-level journey matrix method and neighbourhood grey-level correlation matrix method, wherein the spatial correlation matrix method is in common use. The spatial grey-level co-occurrence matrix p(u, v, d, θ ) is used to conduct statistics about occurrence times of two pixels with gray values of u and v, adjacent distance of d and position angle of in a digital image with grey level of G. The spatial grey-level co-occurrence matrix of P is an L * L matrix, wherein L is the grey level. For an

10.4 Froth Image Analysis of Flotation Machines

383

Fig. 10.22 Iterative schematic of Kalman filtering

image with grey level of 28 = 256, namely, when the grey level of each pixel is represented with 8-bit binary system, the spatial grey-level co-occurrence matrix of P is a 256 * 256 matrix. The selection of d is related to the textural fineness. The value of d shall be smaller if the texture is finer. In the spatial grey-level co-occurrence matrix, calculate the statistical parameter as the textural descriptor, which is used to quantitatively describe the textural features. The common textural features are as follows: 1.

Energy of E E=

L−1  L−1 

[P(u, v)]2

u=0 v=0

Energy reflects the image grey-level distribution uniformity coefficient and textural fineness. The more uneven the distribution, the larger the difference, and the greater the energy; energy is the quadratic sum of grey-level co-occurrence matrix elements. The greater the energy, the thicker the texture, and vice versa. 2.

Entropy of ENTS S=−

L−1  L−1 

P(u, v)lgP(u, v)

u=0 v=0

Entropy is a parameter used to represent the complexity of image texture. The more complex the image texture, the larger the entropy, and vice versa.

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Contrast (inertia moment) I=

L−1  L−1  

(u − v)2 P(u, v)



u=0 v=0

Contrast reflects the definition of image and the degree of textural groove depth. The deeper the textural groove, the greater the contrast, and vice versa. From the earlier stage to the later stage of flotation, the texture becomes thicker and thicker, the energy of froth image becomes greater and greater, and the entropy and inertia moment become smaller and smaller.

10.4.2.3

Colour Features

Extraction of colour features of froths: since there are many harsh environment interference factors in the production field and inaccurate data may be caused if only the methods based on RGB, HSI and LAB are used, the froth colour feature extraction method of multi-colour space information fusion was adopted, thus effectively eliminating the interferences of field light and other adverse factors on colour information. The main implementation method is to perform in the RGB space and HSI space. 1.

RGB space

Served as a currently common colour information expression space, RGB space quantitatively represents colour with the brightness of three primary colours, i.e. red, green and blue. This model is also called additive colour and colour mixture model, which is used to realize colour mixture by means of RGB overlapping, as shown in Figs. 10.23 and 10.24. As seen from the original image, there will be bright spots at the top of froths, and these bright spot regions will generate interferences on colour space values, resulting in inaccurate RGB component resulting in the direct colour channel. Therefore, it is necessary to first consider removing the bright spots. In Fig. 10.25, the higher the brightness, the bigger the grey level of this point, and vice versa. 2.

HSI space

HSI (Hue–Saturation–Intensity) model describes the colour characteristics with “H”, “S” and “I” parameters. “H” defines the wavelength of colour, called hue; “S” represents the depth of colour, called saturation; “I” represents the intensity or brightness. HSI model is widely used in image processing and recognition, because the “I” component is irrelevant to the colour information of image, while the “H” and “S” components are closely related to the way of human feeling colour. HIS cone space is shown in Fig. 10.26, and the relation between HIS and grey-level distribution is shown in Figs. 10.27, 10.28 and 10.29. As seen from the analysis result of HSI spatial image features, not like GRB space, human eyes have no intuitive feelings to the decomposed HSI space, and fail

10.4 Froth Image Analysis of Flotation Machines

Fig. 10.23 RGB space colour diagram

Fig. 10.24 Original froth image

Fig. 10.25 Removing exposure point image

385

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Fig. 10.26 HSI cone space

Fig. 10.27 H-space image and gray value distribution

Fig. 10.28 S-space image and gray value distribution

to differentiate the froths from bright spots with grey level. Therefore, the grey-level range of RGB space was used to remove the bright spot region so that the H\S\I value can represent the froth features without bright spots only, and then the corresponding bright spot regions were removed in the H, S and I spaces to obtain the spatial model without bright spots, as shown in Figs. 10.30, 10.31 and 10.32.

10.4 Froth Image Analysis of Flotation Machines

Fig. 10.29 V-space image and gray value distribution

Fig. 10.30 H-space of removing exposure points

Fig. 10.31 S-space of removing exposure points

387

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Fig. 10.32 I-space of removing exposure points

10.4.3 Application of Froth Image Analysis in the Flotation Process Control System The froth image analyzer developed by BFVS is installed and used in lots of concentrators. Its application effectively guides the field production and improves the flotation efficiency. The structure chart of optimal control system of froth image is shown in Fig. 10.33. With Hebei Fengning Xinyuan as an example, its concentrator focuses on recovery of molybdenum concentrates, and adopts 8 BGRIMM KYF-160 external aeration flotation machines as roughing and scavenging, six U-tank KYF-10 external aeration flotation machines as preconcentration, and four KYZB flotation columns as concentration, wherein its daily processing capacity is 20,000 t, selected average grade is 0.076% and selected concentration is between 43 and 46%. The froth image analyzer is installed on two KYF-160 flotation machine platforms before roughing, wherein such two devices are adjacent and located in the same ladder plane. Adopt the BFVS flotation froth image analyzer to detect the static and dynamic characteristics of froths in real time, and detect the froth overflow height by means of its built-in laser sensor, wherein, the aeration rate value (Nm3 /min) of each flotation machine is from hot mass flowmeter mounted on the field air hose. The flotation machine is designed to internal and external dual froth tank structure, and the image analyzer is installed on the pedal platform above the external froth tank overflow weir of two flotation machines, as shown in Fig. 10.34. The image interest region is selected in a region (60 × 60 mm) near the overflow weir, and is always kept at fixed position in order to ensure consistency and repeatability of all test data. In order to research the use effect of the optimal control system, the optimal control system has been used in the day shift for one consecutive month compared

10.4 Froth Image Analysis of Flotation Machines

Fig. 10.33 Froth image optimization control system architecture diagram

Fig. 10.34 Installation location of froth image analyzer

389

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Table 10.4 Comparison between optimal control and manual operation Operation mode

Raw ore grade (%)

Concentrate grade (%)

Tailings grade (%)

Comprehensive recovery rate (%)

Optimal control

0.0610

47.69

0.0102

83.14

Manual operation

0.0626

47.74

0.0110

82.94

Manual operation

0.0601

47.78

0.0109

81.47

Manual operation

0.0621

47.72

0.0109

81.91

with the swing shift and graveyard shift on that day and the day shift of manual operation 1 month ago, respectively. The comparison results are as shown in Table 10.4. Both original concentrate grade and comprehensive recovery rate in the table are the accumulated mean in a month. It can be seen that after the shift of implementing the optimal control of froth image was compared with other manual operation shifts; in the case where the raw ore grade was approximate, the minimum comprehensive recovery rate of molybdenum metal was increased by 0.2% and the maximum was increased by 1.67%, and the concentrate grades basically held the line and met the requirement (not lower than 45%) of concentrators for molybdenum concentrate powder grade.

10.5 Process Control Problems and Development Trend of Flotation Machines 10.5.1 Process Control Problems of Flotation Machines Although the process control of flotation machines has been rapidly developed in recent 10 years, its development is still relatively slow compared with other industries. The main factors affecting its development are as follows: (1)

(2)

Automation-related instruments have no breakthrough progress, and some pulp-related detection instruments still have old problems of poor reliability, low measurement accuracy, short service life, etc. [27], e.g., there is still no mature product in the current sensor market that can detect the froth layer thickness of flotation machines. All of these are important factors affecting the application level of mineral separation process control. Now simple PID control is still mostly used in the flotation process control algorithms. Although the flotation control field combines with many optimization algorithms such as fuzzy control, neural network, genetic algorithm, most of these algorithms are in the theoretical research and discussion stage, and high performance control algorithms that are practically applied in concentrators are few.

10.5 Process Control Problems and Development Trend …

(3)

(4)

391

With the upsizing development of flotation machines, the requirement for automation integration degree is higher and higher. For example, it is necessary to install all the pulp flow detection, gas volume and froth layer thickness control, froth image analysis system, X-ray fluorescence analyzer and other grade detection devices. However, the data detected by the system can reflect partial flotation process characteristics only. Some flotation parameters still need to be detected depending on more advanced control technology. Most concentrators have shortages in aspects of field equipment and system maintenance. Since professional technical backbone is lacking for system maintenance and adjustment in the field, although the control devices are in a good condition in a short time after production, it is difficult for field technicians to solve in case the devices are faulty, and especially for electric automatization, it will affect normal production of concentrators if the solving is late.

10.5.2 Development Trend 10.5.2.1

Intelligence, Digitization and Virtualization of Sensor Technology

In recent years, the sensor technology has been rapidly developed, and many new sensors have emerged in industries, but the requirement for product quality also has become higher and higher, such as stability, accuracy, timeliness and repeatability of sensor, which are extremely useful for providing reliable data for process control. Intelligence and digitization of a sensor provide conditions for the realization of network connection with control devices, successfully realize multi-direction and multivariable data transfer depending on field bus technology, and replace the old univariate and unidirectional direct input and output devices one by one. Virtualization technology realizes the specific hardware functions of a sensor completely depending on software technology, based on general hardware platform. All of these are essential for shortening product development cycle and reducing cost.

10.5.2.2

Improvement of Automatic Control Theory and Method and Its Optimization

Flotation process is not a simple industrial process, because it includes many difficult and complicated automation technology difficulties, such as nonlinearity, time varying, easy overshoot, multivariate, random jamming and other characteristics that easily occur in the control system. Therefore, the control unit is required to have strong robustness and adaptation. With constant development of the intelligent control technology, more and better control strategies will be applied in the flotation production process. The following several control strategies will guide the development direction of process control technology [28]:

392

1.

2.

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Model prediction control, which is mainly introduced according to difficultly accurate building of some mineral separation process models. The modelbased analytical method can be further divided into two subclasses, namely, experience model and phenomenology model. Experience model consists of various statistical approaches that correlate the measured input and output data, concerning two or more independent variable and dependent variable of multivariate models, and can be used for predictive control. In addition, by constantly analyzing the flotation loop data, and constantly correcting and adjusting the model-based prediction controller, it may adapt it with constantly changing conditions (i.e. self-adaptive control). Self-adaptive control appears to be particularly important for such nonlinearity and complicated process of flotation control. Many flotation prediction control systems often include selfadaptive control aspect. At present, although there are many literatures used to specially discuss about model-based multivariable control system, their application quantity is still relatively less in industries. The first-order flotation kinetic model belongs to one kind of phenomenology model. It is built under such assumed condition: the quantity of pulp particles is the first element deciding the velocity of particles against bubbles, and the bubble concentration shall be kept constant. We can use the chemical reaction analogy method to model the flotation machine, namely, the process that the solid particles are removed from the pulp can be defined by the first-order rate equation. The experimental result of the above model is ideal, especially embodied in robustness and stability. Therefore, it will become a very important control strategy in the future automatic control field of mineral separation. Optimal control. Its most basic function is to ensure concentrators obtain the biggest economic benefits by means of the fewest resource costs, and to optimize its flotation indicators by finding the optimal process parameter combination. The applied technology mainly includes artificial neural network, inductive machine learning and other intelligent control algorithms. In some mining enterprises at home and abroad, the Distributed Control System (DCS) has been widely applied, but the optimization based on flotation process parameters in the DCS will become a development direction in future.

10.5.2.3

Stepping into “Intelligent Mine”

With the constant development of computer technology, network technology and automation technology, the informatization of the mine industry should develop towards the directions of integration, digitization and multifunction fields. From the practical industry, it shall regard the digital mine focused on network information technology as the direction and objective of information development [29]. The mine informatization is mainly reflected in production process control, building of business management system and monitoring of production safety; the problem of “Information Island” can be effectively solved, as long as the overall planning is strengthened, and the information flow between each function and between each

10.5 Process Control Problems and Development Trend …

393

system of concentrators is gradually improved. In addition, the development for relevant software shall be enhanced, in order to expedite the key cultivation for high-tech IT talents in the mine field and increase their introduction intensity.

References 1. Long H (2000) Development status and prospects of mineral processing process control. Nonferrous Met 52(4):123–125 2. Zhenxing L, Shuming W, Liangfeng L (2008) Summary of automatic detection and automation of mineral processing. Yun Nan Metall 37(3):20–21 3. Changxing D, Long H (1999) Realizing the control of mineral processing is the only way for the development of mineral processing industry. For Met Ore Dress 36(9):29–33 4. Lynch AJ, Watt JS, Finch JA, Harbort GJ (2005) History of flotation technology. In: Proceedings centenary of flotation symposium, pp 15–18 5. Amsden MP, Chapman C, Reading MB (1973) Computer control of flotation at Ecstall concentrator. CIM Bull 84–91 6. AusIMM Broken Hill Branch (1930) The development of processes for the treatment of crude ore, accumulated dumps of tailing and slime at Broken Hill, New South Wales. In: AusIMM proceedings, vol 80, pp 379–444 7. Behrend GM (1978) Mill instrumentation and process control in the Canadian mining industry. In: Milling practice in Canada. Canadian Institute of Mining and Metallurgy, Montreal, pp 23–44 8. Hughes DV (1983) Sampling systems for on-stream X-ray analysers in ore-dressing plants. Trans Inst Meas Control 5(4):185–191 9. Guanghua N, Herong L (2007) Current status and development prospects of process control in mineral processing plants. Comp Util Miner 5:28–29 10. Stump NW, Roberts AN (1974) On-stream analysis and computer control at the New Broken Hill Consolidated Limited concentrator. AIME Trans 256:143–148 11. Watt JS, Gravitis VL (1973) Radioisotope X-ray fluorescence techniques applied to onstream analysis of mineral process streams. In: Automatic control in mining, mineral and metal processing, IFAC international symposium, Sydney, 13–17 Aug 1973. Institution of Engineers, pp 199–205 12. Leskinen T, Koskinen J, Lappalainen S, Niitti T, Vanninen P (1972) On-stream analysers and Outokumpu concentrators. Presented to 74th annual meeting of the CIM, 9–12 Apr 1972. Canadian Institute of Mining and Metallurgy, Montreal 13. Muller B, Smith GC, Smit S, Singh A, Strobos PJJ, Reemeyer L (2004) Enhancing flotation performance with process control at Century Mine. In: Proceedings metallurgical plant design and operating strategies (MetPlant) 2004 conference. The Australasian Institute of Mining and Metallurgy, Melbourne, pp 337–350 14. Fengyu W, Tan Z, Songwei H (2006) Review of China’s mineral processing automation. For Miner Sep 8:18–21 15. Jihua D (1998) Application of automatic control technology in domestic concentrator. Met Mine 10:42–44 16. Singh A, Louw JJ, Hulbert DG (2003) Flotation stabilization and optimization. J South Afr Inst Min Metall 581–588 17. Steven JAH (1993) Control system for flotation operation. Met Mine 2:40–44 18. Jun S, Chaohong Y (2008) Application of flotation machine pulp level control system in potassium flotation. Min Metall 17(2) 19. Wenwang Y, Tao W (2011) Design and research of micro-processing flotation column pulp level control system. Nonferrous Met 6:53–55

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20. Jinkun L (2010) Advanced PID control MATLAB simulation. Electronic Industry Press, Beijing 21. Guoyong L (2009) Intelligent predictive control and its MATLAB implementation. Electronic Industry Press, Beijing 22. Shean BJ, Cilliers JJ (2011) A review of froth flotation control. Int J Miner Process 100:57–71 23. Guichun H, Kaiqi H (2008) Study on the relationship between flotation target and digital image of flotation froth. Met Mine 8:96–101 24. Runge K, McMaster J, Wortley M, La Rosa D, Guyot O (2007) A correlation between VisioFroth measurements and the performance of a flotation cell. In: Proceedings ninth mill operators’ conference. The Australasian Institute of Mining and Metallurgy, Melbourne, pp 79–86 25. Donghua L, Fei Y, Jianjun Z (2011) Application and research of BFIPS_I flotation froth image processing system. Nonferrous Met 1:43–45 26. Zhongwei W, Donghua L (2011) Application research based on feature parameters of flotation froth image. Min Metall 20:82–85 27. Bo L, Yinggen L (2009) Design and application of dedicated flotation level controller. Min Metall 18(3):91–93 28. Hu Q, Zhihong L, Songwei H (2010) Development trend of crushing ore grinding and flotation automation. Yun Nan Metall 39(3):13–16 29. Jingming J, Liguan W (2009) Mining and metallurgical software promotes the development of digital mines in China. China Min 18(10):91–93

Chapter 11

Model Selection and Design of Flotation Machines

There are many influencing factors for model selection and design of flotation machines. Not only the conditions such as the ore properties, throughput, flotation size, concentration and reagent system shall be considered but also the factors such as the flotation machine type, equipment configuration, investment cost and maintenance operations shall be considered. For design and model selection of flotation machines, the following shall be mainly determined: (1) types of flotation machines; (2) specifications of flotation machines; (3) configuration of flotation machines; (4) selection of supporting equipment. This chapter compares the technical characteristics of Chinese typical flotation machines, and then introduces the type, specification, configuration and supporting equipment model selection of the flotation machine. Finally, it introduces the fuzzy comprehensive evaluation method of the flotation machine section and the rapid model selection method of flotation machines of CBR.

11.1 Technical Characteristics of Flotation Machines Now, the most common flotation machines include KYF, XCF, BF, JJF, GF, CLF, CGF, XJK, etc., in China. They have been described in detail in the above chapters. This section mainly compares them with the aspects of functional difference, aeration mode, power consumption, equipment configuration, adaptation to the separation of ores, etc. (1)

Functional difference

Both KYF and CLF belong to the scope of pneumatic mechanical agitation flotation machine. They cannot automatically suck the pulp, and their impellers are used to disperse air and agitate the pulp only. The XCF pneumatic mechanical agitation flotation machine can automatically suck the pulp while being aerated for special structural design. BF, GF and other mechanical agitation flotation machines can realize © Metallurgical Industry Press 2021 Z. Shen, Principles and Technologies of Flotation Machines, Springer Tracts in Mechanical Engineering, https://doi.org/10.1007/978-981-16-0332-7_11

395

396

11 Model Selection and Design of Flotation Machines

automatic suction feeding or middlings. These flotation machines with multiple functions provide great flexibility for their model selection and configuration. (2)

Air inflation method

Air is the cheapest and the most useful reagent for flotation machines, and different aeration conditions are required for different processing materials of the flotation system. BF, GF and JJF flotation machines are mechanical agitation flotation machines with a suction rate of 0.8–1.0 m3 /(m2 min). KYF, XCF and CLF flotation machines are pneumatic mechanical agitation flotation machines of which the aeration rate can be adjusted as required. For the ore properties with larger or lower requirements for gas volume, it is reasonable to select the pneumatic flotation machine with a wide gas volume adjustment range and accurate adjustment. However, the automatic suction flotation machine is applicable to the separation of minerals with wide requirements for the gas volume range, wherein, its suction rate depends on the structure and operating parameter, its gas volume adjustment range is narrower and its adjustment is inaccurate. (3)

Power consumption

Large volume flotation machine has small power intensity. For example, the unit volume installed power of JJF-16 m3 is 1.9 kW/m3 , and that of JJF-200 m3 is 1.1 kW/m3 only; The unit volume installed power of KYF-16 m3 is 1.35 kW/m3 , and that of KYF-320 m3 is 0.65 kW/m3 only. From this perspective, the large volume type shall be selected in the case that the processing capacity of concentrators is definite. (4)

Equipment configuration

Since the flotation machines abroad have no function of automatic pulp suction, they are basically configured in a stepwise way and equipped with a middlings return pump. Chinese flotation machines have diversified functions and configurations. KYF and JJF flotation machines need to be configured in a stepwise way if used separately, and middlings need to be returned through the froth pump; GF, BF, CGF and XCF flotation machines can be configured in a horizontal way, and their process configuration is simple without the need of froth pump. From the perspective of volume, most flotation machines with the volume of 70 m3 and below are configured in a horizontal way, while all the flotation machines with the volume of above 70 m3 are configured in a stepwise way. For flotation machines with a volume of 70 m3 and below, the horizontal configuration is suggested due to small middling and pulp quantity, which can reduce the height of plant and arrange the flotation machines orderly and beautifully; For flotation machines with a larger volume, the stepwise configuration is suggested due to larger pulp and middling quantity and restricted pulp suction capacity of the pulp suction tank.

11.1 Technical Characteristics of Flotation Machines

(5)

397

Adaptation to the separation of ores

KYF, JJF and BF flotation machines are applicable to the separation of conventionally non-ferrous metals, ferrous metals and non-metallic minerals, while for the minerals with coarser or large density particles, CLF, GF or CGF flotation machines may be selected. It is necessary to select special flotation machine because the flotation of saline minerals and oxidized ores has its particularity.

11.2 Preliminary Determination of Flotation Machine Type and Specification The selection of flotation machine type is related to the factors such as raw ore properties (ore density, size, silt content, grade, floatability, etc.), equipment performance, scale of concentrator, process structure and system division. In the model selection, pay attention to the following four problems: (1)

Ore properties and requirements for separation operation

For the ores with coarse size or large density, generally, the high concentration flotation method is adopted to reduce the settling velocity of particles and reduce the sedimentation of mineral particles. In order to adapt to this characteristic, the flotation machine with shallow tank or the flotation machine special for coarse particles (such as CLF flotation machine) shall be selected in design; For the sulphide ore with larger demand for the gas volume and the oxidized ore sensitive to the aeration rate, generally, the pneumatic mechanical agitation flotation machine is selected, easy for effective control of gas volume. For the minerals with moderate requirements for the aeration rate, both mechanical agitation flotation machine and pneumatic mechanical agitation flotation machine apply. The rougher and scavenger banks lie in improving the recovery rate, and generally need a longer overflow weir with a fast froth discharge rate; the cleaner bank mainly lies in improving the concentrate grade, wherein, the flotation froth layer will be thicker and the flotation aeration rate is smaller. Therefore, the selection and operation of the flotation machine of cleaner bank shall be different from those of the flotation machine of rougher and scavenger banks. (2)

Reasonably selecting the specification of flotation machine according to the pulp flow

In order to ensure separation effect, it must ensure that the pulp in each flotation tank has a certain residence time. Longer or shorter time will cause loss of useful minerals and reduce the recovery rate of operations. Therefore, the specification of flotation machine must adapt to the scale of concentrator. The flotation system shall be reduced where possible to play the superiority of a large flotation machine. For some easily floatable ores, in conditions permitting, even

398

11 Model Selection and Design of Flotation Machines

take single series production into consideration. Considering according to the current domestic largest flotation machine (volume of 680 m3 ), each series can be up to above 50,000 t/d. The specification and quantity of flotation machine are determined through technical and economic comparison. In the solution comparison, generally, it shall conduct comprehensive comparison in aspects of separation indicator, operating expense, operation management, maintenance and overhaul, etc., to ensure unified model and specification of equipment. However, for concentrators, the separation indicator shall be regarded as a dominating factor and given enough attention. (3)

Paying attention to the manufacturing quality of equipment and supply of spares

Served as the necessary conditions for ensuring the production of concentrator, good equipment quality and sufficient spares supply sources should not be neglected in model selection.

11.3 Selection for the Specification of Flotation Machines 11.3.1 Calculation of Flotation Pulp Volume W =

  K 1 Q R + ρ1 60

(11.1)

where W Q R ρ K1

Calculated pulp volume rate, in m3 /min; Design operation process amount (including return amount), in t/h; Ratio between the liquid and solid mass of the operation pulp; Density of ores; Fluctuation coefficient of the pulp. When it is ball milling before flotation, K 1 = 1.15; When it is semi-automatic milling or automatic milling before flotation, K 1 = 1.2.

11.3.2 Determination of Flotation Time of Operations The flotation time greatly affects the flotation tank volume and flotation indicators, so it must be selected carefully. Generally, the flotation time of an operation is determined according to the test results and with reference to the production case of similar ore concentrators. The flotation time is determined by means of small closedcircuit test time, hunting test time, pilot-scale test time and actual flotation time of concentrator of this type, and the common flotation time takes small closed-circuit

11.3 Selection for the Specification of Flotation Machines

399

test time and hunting test time as the model selection basis. Generally, the above two times are shorter than the industrial production time. In design, the test flotation time shall be lengthened and is multiplied by the adjustment coefficient of K rt generally. The formula is as follows:   1/2 + t t = t0 q 0 q

(11.2)

where t t0 K rt

Design flotation time, in min; Small flotation test time in the laboratory, in min; Adjustment coefficient of flotation time.

The short circuit of the flotation machine is inevitably increased. In order to compensate for the shortage of flotation time, the adjustment coefficient of K rt of flotation time must be adjusted with the volume of flotation machine.  K1 =

1.5−3, V0 ≤ 40 2.0−3.5, V0 < 40

(11.3)

where V0

Volume of flotation machine, in m3 .

The residence time of the pulp is generally deemed as the average detention time of the pulp in the tank body of the flotation machine, from entering the operation feed inlet to discharging from the outlet. At home, the residence time of the pulp in the tank body of the flotation machine is deemed as approximate to the flotation time. In case the froth productivity of the flotation machine is not large or the volume of the flotation machine is small, one operation shall be considered and calculated overall and the overflow volume of froth shall not be considered. In case the froth productivity of the flotation machine is large or the volume of the flotation machine is large, the overflow volume of froth shall be particularly considered.

11.3.3 Calculation and Determination of Tank Quantity of Flotation Machines In view of two calculations of the residence time of tr of the flotation machine, the calculation of tank quantity of the flotation machine is determined based on the above two cases. (1)

In case the froth productivity of the flotation machine is not large or the volume of the flotation machine is small, the t r shall be kept equal to the value of t. The tank quantity of the flotation machine is calculated as follows:

400

11 Model Selection and Design of Flotation Machines

n =

→

WF t Ve

(11.4)

where n WF t Ve

Calculated quantity of tanks of the flotation machine; Calculated pulp volume, in m3 /min; Flotation time, in min; Effective volume of the selected flotation machine, in m3 ;

where V e = VK 2 . V K2

Geometric volume of the flotation machine, in m3 ; Ratio between effective volume and geometric volume of the flotation tank. In case of separation of non-ferrous metal ores, take K 2 = 0.8 − 0.85; In case of separation of iron ores, take K 2 = 0.65 − 0.75. When the froth layer is thick, take a small value.

(2)

In case the froth productivity of the flotation machine is small or the volume of the flotation machine is large, the t r shall be kept equal to the value of t. The tank quantity of the flotation machine is calculated as follows: n=i

(11.5)

Conditions of satisfaction: t = Ve /WF1 + Ve /WF2 + · · · + Ve /WFi . The total quantity of tanks of the flotation machine can be worked out once as per Formulas 11.4 and 11.5, and then divided into several series, and can also be first divided into several series, and then the quantity of tanks of the flotation machine required for each series can be worked out. Principles of determining the series number of flotation operations: (1)

(2)

As same as the grinder series. This method is easy for automatic pulp flow but against the stabilization for interchange between the pulp flow and the series and against the production testing; Different from the grinder series. This method is easy for stabilization for interchange between the pulp flow and the series and for production testing, and more favourable to the realization of requirement for large flotation machine but always difficult to realize the automatic flow transport of the main ore. This method is chiefly used in large concentrators with a higher requirement for the automatic control level.

The phenomenon of “short circuit” shall be avoided when the quantity of flotation machine is calculated and determined. In the small test, all mineral particles in the tank have the same residence time and the equal flotation opportunity. However, in the continuous flotation process of industrial production, the residence time of the mineral particles in the flotation tank is unbalanced, there is a distribution problem of residence time, wherein, the rate of partial pulps (or mineral particles) passing

11.3 Selection for the Specification of Flotation Machines

401

through the flotation circuit is faster than the average rate or the rate calculated as per the nominal residence time, and this part of partial pulps may flow into the tailings soon without sufficient recovery, causing the phenomenon of “short circuit”. Therefore, in order to reduce the possibility of “short circuit”, the quantity of tanks of rougher–scavenger banks of each series shall not be too little, and shall not be less than 6 generally. With the application of large flotation machine and the improvement of the flotation unit reactor technology, the concept of tank quantity of the flotation machine also changes. At present, there have been many examples of large concentrators with less than six rougher–scavenger flotation tanks. Even the single flotation machine as the design concept of an operation has been gradually adopted by the engineering technicians. Therefore, when the quantity of tanks of flotation machine of each series is determined, the flotation machine shall be selected with reference to similar example enterprises according to different factors such as the specification and flotation time of the flotation machine. The selection of intermediate boxes shall also be paid attention to in the selection of flotation machine. Generally, the medium and small flotation machines shall be arranged with an intermediate box every 2–5 tanks so that each separated section can separately control the pulp and froth level, thus achieving the optimal overall recovery rate; The configuration of an intermediate box of the large flotation machine with a volume of above 50 m3 depends on the process conditions and 2–4 tanks are appropriate generally. Generally, the ultra-large flotation machine with a volume of above 200 m3 is arranged with an intermediate box every 1–2 tanks, and this intermediate box can be designed to external and internal types according to process. In addition, for the convenience of maintenance, management and configuration, it is better to select the same model and specification of equipment for operations other than cleaner bank. The cleaner bank shall depend on the concentrate productivity and operation concentration. If the concentrate productivity is larger, the flotation machine having the same model with the rougher and scavenger can also be considered, without affecting the separation effect.

11.3.4 Calculation Example With a Cu–Mo concentrator as the example, the initial conditions are as follows: semi-automatic milling for grinding circuit; daily processing capacity: 150,000 t/d; for the large demand for the aeration rate of sulphide ore, the pneumatic mechanical agitation flotation machine is selected. For small froth produn.ctivity of each operation, Formulas 11.1–11.5 are adopted for calculation. See Table 11.1 for relevant process parameters and calculation results.

Cu–Mo and other floatable scavenger 2

Copper rougher

Copper scavenger 1

Copper scavenger 2

Cu–Mo and 307.5 other floatable concentration 1

3

4

5

6

7

6095

6226

6314

6308

6464

Cu–Mo and other floatable scavenger 1

2

6579

Cu–Mo and other floatable rougher

21

32.5

32.2

32.4

32.5

32.2

32.1

21.23

249.61

257.95

259.57

258.33

267.81

273.63

5

2

2

4

2

2

3

2

3

3

3

3

3

3

10

6

6

12

6

6

9

1.1

1.2

1.2

1.2

1.2

1.2

1.2

0.8

0.85

0.85

0.85

0.85

0.85

0.85

Dry ore Concentration Pulp Small Amplification Selection Fluctuation Volumetric quantity (%) volume flotation coefficient, flotation coefficient, coefficient 3 (t/h) (m /min) time K rt time K1 (min) (min)

1

Operation name

Table 11.1 Model selection calculation results of the flotation equipment in a Cu–Mo concentrator

265

2349 ara>

2427

3664

1519

2520

3219

Total volume of flotation machine (m3 )

30

300

300

300

300

300

300

Specification of flotation machine (m3 )

9.73

7.05

7.28

14.66

7.29

7.56

11.59

Calculation of flotation machine quantity (quantity)

8

8

8

16

8

8

12

2

2

2

4

2

2

3

(continued)

4

4

4

Selection Single Number of series of series flotation machine quantity (quantity)

402 11 Model Selection and Design of Flotation Machines

86.375

86.375

86.375

11 Cu–Mo separate scavenger 1

12 Cu–Mo separate scavenger 2

Cu–Mo and 93.75 other floatable concentration 3

9

10 Cu–Mo separate rougher

Cu–Mo and 160.62 other floatable concentration 2

20

20

20

21

21

6.31

6.31

6.31

6.47

11.09

5

5

7.5

4

4

2

2

2

2

2

10

10

15

8

8

1.5

1.5

1.5

1.1

1.1

0.8

0.8

0.8

0.8

0.8

Dry ore Concentration Pulp Small Amplification Selection Fluctuation Volumetric quantity (%) volume flotation coefficient, flotation coefficient, coefficient 3 (t/h) (m /min) time K rt time K1 (min) (min)

8

Operation name

Table 11.1 (continued)

78.82

78.82

118.23

64.72

110

Total volume of flotation machine (m3 )

30

30

30

30

30

Specification of flotation machine (m3 )

3.94

3.94

5.91

2.37

4.07

Calculation of flotation machine quantity (quantity)

4

4

6

8

8

2

2

3

2

2

2

Selection Single Number of series of series flotation machine quantity (quantity)

11.3 Selection for the Specification of Flotation Machines 403

404

11 Model Selection and Design of Flotation Machines

11.4 Configuration of Flotation Machines After the specification and model of the flotation machine are determined, the configuration method of the flotation machine shall be considered. Under the condition of meeting the flotation process, the selection for flotation machine or flotation machine unit decides the horizontal configuration or stepwise configuration, involving flow mode of the pulp and return mode of the middling froth. However, the configuration method decides the design of flotation plant and flotation machine foundation. A good configuration method of the flotation machine can simplify the design of flotation machine foundation, reduce the plant height and reduce the basic investment.

11.4.1 Horizontal Configuration The horizontal configuration means that the flotation machines of different operations are installed on the same horizontal plane, and the middlings can be completed by means of automatic suction of the flotation machine in the workshop. The horizontal configuration saves the pulp pump, froth pump and other auxiliary equipment, reduces the energy consumption of concentrator and equipment maintenance cost, simplifies the concentrator design and reduces the plant height. See Fig. 11.1 for horizontal configuration. The flotation machines or flotation machine units that can be configured in a horizontal way include BF flotation machine, GF flotation machine, BF/JJF flotation machine unit, GF/JJF flotation machine unit, XCF/KYF flotation machine unit, GF/KYF flotation machine unit, CLF flotation machine unit with pulp suction tank and free-flow tank, etc. These flotation machines or units are briefly introduced below and typical application examples are cited for reference. (1)

BF and GF flotation machines

Both BF and GF flotation machines are the mechanical agitation flotation machines developed by BFVS: they have four functions, i.e. automatic air suction, automatic pulp suction, automatic middling froth suction and flotation, they can automatically form flotation circuit, without the need of auxiliary equipment such as blower and pump, they are configured in a horizontal way in the workshop, they can be served as the pulp suction tank and free-flow tank and they are convenient for flotation process

Fig. 11.1 Horizontal configuration

11.4 Configuration of Flotation Machines

405

Table 11.2 Typical concentrators of BF and GF flotation machines S. No.

Mine name

Ore type

Model

1

Gongchangling Mining Company of Ansteel Iron ore

BF-20

2

Xinjiang Ashele Copper Co., Ltd

Copper-zinc ore

BF-20 and BF-10

3

Yunnan Chihong Zn & Ge Co., Ltd. (Huize Pb–Zn Deposit)

Pb–Zn deposit

BF-16 and BF-8

4

CHALCO Shandong Co., Ltd

Bauxite

5

Qinghai Yuantong Potash Fertilizer Co., Ltd Potassic salt ore

BF-20

6

Jilin Ji’en Nickel Industry Co., Ltd

BF-8 and GF-4

7

Xinjiang Axi Gold Mine

Gold ore

BF-8 and BF-2.8

8

Dahongshan Copper Mine

Copper ore

GF-1.1

9

Changqing Tungsten and Molybdenum Co., Ltd

Molybdenum ore

GF-4 and GF-2

10

Chengde Yanshan Silver Industry Co., Ltd

Silver ore

GF-2

11

Songxian Miaoling Gold Mine

Gold ore

GF-1.1

12

Liaoning Haicheng Houying Group

Magnesium ore

BF-40 and 24

Nickel ore

BF-16 and BF-8

change. GF flotation machine places extra emphasis on solving the flotation problem of precious metal minerals containing gold, silver, etc., and is mostly applied in the gold and silver concentrator when used separately. Such two flotation machines are widely applied in Chinese medium and small concentrators, with a single tank volume of 0.15–50 m3 . See Table 11.2 for typical concentrators. (2)

BF/JJF and GF/JJF flotation machine integral units

JJF flotation machine is a kind of mechanical agitation flotation equipment: the capacity of automatic air suction is available, but the capacity of automatic pulp and middling froth suction is unavailable, the flotation machine shall be configured in a stepwise way if used separately and the pulp and middling froth shall be returned through a pump. In order to realize the horizontal configuration of the flotation machine, BF/JJF or GF/JJF flotation machine unit is often used, wherein, BF or GF flotation machine is served as the pulp suction tank and JJF flotation machine is served as the free-flow tank. The single tank volume of BF/JJF and GF/JJF flotation machine units is 1–50 m3 , meeting the requirement of most medium and small concentrators at home and abroad. See Table 11.3 for the typical users of BF/JJF and GF/JJF flotation machine units. (3)

XCF/KYF flotation machine unit

The KYF flotation machine is a pneumatic mechanical agitation flotation machine: it needs to complete flotation by means of the air supplied by the blower, the capability of automatic pulp and middling froth suction is unavailable, the flotation machine

Mine name

Xilin Pb–Zn Deposit

Anqian Mining Company

Shanxi Daxigou Mining Company

Jinchuan Nickel Industrial Company

Luanchuan Sanqiang Tungsten and Molybdenum Co., Ltd

Dahongshan Iron Mine

Sizhou Concentrator of Dexing Copper Mine of Jiangxi Copper Corporation Limited

Jinchuan Group

S. No.

1

2

3

4

5

6

7

8

Table 11.3 Typical users of BF/JJF and GF/JJF flotation machine units Ore type

Nickel ore

Copper ore

Iron ore

Molybdenum ore

Nickel ore

Iron ore

Iron ore

Pb–Zn

Model

GF/JJF-28 and 24

GF/JJF-28

GF/JJF-20

GF/JJF-16

GF/JJF-24

BF/JJF-20

BF/JJF-20

BF/JJF-8

406 11 Model Selection and Design of Flotation Machines

11.4 Configuration of Flotation Machines

407

needs to be configured in a stepwise way if used separately and pulp and middling froth need to be returned through a pump. XCF flotation machine is a pneumatic mechanical agitation flotation machine with the capacity of automatic pulp and middling froth suction: it needs to pump the air by means of blower, and conquered the technical problem of unavailable automatic pulp and middling froth suction of the pneumatic flotation machine for the first time in the world, becoming exclusive in China. XCF flotation machine is served as the pulp suction tank, KYF flotation machine is served as the free-flow tank, XCF/KYF flotation machine unit can realize horizontal configuration of the flotation machine better and the use of pump is canceled. With the maximum single tank volume of 70 m3 , XCF/KYF flotation machine unit is currently a pneumatic mechanical agitation flotation machine unit having the widest application range and the largest application amount in China. See Table 11.4 for typical cases in recent years. (4)

GF/KYF flotation machine unit

The GF/KYF flotation machine unit uses the GF flotation machine as the pulp suction tank and uses the KYF flotation machine as the free-flow tank. This kind of flotation machine unit is applied widely in the concentrator with large middling return volume and can give full play of the characteristic of the large pulp suction capacity of the GF flotation machine. The maximum single tank volume of GF/KYF flotation machine unit is 50 m3 . In the reverse flotation of iron ore and bauxite and other mineral separation processes, the middling froth return volume is large, the froth is adhesive, the mobility is poor and the aeration rate is sensitive, thus GF/KYF flotation machine unit is often selected. See Table 11.5 for typical cases. (5)

CLF flotation machine unit with pulp suction tank and free-flow tank

The CLF flotation machine is a kind of widely graded pneumatic mechanical agitation flotation machine developed based on the new concept of flotation dynamics. It is characterized in special tank body structure and new pulp circulation mode so that no sediment in the tank occurs in case of processing of coarsely graded materials when the pulp circulates; A grid plate is arranged in the tank to form a suspended layer of coarse minerals above it, thus achieving the flotation aim of coarse minerals, and a circulation channel is arranged inside, meeting the mineralization and separation of fine minerals. The maximum single tank volume of CLF flotation machine unit can be up to 40 m3 . See Table 11.6 for the typical concentrators selecting this kind of flotation machine unit.

Mine name

Mongolia T-D Zinc Mine

Jilin Huichun Gold Mine

Qinghai Wister Co., Ltd

JISCO

Wusteel Daye Iron Mine

Yunnan Phosphate Chemical Group Co., Ltd

Fengning Xinyuan Molybdenum Industry Co., Ltd

CHALCO Zhongzhou Co., Ltd

SDIC Lop Nor Leopoldite Co., Ltd

China Gold Inner Mongolia Mining Co., Ltd

S. No.

1

2

3

4

5

6

7

8

9

10

Table 11.4 Typical users of XCF/KYF Flotation machine unit

Copper concentration

Leopoldite

Bauxite

Molybdenum ore

Phosphorite

Iron ore

Iron ore

Copper ore

Gold ore

Zinc ore

Ore type

XCF/KYF-70

XCF/KYF-50

XCF/KYF-40

XCF/KYF-50

XCF/KYF-50 and 30

XCF/KYF-50

XCF/KYF-50

XCF/KYF-16

XCF/KYF-40 and 24

XCF/KYF-8

Model

408 11 Model Selection and Design of Flotation Machines

11.4 Configuration of Flotation Machines

409

Table 11.5 Typical users of GF/KYF flotation machine unit S. No.

Mine name

Ore type

Model

1

Baogang concentrator

Iron ore

GF/KYF-50

2

CHALCO Zhongzhou Co., Ltd

Bauxite

GF/KYF-40

3

Nicolae copper concentrator of Kazakhmys PLC

Copper ore

GF/KYF-40

Table 11.6 Typical concentrators of CLF flotation machine unit or flotation machine S. No.

Mine name

Ore type

Model

1

Guixi Smelter of Jiangxi Copper Corporation Limited

Slag

CLF-8

2

Tongliao Silica Mining Company

Quartz sand

CLF-8

3

Fengning Sanying Mining Company Phosphorus

CLF-8

4

Shuangluan Jianlong Mining Company

Titanium and phosphorus

CLF-8

5

Shandong Yanggu Xiangguang Copper Co., Ltd

Slag

CLF-8

6

Taihe Iron Mine of Chongqing Iron and Steel Group

Titanium and iron

CLF-16

11.4.2 Stepwise Configuration Stepwise configuration means that the flotation machines of different operations are not installed on the same horizontal plane, and there is a height difference between flotation workshops. Generally, there are two methods: One method is that the pulp in the last operation flows to the next operation by gravity and the middling froth is returned by froth pump; the other method is that the middling froth is returned by automatic flow and the underflow pulp is transported by pump. When stepwise configuration is adopted, the foundation between workshops of the flotation machine shall have a height difference for the convenience of automatic pulp flow or automatic froth return. Therefore, the plant height and investment cost will be increased in case the process is complex. However, in the stepwise configuration, the pulp throughput or the froth return are not restricted by the pulp suction capacity of the flotation machine, which is the most remarkable advantage of stepwise configuration. The stepwise configuration is shown in Fig. 11.2a and b, respectively. The calculation of height difference between steps is very important after stepwise configuration is selected. The first form needs to comprehensively consider the volume of underflow pulp, the size fraction of particles, the ratio of particles, the froth layer thickness and the aeration rate of the previous and next operations, nominal opening of level control valve and other factors. The formula is as follows:  H s = 0.5 ·

W Ss · K 00

2

· g −1 · K F · Kρ · K s

(11.6)

410

11 Model Selection and Design of Flotation Machines

Fig. 11.2 a Stepwise configuration allows gravity flow of slurry, b Stepwise configuration allows gravity flow of froth

where Hs W K 00 Ss g KF Kρ KS

Height difference between steps, in m; Pulp flow, in m3 /s; Influence coefficient of the flotation machine structure to the height difference, 0.65–0.8 generally; Flowable valve area of the pulp in the nominal opening of the valve, in m2 ; Gravitational acceleration, in 9.8 m/s2 ; Influence coefficient of froth layer thickness; Influence coefficient of particle ratio; Influence coefficient of particle size.

For the second form, the height difference of Hf needs to consider the froth volume, the size and ratio in the froth and the collision coefficient and viscosity of froth and calculated with reference to the froth tank gradient in the mineral separation practice. A detailed calculation process will not be given.

11.4 Configuration of Flotation Machines

411

The common flotation machine used for stepwise configuration includes KYF, JJF and CLF types. (1)

KYF flotation machine

The KYF flotation machine is a pneumatic mechanical agitation flotation machine: this machine features the inverted-cone impeller with backward-inclined blade, the porous cylindrical air distributor and the low damping suspended stator. In recent 10 years, flotation equipment has been developed towards upsizing, high efficiency and high degree of automation. The advantages of flotation equipment with large volume lie in that the space required for concentrator can be reduced, or the processing capacity can be improved provided that the existing concentrator space is not changed; the design layout of the flotation section is simplified; the complexity of the control device is simplified and the operating flexibility of the flotation section is improved; the maintenance cost is significantly reduced; and the total cost of power consumption and production of processing each ton of ore is reduced, etc. At present, the large and ultra-large KYF flotation machines have been popularized on a large scale at home and abroad, obtaining good economic and social benefits. See Table 11.7 for the typical users of large and ultra-large KYF flotation machines. (2)

JJF flotation machine

JJF flotation machine is a self-inspiring type mechanical agitation flotation machine that is designed with a large lower circulation for the pulp in the tank. Since the capacity of automatic pulp suction is unavailable, JJF flotation machine shall be configured in a stepwise way if used separately and the middlings shall be returned through the froth pump. JJF flotation machine is widely applied to flotation operations of non-ferrous metals, ferrous metals, non-metallic and chemical materials with very strong adaptation. At present, more than 1000 different specifications of JJF flotation machines have been served in various concentrators, and have obtained satisfying technical and economic indicators. Table 11.7 Typical users of large KYF flotation machines S. No.

Mine name

Ore type

Model

1

China Gold Wunugetushan Mine

Cu–Mo ore

KYF-320 and 160

2

Dexing, Copper Deposit of Jiangxi Copper Corporation Limited

Copper ore

KYF-200, 160, 130 and 70

3

KISC Dahongshan Iron Mine

Copper ore

KYF-200

4

Jinchuan Group Co., Ltd

Nickel ore

KYF-160 and 50

5

Guizhou Jinfeng Gold Mine

Gold ore

KYF-100, 50 and 40

6

Luoyang Molybdenum Co., Ltd

Molybdenum ore

KYF-100 and 50

7

Jinduicheng Molybdenum Group Co., Ltd

Molybdenum ore

KYF-50 and KYF-260

412

11 Model Selection and Design of Flotation Machines

Since the small JJF flotation machine is often used with other flotation machine units with the pulp suction capacity as integral units, there are a few concentrators separately using JJF flotation machine. The typical concentrators are listed in Table 11.8. (3)

CLF flotation machine

CLF flotation machine is often configured in a stepwise way when used for operations with large processing capacity and simple process. The raw ore of Slag Workshop of Guixi Smelter of Jiangxi Copper Corporation Limited is the slag, the copper in the slag is recovered through flotation, the separation process of two-time rougher–twotime scavenger–three-time concentration is adopted, 15 CLF-40 flotation machines are used for rougher and scavenger banks, the pulp does not have to be returned due to single minerals and simple process, and the CLF-40 flotation machines are configured in a stepwise way. Chengde Shuangluan Jianlong Mining Company adopts the process of one-time rougher–one-time scavenger–three-time concentration for flotation of phosphorus, equally, the pulp does not have to be returned due to simple process and large processing capacity, and the CLF-40 flotation machines are configured in a stepwise way. See the concentrators listed in Table 11.9 for typical cases. Table 11.8 Typical concentrators of JJF flotation machine S. No. Mine name

Ore type

Model

1

Yinshan Deposit of Jiangxi Copper Corporation Limited

Pb–Zn

JJF-4

2

Jinchuan Group Co., Ltd

Nickel ore

JJF-4

3

Dexing Copper Deposit of Jiangxi Copper Corporation Limited Copper ore JJF-16

4

Sichuan Lala Copper Deposit

5

Tongling Non-Ferrous Group

Copper ore JJF-130

6

Heilongjiang Duobaoshan Copper Mine

Cu–Mo ore JJF-320

Copper ore JJF-16

Table 11.9 Typical concentrators of JJF flotation machine S. No. Mine name

Ore type

Model

1

Guixi Smelter of Jiangxi Copper Corporation Slag Limited

CLF-40

2

Smelter of Jinchuan Group Co., Ltd

Slag

CLF-40

3

Smelter of Tongling Non-Ferrous Group

Slag

CLF-40

4

Smelter of Zijin Group

Slag

CLF-40

5

Smelter of Glencore International AG in the Philippines

Slag

CLF-40

6

Shougang Hierro Peru SAA

Iron ore

CLF-8

7

Fengning Sanying Mining Company

Iron phosphorite

CLF-40 and CLF-8

11.4 Configuration of Flotation Machines

413

11.4.3 Selection of Two Configuration Methods Such two configuration methods have their respective advantages and disadvantages. See Table 11.10 for comparison results. For the selection of configuration methods, generally, the following principles are complied with: A.

B.

C.

Give preference to horizontal configuration. Horizontal configuration has such advantages as unnecessary froth pump, easy operation, low maintenance cost and small investment, in addition, the horizontal configuration process becomes simpler, and the process becomes easier when the raw ore properties or mineral separation process is changed. For medium and small concentrators with many separation process sections and complex process structures, the flotation machine configured in a horizontal way is selected with easy and flexible configuration. Many froth pumps or pulp pumps are required for many process sections and complex process, at this time, the superiority of horizontal configuration will be shown better. For a large concentrator with large processing capacity and simple process, the stepwise configuration is often adopted. For the sulphide ores with lesser froth productivity and froth viscosity, the stepwise configuration in which pulp automatically flows and froth is returned through a pump is adopted generally; however for some oxidized ores, especially for minerals with large froth viscosity and difficult to pump, the stepwise configuration in which pulp is returned by automatic flow and underflow pulp is pumped is adopted generally.

Table 11.10 Comparison between two configuration methods Item

Configuration type

Description of features

Horizontal configuration

Processing capacity

Medium and small concentrator Large concentrator

Process

Complex

Simple

Height

There is no height difference between workshops and the height is small

There is a height difference between workshops and the height is large

Investment of capital construction

Simple foundation and low cost Complex foundation and high cost

Auxiliary equipment

Little, middling pump is unavailable

Much, middling pump is available

Channel above the flotation machine

Easy layout

Step ladder is required

Spares

Add mechanical agitation flotation machine

Add spares for the pump

Running power consumption

Low

10–20% higher than horizontal configuration

Stepwise configuration

414

D.

E.

11 Model Selection and Design of Flotation Machines

The same concentrator can select the stepwise configuration for a part of operation and select horizontal configuration for the other part of operation, which can play the advantages of the two configurations. Generally, if the rougher and scavenger banks have large processing capacity and the selected flotation machine has a large volume, the stepwise configuration shall be adopted; if the cleaner bank has small processing capacity and the selected flotation machine has small volume, the horizontal configuration shall be adopted. Natural conditions of concentrator geography.

In a word, during the configuration of flotation machine, all aspects of factors shall be comprehensively considered and flexibly mastered from the starting point of economic and social benefit maximization.

11.4.4 Selection Cases of Configuration Methods According to the calculation result in Sect. 11.3.4, the configuration method is determined. See Table 11.11 for the results.

11.5 Selection of Supporting Equipment The supporting equipment for flotation machine includes flotation process control system and supporting equipment used for the process. The flotation process control system belongs to the field of automatic control instrument, generally including automatic level control system, aeration rate control system, flotation machine bearing temperature detection system and flotation froth monitoring system. The supporting equipment used for the process mainly includes dosing machine, air compressor, low-pressure blower, etc.

11.5.1 Flotation Process Control System (1)

Scale of concentrator

Small concentrator may not be adopted due to simple process and less equipment. For large concentrator with larger scale and larger influence of artificial improper factors on mineral separation indicators, generally, the automatic level control system, aeration rate control system and flotation machine bearing temperature detection system need to be adopted, ensuring the stability and accuracy of flotation operations and guaranteeing the normal operation of equipment.

11.5 Selection of Supporting Equipment

415

Table 11.11 Determination results of configuration methods S. No. Operation name

Specification of flotation machine (m3 )

Quantity Configuration Configuration Height of type type difference, in flotation m machines of single series (quantity)

1

Cu–Mo and other floatable rougher

300

3

2

Cu–Mo and other floatable scavenger 1

300

2

3

Cu–Mo and other floatable scavenger 2

300

2

4

Copper rougher

300

4

5

Copper scavenger 1

300

2

6

Copper scavenger 2

300

2

7

Cu–Mo and other floatable concentration 1

30

2

8

Cu–Mo and other floatable concentration 2

30

2

9

Cu–Mo and other floatable concentration 3

30

2

10

Cu–Mo separate rougher

30

3

11

Cu–Mo separate scavenger 1

30

2

Stepwise configuration

(2 + 1) + 1 +1+1+1

1.1–1.5

2 + 2 + 2 + 2 1.1–1.5

Horizontal configuration

2 + 2 + 2 + 2 Unnecessary

3+2+2

Unnecessary

(continued)

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11 Model Selection and Design of Flotation Machines

Table 11.11 (continued) S. No. Operation name

12

(2)

Cu–Mo separate scavenger 2

Specification of flotation machine (m3 )

30

Quantity Configuration Configuration Height of type type difference, in flotation m machines of single series (quantity) 2

Automation level

The design idea and matching automation level of each concentrator are inconsistent. For a concentrator with a lower requirement for the automation level, generally, only a single operation level automatic control system is selected. For a concentrator with higher requirements for the automation level, it is suggested to adopt the centralized control system, including the automatic level control system, aeration rate control system, flotation machine bearing temperature detection system and flotation froth monitoring system. The flotation machine control system will be reserved with interfaces to communicate with the DCS system of the whole concentrator.

11.5.2 Supporting Equipment for Process (1)

Model selection of low-pressure blowers

Only the concentrator adopting the pneumatic mechanical agitation flotation machine needs to consider the selection of low-pressure blowers. The low-pressure blower of the concentrator generally includes a centrifugal blower and roots blower. Centrifugal blower has low noise but has larger fluctuations in exhaust pressure. Roots blower belongs to a positive displacement fan with larger noise and lower fluctuations in exhaust pressure. In view of the reliability of the low-pressure blower, generally, a concentrator blower is arranged in an independent workshop, adopting the mode of 2-working and 1-standby or 3-working and 1-standby. If the flotation machine specifications are greatly different in the rough scavenger and concentration stages, blowers will be configured, respectively. The calculation of the low-pressure blower involves pressure and flow. (2)

Air volume selection of blower

Generally, the air volume mainly depends on the aeration rate determined in the flotation process test. The calculation formula of the total air volume of Qair of the

11.5 Selection of Supporting Equipment

417

blower is as follows: Q air = k × p × s × n

(11.7)

where k p s n (3)

Air volume coefficient. The aeration rate depends on the flotation process test (m3 /m2 min− 1 ). Surface area of flotation machine of each tank (m3 ) Quantity of flotation machines Pressure rise of blower

The selection for pressure rise of blower generally needs to consider the minimum inlet air pressure required for flotation machine, pipe loss between blower and flotation machine and altitude influence, etc. (a)

Calculation of the minimum inlet air pressure required for flotation machine

Multiply the impeller submergence depth of the flotation machine by the maximum pulp ratio in all flotation tanks, i.e.: P1 = H × ρ

(11.8)

where H ρ (b)

Impeller submergence depth of the flotation machine. Maximum pulp ratio in all flotation tanks. Calculation of pipe pressure loss between the blower and the flotation machine   P2 = ξtotal × r × v2 /2g

where ξtotal = ξ1 + ξ2 + ξ3 . ξ1 (straight pipe) ξ2 (bend) ξ3 (valve) r v2 g a b c (c)

a * L/D = a * straight pipe length/diameter b * quantity of bend c * quantity of valve Medium density Wind speed square 9.807 Pressure loss coefficient of straight pipe Pressure loss coefficient of bend Pressure loss coefficient of valve

Altitude influence

(11.9)

418

11 Model Selection and Design of Flotation Machines

The air density varies with the altitudes. When air density is ρ 0 and pressure is P0 at altitude of 0 m, the pressure rise of Ps of the blower at altitude of S is: Ps = (ρ0 /ρs ) × P0

(11.10)

where ρs

Air density at altitude of S.

(4)

Air compressor

Air compressor is mainly used to provide power for the level control system and aeration rate detection system, and the airflow and pressure need to be calculated according to the specification and quantity of the matching control systems of the flotation machine. (5)

Dosing machine

Addition and regulation of reagents are important process factors in the flotation process, having a great influence on the improvement of reagent efficiency and flotation indicators. Reasonable addition of reagents aims to ensure the maximum efficiency of reagents in the pulp and maintain the optimal concentration. Therefore, according to the ore characteristics and the properties and process requirements of reagents, the dosing place and method can be selected and the optimization and control of the flotation circuit reagent system can be determined. In order to ensure the accurate addition of reagents, it is suggested to select an automatic dosing machine. The dosing machine is mainly configured based on the dosage and dosing point.

11.6 Fuzzy Comprehensive Evaluation of Flotation Machine Section In the model selection process of flotation equipment, enterprises need to reduce the production cost and improve economic benefits, which requires selecting the flotation equipment with the highest cost performance, namely, it is necessary to consider many difficultly quantitative factors such as price, service life, operability and maintainability of equipment. Therefore, the optimization of flotation equipment is a fuzzy conceptual multi-objective evaluation problem. Therefore, it is an important basis for enterprises to configure equipment scientifically, economically and reasonably, by applying the fuzzy comprehensive evaluation to comprehensively consider all aspects of factors to give mathematical models of fuzzy comprehensive evaluation and make a reasonable fuzzy evaluation on flotation equipment [1].

11.6 Fuzzy Comprehensive Evaluation of Flotation Machine Section

419

11.6.1 Process of Fuzzy Comprehensive Evaluation The fuzzy comprehensive evaluation method is widely applied in fuzzy mathematics, and its essence lies in quantizing the fuzzy information for quantitative evaluation by using the set and fuzzy mathematical method. For the solution of multiple evaluation objectives, obtain the membership of each evaluation objective, respectively, consider the weight coefficient, obtain the membership of comprehensive fuzzy evaluation according to the synthesis law of fuzzy matrix, and then obtain the optimal solution through comparison [2].

11.6.2 Factor Sets and Factors In the model selection process of equipment, the evaluation factor set of flotation equipment includes price, function, operability and maintainability and service life. They are represented as follows: U = {u 1 , u 2 , u 3 , u 4 , u 5 }

(11.11)

Several sub-factors are included in each factor. They can be represented as:

Ui = {u i1 , u i2 , . . . , u i j , . . . , u im i i = 1, 2, 3, 4, 5 where U Ui ui j mi

Evaluation factor set; Numbered i factor in the factor set; Sub-factors j in the numbered i factor; Quantity of sub-factors in the factor i.

11.6.3 Determination of Weight Coefficient Since each element in factor set U is the evaluation indicator, and each element has different influence degrees on the evaluation result, the weight vector A shall be used quantitatively to describe the consideration factor set U . When research is second-order fuzzy comprehensive evaluation, the weight coefficient shall include the weight coefficient of factors and the weight coefficient of sub-factors. 1.

Determination of weight coefficient of factors

Weight coefficient of factors reflects the internal relation between factors, embodying the importance degree of each factor in the factor set. Since the weight coefficient of

420

11 Model Selection and Design of Flotation Machines

factors has fuzziness, the expert opinion shall be comprehensively considered when the weight size is determined. Weight set of factors is recorded as follows: A = {a1 , a2 , a3 , a4 , a5 }

(11.12)

where A

Fuzzy subset on U .

And the weight ai corresponding to the numbered i factor Ui in the formula is  specified: ai = 1. 2.

Determination of weight of sub-factors

Weight coefficient of sub-factors reflects the internal relation between the sub-factors within a certain factor, embodying the importance degree of each sub-factor in a certain factor. Similar to the above weight coefficient of factors, the weight set of sub-factors is recorded as follows:

Ai = {ai1 , ai2 , k, aim i i = 1, 2, 3, 4, 5

(11.13)

where Ai

Fuzzy subset on u i .

3.

Determination of evaluation grade set

Each element in the evaluation set V is the evaluation result, and the quantity of elements is the divided grade quantity. In the practical application, the evaluation results of flotation equipment are often divided into four grades: Excellent/very good, good/well, middle/general and poor. After generalization they are represented as follows: V = {v1 , v2 , v3 , v4 }

(11.14)

11.6.4 Fuzzy Conclusion Set 11.6.4.1

Fuzzy Evaluation Matrix

Fuzzy evaluation matrix describes the relation between factor set and evaluation set, and each row is corresponding to one consideration factor, and each line is corresponding to one evaluation result in the evaluation set. The fuzzy subset on V by fuzzy evaluation of single factors for numbered i factors:

11.6 Fuzzy Comprehensive Evaluation of Flotation Machine Section

421

R = (R1 , R2 , R3 , R4 )

(11.15)

If the membership ri jk of the expression sub-factor u i j against the grade Vi is used. ri jk is the ratio between voter turnout and a total number of tested people for sub-factor u i j on grade Vi by the tested personnel. The fuzzy evaluation matrix for any sub-factor can be obtained ⎤ ⎡ ri11 Ri1 ⎢ Ri2 ⎥ ⎢ ri11 ⎥ ⎢ Ri = ⎢ ⎣ ... ⎦ = ⎣ ... Rim i ri11 ⎡

ri11 ri11 ... ri11

ri11 ri11 ... ri11

⎤ ri11 ri11 ⎥ ⎥ ... ⎦ ri11

where Ri

Fuzzy matrix on [u i × V ] is called evaluation matrix,

4 

ri jk = 1.

k=1

For each factor, its evaluation matrix needs to be determined through a fuzzy statistical test Ri .

11.6.4.2

Fuzzy Matrix Operations

In the practical fuzzy operations, four kinds of fuzzy operation models may be used, respectively, are Fuzzy transformation, replacing “take small” with “multiply”, replacing “take large” with “add” and method of weighted mean [3]. (1)

Fuzzy transformation

The fuzzy transformation is calculated according to the principle of “maximum and minimum” to obtain the evaluation result vector, and the calculation formula is as follows: bj =

m   ∨ ai ∧ ri j (i = 1, 2, ...) i =1

where ∨ ∧ (2)

Take large operation; Take small operation. Replacing “take large” with “add”

The calculation formula is as follows:

(11.16)

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11 Model Selection and Design of Flotation Machines

bj =

(3)

m   ai ∧ ri j (i = 1, 2, ...) i =1

(11.17)

Replacing “take small” with “multiply”

The calculation formula is as follows: bj =

(4)

m   ∨ ai ri j (i = 1, 2, ...) i =1

(11.19)

Method of weighted mean

The calculation formula is as follows: bj =

11.6.4.3

m    ai ri j (i = 1, 2, ...) i =1

(11.20)

Fuzzy Conclusion Set

The fuzzy conclusion set is the final result of fuzzy operations, and the grade can be evaluated based on this result. In the comprehensive evaluation space consisting of the fuzzy conclusion set of the evaluation object is the fuzzy subset on [4]. (U, V, R) B V Combining with the practical bidding of flotation equipment, i.e. second-order fuzzy evaluation matrix and second-order fuzzy set: B = A · R = (b1 , b2 , b3 , b4 )

(11.21)

where B bk =

4 

Evaluation conclusion set; ai · bik

Membership of system performance U against grade Vk .

i=1

In conclusion, the process of fuzzy comprehensive evaluation shall first determine the consideration factor set U and evaluation set V ; and then establish an evaluation matrix; next, conduct operation according to the above fuzzy operation models; finally, process the evaluation conclusion set B according to the maximum membership principle or transformation C = B · V T to obtain the final result of evaluation C (Fig. 11.3).

11.7 Model Selection of Flotation Machines of CBR

423

Fig. 11.3 Fuzzy comprehensive evaluation method

11.7 Model Selection of Flotation Machines of CBR For a long time, the model selection of flotation machines has combined with the historical experiences according to the mineral separation process conditions. The design and selection of flotation machines would not begin from anything. For a new mineral separation process condition, designers always find both differences according to the similar conditions that have occurred in the previous work and then determine the new design and selection solutions based on that [5]. Under the same mineral separation process condition, different results will be obtained due to different experiences of design and selection personnel, resulting in a very large separation effect gap. As for the above problem, the method of case-based reasoning is adopted herein to integrate the previously accumulated knowledge and experiences into a system, and the computer technology is used so that each designer has lots of professional knowledge and experiences to improve the accuracy of design and selection. Therefore, the implementation of research on flotation machine design and selection system for case-based reasoning has an important practical significance.

11.7.1 Design and Selection of CBR The Case-based Reasoning (CBR) technology has been developed in the field of artificial intelligence in recent several decades [6], and its core is to solve the current problem depending on the past solving experiences. The CBR is characterized in that the complete domain knowledge model is unnecessary, the example acquisition is relatively simple, the past solving experiences can be directly reused, the reasoning speed is fast, the solving efficiency is high, the incremental self-learning ability is available and the system is easy to realize, etc., suitable for solving complex problems such as process design [7], and it has been widely applied in fields of commerce and trade, medical diagnosis, legal action, engineering design, system

424

11 Model Selection and Design of Flotation Machines

Fig. 11.4 Sizing calculation method

diagnosis, software engineering, etc., in recent years [8]. The CBR system consists of four parts, i.e. example expression, example retrieval, example modification and example storage [9], and the difficulties lie in (1) Example expression, emphatically solving the logical expression structure of design examples and access modes. (2) Example retrieval, focusing on research on dynamic retrieval and matching principle of design examples, to realize the CBR process. The design and selection of flotation equipment are a complicated design problem based on previous experiences. It is very suitable to adopt CBR method for solving. On the basis of summarizing the previously relevant studies, by analysing the design and selection characteristics of flotation equipment, the planning block diagram of the dynamic design and selection computing system of the flotation machine of CBR is determined herein, as shown in Fig. 11.4, and the corresponding process example library and example retrieval method are designed.

11.7.2 Example Expression and Example Retrieval 11.7.2.1

Example Expression

The example expression is the basis of the CBR system. It shall not only correctly and comprehensively express the common problem in the expression example but also shall express the specific background of example occurrence, and meanwhile shall have enlightenment and guiding significance on the same kind of problems. Whether the example can be expressed correctly and comprehensively concerns

11.7 Model Selection of Flotation Machines of CBR

425

the practicability of the CBR system. According to the lifecycle of the design and selection example of flotation equipment, the example can be expressed as follows: (1)

Problem description. There are many influencing factors for the design and selection of flotation equipment, including ore properties, process, process conditions, etc.;

Ore properties: Ore category, ore ratio and concentrator place. Process: Rougher, concentration and scavenger. Process conditions: Processing capacity, selected concentration, selected size, flotation time and productivity. (2)

(3)

Solution. Select the model of flotation equipment according to the influencing factors, and determine the model, specification, quantity and configuration of flotation equipment; at the same time, decide whether it is necessary to and how to modify the design of flotation equipment, including whether the motor is to upgrade, whether the speed is to upgrade, etc. Result. It includes running time, flotation indicators, debugging condition, running condition (actual power consumption, wear pattern and sediment), spares condition and fault condition.

Therefore, the design and selection example of flotation equipment   can be described as T = P(x, y, z), S(α, β, γ , δ, ε), R(ζ, η, θ, λ, μ, ϕ) , and its characteristics are as shown in Table 11.12.

11.7.2.2

Example Retrieval

To rapidly and effectively retrieve similar examples from the example library, the following must be met during retrieval: ➀ The examples retrieved shall be as less as possible. ➁ The examples retrieved shall be as similar as possible with new problems. Therefore, the retrieval strategies are especially important [10]. At present, most retrieval strategies used by the CBR system mainly include nearest neighbour strategy, inductive retrieval method, knowledge guide method, etc. [11] Firstly, we adopt the method of characteristic matrix for preliminary screening, and then conduct fine screening according to the method of item-by-item matching of characteristic weight sequence, to extract the most similar example from the process example library. The characteristic matrix algorithm is subject to similarity matching according to the characteristics and example characteristics required by design and selection. There are m examples in the example library, and each example has n characteristic attributes. The f ij represents the jth characteristic of the ith example, wherein i = 1, 2, …, m; j = 1, 2, …, n. The function of Pc (f ij ) represents the attribute value corresponding to the example characteristic of f ij , the Pr (fj) represents the attribute value corresponding to the characteristic attribute of f j of a new part, and the f j represents the jth characteristic of a new part. According to different characteristic value data

426

11 Model Selection and Design of Flotation Machines

Table 11.12 Characteristic parameters Characteristics

Characteristic parameters

Description of characteristic parameters

Problem description, P (x, y, z)

Ore properties, x (a, b, c)

a—Ore category: Copper, molybdenum, lead, zinc, phosphorus, etc b—Ore ratio c—Concentrator place

Process, y (d)

d—Process: Rougher, concentration and scavenger

Process conditions, z (e, f , g, h, i)

e—Processing capacity f —Selected concentration g—Selected size h—Flotation time i—Productivity

Solution, S (α, β, γ , δ, ε)

Model, α (j)

j-Model: XCF, KYF, CLF, JJF, BF, GF and SF

Specification, β (k)

k—Specification

Quantity, γ (l)

l—Quantity

Configuration, δ (m)

m—Configuration:

Design improvement, ε (n, o, p)

n—Power

Running time, ζ (q)

q—Running time: Half a year, 1 year, 2 years, 3 years, and more than 5 years

Flotation indicators, η (r, s)

r—Concentrate grade

Debugging condition, θ (t)

t—Debugging condition

Running condition, λ (u, v)

u—Actual power consumption

o—Speed p—Others

Result, R (ζ, η, θ, λ, μ, ϕ)

s—Recovery rate

v—Wear pattern Spares condition, μ (w, x)

w—Spares: Impeller, stator, air distributor, bearing, etc x—Replacement time: Half a year, 1 year, 2 years, 3 years, and more than 5 years

Fault condition, ϕ (y)

y—Fault condition

11.7 Model Selection of Flotation Machines of CBR

427

types, the following different methods are adopted to calculate the similarity of S (f ij ) between the ith example and the jth characteristic of a new part. (1)

Similarity of continuous numeric characteristics (S c ): Sc ( f i j ) =

(2)

min(Pc ( f i j ), Pr ( f j )) max(Pc ( f i j ), Pr ( f j ))

Similarity of discrete numeric characteristics (S d ):   1(P ( f )=P ( f )) Sd f i j = 0(Pcc ( fii jj )= Prr ( f jj ))

(3)

(11.22)

(11.23)

Similarity of character string characteristics (S s ): Ss ( f i j ) =



1(Pc ( f i j )=Pr ( f j ) 0(Pc ( f i j )= Pr ( f j )

(11.24)

Therefore, the characteristic matrix of example i is Ci =   (Ci1 , Ci2 , . . . , Ci j , . . . , Cin ), Ci j = S f i j . After the characteristic matrix is determined, designers manually input the weight coefficient of W j of each characteristic according to the design and selection requirements, wherein j = 1, 2, …, n; and n 

Wj = 1

(11.25)

i=1

Then the similarity of example i (S i ) is Si =

n 

Ci j W j

(11.26)

i=1

The retrieved results are arranged from high to low according to the similarity, and designers select examples and modify examples according to the design and selection requirements to finally determine the design and selection result of the flotation machine. For the design and selection system of the flotation equipment of CBR, concentrator designers rapidly and accurately modify the design of flotation machine according to the mineral separation process conditions based on lots of design experiences, greatly reducing the design and selection time, and improving the design and selection accuracy. This system is especially applicable to the separation of minerals with a mature flotation process but has not large significance on the flotation equipment with immature flotation process or the newly developed flotation equipment, still needing to adopt the traditional method for model selection and design.

428

11 Model Selection and Design of Flotation Machines

11.8 Model Selection of Flotation Machines Based on JK Technology From the early 1970s to the late 1990s, the domestic representative research personnel of Chen Ziming and Yin Di have abundantly studied the contents of flotation dynamics and industrial flotation circuit analog computation and published lots of research achievements, but regrettably, they have not launched any commercialized analog computation software to apply to industrial practice. In recent years, the domestic studies and applications about mathematical models of flotation rate and process simulation have been declined, forming an obvious comparison with the foreign rapid development. At present, the foreign flotation process simulation software that has been reported mainly includes JKSimFloat developed by JKtech, HSC Sim launched by Outotec, USIM PAC developed by BRGM and Supasim developed by Eurus, etc., and the flotation process simulation software has increasingly become an important tool for foreign preparation engineers researching, designing and optimizing the flotation process.

11.8.1 Flotation Process Simulation Software of JKSimFloat The JKSimFloat JKSimFloat is a software product used for flotation circuit analog that was launched by the research institute of JKTech under the University of Queensland in Australia. The launch of the software benefits from the long-term funds of P9 Project of Ausmine Research Association and combines with the latest academic research achievements of the University of Queensland, McGill University and the University of Cape Town. The modelling idea of the software is to divide the mineral particles in the feed into n units according to different flotation rates and regard the mineral particles with similar flotation rate as the same category. In this way, each mineral in the selected materials can be roughly divided into four floatability components, i.e. fast floating component, medium-speed floating component, slow floating component and nonfloating component. When the flotation circuit analog computation is conducted, it is assumed that the flotation rate between different flotation banks of the floatable component of each mineral remains unchanged. Based on the floatable component model of minerals, the mathematical models of floatability component recovery of minerals are built [11], as shown in the formula. Ri =

Pi Sb τ R f (1 − Rw ) + ENTi Rw (1 + Pi Sb τ R f )(1 − Rw ) + ENTi Rw

where Ri

Recovery of the floatable component i;

(11.27)

11.8 Model Selection of Flotation Machines Based on JK Technology

Pi Sb Rf Rw τ ENTi

429

Floatability of the floatability component i in a mineral; Surface area flux of bubbles; Recovery in froth zone; Recovery of water in the froth concentrate; Residence time of pulp; Froth entrainment.

Based on the above equation, it is believed that the flotation recovery is related to the mineral properties and flotation equipment performance, wherein, the mineral properties can be represented by the floatability of minerals, and the flotation equipment performance is related to the fluid dynamics performance and froth characteristics. Actually, the process of applying the JKSimFloat software includes many previous tests, measurements and other preparations. The general steps of using the numerical simulation for flotation circuit optimization are as follows: ➀

➁

➂ ➃

➄

➅

Data measurement. Acquire the original data about the flotation process circuit and the working condition of equipment, by means of methods such as field process investigation sampling analysis, working characteristic parameter measurement of flotation equipment and small flotation test of the laboratory; Data analysis. Conduct analytical processing of original data, including calculation of bubble dispersion characteristic parameters, material balance data coordination, analysis of characteristic parameters of the pulp zone and froth zone and composition analysis of floatability components, to acquire all parameters required for numerical simulation calculation. Draw industrial flotation circuit for design, reasonably add different equipment and name all equipment and materials, respectively, and then set all parameters. Analog computation. Apply the JKSimFloat software for numerical simulation calculation of process, to acquire the separation results of process and unit operations under all possible circuit structures and working conditions of unit devices; Process optimization. Analyse and compare the influence of different variations of flotation machine performance parameters in the operating unit on the separation result of process, to find the optimum operating parameter and the attainable optimum recovery. Field implementation. According to the analog computation result and process optimization requirement, guide the optimized direction of implementing the flotation process in the industrial production, and it may track and analyse the implementation effect.

In 2012, BGRIMM Technology Group introduced the latest corporate customeroriented KSimFloat-V6.2. The user interface of the JKSimFloat software is shown in the Fig. 11.5. Generally, the floatability characteristic parameters of ores do not have to be changed after being set in the simulation process, while the influence of characteristic parameters of the flotation equipment on the separation result of flotation shall

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11 Model Selection and Design of Flotation Machines

Fig. 11.5 The diagram of industrial flotation circuit by JKSimFloat soft

be mainly adjusted. At present, JKtech has established a JKFIT floatability index standard test and analytical method, which can calculate and obtain the floatability parameters of different minerals in the ore. In addition, because the JKSimFloat software fully considers the basic behaviours of mineral particles in the pulp phase and froth phase, such as recovery rate in froth zone, entrainment, recovery of water in the froth concentrate, surface area flux of bubbles and other important influencing factors, the variations in separation indicator of the flotation circuit can be predicted better by adjusting the flotation process parameters, thus guiding the optimization of industrial production operation. In the real flotation process, the surface properties of mineral particles in different operations are always constantly changed, e.g. the subsequently supplemented reagent greatly changes the superficial floatability of mineral particles; while the software can set the floatability and composition only of the feed materials, fails to set the feed properties of subsequent operations, and still fails to directly and quantitatively calculate the separation result varying with the reagent system. As see from some specific analog computation examples published by JKMRC, the prediction on flotation recovery is basically correct compared with the measured indicators but some predicted values still have larger deviations from the true values.

11.8.2 Flotation Process Simulation Software of HSC Sim The HSC Sim developed by Outotec is the software originally used to simulate the chemical reaction course and hydrometallurgical process [12, 13], and later applied to

11.8 Model Selection of Flotation Machines Based on JK Technology

431

flotation process simulation after being improved. The earlier research suggests that the flotation rate constant is the first-order equation, and based on this, the flotation recovery rate model of laboratory batch run is built, as shown in the formula below. R = m S(1 − e−k St ) + m F(1 − e−k Ft ) + m N (1 − e−k N t )

(11.28)

where R mS kS mF kF mN kN t

the cumulative recovery; the slowing floating fraction in minerals; Flotation rate constant of the slowing floating fraction in minerals; Mass fraction of the rapid floating fraction in minerals; Flotation rate constant of the rapid floating fraction in minerals; Mass fraction of non-floating fraction in minerals; Flotation rate constant of non-floating fraction in minerals; the cumulative flotation time.

Since the industrial flotation production is a consecutive circuit, the mineral recovery rate equation applicable to consecutive flotation circuit is established, as shown in the formula below.    k Ft kNt k St + mF + mN (11.29) R = mS 1 + k St 1 + k Ft 1 + kNt Based on the laboratory batch flotation test results, through the above formula, the mass fraction of different floatable components in different minerals and the flotation rate constant can be obtained, respectively. Then, draw industrial flotation circuit in the HSC Sim steady-state simulator, adopt the dynamic parameters by a laboratory test, magnify the industrial flotation time according to the engineering practice experiences, set the feeding quantity, pulp density of each operation and other parameters and select the mineral recovery rate equation of the consecutive flotation circuit for analog computation, thus predicting the separation indicator of the whole flotation process circuit. The industrial flotation circuit that is drawn through the HSC Sim software is shown in the Fig. 11.6.

11.8.3 Flotation Process Simulation Software of USIM PAC The USIM PAC is the mineral separation process steady-state simulation software developed by BRGM [14]: its service industrial process includes many aspects such as crush, grinding, classification, flotation, gravity separation, magnetic separation, hydrometallurgy and biological metallurgy. The USIM PAC also allows users to add their models as required and is equipped with a special development tool (USIM PAC Development Kit). The USIM PAC software also has the material balance data

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11 Model Selection and Design of Flotation Machines

Fig. 11.6 The diagram of industrial flotation circuit by HSC Sim SoftThe HSC Sim software equally believes that the minerals in the selected materials can be divided into three floatable components to build mathematical models, respectively. This idea is very close to the modelling idea of JKSimFloat, which may be related to the case that Outotec participated in the sponsorship of the Australian P9 Project in the early stage

coordination function, model parameter fitting function, equipment dimensions and model selection function and investment cost analysis function. Parameters required for analog computation by USIM PAC can be divided into material parameters and unit model parameters. Material parameters can be described through different methods according to the selection of software users. For the material parameters of flotation circuit, the feeding quantity, water supply quantity, composition of the selected material, floatability parameter of ores, etc., can be set. Unit model parameters are divided into visible parameters and hidden parameters, of which the former can be directly operated by the software user; the latter is used for model calibration only, and the parameter values shall be obtained through test data analysis. The USIM PAC software is applied to flotation process, mainly including three aspects:

11.8 Model Selection of Flotation Machines Based on JK Technology

(1)

(2)

(3)

433

In the preliminary design stage, according to the small test result, recommended process and production objectives, calculate the rate, grade and particle composition of each material flow in the process through forward simulation method, then inversely calculate the dimensions of the required major equipment through reverse simulation method, finally calculate the operation result of the future concentrator through forward simulation method and estimate the investment cost. Repetitively applying this method can compare different solutions. In the detailed design stage, conduct material balance data coordination according to the pilot plant test data, calibrate the model parameters of pilot plant test process through reverse simulation method with the coordinated data, and calculate the dimensions of the actual concentrator equipment according to the proportional amplification rule. Then, calculate the operation result of the future concentrator through forward simulation method and estimate the required investment cost. Optimization and upgrade of the existing process. Conduct material balance data coordination according to the data obtained from the existing concentrator process investigation, calibrate the model parameters of production process through reverse simulation method with the coordinated data, then calculate all possible solutions and the operation results of process under process conditions through forward simulation method, and it may conduct comparative analysis on technical, economic and environmental influencing indicators.

Adopt the flotation process simulation software for model selection of flotation equipment and analog computation of flotation circuit, which not only can predict the separation indicator of flotation circuit, but also can reversely argue the model selection reasonableness of flotation equipment, and can guide the optimization of production flotation process of the concentrator. However, it is necessary to specially note that it must pay attention to comparatively analysing the contrast between the predicted result and the actual production when applying such software, and for certain “blindness” of the setting of individual parameters in the simulation process, it shall not preset objectives, break away from the general actual production and makeup parameter set values to achieve a purpose, otherwise, such analog computation will obviously lose its original meaning. Software users can obtain the preferable analog computation result only depending on rich professional knowledge accumulation, deep understanding of the physical significance of parameters, reasonable test methods and rigour of data analysis.

References 1. Yitai Ma, Zhiguo W, Zhao Y, Canren Lv (2003) Fuzzy comprehensive method for gas turbiine evaluation. Proc Chin Soc Electr Eng 9:218–220 2. Li A, Zhang Z, Duan F (1991) Fuzzy mathematics and its application. Metallurgical Industry Press, Beijing, pp 248–267

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3. Cao W, Wang H (2005) The apply of fuzzy evaluation about the equipment of mineral procession. Nonferrous Metals 4:42–45 4. Sun W, Liu J, Li X, Wen B (2007) Design quality evaluation of mechanical products and development research of evaluation system. J Machine Des (6):5–7 5. Li L (2002) Research on sequence generation, evaluation and optimization of digital product pre-assembly: [Dissertation]. Northwestern Polytechnical University, Xian 6. Liu X, Liu C, Ma Y (2005) Research on process planning system based on HCBR for hybrid production industries. Comput Integr Manuf Syst 11(7):9412946 7. Zhou X, Nie M, Ruan X (1996) Research on computer integrated manufacturing technology of mould. Forging Stamping Technol (1):43–46 8. Ong NS, Wong YC (1999) Automatic subassembly detection from a product model for disassembly sequence generation. Int J Adv Manuf Technol 15:425–431 9. Yuan X, Wang Y (1999) Case-based reasoning: review and analysis. Pattern Recognit Artif Intell 12:19–31 10. Luo S, Yin J, Dong J (2002) Instance matching for manufacturing process planning. J ComputAided Des Comput Graph (6):590–593 11. Yuan G (2000) Research on key technology of intelligent progressive die layout system. Doctoral Dissertation of Shanghai Jiaotong University, 12 12. Savassi ON, Alexander DJ, Franzidis JP et a (1998) An empirical model for entrainment in industrial flotation plants. Min Eng 11(3):243–256 13. Grau R, Gronstrand S, Pentti S (2009) Tisco Yuanjiacun iron ore laboratory tests at CRIMM, pp 17–18 14. HSC Chemistry◯R 7.0 User’s Guide [EB/OL]. https://www.Outotec.com/hsc

Chapter 12

Application Examples of Flotation Machines

Flotation machines are important equipment for realizing the flotation process and have been widely applied to the fields of non-ferrous metal ores, ferrous metal ores, rare and precious metal ores and some nonmetallic ores because of their high reliability and good technical and economic indexes. Flotation machines with a volume of 0.15 ~ 680 m3 are used. Forced air flotation machines and mechanical flotation machines are applied. Both horizontal configuration and stepwise configuration are applied to flotation machines. At present, there are more than 30,000 BGRIMM flotation machines to be used in China and other countries. Taking a typical mine as an example, this chapter describes the selection, configuration characteristics and application effects of different types and specifications of the BGRIMM flotation machine for different ore types.

12.1 Applications of Flotation Machines for Non-Ferrous Metal Ores About 80% of non-ferrous metal ores in the natural world are treated by flotation. This section describes the applications of flotation machines in the fields of bauxite, copper ores, lead–zinc ores, nickel ores, molybdenum ores and other important non-ferrous metal minerals.

12.1.1 Application of Flotation Machines for Bauxite The separation of bauxite ores has the characteristics of low aeration rate, sensitivity, bubble stickiness, high froth yield, difficult froth transportation, long residence time of pulp in the flotation machine, etc., which has always been the difficulty in research on flotation equipment for bauxite dressing. At present, flotation equipment such as © Metallurgical Industry Press 2021 Z. Shen, Principles and Technologies of Flotation Machines, Springer Tracts in Mechanical Engineering, https://doi.org/10.1007/978-981-16-0332-7_12

435

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12 Application Examples of Flotation Machines

flotation machines and flotation columns have been applied successively, and the flotation machines have been used for the separation of bauxite ores on a large scale because of high ore adaptability and good mineral separation indexes. Beijing General Research Institute of Mining & Metallurgy has successively developed the complete flotation machine technology by which the KYF flotation machine, GF flotation machine and XCF flotation machine are integrated with each other overcome a series of problems such as froth stickiness, small aeration rate and sensitivity in the separation of bauxite ores and spread the application of more than 200 sets in Zhongzhou Aluminum Works, Tianzhang Aluminum Industry Co., Ltd.; Changcheng Aluminum Industry Co., Ltd.; and other concentrators in China.

12.1.1.1

Application of Flotation Machines in Zhongzhou Aluminum Works

Zhongzhou Aluminum concentrator has a total of seven parallel lines of flotation circuits, each of which has a throughput of 2000 t/d, totalling up to 14,000 t/d. It is a bauxite concentrator applying the largest specification of the Bayer process for mineral separation in China, and 126 sets of flotation machines with a volume of 40 m3 have been used. The direct flotation process is used by Zhongzhou Aluminum concentrator. The rougher and scavenger circuit consist of one rougher bank and two scavenger banks, and the cleaner circuit consists of two cleaner banks and one scavenger bank cleaner–scavenger bank. The tailings from the scavenger bank and the scavenger bank cleaner–scavenger are merged into the final tailings, and the concentrates from the second cleaner bank are the final concentrates. The flotation circuit is shown in Fig. 12.1. Rougher 1 Condition

KYF-40 GF-40 KYF-40

Cleaner 2 GF-40 KYF-40 KYF-40 KYF-40

Rougher 2 GF-40

KYF-40 KYF-40

Cleaner 1 GF-40 XCF-40 KYF-40 KYF-40

Scavenger XCF-40 KYF-40

Cleaner Scavenger XCF-40 KYF-40

Final Tail

Final Concentrate

Fig. 12.1 The basic flotation circuit at the Zhongzhou aluminum concentrator

Final Tail

12.1 Applications of Flotation Machines for Non-Ferrous Metal Ores

437

Based on the ore properties of bauxite, the flotation machine configuration has the following characteristics: (1) (2)

(3)

(4)

(5)

The main flotation equipment is the forced air KYF flotation machine, allowing precise regulation of the aeration rate of the flotation machine; The GF and XCF flotation machines with pulp suction tanks are provided according to the characteristics of different operations. Through the optimal design of rotors and cover plates, the degree of air dispersion is increased, the pulp sucking capacity of the flotation machines is greatly improved, and the capacity of transporting viscous froth at a high flow rate is improved, thus facilitating the improvement of flotation performance; The horizontal configuration is adopted in the different flotation banks. The selection of the GF and XCF flotation machines with pulp suction tanks realizes the middlings return function and saves the froth pump; The first flotation machine for the rougher banker is the KYF flotation machine to avoid the phenomena of excessive froth yield and difficult grade control in the first flotation tank. With a high-precision float ball-laser liquid level measuring device and a specially designed froth isolation device, the pulp level tends to be stable and faster with smaller fluctuation, providing a good environment for the direct flotation process of bauxite.

According to the above characteristics, the flotation machine configuration is shown in Fig. 12.2. The field application status is shown in Fig. 12.3. Since the commencement of operation of the concentrator in 2004, the flotation performance has been improved continuously through optimization and improvement Rougher 1 Condition

XCF-40

Cleaner 2 GF-40 KYF-40 KYF-40 KYF-40

GF-40 KYF-40

Rougher 2 GF-40

KYF-40 KYF-40

Cleaner 1 GF-40 XCF-40 KYF-40 KYF-40

Scavenger XCF-40 KYF-40

Cleaner Scavenger XCF-40 KYF-40

Final Tail

Final Concentrate

Final Tail

Fig. 12.2 The flotation machine configuration at Zhongzhou aluminum concentrator

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12 Application Examples of Flotation Machines

Fig. 12.3 Flotation machine production scenario at Zhongzhou aluminum concentrator

Table 12.1 Flotation results of the concentrator Product name

Yield/ %

Al2 O3 grade/%

SiO2 grade/%

A/S

Al2 O3 recovery rate/%

Concentrate

78.78

69.20

6.23

11.11

84.92

Tailings

21.22

45.65

27.67

1.65

91.00

Raw ore

100.00

63.47

11.38

5.58

of the process and some equipment. The flotation results of the concentrator are shown in Table 12.1 [1].

12.1.1.2

Application of Flotation Machines in a Shanxi Aluminium Industry Company

The ores produced by an aluminium industry company in Shanxi belong to the typical diasporic bauxite, with complex ore patterns. Most of the ores are granular and flaky, some are slab-flaky or cryptomerous, and the crystal size is generally 0.005 ~ 0.03 mm. The ores have the typical characteristics of high aluminium, high silicon and low alumina–silica ratio. The useful minerals of these ores have finely disseminated grain sizes. To achieve a good degree of liberation, the only method is fine grinding, which increases the difficulty of flotation.

12.1 Applications of Flotation Machines for Non-Ferrous Metal Ores

439

The mine was built and went into operation in 2011, and the direct flotation process was applied. A total of 27 flotation machines with a volume of 40 m3 are used in the concentrator, consisting of three types, i.e. KYF, XCF and GF. The latter two types are used as pulp suction tanks. Their configuration characteristics are similar to those in Zhongzhou Aluminum concentrator, and the horizontal configuration is adopted for all the flotation machines. The whole flotation process is simple and economic in the froth pump. It not only greatly reduces the energy consumption of the concentrator, but also reduces the investment of capital construction of the concentrator. Meanwhile, the horizontal configuration of the flotation machines is convenient for the workers’ process operations, thus reducing the costs for equipment management and maintenance. The flotation circuit is shown in Fig. 12.4. Since the concentrator went into operation, the equipment has been running reliably, and the pulp level has been stable. The flotation machine has a strong agitation force, a stable pulp suspension layer is formed in the upper-middle part of the flotation machine without the phenomena of fluctuation of the pulp level and sediment in tank, and the froth layer is stable. The production indexes show that, when the mean alumina–silica ratio of run-of-mine is 5.31, the alumina–silica ratio of concentrate can reach 9.33, the mean grade of Al2 O3 in concentrate reaches 69.70%, the mean recovery rate reaches 66.51% and the final mineral separation index can fully Feed

Classification

Ball Mill

Condition

Rougher

Classification

Pump Sump

Ball Mill Cleaner 2

Cleaner 1 Pump Sump

Cleaner 3

Separation Rougher

Separation Scavenger

Scavenger

Separation Cleaner Final Tail

Final Concentrate 2 Final Concentrate 1

Fig. 12.4 The flotation circuit at an aluminium concentrator in Shanxi

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12 Application Examples of Flotation Machines

Fig. 12.5 Flotation machine production scenario at an aluminium concentrator in Shanxi

meet the technological design requirements of the concentrator [2]. The production scenario on site is shown in Fig. 12.5.

12.1.2 Application of Flotation Machines for Copper Mine There are many kinds of flotation machines applied in copper mines. The KYF and JJF flotation machines are the main types of large flotation machines used in large mines, and KYF/XCF aggregate units, JJF, BF, GF, etc., are the main types used in small mines. The configuration method of flotation machines includes the horizontal configuration and the stepwise configuration, in which the horizontal configuration is the main configuration method. As the copper ores grades become lower and lower, the throughput also becomes larger and larger. Therefore, large-scale, energy-saving and high-efficacy separation equipment is an effective way to improve the economic benefits of copper mines. The flotation machines with the volume of greater than 40 m3 are used for rougher and scavenger in mines such as Dexing Copper Mine (daily throughput 130,000 t/d), Chengmenshan Copper Mine (throughput 10,000 t/d), Yongping Copper Mine (throughput 10,000 t/d), Wunugetushan Copper–Molybdenum Mine (throughput 75,000 t/d), Deerni Copper Mine (throughput 15,000 t/d), Huichun Zijin Copper and

12.1 Applications of Flotation Machines for Non-Ferrous Metal Ores

441

Gold Mine (throughput 15,000 t/d) and Zijin Copper Mountain Mine (throughput 15,000 t/d). The selection of flotation machines gives priority to forced air flotation machines, and mechanical flotation machines are also the options. There are both horizontal and stepwise configurations in terms of configuration method. The Dashan Concentrator of Dexing Copper Mine and the Wunugetushan Copper–Molybdenum Mine will be highlighted below as representatives.

12.1.2.1

Application of Flotation Machines at Dashan Concentrator of Dexing Copper Mine

Dashan Concentrator of Dexing Copper Mine, the largest copper concentrator in China, mainly processes porphyry copper ores. In 2010, the throughput of the concentrator was increased from 60,000 t/d to 90,000 t/d after flotation circuit improvement. There are three series, in which flotation machines are used in the rougher bank, scavenger bank and scavenger–cleaner–scavenger bank and flotation columns are used in the cleaner bank. The flotation machines are of stepwise configuration, and the middlings are returned by the froth pump. The flotation circuit is shown in Fig. 12.6. The configuration status of each series of flotation machines is shown in Table 12.2. In July 2009, nine KYF-200 flotation machines were first put into operation in series I, while the original CNNC-39 flotation machine was still used in Series II. The equipment runs well after the—KYF-200 flotation machines went into operation; the froth layer is stable without slurry level fluctuation; the agitation force is powerful, and the pulp flow direction is stable; when the flotation machine is shut down, there is neither dead zone in the flotation tank nor pulp deposition; the air is evenly dispersed, with a high degree of dispersion and reasonable bubble size distribution; the automatic pulp level control system of the flotation machine can be freely adjusted as required, and the control accuracy meets the process requirements; the froth layer thickness can be adjusted according to the process; the flotation machine can be started normally after full-load shutdown. The production indexes from July to November 2009 after the 200 m3 flotation machines went into operation are shown in Table 12.3. Table 12.3 shows that the copper recovery in the concentrates is higher than that of the CNNC-39 flotation machine when the KYF-200 flotation machine is used in the rougher banker with the production throughput increased by 3750 t/d. This fully demonstrates that the KYF200 flotation machine has a good metallurgical performance, which is favourable for the improvement of technical indexes of mineral separation [3]. The mineral separation indexes are shown in Table 12.3. The energy consumption data of the KYF-200 flotation machine and the CNNC39 flotation machine is shown in Table 12.4. Table 12.4 shows that the KYF-200 flotation machine can save electricity of 0.18 kWh per 1 t ores under the same work conditions. After the 39 m3 flotation machine is replaced with the 200 m3 flotation machine, the number of flotation machines to be configured in the flotation circuit of flotation decreases to facilitate maintenance, thus reducing the spare parts consumption and saving the maintenance and labor costs. To sum up, the replacement

442

12 Application Examples of Flotation Machines Feed Classification 1st Step Rougher 1 1st Step Rougher 2 Ball Mill

1st Step Scavenger

Classification 1st Step Cleaner 1st Step Cleaner Scavenger 2 Scavenger 3

1st Step Cleaner 1st Step Cleaner Scavenger 1

Final Tail Classification

1st Step Copper Concentrate

Ball Mill

1st Step Tail

2nd Step Cleaner Scavenger 1

2nd Step Cleaner 2nd Step Rougher Scavenger 1

2nd Step Cleaner 1

2nd Step Tail 2nd Step Cleaner 2

2nd Step Copper Concentrate

Fig. 12.6 The flotation circuit at the dashan concentrator of dexin copper mine Table 12.2 Configuration status of flotation machines at dashan concentrator Operation name Throughput, 10,000 t/d

Flotation machine model

Quantity

Configuration type

Operation height difference, in m

Series I rough 3.375 scavenger banks

KYF-200

9

Stepwise layout

1.0

Series II rough 3.375 scavenger banks

KYF-200

9

Stepwise layout

1.0

Series III rough 2.25 scavenger banks

KYF-160

9

Stepwise layout

0.8

Fine scavenger bank

KYF-70

18

Stepwise layout

0.8

0.55

12.1 Applications of Flotation Machines for Non-Ferrous Metal Ores

443

Table 12.3 Copper index for rougher bank (%) Equipment specification

Raw ore grade

Concentrate grade

Tailings grade

System recovery rate

KYF-200flotation machine

0.442

5.74

0.062

86.81

CNCC-39 flotation machine

0.444

5.76

0.063

86.79

−0.002

−0.02

−0.010

0.02

Difference

Table 12.4 Energy Consumption Data Equipment Name

Installed power, in kW

Actual power consumption, in kW

Electricity consumption, in kW/t

200 m3 flotation machine

220

130.73

0.75

39 m3 flotation machine

45

38.77

0.93

of small flotation machines with large ones can produce better technical and economic indexes. The production of KYF-200 flotation machines at Dashan Concentrator is shown in Fig. 12.7.

12.1.2.2

Application of Flotation Machines in Wunugetushan Copper–Molybdenum Mine

The Wunugetushan Copper–Molybdenum Mine is a new large copper mine built in 2008. Basic flotation circuits: The raw ores are grinded and classified to obtain the mixed copper–molybdenum concentrate after bulk flotation. The mixed concentrates are regrinded and classified after reagent removal, dewatering and concentration to enter the copper–molybdenum separation flotation circuit, and the copper concentrate and molybdenum rough concentrate are obtained, respectively. The molybdenum rough concentrate is scrubbed and regrinded by a vertical mill and supplied into the cleaner bank before the final molybdenum concentrate is obtained. The flotation circuit is shown in Fig. 12.8. The Wunugetushan Copper–Molybdenum Mine Phase I has a throughput of 36,000 t/d, and the copper–molybdenum bulk flotation circuit consists of two series, with a throughput of 18,000 t/d for a single series. Because of the large throughput and low run-of-mine grade, the rougher and scavenger banks are provided with 32 KYF-160 flotation machines in total and configured with the automatic liquid level control system and aeration rate control system in consideration of the outstanding advantages of a small number of installation, less footprint, easy realization of automatic control, less investment cost of capital construction, small installed power per unit volume, high comprehensive economic benefit, etc., of the large flotation

444

12 Application Examples of Flotation Machines

Fig. 12.7 KYF-200 flotation machine production scenario at the dashan concentrator

machines. The throughput in Phase II was 45,000 t/d, with 16 KYF-160 floatation machines used in the rougher and scavenger banks. The mine achieved the production and standard and produced qualified concentrates in March 2010. The industrial applications show that: The main motor of KYF160 flotation machine has an installed power of 160 kW, actual power consumption of about 115 ~ 120 kW and power index per unit pulp of about 0.94 kW/m3 . When the grade of copper in the run-of-mine ores is about 0.4%, the grade of copper in concentrates can reach 27.3% and the recovery rate reaches 89.13%. Therefore, the metallurgical performance of the KYF-160 flotation machine has reached the advanced level of large flotation machines.

12.1.3 Application of Flotation Machines for Lead–zinc Ore There are many kinds of flotation machines applied in lead–zinc separation. Because of the complex flotation circuit and the small scale of processing, the flotation machines are dominated by small volume equipment, and all the flotation machines are of horizontal configuration. The configurations of flotation machines in major lead–zinc concentrators in China in the last few years are shown in Table 12.5.

12.1 Applications of Flotation Machines for Non-Ferrous Metal Ores Feed

445

Classification

Ball Mill

Cu-Mo Bulk Flotation Rougher

Scavenger 1

Scavenger 2

Scavenger 3

Cu-Mo Bulk Flotation Cleaner 1

Cu-Mo Bulk Flotation Cleaner 2 Final Tail

Cu-Mo Bulk Flotation Cleaner 3

Separation Rougher

Separation Scavenger 1

Separation Scavenger 2

Classification Separation Cleaner 1 Ball Mill Separation Cleaner 2

Final Cu Concentrate

Separation Cleaner 3

Final Mo Concentrate

Fig. 12.8 Copper–molybdenum bulk flotation circuit

12.1.3.1

Application of Flotation Machines in Huize Pb–Zn Deposit

Huize Pb–Zn Deposit is one of the several rare high-grade Pb–Zn deposits in China with a throughput of 2000 t/d. There are more than 5 million tons of sulphide ores and mixed ores and about 2 million tons of oxidized ores in the ore body, with the mean geological grades of 8.35% for Pb and 17.41% for Zn. The oxidation rate of lead and zinc is 4 ~ 90%, with 486,700 t of lead metal, 1,014,200 t of zinc metal 404.29 t of silver (an accompanying rare and expensive element), 154.41 t of germanium and 2010.39 t of cadmium.

446

12 Application Examples of Flotation Machines

Table 12.5 Configurations of flotation machines in major lead–zinc concentrators in China Serial No. Mine name

Throughput, t/d Series Flotation machine model

1

Huize Pb–Zn deposit

2000

1

BF-16, BF-8 and BF-4

2

Zhaotong Pb–Zn deposit

2000

2

BF-16 and BF-8

3

Fankou Pb–Zn deposit

4500

2

BF-4, BF-2.8, BF-1.2, JJF-8 and JJF-4

4

Caijiaying Pb–Zn deposit

1000

5

Changba Pb–Zn deposit

4500

1

XCF/KYF-50 and XCF/KYF-10

7

Tumuerting-Aobao Pb–Zn deposit

1000

1

XCF/KYF-8 and XCF/KYF-4

8

Bashijiazi Pb–Zn deposit in 1500 Huludao

XCF/KYF-10 and XCF/KYF-2

XCF/KYF-24 and XCF/KYF-8

The flotation process is selected in the principle of “sulfide ores first, oxidized ores second” and “lead ores first, zinc ores second". The “asynchronous iso-flotation— zinc-sulphur mixture flotation—separation” process, i.e. asynchronous iso-flotation flow structure is used in the sulphide ore flotation, high selectivity collectors are applied for asynchronous iso-flotation of lead sulphide and iron minerals, and rough concentrates are reground before concentration to produce lead concentrates; Then the bulk flotation of zinc sulphide and iron sulphide is conducted, and the zinc sulphide concentrates and sulphur concentrates are obtained, respectively, after separation of zinc and sulphur of the mixed concentrate. High-quality lead concentrates, zinc concentrates and sulphur concentrates were obtained from this flotation circuit. In view of the floatability of lead–zinc oxide in the flotation of lead–zinc oxide ores, a new process using the new non-desliming sulphidizing flotation technology and new electrochemical controlled flotation technology was used for efficient recovery of lead and zinc metals. The flotation circuit is shown in Fig. 12.9. Due to the complexity of the process, the BF flotation machine having the capacities of self-aspirated function and self-suction function is used, and the BF flotation machine is used as a free-flow tank and a pulp suction tank simultaneously. The BF-16 flotation machine with the dual-froth scraping device and the single froth scraping device is configured according to the froth yield. The rougher banker bank of sulphide ores is provided with 54 BF-16 flotation machines, and the cleaner bank is provided with 21 BF-8 flotation machines. Huize Pb–Zn Deposit went into operation in 2004. The statistical results of production indexes are shown in Table 12.6. From the production data, it is seen that the BF flotation machine supports the realization of the process well and achieves better flotation performance.

12.1 Applications of Flotation Machines for Non-Ferrous Metal Ores Feed

447

Classification

Ball Mill

Ball Mill

Pyrite Concentrate Zinc Sulfide Concentrate

Lead Sulfide Concentrate

Final Tail

Lead Oxide Concentrate

Zinc Oxide Concentrate

Fig. 12.9 The flotation circuit at the Huize Pb–Zn deposit Table 12.6 Statistical results of production indexes (%) Raw ore

Concentrate Tailings

Name

Grade

Recovery rate

Pb

8.8

Zn

22.8

FeS

15.3

Pb

Pb65.56 and Zn4.84

78.90

Zn

Zn51.85 and Pb2.71

89

Pb

1.51

Zn

4.26

448

12 Application Examples of Flotation Machines

12.1.3.2

Application of Flotation Machines in Zhaotong Pb–Zn Deposit

Zhaotong Pb–Zn Deposit was completed and put into production in 2009, with a throughput of 2000 t/d. The two-stage grinding is used, the ore is ground to 60 ~ 80% passing 74 µm prior to flotation, the feed concentration is 30%, and lead–sulphur rougher banker bank is organized first; rougherthe rough concentrate is reground to 90% passing 43 µm, the concentrate after two-time lead–sulphur cleaner banks enters the lead–sulphur separation flotation circuit, and the lead concentrate and sulphur concentrate are, respectively, obtained after one-time rougher bank, twotime scavengers bank and two-time cleaner bank; the tailings of lead rougher enter the zinc rougher bank after scavenger bank, and the zinc concentrate is produced after one-time rougher, three-time scavenger and two-time cleaner. The flotation circuit is shown in Fig. 12.10. Feed

Classification

Classification

Ball Mill Ball Mill

Bulk Flotation Rougher 1

Bulk Flotation Rougher 2

Scavenger 1

Scavenger 2

Bulk Flotation Bulk Flotation Bulk Flotation Cleaner 1 Scavenger 1 Scavenger 2

Zinc Rougher

Zinc Scavenger 1

Zinc Scavenger 2

Zinc Scavenger 3

Zinc Cleaner

Bulk Flotation Cleaner 2

Lead Rougher

Lead Scvenger 1

Lead Scvenger 2

Zinc Concentrate Final Tail

Lead Cleaner 1

Lead Cleaner 2

Pyrite Concentrate

Lead Concentrate

Fig. 12.10 The flotation circuit at the Zhaotong Pb–Zn deposit

12.1 Applications of Flotation Machines for Non-Ferrous Metal Ores

449

The flotation process of the concentrator consists of two series, and 7 BF-16 flotation machines and 103 BF-8 flotation machines are used. The BF flotation machine can be used as both a free-flow tank and a pulp suction tank, all the flotation machines are horizontally configured for a simple. The flotation machine makes automatic liquid level control possible. It is simple in operation and convenient in maintenance. Since 2009, the flotation machines have been running stably, and the production indexes have fulfilled the process design requirements for a long time.

12.1.3.3

Application of Flotation Machines in Changba Pb–Zn Deposit

Changba Pb–Zn Deposit has a throughput of 4500 t/d, with the specific gravity of run-of-mine ores of about 2.85 t/m3 . The concentrator uses the two-stage grinding process, the ore is ground to about 85% passing 74 µm prior to flotation, the feed concentration is not more than 30% and the lead rougher bank is organized first; the lead rough concentrate is reground to 92.5% passing 74 µm rougher, and the lead concentrate is produced after four-time cleaner bank; the tailings of lead rougher enter the zinc rougher bank after scavenger, rougher the zinc rough concentrate is reground to 92.5% passing 43 µm, the zinc concentrate is produced after four-time zinc cleaner bank and the flotation circuit is shown in Fig. 12.11. The flotation process of the concentrator consists of a single series, 18 XCF/KYF50 flotation machines are used for lead–zinc rougher and scavenger banks, and 15 Feed Classification

Classification

Classification

Ball Mill

Ball Mill

Cleaner 2

Cleaner 3

Ball Mill

Ball Mill

Lead Rougher Lead Scavenger 1 Lead Scavenger 2

Cleaner 1

Classification

Zinc Rougher Zinc Scavenger 1 Zinc Scavenger 2

Cleaner 4 Cleaner 1

Cleaner 2

Cleaner 3

Cleaner 4

Final Tail Lead Concentrate

Fig. 12.11 The flotation circuit at the Changba Pb–Zn deposit

Zinc Concentrate

450

12 Application Examples of Flotation Machines

XCF/KYF-10 flotation machines are used for lead and zinc cleaner banks, respectively. The XCF flotation machine is used as a pulp suction tank, the KYF flotation machine is used as a free-flow tank, and the flotation machines are horizontally configured. Since the concentrator went into operation, the flotation machines have been running stably, and the production indexes have met the design requirements. The configuration of flotation machines in the whole concentrator is shown in Fig. 12.12. Lead Rougher Condition

XCF-50 KYF-50 KYF-50

Classification

Ball Mill

Lead Scavenger 1 XCF-50 KYF-50 KYF-50

Lead Scavenger 2 XCF-50 KYF-50

Pump Sump

Lead Cleaner 1 XCF-10 KYF-10

Lead Cleaner 2 XCF-10 KYF-10

Lead Cleaner 3 XCF-10

Lead Cleaner 4 XCF-10

Zinc Concentrate

Condition

Zinc Rougher XCF-50 KYF-50 KYF-50 KYF-50

Classification

Ball Mill

Zinc Scavenger 1 XCF-50 KYF-50 KYF-50

Zinc Scavenger 2 XCF-50 KYF-50

Pump Sump

Zinc Cleaner 1 XCF-10 KYF-10

Zinc Cleaner 2 XCF-10 KYF-10

Zinc Cleaner 3 XCF-10

Zinc Cleaner 4 XCF-10

Final Tail

Zinc Concentrate

Fig. 12.12 The flotation machine layout at the Changba Pb–Zn deposit

12.1 Applications of Flotation Machines for Non-Ferrous Metal Ores

451

12.1.4 Application of Flotation Machines for Nickel Ore There are many kinds of alternative flotation machines in the flotation process of nickel ore as a kind of sulphide ore. There are not only mechanical agitation JJF flotation machines, GF flotation machines, but also forced air KYF flotation machines. All single tank volumes ranging from 0.7 to 160 m3 are used for the flotation machines. The tank structure has three contours: U shape, regular octagon and circular shape. Small flotation machines are generally horizontally configured, and those flotation machines with a single tank volume of more than 50 m3 use the stepwise configuration. Jilin Nickel Industry uses small volume GF flotation machines because of its small throughput. As the largest nickel producer in China, Jinchuan Group has a mineral separation throughput of about 30,000 t/d and uses many kinds of flotation machines, mainly including KYF, JJF and GF flotation machines. This section mainly describes the application of flotation machines in No. 3 Concentrator (6000 t/d) and the new concentrator (14,000 t/d) in Jinchuan Group.

12.1.4.1

Application of Flotation Machines in the No. 3 Concentrator of Jinchuan Group

The No. 3 Concentrator in the Jinchuan Group has a throughput of 6000 t/d, and the metallic minerals mainly include pyrrhotite, nicopyrite and chalcopyrite. Gangue minerals used are mainly serpentine, olivine and pyroxene. The process of mineral separation is as follows: After two-stage grinding, the concentrates are fed into one-stage rougher, the one-stage rougher concentrates are of higher grades, and the nickel concentrate is obtained after two-time cleaner. After regrinding, the one-stage rougher tailings enter the two-stage rougher and scavenger banks, the middlings are returned in sequence, and the nickel concentrate is obtained after the concentrate produced in two-stage rougher is subject to two-time concentration. The one-stage and two-stage nickel concentrates are merged into the total concentrate before entering the dewatering operation. For the particle size of grinding products, the particle size of one-stage grinding product P80 is 100um; the particle size of the two-stage grinding product P80 is 74 µm, and that of the regrinding circuit product P80 is 50 µm. The concentration of the ore feed pulp is about 30%. The rougher and scavenger banks are provided with the KYF-50 flotation machines, and the cleaner bank is provided with the KYF-24 flotation machines. The detailed configuration is shown in Fig. 12.13, and the details of the flotation machine configuration for each operation are shown in Table 12.7. The installed power of a single KYF-50 flotation machine is 75 kW, and the power per unit of volume is 1.5 kW/set. The installed power of the KYF-50 flotation machine is saved by 25% as compared with the forced air BS-M8 flotation machine which has the single-unit installed power of 30 kW and the power per unit of volume of 1.875 kW/set; the installed power of the KYF-50 flotation machine is saved by 160%

452

12 Application Examples of Flotation Machines 2nd Step Scavenger 1

2nd Step Scavenger 2

KYF-50 KYF-50 KYF-50 KYF-50 KYF-50

KYF-50 KYF-50 KYF-50 KYF-50 KYF-50

Pump Sump

2nd Step Rougher KYF-50 KYF-50 KYF-50 KYF-50 KYF-50 KYF-50

Classification

Condition Final Tail

1st Step Rougher

KYF-50 KYF-50 KYF-50 KYF-50 KYF-50 KYF-50

Ball Mill

Condition

2nd Step Cleaner 1 KYF-24 KYF-24 KYF-24 KYF-24 KYF-24

1st Step Cleaner 1 KYF-24 KYF-24 KYF-24 KYF-24 2nd Step Cleaner 2 KYF-24 KYF-24 KYF-24 KYF-24

1st Step Cleaner 2 KYF-24 KYF-24 KYF-24

Low Grade Nickel Concentrate 1st Step Cleaner Scavenger KYF-24 KYF-24 KYF-24 KYF-24 High Grade Nickel Concentrate

Final Tail

Fig. 12.13 The flotation machine layout at the no. 3 concentrator in Jinchuan group Table 12.7 Details of configuration of flotation machines Operation name

Flotation machine model

One-stage rougher

Qty

Number of pulp suction tanks

Configuration characteristics Horizontal configuration

KYF-50

6

1

One-stage 1st cleaner KYF-24

4

1

One-stage 2nd cleaner

KYF-24

3

1

Two-stage rougher

KYF-50

6

1

Two-stage 1st scavenger

KYF-50

5

1

Two-stage 2nd scavenger

KYF-50

5

1

Two-stage 1st cleaner KYF-24

5

1

Two-stage 2nd cleaner

KYF-24

4

1

Two-stage cleaner scavenger

KYF-24

4

1

12.1 Applications of Flotation Machines for Non-Ferrous Metal Ores

453

as compared with the mechanical agitation 6A flotation machine which has the singleunit installed power of 11 kW and the power per unit of volume of 3.928 kW/set. To sum up, this fully demonstrates the remarkable energy-saving effect of the KYF-50 flotation machine. Since the concentrator went into operation, the flotation machines have been running smoothly with low failure rate; the agitation force is powerful, and the pulp flow direction is stable without the phenomenon of fluctuation of the pulp level; the mineral particles in the tank are evenly distributed without the phenomenon of stratification; the froth layer is as thick as 100 ~ 200 mm and can be regulated according to the process requirements, which will be favorable for improvement in the concentrate grade and reduction of the magnesium oxide content; the flotation machine can still be started normally 8, 24, 48 and 144 h after full-tank shutdown, which meets the requirement for a normal start after long-time shutdown with the tank full of pulp. The production practice shows that when the nickel grade is 1.45% and the copper grade is 0.89% in the run-of-mine ores, the nickel grade in concentrate is 9.36%, the copper grade is 4.58%, the magnesium oxide grade in concentrate is reduced to 6.7%, the nickel grade in tailings is 0.22%, the copper grade is 0.21%, the nickel recovery is 86.69%, the copper recovery is 71.65%, the production indexes meet the design standards and the production indexes of the system are better than those of the No. 5 system in the secondary separation workshop in the same stage on the whole [4].

12.1.4.2

Application of Flotation Machines in the New Concentrator of Jinchuan Group

The new concentrator of Jinchuan Group has a throughput of 14,000 t/d, which is designed into two series whose flotation circuit is basically the same as that of No. 3 Concentrator (6000 t/d). The KYF-160 forced air flotation machine with the largest single-unit volume in China at that time was adopted, and the aggregate unit of GF/JJF-24 and GF/JJF-28 was adopted for the cleaner bank. The details of configuration of flotation machines for each flotation bank are shown in Table 12.8.

12.1.5 Application of Flotation Machines for Molybdenum Ore The molybdenum ore is a kind of sulphide ore, which generally exists in the form of molybdenite and has good floatability. The type of flotation machine applied is similar to that of copper ore and is dominated by the external pneumatic flotation machine. The BF flotation machine and GF flotation machine are widely applied in the concentration and cleaner scavenger banks. The maximum flotation machine volume applied to molybdenum ores in China is 320 m3 . Beginning in 2004, the

454

12 Application Examples of Flotation Machines

Table 12.8 Details of configuration of flotation machines Operation name

Flotation machine model

Quantity

Number of pulp suction tanks

Configuration characteristics

One-stage rougher

KYF-160

6

Stepwise configuration, with the height difference of 0.8 m

Two-stage rougher scavenger

KYF-160

12

Stepwise configuration, with the height difference of 0.8 m

One-stage 1st cleaner

GF/JJF-28

12

4

Horizontal configuration

One-stage 2nd cleaner

GF/JJF-28

6

2

Horizontal configuration

Two-stage 1st cleaner

GF/JJF-28

8

2

Horizontal configuration

Two-stage 2nd cleaner

GF/JJF-28

4

1

Horizontal configuration

Two-stage 3rd cleaner

GF/JJF-28

4

1

Horizontal configuration

Middlings rougher

KYF-160

2

Stepwise configuration, with the height difference of 0.8 m

Middlings scavenger

KYF-160

2

Stepwise configuration, with the height difference of 0.8 m

Middlings 1st cleaner

GF/JJF-28

4

1

Horizontal configuration

Middlings 2nd cleaner

GF/JJF-24

4

1

Horizontal configuration

Middlings 3rd cleaner

GF/JJF-24

2

1

Horizontal configuration

spread application of flotation columns was initiated in the molybdenum ores cleaner bank, and there is a trend of replacing the cleaner bank of flotation machines. This section selects the typical molybdenum concentrators in China for introduction. The configuration of flotation equipment is shown in Table 12.9.

12.1 Applications of Flotation Machines for Non-Ferrous Metal Ores

455

Table 12.9 Configuration of flotation machines in typical Chinese molybdenum concentrators Name of concentrator

Throughput, t/d

Operation name

Type of flotation machine

Qty

Configuration type

Concentrator of the second mineral processing company of China molybdenum Co., Ltd

10,000

Scavenger

KYF-320

5

Stepwise configuration

Hebei Xinyuan 8000 molybdenum industry Co., Ltd

Rougher Scavenger

KYF-50 KYF-10

12 6

Horizontal configuration

Longyu 10,000 molybdenum ore concentrator of yongcheng coal and electric power group

Scavenger

KYF-40

32

Stepwise configuration

Yichun luming mining industry

Rougher Scavenger

KYF-320 KYF-130 KYF-100

18 8 4

Stepwise configuration

Cleaner

XCF/KYF-20 GF-2

10 7

Horizontal configuration

12.1.5.1

50,000

Application of Flotation Machines in Concentrator of the Second Mineral Processing Company of China Molybdenum Co., Ltd.

The Concentrator of the Second Mineral Processing Company of China Molybdenum Co., Ltd. has the throughput of 10,000 t/d, and the flotation circuit is that: The feed enters rougher after one-stage coarse grinding, the rougher concentrates enter the flotation column for concentration after regrinding, the tailings of cleaner bank enter the fine scavenger bank and the middlings are returned in sequence and reground through the bottom current. Flotation machines are used in the rougher and scavenger banks, flotation columns are used in the cleaner bank and flotation machines are used in the cleaner scavenger bank. The detailed flotation circuit is shown in Fig. 12.14. Four  4 m × 12 m flotation columns are used in the rougher bank, with the flotation time of about 26 min; Five flotation machines with a volume of 320 m3 and a flotation time of about 64 min are used in the scavenger bank. The flotation machines in the scavenger bank are of stepwise configuration, and the middlings are returned by the froth pump.

456

12 Application Examples of Flotation Machines Feed

Classification

Ball Mill

Condition

Rougher

Scavenger

Precleaner

Final Tail Classification

Cleaner 1 Cleaner 2 Cleaner 3 Cleaner 4

Ball Mill

Precleaner Scavenger

Molybdenum Concentrate

Final Tail

Fig. 12.14 The flotation circuit at the concentrator of the second mineral processing company of China molybdenum Co., Ltd. The feed is ground to about 65% passing to 74 µm, and the feed may be ground to 55% passing to 74 µm in order to increase the yield. To adapt to the changes of the run-of-mine properties, flotation machines are used in rougher and scavenger bank, which is favorable for ensuring the recovery of molybdenum concentrate; The regrinding fineness of rough concentrate is −43 µm, accounting for about 90%, then the rough concentrate is fed into the cleaner bank in which the flotation columns are used, which is favourable for improvement of the grade of molybdenum in the concentrate. This flotation circuit makes good use of the advantages of flotation machines and flotation columns and effectively guarantees the realization of technical and economic indexes. However, when the contents of pyrite, chalcopyrite or kaolin in the run-of-mine ores are higher, the tailings of the fine scavenger bank have a finer particle size of −43 µm, accounting for more than 90%, sodium silicate is to be added to disperse the fine silt, and the fine-particle minerals have serious surface contamination [5], leading to poor selectivity of flotation. If directly returned to rougher, on the one hand, the fine silt contaminates the flotation environment of the rougher bank; on the other hand, it aggravates the accumulation of pyrite or chalcopyrite in the flotation process and increases the circulating load of middlings in the flotation process. In this case, open circuit flotation needs to be properly organized for the cleaner bank, and the separation indexes can be effectively guaranteed only by discharging the bottom current of fine scavenger timely. The production practice shows that when the grade of molybdenum in the run-of-mine ores is about 0.1%, the grade of molybdenum in concentrate is about 45–52% and the recovery rate of molybdenum is about 76%

12.1 Applications of Flotation Machines for Non-Ferrous Metal Ores

12.1.5.2

457

Application of Flotation Machines in Hebei Xinyuan Molybdenum Concentrator

The mineral separation process of the concentrator has the technological characteristics of two-stage closed-circuit grinding and double open-circuit flotation of concentration and scavenger. The flotation circuit is that: The feed enters the rougher bank after one-stage coarse grinding, and the rough concentrates are fed into the flotation column for concentration after regrinding; the tailings of the cleaner bank are fed into the cleaner scavenger bank, the middlings are returned in sequence and the tailings are directly discarded through the bottom current; flotation machines are used in the rougher and scavenger bank, flotation columns are used in the cleaner bank and flotation machines are used in the cleaner scavenger bank. The detailed process is shown in Fig. 12.15. Based on the above characteristics, the flotation circuit of mineral separation solves the problem of difficult separation of micro-fine particles brought about by the high content of pyrite, chalcopyrite or kaolin. Since unnecessary repeated grinding operations are reduced, the copper and pyrite tailings restrained by the Feed Classification Condition

Rougher

Scavenger

Ball Mill

Precleaner Final Tail

Classification

Cleaner 4 Cleaner 3 Cleaner 2 Cleaner 1

Ball Mill

Precleaner Scavenger Final Concentrate

Final Tail

Fig. 12.15 The flotation circuit at the Hebei Xinyuan molybdenum concentrator

458

12 Application Examples of Flotation Machines

cleaner bank are separated separately, and the “excessive” flotation reagents can be timely discharged from the systemic circulation, which becomes the key to solving the problem.

12.1.5.3

Application of Flotation Machines in Longyu Concentrator of Yongcheng Coal and Electric Power Group

The Longyu Concentrator of Yongcheng Coal and Electric Power Group has a throughput of 10,000 t/d and grinding fineness of −74 µm in the rougher bank, accounting for 65%. The flotation circuit is as follows: The feed enters rougher after one-stage coarse grinding, the rough concentrates enter the flotation column for concentration after regrinding, the tailings of cleaner bank enter the cleaner scavenger bank and the middlings are returned in sequence and the tailings are discarded through the bottom current. The detailed flotation circuit of mineral separation is shown in Fig. 12.16. Four 4 × 12 m flotation columns are used in the rougher bank and 32 flotation machines with a volume of 40 m3 are used in the scavenger bank. The flotation machines in the different flotation operation rooms are of stepwise configuration, and the middlings are returned by the froth pump. The flotation time of the rougher bank is about 26 min and that of the scavenger bank is about 78 min.

12.1.5.4

Application of Flotation Machines in Yichun Luming Mining Industry

The Yichun Luming Mining Industry has a throughput of 50,000 t/d and uses the semi-autogenous grinding plus ball-milling process in its grinding system, and the grinding products enter rapid flotation after grading to obtain the qualified concentrate as soon as possible. The tailings of rapid flotation enter the rougher scavenger bank, the froth products enter the pre-cleaner bank, the pre-cleaner bank froth enters the cleaner bank after regrinding, the flotation columns are used in the cleaner bank and flotation machines are used in the cleaner scavenger bank. Large flotation machines with single tank volumes of 320 m3 , 130 m3 , 100 m3 , etc., are selected. The flotation circuit is shown in Fig. 12.17.

12.2 Applications of Flotation Machines for Ferrous Metal Ores With the development of the iron and steel industry in China, the pressure of energy saving and emission reduction is increasing and the “beneficiated burden materials policy” has become an industry consensus. For the iron ores with poor resource

12.2 Applications of Flotation Machines for Ferrous Metal Ores

459

Classification Classification

Feed

Ball Mill

Tower Mill

Rougher Cleaner 1

Cleaner 2

Cleaner 3

Condition Rougher

Scavenger 1

Cleaner Scavenger

Scavenger 2

Scavenger 3

Final Tail

Molybdenum Concentrate

Fig. 12.16 The flotation circuit at the Longyu concentrator. In this flotation circuit layout, the purpose of applying the flotation columns in the rougher bank is to firstly separate target minerals easily floatable in the rougher bank and directly feed the rough concentrate into the cleaner bank after regrinding, which is favourable for improving the grade of molybdenum concentrate; the flotation machines are used in the scavenger bank to ensure the overall recovery of molybdenum. Because of the use of flotation columns, we must ensure the grinding fineness in the rougher bank and the configuration of efficient pulp agitation tanks before the flotation columns. For the pulp entering the flotation machine in the scavenger bank, the mineral liberation surface is deactivated due to the long-time reaction with reagents, making it impossible to ensure the effective recovery of coarse fraction and aggregate. To improve the recovery, the flotation time of the scavenger bank needs to be multiplied, which leads to excessive energy consumption and fails to achieve the purpose of energy consumption saving of the flotation columns. In addition, the flotation circuit cannot overcome the adverse effects of high content of pyrite, chalcopyrite or kaolin in ores. The grade of molybdenum in the run-of-mine ores of this concentrator is about 0.12%, the overall recovery rate of molybdenum is about 90% and the grade of molybdenum in the concentrate is about 45–52%

460

12 Application Examples of Flotation Machines Condition

Rougher 1

Rougher 2

Pump Sump

Rougher Scavengerer 1 Scavengerer 2

Cleaner 1

Precleaner

Ball Mill

Final Tail Pump Sump

Cleaner 2

Ball Mill

Cleaner 5

Cleaner 6 Cleaner 1

Cleaner Scavenger 1

Cleaner Scavenger 2

Cleaner 7

Cleaner Scavenger 3

Pyrite Concentrate

Cleaner 2 Cleaner 8

Cleaner 3

Cleaner 4 Molybdenum Concentrate

Final Tail

Fig. 12.17 The flotation circuit at the Yichun luming mining industry concentrator

endowment and complex components in China, it is difficult to obtain high-quality iron concentrates by the conventional technological process of magnetic separation. Therefore, more and more attention has been paid to the process technology for producing high-quality iron concentrate by the reverse flotation technology of magnetic separation concentrates. Compared with the flotation of non-ferrous metal ores, the reverse flotation of iron ores has the characteristics of high specific gravity of pulp, high concentration of ore feed pulp, high froth output, high froth viscosity, low gas volume required for the process, etc., which has been recognized as one of the most difficult problems in the field of mineral separation worldwide. Most of Chinese iron ore concentrators, including Baotou Iron and Steel Company’s Concentrator, Anshan Group’s Gongchangling, Qidashan and Hujiamiao Concentrators, Dahongshan Iron Ore’s Concentrator, Hainan Iron and Steel Company’s Concentrator, Anyang Iron and Steel Company’s Concentrator, etc., used middle- and small-sized BF/JJF flotation machines before 2005. After 2005, with BGRIMM’s successful development of large flotation equipment, large flotation machines such as XCF/KYF-50, GF/KYF-50, CLF-40 and KYF-200 are gradually and widely applied in Baotou Iron and Steel Company, Wuhan Iron and Steel (Group) Corp., JISCO, Panzhihua Iron and Steel Company, Chongqing Iron & Steel (Group) Co., Ltd., Shougang Group, Longhua Shunda Mining Company, Chengde Shuangluan Jianlong Mining Co., Ltd., Dahongshan Iron Mine and other non-ferrous metal mines due to changes in the situation of mining industry and the need for development of large-scale mines.

12.2 Applications of Flotation Machines for Ferrous Metal Ores

461

12.2.1 Application of Flotation Machines in JISCO’s Concentrator Jingtieshan Mine, as the main raw material base of JISCO, has a complex mineral composition and poor ore preparability, which set a natural obstacle to the progress of mineral separation technology. In over 40 years before 2005, JISCO carried out a lot of mineral separation technology studies in pre-concentration of run-of-mine ores, magnetizing roasting, magnetic separation, mineral separation process and other aspects, but the quality of iron concentrate has not been fundamentally improved, and the grade of iron in comprehensive concentrate has always been hovering around 56 ~ 57% and never reached 60%. In 2005, JISCO decided to treat its iron concentrate of low-intensity magnetic separation through quality improvement and impurity reduction by the cationic reverse flotation process and used the “low intensity magnetic separation—two-time regrinding of secondary magnetic separation concentrate—reverse flotation circuit by one-time rougher, one-time cleaner and four-time scavenger”. The flotation operation consists of two series, 38 flotation machines (XCF/KYF-50) are used and an automatic liquid level control system is configured. The horizontal configuration of flotation machines is adopted for each single series, saving the froth pump required for return of middlings and making the whole process concise. Since it went into operation in 2008, the full-load production has been achieved, and all the mineral separation process indexes have met the design requirements. The production practice shows that, under the condition of full-load production, the iron grade in the flotation concentrate is 59.56% and the SiO2 grade is 6.4% with the iron grade in the flotation feed is 55.04% and the SiO2 grade is 10.55%. The concentrate grade is increased by 4.52% points and the SiO2 grade is decreased by 4.15% points. The quality of iron concentrate is further improved by the reverse flotation process, thus the economic benefits of more than RMB 70 million can be directly produced each year.

12.2.2 Application of Flotation Machines in the Concentrator of Daye Iron Mine The Concentrator of Daye Iron Mine of Wu Steel Mining Co. went into operation in the 1950s, with the design of run-of-mine ore throughput of 2,640,000 t/a. After several technological transformations, the maximum processing capacity can reach 4,000,000 t/a. Because of the complex properties of ores and the fine disseminated grain size of the iron-bearing minerals, the grade of iron in the final concentrate of mineral separation is only around 65%, but the sulphur content is as high as 0.33%, so it cannot meet the quality requirements of the iron concentrate fed into the furnace. Therefore, Daye Iron Mine launched the technological transformation of iron concentrate

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12 Application Examples of Flotation Machines

for iron improvement and sulphur reduction and determined the process of flotation followed by magnetic separation (copper-sulphur mixed flotation—magnetic separation—grading—desulphurization flotation), and ten XCF/KYF-50 flotation machines were used in the rougher bank and scavenger bank of the flotation process. The production practice shows that the quality of iron concentrate is improved after the transformation of the technological process of mineral separation.

12.2.3 Application of Flotation Machines in Baotou Iron and Steel Company’s Concentrator The GF/KYF flotation machine unit is a special unit belonging to the XCF/KYF unit, which is applicable to the characteristics of a large quantity of returned middlings and froth stickiness. The BF/JJF-20 flotation machines have been used for a long time in the reverse flotation process of No. 3 and No. 6 systems of Baotou Iron and Steel Company’s Concentrator, and there are many problems such as a large quantity of equipment, high energy consumption, difficult maintenance and management and low economic benefits. To further improve the concentrate quality and reduce the production cost, Baotou Iron and Steel Company firstly performed technical transformation on No. 3 system. Aiming at the characteristics of the reverse flotation process for iron ores in Baotou Iron and Steel Company, the GF-50 flotation machine having the functions of automatic air suction and automatic pulp suction is selected as the pulp suction tank and the KYF-50 pneumatic flotation machine is selected as the freeflow tank. In 2004, the No. 3 system was successfully reformed, the middlings could flow automatically and return, the whole mineral separation process was smooth, the mineral separation indexes were obviously improved, and the economic benefit was remarkable. After that, Baotou Iron and Steel Company performed technical transformation on No. 6 system in 2006, which was also successful. A total of 20 flotation machines with a volume of 50 m3 were used for the joint transformation of the two series.

12.2.4 Application of Flotation Machines in Jianshan Iron Ore Mine of Taiyuan Iron & Steel (Group) Co., Ltd. The raw ore of Jianshan Iron Mie of Taiyuan Iron & Steel (Group) Co., Ltd. was the Anshan type sedimentary metamorphic type of poor magnetite. In 2003, Jianshan Iron Min carried out the mineral processing transformation by use of “stage grinding, weak magnetic separation, anion reverse flotation process”; the BF/JJF-16 and BF/JJF10 flotation machine unit was applied in the reverse flotation operation; before the transformation, the iron grade in the concentrate was about 65.5% and the SiO2 grade was about 8%; after the transformation, the following indicators were received: the

12.2 Applications of Flotation Machines for Ferrous Metal Ores

463

concentrate iron grade after flotation was higher than 68.9% and the content of SiO2 was reduced below 4% and the recovery of the reverse flotation operation was about 98.5%.

12.2.5 Application of Flotation Machines in Anshan Iron and Steel Group Corporation (1)

Diaojuntai Concentrator

The Diaojuntai Concentrator of Anshan Iron and Steel Group Corporation processes Anshan type oxidized iron ores with the design throughput of 9 million tons per year, applies the technological process of “continuous grinding, field weakening— medium intensity field—high intensity magnetic, anionic reverse flotation”, and uses the BF/JJF-20 and BF/JJF-10 flotation machine units. In the case that the grade of iron in run-of-mine ores was 29.6%, the better separation indexes, including the grade of iron in the flotation concentrate of 67.59%, the grade of iron in tailings of 10.56% and the iron recovery rate of 82.24% were obtained. (2)

Qidashan Concentrator

The run-of-mine ores of Qidashan Concentrator of Anshan Iron and Steel Group Corporation belong to Anshan type hematite ores, which use the technological process of “stage grinding, coarse and fine separation, gravity concentration— magnetic separation—anionic reverse flotation”. The BF/JJF-10 and BF/JJF-6 flotation machines are used in the reverse flotation operation. The production practice shows that The grade of iron in concentrates has been stabilized at over 67%, the grade of iron in tailings is reduced from original 12.5% to 11.14%, the grade of SiO2 is reduced from the original 8% to less than 4%, the grade of iron concentrate is 3.8% points higher than that, before transformation, the grade of tailings is reduced by 1.36% points and the ratio of first-grade products reaches over 99.8%. (3)

Donganshan Sintering Plant

Donganshan Sintering Plant of Ansteel processed the Anshan type martite. In 2003, Donganshan Sintering Plant carried out the process and equipment transformation by use of “two-stage continuous grinding, middling re-grinding, reselection—magnetic separation—anion reverse flotation process”; the BF/JJF-16 flotation machine was applied in the reverse flotation process; after the transforma-

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12 Application Examples of Flotation Machines

tion, the iron concentrate grade was higher than 66% and the iron grade in tailings was reduced to about 19.53%. (4)

Application in Gongchangling Mining Company

The run-of-mine ores processed by Gongchangling Mining Company’s No. 2 Concentrator, Anshan Iron and Steel Group Corporation are Anshan-type magnetite. In 2003, Gongchangling Mining Company of Anshan Iron and Steel Group Corporation implemented the technical transformation of the reverse flotation process for “iron improvement and silicon reduction”, performed reverse flotation for iron improvement and silicon reduction on the iron concentrates of magnetic separation by the cationic reverse flotation process, and 39 BF/JJF-20 flotation machine units were adopted. The grade of iron concentrates increased from 65.55% before upgrading to 68.89%, an increase of 3.34% points; the grade of SiO2 in iron concentrates decreased from the original 8.31–3.90%, a decrease of 4.41% points; the recovery of iron in the technological process of reverse flotation reached 98.50% and the quality of iron concentrates ranked world class. Gongchangling Mining Company’s No. 3 Concentrator of Anshan Iron and Steel Group Corporation is a concentrator with an annual output of 1 million tons of hematite concentrate. The run-of-mine ore processed by the concentrator is hematite, the concentrator uses the mature anionic reverse flotation process and forty-four BF/JJF-20 flotation machines. Since it went into operation, 2500 t/d of hematite concentrate can be obtained, and the concentrate grade reaches over 66.5%.

12.2.6 Application of Flotation Machines in Shougang Peru S.A.A At present, the ore processed by Shougang Peru S.A.A. is the copper-bearing, low phosphorus and high sulphuric acid magnetite. In the ores, the main metals that are available for mineral separation and recovery are iron, copper, cobalt and sulphur, and gangue minerals mainly contain SiO2 , Al2 O3 , CaO, MgO, etc. The metal minerals in the ores are dominated by magnetite, followed by semi-martite, martite, limonite, pyrite, marcasite, pyrrhotite and chalcopyrite, with small amounts of hydrocyanite, sphalerite, galena, chalcocite, etc. The gangues are mainly actinolite, tremolite and common hornblende. The contents of phosphorus and arsenic in ores are very low, having little impact on the quality of concentrate products. However, the sulphur content is very high, and the desulphurization operation must be added during mineral separation to obtain qualified iron concentrate. Therefore, the concentrator uses the technological process of separation in order to obtain the final concentrates by recovering the iron minerals using stage grinding and low-intensity magnetic separation

12.2 Applications of Flotation Machines for Ferrous Metal Ores

465

and desulphurizing them by flotation. The properties of the run-of-mine ores are shown in Table 12.10. At present, the concentrator consists of ten series, two of which are coarse powder series for producing coarse-grained iron concentrates, and the remaining eight are fine powder series for producing fine-grained iron concentrates. The coarse powder series was designed by the concentrator for producing coarse iron concentrates in order to reduce the grinding quantity and grinding energy consumption. For the coarse powder series, rod mills and cyclones are used to form closed circuit grinding. The cyclone overflow is graded by the low-intensity magnetic separation, flotation desulphurization and flotation concentrate cyclones. After dewatering by low-intensity magnetic separation, the cyclone overflow is transferred into the fine powder series after fine grinding with the ball mill. The cyclone sand becomes the coarse powder product after screening and dewatering. The feed particle size of coarse powder series flotation machines was −74 µm, accounting for 48.3%. The feed particle size was coarse, so the CLF-8 wide size fraction flotation machines were used for reverse flotation. A total of ten CLF-8 wide size fraction flotation machines were used for the two coarse powder series and went into operation in 2008 and 2011, respectively. The production practice shows that: The CLF-8 wide size fraction flotation machines run smoothly, with stable pulp levels, and good flotation performance was obtained. The production indexes of the coarse powder series are shown in Table 12.11. The coarse powder concentrates are the oversize products after concentrate screening after coarse powder series flotation, and the undersize products enter the fine-powder series process. Table 12.10 Ore properties Raw ore

Specific gravity of ores

Total Fe content

FeO content

S content

4.2

55.8%

21.5%

3.232%

Table 12.11 Production indexes of coarse powder series −74 µm size fraction content/%

Pulp concentration/%

Specific gravity of ores/g.cm−3

Fe content/%

Flotation feed

48.3

38.5

5.0

63.8

1.336

Flotation concentrate

55.4

36.8

5.0

67.0

0.432

Flotation tailing

58.0

5.2

4.8

30.5

13.212

Coarse powder concentrate

23.7

66.6

0.432

S content/%

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12 Application Examples of Flotation Machines

12.3 Application of Flotation Machines in the Separation of Rare and Precious Metal Ores 12.3.1 Application of Flotation Machines for Gold Ore Separation Gold ore is a representative ore type of rare and precious metals. Gold ore separation is generally provided with the external pneumatic flotation machines, the GF or BF flotation machines are also used in small mines, and both stepwise configuration and horizontal configuration are adopted for the flotation machines. The configurations of flotation machines in major gold ore concentrators in China are shown in Table 12.12. Jinfeng Gold Mine belongs to a typical gold concentrator in China. The application of flotation machines in the Jinfeng Gold Mine is described below. Located in Zhenfeng County, Southwest Guizhou Autonomous Prefecture, Jinfeng Gold Mine (also known as Lannigou Gold Mine) is a mine with the earliest discovery, development and utilization and the largest proven and control reserves of Carlin-type refractory primary gold deposit in China. The gold reserve in the mining area reaches 110 tons, and the prospective reserve is more than 130 tons. It is a world-class supersized gold deposit whose reserve accounts for 42% of the total gold deposits in the metallogenic region in Qianxinan. Lannigou Gold Mine is a micro-disseminated refractory primary gold deposit. It is rich in resources but low in grade and refractory, which has been restricting the efficient development and utilization of the gold mine. The mine expanded propagation by on-site cultivation of strains using the mature technology of bacterial pre-oxidation and used the flotation–bacterial pre-oxidation–carbon leaching–analytical smelting process. After the mine was built and went into operation, it processes more than 1.2 million tons of ores each year with an annual gold output of 6.25 t, making it the largest world-class supersized gold mine in Asia. The types of flotation machines used in the flotation operation are shown in Table 12.13 below. The flotation machine in production is shown in Fig. 12.18.

12.3.2 Application of Flotation Machines in Lithium Ore Separation Lithium, the lightest metallic element in the natural world, has extremely high electrochemical activity and has important uses in high-energy battery, aerospace, nuclear fusion power generation and other fields. Lithium resources in the natural world mainly occur in lithium-bearing minerals and salt lake brine. At present, lithium is mainly extracted from lithium ores because it is technically very difficult to extract lithium from salt lakes. Lithium ores mainly contain spodumene, lithium

12.3 Application of Flotation Machines in the Separation of Rare …

467

Table 12.12 Configuration of flotation machines Mine name

Flotation machine model

Quantity

Throughput, t/d

Configuration type

Zijin mining, Chongli

XCF/KYF-30

12

3000

Horizontal configuration

XCF/KYF-6

8 Horizontal configuration

Zijin mining, Hunchun XCF/KYF-40

40

10,000

XCF/KYF-24

42

6000

XCF/KYF-4

10

CLF-30

13

CLF-8

6

KYF-100

9

KYF-40

6

YSJY

Jinfeng gold mine

3000

Horizontal configuration

4000

Stepwise configuration

2500

Horizontal configuration

6000

Stepwise configuration

KYF-50

6

Tanjianshan gold mine

XCF/KYF-20

8

XCF/KYF-6

4

Jiaojia gold mine

KYF-100

9

XCF/KYF-8

3

KYF-160

5

XCF/KYF-8

3

Zhaojinguihe science and technology Ltd

KYF-100

5

4000

Horizontal configuration

Axi gold mine

XCF/KYF-40 XCF/KYF-6

12 6

2000

Horizontal configuration

Sanshandao

Horizontal configuration 6000

Stepwise configuration Horizontal configuration

mica, montebrasite, castorite and zinnwaldite, and the main paragenous minerals are quartz, feldspar, mica, etc.

12.3.2.1

Industrial Application of Flotation Machines in Yichun Tantalum–Niobium–Lithium Mine

Yichun Tantalum–Niobium–Lithium Mine is an important production base for tantalum–niobium–lithium raw materials in China, with a throughput of about 2500 t/d. The proven recoverable lithium oxide reserve of the mine is 1.1 million

468

12 Application Examples of Flotation Machines

tons, and it is the largest lithium mine in the world. The 6A flotation machines were used in the early stage of lepidolite flotation. The separation effect was bad because of the obsolete equipment, especially for coarse-grained ore feeding which was not powerful in adaptability and obviously insufficient in automatic air suction capacity. After process improvement, the flotation machines were replaced with CLF-4 flotation machines designed for coarse particle flotation, the grade of lepidolite concentrate tended to be stable, the product qualification ratio reached 93%, the average Table 12.13 Configuration of flotation machines Operation name

Flotation machine model Quantity Configuration

Pre-flotation

KYF-50

2

1 feed box + 2 KYF-50 flotation machines + 1 tailing box; 1 set of liquid level detection and automatic control system, and 1 set of automatic aeration rate control system

First-stage rougher flotation KYF-50 machine

4

1 feed box + 2 KYF-50 flotation machines + 1 intermediate box + 2 KYF-50 flotation machines + 1 tailing box, 2 sets of liquid level detection and automatic control systems, and 2 sets of automatic aeration rate control systems

Second-stage rougher flotation machine

KYF-100

3

1 feed box + 3 KYF-100 flotation machines + 1 tailing box, 1 set of liquid level detection and automatic control system, and 1 set of aeration rate control system

Second-stage scavenger flotation machine

KYF-100

6

1 feed box + 2 KYF-100 flotation machines + 1 tailing box, 1 feed box + 2 KYF-100 flotation machines + 1 tailing box, 1 feed box + 2 KYF-100 flotation machines + 1 tailing box, 3 sets of liquid level detection and automatic control systems, and 3 sets of automatic aeration rate control systems (continued)

12.3 Application of Flotation Machines in the Separation of Rare …

469

Table 12.13 (continued) Operation name

Flotation machine model Quantity Configuration

Concentration/ cleaner KYF-40 scavenger flotation machine

6

1 feed box + 2 KYF-40 flotation machines + 1 intermediate box + 2 KYF-40 flotation machines + 1 intermediate box + 2 KYF-40 flotation machines + 1 tailing box, 3 sets of liquid level detection and automatic control systems, 3 sets of automatic aeration rate control systems, and 3 sets of scraper driving devices

Fig. 12.18 Flotation machine production scenario at Jinfeng gold mine concentrator

recovery was increased by 8.5% and the economic benefit of the concentrator was significantly improved. Thereafter, the industrial tests of lepidolite flotation were organized on CGF-2 flotation machines in view of the coarser disseminated grain size of lepidolite during production. The results of the industrial tests show that: When the lithium grade of feed ore in flotation is 1.43%, the lepidolite concentrate grade reaches 3.82%, the tailings grade is only 0.63% and the recovery of flotation operation reaches 70%. The wide size fraction flotation machine further improves the

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12 Application Examples of Flotation Machines

recovery rate of coarse fraction lepidolite and can simultaneously meet the efficient recovery of lithium of different size fractions.

12.3.2.2

Industrial Application of Flotation Machines in Pilganugoora Lithium Deposit

The Lithium Project of Altura Mining Limited has an annual ore throughput of 1.4 million tons, a maximum annual ore throughput of 1.54 million tons and an annual output of 219,000 tons of concentrates containing spodumene at the grade of 6%. The design throughput of the concentrator is about 2000 t/d, and the feed particle-size is −106 µm, which accounts for 80%. The final lithium concentrate can be obtained by one-time rougher and two-time cleaner. In the flotation process, 8 KYF-16 flotation machines were used for rougher and 16 KYF-8 flotation machines were used for the cleaner bank.

12.4 Applications of Flotation Machines for Non-Metal Ores This section mainly describes the application of flotation machines in non-metallic minerals such as potash mine, phosphate rock and quartz sand deposit.

12.4.1 Application of Flotation Machines for Potassic Salt Ore The main problems in the potassium salt flotation are the large froth output, vacuity of froth, easy salt deposition, etc. Especially salt deposition easily leads to blockage of the air distributor. In addition, the phenomenon of mineral sand deposition is easy to occur in blind angle areas in the feed box, intermediate box, tailings box and flotation tank. Therefore, this brings new design problems to the design of flotation machines. There are more types of flotation machines applied to potash mines, the common types include XCF/KYF, BF, JJF and CLF, and the configuration is primarily horizontal. The representative potassium salt concentrators include SDIC, Qinghai Salt Lake, Qinghai Yuantong and other companies. The types of flotation equipment applied are shown in Table 12.14. SDIC, the largest potash corporation in China, adopts the most advanced packaged technology of flotation machines. Its mineral separation project of 1.2 million tons/year is divided into a potassium chloride system and a soft potassium system and provided with a total of 80 improved XCF/KYF-50 flotation machines. The feed of

12.4 Applications of Flotation Machines for Non-Metal Ores

471

Table 12.14 Types of flotation machines used in different potash mines Mine name

Flotation machine model

Quantity

Yield, 10,000 t/a

Configuration type

SDIC

XCF/KYF-50

80

120

Horizontal configuration

Qinghai salt lake potash

JJF-42

39

100

Stepwise configuration

Qinghai Yuantong

BF-20, BF-16

20、10

40

Horizontal configuration

Lao Kaiyuan mining sole company limited

CLF-30

12

50

Horizontal configuration

CLF-16

12

Horizontal configuration

flotation machines is carnallite decomposition slurry/potassium mixed salt conversion slurry. The solid phase contains the mixed materials of KCl, NaCl, MgSO4 , K2 SO4 , etc.; the mother liquor mainly contains the saturated mother liquor of K+ , Na+ , Mg2+ , Cl− and SO4 2− ; the pH value of the slurry is 6 ~ 7; particle size: potassium chloride system: 0.2 mm; soft potassium system: −0.15 mm, accounting for 80%, where. (1)

(2)

Potassium chloride system. Feed pulp volume (containing return volume): Rougher: 3818.6 m3 /h, pulp concentration: 20 ~ 28%; Cleaner: 1981.3 m3 /h, pulp concentration: 16 ~ 18%; Scavenger: 2909.2 m3 /h, pulp concentration: 15 ~ 20%. Soft potassium system. Feed pulp volume: Rougher: 2280.1 m3 /h (containing the return volume of scavenger: 430 m3 /h), pulp concentration: 2 ~ 30%; Scavenger: 1364.3 m3 /h, pulp concentration: 22 ~ 28%.

In view of the characteristics of potassium salt flotation, a special flotation machine for potassium salt has been designed, which completely meets the requirements of SDIC mineral separation for flotation machines. This flotation machine has the following characteristics: (1) (2)

(3)

(4)

The aeration rate of the external pneumatic flotation machine is adjustable so that it is easy to guarantee the optimal aeration rate required for flotation; The XCF/KYF flotation machine has fewer members in the tank and simple structure so that the attachment points of soft potassium precipitation and crystallization are reduced. Upsizing is easily realized for the XCF/KYF flotation machine, the in-tank structure is relatively simple after upsizing, and precipitation and crystallization of soft potassium are not prone to occur; In view of the characteristics of easy crystallization of soft potassium, a small amount of flushing water can be added regularly into the hollow shaft for

472

12 Application Examples of Flotation Machines

washing and timely dissolution of the crystallized soft potassium in time, making the flotation machine more suitable for potassium salt separation. The potassium salt project of Lao Kaiyuan Mining Sole Company Limited is located in the Thakhek region of Ganmeng Province. The potassium chloride concentrator with the yield of 500,000 tons/year went into normal operation in May 2014 and produced 480,000 t of concentrates (design 500,000 t/y) in 2015. Sylvite is the main mineral in the separation design, Phase I. At present, there is a small mining yield of sylvite in production, and most of the ores are mixed ores of sylvite and carnallite. When the grade of KCl contained in run-of-mine ores is 18 ~ 22%, the grade of KCl in the final concentrate can reach 95%, with a mean recovery rate of about 73 ~ 75%. The run-of-mine ores enter the flotation process after rod milling, screening and cold-decomposition operations. The flotation process is divided into two series, six CLF-30 flotation machines are used in the rougher bank, and three CLF-16 flotation machines are used in each of the first cleaner bank and second cleaner bank. The flotation circuit is shown in Fig. 12.19. Feed Classification

Ball Mill

Condition

Rougher

Cleaner 1

Final Tail Cleaner 2

Final Concentrate

Fig. 12.19 The flotation circuit at the Lao Kaiyuan mining sole company limited concentrator

12.4 Applications of Flotation Machines for Non-Metal Ores

473

12.4.2 Application of Flotation Machines in Phosphorite Separation Phosphate rocks are the main raw materials for extracting phosphorus and can be used to manufacture phosphate fertilizer in the chemical industry. There are abundant phosphate rock resources in China. There are more lean ores, less rich ores, more refractory ores and less easily beneficiated ores although both basic reserve and economic reserve are in the front row in the world. The P2 O5 grade of phosphate ores in most countries of the world is about 30% and the average P2 O5 grade of phosphate ores in China is about 17% [6]. Among the world’s phosphate rocks, the sedimentary phosphate rock mineral (the phosphorous mineral is collophane) has the greatest magnitude of stock, accounting for about more than 70%. The utilization of middlelow grade silicon calcium collophane is the most difficult, and the requirements of phosphate fertilizer processing can be met provided that the carbonate and silicate gangue minerals are firstly removed. Flotation has been considered the most effective method in phosphate rock separation. The phosphorite flotation method includes the processes of direct flotation, reverse flotation, direct and reverse flotations, reverse and direct flotations and double reverse flotation. In the process of separation, the single direct flotation process often cannot completely meet the separation requirements due to large froth output, froth stickiness, poor flowability and other reasons. Therefore, the reverse flotation process or the combination of direct and reverse flotation processes is often used for phosphate rock separation. The properties of phosphate rocks determine the separation process and the characteristics of the separation process determine the particularity of the flotation equipment. Years of production practices prove that the flotation equipment suitable for the phosphate ore flotation process shall have the characteristics of small air volume, large tank depth, good circulation, easy operation and maintenance, etc. For flotation machines, the valves of inflatable components shall have high sensitivity and shall be easy to control; the impeller shall have proper agitation intensity and ensure adequate circulation rate; the flotation machine with pulp suction tank shall also have sufficient pulp suction capacity, and there shall be no contradiction between pulp suction and separation. The representative phosphate mines in China include many mines, such as Huangmailing Phosphate Mine in Hubei, Dayukou Phosphate Mine, Wangji Phosphate Mine, Wengfu Phosphate Mine, Haikou Phosphate Mine of Yunnan Phosphate Chemical Group Co., Ltd., Anning Phosphate Mine and Kunyang Phosphate Mine. The flotation machines used are dominated by the XCF/KYF pneumatic flotation machines. With respect to the configuration, they are mainly of horizontal configuration. The conditions of the selected flotation machines are shown in Table 12.15.

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12 Application Examples of Flotation Machines

Table 12.15 Use of flotation machines in phosphate mines Mine name

Flotation machine model

Quantity

Throughput, 10,000 t/d

Configuration type

Huangmailing phosphate mine

XCF/KYF-4

120

100

Horizontal configuration

Dayukou phosphate mine

XCF/KYF-16

124

150

Wangji phosphate mine

XCF/KYF-8, XCF/KYF-4

Wengfu phosphate mine

XCF/KYF-16

24

250

Horizontal configuration

Wengfu phosphate mine in Saudi Arabia

KYF-50

20

1250

Stepwise configuration

Haikou phosphate mine

XCF/KYF-50

20

200

Horizontal configuration

Anning phosphate mine

XCF/KYF-30

28

150

Horizontal configuration

Kunyang phosphate mine

XCF/KYF-30 and KYF-130

44 and 8

450

Horizontal/Stepwise Configuration

Horizontal configuration

12.4.3 Application of Flotation Machines in the 4.5 Million t/a Project of Kunyang Phosphate Mine The 4.5 million t/a project at Kunyang Phosphate Mine of Yunnan Phosphate Chemical Group Co., Ltd. is the largest single phosphorus concentrator in China, in which the KYF-130 flotation machine, the largest flotation device in China, is selected and used. An introduction to the flotation machines used in the 4.5 million t/a project at Kunyang Phosphate Mine is given below. The 4.5 million t/a project at Kunyang Phosphate Mine of Yunnan Phosphate Chemical Group Co., Ltd. is provided with two mineral separation workshops. The No. 1 workshop is originally designed with the direct and reverse flotation process, having a processing capacity of 1.5 million t/a. It consists of two series and uses a total of 44 XCF/KYF-30 flotation machines, with 22 flotation machines in a single series. For the first tank during direct flotation operation, the GF-30 flotation machine with larger pulp suction volume is used in conjunction with the KYF-30 flotation machine and the flotation machines are horizontally configured; In the No. 2 workshop where the process of combined configuration of flotation machines and flotation columns is used, a total of 8 flotation columns with the diameter of 4.5 m and 8 pneumatic flotation machines with the volume of 130 m3 are used, and the flotation machines between operations are horizontally configured. All the flotation machines are configured with the advanced automatic liquid level control system and the aeration rate control system. The configuration method of a series of flotation machines in No. 1

12.4 Applications of Flotation Machines for Non-Metal Ores Rougher 1 Condition

Condition

GF-30 KYF-30 KYF-30

475

Rougher 2 GF-30 KYF-30 KYF-30

Scavenger 1 GF-30 KYF-30 KYF-30

Anti-Flotation Rougher KYF-30 XCF-30 Condition

Scavenger 2 GF-30 KYF-30 KYF-30

Anti-Flotation Cleaner XCF-30 KYF-30 KYF-30 KYF-30

Cleaner 1 GF-30 KYF-30

Cleaner 2 GF-30 KYF-30

Final Tail Final Tail

Phosphate Concentrate

Fig. 12.20 Flotation machine layout in the direct–reverse flotation circuit

workshop is shown in Fig. 12.20. The configuration method of flotation machines and flotation columns in No. 2 workshop is shown in Fig. 12.21.

12.4.4 Application of Flotation Machines in Silica Sand Separation High-purity quartz sand is generally prepared by the processes of rod milling and scrubbing–desliming–magnetic separation–flotation. In the 1960s, the hydrofluoric acid method was widely used to remove feldspar. Although this method had certain effects, the discharge of fluorine-containing wastewater caused serious environmental pollution problems. At present, this process has been completely abandoned. The fluorine-free flotation process technology has been successfully applied to largescale industrial mineral separation production, making a major breakthrough in the research and development of silica sand mineral separation technology in China.

12.4.4.1 (1)

(2)

Particularity of Quartz Sand Flotation

The material size for quartz sand flotation is coarse, with a single size fraction, the feed particle-size is generally 0.2 ~ 0.7 mm, and the pulp concentration is generally 30 ~ 40%; The adhesion between bubbles and mineral particles is weak;

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12 Application Examples of Flotation Machines Rougher

Fig. 12.21 The joint configuration of flotation machine and flotation column

Rougher

Condition Rougher

Rougher

Cleaner 2

Cleaner 1 Condition

Phosphate Concentrate

(3) (4) (5) (6) (7) (8)

Final Tail

A longer actuation duration of pulp conditioning is required for the reagents and target minerals; The flotation rate of target minerals is high; A higher aeration rate is required; The yield of froth products is high; The products in the tank must be discharged or fed into the next operation timely and smoothly; The impeller–stator is used in a harsh environment and easy to wear seriously, and the problem of secondary pollution caused by the invasion of iron chips generated from wears into the concentrate products must be solved.

12.4.4.2

Requirements of Quartz Sand Mineral Separation for Flotation Machines

Through the analysis on the particularity of quartz sand flotation, it is seen that for flotation equipment, the requirements of quartz sand flotation for the fluid dynamics state in different stages and in the same stage are not exactly the same. Therefore,

12.4 Applications of Flotation Machines for Non-Metal Ores

477

the principles that the special flotation machine for quartz sand mineral separation shall abide by are as follows: (1) (2)

(3)

(4)

(5)

(6) (7)

Build a relatively stable separation area and a steady froth layer to reduce the falloff probability of mineral particles. A high suction rate (or aeration rate) is required to form a part of relatively larger bubbles, which is good for floating up while carrying coarse-grained minerals on the back to increase the chance of contact between mineral particles and bubbles. A powerful agitation area is required to ensure that the pulp is fully suspended. If the mineral particles cannot be effectively suspended, the phenomenon of mineral precipitation or stratification will occur, which will seriously affect the progress of the flotation process. The volume of pulp passing through the impeller should be appropriately large to facilitate the suspension of materials and increase the chance of contact between bubbles and mineral particles. The input power should be low, and the impeller agitation force on the pulp should be relatively weak so as to reduce the turbulence intensity of the pulp and facilitate the formation and smooth floating of the aggregate of coarse quartz sand particles and bubbles. Under low agitation force, make sure that the bubbles can be uniformly dispersed in the pulp, and that the quartz sand particles are fully suspended. The floatation tank should be as shallow as possible so that the floating distance for carrying minerals or bubbles with high specific gravity is short, and the separation area and froth layer should be more stable.

In 2004, Tongliao Silicon Sand Industry Co., Ltd. completed the first flotation concentrate production line with an annual output of 300,000 tons in China. By combining CLF-8 and CLF-4 flotation machines, products with SiO2 ≥ 98%, Ai2 O3 ≤ 1.0% and Fe2 O3 ≤ 0.1% were produced and met the national quality standard of the firstgrade glass products. In 2005, 15 sets of CGF-1 flotation machines were used for the production of flotation concentrate. The successful application of fluorine-free flotation process technology in large-scale industrial mineral separation production in this project is a major breakthrough in the research and development of silica sand mineral separation technology in China. The development of the flotation concentrate product successfully meets the demands of the silica raw material market and ends the history that the silica sand in North China is of low grade and can only be used as the raw material of float glass. The flotation concentrate product becomes an alternative to sandstone to serve as the main material used in the float glass production.

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12 Application Examples of Flotation Machines

12.4.5 Application of Flotation Machines in Fluorite Separation Fluorite is classified (by grade) into metallurgical-grade fluorite (CaF2 60 ~ 85%), ceramic-grade fluorite (CaF2 85 ~ 95%) and acid-grade fluorite (CaF2 > 97%) according to its industrial use. Metallurgical-grade fluorite is used for steelmaking and iron casting. A mixture of fluorite, lime and dolomite is added in the process of EAF iron making production in which fluorite is used as a viscosity modifier and a desulphurizing agent. Fluorite is added as a flux in the processes of oxygen-based furnace steelmaking and steel scrap refining. Ceramic-grade fluorite is used for glass, ceramics, cement, welding electrodes and other fluxes. Acid-grade fluorite is used for producing hydrofluoric acid, aluminium fluoride and spinel. Hydrofluoric acid is mainly used for synthesizing fluorocarbons. Therefore, fluorite is an important raw material for the traditional chemical industry, iron & steel and aluminium-making industries, as well as an important raw material for an emerging series of green high-tech products. There are mainly three types of fluorite in the natural world, i.e. quartz–fluorite type, quartz–fluorite–barite type and quartz–fluorite–calcite type. Different types of fluorite deposits have very different flotation circuit and equipment configurations. The fluorite deposits in China are mainly accompanying deposits, and the typical example is the Shizhuyuan Mo–Bi–W polymetallic deposit.

12.4.5.1

Application of Flotation Machines in Chaishan Concentrator of Hunan Shizhuyuan Nonferrous Metals Co., Ltd.

The Chaishan Concentrator of Hunan Shizhuyuan Nonferrous Metals Co., Ltd. mainly sorts molybdenum, bismuth, wolfram and fluorite, with a run-of-mine throughput of 3000 t/d. The concentration of the feed pulp is 30 ~ 35%, the grade of rich concentrate in fluorite can reach 93 ~ 95%, the grade of lean concentrate in fluorite is about 80%, the tailings grade is about 8% and about 300 ~ 400 t concentrates are produced each day. Rich concentrates are used as raw materials for the production of hydrofluoric acid, and lean concentrates are used for making pellets which are supplied to the smelting industry. The Shizhuyuan polymetallic deposit adopts the technical route of flotation of molybdenum, bismuth and other sulphide minerals first, flotation and recovery of wolframite and scheelite second, and flotation of fluorite last. The grade of fluorite in flotation tungsten tailings is generally 18 ~ 22%, the grade of SiO2 is 30 ~ 40% and the grade of CaCO3 is 7 ~ 8%. The flotation circuit is shown in Fig. 12.22.

12.4 Applications of Flotation Machines for Non-Metal Ores Feed

479

Classification Rougher Condition

Rougher 1

Rougher 2

Ball Mill

Cleaner 1

Scavenger

Cleaner 1

Cleaner 2

Cleaner 2

Cleaner 5 Final Tail Final Tail Cleaner 3

Cleaner 3

Cleaner 6

Cleaner 4 Cleaner 7 Low Grade Concentrate

Cleaner 8

High Grade Concentrate

Fig. 12.22 The flotation circuit of fluorite ore at the Chaishan concentrator

12.4.5.2

Application of Flotation Machines in the Rokeng Fluorite Mineral Separation Project

Sepfluor, a SA fluorite company, has four mining projects, and Nokeng is one of them. The annual yield of the concentrator will reach 130,000–180,000 tons of chemicalgrade fluorite and 30,000 tons of metallurgical-grade fluorite to satisfy the domestic and export markets. A total of 26 KYF-20 flotation machines, 33 KYF-10 flotation machines and 3 KYF-4 flotation machines are used in this concentrator.

12.4.6 Application of Flotation Machines in Graphite Separation Flake graphite has been widely applied in metallurgical, chemical, electrical and other industrial sectors due to its unique physical and chemical properties. On the

480

12 Application Examples of Flotation Machines

one hand, large flake graphite (generally refer to +0.3 mm and +0.18 mm) is of higher economic value than that of fine fraction, while it must be used for the purpose of making crucibles, expandable graphite, etc., so large flakes must be protected to the greatest extent in the process of graphite separation. The larger the flakes are, the higher the quality of graphite products is; the higher the concentrate grade is, the higher the quality of graphite products is. The graphite flotation process generally has the following characteristics: The stage grinding and stage separation process is used in order to protect the large flake graphite against damage or less damage; It needs to undergo several cleaner banks in order to achieve the fixed carbon content of more than 95%. There are abundant graphite ore resources in Balama located in Northern Mozambique. According to the graphite marginal grade of 5%, Balama has graphite ore resources amounting to about 564 million tons and has become the largest graphite mine in the world. Because of the low impurity content and high grade, it may become the graphite mine with the lowest cost in the future. Balama has a graphite mine throughput of 6000 t/d. Using the workflow of stage grinding and stage separation, the rough concentrate is obtained through rougher, scavenger, pre-cleaner and three-time cleaner bank of the run-of-mine ores. Large flake concentrate and fine concentrate are obtained, respectively, through screening, coarse separation and fine separation of the rough concentrates. In view of the characteristics of high concentrate yield, froth stickiness, inconvenient automatic flow, high requirement for safety protection, etc., a novel structural design scheme combining the double transverse and four radial froth flowing grooves which are integrated with the tank body with multiple grooves jointed for fully enclosed protection is used for the flotation machine, thus achieving customer recognition at one stroke. A total of 30 KYF-20 flotation machines, 15 KYF-10 flotation machines and 6 KYF-6 flotation machines are used in this process. The concentrator went into operation at the end of 2017, allowing the production of graphite concentrate with a fixed carbon content of more than 95%. The flotation circuit is shown in Fig. 12.23.

12.5 Application of Flotation Machines in Reconcentration of Tailings 12.5.1 Application of Flotation Machines in Tailings Concentrator of Dexing Copper Mine The comprehensive recovery of copper separation at the concentrator of Dexing Copper Mine is about 86.5%, and there are still about 13.5% of copper metal lost in tailings. About 50% of them are lost in the size fraction of +125 µm, and about 10,000 tons of copper metal are lost in the coarse size fraction every year. In order to further recover the copper metal from the tailings, a tailings concentrator was established, with a small part of the tailings from Sizhou and Dashan concentrators

12.5 Application of Flotation Machines in Reconcentration of Tailings

481

Classification

Condition Rougher

Ball Mill Scavenger

Cleaner 1

Precleaner Scavenger

Polishing Mill

Cleaner 2

Flake Cleaner 1

Screen Polishing Mill

Precleaner

Polishing Mill Flake Cleaner 2

Fine Cleaner 1

Fine Cleaner Scavenger

Flake Concentrate

Fine Cleaner 2

Fine Cleaner 3

Final Tail Fine Concentrate

Fig. 12.23 The flotation circuit at the Balama concentrator

as ore feed raw materials. In order to improve the recovery rate of coarse fraction copper-bearing minerals for tailings separation, the application research on industrial tests of the CGF-40 mechanical agitation flotation machine was carried out. The results of the industrial tests show that: The CGF-40 mechanical agitation flotation machine used for the concentrator’s pre-flotation operation for reconcentration of the one-stage tailings has stable equipment performance, allowing effective recovery of

482

12 Application Examples of Flotation Machines Classification Classification

Condition

Condition

Prerougher

Rougher

Scavenger

Ball Mill

Cleaner 1 Final Tail Final Tail Cleaner 2

Final Concentrate

Fig. 12.24 The flotation circuit at the tailings concentrator of Dexing copper mine

coarse-grained target minerals in one-stage tailings of the concentrator. In the preflotation operation, the copper enrichment ratio reaches 3.018, the copper recovery rate reaches 21.13% and the accumulated value of copper enrichment ratio reaches 2.63 times. The flotation circuit is shown in Fig. 12.24.

12.5.2 Application of Flotation Machines at Sizhou Concentrator of Dexing Copper Mine The throughput of the Tailings Concentrator of Dexing Copper Mine only accounts for a small part of the total tailings of Dexing Copper Mine, which cannot meet the processing demand of all tailings. It is urgently needed to develop tailings flotation equipment technology with super processing capacity. After continuous research and accumulation, BGRIMM developed the 680 m3 supersized flotation machine technology, making large-scale recovery of tailings resources possible. The 680 m3 supersized flotation machine processed the tailings of the original separation process in the Phase I 18,000 t/d system in Sizhou Concentrator. A purpose-made intermediate box with four valves (with two valves open, two valves for standby use) is arranged between the last 130 m3 flotation machine and the 680 m3 supersized flotation machine in the original scavenger bank, achieving on-line switching between the original production process and 680 m3 supersized flotation machine. The tailings of the original production process automatically flow into the 680 m3 flotation machine through the purpose-made intermediate box. After the flotation by the supersized flotation machine, the tailings are automatically discharged

12.5 Application of Flotation Machines in Reconcentration of Tailings

483

Fig. 12.25 KYF-680 flotation machine production scenario at Sizhou concentrator of Dexing copper mine

into the original tailings discharge pipeline, and the concentrate froth is returned to the first rougher bank of the original flotation process after regrinding. The industrial practice shows that the comprehensive recovery rate of copper in Phase I system of Sizhou Concentrator was 1.48% points higher than that in Phase II system in the same period when the grades of run-of-mine ores entering the separation operation are basically equivalent after the industrial test for more than one month, and the final concentrate grades are basically equivalent. The industrial test on the 680 m3 supersized flotation machine is shown in Fig. 12.25.

12.5.3 Application of Flotation Machines in Chengde Shuangluan Jianlong Mining Co., Ltd The company’s Luoguozigou Iron Mine has the characteristics of large scale of ore deposit, low ore grade, more associated elements and complex ore properties, and the ores here are typical low-iron, low-phosphorus, low-titanium, low-scandium and low-cobalt vanadium-bearing ores. The tailings of magnetic separation recovered in this project contain valuable metals such as phosphorus and titanium, and the tailings of magnetic separation are not recoverable under the original technical conditions of flotation equipment due to the characteristics of high specific gravity, coarse grain size, high concentration and easy sediment in tank. In 2005, the company solved the technical problems of tailings recovery with fourteen CLF-40 flotation machines, applied the new process and new technology for the comprehensive recovery and utilization of titanium and phosphorus to the production practice, activated the large

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12 Application Examples of Flotation Machines

mineral field that had been stagnant for more than a year, and realized the synchronous improvement of economic, social and environmental benefits. This not only brought new economic income to the company but also improved the resource utilization rate, forming the production capacity of 4000 t/d.

12.6 Application of Flotation Machines in Copper Smelting Slag In the modern pyrometallurgical copper smelting process, the copper slag mineral separation has become an indispensable operation step for copper smelting enterprises no matter which smelting process is adopted. Whether it is to improve the total recovery rate of smelters or to “save energy and cut down consumption”, slag concentration is of great significance. At present, the copper slag disposal methods mainly include three broad categories, i.e. flotation, pyrometallurgical dilution and wet leaching, and flotation is the most promising method for disposal of slag with lower copper content. The copper slag has the characteristics of small grain size, fine disseminated grain size and complex symbiotic relationship between ores. The copper slag has a fine disseminated grain size, copper in the slag is associated with iron and other minerals, and a high degree of liberation can only be achieved by full fine grinding. The density and hardness of copper slag are higher than those of unremarkable ores, and the conventional flotation machines generally cannot meet the technological requirements of slag flotation. In view of the process characteristics of slag flotation, BGRIMM successively developed special flotation machines for slag melting with six specifications ranging from 2 to 40 m3 , which were respectively applied in multiple domestic slag concentrators such as Noranda Furnace Slag Concentrator of Daye Nonferrous Metals Co., Ltd., Jinkouling Slag Flotation Plant of Tongling Nonferrous Metals Group Co., Ltd. and Guixi Smelter’s Slag Concentrator of Jiangxi Copper Corporation Limited.

12.6.1 Application of Flotation Machines at Guixi Smelter of Jiangxi Copper Corporation Limited Guixi Smelter of Jiangxi Copper Corporation Limited built the first concentrator for disposal of diluted electric furnace slag in China in 2005. The run-of-mine ores were formed by proportionally mixing the converter slag and electric furnace slag in the ratio of 1:4, with a specific gravity of about 3.75 g/cm3 . The flotation run-of-mine ores with the grinding fineness of −43 µm accounting for more than 80% were obtained by grading of the run-of-mine ores. The concentration of one-stage rougher flotation is about 70%, which is not only much higher than that of the concentration of ore feed pulp in the conventional flotation but also higher than the general slag flotation

12.6 Application of Flotation Machines in Copper Smelting Slag

485

concentration. The concentrator can dispose 2500 t of diluted electric furnace slag every day. In the case that the average grade of copper concentrate in the slag flotation method is 26%, more than 5000 tons of copper metal can be recovered from the waste electric furnace slag every year, and rare and precious metals such as gold and silver are also recovered. The flotation circuit is shown in Fig. 12.26. Feed Classification

Classification Classification

SAG Mill Ball Mill

Classification Rougher 2

Scavenger

Rougher 1

Cleaner 1

Final Tail

Cleaner 2

Cleaner 3

Final Concentrate

Fig. 12.26 The flotation circuit at the Guixi smelter concentrator of Jiangxi copper corporation limited

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12 Application Examples of Flotation Machines

12.6.2 Application of Flotation Machines in PASAR Philippines Alliance Smelting and Refining Company (PASAR), a subsidiary of sole investment subordinate to Glencore International AG, is the only copper producer in the Philippines. The Copper Smelter’s Slag Concentrator of PASAR is a slag concentration system newly built after the original slag concentrator (for disposal of water-quenched slag and intermediate materials) was dismantled. It disposes the mixed slag of flash smelting slag and converter slag after slow cooling, with the design processing capacity of 3000 t/d. Its flotation circuit is as follows: After ore grinding, the copper-bearing slag pulp is graded by the cyclone, the overflow (the content of the −45 µm size fraction is 80%) is subject to the one-time rougher bank after being agitated by the agitation tank, the concentrate is taken as the final concentrate and the first rougher tailings enter the second rougher. The second rougher concentrate enters the cleaner bank, and the tailings enter the scavenger bank. The final concentrates are obtained from the concentrates of second rougher after the two-time cleaner bank, and the final tailings are obtained from the tailings of second rougher after the two-time scavenger bank. The concentrates from the scavenger bank and the tailings from the concentration I are merged and supplied into the middlings regrinding system as middlings. After agitation, the pulp overflow (F80 = 22 µm) from middling classifier for regrinding enters the fine scavenger bank, the concentrates from the cleaner scavenger bank are returned to the flotation columns of concentration II and the tailings from the cleaner scavenger bank enter the two-time rougher. Since the specific gravity of ore feed slag reached 3.5 g/cm3 and the concentration of ore feed pulp was about 40%, the CLF wide size fraction flotation machines were selected. Two and four CLF-40 flotation machines were, respectively, used for rougher I and rougher IIbank, and four and three CLF-40 flotation machines were, respectively, used for scavenger I and scavenger II bank. The production practice shows that: The flotation circuit of the slag concentrator runs steadily, with the reliable performance of flotation machines. When the copper grade in the mixed slag of feed was 2.5% in the practical production, the good indexes of the final copper concentrate grade 26.22% and the copper recovery rate 88.52% were obtained. The detailed flotation circuit is shown in Fig. 12.27.

12.6 Application of Flotation Machines in Copper Smelting Slag Condition

Rougher 1

Rougher 2

Scavenger 1

487

Scavenger 2

Cleaner 1

Cleaner Scavenger

Cleaner 2

Classification Final Tail Ball Mill

Final Concentrate

Fig. 12.27 The flotation circuit at the PASAR copper slag concentrator

References 1. Jiarui L, Xiangmin L (2005) Application of treating middle and low grade bauxite by ore-dressing bayer process in alumina production. Light Met 4:11–14 2. Hongxi Z, Yuejun Z, Ming T et al (2012) Application of flotation cells in bauxite ores direct flotation. Nonferrous Met-Miner Process Sect 3:54–57 3. Weihong X (2010) Research and application of 200 m3 super large pneumo-mechanical flotation machine. Nonferrous Metall Equipment 2:5–8 4. Rui G (2006) Application of KYF-50 flotation machine at the 6000 t/d concentrator. Kunming University of Science and Technology 5. Zhuguo Li (2009) Experiment study on the comprehensive recovery of copper resource. China Molybdenum Ind 33(3):6–8 6. China Chemical Mining Association (2004) Analysis of supply and demand situation of phosphate rock in China and countermeasures 5:1–2