Light Metals 2021: 50th Anniversary Edition (The Minerals, Metals & Materials Series) 3030653951, 9783030653958

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50TH ANNIVERSARY EDITION

Edited by LINUS PERANDER

The Minerals, Metals & Materials Series

Linus Perander Editor

Light Metals 2021 50th Anniversary Edition

123

Editor Linus Perander Outotec Norway AS Oslo, Norway

ISSN 2367-1181 ISSN 2367-1696 (electronic) The Minerals, Metals & Materials Series ISBN 978-3-030-65395-8 ISBN 978-3-030-65396-5 (eBook) https://doi.org/10.1007/978-3-030-65396-5 © The Minerals, Metals & Materials Society 2021, corrected publication 2021 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, 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 publisher, 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 publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

It is my honor and privilege to present to you the Light Metals 2021 proceedings. This year we are celebrating the 50th anniversary of the Light Metals proceedings as well as the 150th anniversary of the TMS annual meeting, both marking significant milestones and being a clear testament to the lasting impact and importance these forums have. The Light Metals proceedings are the culmination of the efforts of all the authors, session chairs, subject organizers, and TMS staff who have contributed to this work. Firstly, I would like to thank the authors; it is their engagement, contributions, and active participation which makes TMS Light Metals such a valuable forum for the exchange of ideas and information. I would also like to acknowledge the subject organizers, Anne Duncan, Dimitry Sediako, Nadia Ahli, Arne Petter Ratvik, Marc Dupuis, Kristian Etienne Einarsrud, Samuel Wagstaff, Derek Santangelo, and Les Edwards, for their hard work and dedication. It’s been a pleasure and a privilege to work with you. The same goes for the TMS staff, Patricia Warren and Trudi Dunlap in particular, thank you for your guidance and the prompt and timely support you have provided. Also, a big thanks to the reviewers and session chairs who have made a tremendous contribution. Finally, the past editors, Alan Tomsett and Corleen Chesonis, have been a great help and support, my sincerest appreciation to you as well. In addition to the traditional subjects, this year’s program also includes an honorary symposium held for Alton Taberaux (Reduction Cell Operation and Process Control) and Harald Øye (Fundamentals in Anode and Cathode Technology). The honorary symposium is titled Aluminum Reduction Technology Across the Decades, which is very apt considering the celebration of the 50th birthday of the Light Metals proceedings. The honorary symposium initially included also a joint session with Aluminum Reduction Technology dedicated to Halvor Kvande; this session has however been postponed to a later date. Furthermore, the keynote session arranged by Les Edwards will discuss some of the sustainability challenges our industry faces. At the time of writing these words the COVID-19 pandemic has spread across the world with far reaching consequences. In terms of global impact, and particularly for the aluminum industry, it is clear that we are still only seeing the beginning of the effects. In the short term, the effects have perhaps been mitigated by agile responses, quickly shifting priorities, and adapting to new ways of working. Mid- to long-term effects to our industry are much harder to predict. The global lockdown and reduced demand for air travel is influencing the aerospace sector heavily, whereas the automotive and battery industries are still expecting growth driven by demand for lower emissions and improved efficiency. Other sectors, such as packaging, electronics, construction, and building materials are all affected to various degrees as influenced by changes in consumption pattern and market demand. Although much of the focus this year has been on getting through the immediate challenges the pandemic has caused, the sustainability challenges facing our industry have not disappeared. Carbon and other emissions, red mud, spent potlining and other waste streams, raw material scarcity, and declining raw material quality are all still very real and pressing issues. It is important to remain optimistic and not let the challenges of today overshadow recent achievements. This year we are celebrating two significant milestones, both the 50th anniversary of the Light Metals proceedings and the 150th annual TMS event. The Light v

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Preface

Metals proceedings publication has established itself as a key resource of information in our field and the annual conference continues to attract ever increasing numbers of researchers, students, industry professionals, and other participants. Our industry has faced great challenges in the past; however, this has also sparked innovation and developments which might otherwise have taken much longer to achieve or might not have occurred at all. I sincerely believe that by continuing to collaborate and share information on technology and research in our field, we will we able to tackle the big challenges facing our industry now and in the future. Linus Perander

Contents

Part I

Alumina and Bauxite

The Application of Intelligent Control to Red Mud Settling and Washing in an Alumina Refinery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jin Long Tian, Zheng Yong Zhang, and Yue Hua Jiang Alumina Refinery Volume Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thiago T. Franco

3 10

The Study of TCA Applied in Organic Removal from Sodium Aluminate Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Er-wei Song, Dong-zhan Han, Li-juan Qi, and Feng-jiang Zhou

18

Flotation Desulfurization of Acidified High-Sulfur Bauxite: Effects of Regulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Huaxia Li, Wencui Chai, and Yijun Cao

24

Optimization of Zinc Removal Process in Sodium Aluminate Solution Based on Orthogonal Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dong-zhan Han, Er-wei Song, Li-juan Qi, and Xiao-ge Guan

31

Collection and Selectivity Contrast of Propyl Gallate and Sodium Oleate for Diaspore and Kaolinite Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yankun Wu, Wencui Chai, and Yijun Cao

36

Effect of High Shear Agitation on Surface Properties of Diaspore and Kaolinite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shichong Yang, Wencui Chai, Yijun Cao, and Huaxia Li

41

Silicon Rich Iron Alloy from Bauxite Residue . . . . . . . . . . . . . . . . . . . . . . . . . . . Halvor Dalaker and Casper van der Eijk Bauxite Residue Neutralization Potential Using Biogenic Sulfuric and Citric Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Patricia Magalhães Pereira Silva, Roseanne Barata Holanda, Andre Luiz Vilaça do Carmo, Fernando Gama Gomes, Raphael Vieira da Costa, Caio César Amorim de Melo, Adriano Reis Lucheta, and Marcelo Montini Study on the Acid Leaching of Metal Components in Bayer Red Mud . . . . . . . . Peiyuan Liu, Jing Zhao, Yanfang Huang, Guihong Han, and Shengpeng Su Gravity Methods Applied to Bauxite Residue for Mineral Pre-concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Paula de Freitas Marques Araújo, Patricia Magalhães Pereira Silva, Andre Luiz Vilaça do Carmo, Marcus Vinícius Lins Gonçalves, Raphael Vieira da Costa, Caio César Amorim de Melo, Adriano Reis Lucheta, and Marcelo Montini

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52

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Part II

Contents

Aluminum Alloys, Processing and Characterization

Anodization Compatibility of Eutectic Aluminum–Cerium Alloys . . . . . . . . . . . . Zachary Sims, David Weiss, Hunter Henderson, Orlando Rios, Jiheon Jun, Sur Debashish, Ryan Ott, Fangqiang Meng, and Max Wiener

79

Al-Sm Alloys Under Far-From-Equilibrium Conditions . . . . . . . . . . . . . . . . . . . Can Okuyucu, Burçin Kaygusuz, Cemil Işıksaçan, Onur Meydanoğlu, Amir Motallebzadeh, Sezer Özerinç, and Yunus Eren Kalay

85

Effect of Minor Additives to Al–Zn–Mg Alloys on Welding and Corrosion Performance for Building Constructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Yu. Gradoboev, D. K. Ryabov, A. O. Ivanova, A. Yu. Krokhin, V. Kh. Mann, R. O. Vakhromov, and A. N. Legkikh Mechanism Behind Al/Cu Interface Reaction: The Kinetics and Diffusion of Cu in Forming Different Intermetallic Compounds . . . . . . . . . . . . . . . . . . . . . Yongqiong Ren, Jie Chen, and Bingge Zhao Phase Formation of Mo- and Cr-Rich Compounds in an Al–Si Cast Alloy . . . . . P. Decker, J. Steglich, A. Kauws, A. Kiefert, L. Marzoli, and M. Rosefort

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100 105

Understanding the Effect of Quench Delay and Alloy Chemistry on Various 6000 Series Alloy Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . David J. Shoemaker and Robert A. Matuska

111

Effect of Heat Treatment on the Microstructure and Mechanical Properties of LB-PBF AlSi10Mg and Scalmalloy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shaharyar Baig, Seyed R. Ghiaasiaan, and Nima Shamsaei

119

Thermal Properties of Hybrid Al–Cu-Components Produced by Combining Powder Pressing and Semi-solid Forming Strategies . . . . . . . . . . . . . . . . . . . . . . Marco Speth, Mathias Liewald, and Kim Rouven Riedmüller

126

Simulations of Wear-Induced Microstructural Evolution in Nanocrystalline Aluminum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yeqi Shi and Izabela Szlufarska

132

High-Throughput Aluminum Alloy Discovery Using Laser Additive Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Qingyu Pan, Monica Kapoor, Sean Mileski, John Carsley, and Xiaoyuan Lou

140

Manufacturing A206 Aluminum Alloy by Step Sand Casting: Effect of Solidification Time on Mechanical and Surface Properties of the Cast Samples Using Experimental and Simulation Results . . . . . . . . . . . . Amir Kordijazi, David Weiss, Sourav Das, and Pradeep Rohatgi Experimental and Numerical Examinations Regarding the Material Flow of Combined Rolling Extrusion Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Christoph Heinzel, Aleksandr Salnikov, and Sören Müller Comparison of Simulation and Real Life to Set Up a Holistic Approach for the Extrusion Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Zeynep Tutku Özen, Mehmet Buğra Güner, Osman Halil çelik, Görkem Özçelik, Tolga Demirkıran, Murat Konar, Turgay Güler, Cem Mehmetalioğlu, and Mustafa Serkan Özcan Computational Simulation of Nanoparticle Distributions in Metal Matrix Composite Casting Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Zheng, J. Jakumeit, T. Pabel, C. Kneissl, and L. Magagnin

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Effect of Thermomechanical Processing on Strengthening of the 5181 Alloy (with 0.03% Sc) Sheets for Preservation of 40% Improved Strength Compared with 5083 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dmitry Fokin, Aleksandr Alabin, Sergey Valchuk, Viktor Mann, and Aleksandr Krokhin

180

The Effect of Rare Earth Mischmetal on the High Temperature Tensile Properties of an A356 Aluminum Alloy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. Stroh, D. Sediako, and D. Weiss

184

Effects of Ultrasonic Melt Processing on Microstructure, Mechanical Properties, and Electrical Conductivity of Hypereutectic Al–Si, Al–Fe, and Al–Ni Alloys with Zr Additions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Suwaree Chankitmunkong, Dmitry G. Eskin, and Chaowalit Limmaneevichitr The Corrosion Behavior of 5xxx and 6xxx Aluminum Alloys with Trace Calcium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S. Singh, S. Kumar, and B. Pesic Review of Retrogression Forming and Reaging for AA7075-T6 Sheet . . . . . . . . . Katherine E. Rader, Jon T. Carter, Louis G. Hector Jr., and Eric M. Taleff Fatigue and Failure Analysis of an Additively Manufactured Contemporary Aluminum Alloy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . P. D. Nezhadfar, Spencer Thompson, Ankit Saharan, Nam Phan, and Nima Shamsaei Investigation of Weld Quality for Friction Stir Welding of Extrued 6XXX Series Aluminium Alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Murat Konar, Salim Aslanlar, Erdinç İlhan, Melih Kekik, Görkem Özçelik, Mehmet Buğra Güner, Arif Fatih Yiğit, and Tolga Demirkıran The Effect of Al3Er Particles on the Structure and Mechanical Properties of an Al-Mg Alloy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Anton Khrustalev, Ilya Zhukov, Vladimir Platov, and Alexander Vorozhtsov Microstructure Evolution of an Al–Fe–Ni Alloy with Zr and Sc Additions Upon Different Cooling Rates During Solidification for Improving the Mechanical and Electrical Conductivity Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Suwaree Chankitmunkong, Dmitry G. Eskin, and Chaowalit Limmaneevichitr

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Microstructure and Mechanical Properties of a Precipitation-Hardened Al–Mn–Zr–Er Alloy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Amir R. Farkoosh, David N. Seidman, and David C. Dunand

239

Characterization of the Microstructure of Al–Mg Alloy Matrix Syntactic Foam by Three-Dimensional Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jeki Jung, Su-Hyeon Kim, Won-Kyoung Kim, Cha-Yong Lim, and Yong Ho Park

245

Thermal Analysis of the Solidification Behavior of AA7075 Containing Nanoparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maximilian Sokoluk, Igor De Rosa, Shuaihang Pan, and Xiaochun Li

250

Microstructural Evolution of Ultra-Fine Grained (UFGs) Aluminum in Tribological Contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shuguang Wei, Chaiyapat Tangpatjaroen, Hongliang Zhang, and Izabela Szlufarska Microchemistry Evolution for 8xxx Alloys by Homogenization . . . . . . . . . . . . . . Erik Santora and Roland Morak

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Contents

Evaluation of Microstructures and Hardness of Al-10Si-0.45Mg-0.4Sc Alloy Powders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carlos E. S. Junior, Rodrigo V. Reyes, Leonardo F. Gomes, José E. Spinelli, Abdoul-Aziz Bogno, and Hani Henein Shear Assisted Processing and Extrusion of Aluminum Alloy 7075 Tubing at High Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scott Whalen, Md. Reza-E-Rabby, Tianhao Wang, Xiaolong Ma, Timothy Roosendaal, Darrell Herling, Nicole Overman, and Brandon Scott Taysom

270

277

Shear Assisted Processing and Extrusion of Thin-Walled AA6063 Tubing . . . . . Brandon Scott Taysom, Scott Whalen, M. Reza-E-Rabby, Tim Skszek, and Massimo DiCiano

281

Influence of the Quench Rate and Trace Elements on 6XXX Alloys . . . . . . . . . . A. Wimmer and A. Hämmerle

286

The Combined Method for Producing Long Products from Aluminium and Aluminium Alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Salnikov and C. Heinzel Effect of Extrusion Process on Mechanical, Welding, and Corrosion Behaviour of 6XXX Series of Aluminium Alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mehmet Buğra Güner, Murat Konar, Görkem Özçelik, Tolga Demirkıran, and Afife Binnaz Yoruç Hazar Development and Characterization of the Integrally Stiffened Cylinder (ISC) Process for Launch Vehicles and Aircraft Fuselage Structures . . . . . . . . . . . . . . Wesley Tayon, Marcia Domack, John Wagner, Karen Taminger, Eric Hoffman, and Sydney Newman TIG Welding of Dissimilar High-Strength Aluminum Alloys 6061 and 7075 with Nano-Treated Filler Wires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Narayanan Murali and Xiaochun Li Part III

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316

Aluminum Reduction Technology

Optimization of Thermal Characteristics and “Output Side Energy Saving” of Aluminum Reduction Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Xuemin Liang

325

R&D Projects for Improving Aluminium Smelting Technology: An Energy Reduction Initiative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ved Prakash Rai and Vibhav Upadhyay

333

Mass Transport by Waves: Bath-Metal Interface Deformation, Rafts Collision and Physical Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L. Rakotondramanana, L. I. Kiss, S. Poncsák, R. Santerre, S. Guerard, J.-F. Bilodeau, and S. Richer

344

Modeling Anode Current Pickup After Setting . . . . . . . . . . . . . . . . . . . . . . . . . . Choon-Jie Wong, Yuchen Yao, Jie Bao, Maria Skyllas-Kazacos, Barry J. Welch, and Ali Jassim

351

Superconductor Busbars—High Benefits for Aluminium Plants . . . . . . . . . . . . . Wolfgang Reiser, Till Reek, Carsten Räch, and Daniel Kreuter

359

Contents

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Coupled SPH-DEM to Simulate the Injection of a Powder into a Liquid with Heat Transfer and Phase Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . T. Roger, K. Fraser, L. Kiss, S. Poncsák, S. Guérard, J. F. Bilodeau, G. Bonneau, and R. Santerre Individual Anode Current Monitoring During Aluminum Reduction Cell Power Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yuchen Yao, Jie Bao, Maria Skyllas-Kazacos, Barry J. Welch, and Ali Jassim Carbon Dust—Its Short-Term Influence on Potroom Operations During Anode Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Matthias Dechent, Mark Philip Taylor, Richard Meier, Lea Tiedemann, Markus Meier, and Bernd Friedrich

368

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384

Experience with Lengthy Pot Hibernation at Alcoa Baie-Comeau . . . . . . . . . . . . Xiangwen Wang, M. Laframboise, and P. Gagnon

393

The Rise and Fall of CVG Venalum Primary Aluminium Plant . . . . . . . . . . . . . H. Medina

401

Prevention and Control Measures of the Cathode Voltage Drop Rise of Aluminum Electrolytic Cell Due to Unstable Power Supply Load . . . . . . . . . . Bao Shengzhong, Li Changlin, Wang Chengzhi, Wang Yanfang, Chai Dengpeng, and Hu Qingtao The Aluminium Electrolysis Cell Heat Balance Challenge Under Low Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Changlin Li, Junqing Wang, Yunfeng Zhou, Dengpeng Chai, Zhirong Shi, Yanfang Wang, and Shengzhong Bao

406

413

Production Management of Aluminum Electrolysis at Super Low Voltage . . . . . Bin Fang, Junwei Wang, Changlin Li, Dengpeng Chai, Shilin Qiu, Yunfeng Zhou, Qingguo Jiao, and Yanfang Wang

419

Improvement to Alpsys Instability and Alumina Feeding Control . . . . . . . . . . . . Anne Gosselin, Pierre Marcellin, Claude Gilbert, and Hervé Roustan

423

Low and High Voltage PFC Slope Coefficient Monitoring During Pot Start-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Christine Dubois and Luis Espinoza-Nava

432

Research and Application of Direct Welding Technology on Super Large Section Conductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Xudong Wang, Yingwu Li, and Zhongyuan Li

441

Latest Developments in GTC Design to Reduce Fluoride Emissions . . . . . . . . . . Youssef Joumani, Bassam Hureiki, Jérémy Neveu, and Philippe Martineau Process and Environmental Aspects of Applying Unshaped Carbon Materials for Cell Lining Purposes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aleksandr V. Proshkin, Vitaly V. Pingin, Viktor Kh. Mann, Aleksey S. Zherdev, Andrey G. Sbitnev, and Yury M. Shtefanyuk

451

459

Research on Wet Acid-Free Treatment Technology for SPL . . . . . . . . . . . . . . . . Xuemin Liang, Jianxun Zhang, Zhifeng Lu, Zhansheng Liu, and Peipei Liu

467

Characterisation of Powders-Precondition for Plant Engineering . . . . . . . . . . . . Peter Hilgraf, Arne Hilck, and Jan Paepcke

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Contents

Gas Treatment in the GE Pot Integrated ABART Modules (PIA) . . . . . . . . . . . . Anders Sørhuus, Håvard Olsen, Eivind Holmefjord, Roger Theodorsen, and Mikkel Sørum Instant Monitoring of Aluminum Chemistry in Cells Using a Portable Liquid Metal Analyzer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sveinn Hinrik Gudmundsson, Birna Björnsdóttir, and Kristjan Leosson Dissolution Characteristics and Concentration Measurements of Alumina in Cryolite Melts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Luis Bracamonte, Vegard Aulie, Christian Rosenkilde, Kristian Etienne Einarsrud, and Espen Sandnes On Gaseous Emissions During Alumina Feeding . . . . . . . . . . . . . . . . . . . . . . . . . Sindre Engzelius Gylver, Åste Hegglid Follo, Vegard Aulie, Helene Marie Granlund, Anders Sørhuus, Espen Sandnes, and Kristian Etienne Einarsrud On the Feasibility of Using Low-Melting Bath to Accommodate Inert Anodes in Aluminium Electrolysis Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Asbjørn Solheim Electrochemical Reduction and Dissolution of Aluminium in a Thin-Layer Refinery Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Andrey Yasinskiy, Peter Polyakov, Ilya Moiseenko, and Sai Krishna Padamata On Optimal Control of Al2O3 Concentration in the Aluminum Reduction Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yanfang Zhang, Qiaoyun Liu, Dengpeng Chai, Qingjie Zhao, Yueyong Wang, and Baowei Zhang Influence of Additives on Alumina Dissolution in Superheated Cryolite Melts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jonathan Alarie, László I. Kiss, Sándor Poncsák, Renaud Santerre, Sébastien Guérard, and Jean-François Bilodeau Part IV

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533

Aluminum Reduction Technology Across the Decades: An LMD Symposium Honoring Alton T. Tabereaux and Harald A. Øye

Alton Tabereaux: A Humble Individual Who Dedicates His Lifetime to Aluminum—An Aluminum Legend of Our Time . . . . . . . . . . . . . . . . . . . . . . Xiangwen Wang

543

Awakening of the Aluminum Industry to PFC Emissions and Global Warming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alton T. Tabereaux and David S. Wong

554

Application and Adaptability of MHD Stability Computation for Modern Aluminium Reduction Cells at Extreme Conditions of Low ACD . . . . . . . . . . . . V. Bojarevics and M. Dupuis

565

Investigation of Cyclic Process Variations Within Hall–Héroult Reduction Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jayson Tessier and Samuel Duplessis

572

In-Line Cell Position and Anode Change Effects on the Alumina Dissolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V. Bojarevics

584

Contents

xiii

History of Computer Control of Aluminum Reduction Cells . . . . . . . . . . . . . . . . Vinko Potocnik and Michel Reverdy Balancing the Modern Challenge of Operating Aluminium Smelters—Minimizing Energy Consumption, Minimizing Greenhouse Gas Emissions, and Maximizing the Productivity of Assets . . . . . . . . . . . . . . . . . Barry Welch, Jie Bao, Sergey Akhmetov, Pablo Navarro, Gudrun Saevarsdottir, and Halvor Kvande

591

600

Hydro’s New Karmøy Technology Pilot: Start-Up and Early Operation . . . . . . . Pierre Reny, Martin Segatz, Haakon Haakonsen, Håvard Gikling, Mona Assadian, Jan Frode Høines, Espen Kvilhaug, Asgeir Bardal, and Erik Solbu

608

AP12 Low-Energy Technology at ALRO Smelter . . . . . . . . . . . . . . . . . . . . . . . . Marian Cilianu, Bertrand Allano, Ion Mihaescu, Gheorghe Dobra, Claude Ritter, Yves Caratini, and André Augé

618

New Phase in Upgrade of Søderberg Technology at RUSAL’s Smelters . . . . . . . Victor Mann, Victor Buzunov, Vitaly Pingin, Alexey Zherdev, Maxim Kazantsev, Andrey Pinaev, and Yuri Bogdanov

630

Stepped Collector Bar––Continuous Developments in Low Amperage Hall-Héroult Cell to Reduce Voltage Drop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ved Prakash Rai and Vibhav Upadhyay Biocarbon in the Aluminium Industry: A Review . . . . . . . . . . . . . . . . . . . . . . . . Samuel Senanu and Asbjørn Solheim Forty Years of Trondheim International Course on Process Metallurgy of Aluminium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Michel Reverdy and Vinko Potocnik Establishing a Chemical Model of the Melt in the Cathode . . . . . . . . . . . . . . . . . Lorentz Petter Lossius and Harald A. Øye Heating New Anodes Using the Waste Heat of Anode Butts Establishing the Interface Thermal Contact Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Marc Dupuis, Henrik Gudbrandsen, and Kristian Etienne Einarsrud

638 649

657 668

676

Forty Years of Cathode Block Evolution at EGA . . . . . . . . . . . . . . . . . . . . . . . . Mustafa Mustafa, Michel Reverdy, and Mohamed Tawfik

690

Wetting of Carbon Cathodes by Molten Electrolyte and Aluminium . . . . . . . . . . Samuel Senanu, Arne Petter Ratvik, Zhaohui Wang, and Tor Grande

699

Optimising Anode Performance in Albras Potlines . . . . . . . . . . . . . . . . . . . . . . . Benigno Ramos Pinto Junior, Nilton Freixo Nagem, Valfredo Costa Filho, and Thais Almeida Morais Simoes

708

Part V

Cast Shop Technology

Impact of COVID-19 Pandemic on British Foundries . . . . . . . . . . . . . . . . . . . . . Prateek Saxena, Pam Murrell, Tharmalingam Sivarupan, John Patsavellas, Konstantinos Salonitis, and Mark R. Jolly

719

Effect of Steam on Aluminium Packaging Multilayers . . . . . . . . . . . . . . . . . . . . . M. Syvertsen, A. Kvithyld, S. Kubowicz, B. Vågenes, and R. Gaarder

727

xiv

Compaction of Aluminium Foil and Its Effect on Oxidation and Recycling Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alicia Vallejo-Olivares, Harald Philipson, Mertol Gökelma, Hans J. Roven, Trond Furu, Anne Kvithyld, and Gabriella Tranell

Contents

735

Influence of Mg Concentration on the Inhibiting Effect of CO2 on the Rate of Oxidation of Aluminum Alloys 5182 and 6016 . . . . . . . . . . . . . . . . . . . . . . . . Cathrine Kyung Won Solem, Egil Solberg, Gabriella Tranell, and Ragnhild E. Aune

742

Mold Design for More Accurate Chemical Composition Analysis of Aluminum Alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ghadir Razaz and Torbjörn Carlberg

751

Automated Chemical Analysis of Liquid Aluminum for Process Control . . . . . . Sveinn Hinrik Gudmundsson, Halldor Gudmundsson, and Kristjan Leosson Characteristic Impurities of Silicon Metal Si-441 as Additive Material to Produce Aluminium Foundry Alloy A356.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . Reggy Zurcher, Rainaldy Harahap, Edi Mugiono, M. Yasir Q. Parapat, and Masrul Ponirin

758

763

Molten Aluminium Transfer: Review and Comparison of Different Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Olivier Dion-Martin, Jean-Francois Desmeules, and Robert Dumont

769

Automated Metal Cleanliness Analyzer (AMCA)—An Alternative Assessment of Metal Cleanliness in Aluminum Melts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hannes Zedel, Robert Fritzsch, Shahid Akhtar, and Ragnhild E. Aune

778

Overview of the Possibilities and Limitations of the Characterization of Ceramic Foam Filters for Metal Melt Filtration . . . . . . . . . . . . . . . . . . . . . . . Claudia Voigt, Jana Hubálková, Are Bergin, Robert Fritzsch, Ragnhild Aune, and Christos G. Aneziris Compression Testing of Ceramic Foam Filters (CFFs) Submerged in Aluminium at Operating Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Are Bergin, Robert Fritzsch, Shahid Akhtar, Lars Arnberg, and Ragnhild E. Aune

785

794

The Effect of Grain Refiner on Aluminium Filtration . . . . . . . . . . . . . . . . . . . . . Sarina Bao, Jiawei Yang, Shahid Akhtar, Stig Tjøtta, Ulf Tundal, Tanja Pettersen, and Yanjun Li

803

Next-Generation Electrical Preheating System for Filter Boxes . . . . . . . . . . . . . . Jochen Schnelle and Markus Byczek

810

Reduction of Impurity Elements by Applying Electromagnetic Stirring in Fractional Crystallization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yuichiro Murakami and Naoki Omura

818

Nature Alu: Manufacturing High Purity Aluminum from the Concept Idea to the Production Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jean-Francois Desmeules and Denis Mazerolle

822

Grain Refinement Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rein Vainik, John Courtenay, and Frode Lien

829

Contents

xv

A Comparison of AA6060 Grain Structures Achieved Using AMG’s TiBAl Advance™ and Alternative Al-Ti-B Grain Refiners via a 1D Upward Solidification Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Matthew Piper, Shahid Akhtar, and Phil Enright Mechanism of High Grain Refinement Effectiveness on New Grain Refiner “TiBAl Advance” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Akihiro Minagawa and Matthew Piper Ultrasonic Melt Treatment in a DC Casting Launder: The Role of Melt Processing Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Christopher Beckwith, Tungky Subroto, Koulis Pericleous, Georgi Djambazov, Dmitry G. Eskin, and Iakovos Tzanakis Residual Stress Prediction in the Casting Process of Automotive Powertrain Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S. Kianfar, J. Stroh, N. Bahramian, D. Sediako, A. Lombardi, G. Byczynski, P. Mayr, M. Reid, and A. Paradowska Coupled Modeling of Misrun, Cold Shut, Air Entrainment, and Porosity for High-Pressure Die Casting Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. Jakumeit, H. Behnken, R. Laqua, S. Mbewou, M. Fehlbier, J. Gänz, and L. Becker Study on the Mechanical Properties of Commercial Vehicle Wheel Through the Molten Forged on the A356 Alloy with a Multi-cavity Fabrication Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Min Seok Moon, Myeong Han Yoo, Kee Won Kim, Joon Hyuk Song, and Je Ha Oh

837

844

850

858

865

871

Simulation-Based Analysis for Optimization of Casting Process in AA7075 . . . . Rafiezadeh Siamak, Pucher Philip, Neubert Steffen, and Ivanov Waldemar

878

Characterization of Ingots Cast with the APEX™ Casting System . . . . . . . . . . . Craig R. Cordill, Bin Zhang, and Gerhard Castro

886

Effect of Ultrasonic Melt Treatment on the Sump Profile and Microstructure of a Direct-Chill Cast AA6008 Aluminum Alloy . . . . . . . . . . . . . . . . . . . . . . . . . Tungky Subroto, Gerard S. Bruno Lebon, Dmitry G. Eskin, Ivan Skalicky, Dan Roberts, Iakovos Tzanakis, and Koulis Pericleous The Influence of the Casting Speed in Horizontal Continuous Casting of Aluminium Alloy EN AW 6082 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Akin Obali, Kerem Ahmet Dilek, Seracettin Akdi, Deniz Kavrar Ürk, and Mertol Gokelma The Impact of Casting Conditions on Edge Cracking of AA5182 Ingots During Hot Rolling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Samuel Robert Wagstaff Reducing Gas Shrinkage Porosity in Al–Mg Alloy Slabs . . . . . . . . . . . . . . . . . . . I. Kostin, A. Sidorov, S. Belyaev, A. Startsev, A. Krokhin, A. Krechetov, and A. A. Iliin Molecular Dynamics Simulations of the Evolution of Residual Stresses During Rapid Solidification of Aluminium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Michail Papanikolaou, Konstantinos Salonitis, and Mark Jolly

894

900

907 912

918

xvi

Part VI

Contents

Electrode Technology for Aluminum Production

Digitalization in the Carbon Area as a Means to Improve Productivity . . . . . . . Koulumies Antti, Merlin Paul, Becerra Ana Maria, and Piechowiak Lasse

931

AMELIOS Suite or the Fives Digital Package for Carbon 4.0 . . . . . . . . . . . . . . . Christophe Bouché, Xavier Genin, Pierre Mahieu, and Sylvain Georgel

940

Development and Applications of the Four Points Probe (4PP) Electrical Resistivity Measurements for Anode Process Optimization . . . . . . . . . . . . . . . . . Julien Lauzon-Gauthier and John Secasan

951

The Readiness and Compatibility of a Modern Anode Handling and Cleaning System for Industry 4.0 Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kevin Williams

957

Start-Up of a New “Smart and Green” Anode Plant . . . . . . . . . . . . . . . . . . . . . . Christophe Bouché, Xavier Genin, Vincent Philippaux, and Jérôme Morfoise

965

The Steps to Optimize and Implement an Anode Stub Hole Cleaning Machine Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Valérie Langelier, Derek Santangelo, René Provost, Stéphane Caron, and Philippe Noreau

976

Baking Furnace Optimizations at Aditya to Maintain Consistent Quality and Productivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Suryakanta Nayak and M. Katharbatcha

984

Anode to Cathode Electrical Current Modelling for Cell Retrofit Application of Conductive Nails Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . W. Berends

992

Managing Anode Performance with a Versatile Reactivity Analysis Method . . . . 1001 Lorentz Petter Lossius, Juraj Chmelar, and Viktorija Tomkute New Partial Repair Technique for Deformed Yoke . . . . . . . . . . . . . . . . . . . . . . . 1010 Safwat Zayed, Abdul-Mageed Shamroukh, A. M. Omran, W. Y. Aly, and G. T. Abdel-Jaber Correction to: Compaction of Aluminium Foil and Its Effect on Oxidation and Recycling Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alicia Vallejo-Olivares, Harald Philipson, Mertol Gökelma, Hans J. Roven, Trond Furu, Anne Kvithyld, and Gabriella Tranell

C1

Author Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1019 Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1025

About the Editor

Linus Perander is the head of Calcination with Metso: Outotec where he is responsible for the process design and product development of Circulating Fluidized Bed calciners used for alumina production as well as thermal processing of a wide range of ores and minerals. Prior to taking up this role, Dr. Perander worked as a senior research engineer, and later as a project manager, at the Light Metals Research Centre (The University of Auckland, New Zealand), while also attaining his doctorate in 2010. He also has a M.Sc. in inorganic chemistry from the Åbo Akademi University in Finland. Dr. Perander has over a decade of industrial experience and more than 8 years of academic experience prior to this, mainly from the fields of alumina and aluminum production and research. Much of Dr. Perander’s work is focused on how the calcination process influences the alumina properties and quality and what consequences this has when the material is used as a feedstock and scrubbing medium in the aluminum smelter Dr. Perander has authored/presented over 40 publications in international peer-reviewed journals and industry relevant conference proceedings, including 8 TMS contributions. He has been attending and contributing to TMS since 2008 and has served as session chair on several occasions and as subject organizer for Alumina and Bauxite in 2018. In 2018 he also organized a professional short course on Best Practices in Alumina and Bauxite Processing and Production. Dr. Perander was also an associate editor for the Essential Readings in Light Metals: Volume 1 Alumina and Bauxite book project.

xvii

Program Organizers

Alumina and Bauxite Anne Duncan Hatch Aluminum Alloys, Processing and Characterization Dimitry Sediako has been a professor and a head of the Mechanical Engineering program of the University of British Columbia in Kelowna, Canada since 2017 after working for 12 years as a senior scientist with the National Research Council of Canada and Canadian Nuclear Laboratories. After receiving his Ph.D. in Metallurgical Engineering in 1987, Dr. Sediako’s career covered over 30 years of industrial R&D in steel, aluminum, and magnesium metallurgy. Dr. Sediako worked as a research engineer for a number of foundries and metallurgical companies in Russia, China, Taiwan, and Canada, leading many major projects on technological innovations in the industry. For several major breakthroughs in his research, he received several state awards internationally, including Belarus, Order of White Magnolia, and Order of Friendship from China and Taiwan. Over his long career in industry and research, he made a number of major contributions to steel continuous casting technologies, direct-chill casting of magnesium and aluminum alloys, precision sand and high pressure die casting of aluminum. Along with extensive pilot-plant research, modeling, and state-of-the-art fitness-for-service testing, Dr. Sediako is extensively utilizing the unique properties of neutrons, allowing direct stress measurements and in-situ studies of phase evolution in metal parts and components. These studies enable new alloys development for the most challenging applications and technology optimization in metallurgical manufacturing. He collaborates extensively with many automotive manufacturers, both OEMs and Tier 1 suppliers, enabling new alloys development, stress analysis, and technology optimization for the most challenging applications. A specific focus of his research is stress characterization in automotive, aerospace, and marine powertrain components, as well as in-situ studies of solidification, phase evolution, and high temperature creep in new aluminum and magnesium alloys’ development for the transportation industries. Dr. Sediako is the author of more than 200 peer-reviewed articles and proprietary reports and is a licensed Professional Engineer. In 2014 he was inducted into the Fellowship of the Canadian Academy of Engineering. xix

xx

Program Organizers

Aluminum Reduction Technology Nadia Ahli is the Technology Transfer Contracts manager at Emirates Global Aluminum. She graduated in Chemical Engineering from United Arab University (2008) and received a Master of Business Administration from Canadian University Dubai (2011). She joined EGA Technology Development and Transfer in 2008 as a process control engineer. She worked on developing high amperage technologies like DX+, DX+ Ultra, and DX+ Ultra Retrofit Technologies. Nadia delivers commitment to excellence during Technology Transfer to clients; this was demonstrated during the transfer of EGA technologies to two clients within the last seven years. She led the process team to transfer DX+ Technology to Emirates Aluminum (formerly known as EMAL and now part of EGA) in 2013 when starting up and normalizing the world's longest Potline. She was a team leader for transferring DX+ Ultra Technology to Aluminum Bahrain in 2018–2019 and is currently leading the ALBA Potline 6 amperage creep project to creep the amperage to 480 kA. Her expertise encompasses managing reduction cell operation, process control, pot preheat and preparation, training of clients, preparation of technology packages for the client, the development of PLC-based pot control system, delivering an electrolysis course within EGA, and optimizing reduction cell technology for better current efficiency, low specific energy, and low anode effect. Nadia has contributed to various international conferences such as TMS (2015 and 2016) and Australasian conference (2013) where she was awarded as best presenter. She was the recipient of the 2016 TMS Young Leaders Professional Development Award. Aluminum Reduction Technology Across the Decades: An LMD Symposium Honoring Alton T. Tabereaux and Harald A. Øye Arne Petter Ratvik is a senior research scientist at SINTEF Industry, Metal Production and Processing in Trondheim, Norway. He has his M.Sc. and Ph.D. in inorganic chemistry from NTNU (the Norwegian University of Science and Technology) followed by a postdoc period at University of Tennessee, USA, all related to molten salt chemistry and electrolytic production of light metals. He has industrial research and production management experience from Elkem and Falconbridge (now Glencore) Nikkelverk related to pyrometallurgical and aqueous electrochemical processes. He has been with SINTEF since 1998, except for a four-year term as Head of Department of Materials Science and Engineering at NTNU. Current research interests are mainly within electrochemical production of metals and materials chemistry related to metal processes. He has been a project manager of several large projects co-financed by industry and has co-authored more than 90 papers. He has served TMS as session chair four times, subject chair for the Electrode Technology in 2015, and editor of Light Metals 2017.

Program Organizers

xxi

Marc Dupuis has been a consultant specializing in the applications of mathematical modeling for the aluminum industry since 1994, the year he founded his own consulting company, GeniSim Inc. Before that, he graduated with a Ph.D. in chemical engineering from Laval University in Quebec City, Canada in 1984 and then worked for 10 years as a research engineer for Akan International. His main research interests are the development of mathematical model of the Hall-Heroult cell dealing with the thermoelectric, thermomechanic, electromagnetic, and hydrodynamic aspect of the problem. He was also involved in the design of experimental high amperage cells and the retrofit of many existing cell technologies. Kristian Etienne Einarsrud holds a M.Sc. (2008) in Applied Physics and Mathematics from the Norwegian University of Science and Technology (NTNU), Trondheim, Norway. He was first introduced to aluminum production during his thesis work, which motivated him to pursue a Ph.D. in Fluids Engineering, also at NTNU, on CFD modeling of anodic bubble flow (2012). Following his Ph.D., Dr. Einarsrud spent two years as a researcher in the Flow Technology group in SINTEF, followed by two years as an associate professor at the South Trøndelag University College (HiST). Since 2016 he has been an associate professor at the Department of Material Science and Engineering at NTNU, where he teaches Heat and Mass Transfer, Mechanical Modeling, Energy Materials, and Chemical Engineering. Dr. Einarsrud’s main research topics include Computational Fluid Mechanics, Reactive Multiphase flow and Interface Phenomena, Process Metallurgy, and Electrochemistry. He has published more than 30 peer-reviewed papers, is the principal supervisor of 5 Ph.D. students, and co-supervisor to 4 others. He had also supervised 10 M. Sc. students, and more than 25 B.Sc. candidates. Dr. Einarsrud is currently heading the research on fundamentals and modeling at the Centre for Research-based Innovation in Metal Production (SFI Metal Production) at NTNU. Dr. Einarsrud has participated actively in TMS since 2011, serving as a session chair and as a member in several committees. He was awarded the 2012 TMS Light Metals Subject Award in Aluminum Reduction and the 2019 TMS Young Leaders Professional Development Award in the Light Metal Division.

xxii

Program Organizers

Cast Shop Technology Samuel R. Wagstaff is currently a partner at Oculatus Consulting, specializing in aluminum processing and product development. He earned his B.Sc. degree from Cornell University in Mechanical and Aerospace Engineering in 2013. Samuel then earned a M.Sc. degree at the Massachusetts Institute of Technology focusing on characterizing macrosegregation patterns in large format rolling slabs. He then earned a Sc.D in 2016 also from MIT for his work on engineering convective flows to minimize the appearance of macrosegregation. Following his graduate studies, he worked at Novelis in their rolling facility in Sierre, Switzerland in their automotive development department, focusing on process refinement and product troubleshooting. In 2018 he moved to the Novelis R&D center in Kennesaw, Georgia where he became a lead scientist for product and process development. At Oculatus, he works on next-generation technologies for the aluminum sector and improvements in current processes. His current focus is on improving the profitability of existing centers via casting process improvement and recycle-based product development. Samuel is the author of 16 peer-reviewed articles and inventor of over 25 patent applications. Electrode Technology for Aluminum Production Derek Santangelo has been involved in the study, design, and construction of some of the world’s newest, largest, and most advanced aluminum smelter complexes. He is currently the Global Practice Lead for Carbon at Hatch’s Centre of Excellence for Aluminum, based in Montreal, Canada. He obtained his bachelor’s degree in Mechanical Engineering at McGill University (2005). Since then he has held roles in management, engineering, construction, and start-ups both nationally and internationally for major EPCM Consulting firms and participated in the execution of major projects in North America, Europe, the Middle East, and Asia. While his primary area of expertise lies within the carbon area, Derek has also worked in reduction, potlining, material handling, gas treatment, and casting. Derek joined the TMS Aluminum Committee in 2019 and was an invited speaker for the 2020 Electrode Technology symposium. For 2021 he is the co-author of a paper in addition to serving as the Electrode Technology subject chair.

Program Organizers

xxiii

Sustainability in the Aluminum Supply Chain: Joint Session Les Edwards is Vice President of Production Control and Technical Services at Rain Carbon Inc. and has been with the company since 1998. He is responsible for production planning and control at Rain Carbon’s US operations as well as technical support activities for the calcination business unit, which includes customer technical support, R&D activities, and laboratory operations. Les is a longstanding member of the TMS organization. He has served as program organizer of the Electrode Technology sessions at annual TMS meetings and is the leader of the TMS Anode Technology Course. He is a regular presenter at industry technical conferences and has authored or co-authored over 30 technical papers and holds 6 patents. Prior to joining Rain Carbon, Les spent 11 years in the Australian aluminum industry in a predominantly R&D role. He has a B.Sc. degree from the University of Western Australia and an MBA from Tulane University in New Orleans. He currently lives in Houston, Texas.

Aluminum Committee 2020–2022

Executive Committee 2020–2021 Chairperson Alan David Tomsett, Rio Tinto Pacific Operations, Queensland, Australia Vice Chairperson Linus Perander, Outotec Norway AS, Oslo, Norway Past Chairperson Corleen Chesonis, Metal Quality Solutions LLC, Pennsylvania, USA Secretary Stephan Broek, Hatch Ltd, Ontario, Canada JOM Advisor David Sydney Wong, University of Auckland, Queensland, Australia Light Metals Division Chair Eric Nyberg, Tungsten Heavy Powder & Parts, Wyoming, USA

Members-at-Large Through 2021 Les Edwards, Rain Carbon Inc, Louisiana, USA Kristian Etienne Einarsrud, Norwegian University of Science & Technology, Trondheim, Norway John Griffin, ACT LLC, Pennsylvania, USA Derek Santangelo, Hatch, Quebec, Canada

Members-at-Large Through 2022 Martin Iraizoz, Parque Industrial Pesado, Puerto Madryn, Argentina Anne Kvithyld, SINTEF, Trondheim, Norway Julien Lauzon-Gauthier, Alcoa Corporation, Quebec, Canada Ray Peterson, Real Alloy, Tennessee, USA Etienne Tremblay, STAS, Quebec, Canada Edward McRae Williams, Arconic, Pennsylvania, USA

xxv

Part I Alumina and Bauxite

The Application of Intelligent Control to Red Mud Settling and Washing in an Alumina Refinery Jin Long Tian, Zheng Yong Zhang, and Yue Hua Jiang

Abstract

Efficient operation of the red mud settling and washing system is a key operational goal for an alumina refinery. The concentration of soda in thickener underflow and the dosage of flocculant have great influence on the production cost of alumina. SAMI has developed an intelligent control system for red mud settling and washing, which can monitor the data of thickener online in real time through data mining, optimization of control strategy, and other methods to realize automatic intelligent control. The intelligent control system has been built, deployed, and tested into operation for about two years in an alumina refinery in China. The results show that the consumption of flocculant is reduced by 15%, the concentration of discharged soda is reduced by 16*36%, and the economic benefit is remarkable. Keywords








Settling and washing Intelligent control Soda loss Flocculant consumption Non-contacted interface instrument




settling or washing, and last four as washers. Each thickener has corresponding overflow pumps, underflow pumps, and flocculant pumps. Process RMSW is in the middle of all refinery processes, which have very huge volumes. It can accommodate all incoming materials, but only can control the output materials passively. That means all control methods are limited to be used for the equipment in this process, therefore, during the operation, it always requires the operator to set the flow rate of each pump so as to maintain the process operating in order. The RMSW cannot be adjusted in real time according to the fluctuation of production system under manual control, as a result, the consumption of flocculant and the loss of soda in red mud will be increased. The total soda concentration of discharged slurry in red mud is 3.2*3.7 g(Na2Ot)/L usually. Our Intelligent Control System has such characteristics as real-time monitoring and dynamic adjustment of the control scheme. It can control the fluctuation of the system in a real-time dynamic way, which can further improve the operation stability of the whole RMSW process, and obviously contribute to make the system more steady state. As a result, it can fulfil the target that reducing the consumption of flocculant and minimizing the loss of soda.

Introduction

Control Mode of Process RMSW in Present

Red mud settling and washing (RMSW) is used in the alumina refinery to separate the pregnant liquor from red mud slurry, and then wash the red mud. It is kind of the typical liquid–solid separation operation. In China, the process RMSW of alumina refinery usually consists of seven thickeners which form a Counter-Current Washing System, two as settlers, one as public standby for

Nowadays, the DCS and PLC in the refinery can achieve the control mode of PID control, such as: temperature interlock control, flow interlock control, and level interlock control, etc. These controls are represented as “small system” control, i.e., the measurement position and control unit are interconnected directly, and if the measurement position is affected by multiple “small system” or multivariable factors in the middle interval of the controlled unit, the control results fluctuate greatly and are not operational [1]. For example, the level control factors of a single thickener are affected by four variables: the underflow at the

J. L. Tian
Z. Y. Zhang
Y. H. Jiang (&) Shenyang Aluminum and Magnesium Engineering and Research Institute Co., Ltd., Shenyang, 11001, China e-mail: [email protected]

© The Minerals, Metals & Materials Society 2021 L. Perander (ed.), Light Metals 2021, The Minerals, Metals & Materials Series, https://doi.org/10.1007/978-3-030-65396-5_1

3

4

previous stage, the overflow flow at the next stage, the underflow flow at this stage, and the overflow flow at this stage. To achieve level control, the abovementioned four variables must be analyzed for correlation to determine the appropriate control scheme. Therefore, automated control in the RMSW system is not easy to achieve, and yet it still adopts human judgment and manual control. At the present stage, the RMSW process is equipped with a liquid level meter and manual mud layer measuring device, and some factories adopt automatic measurement mud layer meter. The staff in the main control room can remotely adjust the start–stop operation and flow control of all pumps through DCS system. Although the whole RMSW process can realize simple interlock control through DCS system or PLC system, it cannot realize automatic control completely yet.

J. L. Tian et al.

being strictly supervised by the government. Many factories select the manual sampling rather than densitometers. Another new model densitometer works based on ultrasonic principle, but it has not been widely recognized yet in the industry, so the factories rarely select it. The soda concentration detector is also a key instrument in the RMSW process. The currently used online soda concentration measurement is light transmittance measurement, and the reliability is relatively lower. Some factories still focus on the test of this instrument, which has not been widely used. In this project, since there is no densitometer and soda concentration detector in the test plant, the relevant data analyzed manually was adopted. The non-contacted interface instrument has been installed in the RMSW thickeners (seven sets in total) in the test, which can obtain the slurry status in the thickener in real time.

Key Instruments for Intelligent Control Main Strategy of Intelligent Control When the intelligent control is adopted in the RMSW process, the real-time data of the RMSW process must be analyzed. At present, the main slurry detection instrument in the thickener is the mud layer detector, which can detect and distinguish the clear layer, mix layer, and mud layer in the thickener, so as to reflect the slurry status in the thickener. There are two kinds of mud layer detecting instruments at present. One is the direct contact detector, which needs to put the detection probe into the thickener to detect the slurry directly. This kind of instrument has high accuracy, but it needs a lot of manpower and resources to maintain and calibrate the probe. Especially in the alumina plants in North China, exists the phenomenon of freezing in winter, leads to the practical application effect of this direct contact mud layer detector is not ideal in China (Because most alumina plants are at North of China). Another kind of mud layer detector is installed outside the sidewall of the thickener. This instrument does not contact with the slurry in the thickener directly. It detects the slurry by sound wave and determines the layers of the slurry in the thickener according to the feedback signal. This instrument is called non-contacted interface instrument. The instrument is not in direct contact with slurry and has no mechanical parts, so it can be free of maintenance. It can determine the distribution of the interface in the thickener, and the results are relatively accurate [2]. It has been used in some alumina plants in China widely. The installation of non-contacted interface instrument just showed in Fig. 1. The control unit of non-contacted interface instrument usually at the roof of thickener. The solid content of underflow of thickener should be used to measure by density meter. However, since the most density meters for slurry contain radioactive substances and

The main control strategy of RMSW process in alumina plant is to maintain the quality balance of incoming and outgoing materials. A series of counter-current washing process is used in production, which is a kind of complex process. In the washing process, there are two main materials that need to be focused, they are the washed red mud slurry which would become underflow slurry and washing water which would become overflow water. The washing process is mainly to wash the red mud, so the washed red mud slurry is selected as the main control item. The automatic preparation function is generally used in the preparation and addition process of flocculant, and the intelligent control system only needs to adjust the specific dosage of flocculant. (1) Basic theoretical control strategy The basic control includes underflow control and flocculant dosage control. The underflow control complies with the principle of solid mass balance, that is, the discharging solid in the underflow of a single thickener should be the same as the feeding flow. The amount of flocculant is generally proportional to the solid content in the feed of tank. The overflow rate can be calculated according to the quality accounting of the total material in and out of the tank. In the control process with single thickener as the main control body, only the discharge quantity is controlled other than the feed quantity. (2) Control strategy in actual stat In the RMSW process, it is mainly required to run smoothly. There are many inspection indexes in the process. The common inspection indexes involved in the concentration of pregnant liquor soda, the soda concentration of discharged red mud, the dosage of

The Application of Intelligent Control to Red Mud …

5

Fig. 1 Installation diagram of non-contacted interface instrument. (Color figure online)

Detection unit Detection unit

Control Unit

flocculant, the height of mud layer and clear layer, the torque of harrow machine, and the discharged solid content of red mud slurry. There are corresponding correlations among the above control objectives, some of which are controlled objects (CVS) and some are operational variables (MVS). Therefore, it is necessary to find the main control subjects in automatic control to reduce the influence of associated control [3]. Through correlation analysis, it can be concluded that the main control target and control sequence is the mud layer height, followed by the solid volume (the volume of underflow of thickener), and then the dosage of flocculant and the height of cleared layer. (3) Implementation of control The DCS system in RMSW process can realize the basic control function of the production equipment, and the relevant production data and production instructions are acquired and sent by DCS. The DCS system has the real control right of the equipment. The control center of the refinery has the highest level of trust in DCS, and any control independent of DCS will be strictly reviewed. Therefore, the intelligent control system should be transferred through DCS system but unable to

directly control relevant equipment. Figure 2 shows the way of the signal transferred. Intelligent control systems obtain data from DCS through OPC communication, and the control command will feedback to DCS system through OPC communication. When the DCS terminal is given remote control (LR setting) signal and automatic control (MA setting) signal, the corresponding equipment can accept the command of intelligent control system. Meanwhile, the operator of DCS main control is able to set the corresponding parameters of the intelligent control system at any time or set the control right of the intelligent control system to any equipment according to the demand.

Practical Operation Results and Discussion This intelligent control system has been applied in an alumina refinery in Shanxi Province, China. The plant has three production lines with a total capacity of about 3500 kt/a. The third production line was authorized for the test. This production line was completed in 2018 with a capacity of about

Information feedback

Information feedback

Equipment

Control command

DCS

Authorization

Intelligent control

Control command

Fig. 2 Transmission process of monitoring information and control instructions. (Color figure online)

6

1200 kt/a. There are seven thickeners, including two settlers, one public standby, and four washers, all of which are U 26 m deep cone thickeners. In this series of RMSW, each thickener is equipped with a non-contacted interface instrument. Except that there is no overflow pump in the settler and the pregnant liquor is flowed to the liquor thickener by gravity which in the filtration, the other thickeners are equipped with VSD overflow pumps, VSD underflow pumps, and VSD flocculant pumps. The pipeline of flocculant pumps and underflow pumps are equipped with flowmeter, but there is no flowmeter on overflow pipelines because of the pipe scarring. Therefore, in practical test, the control of overflow pump is temporarily neglected, and only flocculant pump and underflow pump are controlled. The refinery’s industrial network, DCS system, cloud server hardware, and software are complete and preferable, very suitable for the implementation of intelligent control system applications. The intelligent control system program is deployed on the cloud server of the refinery, and the OPC server for communication is set on the server with firewall to ensure the security of the network. The intelligent control system uses web to publish program interface with B/S structure. The server of intelligent control system has corresponding authority control. Only authorized personnel can set program parameters. Figure 3 shows the interface of the intelligent control system on web client. The intelligent control system provides basic monitoring functions such as equipment running status monitoring, historical data query, laboratory data query, etc., and the corresponding control functions are only open to internal testers. Totally three control objectives were set during the test.

J. L. Tian et al.

1. To realize the stable operation of RMSW system and reduce manual participation (Global goal); 2. To decrease the flocculant consumption (stage 1); 3. To minimized the soda concentration of the discharged red mud slurry (stage 2). The intelligent control system program was deployed in June 2019 and lasted about six months. During the test, the relevant functional adjustment of the control program was carried out continuously to meet the control requirements of the refinery. Moreover, we had even experienced the plant digestion process shut down for maintenance, settler cleaning and repair, standby thickener change and other equipment maintenance, no matter whatever problems we had encountered, the intelligent control program still can accurately detect the thickener functional conversion from the beginning to end. In the first stage of the test, the functional dossing control of the flocculant part started from August 11, 2019 to September 21, 2019, and the total test duration was about 40 days. During the operation of the control program, all functional modules were functioning properly. Due to the online test method, the intelligent control would be switched to manual control if some indexes had deviation during the test, and switch back to the intelligent control when the indexes were normal. During the online test, the amount of flocculant added in the 4# to 7# thickeners (first–fourth washers) was mainly investigated. Since the flocculant dosage of the settler directly affects the index of pregnant liquor solid content, the automatic control of flocculant addition in the settler was not authorized, so the intelligent dosing control was not used for the settler temporarily.

Fig. 3 Web client interface of intelligent control system. (Color figure online)

The Application of Intelligent Control to Red Mud …

7

Through the historical data query of the flocculant pump flow in the DCS system of the refinery, the monthly dosing amount of each flocculant pump could be obtained. 1#*5# flocculant pump corresponds to 7# (4th washer) to 4# (first washer). The flocculant consumption from May 2019 to September 2019 is shown in Table 1 below. The data from Jul-19 to Sep-19 is used for a comparative analysis, and the data from May-19 to Jun-19 is used to show the normal consumption of the flocculant. Till 12:00 on September 21, the same period comparison method was adopted, that was, the daily average dosage of flocculant in July and August was converted to 21.5 days, and comparison of flocculant consumption showed in Fig. 4. By comparison, flocculant consumption declined in September from July and August compared to September. The addition amount of flocculant in 6# thickener (corresponding to 2# flocculant pump) was increased due to the high level of solid content in the cleared layer, which caused the dosage charged into the 6# tank in September was basically the same as that in August. The consumption of flocculant is also related to the amount of dry red mud. During the test, the volume of diluted slurry feed and the unit consumption of flocculant during the test are as shown in Fig. 5. The average solid content of diluted slurry is about 113 g/L steady, total diluted slurry volume goes high up to 2050 m3/h, but the unit consumption of flocculant goes down clearly. Through calculation, the unit consumption of flocculant could be reduced to about 118 g/t-mud. The experiment shows that the intelligent control system can stably control the practical operation of the RMSW system, and can save the consumption of flocculant effectively. Through the practical operation test of about 40 days, the dosage of flocculant can be reduced by more than 15%, and the unit consumption of flocculant can be minimized less than 120 g/t-mud. In stage 2, the automatic control test of underflow pump was started. The target of the test is to reduce the loss of soda in discharge red mud by automatically controlling the operation of underflow pumps in each thickener. The test lasted for 20 days from January 5, 2020 to January 25, 2020. Due to the large volume of the RMSW system, the system reaction is slow, and affected by many factors such as

Table 1 Statistics of flocculant consumption

volume of feed and washing water, the monthly average value is used to detect the operation results. During the test, all the instrument data were sourced from the DCS system, and all the test chemical data were sourced from the MES system. In order to effectively compare the volatility of the data, the data used for comparison started from November 1, 2019 and ends in April 2020. Since the RMSW system presented different fluctuation in the feeding state of each month, the theoretical calculation of the RMSW system is carried out using the monthly average data of each input amount, the theoretical value of the soda concentration of red mud in the outer discharge is calculated, and then the comparative analysis is carried out. Figures 6 and 7 show the diluted slurry and washing water average flow monthly, and the average chemical analysis value monthly of discharged soda also add to this comparative analysis. Through the difference analysis, it is apparently that in the test month January 2020, the diluted slurry feed volume was the largest value, the washing water volume was at the average value, the soda concentration of the discharged red mud was very low, the actual soda loss was closer to the theoretical soda loss, and the difference was only 0.81 g/L, which indicates that the soda saving effect under the automatic control in the test month was good, that was, the automatic control is effective. In April 2020, the amount of washing water increased to 18% of the average value of the previous months, which minimized the concentration of discharged soda at most. The automatic control of the RMSW process will continue to be used around April 25, 2020, and the soda loss of the discharged red mud be stable at 2*2.2 g/L. By the middle of May, the digestion system was shut down, and the water source of the sedimentation series would be interrupted. After that, the water source of the sedimentation series would be temporarily modified to come from other RMSW series. And then, the production capacity of the whole plant was adjusted and the third RMSW series was shut down and the test was temporarily suspended. According to the statistics of previous months, the loss of soda is generally between 3.2 and 3.7 g(Na2Ot)/L. If the average soda loss is considered as 3.45 g(Na2Ot)/L, in the usual feed state, the soda loss can be automatically

Pump no

May-19

Jun-19

Jul-19

Aug-19

Sep-19

Memo

1#

1957.47

1792.15

1970.68

1880.99

1081.26

7# Washer

2#

2378.89

2020

2467.36

2067.45

1437.52

6# Washer

3#

2085.14

1637.7

1883.82

1768.57

981.86

5# Washer

4#

1102.73

845.74

1092.2

992.94

607.15

4# Washer

5#

1125.63

849.76

1090.55

993.3

607.46

8 Fig. 4 Comparison chart of flocculant consumption of washer. (Color figure online)

J. L. Tian et al. 2000

1768.27

1800

1564.3

1600

1400

1#

1437.52

1433.88

1412.32

1377.55

1350.07

2#

1304.56

3# 1226.59

1214.61

4#&5#

1200 1081.26 981.86

1000

800 2019-07

Unit consumpƟon

2019-09

Average solid content

Average feed in

170

2100

2050 156.87

2050 150.96

2000

g/t-M ud、g/L

150

1950

1920

140

1900 130

1822

1800

117.65 g/L

110 100

Fig. 6 Monthly data chart. (Color figure online)

1850

118

120

112.93 g/L

113.33 g/L

2020-08

2020-09

2020-07

Discharged soda

Diluteted slurry

1750 1700

Water

4

2600 3.6

3.51

Discharged soda(g/L)

2400

2337

3.5

3.11

2244 3

2200

3.12 2027

2000

1928

2.94

2.5

1932 1793

1800 2.36

2

1600 1400 1200

1.5

m 3/h

160

927

977

947

954

2019-11

2019-12

2020-01

2020-02

1116 902

1000

1

800 2020-03

2020-04

Q(m3/h)

Fig. 5 Flocculant unit consumption trend chart. (Color figure online)

2019-08

The Application of Intelligent Control to Red Mud … Fig. 7 Comparison of theoretical value and actual value of discharged soda concentration. (Color figure online)

9 Actual value

Theoretical value

Difference

5 4.5 1.91

4

Na2Ot(g/L)

3.5

3.51

1.6

3.12

2.94

3.6 1.59

3

3.11 2.5

1.36

2 1.5

2.36

2.13 0.92

1.92 1.69

0.81

1.51

1

1.76 1.44

0.5 0 2019-11

2019-12

controlled to lower than 2.9 g(Na2Ot)/L, and the minimum is 2.2 g/L. It is expected that the discharged soda concentration can be reduced by about 16*36%.

Conclusion The intelligent control system has contributed to the goal of saving flocculant dosage and minimizing the loss of discharged soda in the test. Meanwhile, it greatly saves the manual operation and obtains very favorable test results. By applying the intelligent control system, the consumption of flocculant of RMSW process can be reduced by 15%. It is expected to save about ¥120,000 throughout the year; the soda concentration of discharged red mud slurry will be reduced by 16*36%. According to the conservative calculation based on 16% soda saving, the dry red mud displacement is 1560 kt/a, and the moisture content of filter

2020-01

2020-02

2020-03

2020-04

cake after red mud pressure filtration is 32%. 0.259 kg of Na2O shall be predictively saved per ton of dry red mud, and 520 tons of caustic (100%—NaOH) can be saved in the whole year. At the price of ¥3000 per ton of NaOH (solid), It is expected to save about ¥1.56 million throughout the year. The total cost saved is about ¥1.68 million yuan.

References 1. Robert K. Jonas, “Application and Benefits Of Advanced Control To Alumina Refining”, Light Metals 2004 (TMS, 2004) 2. Liao Xinqin, Yang Qi, Feng zhengmin, “On-line detection and intelligent optimal control of red mud settlement system”, Light Metal (China), 2019–04 3. Ayana Oliveira, Jefferson Batista, Jedson Santos, Márcia Ribero, Jorge Charr, Rafael Lopes3, “Advanced Process Control in Alumina Digestion Unit”, Light Metals 2009 (TMS, 2009)

Alumina Refinery Volume Control Thiago T. Franco

Abstract

Plant volume control is a challenge for all alumina refineries because it involves complex mass and energy balances with numerous variables and conflicting goals. For instance, maximizing tank levels means increased production, but tank overflows mean safety risks and unnecessary cleaning expenses; increased water in red mud filtration means better caustic recovery, but higher costs in water evaporation. Bayer process refineries have a large number of equipment and tanks in which caustic liquor flows and many parameters vary dynamically. Therefore, it is necessary to have well-established control limits, plant volume parameters, and targets to allow daily routines of caustic cleaning and maintenance. This paper presents the development in CBA’s alumina refinery, regarding the tools to support teams to make important decisions in volume control and management system created to support weekly and annual planning. Keywords








Water balance Modeling Process simulation volume control Water balance management




Plant

Introduction The volume control of a hydrometallurgical process is a required routine operational activity done in industries that use large quantities (sometimes in excess of millions of liters) of liquids (typically acidic or caustic) for the chemical solubilization of ores. Raising levels in the tanks often means increasing the production, and that is what normally all company owners look for. On the other hand, working T. T. Franco (&) Companhia Brasileira de Alumínio, Alumínio, Brazil e-mail: [email protected]

with high tank inventories bears the risk of overflows or spillages, which is a hazard to employees, besides incurring expenses associated with the cleanup of the factory area and introduction of material volume in the process. This is just one of the examples of conflicting targets with the volume control, in which activity management must be analyzed and balanced to meet the targets of performance indicators that have an interface between each other and to avoid safety matters to assets and people. Level and inventory management is so important that many factories dedicate process engineers to that specific process control application, or even a whole team to this coordination.

Main Activities A good volume control comprises, at least the following: 1. Daily water balance: mass and energy balance of materials in the liquid phase. In order to have an accurate volume control, it is necessary to have well-defined control limits and also know their material inlets and outlets, enabling the creation of mass and energy balances that indicate the tendency of liquor levels in tanks within the productive process. 2. Daily solids balance: mass balance of materials in the solid phase, with a focal point on the variation of inventory in large volume tanks such as precipitators, settlers, and washers; 3. Volume transfers between tanks in and out of operation. This is used to avoid overflows, to generate new chemical cleanup solution for the tanks out of operation or to fill empty volume available with spent liquor or used caustic solution in the tanks in operation; 4. Inspections to find unwanted volume flow entries or exits: they are the flows unaccounted by flowmeters (e.g., measurement inaccuracies or leaks);

© The Minerals, Metals & Materials Society 2021 L. Perander (ed.), Light Metals 2021, The Minerals, Metals & Materials Series, https://doi.org/10.1007/978-3-030-65396-5_2

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Alumina Refinery Volume Control

5. Management of insertion and isolation of tanks in the process: it requires short-term and long-term organization and planning.

Main Goals For a good management of these activities, the main goals must be taken into account, as follows: 1. Manage the level of tanks in operation so that there isn’t an exaggerated accumulation or depletion of inventory; A. Overflowing tanks generate unwanted costs with cleaning and volume evaporation and hazards to the company’s employees; B. Empty tanks do not produce, therefore they do not generate profit. 2. Enable chemical cleanup in tanks out of process within the planned schedule. 3. Enable routine operation and maintenance; 4. Enable non-routine maintenance; 5. Maintain washing water flow in red mud and in hydrate to minimize caustic losses. 6. Find the adequate wash water flow in decanters to obtain maximum circuit efficiency but also minimize alumina losses by precipitation; 7. Maintain maximum temperature in security filtration to obtain high filtration velocities; 8. Minimize steam consumption in forced evaporation unit; 9. Maintain a constant caustic concentration, aiming at the stability of the whole process; 10. Adapt to special conditions. For instance, fine seed storage, bauxite quality variations.

11

To support the new structure, numerous tools were created to help to make decisions, the most important tools are covered in the next section.

Tools 1. Volume Balance Volume balance comprises mass and energy balances of all processes from ore introduction to the product itself, taking into consideration all entry and exit material flows. The result is the indication of the trend in material levels in tanks, which can be of accumulation, stability, or volume reduction. This is illustrated in the example shown in Figs. 1 and 2. 2. Volume Inventory CBA’s alumina refinery is comprised of more than 150 tanks, which can be in operation, out of operation, and under maintenance. This information is managed through the control panel (see Fig. 3) for better reliability and historization of information. Besides that, the types of material that out-of-operation tanks are storing (spent liquor, caustic cleanup, hydrate seed, encrustation) are constantly updated. From historized information, performance indicators are obtained, such as the total volume of material occupied in tanks and empty volume available in tanks in relation to the safety limit. They are important indicators for volume transfer between tanks in and out of operation. Figure 4 shows an example of such volume control indicators used for the inventory management. 3. Process Simulation

CBA Volume Control Management In view of the goals and activities needed for a good volume control management, Companhia Brasileira de Alumínio started, in July 2019, to develop a program with people, management tools, and technical tools to improve and optimize the process. In the past, there were many decentralized activities with little or no connection between each other. Within the new program these were organized into a structure with connected activities, with formal responsibilities, and with a process engineer responsible for managing the structure and activities.

A simulation model was developed through the SysCAD software, covering all areas of the refinery and equipment with mathematical models calibrated with as much information available as possible for inlet and outlet flows, such as process variables measured through instruments and chemical analyzes. A screenshot of the SysCAD model can be found in Fig. 5. Once validated with process data from the period under analysis, it is possible to execute the simulation and obtain the liquor’s caustic profile in the different areas of the refinery and find unaccounted volume flow entries or identify possible deviations in measuring instruments.

12

T. T. Franco 28/06/2020

BALANÇO DE VOLUME

FALSO

28/06/2020 1 Balanço última hora

(Entradas - Saídas)

↑ ACUMULANDO VOLUME

2000

Volume (m³/dia)

1000

485

0

-333

META -1000

Mês Mês anterior atual

-2000

↓ SECANDO VOLUME -3000

ENTRADAS Realizado 28/06/2020 m³/h Chuveiros KM (NetWash) 15.2

Alvo m³/h 18.0

FADs

28/06/2020

SAÍDAS Realizado m³/h 85.9

Alvo m³/h 82.0

Reposição no Último Lavador

0.0

0.0

EVAP

67.4

32.0

Lavagem Areia

3.2

5.0

HIDs

36.4

40.1

20.6

26.9

Lama (Umidade)

12.3

19.2

0.0

3.4

By-Pass / Vasca

1.3

0.9

18.5

19.9

Decantadores (Evaporação)

3.4

5.0

Soda Virgem

0.0

0.0

Precipitação (Evaporação)

1.1

2.0

Floculante

1.5

4.0

Umidade da Areia

1.0

1.5

Cal

11.8

24.8

Umidade da Hidrato

5.0

7.0

Gaxetas Área Branca

24.6

26.1

Descarte 3GH/ Filtrado H2

0.0

0.0

Gaxetas Área Vermelha

213.9

189.6

Lavagem de Hidrato H2 Colunas (Moagem) Umidade da Bauxita

35.5

37.5

Piso Área Branca

2.9

2.0

Piso Área Vermelha

7.9

7.0

Filt. de Segurança (Corr. de TC)

0.0

0.0

LQ Filtração

0.6

3.0

Chuva Lavagem Vasca H1 Lavagem Vasca H4

0.0 7.4 2.7

0.0 7.0 2.0

FLUXO DA PLANTA

20.0

15.0

Net

172.6

201.5

Hidrajato Estimado TOTAL

TOTAL

ENTRADAS - SAÍDAS

Fig. 1 Process entries and exits and volume balance trends. (Color figure online)

28/06/2020

823.5 Realizado m³/h

m 3 /h Alvo m³/h

-41.3

-20.8

SECANDO VOLUME

Alumina Refinery Volume Control

13

ENTRADAS DE VOLUME DO PROCESSO

ACUMULADO DO MÊS

270.0

Vazão Volumétrica (m³/h)

260.0

-5.0

2.4 -1.3 -7.6

2.1 -2.3

13.5 -2.5

4.3 -1.8 -12.9

-0.2 -7.9 14.3

250.0

4.8 -7.0

2.8

-4.0

2.9

240.0 230.0 220.0 250.9

245.6

210.0

200.0 190.0 180.0

Fluxo Médio: 1007

SAÍDAS DE VOLUME DO PROCESSO

m³/h

ACUMULADO DO MÊS

290.0

Vazão Volumétrica (m³/h)

280.0

15.7

270.0

260.0

-2.1

250.0

8.0

-7.8

6.5

-1.2

-0.6

0.0

-1.5

-0.5 240.0 230.0 220.0

254.1 237.7

210.0 200.0

Fluxo Médio:

1007

m³/h

Fig. 2 Graphic monitoring of accumulated volume in the current month for process entries and exits. (Color figure online)

Fig. 3 Historization system of tank status, stored material and chemical analysis. (Color figure online)

14

T. T. Franco

Fig. 4 Volume control indicators. (Color figure online)

Fig. 5 Simulation set on SysCAD to evaluate the liquor’s caustic profile. (Color figure online)

4. PI Process Book Through the PI Process Book, a monitoring screen for the main volume control variables and an overview of tanks with level indicators and their respective safety limits was developed. This aims to make information available to all teams, helping them make their decisions. The main interface of this tool is shown in Fig. 6.

performance indicator Empty Value must always be above the safety limit. The flowcharts that were developed guides the teams on the need to store liquor or reprocess stored liquor, module volumetric flow in the evaporation unit, discharge liquor in the dam, among other activities. An example of a help chain flowchart can be seen in Fig. 7. 6. Planning and Scheduling

5. Help Chain Flowchart Help chain flowcharts for volume control is another support tool to aid decision making. It assumes that the

Management tools to plan maintenance and operation were also developed to help organizing the teams responsible for these activities.

Alumina Refinery Volume Control

15

Fig. 6 Volume monitoring screen on PI Process Book. (Color figure online)

a. Annual

c. Weekly

An annual timeline of insertion and isolation of crystallization/precipitation tanks in the process was created. Previously, preventive maintenances and chemical cleanups were done by opportunity. Currently, activities are done respecting the order of prioritization and availability of chemical cleanup heat exchangers, also taking into consideration planned maintenances for other areas of the plant and availability of resources. Through this annual planning, it is possible to observe volume forecasting of crystallization/ precipitation tanks along the year and empty volume forecasting.

Weekly, the multidisciplinary team of volume control gathers to schedule activities of the following week and tackle deviations from the previous scheduling, having as a premise monthly and annual planning. Resources will be analyzed and distributed according to their respective availability.

Conclusions The improvement in volume control management at CBA’s alumina refinery brought numerous benefits. The main benefits can be listed as follows:

b. Monthly Every month, a timetable is developed with a monthly planning of chemical cleanup of heat exchangers, taking into consideration delays from the previous month and tanks mapped in the current planning. All deviations and delays are registered and covered in this management.

1. Better integration and coordination of activities among the different teams; 2. Creation of new tools to increase agility when making decisions and planning and scheduling routine activities; 3. Support to control process parameters such as Netwash in mud filters and hydrate filters;

16

Fig. 7 Help chain flowchart for volume control. (Color figure online)

T. T. Franco

Alumina Refinery Volume Control

17

4. Reduction of tank overflows and spillage events; 5. Reduction in waste liquor discharge to the tailings dam by account of volume accumulation in the process tanks.

and a further gain of 400 kUSD to the reduction of consumption of live steam in the evaporation unit.

In 2019, the financial damage associated with liquor discharged was of 2.67 million USD. With the aid of the tools and systems presented in this paper an estimated gain of 200 kUSD could be attributed to the reduction of waste liquor discharged, a gain of 300 kUSD could be attributed to the reduction of specific caustic consumption in the process,

Reference 1. Martin, L. and Howard, S., “Alumina Refinery Wastewater Management: When Zero Discharge Just Isn’t Feasible” Light Metals (2011)

The Study of TCA Applied in Organic Removal from Sodium Aluminate Solution Er-wei Song, Dong-zhan Han, Li-juan Qi, and Feng-jiang Zhou

Abstract

In the process of alumina production using Bayer process technology, organic impurities (like oxalate) can enrich along the production process, which may bring in some serious problems. For example, the mother liquor will thicken, the viscosity will increase, and the sedimentation performance of the red mud will decrease, if the organic impurity content is high. Calcium aluminate hydrate, as one process intermediate product, has small particle size, and a large specific surface area, which has obvious adsorption potential. It has practical significance to study the adsorption and removal of organic in sodium aluminate solution by Tricalcium aluminate hexahydrate (TCA). Based on the above statement, the efficiency of TCA on the oxalate removal was investigated. Besides the influence of different prepared condition for TCA was also investigated using orthogonal experiment method. Keywords

Tricalcium aluminate hexahydrate Orthogonal experiment




Organic removal




Introduction Organic components, as one of the most harmful impurities in the Bayer process, have been widely investigated in the past decades, including their behavior, negative effects, and removal mothods [1]. Among observed organic components in the Bayer process, oxalate was considered to be the most harmful impurities, which will bring series of negative effects like soda consumption, alumina product purity, E. Song (&)
D. Han
L. Qi
F. Zhou Zhengzhou Non-ferrous Metals Research Institute Co. Ltd. of CHALCO, Zhengzhou, 450041, Henan, China e-mail: [email protected]

operation process including settlement performance of red mud, and the efficiency of transfer, of which includes stream traffic and heat transfer [2–4]. Given the negative effects of oxalate on the Bayer process, series of researches have been conducted to eliminate organic in the sodium alumina solution. Mahmoudian et al. [5] proposed using thermal and chemical techniques to eliminate oxalate in the bayer process, they pointed bauxite heating leads to the organic compounds and carbonates in magnesite and calcite minerals exit as CO2. Chen et al. [6] reviewed the source and hazards of organics and various main methods to remove organics in Bayer liquor are summarized, the principle and the removal efficiency are introduced in detail to remove organics with bauxite roasting method, mother liquor roasting method, ion exchange method, crystallization, precipitation, and wet oxidation. Tricalcium aluminate hexahydrate (TCA), coming from the reaction between sodium aluminate and lime within alumina production process, has potential capacity for adsorbing organic matter to eliminate their negative influences in sodium aluminate solution. Typically, TCA is prepared by the reaction of lime or slaked lime with sodium aluminate solution, in which spent liquor or polished liquor are usually used as reaction solution. Major reaction equations are as follows [7]: 3CaO þ 2NaAlO2 þ 7H2 O ! 3CaO
Al2 O3
6H2 O þ 2NaOH 3CaðOHÞ2 þ 2NaAlO2 þ 4H2 O ! 3CaO
Al2 O3
6H2 O þ 2NaOH

ð1Þ ð2Þ

Organic removal efficiency in sodium aluminate solution using Tricalcium aluminate hexahydrate was investigated, and the effects of different prepared method of TCA on organic removal efficiency were also explored in this research, which can bring us useful instruction for organic removal during alumina production process.

© The Minerals, Metals & Materials Society 2021 L. Perander (ed.), Light Metals 2021, The Minerals, Metals & Materials Series, https://doi.org/10.1007/978-3-030-65396-5_3

18

The Study of TCA Applied in Organic Removal …

19

Material and Method

TCA Prepared with Liquor After Precipitation

Material

Single Impact Analysis As expressed above, TCA-1 was prepared with liquor after precipitation. Then reaction temperature, duration time, and TCA dosage were analyzed to investigate their effects on oxalate removal efficiency, respectively. Detailed information is shown in Fig. 1. From Fig. 1, it can be seen that reaction temperature, duration time, and TCA dosage all have effects on oxalate removal efficiency (gC2 O4 2 ). With these process parameters increasing, gC2 O4 2 shows an increasing trend which decreases gradually at the higher end of the parameters within the test range.

Plant lime (available CaO 89.26%), sodium oxalate (AR), spent liquor after precipitation (SLP), cycling liquor (CLP), polished liquor (PL), the total caustic (NT), and caustic soda concentration (NK) are expressed in gpl Na2O, AO is expressed as gpl Al2O3 in the liquor, ak means the mole ratio of caustic soda to Al2O3 in the liquor. C2O42− content in polished liquor is 1.52 g/L, the liquor analysis is displayed in Table 1.

Method Based on the change of C2O42− in sodium aluminate solution before and after organic removal experiments, C2O42− removal yield during purification process was calculated, detailed information as below: gC2 O4 2 ¼

CC2 O4 2 a  CC2 O4 2 b  100% CC2 O4 2 b

ð3Þ

where: C2O42——C2O42− content in liquor after the purification test, mg/L; C2O42——C2O42− content in liquor before the purification test, mg/L. C2O42− content in liquor was analyzed using ICP, in red mud was analyzed using XRF-1800.

Experiment Tricalcium aluminate hexahydrate was prepared according to reaction function 1 using spent liquor after precipitation and cycling liquor, respectively. Given oxalate is the major occurring form of organic in sodium alumina solution, oxalate removal was conducted rather than total organic in this research. TCA prepared above was used to eliminate oxalate in the liquor, analyzing the effects of reaction condition on the oxalate removal efficiency, besides orthogonal experiment was designed to investigate the interactions among process condition parameters, like reaction temperature, duration time, and dosage. Table 1 Composition of various liquor used

liquor type

NT

SLP

194.19

CLP PL

Orthogonal Experiment Analysis In order to investigate potential interactions existing among these reaction process conditions, orthogonal experiment was designed and analyzed, where reaction temperature, duration time, and TCA dosage were selected as variables. According to the design principle of orthogonal experiment, L9(34) orthogonal table [8] was adopted, and each factor identifies three levels (Table 2). Tests were conducted according to above designed experiment, during the analysis process, gC2 O4 2 was selected as objective function, results are shown in Table 3. Ki means the sum of the number in column M and the index value corresponding to “i,” ki means mean value corresponding to Ki, Ri means the range corresponding to ki. According to the range comparison based on gC2 O4 2 in Table 2, the results demonstrate that RA > RC > RB, thus the order of each factor from primary to secondary is A(temperature, °C)、C(TCA dosage, g/L)、B(reaction time, h). And the best oxalate removal reaction conditions are reaction temperature of 60 °C, duration time of 3 h, and TCA dosage of 40 g/L among the experiment selected condition range.

Prepared with Cycling Liquor Single Impact Analysis Experiments were conducted as 2.1.1, TCA-2 was prepared with cycling liquor. Then reaction temperature, duration time, and TCA dosage were analyzed to investigate their

AO

NK

ak

91.37

162

2.92

271.46

130.18

228

2.88

180.80

179.05

153.85

1.42

20

E. Song et al.

Fig. 1 Effects of conditions on the oxalate removal efficiency

45

46 44

40

ηc2o4

ηc2o4

42

35

ηc2o4 (%)

ηc2o4 (%)

40 38 36

30 25

34

20

32

15

30

10

28 30

35

40

45

50

55

50

60

55

60

65

70

75

80

T (℃)

TCA dosage 45 40

ηc2o4 ηc2o4 (%)

35 30 25 20 15 10 5 50

100

t (min)

Table 2 Design of orthogonal table L9(34) (liquor after precipitation)

No

Tem (°C)

Time (h)

TCA dosage (g/L)

1

60

1

20

2

70

2

30

3

80

3

40

4

60

1

30

5

70

2

40

6

80

3

20

7

60

1

40

8

70

2

20

9

80

3

30

effects on oxalate removal efficiency, respectively. Detailed information is shown in Fig. 2. From Fig. 2, it can be seen that reaction temperature, duration time, and dosage, all have effects on oxalate removal efficiency (gC2O42 ). With these process parameters increasing, gC2O42 shows an increasing trend which decreases gradually at the higher end of the parameters within the test range.

Orthogonal Experiment Analysis In order to investigate interaction existing among these reaction process conditions, orthogonal experiment was designed and analyzed, where reaction temperature, duration time, and TCA dosage were selected as variables. According

to the design principle of orthogonal experiment, L9(34) orthogonal table was adopted, and each factor identifies three levels (Table 4). Tests were conducted according to above designed experiment, during the analysis process, gC2O42 was selected as objective function, results are shown in Table 5. According to the range comparison based on gC2 O4 2 in Table 5, the results demonstrate that RA > RC > RB, thus the order of each factors from primary to secondary is A(temperature, °C)、C(TCA dosage, g/L)、B(reaction time, h). And the best oxalate removal reaction conditions are reaction temperature of 60 °C, duration time of 3 h, and TCA dosage of 40 g/L among the experiment selected condition range.

The Study of TCA Applied in Organic Removal …

gC2 O4 2

Exp. No

A

B

C

1

1

1

1

7.78

2

1

2

2

26.86

3

1

3

3

39.23

4

2

1

2

23.88

5

2

2

3

34.12

6

2

3

1

11.43

7

3

1

3

14.3

8

3

2

1

10.38

9

3

3

2

33.2

Kj1

17.46

16.19

12.88426

Kj2

9.47

16.74

20.32

Kj3

4.79

20.34

21.40

kj1

5.82

5.40

4.29

kj2

3.16

5.58

6.77

kj3

1.60

6.78

7.13

Rj

4.22

1.38

2.84

Factor order: Degrade trend

ACB

Optimal scheme

A1B3C3

Fig. 2 Effects of reaction parameters on the oxalate removal efficiency

44 42

ηc2o4

ηc2o4

40 30

ηc2o4 (%)

ηc2o4 (%)

38 36 34

20

32 30 28 30

35

40

45

50

55

10

60

50

55

60

TCA dosage

65

T (℃)

30

ηc2o4

ηc2o4 (%)

Table 3 Experimental scheme and analysis results based on gC2 O4 2

21

20

10

30

60

90

t (min)

120

70

75

80

22 Table 4 Design of orthogonal table L9(34) (cycling liquor)

Table 5 Experimental scheme and analysis results based on gC2 O4 2

E. Song et al. No

Tem (°C)

Time (h)

Dosage (g/L)

1

60

1

20

2

70

2

30

3

80

3

40

4

60

1

30

5

70

2

40

6

80

3

20

7

60

1

40

8

70

2

20

9

80

3

30

Exp. No

A

B

C

gC2 O4 2

1

1

1

1

6.58

2

1

2

2

23.4

3

1

3

3

38.1

4

2

1

2

20.03

5

2

2

3

29.7

6

2

3

1

6.9

7

3

1

3

8.1

8

3

2

1

9.2

9

3

3

2

30.4

Kj1

16.80

13.53

10.98

Kj2

7.27

15.15

18.89

Kj3

3.84

18.44

19.04

kj1

5.60

4.51

3.66

kj2

2.42

5.05

6.30

kj3

1.28

6.15

6.35

Rj

4.32

1.64

2.68

Factor order: Degrade trend

ACB

Optimal scheme

A1B3C3

Conclusion In the process of alumina production using Bayer process technology, organic impurities can enrich along the production process, which may bring in some serious problems, like refining the granulometry of precipitated gibbsite, deteriorating the settling performance of bauxite residue as well as the scaling on the heating pipes. Tricalcium aluminate hexahydrate, with special structure and physical property, has potential capacity to adsorb oxalate in sodium aluminate solution. Thus, it is necessary to study the effects of TCA on the organic(oxalate) removal efficiency. Single and orthogonal experiment was designed and conducted to analyze the effects of process conditions and

prepared process on oxalate removal efficiency were conducted in this research, the results demonstrate that RA > RC > RB, thus the order of each factor from primary to secondary is A (temperature, °C)、C (TCA dosage, g/L)、B(reaction time, h). And the best oxalate removal reaction conditions are reaction temperature of 60 °C, duration time of 3 h, and TCA dosage of 40 g/L among the experiment selected condition range using liquor after precipitation, while the order of each factor from primary to secondary is A(temperature, °C)、C (TCA dosage, g/L)、B(reaction time, h). And the best oxalate removal reaction conditions are reaction temperature of 60 °C, duration time of 3 h, and TCA dosage of 40 g/L among the experiment selected condition range using cycling liquor. TCA has the potential application to eliminate oxalate in the Bayer solution, besides

The Study of TCA Applied in Organic Removal …

this research can bring us to optimize the best condition of prepared TCA organic matters removal during the Bayer process.

References 1. Gan-feng, Y. H.-y. Z. B.-y. P. X.-l. T. Effect of oxalate on seed precipitation of gibbsite from sodium aluminate solution[J]. J. Cent. South Univ 2020, 27, 772-779. 2. Chen GH, Li LS. Influence of organic on Bayer process of alumina industry and counter measure. Light metals, 2012, 08, 15–18 (Chinese)

23 3. Chen WM, Leng XK. A study on build up of organic substances in Bayer liquor. Light metals, 2011, 09, 11–15 (Chinese) 4. Zhang Ni. The behavior of organics in Bayer process. Master thesis, Central South University, 2008 5. Mahmoudian, M.; Ghaemi, A.; Shahhosseini, S., Removal of carbonate and oxalate pollutants in the Bayer process using thermal and chemical techniques[J]. Hydrometallurgy 2015, 154, 137-148. 6. Chen XQ, Chen JZ, Xiong DL, et al. Research progress 0f removing organic in Bayer process of aluminum production[J], Light metals, 2014, 09, 23-28. 7. Jr, L. J. A.; Pollet, G. J., The Manufacture of Tricalcium Aluminate [J]. Essential Readings in Light Metals 2003, 1, 11-17. 8. Phillip J Ross. Taguchi techniques for quality engineering: loss function, orthogonal experiments, parameter and tolerance design. McGraw-Hill, 1988

Flotation Desulfurization of Acidified High-Sulfur Bauxite: Effects of Regulators Huaxia Li, Wencui Chai, and Yijun Cao

Abstract

Introduction

The desulfurization of high-sulfur bauxite via flotation is more difficult than conventional sulphide, since the finely disseminated sulphide in the high-sulfur bauxite can lead to excessive particle entrainment, increase of froth, and low separation efficiency. Acidification of high-sulfur bauxite resulting in changes in mineral surface properties is one of the main reasons for this. Regulators could be used to adjust the mineral surface properties and pulp properties to improve flotation efficiency. The effects of several regulators on the flotation desulfurization were systematically investigated in this work. The results indicate that the regulators have great impacts on the desulfurization efficiency. Sodium silicate could significantly reduce the sulphur content of concentrate from 0.90 to 0.29% and increase the concentrate recovery by more than 10%. Zeta potential results prove that sodium silicate can eliminate the effect of acidification on flotation desulfurization. Keywords

High-sulfur bauxite Regulator




Desulfurization




Flotation




H. Li
Y. Cao (&) School of Chemical Engineering, Zhengzhou University, 450001 Zhengzhou, People’s Republic of China e-mail: [email protected] W. Chai (&) Henan Province Industrial Technology Research Institute of Resources and Materials, Zhengzhou University, 450001 Zhengzhou, People’s Republic of China e-mail: [email protected]

High-sulfur bauxite resources exceed 800 million tonnes in China [1]. Sulfur contained in this kind of bauxite severely disrupts alumina production [2], the high-sulfur bauxite has not yet been exploited and utilized on a large scale. The research on processing high-sulfur bauxites to date has mainly focused on the roasting method [3–5] and wet oxidation. The oxidizing agents used in the wet oxidation process are various, including gases such as air [6], oxygen [7], and ozone [8], and solid oxidizing agents such as chlorinated lime, sodium nitrate, etc. Precipitation agents such as lime [9] and barium salts [10] have also been studied. The above desulfurization methods can reduce the harmful effects of sulfur in Bayer process, but they are limited to bauxite with low sulphur content. Not only that, these technologies have disadvantages, such as costly desulfurization reagent, complicated operation, harsh or dangerous reaction conditions, and requirement of SO2 processing units for calcination [11]. So, there are presently no instances of large-scale industrial application of these processing options. Flotation desulfurization [12] can remove the sulphur from the bauxite before entering the Bayer process (alumina refining process), and has been proven to be an efficienct, flexible, economic method [13, 14]. As the main sulfur mineral in high-sulfur bauxite, pyrite can be flotated using a xanthate collector under normal conditions [15]. However, the collection of single xanthate is very poor for high-sulfur bauxite, especially for acidified high sulphur bauxite. Regulators [16] can change the interaction between collecting agents and ores as well as the floatation properties of pulp, and enhance the selectivity of minerals [17]. In this study, acidified high-sulfur bauxite was used as the research material, where different adjustment agents were tested to eliminate the influence of ions in pulp generated from acidified high-sulfur bauxite. These ions harm flotation, and eliminating their influence improves the separation efficiency.

© The Minerals, Metals & Materials Society 2021 L. Perander (ed.), Light Metals 2021, The Minerals, Metals & Materials Series, https://doi.org/10.1007/978-3-030-65396-5_4

24

Flotation Desulfurization of Acidified High-Sulfur Bauxite …

25

Experimental Materials Bauxite The acidified high-sulfur bauxite used in this work was from different mines in Henan province (1#, 2#, 3#) and Guizhou province (4#). The main chemical and mineralogical compositions of these bauxite ores were analyzed by X-ray fluorescence and X-ray diffraction, and the results are shown in Tables 1 and 2, respectively. The sulfur content of bauxite samples is between 0.86 and 6.83%. The main sulfur-contained mineral is pyrite, the main aluminum-contained mineral is diaspore, and the main silicon-contained minerals are kaolinite, illite, and quartz. Other Materials Unless specifically noted, all chemicals used in the experiments were analytical purity reagents. The pulp pH adjusters are hydrochloric acid and sodium hydroxide. The activator, collector, and frother are copper sulphate, butyl xanthate, 2# oil, respectively. Several regulators were investigated including sodium hexametaphosphate, modified starch, and sodium silicate.

Flotation Desulfurization Tests The flotation desulfurization tests were carried out in a single flotation cell of 1.5 L. In each test run, bauxite with a 30% pulp density was ground to 78 ± 2% < 0.075 mm, and loaded into the flotation tank. The pulp pH was adjusted to the target pH value, and then the regulator, activator, collector, and frother were added successively. The air flotation desulfurization process was begun after stirring for 2 min, with the pulp temperature at 30 °C. The flowchart is shown in Fig. 1.

Acidification Degree Measurements The natural pulp pH value was measured after the test sample ore was ground to 78 ± 2% < 0.074 mm, and pulp density was controlled to 30%. The SO42− concentrations

Table 1 Typical chemical compositions of bauxite samples (%)

were also measured by ion chromatography. The results are shown in Table 3. The result of these oxidation and acidification measurements for the four kinds of ores showed that the degree of acidification of bauxite samples 1# and 2# were weaker. Ore 3# was partly acidified, and the natural pulp pH was 4.2, the SO42− concentration in pulp was 1.21 g/L. Acidification of sample ore 4# was more significant, the ground pulp’s pH was 2.5, and the SO42− concentration was 4.69 g/L. Oxidation and acidification of the bauxite ores were resulted from the oxidation of pyrite and resulted in the production of Fe2(SO4)3 in the slurry.

Zeta Potential Tests The effects of acidification and regulor on the zeta potentials of the main bauxite species including pyrite, diaspore, illite, and pyrophyllite were determined with Zetasizer Nano ZSP (Malvern Panalytical, UK). Pyrite particles were cleaned with pure water through ultrasonic treatment for 20 min and dried in a vacuum to serve as the sample of unoxidized pyrite [18]. For each zeta potential measurement, 20 mg of mineral sample with the size of −10 lm was conditioned for 10 min in 40 mL ultrapure water or a certain concentration of Fe2(SO4)3 or sodium silicate solution. The concentration of Fe2(SO4)3 presents the degree of the oxidation and acidification of bauxite. The conditioned suspension was then transferred to the sample tube for zeta potential measurement. The average value of five measurements was taken as the reported value.

Results and Discussion Effect of Sodium Hexametaphosphate Dosage Ore 3# was taken as the subject of a study on the effect of the dose of hexametaphosphate. The sample was ground to 75% < 0.075 mm, pulp density was 30%, and the pulp pH adjusted to 8.0. Sodium hexametaphosphate, activator, collectors, and foaming agent were added in turn for flotation desulfurization. The effect of sodium hexametaphosphate

Samples

Al2O3

SiO2

Fe2O3

TiO2

K2O

Na2O

CaO

MgO

S

1#

59.61

19.22

2.54

2.51

0.39

0.01

0.27

0.21

1.18

2#

47.58

11.56

11.39

2.30

2.18

0.023

2.57

0.79

6.83

3#

64.48

8.30

6.06

2.79

1.21

0.018

0.56

0.34

2.32

4#

65.61

7.97

6.19

2.88

1.22

0.04

0.13

0.14

0.86

26 Table 2 Mineral phase analysis of bauxite samples (%)

H. Li et al. Samples

Diaspore

Pyrophyllite

Kaolinite

Chlorite

1#

59.0

19.0

9.0

1.6

2#

49.0

/

/

/

23.0

/

3#

68.5

/

4.5

/

11.5

1.0

3.9

4#

69.0

/

4.5

3.0

11.5

/

3.0

Samples

Goethite

Gypsum

Dolomite

Calcite

Anatase

Rutile

1#

/

1.0

/

1.0

1.8

0.6

2#

/

2.0

3.5

1.5

1.0

1.3

3#

4.0

/

1.5

/

2.0

0.7

4#

3.0

/

/

/

1.8

1.0

Fig. 1 The flowchart of the flotation test Table 3 The natural pH and SO42− concentration of experimental bauxite slurry

Illite 4.0

Quartz 1.0

Pyrite 2.0 12.5

Fig. 2 The effect of sodium hexametaphosphate on the recovery and sulfur content of concentrate. (Color figure online)

Samples

Natural slurry pH value

SO42− (g/L)

1#

6.0

0.78

2#

5.5

0.96

3#

4.2

1.21

4#

2.5

4.69

dosage on flotation desulfurization was studied by comparing the yield and sulfur content of aluminum concentrates. The test results are shown in Fig. 2. As shown in Fig. 2 the addition of sodium hexametaphosphate caused a decrease in aluminum concentrate yield during the process of flotation desulfurization. At a dose of 60 g/t, there was an obvious decrease in concentrate yield, and as the dose was increased from 60 to 240 g/t, the concentrate yield gradually increased with increasing sodium hexametaphosphate dose. Hexametaphosphate is an effective dispersing agent and inhibitor of aluminosilicate ore flotation. At low dose, the ore had good initial dispersibility during the process of

flotation, resulting in fine particle entrainment in the flotation froth, and caused a decrease in aluminum concentrates yield. With increasing hexametaphosphate dose, its inhibitory effect on aluminosilicate ore was more obvious, reducing the flotation of aluminosilicate ore, and increasing aluminum concentrate yield. The addition of sodium hexametaphosphate at 60 g/t clearly causes a decrease in sulphur content of aluminum concentrates. As the dose was increased from 60 to 240 g/t, like aluminum concentrate yield, the sulphur content of concentrate also increased. The test results showed that the lowest sulphur content of aluminum concentrate was at the 60 g/t dose, but did not fall below 0.3%.

Flotation Desulfurization of Acidified High-Sulfur Bauxite …

Hu et al. [19] researched the phosphate effection on the reverse flotation system. They drew the conclusion that if the dosage of sodium hexametaphosphate in the diaspore reverse flotation system was low, the inhibition effect of sodium hexametaphosphate on diaspore was weak. When the dose was high, the inhibition effect on diaspore was strong. The inhibition effect of sodium hexametaphosphate on diaspore can be explained as follows; when the dose is high, adsorption density of sodium hexametaphosphate on the surface of diaspore is high, and its surface may be fully covered by sodium hexametaphosphate. Na4P6O182− ionized by sodium hexametaphosphate reacts with aluminum ions yielding insoluble salts, then transfers to stable soluble complexes, resulting in diaspore inhibition [20].

Effect of Modified Starch Dosage

27

aluminium ion. The study of Li et al. [21] showed that during the process of flotation desulfurization, modified starch inhibited diaspore to a certain extent, and reduced the loss of Al2O3 into high-sulfur tailings. When the dose of modified starch increased, its special structure covered micromolecular collectors, and consequently reduced the separation performance of agents, so affecting flotation desulfurization.

Effect of Sodium Silicate Dosage Ore 3# was taken as the subject of a study on the effect of different doses of sodium silicate on flotation desulfurization sodium silicate is a regulator developed for acidified high-sulfur bauxites, and it can activate sulphur minerals while inhibiting aluminosilicate minerals. From the results shown in Fig. 4, the addition of WG can improve aluminum concentrate yield and reduce sulphur content of the concentrate during flotation desulfurization. Under uniform dosing of agents and flotation conditions, a roughing desulfurization can reduce sulphur content of aluminum concentrates from 0.90 to 0.29%. When the dose of sodium silicate is 1000–3000 g/t of raw ore, sulphur content of the aluminum concentrate is low and stable. So for significantly acidified high-sulfur bauxite ore 3#, sodium silicate can obviously improve separation, as reflected in a decrease in sulphur in aluminum concentrate, and increased aluminum concentrate yield.

Ore 3# was taken as the subject of a study examining the effect of different doses of modified starch on flotation desulfurization. The results are presented in Fig. 3. The results show that when the dose of modified starch is low, it can improve aluminum concentrate yield, and reduce sulphur content of aluminum concentrates to a certain extent. When the dose of modified starch increases, aluminum concentrate yield obviously reduces, and sulphur content of aluminum concentrate increases continuously. The main chain of modified starch is composed of glucose monomer rings, linked by glucosidic bonds. Its cyclic structure gives improved rigidity. The absorbed forms of modified starch on the surface of ores are mainly ring-type adsorption. When reacted with ores, modified starch reacts with aluminum ions on the surface of diaspore, and yields the chemical bond Al–O. This means that chelation between them occurs, so electrostatic charge of bonding atoms in agent molecules increases, and electron cloud transfers to the

Sodium silicate was taken as a flotation desulfurization regulator for the other sulfur bauxites: Ore 1#, Ore 2#, and Ore 4#. The flotation desulfurization tests were performed according to the flotation test flowsheet as shown in Fig. 1.

Fig. 3 Effect of modified starch on the recovery and sulfur content of concentrate. (Color figure online)

Fig. 4 Effect of sodium silicate dosage on the recovery and sulfur content of concentrate. (Color figure online)

Effect of Acidification Degree

28

H. Li et al.

As the results show in Table 4, the dosage of sodium silicate increases with the increase of acidification degree of ore. For highly acidified ores, the regulator dose was higher. Doses of regulator for Ore 1#, Ore 2#, Ore 3#, and Ore 4# were1000 g/t, 1500 g/t, 2000 g/t, and 2500 g/t, respectively. Control tests were performed without addition of regulator. For bauxites with different sulfur content and different degrees of acidification, sodium silicate can obviously improve the separation efficiency of flotation desulfurization. Consequently, future studies should focus in detail on the optimization of flotation indices and improving the mechanism of sodium silicate on the separation. The flotation test results obviously show that sodium silicate is an effective regulator for flotation desulfurization and can not only improve inhibition of pyrite caused by acidification of ores, but also solves adverse effects on flotation, such as ore sliming, a common characteristic of oxidized ores.

Zeta Potential Analysis In order to investigate the effect of oxidation and acidification on bauxite species and the interaction mechanism of sodium silicate regulor, the zeta potentials of pyrite, Table 4 Flotation desulfurization results of test bauxites using sodium silicate as regulator

Samples 1#

WG Dose (g/t) 0

1000

2#

0

1500

3#

0

2000

4#

0

2500

diaspore, illite and pynophyllite treated with Fe2(SO4)3 and sodium silicate were analysed. The results are illustrated in Fig. 5. For pyrite, the addition of Fe2(SO4)3 made the zeta potential moving to the positive direction. With the concentration of Fe2(SO4)3 increasing from 1 to 5 g/L, the zeta potential gradually decreased to near the zero point. After sodium silicate being added, the zeta potential of pyrite significantly shifted to the negative direction. Sodium silicate greatly increased the electronegativity of pyrite particles and the repulsive force between particles, which would promote the dispersion of pyrite particles in the slurry. For diaspore, Fe2(SO4)3 treatment increased its zeta potential, and with the concentration increasing, the zeta potentials were located near the zero point. Illite and pyrophyllite underwent the same change after adding Fe2(SO4)3. The lower zeta potentials of particles decrease the repulsive force between particles and increase the sliming influence of aluminosilicate minerals, which would impact the flotation of pyrite in the bauxite. The addition of sodium silicate regulor increased the zeta potential of the minerals, which was conducive to the dispersion of mineral particles in the slurry. Based on the zeta potential results, it could be concluded that sodium silicate can eliminate the adverse effects of oxidation and acidification on flotation desulfurization. Products

Yield %

S%

Recovery rate of S %

Concentrate

69.91

0.26

15.96

Sulfur tailings

30.09

3.18

84.04

Total

100

1.14

100.00

Concentrate

79.75

0.24

15.56

Sulfur tailings

20.25

5.13

84.44

Total

100

1.23

100.00

Concentrate

68.47

0.94

9.70

Sulfur tailings

31.53

19.01

90.30

Total

100

6.64

100

Concentrate

71.37

0.62

6.47

Sulfur tailings

28.63

22.35

93.53

Total

100

6.84

100

Concentrate

68.75

0.90

27.97

Sulfur tailings

31.25

5.10

72.03

Total

100.00

2.21

100.00

Concentrate

71.57

0.29

10.28

Sulfur tailings

28.43

6.37

89.72

Total

100.00

2.02

100.00

Concentrate

66.07

0.19

14.28

Sulfur tailings

33.93

2.22

85.72

Total

100

0.88

100.00

Concentrate

86.95

0.16

16.93

Sulfur tailings

13.05

5.23

83.07

Total

100

0.82

100.00

Flotation Desulfurization of Acidified High-Sulfur Bauxite … 10

Diaspore 0

Pyrite

-10

Zeta Potential /mV

0

Zeta Potential /mV

Fig. 5 Zeta potentials of the main bauxite specials in absence and presence of sodium silicate as a function of Fe2(SO4)3 concentration. (Color figure online)

29

No sodium silicate Sodium silicate added

-20 -30

No sodium silicate Sodium silicate added

-20

-40

-40 -50

0

1

2

3

4

-60 -1

5

0

1

2

3

4

0

Zeta Potential /mV

Zeta Potential /mV

6

Pyrophyllite

Illite 0

No sodium silicate Sodium silicate added

-20

-40

-60 -1

5

Fe2(SO4)3 (g/L)

Fe2(SO4)3 (g/L)

0

1

2

3

4

5

6

Flotation could be the more economical and effective method than other technologies for desulfurization of high-sulfur bauxites. The special properties of high-sulfur bauxites make it difficult for bauxite desulfurization from other sulfide ores. The application of a suitable regulator is essential to achieve efficient flotation separation. The flotation performance was improved significantly through adding sodium silicate as regulator and xanthate as collector. Sodium silicate can not only inhibit the influence of acidification on pyrite flotation, but also solve the adverse effects of sliming. Sodium silicate has wide applicability to different kinds of high-sulfur bauxites, and the dosage increases with the increase of acidification degree of ore. Under the optimized conditions, sulphur content of concentrates can be reduced significantly, concurrently with the increase yield by more than 10%. Acknowledgements The authors acknowledge the financial support of the National Natural Science Foundation of China: U1704252), the Supported by Program for Innovative Research Team (in Science and Technology) in University of Henan Province (IRTSTHN) (No. 19IRTSTHN028), and Scientific Research Start-up Project of Zhengzhou University (No. 32211159).

-40

-60 -1

0

1

2

3

4

5

6

Fe2(SO4)3 (g/L)

Fe2(SO4)3 (g/L)

Conclusions

No sodium silicate Sodium silicate added

-20

References 1. Lv, X., et al., A new desulfurization agent—earthy graphite. Light Metals, 1992. 11: p. 21–23. 2. Peng, X., et al., Development and application of bauxite containing high sulfur. Light Metals, 2010. 11: p. 14–17. 3. Qi, L., Low-grade and high-sulfur bauxite processing method. Light Metals, 1995. 1: p. 14–16. 4. Zhang, F., et al., Present situation and progress of study on desulphurization of high sulphur bauxite. Shanxi Science and Technology, 2011.26 (1): p. 94–95. 5. Hu, X., et al., Roasting desulfurization of high sulfur bauxite with calcium oxide. Light Metals, 2010. 1: p. 9–14. 6. Lan, J., et al., Research advance of desulfurization in production of alumina with bauxite. Applied Chemical Industry, 2008. 4: p. 446– 448. 7. Hu, X., et al., Desulfurization from sodium aluminate solution by wet oxidation. Journal of Central South University, 2011. 42 (10): p. 2911–2916. 8. Lan, J., et al., Research of desulfurization in the course of disposing of high grade bauxite containing sulfur. Applied Chemical Industry, 2008. 37 (8): p. 886–890. 9. He, P., et al., The wet desulfurization technical study from industry sodium aluminate solution. Hydrometallurgy, 2001. 20 (4): p. 186–190. 10. Wang, P., et al., Desulfuration technique research of high-sulfur bauxite. Metal Mine, 2012. 1: p. 108–123. 11. Chai, W., et al., Enhanced separation of pyrite from high-sulfur bauxite using 2-mercaptobenzimidazole as chelate collector: Flotation optimization and interaction mechanisms. Minerals Engineering, 2018. 129: p. 93–101.

30 12. Zhang Nian-bing, Bai Chen-guang, Li Zhi-ying, et al. Research on existence of sulfur mineral in high sulfur bauxite and the desulfurization efficiency. Journal of Chinese Electron Microscopy Society, 2009, 28 (3): p. 229–234. 13. Ma, Z., et al., Commercial experiment of flotation desulfurization of low grade bauxite with high sulfur. Ligh Metals, 2017. p. 1–3. 14. Xie, W., et al., Study on the flotation desulfurization of High-sulfur bauxite in Henan. 15. Sun, W., et al., Activated flotation of pyrite once depressed by lime. Journal of Central South University, 2010. 41 (3): p. 813– 818. 16. Zhang, J., et al., Reagents of Mine. Beijing: Metallurgical Industry Press, 2008. p. 623.

H. Li et al. 17. Zhang, G., Theory and technology of Floatation of Bauxite Desilicate. Changsha: Central South University, 2001. 18. Ozun, S., et al., Collectorless flotation of oxidized pyrite. Colloids and Surface A. 2019. 561: p. 349–356. 19. Hu, Y., et al., Influence of phosphates on diaspore and kaolinite flotation. The Chinese Journal of Nonferrous Metals, 2003. 2: p. 222–227. 20. Li, C., et al., An experimental study on the effects of regulatiors on desulfurization of high-sulfur bauxite. Nonferrous Metals, 2011. 1: p. 56–59. 21. Li, H., et al., Effect of modified starches on depression of diaspore. Transactions of Nonferrous Metals Society of China, 2010. 8(20): p. 1494–1499.

Optimization of Zinc Removal Process in Sodium Aluminate Solution Based on Orthogonal Experiment Dong-zhan Han, Er-wei Song, Li-juan Qi, and Xiao-ge Guan

Abstract

Introduction

Zinc is one of several impurities in alumina products. To reduce zinc in Bayer liquor, a novel method using organic additives was proposed. An orthogonal experiment methodology was applied to explore the interactions between different impacts. L9 (33) orthogonal experiments were designed to optimize the process parameters such as temperature, retention time, and dezinc agent (species and dosage). The results show that the optimum experimental conditions are: temperature 80 °C, retention time 2 h, and dezinc agent dosage 0.4 gpl. Based on the experimental results and in line with theory, it is concluded that the temperature has the main influence, followed by dezinc agent dosage, and then retention time. The impact of organic additive on the content of organics in the Bayer liquor was also investigated. Results show that the organic additives had little effect on the organic content in Bayer liquor, which implies that these additives have great application potential in alumina refineries for impurity control. Keywords

Sodium aluminate solution Organic additive




Orthogonal experiment

D. Han School of Metallurgy and Environment, Central South University, Hunan, 410083, China D. Han
E. Song (&)
L. Qi
X. Guan Zhengzhou Non-Ferrous Metals Research Institute Corporation Limited of Aluminum Corporation of China Limited, Henan, 450041, China e-mail: [email protected]




The zinc content in the Guangxi bauxite of China is about 0.025 wt% (ZnO content). The typical ZnO content in the alumina product of an alumina refinery in this district is >0.015%, which is a serious limitation in the product quality and therefore impacts the competitiveness of the refinery. Though zinc has some positive effects in the Bayer process, such as contributing to aluminum hydroxide crystals growth, there are some serious negative effects in the aluminum electrolysis process in the downstream smelter operation. In aluminum electrolysis, Zn reduces the current efficiency and compromises the purity and material properties of the aluminum ingots and other products. A. Suss et al. [1] pointed out that the current efficiency decreases by 0.13% with per 0.01% increasing of zinc content in the electrolyte. Given the above serious detrimental impacts of zinc impurities in alumina on the aluminum electrolysis process, the reduction or removal of zinc in the alumina products is important. Several authors have investigated the removal of zinc in the alumina production process [2–5]. Although some dezinc agents, like sodium sulfide, have some positive effects in reducing zinc in the liquor, they may also bring in new purities, many of them have a relatively low zinc removal efficiency, others have high costs, and some result in disposal problems or pollution. In order to efficiently remove zinc from Bayer liquor, a novel method is proposed in this research. The effects of temperature, retention time, and dosage on the zinc removal efficiency were investigated, besides the interactions among these parameters were also analyzed. In addition, the effects of dezinc agent on organic content in the system was also investigated, which can help to identify reasonable or optimum process conditions and achieve the optimal dezinc efficiency for industrial applications.

© The Minerals, Metals & Materials Society 2021 L. Perander (ed.), Light Metals 2021, The Minerals, Metals & Materials Series, https://doi.org/10.1007/978-3-030-65396-5_5

31

32

D. Han et al.

Raw Material and Method Raw Materials Bauxite The Bauxite used in the experiments came from an alumina company in Guangxi. The received Bauxite sample was crushed and mixed evenly, and then divided into subsamples, and sealed for use. Chemical composition of the bauxite sample is shown in Table 1. From Table 1, it can be seen that the main chemical components in this bauxite are Al2O3 and Fe2O3, with 52.48 wt% and 23.00 wt%, respectively. Followed by SiO2 and TiO2, with 4.96 wt% and 2.98 wt% respectively. The A/S ratio (Alumina to Silica) is 10.58. The measured zinc content is 0.014 wt% (expressed as ZnO). Lime The lime used in the test was provided by Aluminum Corporation of China Limited Guangxi Branch. The lime was ground through 100 mesh sieves, bagged, and sealed for use. Chemical composition of the lime sample is displayed in Table 2. From Table 2, it can be seen that CaOT content in the lime was 84.42 wt%, of which CaOf is 80.30%. Liquor The Bayer liquor used in the test was provided by Aluminum Corporation of China Limited Guangxi Branch. Chemical composition of the liquor is shown in Table 3.

Test and Analytical Method The digestion experiments were conducted using a molten salt steel bomb. According to the zinc to iron ratio of the bauxite and red mud, the dissolution rate of zinc oxide was calculated, as below (Eq. 1): gZn ¼

ðZn=FÞB  ðZn=FÞR  100% ðZn=FÞB

ð1Þ

where (Zn/F)B is the mass ratio of ZnO to Fe2O3 in the bauxite, and. (Zn/F)R is the mass ratio of ZnO to Fe2O3 in the red mud. Based on the change of zinc in the Bayer liquor before and after dezincification, the zinc removal yield during the digestion process was calculated, as follows: gZn ¼

CZnblank  CZnliquor  100% CZnblank

ð2Þ

where CZn-blank is the Zinc content in the liquor without any zinc removal agent, (in mg/L). CZn-liquor is the Zinc content in liquor after the dezincification using a zinc removal agent (in mg/L). The zinc content in the liquor was analyzed using ICP, and the zinc content in the red mud was analyzed using XRF.

Results and Discussion Comparison Tests for Dezinc Agent The Bauxite slurry was prepared by an initial pre-desilication step followed by a digestion process. The pre-desilication process was carried out at a temperature of 100 °C and with a retention time of 10 h. The digestion process was carried out at a temperature of 265 °C, a retention time of 60 min, a caustic alkali content(NK) of 243 g/L and using a lime addition to adjust the C/S ratio to 1:2. The NK of the liquor obtained from centrifugal separation was adjusted to about 170 g/L. This liquor was then subjected to the zinc reduction trials. The zinc removal tests were conducted at a temperature of 95 °C, a reaction time of 2 h, and using a dezinc agent dosage of 0.4 g/L. Several tests were conducted to investigate the zinc removal efficiency by using different agents. The results are shown in Table 4.

Table 1 Chemical composition of the zinc-bearing bauxite (wt%) Al2O3

SiO2

Fe2O3

TiO2

K2O

Na2O

CaO

MgO

ZnO

A/S

LOI

52.48

4.96

23.00

2.98

0.12

0.055

0.45

0.15

0.014

10.58

14.21

Table 3 Chemical composition of liquor

Table 2 Chemical composition of lime (wt%) SiO2

CaOT

MgO

CaOf

Na2OT (g/L)

Al2O3 (g/L)

Na2Ok (g/L)

ak

SiO2 (g/L)

Zn2+(mg/L)

Al2O3 0.63

0.71

84.42

2.26

80.30

259.79

130.60

243.00

3.06

1.02

5.85

Optimization of Zinc Removal Process in Sodium …

33

Table 4 Comparison of zinc removal efficiency using different dezinc agents Reaction condition

Results

Dezinc agent

Dosage (g/L)

Na2OT (g/L)

Al2O3 (g/L)

Na2Ok (g/L)

ak

Zn (g/L)

ηZn(%)

Blank

0

187.6

203.76

171.6

1.39

0.0238

–

TMT-55

0.4

196.9

209.73

172.4

1.35

0.0158

33.61

HW-400

0.4

196.2

210.96

174.4

1.36

0.0062

73.95

FMN

0.4

197.6

210.38

172.0

1.34

0.0154

35.29

From Table 4, it can be seen that all three dezinc agents have some zinc removal potential. The calculated zinc removal efficiency of TMT-55, HW-400, and FMN were 33.61, 73.95, and 35.29%, respectively. It can be seen that HW-400 has the best zinc removal efficiency. In order to find out the best process stage to add the zinc removal agent HW-400 in the production process, experiments to measure the effects of process conditions on zinc removal from different Bayer liquor were conducted.

Green Liquor In order to investigate the zinc removal potential in the so-called green liquor, orthogonal experiments were designed, where the reaction temperature, the retention time, and the dosage of the dezinc agent were selected as variables. According to the design principles of orthogonal experiments [6], an L9(34) orthogonal table was adopted, and each factor identified three levels (Table 5). Tests were conducted according to the experiment matrix in Table 5. During the data analysis process, ηZn was selected as the objective function, and the results are shown in Table 6. When comparing the impacts of the various parameters on the zinc reduction potential in the green liquor, defined as ηZn, the results demonstrate that RA > RC > RB, or in other words that the temperature has the main influence, followed by dosage of the dezinc agent, retention time. The results

Table 5 Design of orthogonal table L9 (34) for the investigation of dezinc removal in the green liquor

also indicate that the optimum conditions for zinc removal are A3B2C2, namely a reaction temperature of 80 °C, a retention time of 2 h and a dezinc agent dosage of 0.4 g/L.

Dilute Slurry To investigate the zinc removal potential in the dilute slurry, a further set of experiments were conducted, in which the solid concentration in the digestion slurry was adjusted to 85 g/L and the Nk to 170 g/L. A set of orthogonal experiments were designed, where the reaction temperature, the retention time, and the dosage of dezinc agent (HW-400) were selected as variables. According to the design principles of an orthogonal experiment, an L9(34) orthogonal table was used, and each factor identified three levels (Table 7). Tests were conducted according to the above experiment matrix. In the subsequent data analysis process ηZn was selected as objective function, and the results are shown in Table 8. When comparing the impact of the various parameters on the zinc reduction potential in the dilute slurry, the results demonstrate that RA > RC > RB, or in other words that the temperature has the main influence, followed by dosage of the dezinc agent, retention time. According to the results and analysis, the best scheme for the zinc removal in the dilute slurry is A1B3C2, namely a reaction temperature of 95 °C, a retention time of 2 h, and dezinc agent dosage of 0.3 g/L.

No

Tem (°C)

Time (h)

Dosage (g/L)

1

60

1

0.2

2

60

2

0.4

3

60

3

0.6

4

70

1

0.4

5

70

2

0.6

6

70

3

0.2

7

80

1

0.6

8

80

2

0.2

9

80

3

0.4

34 Table 6 Experimental scheme and analysis results for the green liquor experiments

Table 7 Design of orthogonal table L9 (34) (HW-400) for the investigation of dezinc removal in the dilute slurry

D. Han et al. Exp. no

A

B

C

ηZn, %

1

1

1

1

20.37

2

1

2

2

38.94

3

1

3

3

99.41

4

2

1

2

43.94

5

2

2

3

72.94

6

2

3

1

11.02

7

3

1

3

40.23

8

3

2

1

6.00

9

3

3

2

51.53

Kj1

16.56

13.59

10.68

Kj2

11.34

12.62

16.87

Kj3

4.87

14.22

21.75

kj1

5.52

4.53

3.56

kj2

3.78

4.21

5.62

kj3

1.62

4.74

7.25

Rj

3.90

0.53

3.69

Factor order: degrade trend

ACB

Optimal scheme

A3B2C2

No

Tem (°C)

Time (min)

Dosage (g/L)

1

95

60

0.2

2

95

90

0.3

3

95

120

0.4

4

100

60

0.3

5

100

90

0.4

6

100

120

0.2

7

105

60

0.4

8

105

90

0.2

9

105

120

0.3

Verification Experiments for the Optimum Conditions A verification test at the optimum processing condition was conducted. For this set of experiments, the solids concentration in the digestion slurry was adjusted to 85 g/L and the caustic Nk to 170 g/L. The reaction temperature was 95 °C, and the retention time was 2 h and the dosage of HW-400 was 0.3 g/L. At the optimum process conditions the dezincification yield was measured to be 73.25%. As an additional benefit, the results show this agent has certain iron removal effects at these conditions as well.

Effects on Organic Content in the System To investigate the impact the dezinc agent on the organic content in the system, numerous experiments were conducted. In these experiments the Nk of the green liquor was adjusted to 170 g/L. The reaction temperature was 95 °C and the retention time was 2 h, and the dosage of HW-400 was 0.3 g/L. The results of the effects of dezinc agent on the organic content in the system are shown in Table 9. From Table 9, it can be seen that in the dezinc reaction process, the Corg (organic carbon) in the liquor does not increase with the dosage of organic dezinc agent, while Corg

Optimization of Zinc Removal Process in Sodium … Table 8 Experimental scheme and analysis results for the dilute slurry experiments

Table 9 Impact of dezinc agent on the organic concentration in liquor

35

Exp. no

A

B

C

ηZn, %

1

1

1

1

6.27

2

1

2

2

30.86

3

1

3

3

44.23

4

2

1

2

27.88

5

2

2

3

40.12

6

2

3

1

14.57

7

3

1

3

11.58

8

3

2

1

12.97

9

3

3

2

41.90

Kj1

17.83

18.12

14.30

Kj2

9.38

18.44

22.42

Kj3

6.56

22.40

21.28

kj1

5.94

6.04

4.77

kj2

3.13

6.15

7.47

kj3

2.19

7.47

7.09

Rj

3.76

1.43

2.71

Facter order: degrade trend

ACB

Optimal scheme

A1B3C2

Na2OT, g/L

Al2O3, g/L

Na2Ok, g/L

ak

Zn, g/L

Corg, g/L

188.24

195.56

170

1.43

0.025

3.06

188.79

194.02

170

1.44

0.010

2.65

189.09

196.04

181

1.43

0.011

2.63

decreases slightly when compared with the blank liquor. The reason for this may be that complexation reactions occurred between the dezinc agent and the organic species, which would result in a decrease in Corg in the liquor. It can be concluded that adding an organic dezinc agent to an alumina production process does not increase the Corg in the process.

Conclusion For zinc removal efficiency, HW-400 is the best agent of the three agents tested in this study. The results of the orthogonal experiments show that the temperature has the main influence on zinc reduction, followed by dezinc agent dosage, retention time. The addition of an organic dezinc agent does not only remove zinc, but also has some effects on the removal of iron. It was also shown that addition of the organic dezinc agent would not increase the organics concentration in the Bayer process.

References 1. A. Suss et al., Optimization of elemental sulfur utilization of zinc removal from Bayer cycle. Proceedings of 10th Alumina Quality Workshop 2015. pp. 383–388. 2. Jiang B. Removal of zinc from Bayer process liquor with sodium sulfide [D].Changsha: Central South University, 2006: 8–11. 3. Zhang XQ, Yang JH, Li QY, et al. Behavior and elimination of zinc in alumina production[J]. Journal of Central South University of Technology (Natural Science),1999( 6):589-591. 4. Hansen, R. M. Removal of Zinc from Bayer Process Liquors with Sodium Sulfide[J]. JOM, 1969, 21(9):32-34. 5. Liu BW, Wu HW, Peng QY, ET AL. A method to remove zinc oxide from industrial sodium alumina solution: CN 101913631 A [P].2010–08–09. 6. Phillip J Ross. Taguchi techniques for quality engineering: loss function, orthogonal experiments, parameter and tolerance design [M]. McGraw-Hill, 1988.

Collection and Selectivity Contrast of Propyl Gallate and Sodium Oleate for Diaspore and Kaolinite Flotation Yankun Wu, Wencui Chai, and Yijun Cao

Abstract

Introduction

Using an effective collector is often the key to improving the flotation recovery of valuable mineral concentrates. China’s diaspore-type bauxite is a refractory ore, since silicate minerals, such as kaolinite, are often closely embedded with diaspore. Propyl gallate (PG) is an effective and novel collector of diaspore. Detailed flotation behaviors of diaspore and kaolinite with PG and traditional collector sodium oleate (NaOL) were investigated in this work. The effects of stirring speed, aeration volume, slurry pH, and collector dosage on the flotation recovery of the two minerals were discussed. The results show that, compared with the traditional collector NaOL, PG had better collection and selectivity for diaspore since the collector PG could increase the hydrophobic difference of diaspore and kaolinite than NaOL. Under the optimal flotation conditions: 1600 r/min of stirring speed, 60 mL/min of aeration volume, 60 mg/L of PG dosage, and slurry pH 9, the flotation recovery of diaspore and kaolinite are 88.5% and 23.4%, respectively. Keywords

Diaspore




Kaolinite




Collector




Flotation recovery

W. Chai (&)
Y. Cao Henan Province Industrial Technology Research Institute of Resources and Materials, Zhengzhou University, Zhengzhou, 450001, China e-mail: [email protected]

As an integral metal, aluminum has been widely used in modern industry. Bauxite is a significant aluminum-bearing mineral, and it is always associated with other silicon-bearing minerals such as kaolinite. The Bayer process is the most commonly used method to produce alumina, which requires a high aluminum–silicon ratio of bauxite. Therefore, improving the aluminum–silicon ratio of bauxite is an important research topic [1, 2]. Flotation is the most widely used method to separate useful minerals from gangue minerals. According to the existence of useful minerals in concentrate or tailings, it can be divided into two types: flotation and reserve flotation. The principle is that the surface properties of minerals are changed by agents, and the differences between the surface properties of useful minerals and gangue minerals are increased, so that the useful minerals are separated from gangue minerals. The separation of the main components of bauxite from silicon-bearing gangue minerals is also realized by foam flotation and has been realized in industrial production. In the process of mineral flotation, the main role of reagents among these reagents, oleic acid has long been shown to be an effective collector for flotation desilication [3]. In recent studies, propyl gallate collector has been shown to effectively separate diaspore from kaolinite [4, 5]. In this study, propyl gallate and sodium oleate were used as collectors to study the flotation properties of the main aluminum-bearing mineral diaspore and silicon-bearing mineral kaolinite.

Experiments

Y. Cao e-mail: [email protected]

Materials and Reagents

Y. Wu
Y. Cao School of Chemical Engineering, Zhengzhou University, Zhengzhou, 450001, China

The single mineral samples of diaspore and kaolinite were obtained from Henan Province of China. After a series of

© The Minerals, Metals & Materials Society 2021 L. Perander (ed.), Light Metals 2021, The Minerals, Metals & Materials Series, https://doi.org/10.1007/978-3-030-65396-5_6

36

Collection and Selectivity Contrast of Propyl Gallate …

37

treatments, the same samples with a particle size of −74 lm were obtained. The basic chemical composition and the mineralogical composition of two single minerals were respectively shown in Table 1 and Fig. 1. As seen from Table 1, the main components of diaspore are Al2O3 and SiO2, accounting for 77.71% and 2.75%, respectively. The main components of kaolinite are Al2O3 and SiO2, accounting for 37.95% and 45.92%, respectively. The XRD patterns in Fig. 1 reveal that the main crystal phases in the diaspore sample are diaspore and anatase, and that in the kaolinite sample are kaolinite and quartz [6, 7]. Unless specifically noted, all chemicals used in the experiments were analytical purity reagents. Propyl gallate (PG) and sodium oleate (NaOL) were used as collectors. Sulfuric acid (H2SO4) and sodium hydroxide (NaOH) were used as pH regulators.

R¼

m1 m1 þ m2

where, R represents flotation recovery, m1 and m2 respectively represent the mass of the concentrate and the tailing.

Contact Angle Measurements The contact angles of diaspore and kaolinite before and after treated with collectors were measured using the sessile drop method. In each measurement, the water/collector solution was dropped onto the mineral pellet surface by a microsyringe, and then the images of the stable solution drop were recorded by a camera. The Image J software was used for measuring the contact angle. The reported contact angle is the average value for at least five fresh drops placed on different locations of the same mineral pellet.

Flotation Tests

Results and Discussion For each micro-flotation test, 2 g of single mineral sample was placed in a 40 mL flotation cell with a spindle speed of 1200–1800 r/min. Then, an appropriate amount of a solution which has been adjusted to pH with H2SO4 and NaOH was added for 1 min, and a quantitative collector was added. After stirring for 1 min, the foam products were manually collected for 3–6 min. The obtained concentrate and tailings were dried and weighed, and the flotation recovery of concentrate was calculated as the following formula.

Table 1 Chemical composition analysis results of two single minerals

Fig. 1 XRD patterns of diaspore and kaolinite samples

Effect of Stirring Speed on Flotation Recovery The stirring speed is one of the main factors affecting the flotation recovery [8]. During the flotation process, the fluid dynamics in the flotation tank is a very complicated three-phase mixed system. The tank must have sufficient stirring strength to fully suspend the slurry, and the ore particles and bubbles are fully contracted, and the ore

Mineral

Al2O3

Diaspore

77.71

2.75

1.09

2.64

0.48

0.041

0.067

0.068

14.43

Kaolinite

37.95

45.92

0.38

1.27

0.02

0.074

0.16

0.14

13.84

SiO2

Fe2O3

TiO2

K2O

Na2O

CaO

MgO

LOI

38

Y. Wu et al.

Fig. 2 Effects of stirring speed on flotation recovery of diaspore and kaolinite

Fig. 3 Effects of aeration volume on flotation recovery of diaspore and kaolinite

particles and bubbles are increased. The collision probability is high, but the stirring in the flotation cell should not be too strong, so as not to damage the stability of the separation zone and the foam zone, resulting in a decrease in the recovery. Using PG and NaOL as collectors respectively, the effect of stirring speed on the flotation recovery of diaspore and kaolin was studied, as shown in Fig. 2. It can be seen from Fig. 2, at pH 9, as the stirring speed increases, the collision probability of particles and bubbles increases, and the corresponding flotation recovery has also been significantly improved. When the stirring speed reaches 1600 r/min, the flotation recovery reaches the maximum value of 83.32%. If the stirring speed continues to increase, the flotation recovery would not increase, but have a downward trend. This is because when the stirring speed increases, the collision probability of particles and bubbles increases. However, when the stirring speed is too high, the stability of the separation area and the foam area is destroyed, and the existence time of the bubbles becomes shorter, resulting in that the mineral particles have not been floated out. At this time, the bubbles burst, so that the flotation mineral particles are reduced, and the flotation recovery is reduced. It can be seen from the above analysis that the optimal stirring speed is 1600 r/min.

float, and the recovery is low; when the aeration is large, the bubbles will entrain the slurry and overflow, and the merger rate of the bubbles will increase. Is not conducive to the increase of flotation recovery. It can be seen from Fig. 3 that under the conditions of pH 9 and stirring speed of 1600 r/min, the flotation recovery first increases and then decreases with the increase of the aeration volume. When the aeration volume reaches 60 mL/min, the flotation recovery reaches the maximum. If the aeration volume continues to increase, the flotation recovery would decrease. This is because flotation is a complex process with solid, liquid, and gas three phases. When the aeration volume increases, the gas holdup in the solution increases. This increases the probability of contact between mineral particles and bubbles. It is easier for mineral particles to be brought out to the surface of the solution, which is conducive to collection. Therefore, the recovery increases. However, when the amount of aeration volume is too large, it is possible that the mineral particles may contact the agent. The performance is reduced, a small amount of minerals are entrained by bubbles, and most of the minerals cannot be brought out, so the recovery is reduced. From the above analysis, it can be seen that the aeration volume of the optimized flotation test is 60 mL/min.

Effect of Aeration Volume on Flotation Recovery The amount of aeration is also one of the important parameters that affect the flotation recovery [9]. Whether the ore particles can be floated is to use the collision of bubbles and the ore particles to adhere, and then the ore particles are floated out. The aeration is small, the gas content of the slurry is low, the probability of collision between ore particles and bubbles is low, there are few ore particles that

Effect of Solution pH on Flotation Recovery The pH of the solution has a greater impact on the wettability and electrical properties of the mineral surface, and affects the existence of the collector in the aqueous solution, thereby affecting the mineral flotation recovery. When the amount of collector is 60 mg/L, the stirring speed is 1600 r/min, and the aeration rate is 60 mL/min, the effect of the

Collection and Selectivity Contrast of Propyl Gallate …

Fig. 4 Effects of pulp pH on flotation recovery of diaspore and kaolinite

pH of the solution on the recovery of diaspore and kaolinite is shown in Fig. 4. It can be seen from Fig. 4 that with the increase of pH, the flotation recovery of diaspore first gradually increases and then decreases. Under the condition of pH = 9, the flotation recovery reaches the maximum, 81.35% and 84.05%, respectively. When using sodium oleate as a collector to float kaolinite, the flotation recovery of kaolinite also increases slowly with the increase of pH, and then decreases. Under the condition of pH = 9, the recovery reaches the largest, and when propyl gallate is used as a collector, the flotation recovery of kaolinite does not increase with the increase of pH, which indicates that the propyl gallate collector has a better effect on kaolinite pH has little to do with it.

Effect of the Amount of Collector on Flotation Recovery When the stirring speed is 1600 r/min, and the aeration rate is 60 mL/min, the effect of the amount of collector on the recovery of diaspore and kaolinite is shown in Fig. 5. It can be seen from Fig. 5 that when sodium oleate or propyl gallate is used as a collector, as the concentration of the agent increases, the recovery of diaspore increases gradually, but when the concentration of the reagent reaches 60 mg/L, its growth trend tends to be flat. Considering economic benefits, 60 mg/L is the best dosage. However,

39

Fig. 5 Effects of the amount of collector on flotation recovery

under the condition of sodium oleate as a collector, the recovery of kaolinite increases with the increase of the concentration of the agent, and the increasing trend tends to be flat after 80 mg/L. When propyl gallate is used as a collector, the concentration of the reagent has almost no effect on the recovery of kaolinite. Therefore, it can be concluded that propyl gallate is more selective to diaspore.

Wettability Analysis It can be seen from Fig. 6 that both the collector PG and NaOL could increase the hydrophobicity of diaspore. The contact angle of diaspore treated with NaOL increases with the increase of pH, reached a maximum of 89.87° at pH 9, and then decreases. The contact angle of diaspore treated with PG has the same trend as that of treated with NaOL as a function of pH, and the maximum contact angle of 89.38° was reached at pH 9. For kaolinite, it is worth noting that the collector NaOL treating increases its contact angle in the investigated pH range, while the collector PG treating increases its contact angle under acidic conditions, but decreases under alkaline conditions. The contact angle of kaolinite treated with NaOL reached a maximum of 29.25° at pH = 9, higher 3° than the raw kaolinite. The contact angle of kaolinite treated with PG at pH 9 as only 20.5°, lower 6.25° than the natural kaolinite. Therefore, the collector PG could improve the hydrophobicity difference of diaspore and kaolinite, which is the reason for the better flotation selectivity of PG than NaOL.

40

Y. Wu et al.

Fig. 6 Contact angles of diaspore and kaolinite before and after treated with collectors

Conclusions 2.

Flotation experiment results illustrate that the optimum flotation conditions of PG for diaspore are as follows: the stirring speed 1600 r/min, inflating volume 60 mL/min, pH = 9, collector dosage 60 mg/L, and flotation time 6 min. Under the optimum conditions, the flotation recovery of diaspore is 87.28%. Under the same conditions, no matter what kind of collector is used, the recovery of diaspore was found to be above 80%, while the recovery of kaolinite was 23.35% and 43.58% using PG and NaOL as collectors, respectively. The collector PG has better selectivity for diaspore than NaOL, since the hydrophobicity difference of diaspore and kaolinite treated with PG was greater than that treated with NaOL.

3. 4.

5.

6.

7.

8. Acknowledgements The authors acknowledge the financial support of the National Natural Science Foundation of China (No. U1704252), Program for Innovative Research Team (in Science and Technology) in the University of Henan Province (No. 19IRTSTHN028), and Scientific Research Start-up Project of Zhengzhou University (No. 32211159).

References 1. Jiang Y R, Zhou L Y, Zhou X H, et al (2010). Novel condensed ring carboxylic hydroxamic acid studied in the flotation behavior of

9.

diaspore and aluminosilicates. Sep. Sci. Technol., 45(16): 2475– 2480. Sun, W., Ouyang, K., Zhang, L., et al (2010). Preparation of hydrolyzate of hogwash oil(HHO) and its application in separation diaspore from kaolinite. Miner. Eng., 23, 670–675. Liu S, Hu Y, Qin W (2012) Study on the accelerant to the sodium oleate during bauxite flotation. Eng Sci, 2:006. Dou kali M, Patel R B, Stepanov V, et al (2017). The effect of ionic strength and pH on the electrostatic stabilization of nano RDX. Propellants, Explos., Pyrotech., 45(9): 1066–1071 F Lyu, Sun W, et al (2019). Adsorption mechanism of propyl gallate as a flotation collector on scheelite: A combined experimental and computational study. Miner. Eng., 133: 19–26. Zhang N, Nguyen A V, Zhou C (2018). Impact of interfacial Al-and Si-active sites on the electrokinetic properties, surfactant adsorption and floatability of diaspore and kaolinite minerals. Miner. Eng., 122: 258–266. Deng L, Wang S, Zhong H, et al (2016). A novel surfactant 2-amino-6-decanamidohexanoic acid: Flotation performance and adsorption mechanism to diaspore. Miner. Eng., 93:16–23. Gui Xiahui, Liu Jiongtian, Cheng Gan, et al (2012). Effect of energy input on coal flotation process. J. Cent. South Univ., 43(6): 2076– 2083. Gao S L, Wei D Z, Fang P, et al (2009). Effect of aeration quantity on separation of low-grade bauxite by cyclone-reverse flotation. J. Northeast. Univ., 30(1): 141–144.

Effect of High Shear Agitation on Surface Properties of Diaspore and Kaolinite Shichong Yang, Wencui Chai, Yijun Cao, and Huaxia Li

Abstract

Introduction

Silicate minerals (such as kaolinite) are common gangues in diaspore type bauxite, which are easy to be mudding and adhered to the diaspore surface in the flotation system, thus affecting the flotation recovery. Fluid flow enhancement with agitation is one of the more effective ways to improve the dispersion of aluminum–silicate minerals and reduce flotation entrainment. Whether high shear agitation could also change the surface properties of mineral particles was investigated through dispersion experiment of diaspore and kaolinite slurry in this paper. The results show that a high turbulence environment was beneficial to enhance the mass transfer of reagents and change the surface properties of mineral particles. With the increase of stirring strength, the contact angle and zeta potential of two minerals were increased at the same dispersant dosage, and the dispersion of two minerals was further improved. Keywords




Diaspore Kaolinite properties




High shear agitation




Surface

W. Chai (&)
Y. Cao Henan Province Industrial Technology Research Institute of Resources and Materials, Zhengzhou University, Zhengzhou, 450001, China e-mail: [email protected] Y. Cao e-mail: [email protected] S. Yang
Y. Cao
H. Li School of Chemical Engineering, Zhengzhou University, Zhengzhou, 450001, China

Diasporic bauxite is the primary mineral resource of alumina production in China. With the growth of the alumina industry, the supply problems of high-grade bauxites become increasingly severe [1]. In order to ensure continuous growth for the alumina industry, the utilization of low-quality bauxite has been a special focus in China [2]. As an efficient method of enrichment, flotation has been proven to be particularly suitable for upgrading of low-quality bauxite in term of flexible operation, low environmental pollution, low equipment cost, and comprehensive use of resources [3, 4]. Silicate minerals (such as kaolinite) are common gangues in diaspore type bauxites, which are easy to form muds and adhere to the diaspore surface in the flotation system [5, 6]. This affects the flotation recovery adversely. The operation of stirring and mixing the slurry is the starting point for the bauxite flotation process, this operation can promote the adhesion of minerals and reagents, prevent the agglomeration of particles and scrub the surface of bauxite [7]. Pulp blending is part of the key factors affecting flotation efficiency [8]. For low-quality bauxite, the purpose of shear mixing is to fully expose the fine bauxite particles, on the other hand, to promote the slurry and chemicals to fully disperse and achieve operational contact [9]. In this work, it was systematically investigated whether high shear agitation could also change the surface properties of the mineral particles. For this purpose, a set of dispersion experiment of diaspore and kaolinite slurries were conducted. The results show that a highly turbulent environment is beneficial to enhance the mass transfer of reagents and change the surface properties of mineral particles. With increasing stirring intensity, the contact angle and the zeta potential of two minerals are increased at the same dispersant dosage, and the dispersion of the two minerals can be further improved.

© The Minerals, Metals & Materials Society 2021 L. Perander (ed.), Light Metals 2021, The Minerals, Metals & Materials Series, https://doi.org/10.1007/978-3-030-65396-5_7

41

42

Experiments Materials and Reagents The single mineral samples of diaspore and kaolinite used in this study were originated from Henan Province of China. The typical chemical and mineralogical compositions of the samples were determined by X-ray diffraction (XRD) and X-ray fluorescence (XRF), the XRD spectra is shown in Fig. 1 and the chemical analysis results are presented in Table 1. The sodium hexametaphosphate (SHMP) used in this study was analytical reagent (AR) and acted as a dispersant [10, 11]. The hydrochloric acid (HCl) and sodium hydroxide (NaOH) were chemically pure and acted as pH regulators [12]. Distilled water was used in all of the tests and the pH was adjusted to 9.

Experimental Methods The difficulty of realizing efficient mineral dispersion and slurry blending mainly lies in: on the one hand, how to expose the fresh surface of fine minerals, and on the other hand, how to fully disperse the slurry and medicament and achieve effective contact between them. The above objectives need to restrain the aggregation of mineral particles and expose more active sites through the chemical force of high shear fluid, so as to promote the effective contact between the ore and the reagent, which can improve the hydrophobicity and floatability of minerals. The apparatus for mixing which was used in this set of experiments was the stirring accessories of a Malvern Mastersizer 3000 (Malvern Panalytical Ltd., Malvern, UK), and the range of speed (n) is 0–3000 rpm. The turbidity of the slurry was measured by TL-2300 turbidimeter (NASH Ltd., USA). The zeta potential of the slurry was obtained by Malvern Zetasizer nano series (Malvern Panalytical Ltd., Malvern, UK). The particle size distribution of the slurry was acquired by a Malvern Mastersizer 3000. The static

Fig. 1 XRD patterns of the diaspore (left) and kaolinite (right) samples

S. Yang et al.

contact angle of the slurry was measured using a JC2000D model Contact Angle Goniometer (Powereach.com, China) by the sessile drop method.

Results and Discussion Effect of Stirring Intensity on Contact Angle of Mineral Particles The changes of hydrophilicity and hydrophobicity of diaspore and kaolinite are mainly characterized by the contact angle. The larger the contact angle of mineral particles, the easier the collector adsorption and the higher the flotation selectivity. The contact angle of minerals after mixing was tested as a function of rotation speed, and the results when the dosage was 0.06 kg/t are presented in Fig. 2. The foremost reason for the observed trend is that the mineral particles are activated in a highly turbulent environment. The strong fluid shear forces can expose fresh mineral surfaces and promote the interaction between minerals and reagents. For kaolinite, the static contact angle increases with the increase of stirring intensity at the same reagent level. For diaspore, the static contact angle decreases with the increase of stirring intensity. This is because the shear flow field provided by intense stirring, the shear stress around the particles has obvious turbulent characteristics, that is, the force changes with time and has pulsation. As a result, the movement of particles in the fluid environment changes, and the particles rotate due to the velocity circulation imposed by the flow field, leading to the change of the trajectory. The rotation force and transverse force act on the surface of mineral particles, which restrain the aggregation of mineral particles, and expose more active sites that can contact with reagents on the surface of mineral particles, thus changing the hydrophilicity and hydrophobicity of mineral surface significantly. The opposite trends in contact angle as influenced by rotation speed for the two minerals also indicates that stirring slurry mixing increases the difference of surface

Effect of High Shear Agitation on Surface Properties … Table 1 Chemical composition analysis results of the diaspore and kaolinite samples

43

Sample

Al2O3

Fe2O3

TiO2

CaO

K2O

A/S

Diaspore

54.53

1.67

0.84

2.58

0.27

0.30

32.65

Kaolinite

27.03

29.79

0.34

1.26

0.28

0.01

0.91

SiO2

Fig. 2 Contact angles of the diaspore and kaolinite samples with different stirring intensity

Fig. 3 Zeta potential of the diaspore and kaolinite samples with different stirring intensity

hydrophobicity between target minerals and non-target minerals in the actual flotation process, which is conducive to the flotation process.

The reason is that the stronger the chemical force of the shear fluid on the mineral surface is, the more active sites are exposed, and the greater adsorption chance of the reagents onto the mineral surface, and the increase of the absolute potential value. Furthermore, the electrical repulsion between particles is enhanced, which makes the particles exist as monomers in water and improves the dispersion, which is an effective path to realize the dispersion of flotation slurry. Therefore, for the fine particles, the greater the specific surface effect, the more need to strengthen the dispersion and slurry mixing before flotation.

Effect of Stirring Intensity on Zeta Potential of Mineral Particles According to DLVO theory, due to the existence of electrical properties on the mineral surface, an electric double-layer structure and a solid hydration layer are formed on the mineral surface. These coordination ions and polar water molecules are closely and orderly arranged on the mineral surface, which hinders or repels the interaction between the non-polar molecules and the mineral surface and hinders the adhesion on the mineral surface. By reducing the surface potential of minerals, the above repulsion can be weakened and the adsorption capacity of reagents on the surface of minerals can be enhanced. When the zeta potential is low, the diffusion layer of the electric double layer on the mineral surface is also thin, and the hydration of the mineral surface is weak, which is beneficial to improve the hydrophobicity and floatability of bauxite. Figure 3 shows the relationship between the zeta potential of diaspore and kaolinite surface as a function of the stirring intensity, the SHMP was 0.06 kg/t. With the increase of stirring intensity, the absolute value of the zeta potential on the mineral surface gradually increases.

Effect of Stirring Intensity on Slurry Turbidity Turbidity can be utilized to characterize the dispersion of solid particles in a slurry. The higher the turbidity is, the easier it is for the particles to disperse to form a stable suspension. The decrease of turbidity indicates that agglomeration occurs between mineral particles, and the particles are not easily dispersed in the slurry. The procedure to measure the turbidity was as follows: after mixing for 5 min, the slurry was allowed to stand for 5 min, and then 30 mL of its supernatant was extracted to measure the turbidity. Figure 4 indicates the variation of turbidity of diaspore and kaolinite as a function of the stirring intensity. It can be observed that the turbidity of diaspore and kaolinite

44

S. Yang et al.

Fig. 4 Turbidity of the diaspore and kaolinite samples with different stirring intensity

increases with the increase of stirring intensity when dispersant dosage is 0.06 kg/t. This is because the dispersant sodium hexametaphosphate can effectively adsorb on the surface of the mineral particles, which makes it a significant negative potential, increases the electrostatic repulsion potential energy between particles and improves the dispersion of the slurry. At the same time, the macromolecular structure of sodium hexametaphosphate produces steric hindrance effects on the surface of the mineral particles, which significantly increases the steric repulsion potential energy between mineral particles and improves the dispersion. Therefore, with the increase of the stirring intensity, more active sites are exposed on the mineral surface, and the interaction efficiency between the reagent and the mineral particles is higher. In addition, under the same reagent concentration, the slurry turbidity will increase with the increase of stirring intensity, the highly turbulent fluid environment is likely to prevent the aggregation between broken particles.

Fig. 5 Particle sizes of the diaspore and kaolinite samples with different stirring intensity

This is because the dispersant sodium hexametaphosphate can effectively adsorb on the surface of the mineral particles, which makes it have a significant negative potential and increases the electrostatic repulsion between particles and reduces the particle size. At the same time, the macromolecular structure of sodium hexametaphosphate has a steric effect on the surface of mineral particles, which significantly increase the space repulsion potential energy between mineral particles, enhances the repulsion between mineral particles, and decreases the pulp size. In addition, with the increase of stirring intensity, more active sites will be exposed on the surface of minerals, and the interaction efficiency between reagents and the mineral particles is higher. Therefore, under the same dosage of reagents, the pulp particle size decreases with the increase of the stirring intensity, as the higher turbulence environment is likely to inhibit the aggregation of particles and also provides greater desorption force between particles.

Effect of Stirring Intensity on Mineral Particle Sizes

Conclusions The particle size of the mineral species in the slurry is one of the crucial factors affecting the flotation efficiency. Minerals are often in an aggregated state under natural conditions. Therefore, it was necessary to fully mix the minerals to break the aggregation between mineral particles and improve the dispersion of the slurry before flotation. The smaller the measured particle size of the blended mineral is, the better the mineral dispersion is. Figure 5 indicates the change in the particle size (expressed as D90) of diaspore and kaolinite as a function of rotation speed. It can be observed that the slurry particle size of diaspore and kaolinite decreases with the increase of stirring intensity.

The influences of high shear mixing on the surface properties of diaspore and kaolinite particles were characterized by measuring the contact angle, zeta potential, turbidity, and particle size of diaspore and kaolinite particles. The results demonstrate that the surface properties of particles are changed under high shear stress. (1) At the same reagent level, the surface contact angle of diaspore decreases with the increase of stirring intensity, while that of kaolinite increases with the increase of stirring intensity. That is to say, the difference of surface hydrophobicity between diaspore and kaolinite

Effect of High Shear Agitation on Surface Properties …

increases, which are conducive to the further mineral flotation process. (2) After adding dispersant sodium hexametaphosphate into the slurry, the stronger the shear fluid chemical force on the mineral surface, the more active sites exposed on the mineral surface, the greater the chance of contact and adsorption between the reagent and mineral surface, and the greater the absolute potential value. (3) As for the turbidity and particle size of pulp, better results can be obtained when the dosage of dispersant is 0.06 kg/t. The slurry turbidity increases with the increase of stirring intensity, while the pulp particle size decreases. In addition, the change of kaolinite is more significant under the same operating conditions. Generally speaking, in the process of high shear mixing, adequate energy input to provide a suitable fluid environment is conducive to the activation of mineral particles and the improvement of mineral floatability. Acknowledgements The authors acknowledge the financial support of the National Natural Science Foundation of China (Nos. U1704252 and 52004249), and Program for Innovative Research Team (in Science and Technology) in the University of Henan Province (IRTSTHN), and the Scientific Research Start-up Project of Zhengzhou University (No. 32211159).

References 1. Gibson, B., D.G. Wonyen and S. Chehreh Chelgani, A review of pretreatment of diasporic bauxite ores by flotation separation. Minerals Engineering, 2017. 114: p. 64–73

45 2. He, J., Q. Bai and T. Du, Beneficiation and upgrading of coarse sized low-grade bauxite using a dry-based fluidized bed separator. Advanced Powder Technology, 2020. 31(1): p. 181–189. 3. Rodrigues, O.M.S., et al., Kaolinite and hematite flotation separation using etheramine and ammonium quaternary salts. Minerals Engineering, 2013. 40: p. 12–15. 4. Hu, Y., P. Chen and W. Sun, Study on quantitative structure– activity relationship of quaternary ammonium salt collectors for bauxite reverse flotation. Minerals Engineering, 2012. 26: p. 24–33. 5. Jiang, H., et al., A comparison study of the flotation and adsorption behaviors of diaspore and kaolinite with quaternary ammonium collectors. Minerals Engineering, 2014. 65: p. 124–129. 6. Zhang, N., et al., Effects of particle size on flotation parameters in the separation of diaspore and kaolinite. Powder Technology, 2017. 317: p. 253–263. 7. Bubakova, P., M. Pivokonsky and P. Filip, Effect of shear rate on aggregate size and structure in the process of aggregation and at steady state. Powder Technology, 2013. 235: p. 540–549. 8. Bhutani, G. and P.R. Brito-Parada, A framework for polydisperse pulp phase modelling in flotation. Separation and Purification Technology, 2020. 236: p. 116252. 9. Neelakantan, R., F. Vaezi G. and R.S. Sanders, Effect of shear on the yield stress and aggregate structure of flocculant-dosed, concentrated kaolinite suspensions. Minerals Engineering, 2018. 123: p. 95–103 10. Wu, Y., et al., Dissolution kinetics and removal mechanism of kaolinite in diasporic bauxite in alkali solution at atmospheric pressure. Transactions of Nonferrous Metals Society of China, 2019. 29(12): p. 2627–2637. 11. Ramirez, A., et al., Sodium hexametaphosphate and sodium silicate as dispersants to reduce the negative effect of kaolinite on the flotation of chalcopyrite in seawater. Minerals Engineering, 2018. 125: p. 10–14. 12. Han, Y., et al., Interactions between kaolinite AlOH surface and sodium hexametaphosphate. Applied Surface Science, 2016. 387: p. 759–765.

Silicon Rich Iron Alloy from Bauxite Residue Halvor Dalaker and Casper van der Eijk

Abstract

The iron oxide (typically 20–50%) contained in bauxite residue (BR) can be recovered as pig iron. But this is not economically viable due to the low market price of pig iron. Silicon rich iron alloys have higher value than pig iron, and BR typically contains 5–15% silicon oxide. To increase the value of the produced metal, it is attempted to maximise the silicon content of iron alloys produced from BR. This option has been explored with experiments and thermodynamic models (FactSage) focusing on BR from one legacy site and three alumina refineries, obtaining a maximum of 17 wt.% Si in experimentally produced alloys. The paper discusses the thermodynamics around the results and looks at the influence of slag viscosity. Keywords

Bauxite residue




Circular economy




Thermodynamics

Introduction Production of aluminium metal also produces large amounts of bauxite residue (BR). This represents a potential environmental issue, since the BR is strongly alkaline, and a potential land use issue, as land availability is becoming limited in many regions. Moreover, it is an issue of resource inefficiency, since the BR contains many potentially useful materials, among them the oxides of iron and silicon. The iron oxide content of BR is typically 20–50%. From the perspective of waste utilisation, it is an attractive proposition H. Dalaker (&)
C. van der Eijk Department of Metal Production and Processing, SINTEF, Trondheim, Norway e-mail: [email protected] C. van der Eijk e-mail: [email protected]

to recover this material as iron, and this has been the focus of many studies [1, 2]. However, the resulting pig iron is of low value, which is the main reason why these processes have never been implemented industrially. High silicon iron is more valuable than pig iron. If the silicon oxide in the BR could be recovered as silicon alloyed with the iron in a silicon-rich alloy, this would mean a significant increase in the value of the product and a decrease in the amount of waste. This would have a meaningful positive impact on the business case and make the realisation of these processes more feasible.

Experimental Details and Methods Four types of BR qualities were used, three from operating bauxite refineries (BR A, C, & D) and one from a legacy site (BR B). The compositions of the materials are shown in Table 1. The materials were charged into a graphite crucible and heated in an open induction furnace to the target temperature (of 1650 or 1750 °C) with a gradient of 20–25 °C/min, and kept at the target temperature for 1 h. Slow cooling was achieved by shutting off the furnace and leaving the crucible inside. Three series of experiments were performed. A first, baseline series of experiments used BR and coke with no further fluxing at 1650 °C. The second series of experiments were fluxed with approximately 20 wt.% quartz fines, while the third series of experiments were fluxed with this same amount of quartz fines but run at an increased temperature of 1750 °C. The coking levels were set based on complete stoichiometric reaction of all iron and silicon in the system according to Fe2O3 + 3C = 2Fe + 3CO and SiO2 + 2C = Si + 2CO, respectively. The third experimental series also charged some charcoal on top of the rest of the charge, in order to possibly capture SiO-gas (see discussion below). An overview of the experiments is shown in Table 2. The coke

© The Minerals, Metals & Materials Society 2021 L. Perander (ed.), Light Metals 2021, The Minerals, Metals & Materials Series, https://doi.org/10.1007/978-3-030-65396-5_8

46

Silicon Rich Iron Alloy from Bauxite Residue Table 1 Material composition of the different bauxite residues. Simplified, normalised, measured by XRF

a

Table 2 Overview of experiments

47

Wt.%

BR A

BR Ba

BR C

BR D

CO2

2.1

18.9

2.4

3.4

Na2O

5.3

3.0

3.0

9.0

MgO

0.1

1.2

0.3

0.1

Al2O3

15.7

14.2

24.5

21.3

SiO2

8.6

13.6

7.6

12.5

CaO

5.9

17.4

9.2

4.5

TiO2

8.7

3.7

6.6

2.9

MnO

0.2

0.2

0.0

0.0

Fe2O3

53.3

27.8

46.4

46.2

Initial moisture content (%)

23

22

26

36

BR B is from a legacy site

Exp. # Series 1

Series 2

Series 3

BR

BR-amount (%)

T (°C)

1

BR A

92

1650

8

0

0

2

BR B

94

1650

6

0

0

3

BR C

93

1650

7

0

0

4

BR D

93

1650

7

0

0

5

BR A

74

1650

10

16

0

6

BR B

76

1650

8

16

0

7

BR C

74

1650

9

17

0

8

BR D

74

1650

10

16

0

9

BR A

68

1750

9

15

8

10

BR B

69

1750

8

15

9

11

BR C

67

1750

8

16

8

12

BR D

68

1750

9

15

8

had a fixed carbon content of 87.7 wt.%, the quartz was more than 99.2 wt.% SiO2. The metallic phase was analysed for silicon content after the experiments.

Coke (%)

Quartz (%)

Charcoal on top (%)

Results and Discussion Silicon Levels

Thermodynamic Modelling Thermodynamic modelling with FactSage 7.3 was used in preparation of experiments and interpretations of results. Data from FACTSteel was used for the liquid metal phases, while the slags and oxide phases used FACTOxide database. The viscosities of slags were calculated using the viscosity module of FactSage 7.3.

After each experiment, the crucibles with contents were sawn in two. Sometimes the slag and metal phases separated easily, as shown in the cross section in Fig. 1a but sometimes they did not, as shown in Fig. 1b. It is qualitatively remarked that the level of slag–metal separation appeared to increase with Na-content of the solidified slag. Since material was lost in the cutting process, it was not possible to reliably quantify the amounts of metal and slag obtained.

48

H. Dalaker and C. van der Eijk

Fig. 1 Cross-section of the graphite crucible showing the metal and slag phases from experiment No. 4 (a) and No. 9 (b) Table 3 Si-levels in the metal phases as measured by XRF, together with theoretical Si-levels as calculated by Factsage for the low and high carbon cases (wt. %) Exp. #

Si, exp Si, thermo-dynamic equilibrium

1650 °C, fluxed

1650 °C, unfluxed 1

2

3

4

5

1.0

1.8

1.0

0.8

2.7 0.09

PA-S > PA-C (Fig. 1). Neutralization reaction was buffered closer pH 8–9, which in the Bio-S occurred at the 14th day (336 h) and at the 21st day

(504 h) in PA-S. In Bio-C treatment, pH was buffered at *9 after 4 h and maintained until the 63rd day, while PA-C pH only reached equilibrium around 10 after 56th day (1344 h). The obtained pH values indicated that the biogenic acids were most effective in reducing BR’s alkalinity that their pure ACS grade equivalents. The observed EC behavior was similar to pH. During the reaction time, the EC of Bio-S treatment was greater than the PA-S one, as well as Bio-C when compared with PA-C. Bio-S EC reached maximum value (39 mS cm−1) at 14th day (336 h), however a sharp decrease occurred after 55 days until the end of the experiment. PA-S and Bio-C EC behavior were quite similar after the 14th day (*15 mS cm−1) while PA-C treatment showed the lowest EC after the 63rd day (10 mS cm−1). The lowest EC found in the citric acid treatments (Bio-C and PA-C) can be associated with metal complexation processes forming non-anionic organominerals [15]. Regarding ionic strength (IS), Bio-S had the highest value, which can be associated with the magnesium ions (Mg2+) present in the bacterial culture broth composition. The lowest pH, and highest EC and IS values of Bio-S suggest that this acid has a greater potential to neutralize the BR, due to the contribution of ionizable species, from 1st to 2nd ionization of H2SO4 (pKa < 1) and HSO4− (pKa = 1.92) [16] and from other sulfur compounds, such as thiosulfate, polysulfides, higher polythionates, sulfite, and sulfide, generated during incomplete oxidation of S0 by At. thiooxidans. Besides these ionizable chemical species derived from sulfur incomplete oxidation, additional contribution to pH buffering can be found in anionic species (sulfate, chlorate, phosphate) also present in the culture broth, that act in solid-liquid mechanism interactions, with an re-precipitation of ionic species such as: OH , CO32−/ HCO3−, Al(OH)4−/Al(OH)3, and H2SiO42−/H3Si4− of liquid phase and dissolution of BR solid phase [14].

Chemical and Mineral Composition of Untreated and Acid-Treated BR Solid Phase The chemical composition of the BR sample used in this study is describe in the Table 2. BR major elements concentrations were Fe2O3 (wt%, 40.8), Al2O3 (wt%, 17.32), SiO2 (wt%, 14.01), and Na2O (wt%, 9.68). Sodium (Na) content was mainly related to sodium aluminate silicate phases known as desilication product (DSP), which is formed during the Bayer process bauxite digestion stage. A small sodium content may also be related to the remaining Bayer liquor, although this specific BR sample was processed by a press filter to remove the excess of moisture. The chemical composition of BR was similar to the previously reported [3, 17].

Bauxite Residue Neutralization Potential Using Biogenic … Table 1 pH and EC values (average of 4 replicates followed by standard deviation), in supernatants of the BR treated with biogenic sulfuric acid (Bio-S), biogenic citric acid (Bio-C), ACS grade sulfuric acid (PA-S), and ACS grade citric acid (PA-C). Ionic strength (mol L−1) according to Eq. 1

Treatments

55

pH 1st minute

63rd day

EC 25 °C (mS cm−1)

IS Ionic Strength (mol L−1)

1st minute

1st minute

63rd day

63rd day

Bio-S

4.68 ± 0.12

8.03 ± 0.03

13.76 ± 0.12

27.99 ± 5.57

0.18

0.36

PA-S

6.13 ± 0.36

9.39 ± 0.07

4.79 ± 0.1

13 ± 0.32

0.06

0.17

Bio-C

6.85 ± 0.11

9.44 ± 0.27

4.09 ± 0.51

13.13 ± 1.62

0.05

0.17

PA-C

10.51 ± 0.1

10.5 ± 0.2

2.1 ± 0.1

7.9 ± 0.4

0.03

0.10

BR-DI

12.14 ± 0.06

12.01 ± 0.95

3.19 ± 0.21

6.59 ± 0.91

0.04

0.09

Fig. 1 pH and EC evolution (hours) in the supernatants of BR treated with biogenic sulfuric acid (Bio-S), biogenic citric acid (Bio-C), ACS grade sulfuric acid (PA-S), and ACS grade citric acid (PA-C)

Table 2 XRF elemental composition (%wt) of the remaining BR solid fractions after treatment with biogenic sulfuric acid (Bio-S), biogenic citric acid (Bio-C), ACS grade sulfuric acid (PA-S), and ACS grade citric acid (PA-C), after one minute and 63 days, compared with untreated BR

Oxides (wt%)

a

BR

BR-DI 1st min

Bio-S 63rd day

1st min

PA-S 63rd day

1st min

Bio-C 63rd day

1st min

PA-C 63rd day

1st min

63rd day

Na2O

9.68

8.73

10.52

6.70

6.29

7.48

8.30

8.22

8.78

7.97

9.62

MgO

–

–

–

0.51

1.19

–

–

–

–

–

–

Al2O3

17.32

18.72

20.60

20.67

18.99

20.34

19.78

20.27

20.34

18.91

20.01

SiO2

14.01

14.79

16.81

15.54

15.43

15.74

15.75

16.07

16.25

14.99

15.88

SO3

0.14

0.15

–

2.13

2.89

0.50

0.43

0.18

–

0.15

–

CaO

1.43

1.36

1.37

0.79

0.98

1.13

1.19

1.20

1.32

1.29

1.33

TiO2

5.93

5.35

5.84

5.37

5.29

5.64

5.51

5.39

5.29

5.36

5.42

V2O5

0.16

0.14

–

0.15

–

0.15

–

0.14

–

0.14

–

MnO

0.12

–

–

–

–

–

–

–

–

–

–

K2O

–

–

–

–

0.12

–

–

–

0.10

–

–

P2O5

0.11

–

0.10

–

0.12

–

0.11

–

0.12

–

0.13

Fe2O3

40.8

40.01

39.46

37.95

36.58

39.17

38.73

39.07

36.33

38.43

37.62

ZrO2

0.92

0.76

0.86

0.81

0.79

0.83

0.82

0.79

0.73

0.79

0.82

LOIa

9.12

9.64

4.44

9.01

11.33

8.65

9.37

8.29

10.75

11.60

9.19

LOI loss of ignition

56

Fe2O3, Al2O3, and SiO2 concentrations of BR after acid treatments were similar to untreated BR. Na2O (wt%) of Bio-S ranged from 6.70 to 6.29, PA-S (7.48–8.30), Bio-C (8.22–8.78), PA-C (7.97–9.62), BR-DI (8.73–10.52), and BR (9.68). PA-S sample exhibited a slight increase in Na content at the 63rd day possibly due to NaSO4 precipitation, while Na increase in the Bio-C and PA-C samples could be attributed to metal complex formation. Bio-S sample had greatest Na dissolution (*35%) while PA-C had the lowest (0.6%). These results indicated that biogenic sulfuric acid was the most effective treatment in reducing BR alkalinity, since DSP is a significant source of alkalinity. Therefore, it can be suggested that biogenic sulfuric acid associated with sulfur anionic species and magnesium (Mg) (originated from the culture broth) contributed with the exchangeable sodium cations in sodalite cage [18]. Detected sulfur (S), potassium (K), magnesium (Mg), and phosphorus (P) elements found in the Bio-S treatments were probably remaining from the bacterial medium broth (Table 2). Mineralogy of untreated and acid-treated BR is shown in Fig. 2. XRD diffractograms revealed that the total iron content was associated with the hematite (Fe2O3) and goethite (FeOOH) phases, whereas the aluminum (Al), silicon (Si), and sodium (Na) were associated at sodalite (Na6(AlSiO4)6.Na2X.nH2O), where X: SO42−, CO32−, OH-, Cl− and n = 0 at 4, and one little fraction of Al and Si was associated to gibbsite (Al(OH)3) and quartz (SiO2). Mineralogy of both biogenic and pure acid-treated BR showed the presence of the same minerals with very few variations in the diffractogram peak intensities. Despite XRD Fig. 2 XRD diffractograms of untreated BR and remaining BR solid fractions after treatment with biogenic sulfuric acid (Bio-S), biogenic citric acid (Bio-C), ACS grade sulfuric acid (PA-S), and ACS grade citric acid (PA-C), after one minute and 63 days

P. M. P. Silva et al.

is mostly a qualitative method, when comparing Bio-S with untreated BR, the sodalite peak of 2h = 40.02° and d = 2.6 Å reduced its intensity, but the principal main peaks (2h = 16.01°, d = 6.4 Å) and (2h = 28.01° and d = 3.66 Å) remained unaltered. Beside the sodalite, quartz related peak intensity (d = 3.34 Å) decreased after 63 days in Bio-S treatment. These modifications were not observed for the PA-S, Bio-C, and PA-C samples. The reduction of sodalite peak intensity and the low ordering crystallinity of quartz may be an indicative that biogenic sulfuric acid promoted some effect in the crystalline structure of the sodalite and quartz. As described by [18], this effect can be explained by sodalite framework, which consists of alternating Si-O-T units (T = Si or Al) constructed from SiO4 and AlO4 tetrahedra. The arrangement of these tetrahedra is such that the SOD structure contains a negative charge in the cage. Thus, to obtain electrical neutrality it is necessary the presence of cations to balance the negative charge. As reported by Peng et al. [18], these cations are located at sites S1 and S2, where cations at S2 can be easily exchanged for other ions. Therefore, the reduction of sodalite peak can be associated with the exchanged cations in sodalite S2 site, since ionic ratio of Mg2+ ion 0.86 Å, from culture broth, is lower than sodium ionic ratio of 1.16 Å. Besides, sulfur anions (S2O32−, S4O62 − , HS−, Sx2−, and SnO62−), H3O+ and SO42− from biogenic sulfuric acid can promote the ion exchange capacity of sodalite cage. For the quartz, sulfuric acid promoted silica delamination resulting in a decrease of the diffractogram peak.

Bauxite Residue Neutralization Potential Using Biogenic …

57

Morphological Analyses of BR After Acidic Treatments

A. niger and At. thiooxidans culture broths, as also observed in the solid BR characterization previously described. All treatments supernatants, including the blank sample (BR-DI), showed Na concentrations above 500 mg L−1 in solution. For Bio-S, Na concentration increased from 3472 mg L−1 in 1st minute to 5172 mg L−1 in 63rd day, which can be estimated that 67% of Na into solution after final reaction. Sodium percentage values corroborate with Na oxides value (35%) obtained from XRF analyses of solid phase. Sodium concentration increased in all treatments at the 63rd day, this can be associated with a precipitation/dissolution reaction affected by pH. For example, the PA-C sample exhibited the highest pH within treatments, therefore it showed the lowest Na concentration. Although Bio-C and PA-S samples exhibited similar pH values, Na concentration of Bio-C was higher than PA-S. This can be explained by the differences in acids’ strength of organic and inorganic acids. Magnesium concentration slightly decreased from 4675 to 4404 mg L−1 after 63 days reaction. Results reported here are another indicative to the hypothesis of exchanging cations of sodalite cage [18] since the Mg decreased in solution along time while Na increased. Sodium concentration of PA-S sample was smaller than Bio-S. Biogenic sulfuric acid was more effective than its pure ACS grade equivalent in the dissolution of solids alkaline from aluminosilicates and in the neutralization of alkaline species, e.g. free soda [19]. This can be associated with the high ionic potential of biogenic acid due to the contribution of ions and ionizable chemical species from biogenic source. Comparing Na concentration between Bio-C and PA-C, the biogenic acid was more effective in the dissolution of the solid fraction that the analytical equivalent resulting in a higher Na concentration in the supernatant.

SEM micrographs of acidic treated BR after 1 min and 63 days are shown in Fig. 3a–j. Untreated BR (Fig. 3a) exhibited the prevalence of small particles aggregates, such as sodalite, also observed in the PA-S sample (Fig. 3e–f) and PA-C samples (Fig. 3i–j). In the Bio-S sample, EDS analyses were performed (1st minute) and Mg was identified in the grain, associated with Fe, Al, Na, Si and O elements (Figs. 3c and 4). BR after biogenic citric acid treatment (Fig. 3g–h) showed a “spongious” aspect in the crystal structure. Reyes et al. [19] evaluated the synthesis of low silica zeotypes by hydrothermal transformation of kaolinite-rich clay and the nucleation and growth process of sodalite and cancrinite in the system Na2–Al2O3–SiO2–H2O and showed that sodalite grows with spherical aggregates out onto the surface. Thus, it can be inferred that during treatment with biogenic sulfuric acid (Bio-S) a partial dissolution of the sodalite phase may occurred. These results agree with other analytical results obtained in this study, such as sodium decrease observed by XRF, reduction in the intensity peak of XRD, and increase of sodium into liquid phase (supernatant).

Chemical Composition of BR Supernatants After Acid Treatments Table 3 describes the major elements concentration after 1st min and 63 days BR treatment with the biogenic and pure acids. Aluminum, Ca, Na, and Si were solubilized from BR, whereas Mg, K, and copper (Cu) were probably derived from

Fig. 3 SEM micrographs of a BR untreated; b BR + H2O; c Bio-S (1st minute); d Bio-S (63rd day); e PA-S (1st minute); f PA-S (63rd day); g Bio-C (1st minute); h Bio-C (63rd day); i PA-C (1st minute) and j PA-C (63rd day)

58

P. M. P. Silva et al.

Fig. 4 SEM and EDS micrographs of Bio-S (1st minute)

Table 3 Chemical composition (ICP-OES) of major elements (mg L−1) in the BR acid treatments (Bio-S, PA-S, Bio-C, and PA-C) and blank sample (BR-DI) supernatant (liquid phase) after 1st min and 63 days reaction incubation

Elements

Reaction time

Concentration (mg L−1) BR-DI

Bio-S

PA-S

Bio-C

PA-C

117.7

51.6

3.0

625.6

153.1

Al

1st min 63rd day

350.9