Beneficiation of Phosphates : Comprehensive Extraction, Technology Innovations, Advanced Reagents [1 ed.] 9780873354288, 9780873354271

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BENEFICIATION

OF PHOSPHATES

EDITED BY: PATRICK ZHANG

I

JAN MILLER

I

EWAN WINGATE

I

COMPREHENSIVE EXTRACTION TECHNOLOGY INNOVATIONS ADVANCED REAGENTS

LAURINDO LEAL FILHO

BENEFICIATION

OF PHOSPHATES COMPREHENSIVE EXTRACTION TECHNOLOGY INNOVATIONS ADVANCED REAGENTS

EDITED BY: PATRICK ZHANG

I

JAN MILLER

I

EWAN WINGATE

I

LAURINDO LEAL FILHO

PUBLISHED BY THE SOCIETY FOR MINING, METALLURGY & EXPLORATION Copyright © 2016 Society for Mining, Metallurgy & Exploration Inc. All rights reserved.

Society for Mining, Metallurgy & Exploration (SME) 12999 E. Adam Aircraft Circle Englewood, Colorado, USA 80112 (303) 948‑4200 / (800) 763‑3132 www.smenet.org The Society for Mining, Metallurgy & Exploration Inc. (SME) is a professional society (nonprofit 501(c)(3) corporation) 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. Copyright © 2016 Society for Mining, Metallurgy & Exploration Inc. Electronic edition published 2016. All Rights Reserved. Printed in the United States of America. 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. Any statement or views presented herein are those of individual authors and editors and are not necessarily those of SME. 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 978‑0‑87335-427-1 Ebook 978‑0‑87335-428-8 Library of Congress Cataloging-in-Publication Data has been applied for

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Contents Preface v PART 1. COMPREHENSIVE EXTRACTION 1. Recovery of REE from an Apatite Concentrate in the Nitrophosphate Process of Fertilizer Production Mahmood Alemrajabi, Kerstin Forsberg, and Åke Rasmuson.................................................................................. 3

2. Upgrading Phosphate Flotation Tailings for REE Extraction Salah Al-Thyabat and Patrick Zhang................................................................................................................... 11

3. Recovering Sulphur from Phosphogypsum: A Historical Review and Prospects for the Future Gary Albarelli.................................................................................................................................................. 21

4. Removal and Recovery of MgO from Phosphate Rock by Acid Leaching Patrick Zhang.................................................................................................................................................. 29

PART 2. PROCESS INNOVATION 5. An Optimized Approach to Phosphate Recovery Ewan Wingate and Jaisen Kohmuench............................................................................................................... 43

6. A Tailor-Made Approach for the Beneficiation of Phosphate Rock Leonid Lisiansky, Mike Baker, Keren Larmour-Ship, and Olga Elyash................................................................... 55

7. Newcomer in Phosphoric Acid Process Routes: The DA-HF Process Tibaut Theys.................................................................................................................................................... 63

8. Water Quality Effect in Phosphate Flotation: Understanding Leads to Overcoming

Lucas R. Moore, David L. Taylor, Aaron K. Fallaw, Daris Anderson, James Gu, Ryan Xiong and Guoxin Wang.......................................................................................................................... 71

9. An Alternative Flotation Process for Apatite Concentration of the Santa Quitéria (Brazil) Carbonaceous Uranium-Phosphate Ore Elves Matiolo, Lígia Mara Gonzaga, and Ana Luíza Guedes.................................................................................. 81

10. Study on Mineral Processing of a Medium to Low Grade Phosphate Ore in Western Hubei, China Mei Yang, Wending Xiao, Dapeng Zhang, Xiang Yang, and Yan Wu...................................................................... 91

11. Application of Pico-Nano Bubble Generator in Phosphate Reverse Flotation Yu Xiong and Felicia Peng................................................................................................................................. 97

12. Reducing MgO Content in Florida Phosphate Concentrate Patrick Zhang, Shibo Zheng, Wenyi Song, and Jan Miller.................................................................................. 105 iii Copyright © 2016 Society for Mining, Metallurgy & Exploration Inc. All rights reserved.

iv Contents

PART 3. FLOTATION REAGENTS 13. Effect of Dissolution Kinetics on Flotation Response of Apatite with Sodium Oleate D.G. Horta, S.G. Antonio, C.O. Paiva-Santos, and L.S. Leal-Filho..................................................................... 117

14. The Surface and Colloid Chemistry of Layered Silicate Minerals J.D. Miller and Jing Liu.................................................................................................................................. 139

15. Application of Custofloat® Carbonate Collectors in Beneficiating Phosphate Ores in China Guoxin Wang................................................................................................................................................ 147

16. Processing Florida Dolomitic Phosphate Pebble with Custofloat® Carbonate Collectors Guoxin Wang and Zhengxing (James) Gu........................................................................................................ 151

17. Improvement of Dolomite Collector on High‑Dolomite Phosphate Pebble from Florida Chunhui Feng, Wenyi Song, Patrick Zhang, and Yuntao Liu.............................................................................. 157

18. Phosphate Beneficiation with Novel Collectors for Direct and Reverse Flotation: Beyond Low Cost Fatty Acids

Pablo Dopico, Gunter Lipowsky, Mduduzi Mbonambi, Linda Mahlangu, Brandi Makin, Klaus-Ulrich Pedain, and Wagner Silva............................................................................................................. 163

19. The Use of Lanthanum and Cerium Ions as Phosphate Activators in Low Grade Phosphate Flotation S. Al-Thyabat................................................................................................................................................. 171

PART 4. EQUIPMENT INNOVATION AND PROCESS ANALYSIS 20. Progress in Particle Characterization by X-ray Tomography for Improved Mineral Processing Technology Y. Wang, C.L. Lin, and J.D. Miller.................................................................................................................. 183

21. Remote Real-Time Analyses of Phosphate by Laser-Induced Breakdown Spectroscopy M. Gaft and R. Stana...................................................................................................................................... 197

22. Column Flotation of Phosphate Ore—An Engineer’s Perspective Ewan Wingate................................................................................................................................................ 207

23. Phosphate in Australia—So Near Yet So Far Ewan Wingate and John Dunster..................................................................................................................... 215

24. Gravitational Separation Behavior of Low-Grade Collophanite Ore in a Packed Column Jig Yan Wu, Dapeng Zhang, Xiang Yang, Wending Xiao, Mei Yang, and Patrick Zhang............................................. 225

25. Application of Classification and Fluidized‑Bed Flotation at PCS Aurora George Piegols, David DePlato, Jaisen Kohmuench, and Eric Yan....................................................................... 233

26. Understanding the Comminution Mechanism of High-Pressure Grinding Rolls: Lower Cost, Higher Efficiency, and Selectivity Francisco J. Sotillo.......................................................................................................................................... 243

27. Suitability of Geoscan-M Elemental Analyser for Phosphate Rock H. Kurth....................................................................................................................................................... 259

28. Environmentally Friendly, Energy Efficient Slurry Handling by Multisafe Double-HoseDiaphragm Pumps Alan Frost...................................................................................................................................................... 265

Index

273

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Preface

The crash of the materials supercycle is being felt by the global phosphate industry. 2015 was perhaps the toughest year for the industry of the last 15 years, with the fortunate phosphate companies watching their profits dropping manyfold and the not-so-lucky ones turning to survival mode. It has been particularly tough for the phosphate industry in China. Statistics show that in 2015, China produced about 14 million tons of P2O5 in the form of diammonium phosphate and monoammonium phosphate, which accounts for almost 50% of total world production. This represents about 40% more than the supply for the Chinese phosphate fertilizer market at a time when much of the world market is saturated. This market squeeze and ever-increasing environmental pressure have presented opportunities for developing technologies for extracting the most valuable elements from phosphate. This trend is designated as “comprehensive extraction” by many, or “all-element extraction” by some. The core principles of comprehensive extraction are best summarized by Julian Hilton of Aleff Group in the United Kingdom: 1. Disturb the ground only once. 2. All useful materials must be extracted from the ore in an optimized, integrated sequence. 3. By-products and residues should be used or reused. 4. Mine/by-products/tailings at End of Life should be “future proofed.” 5. Waste streams should be minimized and legacy costs greatly reduced. 6. Sustainable service delivery must be employed. 7. New business model(s) must be generated. 8. Triple-bottom-line returns should be the focus: economic, social, and environmental. Comprehensive extraction could often save a phosphate company when its major business of fertilizer manufacturing faces a downturn. For example, during late 2014 and early 2015, one of the largest phosphate companies in China, Wengfu Group, was generating income only from its iodine and fluorine extraction units. This trend prompted the organizing committee of the seventh Beneficiation of Phosphate Conference, held in 2015 in Melbourne, Australia to set comprehensive extraction as the theme for the conference. Although this book, which is a compilation v Copyright © 2016 Society for Mining, Metallurgy & Exploration Inc. All rights reserved.

vi Preface

of papers from that conference includes just four papers on comprehensive extraction, many presentations and discussions at the conference focused on this subject. Topics included recovery of rare earths from phosphate, uranium recovery from phosphoric acid, recovery of magnesium from high-dolomite phosphate rock, and phosphoric acid purification via by-products production. 2 2 2 2 The editors express their appreciation for SME’s continued endorsement and publication of this book, despite limited sales potential for such a highly specialized topic. We appreciate Jane Olivier and her staff who spend numerous hours editing the papers, many of which were submitted without following a consistent format. We are also grateful to the members of the conference organizing committee, the authors, and the staff of Engineering Conference International for their efforts in making this conference a success and for turning the proceedings into a quality product. All the conference sponsors are highly appreciated. WorleyParsons of Australia deserves special recognition for “heavy lifting” regarding financial support, leadership commitment, and staff enthusiasm and involvement in every detail. Many thanks are extended to our media partners, Australasian Institute of Mining and Metallurgy and Minerals Engineering International, who played an important role in publicizing this conference.

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Conference Organizing Committee CHAIR

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

Laurindo Leal Filho, University of Sao Paulo/Vale, Brazil Julian Hilton, Aleff Group, United Kingdom Abdelaâli Kossir, OCP Group, Morocco Jan Miller, University of Utah, USA Ewan Wingate, WorleyParsons Services Pty Ltd, Australia COMMITTEE MEMBERS

Tariq Alfariss, King Saudi University Salah Al-Thyabat, Al-Hussein BinTalal University, Jordan Ricardo de Lima Barreto, Vale Fertilizantes, Brazil Bruce Bodine, Mosaic Company, USA Hassan El-Shall, University of Florida, USA Glenn Gruber, Jacobs Engineering Group, USA Hans Huckstedt, LL Namibia Phosphates Chaucer Hwang, Mosaic Company, USA Pieter Jacobs, Foskor, South Africa Andrew James, Phosphate Australia Limited, Australia Jaisen Kohmuench, Eriez Magnetics, USA Tianxiang Li, Wengfu Group, China Hamid Mazouz, OCP Group, Morocco Wenyi Song, China Bluestar Lehigh Eng. Corp., China Jorgen Stenvold, Yara International ASA Wending Xiao, Wuhan Institute of Technology, China

vii Copyright © 2016 Society for Mining, Metallurgy & Exploration Inc. All rights reserved.

Corporate Sponsors

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PART 1

Comprehensive Extraction 1. Recovery of REE from an Apatite Concentrate in the Nitrophosphate Process of Fertilizer Production  3 2. Upgrading Phosphate Flotation Tailings for REE Extraction  11 3. Recovering Sulphur from Phosphogypsum: A Historical Review and Prospects for the Future  21 4. Removal and Recovery of MgO from Phosphate Rock by Acid Leaching  29

1 Copyright © 2016 Society for Mining, Metallurgy & Exploration Inc. All rights reserved.

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CHAPTER 1

Recovery of REE from an Apatite Concentrate in the Nitrophosphate Process of Fertilizer Production Mahmood Alemrajabi,* Kerstin Forsberg,* and Åke Rasmuson*

ABSTRACT

INTRODUCTION

The present study concerns the recovery of rare earth elements (REE) from an apatite concentrate in the nitrophosphate process of fertilizer production. The apatite concentrate was recovered from iron ore tailings in Sweden by flotation and was delivered by LKAB. Digestion of the phosphate mineral in concentrated nitric acid is the first step in the nitrophosphate process, after which Ca(NO3)2 · 4H2O is separated from the nitrophosphate (NP) solution by cooling crystallization. Then the REEs can be separated by neutralization of the NP solution with ammonia. The solubility of calcium nitrate tetrahydrate (CNTH) in acidic nitrophosphate solutions in the temperature range of –2°C to 20°C was determined. Further, the degree of rare earth coprecipitation during seeded cooling crystallization of CNTH was studied. It was shown that the calcium removal and the final pH in the partial neutralization step play an important role in determining the concentration of REEs in the precipitates obtained in the partial neutralization.

Phosphate minerals, such as apatite, are one of the main sources for production of fertilizer and phosphoric acid. These minerals contain small quantities of rare earth elements, and are considered as one of the secondary sources for rare earth element extraction. The industrial demand for many of the rare earth elements is high. Due to their unique spectroscopic and magnetic properties they are needed for a wide variety of products such as catalysts, rechargeable batteries, mobile phones, plasma televisions, disk drives and catalytic converters. The common chemical formula for apatite is Ca10(PO4)6(OH, F, Cl) (Gupta and Krishnamurthy 2005). In the present study, a fluorapatite from northern Sweden containing 2000–7000 ppm rare earth elements (Sandström and Fredriksson 2012) and delivered by LKAB was used. By digestion of phosphate rock with concentrated nitric acid in the nitrophosphate process (ODDA process), NPK fertilizer can be produced (Wiesenberger 2002, Binnemans et al. 2015). Although numerous researchers have reported details of the process (Wiesenberger 2002, Kongshaug et

*Department of Chemical Engineering and Technology, Royal Institute of Technology (KTH), Sweden

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4

Comprehensive Extraction

al. 2000), there are only a few reports on recovery of REE during the ODDA process. If separation of REE could be integrated into the process, it would be more environmentally friendly and could become a source for REEs. In Figure 1, a block diagram for the process with an integrated REE recovery unit is shown. The process mainly consists of the following steps for production of multinutrient fertilizers (European Fertilizer Manufacturers’ Association 2000): ■■ ■■

■■ ■■

Digestion of phosphate minerals with nitric acid. Cooling crystallization and separation of calcium nitrate tetrahydrate (CNTH) from nitrophosphoric acid solution (NP-acid). Neutralization of NP-acid with ammonia (adjustment of N/P ratio). Granulation of the slurry and coating of the product.

Calcium is a non-nutrient in NPK fertilizer and is seen as a diluent. Calcium nitrate tetrahydrate is therefore removed from the solution after the digestion of

apatite in order to increase the nutrient content in multinutrient fertilizers to reach the appropriate CaO:P2O5 ratio, by cooling crystallization down to –2 to 0 °C (Wiesenberger 2002). It is desirable to have the lowest possible CaO: P2O5 ratio in the rock in order to reduce the amount of CNTH that must be removed to a minimal level and make the process economically feasible. The overall nutrient content and N:P2O5 ratio of the final NPK are the main factors that determine the minimum amount of CNTH which has to be eliminated. The best range for this ratio is 0.3–1 (Kongshaug 2000). The CNTH that is separated from the ODDA process is a byproduct, and with NH3 and CO2 results in the production of ammonium nitrate and lime, which are feed materials for the production of calcium ammonium nitrate fertilizers (CAN) (Association European Fertilizer Manufacturers’ 2000). The rare earth elements are dissolved in the NP-acid in the digestion of apatite and appear in the NP-acid solution. After the CNTH cooling crystallization, the REE can be separated by means of partial neutralization with ammonia (A. Al-shawi 2002).

Figure 1. The ODDA process with integrated rare earth recovery Copyright © 2016 Society for Mining, Metallurgy & Exploration Inc. All rights reserved.



Recovery of REE from an Apatite Concentrate in the Nitrophosphate Process of Fertilizer Production 5

REE recoveries during leaching of apatite with different acids have been investigated (Sandström and Fredriksson 2012, Forsberget al. 2014). The highest recoveries of REE were reported in 5 mol/L nitric acid, at 60 °C, solid to liquid ratio of 1:6 g/mL and after 120 minutes of leaching (Forsberget al. 2014). The digestion of apatite in the ODDA process is performed in more concentrated acid in order to reduce the amount of water in the processing. The purpose of our study was to find the optimum conditions for an integrated rare earth recovery from the nitrophosphate process. MATERIALS AND METHODS Characterization of the Apatite Concentrate

A portion of apatite was dried and dissolved completely in a mixture of nitric acid, hydrochloric acid and perchloric acid at elevated temperature and diluted with an appropriate amount of milli-q water. The REEs, Fe, Ca, P and a number of heavy metals were analyzed by ICP-OES (Thermo Fisher iCAP 7000). The concentrate was also analyzed by powder XRD (Forsberg et al. 2014). The particle size was measured by means of a microscope fitted with a digital camera and analyzing the images with ImagePro Plus software. Leaching and Cooling Crystallization

The apatite concentrates with particle sizes of typically 150 μm. The voxel resolution for these images is 4.59 μm. Scale parameter is ~36.

Figure 6. Comparison between traditional thresholding segmentation and feature based segmentation for a copper ore for the 106×75 μm size class. The voxel resolution for these images is 4.59 μm. Scale parameter is ~18.

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Progress in Particle Characterization by X-ray Tomography for Improved Mineral Processing Technology189

expected sampling rate of 10–20 kg/min for particles which range in size from 150 mm to 1 mm at a voxel resolution of about 150 microns. This is quite a significant advance in X-ray tomography technology and should be useful for plant site particle characterization (size, shape, composition, density, texture, grain exposure, mineral liberation) with a response time of minutes after receiving the sample. Coarse coal samples were provided to demonstrate the use of the high speed X-ray tomographic system for washability analysis at a plant site. The samples were acquired from the Lady Dumn preparation plant. This operation is located in Cannelton, West Virginia, south of Charleston. The single-size/multiple-density sample with sample size 1¼ × ¼" was provided from this plant. The coal sample (7.1 kg) was scanned using high speed X-ray tomography. The three-dimensional reconstructed image set contains 1280×1230×1690 voxels (voxel resolution = 0.169  mm). Several sectional slices of the 3D reconstructed dataset are shown in Figure  7. Based on calibration, the brightness of

particles in the image reveals their density. A volumerendered 3D view of this reconstructed dataset is shown in Figure 8. The 3D images of the coal particle beds are split and opened to show inside sections for corresponding particles. Coal particles of different density are clearly distinguished from these images based on the gray level, which corresponds to a specific density. In order to obtain information for individual particles, modified watershed segmentation was used to segment contacted coal particles. First, image noise is removed. Then trainable weka segmentation (TWS) is applied to generate a binary image which separates the foreground (solid phase) from the background (air). Third, the binary image is used to apply the distance transformation. Fourth, which is the most important step in many complex segmentation applications, is marker extraction. In order to accurately extract the markers, markers with different sizes are used. The distance transformed image is first thresholded to get big markers. Then for extraction of small

Figure 7. Two-dimensional X-ray CT sectional slices from 3D high speed computed tomographic data for 1¼ × ¼" (31.75 x 6.35 mm) coal particles of different density. Voxel resolution is 169 μm.

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Equipment Innovation and Process Analysis

Figure 8. (a) Three-dimensional volume rendered image from high speed computed tomographic data for 1¼ × ¼" (31.75 x 6.35 mm) coal particles with different density fractions. Voxel resolution is 169 μm. (b) Three-dimensional view of the split particle bed.

markers, the regional maximas of the distance transformed image are extracted. The final markers image is formed by combining the small markers together with large markers. Fifth, the flooding process is carried out to distinguish spatial boundaries. The detailed 3D multiscale image segmentation process is shown in Figure 9. Using multiscale image segmentation, particle boundaries are defined and contacted coal particles can be separated. The segmentation results for this coal sample are presented in Figure 10 which presents the 2D sectional views of the original 3D X-ray CT data. The different colors in the figure indicate the segmented particles. Detailed information regarding density distribution of different macerals and minerals in such a packed bed of coal particles can be established. First, the 3D high speed X-ray tomographic image was segmented using 3D multiscale image segmentation, as explained previously. After that, the mean CT number and the volume of each coal particle was measured and the density was determined based on the calibration established between density and CT number. The washability curve (yield/density) for this coal sample is shown in Figure  11 based on sink-float data. Results from CT analysis (resolution 169  μm) are included for comparison. It is evident that

the washability curves constructed based on X-ray tomography are in good agreement with the sinkfloat analysis. APPLICATIONS IN THE PROCESSING OF PHOSPHATE RESOURCES

Applications of X-ray tomography technology in the phosphate industry include liberation analysis of flotation feed, characterization of pebble phosphate, and identification of rare earth particles. Liberation Analysis of Flotation Feed

Characterization of feed material with respect to expected concentrate grade and recovery is fundamental to the design of improved separation efficiencies and to achieve sustainable development in the utilization of our mineral resources. One of the important reference points for this characterization is the liberation-limited grade/recovery curve which represents the perfect separation, the best separation which can be achieved for a given feed material, limited only by the extent of liberation. Now, liberationlimited grade/recovery curves can be determined based on 3D mineral liberation analysis of feed material. Thus, actual separation efficiencies can be compared to what might be expected for a perfect separation, limited only by the extent of liberation. The analysis of liberation-limited grade/recovery curves using X-ray Micro CT has been used for

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Progress in Particle Characterization by X-ray Tomography for Improved Mineral Processing Technology191

Figure 9. 3D multiscale image segmentation

phosphate samples from Florida phosphate operations to estimate separation efficiencies in fatty acid flotation (Miller et al., 2009). In some cases the flotation separation was, in fact, limited by the liberation state while in other cases additional factors were found to limit the separation efficiency. Also, as expected, the results reveal that 2D polished section analysis overestimates the extent of liberation and confirms the utility of 3D mineral liberation analysis

by HRXMT for the construction of liberation-limited grade recovery curves. Characterization of Pebble Phosphate

A fundamental concept in most mineral processing operations is that the desired product particle size from comminution is governed by the liberation characteristics of the ore. In this regard, plant site coarse particle characterization of crusher product in 3D will

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Equipment Innovation and Process Analysis

Figure 10. Comparison between original images and segmented images for a packed bed of coal particles for the 1¼ × ¼" size class

Figure 11. The sink-float washability curve compared with the results from three-dimensional X-ray tomographic analysis

provide useful information for subsequent size reduction (if necessary), particle separation, and recovery. In the case of Florida phosphate operations crushing is usually not necessary but plant site characterization of coarse particles at phosphate processing plants is needed to improve plant capacity, product quality, and/or process efficiency. Not much plant site coarse particle characterization is done at these phosphate plants. Even laboratory analysis of coarse particles has been difficult because of the large amount of sample required to insure statistical significance of the results.

With advanced X-ray tomography systems that are commercially available, it is now possible to use 3D X-ray tomography analysis for plant site particle characterization at a sampling rate of 10–20 kg/min for particles < 150  mm and >1  mm in size with a voxel resolution of ~100–200 microns. This is quite a significant advance in X-ray tomography technology and should be useful for plant site particle characterization (size, shape, composition, density, texture, grain exposure, mineral liberation) of phosphate pebbles and perhaps coarse flotation feed with

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Progress in Particle Characterization by X-ray Tomography for Improved Mineral Processing Technology193

a response time of minutes after receiving the sample. Unlike other analyzers, such as the LIBS analyzer, the X-ray tomography analyzer will provide information regarding the grain size distribution and the extent of liberation. Identification of Rare Earth Particles

Mineral identification is an extremely important topic in mineral processing, and rare earth particle identification grows increasingly important as national and global demand increases. Dual-energy (DE) radiography followed by high resolution X–ray microtomography (HRXMT) has been used to identify rare earth (RE) particles in several samples obtained from the Florida Industrial and Phosphate Research Institute (Crossman, 2014). DE radiography is extremely

time efficient, especially compared to HRXMT. However, DE radiography has difficulties distinguishing between materials of similar densities and effective atomic numbers. In contrast, one of the prominent features of HRXMT is the ability to differentiate between any two materials, regardless of their similarities in effective atomic numbers. By using both methods together, RE particles were identified and characterized from Florida phosphate resources as shown in Figure 12. SUMMARY AND CONCLUSION

Progress in X-ray tomography technology has been significant, with a unique imaging capability to produce three-dimensional images of multiphase particles. In some cases, it is difficult to identify the

Figure 12. 3D reconstructed image of shaking table concentrate is shown in (a) and broken down to indicate individual minerals such as monazite(b), zircon(c), and apatite(d)

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different minerals due to similar linear attenuation coefficients. In this regard, dual-energy scanning has been introduced and proved to be effective to distinguish different mineral phases having similar attenuation coefficients. An important issue in the 3D analysis of multiphase particles is image segmentation. By using feature based classification, it is now possible to identify particle boundaries of high density or fine particles, which benefits 3D analysis of multiphase particles. High speed X-ray tomography may allow for coarse particle characterization at plant sites. In this way 3D analysis of coarse particles may be accomplished in a few minutes. Applications of X-ray tomography technology in the phosphate industry include liberation analysis of flotation feed, characterization of pebble phosphate, and identification of rare earth particles. ACKNOWLEDGEMENTS

The authors acknowledge ZEISS company for their assistance in this research program. REFERENCES

Breiman, L., 2001. Random forests. Machine Learning, 45 (1): 5–32. Christ, G., 1984. Exact treatment of the dual-energy method in CT using polyenergetic X-ray spectra. Physics in Medicine and Biology, 29 (12): 1501–1510. Coenen, J.G.C. and Maas, J.G., 1994. Material classification by dual-energy computerized X-ray tomography. In: Proceedings of the International Symposium on Computerized Tomography for Industrial Applications, Berlin, Germany, pp. 120–127. Crossman, R., 2014. Characterization of rare earth particles from the Florida phosphate industry through dual energy radiography and X-ray tomography. MS Thesis, University of Utah, Salt Lake City, UT. Engler, P. and Friedman, W.D., 1990. Review of dual energy computed tomography techniques. Materials Evaluation, 48: 623–629. Fiji Is Just Image, 2015. http://fiji.sc/ Trainable_Weka_Segmentation.

Fuerstenau, M.C., 2003. In: M.C. Fuerstenau and K.N. Han (Editors) Principles of Mineral Processing. Society for Mining, Metallurgy, and Exploration, Littleton, CO, pp. 9–35. Gonzalez, R.C. and Woods, R.E., 2008. Digital Image Processing. Prentice Hall Press, Upper Saddle River, NJ. Kaynig, V., Fuchs, T. and Buhmann, J.M., 2010. Neuron geometry extraction by perceptual grouping in ssTEM images. Computer Vision and Pattern Recognition, IEEE Conference, pp. 2902–2909. Lin, C.L. and Miller, J.D., 2005. 3D characterization and analysis of particle shape using X-ray microtomography (XMT). Powder Technology, 154: 61–69. Lin, C.L. and Miller, J.D., 2010. Advances in X-ray computed tomography (CT) for improved coal washability analysis. In: R.Q. Honaker (editor), International Coal Preparation Congress. Society for Mining, Metallurgy, and Exploration, Littleton, Colorado, pp. 888–897. McCullough, E.C., 1975. Photon attenuation in computed tomography. Medical Physics, 2:307–320. Miller, J.D. and Lin, C.L., 2004. Three-dimensional analysis of particulates in mineral processing systems by cone beam X-ray microtomography. Mineral & Metallurgical Processing, 21 (3): 113–124. Miller, J.D., Lin, C.L., Hupka, L. and Al-Wakeel, M.I., 2009. Liberation-limited grade/recovery curves from X-ray micro CT analysis of feed material for the evaluation of separation efficiency. International Journal of Mineral Processing, 93: 48–53. Miller, J.D. and Lin, C.L., 2010. High resolution X-ray micro CT (HRXMT)—Advances in 3D particle characterization for mineral processing operation. In: D. Malhotra, P.R. Taylor, E. Spiller, and M. LeVier (editors), Recent Advances in Mineral Processing Plant Design. Society for Mining, Metallurgy, and Exploration, Littleton, Colorado, pp. 48–59. Schena, G., Chiaruttini, C., Dreossi, D., Olivo, A. and Pani, S., 2002. Grade of fine composite mineral particles by dual-energy X-ray radiograph. International Journal of Mineral Processing, 67: 101122.

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Schena, G., Dreossi, D., Montanari, F., Olivo, A. and Pani, S., 2003. Multiple-energy X-ray radiography and digital subtraction for a particlecomposition sensor. Minerals Engineering, 16 (7): 609–617. Sukovic, P. and Clinthorne, N.H., 2000. Penalized weighted least-squares image reconstruction for dual energy X-ray transmission tomography. IEEE Transactions On Medical Imaging, 19 (11): 1075–1081.

Van Geet, M., Swennen, R. and Wevers, M., 2000. Quantitative analysis of reservoir rocks by microfocus X-ray computerized tomography. Sedimentary Geology, 132 (1): 25–36. Wellington, S.L. and Vinegar, H.J., 1987. X-ray computerized tomography. Journal of Petroleum Technology, 8: 885–898.

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CHAPTER 21

Remote Real-Time Analyses of Phosphate by Laser-Induced Breakdown Spectroscopy M. Gaft* and R. Stana†

ABSTRACT

INTRODUCTION

LDS earlier constructed and produced an industrial LIBS Machine, which enables on-line measurement of the Mg, Fe, Al, Si, Ca and P2O5 content of phosphate rock on a moving conveyer belt. It allows real time shipping and discarding decisions based on sound analytical data. There is an advantage to do the rock characterization much sooner, not only to eliminate the cost of mining, pumping and separation, but also to reduce the possibility of discarding good rock rather than mining it. To prove such opportunity, LDS constructed and successfully tested in real field conditions an industrialized remote LIBS (ReLIBS) unit capable of performing phosphate rock analysis at 5–25  m distances. This remote LIBS device proved the feasibility of distant real time chemical analysis of phosphate rocks excavated by drag line machine enabling differentiation between overburden, matrix and bottom materials and determination the MgO and Fe content in the matrix samples. The optimum position of the ReLIBS was determined to be at washing pit before the matrix is slurried to pump to the beneficiation plant.

Variability in the phosphate rock significantly affects the ability to efficiently digest the rock in the production plant and produce a saleable phosphate fertilizer product. The most significant variables are the CaO, MgO, Fe2O3 and Al2O3 as well as the P2O5 content. Current mining practices require either holding the rock products in bins until the quality control data from sampling become available, or making the shipping or discarding decision based on visual observations of rock. This practice can result in the shipping of undesirable products to the chemical plant or the discarding of acceptable phosphate rock. A method of improving variability would be to continuously analyze the rock received by the production plant and then stack it in places on the pile with similar compositions. Then rock could be retrieved from the pile by pulling from various places on the pile to hold the overall composition relatively constant. While this would significantly improve the variability, it will only become practical when a continuous analyzer becomes available that can accurately and quickly provide the several analyses required on the rock as received without sample

* Laser Distance Spectrometry (LDS), Israel † R. SQUADRED S., Lakeland, Florida, USA 197 Copyright © 2016 Society for Mining, Metallurgy & Exploration Inc. All rights reserved.

198

Equipment Innovation and Process Analysis

preparation. Online and automatic analysis allows phosphate producers to promptly detect changes in incoming materials, enabling them to take appropriate actions in the process streams. Together with FIPR, LDS has already developed an on-line LIBS analyzer for phosphate rock on a moving belt conveyer (Gaft et al., 2007, Gaft et al., 2014a). However, it will be even more effective to put the online analytical system in the actual mine. Presently, areas to be mined are identified by geologists based on analysis of drill cores typically collected at 100 meter intervals. If field samples are collected, they must be transported to the laboratory, analyzed, and the data transmitted back to the mine. This latter process is slow, error prone, and does not allow real-time management of mining. Costs can be significantly reduced by ‘in-situ’ element analysis enabling real-time selection of the highest-grade ore. The best way to solve this problem may be to find the indistinct top and bottom contacts between barren, apatite and dolomite layers and thereby accomplish crude separation by means of selective excavation. This may be accomplished by ReLIBS unit. LIBS standoff mineralogical applications have been considered mostly for space tasks. Nevertheless, for Earth atmospheric pressures remote distances of 10–25 m have been achieved. Excellent LIBS ability for remote sensing was demonstrated in homeland security applications, where the detection and identification of trace amounts of explosives at distances up to 45 m using remote LIBS have been demonstrated (Cremers and Radziemski, 2006; Noll, 2012; Palanco and Laserna, 2006; Salle et al., 2007). This development clearly indicates that LIBS sensors can  be made rugged, compact, and be candidates for mining robotics applications. This manuscript is devoted to an industrialized ReLIBS device for a remote real-time analyzer of phosphate rocks, which could be used to analyze phosphate rock from 5–25 m distances. Such unit is capable of working continuously in real life conditions of the open phosphate mine which include a dusty/dirty atmosphere, varying temperatures, and the presence of strong sun light.

EXPERIMENTAL

Several books and papers have been recently published devoted to Laser Induced Breakdown Spectroscopy (LIBS) (Cremers and Radziemski, 2013, Miziolek et al., 2006, Noll, 2012, Hahn and Omenetto, 2010, Hahn and Omenetto, 2012). The technique employs a pulsed laser and a focusing assemblage to generate a plasma that vaporizes a small amount of a sample. A portion of the plasma light is collected and directed to a spectrometer. The spectrometer disperses the light emitted by excited atoms, ions, and simple molecules in the plasma, a detector records the emission signals, and electronics take over to digitize and display the results. The ReLIBS unit contains two pulsed Nd-YAG lasers (100 mJ, 8 ns) capable to work in single pulse and double pulse modes, two gated spectrometers with changeable delay time (100 ns–100 µs) and gate width (10 µs–1 ms), optical telescopic focusing and collecting assemblages, autofocus and scanning mechanisms, laser distance meter, video camera, heater, chiller, fans, blowers and industrial PC. During the sampling process, telescope automatically scans the defined area and at each sampling point an auto focus process is performed according to the measured target distance. When focusing is accomplished, the exciting laser is being activated and at each laser pulse the spectrometer receives spectra which are transferred for analysis by the corresponding software. RESULTS AND ANALYSES Laboratory Scale Experiments

Figure 1 presents typical breakdown spectra of phosphate rocks with analytical lines of the elements the mostly important for the process control: P, Ca, Mg, Si, Al, Fe by atomic and ionic emission lines (NIST Atomic Spectra Database Lines) and F by molecular CaF emission (Gaft et al., 2014b). During the first step, 21 samples from Mosaic South Pasture rock samples (Table  1) have been studied from 10  m distance in laboratory conditions. All relevant elements, such as P, Mg, Ca, Si, Fe, Al and CaF were definitely detected and reflects the rock compositions (Figure 2). Figure 3 presents the results of such remote

Copyright © 2016 Society for Mining, Metallurgy & Exploration Inc. All rights reserved.



Remote Real-Time Analyses of Phosphate by Laser-Induced Breakdown Spectroscopy199

a CaF

400

0.5

580

Intensity (a.u.)

600

620

640 Ca II

c

660

220 600

317.7

315.7

300

230

240

250

260

270

Fe II 274.4

d

400

200 100

Mg II Mg I 285.0 279.7

0

300 Intensity (a.u.)

PI 255.1

1.0

200

400

253.3

b

603.3

Intensity (a.u.)

600

280

300 251.4 Si I

e

200

Mg I Mg I, Mg II 309.4 293.4 320

340

220

400

Si I 288.0

240

260

f

300

320

340

360

308.9

Al I 308.0

300

200

280

200 100

100 240

260

280

300

320

340

nm

260

280

300

320

340

360

nm

Figure 1. Breakdown spectra of phosphate rocks with analytical lines and bands of the mostly important elements: F (a), P (b), Ca and Mg (c), Fe (d), Si (e), and Al (f)

LIBS analysis for the mostly important rock chemical composition components, such as BPL, Mg, Insol, and Fe. It may be seen that for all those elements the correlations between ReLIBS and analytical data are pretty good with linearity coefficient R2 = 0.9 range. BPL was evaluated by both P I emission lines and CaF emission bands. Consequently, it was concluded that ReLIBS is a promising tool to identify matrix layers with high BPL contents and further subdivide them for high and low MgO segments. Similar results were achieved also for phosphate deposits PCS and JDC (Florida) and Xin Run (China). From 20 m distance the signals are approximately 4–5 times lower compared to 10  m, which corresponds well to reciprocal R2 relation between the signal intensity and the distance. All relevant elements are definitely found from this distance. For all those elements the correlations between ReLIBS and

analytical data are good with linearity coefficient in R2 = 0.85–0.95 range. Field Algorithm Development Signal Evaluation

During the first testing stage, the dragline operator put several piles of different rock, overburden, matrix and bottom, on the ground. Those piles were then subjected to ReLIBS analysis from 5–25  m distances. The autofocus system effectiveness and, correspondingly, plasma creation and its emission detection depend strongly on the distance measuring accuracy. The ability to both create a strong plasma and measure the spectral intensity is a strong function of the degree of focus obtained. It has to be noted, that the materials tested represent one of the worst possible scenario. They are usually crumbly, wet, with grey-black colors which are characterized by the

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200

Equipment Innovation and Process Analysis

Table 1. Chemical composition and description of Mosaic South pasture rocks samples N

BPL

Fe2O3

Al2O3

MgO

Insol

CaO

Designation

1

7.6

0.8

2.5

0.6

85.5

5.49

Overburden

Overburden

Mine?

2

5.1

0.2

3.4

0.2

87.0

2.0

Overburden

Overburden

Not mine

3

17.6

1.8

4.7

51.1

18.8

Interburden

Bottom/Matrix

Not mine

7

6.3

1.00

1.6

0.9

84.1

4.7

Interburden

Interburden

Not mine

8

24.4

1.30

2.7

1.1

61.5

17.3

Matrix

Matrix

Mine

9

24.9

0.73

1.0

2.6

54.4

20.4

Matrix

Matrix

Mine

10

3.2

0.3

2.2

0.1

92.4

0.4

Matrix

Overburden

Not mine

11

5.0

3.1

2.3

0.9

83.6

3.4

12

21.6

1.1

1.6

1.5

62.6

16.0

13

0.3

0.1

0.1

0.0

97.44

14

3.6

0.5

0.5

0.1

92.9

10.

Based on Analyses

Interburden

Interburden

Not mine

Bottom

Matrix

Mine

0.2

Overburden

Overburden

Not mine

2.3

Overburden

Overburden

Not mine

21

0.3

0.1

0.2

0.1

97.7

0.3

Overburden

Overburden

Not mine

22

27.0

1.2

1.4

0.3

59.8

18.4

Matrix

Matrix

Mine

23

11.6

1.1

1.8

2.2

69.7

10.3

Bottom

Matrix?

Mine?

24

2.7

0.3

1.1

0.1

92.6

1.4

Overburden

Overburden

Not mine

25

9.9

1.3

2.0

5.6

56.5

13.8

Bottom

Bottom

Not mine

26

18.3

1.1

1.5

4.9

49.9

18.6

Matrix

Matrix

Mine

27

18.9

1.1

1.7

3.9

51.3

17.7

Bottom

Matrix

Mine

28

6.2

1.2

2.1

0.8

80.9

4.1

Interburden

Interburden

Not mine

29

22.9

1.1

2.1

0.5

64.5

15.3

Matrix

Matrix

Mine

30

0.3

0.1

0.2

0.1

97.7

0.3

Overburden

Overburden

Not mine

low reflection ability. Contrary to this, solid targets, such as pebbles, bones, vertebrates have much high reflection coefficients and are characterized by much stronger plasma emission signals. It was found that plasma was well created and detected by the remote unit from all the studied distances. Figure  4 presents the corresponding spectra received from 15 m distance. Figures 4 (a,b) present the typical breakdown spectra of the sample visually determined as the good rock with the highest P2O5 content of 26.92% and MgO concentration of 1.26% according to the laboratory data. The most important analytical lines in UV range are Ca, Mg, Si, Fe and Al (Figure 4a), while the main feature of the visible range is the relatively narrow bands peaking at approximately 603.0 nm which is connected to the CaF emission. In this spectrum the CaF band is a relatively strong, demonstrating high apatite, and correspondingly P2O5 content. At the other end of the spectrum, Mg lines are relatively strong and the lines of Mg present at 293.1 nm, which usually only occurs at high Mg concentrations. Figures 4 (c,d) present typical breakdown spectra of the sample

visually determined as waste rock with a modest P2O5 content of 15.28% and very high MgO concentration of 7.0% according to the laboratory data. Correspondingly, the CaF band is still detected, while Mg lines are substantially stronger including the emission at 293 nm. With such a high MgO content, the so called concentration quenching already is taking place and the resonance Mg emission lines in the UV range are not the best for analytical applications. In such a case, non resonance Mg I line at 518.0 nm is a preferential one and its relative dominance is easily seen in this sample. Figure 4e presents typical breakdown spectra of the sample visually determined as upper zone with the modest P2O5 content of 14.03% and very low MgO concentration of 0.31% according to the laboratory data. Correspondingly, Mg lines are substantially weaker including the absence of emission at 293  nm. Figure  4f presents a typical breakdown spectra from the sample that was visually determined as overburden with a very low P2O5 content of 0.56% and very low MgO concentration of 0.08% according to the laboratory data. In addition, the CaO content is also very low at 0.54%. In

Copyright © 2016 Society for Mining, Metallurgy & Exploration Inc. All rights reserved.



Remote Real-Time Analyses of Phosphate by Laser-Induced Breakdown Spectroscopy201

8

517.6 Mg I

4

180

BPL - 6.3 % MgO-0.9 %

PI 253.7

Fe II

20

c 517.6 Mg I

14

603.3 CaF

600

10

288.1 Mg I 285.0

60 40

12

279.4

Si I

2

Intensity (a.u.)

Mg II

b

160

603.3 CaF

Intensity (a.u.)

6

BPL - 6.3 % MgO-0.9 %

a

700

800

900

0

140

BPL - 27.0 % MgO-0.3 %

250 d

260

270

280

290

280

290

BPL - 27.0 % MgO-0.3 %

120

100

8 6

PI 253.7

40

4

20

2 600

700

800

900

nm

250

260

270 nm

Figure 2. Representative double pulse breakdown spectra of rocks with different BPL contents from Mosaic South Pasture mine analyzed from 10 m distance

such a case, the visible spectrum where the emissions of Ca, CaF and Mg dominate is not relevant as they have very low intensity spectra. In the UV spectrum, Fe, Si and Al dominate. Quantitative Analysis

The next step was to evaluate the ability for quantitative chemical analysis of all relevant elements. All remotely analyzed materials, 16 total, were sampled and send to the Mosaic laboratory for routine analysis in order to get the calibration curves for all relevant elements, such as P, Mg, Fe, Al, Si, Ca, F. Figure  5a presents the corresponding calibration curve for P2O5, which is one of the most important elements. The linearity coefficient R2=0.91 is very good for real time process control. Another important task is remote evaluation of the MgO content. Figure  5b presents the corresponding correlation

between ReLIBS and laboratory data demonstrating very good linearity coefficient of 0.98. Thus it may be concluded that remote LIBS is a promising tool for real time analyses of the phosphate materials excavated by the drag lines. The linearity coefficient of 0.91 for CaO is also very good, while for SiO2 vs Acid Insol (AI) it is approximately 0.73, which is usually the border value for real time process control (Figures 5 c,d). Selection of the Best Implementation Site

The main task of ReLIBS is to use this analyzer for “horizon control” in open mining. Phosphate rock is usually found 15–50 feet beneath the ground in a mixture of phosphate pebbles, sand and clay known as phosphate “matrix.” The sandy layer above the matrix, called the overburden, is removed using electrically operated draglines. Equipped with large

Copyright © 2016 Society for Mining, Metallurgy & Exploration Inc. All rights reserved.

202

Equipment Innovation and Process Analysis

25

20

2

R = 0.95 4

n=19 15

Mg, LIBS

P, LIBS

n=19

5

2

R = 0.92

10

3 2

5

1

0

0 0

5

10

15

20

25

0

1

2 3 MgO %, Lab

BPL %, Lab

4

5

100 2

2

R = 0.9

3

R = 0.92

80

Fe, LIBS

Si, LIBS

90

70

2

1

60 50 50

60

70

80

90

100

Insol %, Lab

0 0

1

2

3

Fe2O3 Lab

Figure 3. Calibration curves of different elements for ReLIBS analysis from 10 m distance in laboratory conditions for Mosaic South Pasture rocks

buckets, these draglines remove the overburden, placing it in the previously mined voids, and excavate the matrix, depositing it into a shallow containment area or slurry pit. There, high-pressure water guns turn the material into a watery mixture called slurry, which is sent through pipelines to a processing facility, where phosphate rock is physically separated from the sand and clay in the matrix. Presently the dragline operators are advised by field geologists on what to mine based on information from drill cores and visual observation. Nevertheless, such information may be erroneous. This generally results in at least some inclusion of overburden or base material in with the phosphate matrix or matrix is cast aside with the overburden or left it in the mine cut. For example, in one of the tests, 56 samples of

“Overburden,” “Matrix” and “Bed” according to the dragline operator practice were collected from 7 mines and analyzed. Out of the 51 samples which were clearly “Mine” or “No Mine,” only 75% were correct. Compared to what was actually being mined, “correct” mining would have increased production by 9% and reduced MgO by 50%. But actual mining was being controlled by the dragline operators. What if a geologist had been present? The same 56 samples were viewed by 5 geologists and characterized as to “Mine” or “No Mine.” Average accuracy was 79% (73–84%). All 5 got the right answer on 31 of the samples and the wrong answer on 3 of the samples. Both the dragline operators and geologists were mining “Matrix” containing as low as 2% BPL or with an MgO over 8%. Both the dragline

Copyright © 2016 Society for Mining, Metallurgy & Exploration Inc. All rights reserved.



Remote Real-Time Analyses of Phosphate by Laser-Induced Breakdown Spectroscopy203

a

6

2

700

0 900 240

800

c

P2O5 15.28 %

Mg I

MgO 7.0 %

80

260

4

320 Ca

340

360

P2O5 15.28 % MgO 7.0 %

Fe II

Mg I Mg I Si

Al

20

600

700

800

e

900

P2O5 14.03 %

MgO 0.31 %

4

240

260

280

Fe II

320

360

MgO 0.08 %

Si

0.6

340

P2O5 0.56 %

Mg II

0.8

2

300

Fe II

f

1.2 1.0

3

Al

0.4

1 240

300

Mg II

d

40

500

Mg I Si I Mg I 280

60

CaF

Intensity (a.u.)

600

2

Intensity (a.u.)

P2O5 26.92 %

MgO 1.26 % 50

6

5

Ca

Mg II

Fe II 500

0

b

MgO 1.26 %

4

8

100

P2O5 26.92 %

CaF

Intensity (a.u.)

8

0.2 260

280

300

320

340

360

240

nm

260

280

300

320

340

360

nm

Figure 4. Typical breakdown spectra of different rocks received in field conditions from 15 m distance

operators and geologists were leaving overburden or bed containing over 30% BPL and less than 0.2% MgO. It’s not always possible to “See” the difference between matrix and non matrix and chemical analysis is required to make the correct determination. At one mine, samples of overburden, matrix and bed at each dragline were taken each day. Several hundred samples were taken. Depending on the criteria used for “good rock,” accuracy of what was being mined (compared to should) was 70–85%. The impact of “Correct Mining” will be to increase both production and improve mined rock quality. But where is the best place for ReLIBS unit? As result of the field experience, the washing pit was selected which is where the drag line operator places the excavated matrix for its transformation to slurry and the following pumping to the beneficiation plant. The advantages of this position are the following:

■■

■■ ■■

■■ ■■

The information for drag line operator is practically real time, only one bucket later compared to information from a unit mounted on drag line machine being the fastest. Not every bucket has to be controlled, but only those in the unclear excavating zones. The distance from the ReLIBS to the pit can be approximately 15–20  m, which is in the range of existing capabilities; The relief is substantially less changeable compared to the actual surface; The safety issue is substantially less severe because there are no personnel present in this area.

For safety reasons, it was not possible to take actual field samples for laboratory analysis to correlate with the specific ReLIBS samples. Thus we selected the spectral types based on different emission lines

Copyright © 2016 Society for Mining, Metallurgy & Exploration Inc. All rights reserved.

204

Equipment Innovation and Process Analysis

Equation

y = a + b*x

Weight

No Weighting

20

2

R =0.91

43.22447

Residual Sum of Squares Pearson's r

0.95904

Adj. R-Square

0.91174 Intercept

1.08983

0.93635

L

Slope

0.88999

0.08313

Equation

y = a + b*x

Weight

No Weighting

Residual Sum of Squares

1.52455

Pearson's r

0.99138 0.98112

Adj. R-Square

Standard Error

L

Value

6

15

MgO, %, LIBS

P 2O 5, %, LIBS

Value

8

10

Standard Error

B

Intercept

0.18156

0.13115

B

Slope

0.95367

0.03985

4 2

R =0.98 2

5

0

0 0

5

10

15

20

25

0

2

4

P 2O5, % Lab

6

8

MgO, %, Lab 4.0

30

3.5

2

2

R =0.73

R =0.91 SiO2 , %, LIBS

CaO, %, LIBS

3.0 20

10

2.5 2.0 1.5 1.0

0 0

5

10

15

20

25

30

35

40

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

SiO2 , %, Lab

CaO, %, Lab

Figure 5. Correlation between ReLIBS and laboratory for P2O5 (a), MgO (b), CaO (c), SiO2 (d)

relative intensities as an indicator of the rock types. In order to do this, the spectra of the rock samples, previously analyzed by the Mosaic laboratory, were measured in laboratory conditions. Based on calibration curves developed using the calibration samples, spectroscopic data have been used to give the chemical compositions (Table  2). Based on all the information, it looks like 5 of the 24 presented samples represent material that should not have been mined as it would give rock of low value to the chemical plant. This is similar to the results reported previously in 1997 when 20–25% of the matrix mined was found to not be worth mining. While it is highly probable that some of the materials that were not sent to the slurry pit (either cast aside as overburden or left in the mine cut) were good matrix, no samples were obtained of this

material to confirm it. With just the improvement in “not mining” the matrix that should not have been mined, there is significant value. At an annual rock production rate of 4 million tons, and 5/24 of the matrix being mined and subsequently thrown away when it is caught by the MAYA on the pebble belt, the “wasted cost” can be significant. At a probable cost of $5/ton for digging, transporting, washing and screening the rock, the annual cost could be over $4,000,000. The rock that is not mined, but should have(though not verified in this study) would add significantly more value. CONCLUSIONS

Field tests confirmed that ReLIBS enables realization of remote real time chemical analysis of phosphate rocks excavated by the drag line machine. It gives

Copyright © 2016 Society for Mining, Metallurgy & Exploration Inc. All rights reserved.



Remote Real-Time Analyses of Phosphate by Laser-Induced Breakdown Spectroscopy205

Table 2. Evaluation of the pit samples P2O5

Fe2O3

Al2O3

MgO

CaO

F

A.I.

1

Lower

6.20

1.20

2.20

0.80

9.04

0.65

65.75

4

Bottom

5.70

0.90

1.70

4.00

24.00

0.60

62.56

5

Upper

7.90

1.10

3.80

0.90

11.53

0.83

62.71

6

Upper

8.20

1.30

4.20

0.20

11.97

0.86

62.73

7

Upper

10.80

0.60

3.40

0.20

15.76

1.13

67.06

8

Upper

13.90

0.10

3.80

0.80

20.29

1.45

62.97

9

Lower

8.42

1.30

2.20

0.65

12.29

0.88

63.81

11

Upper

6.20

0.50

2.90

2.10

9.04

0.65

64.84

Not mine

12

Upper

7.40

2.30

3.20

1.70

10.80

0.77

61.93

Not mine

13

Upper

7.00

0.40

4.10

0.90

10.21

0.73

63.38

14

Upper

8.90

0.60

2.90

0.70

12.99

0.93

62.13

16

Upper

6.80

0.90

2.80

0.50

9.92

0.71

62.17

17

Upper

8.10

1.00

3.30

0.70

11.82

0.85

75.89

19

Lower

5.37

0.82

2.40

0.69

7.83

0.56

63.24

20

Lower

5.52

0.97

2.30

0.72

8.05

0.58

64.20

21

Lower

6.35

3.20

2.60

0.60

9.26

0.66

61.95

23

Upper

11.20

0.60

4.20

1.10

16.35

1.17

63.16

24

Upper

6.10

0.50

4.40

0.90

8.90

0.64

64.79

25

Lower

6.70

1.02

2.10

0.70

9.77

0.70

65.32

26

Bottom

5.20

2.30

1.50

9.32

20.13

0.55

62.86

27

Upper

8.10

0.50

4.10

0.80

11.82

0.85

62.86

28

Upper

9.70

0.70

5.20

0.60

14.16

1.01

63.14

29

Upper

9.70

0.90

3.90

1.10

14.16

1.01

62.14

30

Upper

10.30

0.70

4.20

0.69

15.03

1.07

64.20

the following: differentiation between overburden, matrix and bottom materials; determination of the P2O5 content; determination of the MgO and iron content in matrix samples. REFERENCES

Cremers, D. and Radziemski, L., 2006. LaserInduced Breakdown Spectroscopy. Wiley, 111 River Street, Hoboken, NJ, USA. Gaft, M., Sapir-Sofer, I. and Stana, R., 2007. Laser induced breakdown spectroscopy for bulk minerals online analyses. Spectrochim. Acta, 62: 1496–1503. Gaft, M., Nagli, L., Groisman, Y. and Barishnikov, A., 2014a. Industrial online raw materials analyzer based on laser-induced breakdown spectroscopy. Appl. Spectr., 68:7–19.

Not mine

Not mine

Not mine

Gaft, M., Nagli, L., Eliezer, N., Groisman, Y. and Forni O., 2014b. Elemental analysis of halogens using molecular emission by laser-induced breakdown spectroscopy in air. Spectrochim. Acta, 95:39–47. Hahn, D. and Omenetto, N., 2010 Laser-induced breakdown spectroscopy (LIBS), Part I: Review of basic diagnostics and plasma–particle interactions: still-challenging issues within the analytical plasma community. Appl. Spectr., 64:335–366. Hahn, D. and Omenetto, N., 2012. Laser-induced breakdown spectroscopy (LIBS), Part II: review of instrumental and methodological approaches to material analysis and applications to different fields. Appl. Spectr., 66:347–419. Miziolek, A., Palleschi, V. and Schechter I., 2006. Laser induced breakdown spectroscopy (LIBS): fundamentals and applications. Cambridge University Press, 32 Avenue of the Americas, New York, NY 10013–2473.

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NIST Atomic Spectra Database Lines: http://physics .nist.gov/PhysRefData/ASD/lines_form.html Noll, R., 2012. Laser induced breakdown spectroscopy: fundamentals and applications. Springer, 11 West 42nd Street, 15th Floor, New York, NY 10036. Palanco, S. and Laserna, J., 2004. Remote sensing instrument for solid samples based on open-path atomic emission spectrometry. Rev. Sci. Instr., 75:2068–2074.

Sallé, B., Mauchien, P. and Maurice, S., 2007. Laserinduced breakdown spectroscopy in open-path configuration for the analysis of distant objects. Spectrochim. Acta, 62:739–768.

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CHAPTER 22

Column Flotation of Phosphate Ore— An Engineer’s Perspective Ewan Wingate

Column flotation cells have been in use since the 1920s when they were first used for upgrading base metal sulphide concentrates. Since then various use of columns and non-agitated flotation cells has grown in popularity. The use of flotation columns in phosphates has been around since 1980s when it was first tested in the Florida phosphate industry. Since then, column flotation has been utilized in various locations around the world. However with ultra-fine phosphates in Australia there is an opportunity to make use of columns and non-agitated flotation cells. Traditionally flotation testwork starts off as bench scale tests using one to three litre mechanically agitated flotation cells. As the testwork program develops and larger metallurgical ore samples become available, testwork programs may then include pilot plant testwork using both mechanically agitated flotation cells and/or column flotation cells. In recent laboratory and pilot plant trials on igneous phosphates, the programs migrated away from the use of mechanically agitated flotation cells to the use of flotation columns. The typical benefits observed include improvements in product P2O5 grade and P2O5 recovery. With the advent of phosphate projects in Australia that require fine grinding to liberate the phosphate minerals, the use of column

flotation cells has afforded a unique opportunity to provide improved metallurgical performance for processing these finely ground ores. The use of non-agitated flotation cells has also been demonstrated to produce similar or better metallurgical results with a reduction in the number of flotation stages when evaluated against mechanically agitated flotation circuits. From an engineering perspective, column flotation offers many benefits both in metallurgical performance, capital costs and operating costs. The advantage offered in terms of metallurgical performance has been previously mentioned. The capital cost benefits achievable by using column flotation cells in place of mechanical cells can result in a reduction in plant foot print which leads to a reduction in steel and concrete quantities. The columns have less mechanical drives and, by inference, less electrical circuits compared to a mechanical flotation cell circuit. The potential to save operating expenses can be realized from a reduction in power consumption and maintenance savings due to a reduction in the number of flotation units. As always there is a catch. As larger mechanical flotation cells (>30  m3) are adopted by operators, there is a decreasing capital and operating cost benefit to be had from the use of columns. The major

* WorleyParsons

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element supporting the selection of columns over mechanical flotation cells is metallurgical performance of columns in the cleaning stages of flotation circuits. In phosphate flotation, however, mechanical flotation cell size has been limited to 10 m3 (300 ft3) and 20 m3 (600 ft3), thus the potential advantages of larger mechanical cell size has not been realized. This paper discusses the potential benefits available to operators, and developers of new projects, from the use of column flotation cells in their metallurgical circuits from the perspective of an engineering company: 1. Metallurgical benefits from using column flotation cells for phosphate flotation 2. Capital cost benefits of column flotation cells 3. Operating cost benefits of column flotation. INTRODUCTION Column Flotation

Flotation columns derive their name from the cylindrical shape of the vessel. Unlike conventional mechanically agitated flotation cells, column cells are tall vessels ranging in height from nominally 5 meters to more than 15 meters. The small surface area and extensive pulp/froth height of a column cell helps to promote a stable and deep froth. The first pneumatic flotation cell, which used air sparging through a porous bottom and horizontal slurry flow, was patented by G.M. Callow in 1914. Cross-current pneumatic flotation machines were widely used in the industry by the 1920s and 1930s, but were later replaced by impeller-type flotation devices that evolved into the mechanical flotation cells utilized today. Klassen and Mokrousov were probably the first investigators to report that improved drainage of gangue particles from the froth was possible by sprinkling water on top of the froth Flotation using column cells essentially began in the early 1960s pursuant to Canadian patents by Boutin and Tremblay for their column operation at Opemiska, Canada. Today, column flotation is utilized for processing coal, ferrous ores, nonferrous ores and industrial minerals, including both igneous and sedimentary phosphate ore. Current manufacturers of column flotation

equipment include: Eriez Flotation Group (formerly CPT) (Canada); Eriez (USA); Xstrata (Australia); Metso (France) and PreQuip (South Africa). Column flotation cells have been utilized in Florida industry since the 1980s and are currently used for sedimentary phosphates in Florida (Mosaic), and Brazil (Cajati and Lagamar). Column flotation cells are also currently utilized in Brazil (Araxa) on igneous phosphates. Development projects where column flotation cells are being considered include: ■■

■■

Sunkar (Kazakhstan), Legend Holdings International (Australia), Rum Jungle Resources (Australia), MMG Century (Australia),, AngloAmerican (Brazil), and Vale (Peru) for sedimentary phosphate ore, PhosCan (Canada), Mine Arnaud (Canada), Arianne Ressources (Canada), and Vale (Mozambique) for igneous phosphate ore.

Comparison of Column and Mechanical Flotation Cells

Among the many different mineral beneficiation techniques, froth flotation has long been one of the most effective processes for the selective separation of fine mineral particles. In many cases, froth flotation is the only separation process that can treat fine particles efficiently. Two general types of flotation “machines” are currently used in froth flotation: mechanically agitated flotation cells and non-mechanical or column flotation cells. The characteristics of both types of flotation “machines” are discussed in the following paragraphs. Mechanically Agitated Flotation Cells

Mechanically agitated flotation cells in use today are characterized by an externally powered driver connected to an agitator mechanism designed to suspend (mix) and aerate the pulp. Air bubbles are formed by a rotating impeller which generates negative pressure and draws in atmospheric air through a hollow drive shaft (induced machine) or compressed air by an external supplemental air blower (forced air machine). The swirling action of the impeller breaks down the stream of incoming air into small bubbles that are dispersed through the pulp where the attachment of mineral particles to air bubbles occurs.

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Column Flotation of Phosphate Ore—An Engineer’s Perspective209

The froth is often removed from a mechanical cell by rotating paddles driven by a gear motor. The froth paddles can be mounted on one side or both sides of the cell. Tailings are removed via a tailings discharge box typically utilizing dart valves. Operational instrumentation for mechanical cells typically consists of automatic pulp level control tied to the tailings discharge dart valve system. Mechanical flotation cells are typically arranged as horizontal series-connected tanks with individual cell tank height to tank diameter ratios near 1:1. Mechanical cells are used for roughing, scavenging and cleaning services.

Column cells are also used for roughing, scavenging and cleaning services. Column cells sometimes require supplemental frother to assist in the formation of fine bubbles and to promote froth stability. Flowsheet Development

To illustrate the potential savings in mechanical drives and power consumption for a phosphate flotation plant a set of pilot plant results in Table  1 are used as a basis. The flotation circuit equipment for the comparison is based on the flow schematics illustrated in Figure 1 and Figure 2.

Column Flotation Cells

The counter current flotation column is a type of non-mechanical flotation system. Column flotation cells may be rectangular or cylindrical and are characterized by large height to diameter ratios. The column cell essentially performs as if it were a multi-stage conventional flotation circuit arranged vertically with slurry flowing downward while the air bubbles travel upward producing a counter current flow. Fine air bubbles are generated using compressed air through a bubble generator located at/near the bottom of the column. Conditioned pulp is fed through an inlet typically located in the upper third of the column and descends against a rising column of bubbles. The bubbles collect the hydrophobic (floatable) particles in the collection zone of the column. This zone is equivalent to the pulp recovery zone in a mechanical cell. The collected particles are then transferred into a froth zone stabilized by wash water.. The use of wash water is a key feature of column cells and typically permits high upgrading. Operational instrumentation for column flotation cells typically consists of automatic pulp level control utilizing 1 or 2 pressure transmitters, a digital controller and a variable frequency drive (VFD) that controls the speed of the tails discharge pump. This system can also be used to control the froth height. In some flotation columns, a percentage of the tails are recirculated through a VFD drive/pump that is also tied to the air sparging system.

Table 1. Pilot plant test results summary Type

Test Date

Recovery

Conc. G rade

Test

Flot.Cells

Mass

P205

%P205

Pilot

Mechanical

Jun-12

23.4

78.2

32.4

Pilot

Column

Mar-13

17.6

91.6

38.6

Pilot

Mechanical

Apr-13

11.7

63.7

37.1

Flotation Feed

High Solids Conditioning

Rougher Flotation

Reagents

Ro. Tails

Scavenger Flotation

Tailings

Ro. Conc.

Cleaner 1 Flotation

Cl. 1 Tails

Cl. 1 Conc.

Cl. 2 Tails

Cleaner 2 Flotation Cl. 2 Conc.

Cl. 3 Tails

Cleaner 3 Flotation Cl. 3 Conc.

Concentrate

Figure 1. Typical mechanical flotation cell lab configuration

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Equipment Innovation and Process Analysis

ENGINEERING DESIGN

A review of the flotation circuits based on the use of mechanical flotation cells when compared with the use of column flotation cells reveals the difference in installed electrical power and the number of flotation Flotation Feed

High Solids Conditioning

Rougher Flotation

Reagents

Ro. Tails

Tailings

Ro. Conc.

Cleaner 1 Flotation

CleanerScavenger

Cl. 1 Tails

Cl. 1 Conc.

Cleaner 2 Flotation

Cl-Scav Tails

Cl-Scav. Conc.

Cl. 2 Tails

Cl. 2 Conc.

Concentrate

cells required. There are also benefits in building foot print and potential savings in structural steel and concrete volumes. The data in Table  2 is based on Figure  1 and Figure  2. summarises the flotation circuit requirements based on the use of conventional mechanical flotation cells. The sizing of the mechanical flotation cells has been corrected to take into account conventional practice in the phosphate beneficiation industry of using cells up to 900 ft3 or 30 m3. The typical sizes are 300 ft3 (10 m3) or 600 ft3 (20 m3). Table 3 summarises the flotation circuit requirements based on the alternative use of flotation column cells. As can be seen, changing from a flowsheet based on mechanical cells to column cells results in a reduction in the number of mechanical drives and a reduction in installed power requirements. Table  4 illustrates the power savings between mechanical and column cell circuit configurations. Savings are also realized when the size of building used to house the flotation circuit is considered.

Figure 2. Typical column flotation cell lab configuration Table 2. Summary of the flotation circuit requirements based on mechanical flotation cells Mechanical Flotation Cells

Stage

Trains

No./stage

Ro Sc Cl1 Cl2 Cl3

2 2 2 2 2

8 5 7 11 11

Size (m3 )

100 70 50 40 30

Corrected for Phosphate Design Cell Size Total Cell kW each kW/cell Total kW Volume/stage Industry unit No.s (m3 ) Practice m3 Based on Design vol 16 110 1760 1441 72 20 37 10 93 930 628 31 20 37 14 75 1050 662 33 20 37 22 56 1232 808 40 20 37 22 45 990 637 32 20 37 84

5962

4176

209

Column Flotation Cells

Ro Cl1 Cl2 Cl-Scv

Trains

No./stage

2 2 2 2

4 2 4 4

Size (m3) 224 187 224 224

Design Total Cell kW each Total kW Volume/stage No.s unit m3 8 150 1200 1796 4 150 600 748 8 150 1200 1796 8 112 896 1796 28

3896

2666 1161 1225 1495 1178 7725

Table 3. Summary of the flotation circuit requirements based on column flotation cells Stage

Total Installed Power (kW)

6135

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Column Flotation of Phosphate Ore—An Engineer’s Perspective211

Table 4. Summary of the flotation circuit based on column flotation cells Item

No. of Flotation Cells

Column Benefit

56 less units

Power (kW)

Design Volume required (m3)

Equipment No.

Power (kW)

2066kW less

1959 m3

181 less

3829kW less

more

ECONOMIC BENEFITS Installed Capital Cost

The relative difference in capital cost between a beneficiation plant designed with column flotation cells versus a beneficiation plant designed with mechanically agitated flotation cells will depend on the size and complexity of the circuit, the ratio of concentration, the plant location, and the degree and type of automation required. Generally speaking, however, the capital cost of the flotation circuit of a beneficiation plant equipped with flotation columns may be 20% to 40% less than the same capacity beneficiation plant equipped with mechanically agitated flotation cells. The reasons for the lower capital cost are: ■■

■■ ■■

■■

A reduction in required floor space with corresponding reductions of other bulk items including, but not limited to concrete, piping, structural steel, electrical, etc. The building size (foot print) can also be reduced although the building height may increase. Fewer column cells may be required. In general, a mechanical flotation machine cannot be used singly to produce final concentrate due to inherent short circuiting. In order to attain a reasonable grade and recovery, there are a minimum number of cells required when using mechanical flotation machines; whereas comparable results may sometimes be achieved using only one flotation column. The column cell does not have any mechanical mixing mechanism. This eliminates the necessity for electric motors, special wear resistant agitators, and the requisite ancillary equipment.

Operating Cost

Generally speaking, the operating cost of a flotation circuit in a beneficiation plant equipped with flotation columns may be up to 50% less than the same capacity flotation circuit equipped with mechanically agitated flotation cells. The reasons for the lower operating cost are:

Figure 3. Layout and structural steel requirements for mechanical flotation cells ■■

■■ ■■ ■■

Reduced power requirements since the agitator drive motors, auxiliary blower/motor, and froth paddle motors are not required. The column cell does not have a mechanical mixing mechanism. Lower inventory requirements since column cells have fewer mechanical components. Possibility of reagent savings, such as depressants, where wash water is used to reduce impurity levels in the concentrate.

Advantages and Disadvantages of Flotation Cell Types

The relative advantages and disadvantages of column flotation cells compared to mechanically agitated flotation cells are discussed below. ■■

In a column cell, the pulp flows downward while the air bubbles travel upward producing a counter current flow. This flow pattern is in direct contrast to that found in mechanical cells, where both the air and the solid particles are driven in the same direction. The result is that columns provide improved hydrodynamic conditions for flotation, and the capability of producing a cleaner product while maintaining high recovery.

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Equipment Innovation and Process Analysis

Figure 4. Layout of a mechanical flotation circuit (columns on 7 m centers) ■■

■■

■■

Columns exhibit higher particle/bubble contact efficiency than conventional machines, due to the particles colliding with the bubbles head-on. As a result, the energy intensity needed to promote contact is less, and so power consumption is reduced. In flotation using mechanical cells, the major loss of product often occurs in both the very coarse and the very fine size fractions. In column flotation, each air bubble must journey up the long vertical column from the bottom of the recovery zone to the top of the cleaning zone in a plug flow fashion, resulting in a long effective residence time. At the same time, the floatability of hydrophobic coarse particles can be enhanced by the absence of external turbulence which facilitates attachment to several small air bubbles simultaneously. The total effect of these factors can result in improved recovery. In mechanical flotation cells, contact occurs primarily in the region surrounding the mechanical impeller. The remainder of the cell acts mainly as a reservoir for material which has not yet been through the collection zone and can create a bottleneck which suppresses the flotation rate. In contrast, column cells have a collection zone that fills a high percentage of the machine so that there are more opportunities for particle/ bubble contact. The reduced level of turbulence

Figure 5. Layout and structural steel requirements for multiple columns

■■

needed to achieve good particle/bubble contact in columns also reduces the tendency of coarse particles to be torn away from the bubbles which they attach to, and therefore columns are more effective for floating coarser particles. Column flotation offers the advantage of controlling froth depth from a few centimeters to over a meter and is only limited by the particular mineral system being processed. This provides

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Column Flotation of Phosphate Ore—An Engineer’s Perspective213

■■

■■

■■

■■

■■

■■

■■

an additional vehicle that can be used to control the flotation separation process. The column cell does not have any mechanical mixing mechanism. This eliminates the necessity for costly items such as electric motors and special wear resistant agitators. In addition, the quiescent condition inside a column cell eliminates the need for abrasion resistant wear liners. The quiescent flotation conditions also prolong the life of the machine, thus reducing the cost of maintenance. Column flotation cells require bubble generators (either internal or external) which have had a history of mediocre operability. More recent bubble generators, such as those used by Eriez Flotation Group (formerly CPT), Metso Cisa and Xstrata, have shown to be less troublesome than their predecessors. In mechanical flotation cells, the bubbles are generated by the shear action of the impeller and the bubble size is therefore dependent on both airflow rate and impeller rpm. The bubble size in column flotation is controlled independently (via the bubble generator) to maximize recovery and grade. The absence of mechanical agitation in column cells may reduce the level of secondary slimes generation within the flotation circuit. Because there are relatively few control points and the flotation mechanism is unique for column flotation cells, the system is highly amenable to modern instrumentation and control techniques. However, column cells generally require a greater degree of automation than do mechanical cells. The entrainment of feed material in the froth product is a serious failing of conventional flotation machines. In most column flotation machines, the entrainment problem is addressed through the use of wash water to displace this feed to the tailings, thus preventing entrained contaminants from reaching the froth overflow. The difference in specific gravity (SG) of minerals can also affect flotation selectivity. The turbulent hydrodynamics of a mechanical flotation cell negatively impacts the differential SG effect. However, the quiescent condition in a flotation

■■

■■

■■

■■

column can take advantage of this effect, particularly when lighter SG minerals are floated from a heavier SG gangue. In general, a mechanical flotation machine cannot be used singly to produce final concentrate due to inherent short circuiting of feed reporting to the wrong products. In order to attain a reasonable grade and recovery, there are a minimum number of cells required for mechanical flotation machines; whereas comparable results may sometimes be achieved using only one flotation column. Because the column flotation cell is a vertical unit, a reduction in capital investment is attained through a reduction in required floor space when used for a new beneficiation plant. Also, the structure required to support a mechanical flotation machine (and the dynamic loading for the drive mechanism) is typically more robust than that required to support column flotation cells. The specific surface area and specific lip length of column flotation cells may limit throughput capacity in certain circumstances. The specific surface area of a flotation cell relates to the formation and drainage of froth and is typically higher for mechanical cells than for column cells. Typically, a lower specific surface area may limit the formation and drainage of froth. The specific lip length is related to the removal rate of froth and may be limiting where the froth product is the major mineral component of the feed. Froth “crowders” or internal froth launders are often utilized in column cells in cases where the froth removal rate is limiting. Some column flotation cell manufacturers utilize tailings recirculation to further optimize recovery. Three manufacturers that utilize tailings recirculation are Eriez Flotation Group (formerly CPT), Metso (Metso Cisa columns) and Xstrata (Jameson cell). Tailings recirculation requires a pump and control valves that are subject to wear and maintenance issues.

CONCLUDING REMARKS

The use of column flotation cells in the beneficiation of fine particles has long been recognised. The use of

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Equipment Innovation and Process Analysis

columns will become more frequent with the extraction of lower grade phosphate ores and the need to potentially grind finer to liberate the minerals. The decision to make use of column flotation cells in place of mechanical flotation cells is generally based on comparable pilot plant testing. The challenge for specifying columns versus mechanical flotation cells will come with the advent of large mechanical flotation cells (>30 m3 or 900 ft3) being developed to beneficiate phosphate ore. Columns do show economic benefit to the client in terms of potential capital savings and operating cost savings. ACKNOWLEDGEMENTS

The author thanks Michael Kelahan of Phosphate Consulting LLC for his contribution to this paper. The author would like to thank the management of WorleyParsons and Phosphate Consulting LLC for permission to present and publish this paper. LIST OF REFERENCES

Finch, J.A., Dobby, G.S., 1990. Column Flotation. Pergamon Press, New York. Sastry, K.V.S. (Ed.), 1988, Proceedings Column Flotation 88, SME/AIME, 12th Annual Meeting, Phonix, Arizona. Luttrell, Dr. G., Mankosa, M., 1996. Column Flotation. A Short Course for the Phosphate Industry. Florida Institute of Phosphate Research, Virginia Polytechnic Institute and State University, Florida. Gruber, G.A., Kelahan, M.E., 1988. Flotaire Cell Applications in Phosphate Flotation. SME Annual Meeting, Phoenix, Arizona.

Wheeler, D.A., Column Flotation—The Original Column, Column Flotation Co. of Canada, Ltd., McGill University Seminar, 1986. Wyslouzil, H.E., Phosphate Producers Improve Plant Performance Using CPT Inc. Flotation Technology. Unpublished paper, Canada. Wyslouzil, H.E., 2009. “The Use of Column Flotation for the Recovery of Ultra-Fine Phosphates,” http://en-ca.eriez.com/Products/ Markets/mineralflotation. Wyslouzil, H.E., Industrial Applications for Column Cells as Roughers, Unpublished paper, Canada. Moon, K.S., Sirois, L.L., 1988. Theory and Industrial Application of Column Flotation in Canada, Canada Centre for Mineral and Energy Technology (CANMET). Corem Project T1225, 2011. Pilot Testing of Apatite., Final Report (unpublished), Quebec. Corem Project T1446, 2013. Validation of Apatite Flow Sheet Using Column Flotation. Final Report – Revised (unpublished), Quebec. Corem Project T1492, 2013. Beneficiation of Apatite Using Pilot Plant Mechanical Cells, Final Report – Revised (unpublished), Quebec. Murdock, D.J., Tucker, R.J., Jacobi, H.P., 1991. Column Cells vs. Conventional Flotation, A Cost Comparison. Column 91, Int. Conf. on Column Flotation, Sudbury. Klassen, V.I., and Mokrousov, V.A. 1963. “An Introduction to the Theory of Flotation,” English translation by J. Leja and G.W. Poling. Butterworths, London. Huls B.J.P.M, 1990, “Interaction between grinding and flotation, specifically column flotation and column scale up,” PhD Thesis, Delft Technical University, Delft.

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CHAPTER 23

Phosphate in Australia—So Near Yet So Far Ewan Wingate* and John Dunster†

central Australian phosphate and a another round of greenfields exploration also began. Companies such as Legend International Holdings (Paradise South), Minemakers (Wonarah), and Rum Jungle Resources (Ammaroo) became the major players. At present, the only commercial exploitation of phosphate ore in Australia remains the Phosphate Hill operations of Incitec Pivot Limited (IPL). The operation consists of strip mining, minimal ore upgrading by washing followed by conversion of the phosphorite ore into phosphoric acid and MAP and DAP granular fertilisers. The major challenge in Australian phosphate projects on the eastern limb of the Georgina Basin is still the logistics of a bulk commodity, namely the location of the deposit relative to infrastructure links to ports. Water can also be an issue locally, but generally the Georgina Basin also contains aquifers with proven supply capability. The supply of natural gas is a major challenge to phosphate projects based on their locations. The Georgina Basin has largely untested petroleum potential with the first exploration wells in decades recently drilled in Queensland. The eastern limb of the Georgina Basin is located near the East coast LNG projects. The western Georgina Basin has the Amadeus pipeline and availability for internal gas in the Northern Territory. In the Northern Territory, an existing gas pipeline parallels the Stuart Highway.

Australia has some of the largest undeveloped phosphate ore deposits in the world. These are located within the Georgina Basin which spans an area from the north west of Queensland into the Northern Territory. It covers about 330,000km2. The host rocks to the phosphate are middle Cambrian sedimentary rocks and the phosphatic facies are restricted to areas of palaeo-highs and embayments along the palaeo-coastline. The first round of phosphate exploration of the Georgina Basin which started in the 1960s resulted in discoveries by the BMR and Broken Hill South such as Duchess, Phosphate Hill, Lady Annie, and Yelvercroft in north western Queensland. WMC established the Phosphate Hill operation, and became one of several companies pioneering the fertiliser industry in Queensland. Later in the 1960s phosphate discoveries were made in Northern Territory side of the Georgina Basin, most notably Wonarah found by IMC Development Corporation. Many of the deposits and prospects found during this initial round of exploration were never developed due to constraints in logistics, water and phosphate markets. During the 1990s, several more phosphate prospects were found while exploring for other commodities, but it was not until the sealing of the Stuart Highway and the completion of the Darwin-Alice Springs railway in 2004 that companies began revisiting

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Equipment Innovation and Process Analysis

INTRODUCTION

Australia is reported to contain in situ resources of phosphate in the region of 3 percent of the global phosphate resources based on 2013 resources estimates. These deposits are located within the Georgina Basin which spans an area from the north west of Queensland into the Northern Territory. It covers about 330,000km2. The host rocks to the phosphate are middle Cambrian sedimentary rocks and the phosphatic facies are restricted to areas of palaeohighs and embayments along the palaeo-coastline located in Queensland and the Northern Territory. The Australian deposits can be very large, with Rum Jungle Resources’ main Ammaroo deposit alone exceeding a billion tonnes at 17% P2O5 along 40km of strike. The original global resource at Duchess in Queensland was of similar tonnage and grade. The sedimentary phosphate ore in Australia is far removed from its Middle Eastern relatives due to the fine nature of the phosphorite crystals and the interwoven silicates and iron oxides found in the deposits in Australia. The Australian deposits also have a different suite of deleterious elements. There are some 41 reported phosphorite deposits in the Queensland and Northern Territory that lie within the Georgina Basin. Australia currently has one producing phosphate operation, Phosphate Hill, which is owned by Incitec Pivot. The country imports phosphate rock for use in blending plants where Single Super Phosphate fertiliser is produced. Phosphate hill produces high value ammoniated phosphate fertilisers from their own phosphate ore that has been converted into phosphoric acid. GEOLOGY OF THE GEORGINA BASIN

The Georgina Basin is a polyphase intracratonic basin containing unmetamorphosed Cryogenian to Devonian sedimentary rocks. It covers an area of 330 000km2  in the central-eastern Northern Territory and extends into western Queensland. The basin is bounded to the northeast and east by Proterozoic terranes of the McArthur Basin, South Nicholson Basin, Lawn Hill Platform and Mount Isa Inlier, and to the west by the Proterozoic Tomkinson, Warramunga and Davenport provinces of the Tennant Region.

To the south, the contact with the Palaeoproterozoic Aileron Province of the Arunta Region is a steep south side up thrust fault system. The Georgina Basin is continuous with the Daly and Wiso Basins, of similar age to the Georgina Basin and form distinct depocentres that are separated from the Georgina Basin by basement ridges formed by basement arches and basaltic rocks of the Kalkarindji Province. In the middle Cambrian, the interconnected Georgina, Wiso and Daly Basins collectively formed part of a vast depositional area that extended across northern, central and southern Australia; contiguous portions of this depositional system in northern and central Australia. The northern and south eastern portions of the Georgina Basin are overlain by Mesozoic sedimentary rocks of the onshore Carpentaria and Eromanga Basins, respectively. The Georgina Basin comprises two distinct domains: a southern basinal depocentre (southern Georgina Basin), essentially south of latitude 21°S, incorporating Ediacaran, Cambrian, Ordovician and Devonian successions (Dunster et al 2007); and a central-northern, quiescent platform (central and northern Georgina Basin) north of that latitude, including some late Neoproterozoic sedimentary rocks, early Cambrian Kalkarindji Province rocks and a relatively thin, platformal middle Cambrian succession. Phosphate Hill is hosted by the Beetle Creek Formation sequence in a 30km wide by 100km long, north-south elongated graben within the southern Mount Isa Block that formed the Duchess Embayment of the Georgina Basin. Within the embayment, the sequence of Cambrian marine sediments is generally less than 150 m thick and is largely obscured by a superficial cover of alluvium. These rocks overlie a local basement of Lower Cambrian Mount Birnie Beds that in turn unconformably rest on Palaeo to Mesoproterozoic basement, principally the Kalkadoon Granite. The Cambrian, marine sedimentary succession was deposited in a shallow to moderate depth marine shelf environment and contains a significant proportion of carbonate minerals. It has been subjected to periods of structural deformation, including both extensions, reflected by faults that bound the embayment to the east and west and

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Phosphate in Australia—So Near Yet So Far217

Figure 1. Regional geological setting of Georgina Basin. Northern Territory geological regions from NTGS 1:2.5M GIS database; Qld geological regions simplified and slightly modified from Denaro and Dhnaram (2009).

subsequent compression which produced open folds within the Cambrian sequence. EXPLORATION FOR PHOSPHATE IN THE GEORGINA BASIN

The first round of phosphate exploration of the Georgina Basin started in the 1960s and resulted in discoveries by the BMR and Broken Hill South in north western Queensland. The discoveries of note were Duchess, Phosphate Hill, Lady Annie and Yelvercroft. Western Mining Corporation (WMC) established the Phosphate Hill operation, and became

one of several companies pioneering the fertiliser industry in Queensland. Later in the 1960s phosphate discoveries were made in Northern Territory side of the Georgina Basin, most notably Wonarah found by IMC Development Corporation. Many of the deposits and prospects found during this initial round of exploration were never developed due to constraints in logistics, water and phosphate markets. Fast forward thirty years and during the 1990s, several more phosphate prospects were found while exploring for other commodities, but it was not until the sealing of the Stuart Highway

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Equipment Innovation and Process Analysis

and the completion of the Darwin-Alice Springs railway in 2004 that companies began revisiting central Australian phosphate and a another round of greenfields exploration also began. Companies such as Legend International Holdings (Paradise South), Minemakers (Wonarah), and Rum Jungle Resources (Ammaroo) became the major players. At present, the only commercial exploitation of phosphate ore in Australia remains the Phosphate Hill operations of Incitec Pivot Limited (IPL). The operation consists of strip mining, minimal ore upgrading by washing followed by conversion of the phosphate concentrate into phosphoric acid and MAP and DAP granular fertilisers. The major challenge in Australian phosphate projects is still the logistics of a bulk commodity, namely the location of the deposit relative to infrastructure links to ports. Water can also be an issue locally, but generally the Georgina Basin also contains aquifers with proven supply capability. The supply of natural gas is a major challenge to phosphate projects based on their locations. The Georgina Basin has largely

untested petroleum potential with the first exploration wells in decades recently drilled in Queensland. In the Northern Territory, an existing gas pipeline parallels the Stuart Highway. The location of the main phosphorite exploration targets within the Georgina Basin are illustrated in Figure 2. In Australia currently there are approximately three known projects that have progressed to some form of engineering and economic assessment. They are: ■■ ■■ ■■

Legend Paradise South Project (BFS)— Queensland Minemakers Wonarah Project (PFS/BFS Deferred)—Northern Territory Rum Jungle Resources Project (PFS)—Northern Territory

Other projects have started off exploring for phosphates (Carbonatite and sediment-hosted) but have then switched commodities when the REE content of the phosphorite resources has become apparent. Projects of this nature include;

Figure 2. Location of phosphate exploration sites and projects within the Georgina and Wiso Basins Note: The Barrow Creek 1 and Arganara deposits are now combined into a single contiguous resource called Ammaroo. Ammaroo 1 is now known as Ammaroo South. Lucy Creek is also known as Patanella.

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Phosphate in Australia—So Near Yet So Far219

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Krucible Metals Limited—Phosphates at Korella 2009, REE at Korella in 2011 Arafura Resources Ltd: Nolans Bore rare earth-phosphate-uranium-thorium.

BENEFICIATION OF AUSTRALIAN PHOSPHATE

The mineralogy of the phosphorite (phosphate) in the Georgina basin is best described as a very fine phosphate crystal interwoven with silicates and iron oxides. The typical mineralogy of the Georgina Basin phosphorite ores can best be summed up as follows: ■■ ■■

■■

Particle size at which phosphate is >80% liberated from silicates is