Beneficiation of Phosphates: Sustainability, Critical Materials, Smart Processes [1 ed.] 9780873354752, 9780873354745

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BENEFICIATION

OF PHOSPHATES

SUSTAINABILITY CRITICAL MATERIALS SMART PROCESSES

Edited by: Patrick Zhang I Jan Miller I Guven Akdogan I Ewan Wingate I Neil Snyders

BENEFICIATION

OF PHOSPHATES SUSTAINABILITY CRITICAL MATERIALS SMART PROCESSES

Edited by: Patrick Zhang I Jan Miller I Guven Akdogan I Ewan Wingate I Neil Snyders

PUBLISHED BY THE SOCIETY FOR MINING, METALLURGY & EXPLORATION Copyright © 2019 Society for Mining, Metallurgy & Exploration. All rights reserved.

Society for Mining, Metallurgy & Exploration (SME) 12999 East Adam Aircraft Circle Englewood Colorado 80112 (303) 948‑4200 / (800) 763‑3132 www.smenet.org The Society for Mining, Metallurgy & Exploration (SME) is a professional society whose more than 15,000 members represent professionals serving the minerals industry in more than 100 countries. SME members include engineers, geologists, metallurgists, educators, students, and researchers. SME advances the worldwide mining and underground construction community through information exchange and professional development. Information contained in this work has been obtained by SME from sources believed to be reliable. However, neither SME nor its authors and editors guarantee the accuracy or completeness of any information published herein, and neither SME nor its authors and editors shall be responsible for any errors, omissions, or damages arising out of use of this information. This work is published with the understanding that SME and its authors and editors are supplying information but are not attempting to render engineering or other professional services. It is sold with the understanding that the publisher is not engaged in rendering legal, accounting, or other professional services. If such services are required, the assistance of an appropriate professional should be sought. Any statement or views presented here are those of the authors and are not necessarily those of SME. Authors assumed the responsibility to obtain permission to include a work or portion of work that is copyrighted. The mention of trade names for commercial products does not imply the approval or endorsement of SME. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. ISBN 978‑0‑87335‑474-5 eBook 978‑0‑87335-475-2 Copyright © 2019 Society for Mining, Metallurgy & Exploration All Rights Reserved. Printed in the United States of America. Library of Congress Cataloging-in-Publication Data Names: Zhang, Patrick, editor. Title: Beneficiation of phosphates. Sustainability, critical materials and smart processes / edited by Patrick Zhang, Jan Miller, Guven Akdogan, Ewan Wingate, Neil Snyders. Description: First edition. | Englewood Colorado : Society for Mining, Metallurgy & Exploration (SME), [2019] | Papers of a conference held April 29-May 4, 2018 in Cape Town, South Africa sponsored by Engineering Conference International and others. | Includes bibliographical references and index. Identifiers: LCCN 2019018759 (print) | LCCN 2019020550 (ebook) | ISBN 9780873354752 () | ISBN 9780873354745 Subjects: LCSH: Phosphates--Purification--Congresses. | Extraction (Chemistry)--Congresses. | Ore-dressing--Congresses. | Phosphate minerals--Congresses. Classification: LCC TN538.P43 (ebook) | LCC TN538.P43 B47 2019 (print) | DDC 661/.43--dc23 LC record available at https://lccn.loc.gov/2019018759

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Contents

PREFACE  v

PART 1. SUSTAINABILITY AND THE ENVIRONMENT 1. Tailoring Collectors to Allow Sea Water Usage in Phosphate Beneficiation Lucas R. Moore, Guoxin Wang, Yu (Ryan) Xiong, James Gu. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. Purification of Phosphogypsum for Production of Calcium Sulfate Whisker Through Complete Chemicals Recycle Zeqiang Zhang, Yixin Shao, Hualin Sun, Patrick Zhang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3. Beneficiation of Dolomitic Phosphate Pebble by Triboelectrostatic Belt Separation Erich Dohm, Abhishek Gupta, Kyle Flynn. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4. Removal of Coarse Fraction from Phosphatic Clays for Clay Settling Area Reduction and Additional Phosphate Recovery Charles Guan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

5. Using Two Alternative Vegetable Oils as Apatite Collector

André Carlos Silva, Elenice Maria Schons Silva, Alex Malüe Machado, Diego Valentim Crescente Cara, Débora Nascimento Sousa. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

6. Purification of Phosphogypsum Using Environmentally Friendly Separation Devices

Wending Xiao, Patrick Zhang, Dapeng Zhang, Peng Liu, Zhengwei Li, Junjie Wu, Qian Yu, Zhangcheng Yu, Mei Yang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

PART 2. COMPREHENSIVE EXTRACTION AND SMART CHEMISTRY 7. A Novel Process to Recover Sulfur, Lime, and Rare Earths from Gypsum David van Vuuren, Johannes Maree. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

8. The Recovery of Rare Earth Elements from Phosphate Rock and Phosphate Mining Waste Products Using a Novel Heterogeneous Adsorption Polymer Joseph P. Laurino, Jack Mustacato, Zachary Huba, Patrick Zhang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

9. Latest Trend for Fluorine in the Phosphoric Industry: Absorption Efficiency Improvement, Conversion into Valuable Products Tibaut Theys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

10. Can Your P2O5 Be Commercially Exploited?

Michael E. Kelahan, M. Robert Kelahan, Ewan Wingate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

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iv Contents

11. How Phosphate Rock Quality Impacts the Phosphoric Acid Plant and Granulation Plant Operations Curtis Griffin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

12. Revisiting the Merseburg Process: Economic Opportunity and Environmental Benefit? Gary Albarelli. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

13. Recovery of Thorium from Phosphogypsum by Acid Leaching Tebogo Mashifana, Jessica Sebothoma, Thabo Falayi, Freeman Ntuli . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

PART 3. FLOTATION FUNDAMENTALS AND REAGENTS 14. History and Future of Phosphate Mining and Beneficiation in South Africa Marius Porteus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

15. How to Truly Optimize Phosphate Flotation, When Feed Grade Is Ever-Changing Lucas R. Moore, Guoxin Wang, Yu (Ryan) Xiong, James Gu. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

16. New Reagent Development for the Beneficiation of Various Phosphate Ores Pablo Dopico, Brandi Makin, Klaus-Ulrich Pedain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

17. Case Study for Processing Phosphate Ores Worldwide Guoxin Wang, Zhengxing (James) Gu, Yu (Ryan) Xiong, Lucas R. Moore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

18. Effect of Calcium Concentration on Calcite Flotation from Apatite Using Carbonic Gas Amanda Soares de Freitas, Elves Matiolo, Rafael Teixeira Rodrigues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

19. Alternative Depressant for Apatite Flotation

André Carlos Silva, Elenice Maria Schons Silva, Antonio Eduardo Clark Peres, Tobias Elwert, Débora Nascimento Sousa, Viviane Ovidio de Almeida. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

PART 4. ADVANCES IN PROCESSING TECHNOLOGY AND EQUIPMENT 20. Reducing MgO Content in Florida Phosphate Concentrate Patrick Zhang, Shibo Zheng, Wenyi Sun, Xiaoqing Ma, Jan Miller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

21. Influence of the Impeller Speed on Phosphate Rock Flotation André Carlos Silva, Elenice Maria Schons Silva, Fernanda Santos Andrade. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

22. Successful Applications of Vertical-Roller-Mills in Phosphate Processing Markus Stapelmann, Carsten Gerolda, Jonathan Smith. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

23. A Comparative Study of Different Column Sizes for Ultrafine Apatite Flotation

Elves Matiolo, Hudson Jean Bianquini Couto, Michelle Fernanda de Lira Teixeira, Renata Nigri de Almeida, Amanda Soares de Freitas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200

24. Phosphate Rock Production Increase Through the Milling of the Apatite Flotation Circulating Load

André Carlos Silva, Michelle Fernanda de Lira Teixeira, Bruno Palhares Milanezi, Anastácio Honório Pessoa de Melo Filho, Thiago Drumond Alvarez de Araujo, Wanderson Ferreira Borges Junior, Elenice Maria Schons Silva. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210



INDEX 221

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Preface

The price spike for rare earth elements (REEs) during the 2010–2011 period served as a impetus for reviewed research interest in recovery of REEs from secondary resources. Phosphate mining and processing streams, coal processing tailings and combustion ash, and some processing tailings from metallic ores have been identified as impor‑ tant secondary resources for REEs. This renewed research interest and the urgency to develop secured supply of REEs have prompted the establishment of Critical Materials Institute (CMI), an Energy Innovation Hub funded by the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office. CMI has been turned into a at least 10-year program with total federal funding of well over $200 million. Recently, the US DOE also initiated a research consor‑ tium focusing on recovery of REEs from coal. Phosphate is significant as a secondary resource for REEs due to its abundance (300 billion tons worldwide) and the fact that much of the REEs in the phosphate rock is dissolved in the phosphoric acid manufacturing process. Recovery of REEs from phosphate processing has been one of the important projects of CMI since its inception. This conference highlighted some findings of the CMI phosphate project. Research along this line is extensive in other parts of the world as well; the paper “A Novel Process to Recover Sulfur, Lime and Rare Earths from Gypsum” is a good example. Competition in the flotation reagent market started heating up in recent years. This stimulated innovative reagent development work. As a result, new reagents have been formulated and targeted at dolomite flotation, calcite flotation, more selective phosphate flotation, and even flotation in seawater. This series of conference always gave reagent suppliers the opportunity to highlight their research with little marketing flavor. The Florida phosphate industry now see some light at the end of the tunnel in terms of processing of the high dolomite reserves. Recent encouraging developments include new reagents that can float dolomite without using phosphoric acid as a phos‑ phate depressant, reducing MgO content in the “Crago” flotation concentrate thus allowing blending of some high-dolomite pebbles in the final product, and innovative gravity separation.

v Copyright © 2019 Society for Mining, Metallurgy & Exploration. All rights reserved.

vi Preface

2 2 2 2 The editors would like to express their appreciation for SME’s continued endorsement and publication of this book despite limited sales potential for such a highly special‑ ized book. Jane Olivier and her staff worked painstakingly editing the papers many of which were submitted in various formats. We are also grateful to the members of the conference organizing committee, the authors, technical session chairs, and the staff of Engineering Conference International for their efforts in making this conference a success, and for post conference production of this high quality book. We truly appreciate all the conference sponsors for their contributions. They include Blue Cube Systems (Pty) Ltd, Foskor (Pty) Ltd, Industrial Oleochemical Products (Pty) Ltd, Loesche, Minerals Engineering International, Multotec Process Equipment, Scantech International Pty Ltd, Stefanutti Stock, Ultimate Flotation, Weir Minerals Africa, and the FIPR Institute of Florida Poly. Foskor is also rec‑ ognized for making all the arrangements for a post conference tour of their mining operation, as well as their hospitalities.

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Conference Organizing Committee CHAIR

Patrick Zhang, Florida Industrial and Phosphate Research Institute,   Florida Polytechnic University, USA CO-CHAIRS

Jan Miller, University of Utah, USA Marius Porteus, Foskor, South Africa Guven Akdogan, Stellenbosch University, South Africa Ewan Wingate, WorleyParsons Services Pty Ltd, Australia Neil Snyders, Stellenbosch University, South Africa Laurindo Leal Filho, University of Sao Paulo, Brazil COMMITTEE MEMBERS

Gary Albarelli, FIPR Institute, USA Guven Akdogan, Stellenbosch University, South Africa Hassan El-Shall, University of Florida, USA Charles Guan, Mosaic, USA Paul Kucera, Mosaic, USA Salah Al-Thyabat, Al-Hussein BinTalal University, Jordan Hans Huckstedt, LL Namibia Phosphates, South Africa Chuncheng Wei, China Bluestar Lehigh Eng. Corp. Andrew James, Phosphate Australia Limited Lucas Moore, Arr-Maz Custom Chemicals, USA Margreth Tadie, Stellenbosch University, South Africa Jaisen Kohmuench, Eriez Magnetics, USA Hamid Mazouz, OCP Group, Morocco Wending Xiao, Wuhan Institute of Technology, China Zeqiang Zhang, Wuhan Institute of Technology, China Wenyi Song, China Bluestar Lehigh Eng. Corp., China

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Corporate Sponsors

Industrial Oleochemical Products (Pty) Limited

www.scantech.com.au

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PART 1

Sustainability and the Environment  1. Tailoring Collectors to Allow Sea Water Usage in Phosphate Beneficiation  3  2. Purification of Phosphogypsum for Production of Calcium Sulfate Whisker Through Complete Chemicals Recycle  11  3. Beneficiation of Dolomitic Phosphate Pebble by Triboelectrostatic Belt Separation  18  4. Removal of Coarse Fraction from Phosphatic Clays for Clay Settling Area Reduction and Additional Phosphate Recovery  28  5. Using Two Alternative Vegetable Oils as Apatite Collector  38  6. Purification of Phosphogypsum Using Environmentally Friendly Separation Devices  47

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CHAPTER 1

Tailoring Collectors to Allow Sea Water Usage in Phosphate Beneficiation Lucas R. Moore,* Guoxin Wang,* Yu (Ryan) Xiong,* James Gu*

ABSTRACT

undrinkable without desalination (Lambooy, 2011; WHO, 2011). Of the 3% of fresh water remaining, only 0.5% is available for consumption, ecological needs, and anthropogenic activities. The rest is inaccessible in glaciers and polar ice sheets. The World Health Organization (WHO) stated that approximately one third of the global population is affected by water scarcity. The Environmental Protection Agency (US-EPA) stated that in 2005 approximately four billion gallons of water, of which approximately 57% was fresh water, were used in oil and mining exploration and processing per day, (USGS, 2012). Many active mining and mineral processors are located in fresh water stressed regions such as Australia, Chile, the Middle East, South Africa, and western USA. Though much of the world’s phosphate deposits are located in regions where fresh water is plentiful, such as Florida, Brazil, and China; phosphate deposits are also in some of these fresh water stressed regions. An increase in water demand would significantly impact the already strained fresh water supply of these regions. This water supply shortfall has highlighted the need for possible usage of alternate water supplies in the processing of phosphate, and new collector innovations are necessary to make this possible.

Water supply is critical for ensuring optimal operation of any beneficiation plant. As ore quality continues to decline, the demand on water for mineral processing will only increase. Traditionally, ground and surface water sources have been extensively utilized for mining and beneficiation. In some regions, these sources are proving to be insufficient to meet the increasing demands of this industry, as well as the local municipal requirements. As a result, alternate water supplies must be considered. The purpose of this investigation was to develop a collector that allows for the flotation of phosphate in sea water, while still meeting the grade (>27.5% P2O5) and recovery (>80%) criteria. INTRODUCTION

Mineral processing is an extremely water intensive industry, with the demand on this water continuing to increase. This increase is due to declining ore grades, and processors becoming more reliant on these lower grades as their primary feedstock. Therefore, more tons of this feedstock must be processed to continue producing the same volume of concentrated good (Arroshola, 2010). However, the availability of fresh water does not increase in response to this increased demand. It is a limited and precious resource. More than 97% of the world’s water is seawater, which is * ArrMaz 3

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4

Sustainability and the Environment

Phosphate is one of the key components in mineral based fertilizers (i.e., diammonium phosphate) (ArgusMedia, 2014 & SRI Consulting, 2009). However, phosphate ore typically exists as a mixture of calcium phosphate, quartz, clay, carbonate, and various metal oxides. Before the phosphate mineral can be converted into a fertilizer component, it must be concentrated by removing the impurities that will limit performance of its conversion. A typical phosphate mineral concentrate will contain ~27–32% P2O5, 27.5% P2O5 (CaO/P2O5 = 1.61). Though this site averages a feed grade > 20% P2O5, grinding is necessary to achieve adequate liberation, which is thought to be P80 of ~500 microns (Figure 2). The feed possesses some calcite cementation, as well as 25% quartz (acid insoluble). This process operates at a neutral pH, which introduces additional challenges associated with using traditional chemistries. Challenges include the lack of activation of the chemistry, reaction kinetics, and cost of the collector. The most impactful water is in conditioning, as it is here that the reaction between the collector and the sparingly soluble calcium on the surface of the phosphate occurs. One route to achieve this task is to attempt to develop a collector that is more selective towards these coordination sites, versus those from the soluble salts associated with sea water. Another possibility is to develop a collector that can use the soluble ions in the water to assist with bridging the coordination to the phosphate (Moore, 2016-B). A performance basepoint was established for the impact of various water conditions on a new series

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Tailoring Collectors to Allow Sea Water Usage in Phosphate Beneficiation5

FIGURE 1.  Generic process flow sheet for the beneficiation of phosphate TABLE 1.  Water chemistry Water

TSS, mg/L

TDS, mg/L

Ca, %

Na, %

Calculated as % NaCl

Tap Water (Fresh)

2.0

300

0.0048

0.0016

0.0041

Tampa Bay Seawater

2.0

13,794

0.0249

0.53

1.35

36.0

24,980

0.0422

1.04

2.64

Not Analyzed

34,483

0.0400

1.06

2.69

Customer’s Potential Water (Seawater) Typical Seawater

    FIGURE 2.  Flotation feed, major components

of collectors, which was being developed for such an application (Figure 3). As expected, the collector (C) appeared to perform poorly when conditioned in fresh water, unless the product was saponified at a conditioning pH of 9. Interestingly, a higher grade and recovery were obtained when the collector was conditioned in Tampa Bay water. The development work continued with the application of water collected from Tampa Bay in the conditioners, and the listed water source for the flotation

water (Figure 4). When fresh water is applied in flotation, Collector B and C could yield a recovery greater than the 80% criteria, while still meeting the ≥27.5% P2O5 grade requirements, at a dosage of 0.7 kg/ton collector. At a dosage of 1.0 kg/ton, Collector C was actually able to achieve 88% recovery, with a concentrate grade of 27.5% P2O5. Increasing the dosage to 1.25 kg/ton did yield significant increases in recovery for all three collectors, but at the cost of grade. When Tampa Bay water was applied in flotation, with a

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6

Sustainability and the Environment

FIGURE 3.  Collector response to conditioning water chemistry (Collector C)

FIGURE 4.  Collector response to flotation water chemistry

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Tailoring Collectors to Allow Sea Water Usage in Phosphate Beneficiation7

FIGURE 5.  Grade and recovery response to dosage of tailor-made collectors

FIGURE 6.  Recovery response to flotation water

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8

Sustainability and the Environment

FIGURE 7.  Grade response to flotation water

1.0 kg/ton collector dosage, the grade was met, but recoveries did not meet the ≥ 80% criteria. Expanding on these learnings, a new collector was synthesized, and compared to Collector C on a new flotation feed sample (Figure 5). These experiments applied the water collected from the mine site in conditioning, and the water collected from Tampa Bay for the flotation water. Collector C met the grade target, and significantly improved recovery, by nearly 12 percentage points. Collector D achieved the grade target, increased recoveries, and required nearly 0.8 kg/ton less collector than C. This new collector is more aggressive, which is evident by its ability to reach a recovery of 98%, with a grade of 26% P2O5. Interestingly, the collectors appear to perform better when conditioning water possesses some ionic characteristics, as found in sea water (Tampa Bay water and potential mine water). However, performance of both collectors is better when fresh water is used in the float cell (Figure 6). Furthermore, this sensitivity to seawater being used in flotation is much less, in regards to recovery, when applying Collector D. This is evident by the recovery deltas between the two flotation water sources at a collector dosage of 1.18 kg/ton. As expected, the higher the collector

dosage and recovery, the lower the concentrate grade (Figure 7). Collector C could not achieve the recovery and grade criteria if seawater was applied to flotation. Collector D required the dosage increase from 0.55 to 1.18 kg/ton to make grade and recovery targets The incumbent collector produces a concentrate grade that meets the plant’s grade criteria, with a 1.61 CaO/P2O5 ratio. Collector D was able to reduce the calcium containing contaminants to a CaO/P2O5 ratio of 1.48, which is a further reduction of ~6.7% calcium containing contaminants (Figure 8). In improving the selectivity of the collector to allow for less recovery of such contaminants, the downstream effect at the phosphoric acid digester would yield reductions in both sulfuric acid and defoamer usage. A reduction in gypsum would also put less of a burden on the gypsum filtration, which can often be the rate limiting step at a phosphoric acid chemical plant. Upon further investigation into the mineralogical selectivity of Collector D, it was learned that the major and moderate species in the concentrate was apatite. The concentrate contained minor (27.5% P2O5 (28.2%) concentrate, but also yielded a 13 percentage point boost in recovery over the 80% target. This boost in recovery, when seawater was applied, did require an increase in collector dosage. However the revenue gain associated with the increase in recovery definitely makes this an economical option. Collector D exceeded the defined success criteria while applying seawater to the conditioners and flotation cells. Considering most phosphate processors have an

operational target of ~35% solids for their slurry entering flotation cells, using seawater would release 2.86 million tons of fresh water from mine consumption, for every 1 million tons of mineral entering the flotation cells. This will obviously change based on percent process water being recycled. Due to the potential contaminants associated with using seawater, such as chloride, there is still a probability that some fresh water would be required for rinsing, prior to sending the concentrate to digestion in the phosphoric acid chemical plant.

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10

Sustainability and the Environment

ACKNOWLEDGMENTS

The authors would like to thank the management and staff at the mine site of focus for their hospitality and assistance throughout the project, as well as ArrMaz for all the support received and for allowing the publishing of this work. REFERENCES

ArgusMedia, “Argus FMB Phosphates“, Methodology and Specifications Guide, http://www.argusmedia .com/~/media/Files/PDFs/Meth/argus_FMB _Phosphate.pdf?la=en. Accessed September 2014. Arroshola, L; Gasson, C.; Gonzalez-Manchon, C.; Lang, H.; Reemeyer, L; Uzelac, J. “Water for mining: Opportunities in scarcity and environmental regulation,” Global Water Intelligence, ISBN: 978-1-907467-16-5, 2010. Lambooy, T., “Corporate Social Responsibility: Sustainable Water Use,” Journal of Cleaner Production, 19, 2011, 852–866.

Moore, L.R.; Taylor, D.L.; Fallaw, A.K.; Anderson, D.; Gu, J.; Xiong, R.; Wang, G., “Water Quality Effect in Phosphate Flotation: Understanding Leads to Overcoming,” Beneficiation of Phosphates: Comprehensive Extraction Technology, 2016, Ch 8, pp. 71–79. Moore, L.R.; Xiong, Y.; Gorken, A.; Wang, G., “Effect of Water Chemistry on the Flotation of Colored Impurities From Feldspar,” XXVIII International Minerals Processing Congress, 2016, Preprint 199, ISBN: 978-1-926872-29-2. SRI Consulting, “Phosphorus Products“, Chemical Economics Handbook, 2009, Page 10–13. USGS, United States Geological Survey, “Mine Water Use,” http://ga.water.usgs.gov/edu/wumi .html, 2012. WHO, World Health Organization, “The Global Annual Assessment of Sanitation and DrinkingWater (GLAAS),” Fact Files on Water, http:// www.who.int/features/factfiles/water/water _facts/en/index2.html, 2011.

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CHAPTER 2

Purification of Phosphogypsum for Production of Calcium Sulfate Whisker Through Complete Chemicals Recycle Zeqiang Zhang,* Yixin Shao,* Hualin Sun,* Patrick Zhang†

ABSTRACT

and lowers the strength; the organic materials have detrimental effects on both the color and strength of PG products. [2–5]. Therefore, for most applications, the impurities in PG must be removed. Over fifty (50) kinds of PG uses have been reported, including construction materials, agricultural uses, and as chemical raw materials [6–10]. However, the amount for any PG use is very limited due to adverse effects of various contaminants, as discussed above. The majority of PG produced worldwide is currently disposed of by the stacking practice, which is neither environmentally safe nor economically favorable. This research aims at developing a process for large-scale PG use in an environmentally sound manner and with broad societal benefits.

In order to utilize the massive calcium sulfate resource in phosphogypsum (PG), an innovative processing flowsheet was developed to purify PG and eventually produce high-grade calcium phosphate whisker through cyclic uses of sodium hydroxide (NaOH) and hydrochloric acid (HCl). In this process, the SO42– and Ca2+ in PG are extracted as soluble Na2SO4 and CaCl2 by accurate control of pH value and dosages of chemicals, and leaving all other impurities in the solid residue. The exchange reaction of calcium chloride solution and sulfuric acid allowed the formation of pure calcium sulfate whicker with an average length to diameter ratio of 23–36, whiteness of higher than 93%, and purity of 99.72% at calcium sulfate recover of 86.04%.

EXPERIMENTAL Materials

INTRODUCTION

The PG sample was collected from a phosphoric acid plant in Yichang, Hubei, China. X-ray diffraction analysis showed that CaSO4·2H2O is the dominant species in the PG followed by SiO2. Table 1 lists chemical analysis of the test sample.

Phosphogypsum is a byproduct of wet process phosphoric acid manufacturing. Calcium sulfate dehydrate (CaSO4·2H2O) is the main component of PG accounting for 70–90% of the total mass.[1] Unlike natural gypsum, PG contains various impurities, which limit its applications. For example, the waste acid in PG is corrosive; the phosphorus accumulated on PG surface reduces its solidification rate and strength; fluoride makes PG products easy to weather

Thermodynamic Analysis of the Proposed Approach

In addition to calcium sulfate in PG, there exist silica, aluminum, magnesium, phosphate compounds,

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12

Sustainability and the Environment

TABLE 1.  Chemical analysis of main composition in phosphogypsum Species Content (%)

H2O

P2O5

CaO

MgO

SiO2

Al2O3

SO3

CaSO4

16.01

1.09

28.98

0.18

6.06

0.42

42.32

70.36

TABLE 2.  Thermodynamic properties of possible side reactions No.

Equilibrium Reaction

5

+ 2OH–Ca(OH)2(s) = Ca2+ + 2OH– Ca(OH)2(s) = CaHPO4·2H2O = Ca2+ + HPO2– 4 + 2H2O – 3CaO·2SiO2·3H2O = 3Ca2+ + 2H2SiO2– 4 + 2OH Ca2+ + 2OH– = Ca(OH)2(aq) Ca2+ + OH– = Ca(OH)+

6

H+

1 2 3 4

7 8 9 10 11 12 13 14 15 16 17 18

Ca2+

H3PO4 = + H2PO–4 H2PO–4 = H+ + HPO2– 4 + 3– HPO2– 4 = H + PO4 H4SiO4(aq) = H+ + H3SiO–4 H4SiO4(s) = 2H+ + H2SiO2– 4 H3SiO–4 = H+ + H2SiO2– 4 Al(OH)3(s) = Al3+ + 3OH– Al3+ + H2O = Al(OH)2+ + H+ Al3+ + 2H2O = Al(OH)+2 + 2H+ Al3+ + 3H2O = Al(OH)3 + 3H+ Al3+ + 4H2O = Al(OH)–4 + 4H+ Mg(OH)2(s) = Mg2+ + 2OH– Mg2+ + 2OH– = Mg(OH)2(aq)

sulfate compounds, soluble phosphorus (H3PO4, H2PO4– and HPO42–), difficult-to-dissolve phosphorus (CaHPO4 etc.) , as well as eutectic phosphorus [9]. This research aims at producing calcium sulfate whisker from PG. In order to do that, all the impurities have to be removed, which is accomplished by first reacting PG with sodium hydroxide to get the SO42– into solution as Na2SO4, followed by dissolution of calcium as, leaving all the acid insoluble in the solid residues. These chemical conversions are represented by the following reactions: CaSO4·2H2O + 2NaOH → Na2SO4 + Ca(OH)2↓ + 2 H2 O (1) Ca(OH)2 + 2HCl → CaCl2+2H2O(2)

The above reactions are ready to complete, because they have very large negative Gibbs energy at 25°C81.33 kJ and –128.68 kJ[10], respectively. There are also many side reactions accompanying dissolution reactions (1) and (2), as are listed in Table 2.

K Value Ksp =

10–5.26

Reference [11]

Ksp = 10–7

[11]

Ksp = 10–9.66

[11]

K = 102.77

[12]

K = 101.4

[12]

10–2.15

[13]

K = 10–7.2

[13]

K = 10–12.36

[13]

K = 10–9.6

[11]

K = 10–24.26

[14]

K = 10–11.8

[11]

K=

Ksp =

10–32.9

[11]

K = 10–4.97

[15]

K = 10–9.3

[15]

K = 10–15

[15]

K = 10–23

[15]

Ksp = 10–11.25

[11]

K=

105.81

[16]

Based on the K values listed in Table 2, the phase diagram 25°C for Ca, Mg, Al, Si, and can be constructed as Figure 1. Figure 1 shows that during the PG dissolution process to transfer sulfate into sodium sulfate, impurity dissolution can be prevented by controlling pH within the range of 11–13. However, the optimal pH for reaction (2) is lies between 5 and 7 to prevent impurities from CaCl2 solution. EXPERIMENTAL The First Reaction and Filtration

Figure 2 shows a block diagram of the overall processing flowsheet developed under this research. In each test, a known amount of PG is placed in a cone shaped glass reactor, a sodium hydroxide solution is added the reactor slowly under agitation, and finally filter the product upon completion of the reaction to obtain a sodium sulfate solution and a calcium residue. The SO3 content in the Na2SO4 solution is measured to calculate the recovery of SO42– based on chemical analysis of the PG sample.

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Purification of Phosphogypsum for Production of Calcium Sulfate Whisker13

FIGURE 1.  Phase diagram for impurity species in PG

FIGURE 2.  The overall processing flowsheet

Regeneration of NaOH Solution

The Na2SO4 solution is treated in an electrodialysis cell with two charged membranes and three-stage countercurrent flow at constant electric current. This process produce two products, sulfuric acid and sodium hydroxide. The SO3 content in the spent solution is analyzed to calculate the conversion rate of Na2SO4. Dissolution of Calcium

The calcium residue from reaction (1) is treated with HCL to convert Ca into CaCl2 solution, and Ca

content in the CaCl2 solution is analyzed to calculate conversion rate of Ca in the PG in this process. Formation of Calcium Sulfate Whisker

In this last step, the CaCl2 solution in a glass container is heated in a water bath to the desired temperature, and then the sulfuric acid is added into the solution. At the reaction completion, the products are kept at the same temperature for certain period of time prior to filtration to obtain a solid product of calcium sulfate whisker and the regenerated hydrochloric acid. The whisker product is analyzed for CaSO4 purity and recovery.

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Sustainability and the Environment

94 93 92 91 90 89 88 87 86 85 84 10.4

95

Ca2+ Recovery, %

SO42- Recovery, %

14

90 85 80 75 70

10.9

11.4

11.9

12.4

8

9

10

11

12

13

HCl Dosage, mole/kg PG

NaOH Dosage, mole/kg PG

FIGURE 4.  Effect of HCl addition on Ca2+ recovery

FIGURE 3.  Effect of NaOH addition on SO42– recovery TABLE 3.  Operating parameters of the electrodialysis process

Solution Analysis Prior to Electrodialysis, mol/·L

Solution Analysis After Electrodialysis, mol/·L

Stage

Current Density mA/cm2

Salt Chamber Na2SO4

Acid Chamber H2SO4

Base Chamber NaOH

Salt Chamber Na2SO4

Acid Chamber H2SO4

Base Chamber NaOH

I

30

1.06

0.50

0.88

0.44

1.35

2.41

II

15

0.44

0.12

0.21

0.14

0.50

0.88

III

12

0.14

0

0

0.04

0.12

0.21

RESULTS AND DISCUSSION Effect of NaOH Dosage on SO42– Conversion Rate

As was analyzed above, chemical reaction (1) for decomposing PG using sodium hydroxide is very ready to take place from the thermodynamics point of view. Experimental results showed that dosage of NaOH was the sole important factor influencing the extraction rate for SO42–, with all other parameters having little impact. Theoretically, two moles of NaOH are required for each mole of CaSO4 in PG, but the optimal dosage needs to be determined by testing. For practical purpose, NaOH dosage was converted to moles per kilogram of PG. Figure 3 indicates the effect of NaOH addition on SO42– recovery. It can be seen that SO42– recovery increases rapidly as NaOH addition increases, but reaches near the maximum (93.62%) around 11.4 mol/kg PG. The pH value at this NaOH dosage is about 12, which is within the optimal pH range for negligible dissolution of impurities. Effect of HCl Addition on Ca2+ Recovery

Reaction (2) is an acid-base neutralization reaction, it is exothermic, and takes place very rapidly. Based on reaction (2) , the theoretically required molar amount

of HCl is twice of Ca(OH)2 moles in the calcium residue. Again, the actual usage must be determined by experiments. Again, HCl dosage was converted to moles per kilogram of PG. Figure 4 shows that Ca2+ recovery increases with HCl addition, and a maximum recovery of 89.12% can be obtained at about 10.0 moles/kg of PG. At the optimal HCl dosage, pH value of the solution was measured at 6.5, favorable for preventing impurities dissolution. Performance Electrodialysis of Na2SO4 Solution

Electrodialysis of Na2SO4 solution is an important step of the overall scheme, because it regenerates both sulfuric acid and sodium hydroxide. The process can be expressed by reaction (3) Na2SO4+H2O → 2NaOH+H2SO4 (3)

In the PG decomposition process, a Na2SO4 solution of 1.06 mol/L was produced. The three-stage countercurrent electrodialysis process obtained a H2SO4 solution of 1.35 mol/L and a NaOH solution of 2.41 mol/L. The overall Na2SO4 rate was 96.59% at electricity consumption of 0.938 kWh /kg Na2SO4. Table 3 lists the major indices of the electrodialysis process.

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Purification of Phosphogypsum for Production of Calcium Sulfate Whisker15

(a)

4.0 mol/kg

(b)

5.0 mol/kg

(c)

6.0 mol/kg

FIGURE 5.  Effect of sulfuric acid addition on the morphological characteristics of calcium sulfate whisker

Calcium Sulfate Whisker Product

Since sulfuric acid is stronger than hydrochloric acid, it will precipitate with calcium when added into a calcium chloride solution in the following manner: CaCl2+H2SO4 → CaSO4↓+2HCl(4)

Reaction (4) not only produces the calcium gypsum whisker, but also allows for cyclic use of hydrochloric acid. According to the mass equilibrium principle, sulfuric acid consumption by reaction (4) should be 5.0 mol/kg PG. Figure 5 shows the morphology of the calcium sulfate whiskers produced at different sulfuric acid dosages under the following conditions. ■■ ■■ ■■ ■■

Reaction temperature: 80°C Reaction time 30 min Mixer speed: 180 rpm Aging time at 80°C: 20 min

Figure 5 clearly shows significant impact of sulfuric acid addition on the morphological characteristics of calcium sulfate whisker. When sulfuric acid use

is 4.0 mol/kg, below the theoretical level, the diffusion of SO42–and Ca2+ towards the crystal surface is limited resulting thin and short whiskers. At sulfuric acid of 5.0 mol/kg, long, needle shaped whiskers were formed with good dispersion degree. After sulfuric acid was further increased to 6.0 mol/kg, the whisker started to conglomerate, and became very thin and short. This may be attributed to calcium sulfate growth towards low-energy surface due to high sulfuric acid concentration. It was discovered that Mg2+ enhanced the growth of calcium sulfate whisker by regulating over saturation of calcium sulfate in the solution thus influencing the shape and growth rate of the whisker. Figure 6 shows a whisker product with good length to diameter ratio and morphology, when the solution had a Ca2+to Mg2+ molar ratio of 16. After further optimization experiments, the best operating conditions were determined as follows: reaction temperature 90°C, reaction time 60 min, aging time 60 min, mixing speed 180 rpm. Tables 4

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16

Sustainability and the Environment

       FIGURE 6.  The effect of

Mg2+ on

the characteristics of calcium sulfate whisker

     FIGURE 7.  Mophological characteristics of the anhydrate calcium sulfate whisker

TABLE 4.  Chemical analysis of the optimized whisker Item

CaO

H2O

SO3

Other

Total

Wt.%

35.61

13.30

50.81

0.28

100.00

23–36. Figure 7 shows very nice morphology of the anhydrate whisker product. CONCLUSIONS

TABLE 5.  Comprehensive analysis of the overall process Material

Yield, /%

CaSO4,%

CaSO4 Recovery, % 86.04

Whisker product

70.03

86.45

Acid insolubles

9.42

—

—

Phosphogypsum

100.00

70.36

100.00

and 5 show analysis of the final product manufactured under these conditions. In summary, the final product analyzes 86.45% CaSO4 and 13.30% crystal water at 86.04% recovery. Anhydrate whisker can be obtained by calcining the above product at 400°C for 2 hours, resulting in a product containing 99.72% CaSO4 with a whiteness of ≥93% and length to diameter ratio in the range of

An innovative process was developed for extracting CA+ and SO 42- from PG and then making a calcium sulfate whisker product with all the chemical used in the process recycled. The final anhydrate whicker contains 99.72% CaSO4 at a CaSO4 recovery of 86.04%. The major parameters influencing the product are dosages of the chemicals used, with the optimal dosages being 11.4 moles of NaOH, 10.0 moles of HCl and 5.0 moles of H2SO4 per kilogram of PG. This process consumes little chemicals and generates a minimal amount of acid insoluble solids residue, and may well be the most environmentally safe use of phosphogypsum.

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Purification of Phosphogypsum for Production of Calcium Sulfate Whisker17

ACKNOWLEDGMENTS

This research program was supported by the Natural Sciences Foundation of China under grant No. 51374156. Appreciation is also due to Hefei Kejia High Molecular Materials Ltd. for their assistance. REFERENCES

  [1] N. Kybartiene, Z. Valancius, V.A. Leskeviciene, L.A. Urbonas. Influence of the composition of phosphate rock on the amount of waterinsoluble phosphate impurities in semi-hydrate phosphogypsum. Ceramics—Silikáty. 2015, 59(1):29–36.  [2] E.M. El Afifi, M.A. Hilal, M.F. Attallah et al.. Characterization of phosphogypsum wastes associated with phosphoric acid and fertilizers production. Journal of Environmental Radioactivity. 2009, 100:407–412.   [3] T. Kuryatnyk, C. Angulski da Luz, J. Ambroise et al. Valorization of phosphogypsum as hydraulic binder. Journal of Hazardous Materials. 2008, 160:681–687.  [4] Hanan Tayibi, Mohamed Choura, Félix A. López et al. Environmental impact and management of phosphogypsum. Journal of Environmental Management. 2009, 90:2377–2386.  [5] L. Reijnders. Cleaner phosphogypsum, coal combustion ashes and waste incineration ashes for application in building materials: A review. Building and Environment. 2007, 42:1036–1042.  [6] Gorakh S. Bandgar, Madhav B. Kumthekar, Amarsinh B. Landage. A Review of Effective Utilization of Waste Phosphogypsum as a Building Material. International Journal of Engineering Research. 2016, 4(1):277–280.

 [7] Denis Lutskiy, Tatiana Litvinova1, Alexandr Ignatovich, Igor Fialkovskiy. Complex Processing of Phosphogypsum—A Way of Recycling Dumps with Reception of Commodity Production of Wide Application. Journal of Ecological Engineering. 2018, 19(2): 221–225.  [8] Hannu-Petteri Mattila and Ron Zevenhoven. Mineral carbonation of phosphogypsum waste for production of useful carbonate and sulfate salts. Frontiers in Energy Research. 2015, 3(2): 1–8.   [9] J. Feng, Phosphogypsum and Its Comprehensive Uses, Journal of Inorganic Industry, 2001, 33(4):34–36. [10] C. Li and B. Fu, Handbook of Applied Chemistry, Chemicals Press, Beijing, 2006. [11] Dean J.A. Lange’s Handbook of Chemistry. 1990. [12] S. Lin, 1993, Solution Equilibrium, Beijing Normal University Press. [13] G. Zhang, Z. Zhao, C. Cao, 2009, Thermodynamics of Decomposition of Calcium Molybdate by Phosphate, Transactions of Beijing University, 2009(11):1394–1399. [14] C. Cao, Z. Zhao, X. Liu, el al., 2012. Thermodynamic Study of White Tungsten Ore Decomposition by Sodium Silicate, Transactions of Non Ferrous Metal. [15] Robert E., 1976, The Hydrolysis of Cations. Wiley, 1976. [16] D. Wang and Y. Hu, 1988, Solution Chemistry of Flotation. Hunan Science and Technology Press, Changsha, China.

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CHAPTER 3

Beneficiation of Dolomitic Phosphate Pebble by Triboelectrostatic Belt Separation Erich Dohm,* Abhishek Gupta,† Kyle Flynn†

ABSTRACT

carbonates and silicates can be challenging, but the technology certainly exhibits potential for silica removal in less complex phosphate ores.

To address the dolomitic phosphate pebble challenge faced by the Florida phosphate industry, a study was conducted to determine the technical feasibility of triboelectrostatic belt separation for beneficiation of this material. A bulk sample was supplied by the Mosaic Company for the study. Preliminary laboratory characterization and dolomite liberation investigations were performed, followed by pilot plant testing of a commercially available triboelectrostatic belt separator supplied by ST Equipment & Technology. The study determined that dolomite association with phosphate minerals in the pebble is primarily linked to Strontium bearing apatite (apatite-Sr), and dolomite liberation can be achieved to a satisfactory degree using a mill product specification (P80) of 212 microns. Triboelectrostatic belt separation testing showed moderate enrichment of phosphate and removal of silica in the product, with the best result providing a product grade of 29.3% P2O5, 5.0% SiO2, and 1.6% MgO at a P2O5 recovery of 43%. Doping the feed material with chemical charge conditioning agents resulted in statically significant improvement in separation efficiency and product grade, and further investigation on this topic could prove beneficial. Overall, the study results indicate that removal of dolomite from phosphate ores with

INTRODUCTION

Phosphate rock production from the state of Florida plays an important role in the state and local economy, and supplies valuable feedstocks for the production of fertilizers widely used in commercial agriculture. With the depletion of high-grade phosphate ore in the Central Florida Phosphate District, mining activities are progressing southward into the Southern Extension. The ore in this region is separated in two distinct zones with different grades and levels of impurities, as summarized in Table 1 (El-Shall and Bogan 1994). It is clear from this data that pebble in the lower zone of the Southern Extension contains a considerably higher dolomite (MgO) constituent than the upper zone. This high dolomitic pebble is problematic for downstream chemical processing and therefore must be either discarded or blended with concentrate to achieve an acceptable rock grade. Various beneficiation techniques have been attempted to address the dolomitic pebble problem, each of which has distinct limitations and disadvantages. As a dry and chemical-free process, electrostatic

* Jacobs Engineering Group Inc., 3149 Winter Lake Rd, Lakeland, Florida, USA † ST Equipment & Technology, 101 Hampton Ave, Needham, Massachusetts, USA 18 Copyright © 2019 Society for Mining, Metallurgy & Exploration. All rights reserved.



Beneficiation of Dolomitic Phosphate Pebble by Triboelectrostatic Belt Separation19

TABLE 1.  Average distribution and chemical assay of Southern Extension phosphate rock

Zone Upper Zone Lower Zone

Matrix Thickness (m) 4.3

8.2

Product

Wt. %

P2O5%

Pebble

11

28

MgO % Insol % 0.52

12.0

Feed

69

7

0.12

75.9

Clay

20

9

1.90

46.1

Pebble

8

17

6.19

13.9

Feed

58

7

0.67

69.3

Clay

34

2

11.50

29.1

separation presents a promising method for beneficiation of phosphate rock. Methods for dry electrostatic processing of phosphate ores have been proposed and demonstrated at small scales for over 70 years. However, commercial applications of these methods have been very limited due to low throughput, low efficiency, and the need to work with narrow particle size distributions (Freasby, 1966; Ciccu et al., 1972; Ciccu et al., 1993; Abouzeid et al., 1996; Stencel and Jian, 2003; Abouzeid, 2008; Tao and Al-Hwaiti, 2010; Bada et al., 2012; Sobhy and Tao, 2014). ST Equipment & Technology’s (STET) triboelectrostatic belt separator (Figure 1) has the demonstrated capability to process fine particles from