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C. K. GuptaN. Krishnamurthy

Extractive Metallurgyof Rare Earths

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Gupta, C. K.Extractive metallurgy of rare earths / C.K. Gupta, N. Krishnamurthy. p. cm.Includes bibliographical references and index.ISBN 0-415-33340-7 (alk. paper)1. Rare earth metals--Metallurgy. I. Krishnamurthy, N. (Nagaiyar) II. Title.

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Foreword

The field of the rare earths is fascinating. Important research and development work conti-nues globally to explore and establish ways and means to put the rare earths to use, individu-ally and collectively, in the service of humankind. In terms of rare earth reserves, India ranksamong the top ten countries of the world. Indian rare earth research and industry date backto the 1950s and have been based on the monazite available in the beach sands of the easternand the southern parts of the country.

Rare earth research, development, and production continue to be among the import-ant activities of our Department of Atomic Energy. Our accomplishments in these areashave derived strength and continue to do so from the work emerging from the MaterialsGroup of Bhabha Atomic Research Centre in Mumbai. In this context, Dr. C.K. Gupta andcolleagues deserve special mention for their continuing significant contributions to rareearth research and development. Dr. Gupta and his colleague, Dr. N. Krishnamurthy, areeminently qualified to author this book. I am pleased to have been invited to write thisforeword. The authors prepared in 1992 a comprehensive review of the state of the art ofextractive metallurgy of the rare earths. This paper was published in the InternationalMaterials Reviews and was well received. The authors’ abiding interest in this field hasfound expression now in the present comprehensive volume.

The authors have done a commendable job and deserve praise for being extremely suc-cessful in fulfilling the need for such a volume. The vast amount of information that hasbeen brought together and organized in this book had remained scattered throughout thescientific and engineering literature. Everyone involved with the extraction of the rareearths and the preparation of their numerous derivatives for a variety of specific applicationswill welcome this comprehensive publication. It should be useful to both experiencedprofessionals and neophytes in the rare earth field.

I would like to mention that Dr. Gupta has authored about a dozen books in the fieldof chemical metallurgy of special metals and materials. The present book is yet anotherimportant addition to this impressive list.

Anil Kakodkar Chairman, Atomic Energy Commission India

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Preface

A chronological account of the chemistry and metallurgy of the rare earths arranges intothree eras or ages. The basis of this division is the availability and purity of the rare earthmetals and materials and the scientific and engineering information about them. The periodprior to 1950 may be called the “Dark Age.” The next two decades were the “Age ofEnlightenment.” The period after the early 1970s may be considered the “Golden Age.” Inthe first three decades of this golden era a number of remarkable advances and discoverieswere made in the field of rare earths, and these have left an indelible mark on the globalmaterials scenario. It is widely perceived that the future of the rare earths will be gloriousand full of excitement, be it in science, technology, or in commercial utilization.

The rare earths are a community of 17 metallic elements, all but one occurring natural-ly (14 lanthanides and 2 associated elements). They are found in combination in mineraldeposits widespread throughout the world. Notably large reserves exist in China, the U.S.,and Australia. The word “rare” in “rare earths” arises more from the historical difficulty inseparating and obtaining them as individual pure elements than from their inherentnonavailability. There have been major developments in the technologies for the productionof separated high purity rare earths. Highly efficient separation technologies have been keyto the exploitation of the rare earths in a wide range of now commonplace applications thathave slowly become an inseparable part of modern living.

The scientists at Bhabha Atomic Research Centre in Mumbai, India are proud to be inthe global mainstream of the scientific and technological research and development ac-tivities in the field of rare earth chemicals, metals, and alloys. The Indian rare earth programalso includes commercial scale manufacture of rare earth products for domestic and inter-national markets. Our long association with rare earth research motivated us some time agoto produce a review on the extractive metallurgy of the rare earths. This was published inthe International Materials Reviews. This review provided a concise guide to access andretrieve information from the vast rare earth literature. It was, however, no substitute for acomprehensive book, which would serve as a reference text that stands on its own withdetailed information on selected topics. With the publication of the review in 1992 and ourprogressively increasing involvement with the rare earths, our thinking gradually trans-formed into a commitment to preserve the available information on the extractive metal-lurgy of the rare earths in the form of a book. This thinking gathered further momentumbecause we found that although a voluminous literature in the form of numerous conferenceproceedings, a highly rated series of volumes on the physics and chemistry of the rare earth

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elements (edited by Gschneidner and Eyring), and important trade publications and news-letters is available, all of these publications have objectives different from that of our book.We are not aware of any other text that covers the subject in the manner we have attemptedhere. We have worked to bring together all relevant matters concerning the extractive metal-lurgy of the rare earths and related information that, at present, remains scattered in a varietyof forms of published literature.

This book has been organized into seven chapters. Chapter 1, The Rare Earths,provides the background information on the properties and applications of the rare earthsand highlights the links of these aspects to the totality of rare earth extraction and processingtechniques. The interesting sequence of the discovery of the rare earths is first presented,followed by a listing and discussion of the currently accepted values and informationpertaining to the various properties of the rare earths. A comprehensive account of all majorapplications of the rare earths is then provided.

Chapter 2, Resources, presents in detail all currently available information on theworld’s rare earth resources, their location, quality, and quantity. The resource utilizationtrends and patterns from the times when the rare earths were first produced as a commodityup to the present are presented. Factors leading to the unequal availability of the rare earthsare highlighted, and the world’s rare earth resources position is dealt with in the context ofcurrent and projected demands.

Chapter 3, Resources Processing, incorporates a detailed account of the techniques forthe processing of the various rare earth resources and the separation of individual rare earthelements. While placing a strong emphasis on the modern methods of solvent extraction andion exchange, the salient features of the classical methods of rare earth separation arecovered in detail. Various options for the treatment of the as-mined rare earth resources byphysical and chemical beneficiation methods prior to separation are discussed.

Chapter 4, Reduction, deals with the techniques for converting the pure rare earthoxide intermediates to the metals. The numerous scientifically interesting and technologi-cally challenging procedures for rare earth metal reduction are described in considerabledetail. Chemical as well as electrochemical reduction methods have been used and the var-iety in the actual processes has come about because of the different physical properties ofthe individual rare earth elements. Particularly, the melting and boiling points of the elem-ents dictate the type of process best suited for reduction. These aspects are discussed.

Chapter 5, Refining, is devoted to the purification of the rare earth metals. Elucidationof the unique properties of the rare earth elements has been possible only with the availabil-ity of these elements in very pure forms; therefore, major efforts have gone into the develop-ment of suitable techniques such as pyrovacuum treatment, zone melting, and electrotrans-port to prepare metals of high purity levels. The chapter covers these refining techniques asapplied to different rare earth metals.

Chapter 6, Rare Earth Materials, is concerned with the techniques for the preparationof the numerous rare earth alloys and compounds and rare earth bearing materials. Amongthe materials described are the traditional products like misch metal and rare earth–iron–silicon alloys, as well as new materials like lanthanum–nickel alloys, permanent magnetmaterials based on samarium and neodymium, magnetostrictive and magnetocaloric mater-ials. The procedures followed by various manufacturers of rare earth materials are outlined.The presentation also covers methods under investigation for newer materials.

Chapter 7 is an overview — a sojourn for the reader in the world of the rare earths.While going through this chapter one can develop a brief but significant acquaintance withthe rare earths in their entirety.

In all the chapters the text is liberally supported by tables and figures. Key property

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values and results have been listed in the tables, and the figures comprise line drawings ofequipment and flowsheets of processes. References to original papers are extensively madein the text and all the references are grouped in one place at the end of the book. The refer-ence list will serve as a very useful guide for those who want to refer to the original sourcesfor more information on specifics.

We hope this book will be useful to professionals involved with the extraction, separ-ation, concentration, and production of the rare earth metals, alloys, and chemicals. Theyinclude process, production, and regulatory staff engineers; management as well as researchand development professionals; graduate students; and libraries attached to universities andR&D establishments.

We would like particularly mention the contributions of certain people who have beenespecially involved, with the preparation of this book. The work pertaining to the produc-tion of the typed version of the manuscript in its finished form was very efficiently handledby Poonam Khattar. All figures for the book were drawn by Yatin Thakur. We are gratefulto the editorial department of G+B, particularly to Catherine Bewick in the initial stagesand to Sally Cheney, Lloyd W. Black, and Matt Uhler in the latter stages for support- ingand encouraging us in the project.

Finally, we wish to dedicate this book to our wives, Chandrima Gupta and KusumaKrishnamurthy, in gratitude for their unique contributions towards the completion of thiswork.

Bhabha Atomic Research Centre C.K. GuptaMumbai, India N. Krishnamurthy

August 15, 2004

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Acknowledgment

The effort to bring out this book on the extractive metallurgy of rare earths has been greatlysupported by many wonderful people. The list is too long. However, there have beentremendous positive contributions to building this work from Mrs. Janie Wardle of Taylor& Francis Books and Mr. Victor D. Selivanov, Production Coordinator, Izdatelsky DomFIAN, Moscow. We gratefully acknowledge their great cooperation and support.

It is our pleasure to acknowledge Mr. Chiradeep Gupta, Scientist from Bhabha AtomicResearch Centre, and his wife Mrs. Nita Gupta, who contributed considerably to the proofcorrection work.

Several figures and tables that appear in this book have originally appeared in publica-tions by Elsevier, The Electrochemical Society, John Wiley and Sons, Wiley-VCH, ASMInternational, The Minerals, Metals and Materials Society, The Institute of Materials,Minerals and Mining, American Powder Metallurgical Institute, National TechnicalInformation Service, Metal Rare Earth Ltd. and American Chemical Society. We are grate-ful to these institutions and other authors who very graciously gave permission to reproducematter from their publications in this book.

Bhabha Atomic Research Centre C.K. GuptaMumbai, India N. Krishnamurthy

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Contents

Foreword Preface Acknowledgment

Chapter 1 The Rare Earths 1.1 INTRODUCTION 1.2 DISCOVERY 1.3 SPECIAL CHARACTERISTICS

1.3.1 Electronic Configuration1.3.2 Lanthanide Contraction 1.3.3 Basicity

1.4 PROPERTIES1.4.1 Melting Point 1.4.2 Boiling Point 1.4.3 Allotropes1.4.4 Resistivity1.4.5 Magnetic Properties 1.4.6 Spectral Properties 1.4.7 Mechanical Properties

1.5 REACTIVITY1.5.1 Air/Oxygen1.5.2 Refractories1.5.3 Nitrogen1.5.4 Hydrogen1.5.5 Carbon1.5.6 Silicon1.5.7 Sulfur, Selenium, Phosphorus 1.5.8 Refractory Metals 1.5.9 Acids and Bases 1.5.10 Water

1.6 AQUEOUS SYSTEMS

pages are not final

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1.6.1 The Trivalent State 1.6.2 Complexes1.6.3 The Tetravalent State 1.6.4 The Divalent State

1.7 APPLICATIONS1.7.1 Metallurgy1.7.2 Magnets1.7.3 Terfenol1.7.4 Magnetic Refrigeration 1.7.5 Magnetooptic Materials 1.7.6 Ceramics1.7.7 Electronics1.7.8 Chemical1.7.9 Optical1.7.10 Phosphors1.7.11 Nuclear1.7.12 Hydrogen Storage 1.7.13 Superconductor1.7.14 Miscellaneous

1.8 SUMMARY

Chapter 2 Resources of Rare Earths2.1 INTRODUCTION2.2 CRUSTAL ABUNDANCE 2.3 MINERALS

2.3.1 Bastnasite2.3.2 Monazite2.3.3 Xenotime2.3.4 Allanite2.3.5 Apatite2.3.6 Brannerite2.3.7 Eudialyte2.3.8 Euxenite, Fergusonite, Florencite, Gadolinite, and Loparite 2.3.9 Perovskite2.3.10 Pyrochlore2.3.11 Zircon2.3.12 Others2.3.13 Scandium Minerals 2.3.14 Promethium

2.4 RARE EARTH DEPOSITS 2.4.1 Primary and Secondary 2.4.2 Carbonatites2.4.3 Pegmatites2.4.4 Hydrothermal Deposits2.4.5 Weathered Deposits2.4.6 Placers2.4.7 Distribution

2.5 RESOURCES AND RESERVES

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2.6 OCCURRENCES2.6.1 Argentina2.6.2 Australia2.6.3 Bangladesh2.6.4 Brazil2.6.5 Canada2.6.6 China2.6.7 Germany2.6.8 India2.6.9 Indonesia2.6.10 Japan2.6.11 Malaysia2.6.12 Malawi2.6.13 Mozambique2.6.14 Myanmar2.6.15 New Zealand 2.6.16 Peru2.6.17 South Africa 2.6.18 Sri Lanka 2.6.19 Taiwan2.6.20 Thailand2.6.21 Turkey2.6.22 United States 2.6.23 Former USSR 2.6.24 Venezuela2.6.25 Vietnam2.6.26 Zaire

2.7 BY-PRODUCTS AND CO-PRODUCTS 2.8 WORLD RARE EARTH PRODUCTION AND AVAILABILITY

2.8.1 Brazil 2.8.2 India2.8.3 United States 2.8.4 Australia2.8.5 China2.8.6 Former Soviet Union 2.8.7 South Africa 2.8.8 Canada2.8.9 Malaysia2.8.10 Thailand2.8.11 Sri Lanka 2.8.12 Zaire and Madagascar

2.9 RARE EARTH PRODUCTION POTENTIAL 2.10 FORECAST2.11 SUMMARY

Chapter 3 Resource Processing3.1 INTRODUCTION3.2 MINING

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3.2.1 Hard Rock Deposits 3.2.2 Placer Deposits

3.3 PHYSICAL BENEFICIATION 3.3.1 Monazite3.3.2 Bastnasite3.3.3 Bayan Obo Ore

3.4 CHEMICAL TREATMENT 3.4.1 Monazite3.4.2 Bastnasite3.4.3 Chlorination3.4.4 Xenotime3.4.5 Elliot Lake Uranium Ore 3.4.6 Gadolinite3.4.7 Euxenite3.4.8 Loparite, Pyrochlore, Fergusonite, and Samarskite 3.4.9 Apatite

3.5 SEPARATION PROCESSES 3.5.1 Selective Oxidation 3.5.2 Selective Reduction 3.5.3 Fractional Crystallization 3.5.4 Fractional Precipitation 3.5.5 Ion Exchange 3.5.6 Solvent Extraction

3.6 SCANDIUM3.7 SUMMARY

Chapter 4 Reduction4.1 INTRODUCTION4.2 FUNDAMENTALS4.3 METALLOTHERMY4.4 PREPARATION OF RARE EARTH CHLORIDES

4.4.1 Preparation of Hydrated Rare Earth Chloride 4.4.2 Dehydration of Hydrated Rare Earth Chlorides 4.4.3 Dry Methods 4.4.4 Purification of Rare Earth Chlorides

4.5 REDUCTION OF RARE EARTH CHLORIDES 4.5.1 Early Attempts 4.5.2 Reduction in a Refractory Bomb 4.5.3 Reduction in Tantalum Crucible 4.5.4 Intermediate Alloy Processes 4.5.5 Kroll Type Processes

4.6 PREPARATION OF RARE EARTH FLUORIDES 4.6.1 Wet Method 4.6.2 Dry Methods 4.6.3 Purification of Rare Earth Fluorides

4.7 REDUCTION OF RARE EARTH FLUORIDES 4.7.1 Lithium Reduction 4.7.2 Calcium Reduction (Ames Process)

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4.7.3 Intermediate Alloy Process 4.7.4 Preparation of Scandium 4.7.5 Reduction of Samarium, Europium, and Ytterbium Halides

4.8 OXIDE REDUCTION PROCESSES 4.8.1 Reduction–Distillation—Lanthanothermy4.8.2 Reduction–Distillation—Other Reductants

4.9 NEW REDUCTION PROCEDURES 4.9.1 Direct Preparation of Gadolinium Metal Powder 4.9.2 Metallothermic Reduction in Molten Salt

4.10 CARBOTHERMIC REDUCTION 4.11 ELECTROLYTIC PRODUCTION OF RARE EARTH METALS

4.11.1 Chloride Electrolysis 4.11.2 Electrowinning at Room Temperature 4.11.3 Electrowinning Solid Metal Deposits 4.11.4 In situ Preparation of Electrolyte 4.11.5 Commercial Electrowinning from Rare Earth Chlorides 4.11.6 Oxide–Fluoride Electrolysis

4.12 RECOVERY OF RARE EARTH METALS AS ALLOYS 4.12.1 Electrolysis of Chlorides 4.12.2 Electrolysis of Oxide–Fluoride Melts

4.13 CURRENT EFFICIENCY 4.14 SUMMARY

Chapter 5 Refining Rare Earth Metals5.1 INTRODUCTION5.2 ORIGIN OF IMPURITIES

5.2.1 Starting Materials 5.2.2 Crucible5.2.3 Environment

5.3 METHODS FOR IMPURITY REMOVAL 5.4 PYROVACUUM TREATMENTS

5.4.1 Distillation5.4.2 Removal of Halogens/Halides 5.4.3 Degassing

5.5 PYROVACUUM TECHNIQUES 5.5.1 Lanthanum, Cerium, Praseodymium, and Neodymium 5.5.2 Yttrium, Gadolinium, Terbium, and Lutetium 5.5.3 Scandium, Dysprosium, Holmium, Erbium, and Lutetium 5.5.4 Samarium, Europium, Thulium, and Ytterbium

5.6 ELECTROREFINING5.6.1 Yttrium5.6.2 Gadolinium5.6.3 Cerium

5.7 ULTRAPURIFICATION METHODS 5.8 ZONE REFINING

5.8.1 Preliminary Studies 5.8.2 Lanthanum, Gadolinium, and Terbium 5.8.3 Lanthanum, Cerium, and Gadolinium

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5.9 SOLID STATE ELECTROTRANSPORT 5.9.1 SSE System 5.9.2 Residual Resistivity Ratio 5.9.3 Lanthanum5.9.4 Praseodymium5.9.5 Neodymium5.9.6 Gadolinium5.9.7 Terbium5.9.8 Yttrium5.9.9 Dysprosium and Holmium 5.9.10 Erbium5.9.11 Lutetium5.9.12 Samarium

5.10 ZONE REFINING AND ELECTROTRANSPORT 5.10.1 Neodymium5.10.2 Gadolinium

5.11 IODIDE REFINING 5.12 MISCELLANEOUS PROCESSES 5.13 SUMMARY

Chapter 6 Rare Earth Materials6.1 INTRODUCTION6.2 MISCH METAL

6.2.1 Preparation of Mixed Rare Earth Chlorides 6.2.2 Electrolysis of Chlorides 6.2.3 Electrolysis of Oxide–Fluoride Melts 6.2.4 Ames Process 6.2.5 Thermal Reduction Process

6.3 RARE EARTH–SILICON–IRON ALLOYS 6.3.1 Reno (USBM) Process 6.3.2 BARC Process 6.3.3 Baotou Process

6.4 RARE EARTH–MAGNESIUM–SILICON ALLOYS 6.5 RARE EARTH–ALUMINUM–ZINC ALLOY 6.6 YTTRIUM–ALUMINUM ALLOY 6.7 PERMANENT MAGNET MATERIALS 6.8 RARE EARTH–Co PERMANENT MAGNETS

6.8.1 Preparation6.8.2 Preparation of Magnets

6.9 NEODYMIUM–IRON–BORON MAGNETS 6.9.1 Production of Nd–Fe–B Alloys 6.9.2 Production of Nd–Fe–B Magnets

6.10 Sm–Fe–N MAGNETS 6.11 NANOCOMPOSITE PERMANENT MAGNET MATERIALS 6.12 TERFENOL-D6.13 MAGNETIC REFRIGERANTS 6.14 THIN FILM DEPOSITION PROCESSES

6.14.1 Bubble Domain Memory Materials

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6.14.2 Magnetooptic Storage Media 6.15 LaNi56.16 SUPERCONDUCTORS6.17 SUMMARY

Chapter 7 A Sojourn in the World of Rare Earths7.1 THE PERIODIC TABLE OF ELEMENTS 7.2 RADIATION7.3 LANTHANIDE AND ACTINIDE ELEMENTS 7.4 PROCESSING RARE EARTHS 7.5 APPLICATIONS OF RARE EARTHS 7.6 METHODS OF PREPARING ELEMENTAL AND COMPOUND

FORMS OF RARE EARTHS 7.7 CONCLUSION

REFERENCES

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