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Preparation of Yttrium and Rare-Earth Metals by Metallothermic Reduction

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Preparation of Yttrium and Rare-Earth Metals by Metallothermic Reduction AN ABSTRACT OF THE THESIS OF Frank Elmer Block for the Ch.E. in Chemical Engineering (Name) (Degree) Date thesis is presented Title PREPARATION OF YTTRIUM AND RARE -EARTH METALS BY METALLOTHERMIC REDUCTION Abstract approved Major Professor An investigation was made of various methods for the preparation of yttrium or rare -earth metals by metallothermic reduction. Particular emphasis was placed on the use of high -purity chloride salts as intermediates. Methods were stressed which appeared adaptable to production of high - purity, ductile metal on a plant scale. Reactions were chosen for study on the basis of thermo- dynamic considerations and also from a standpoint of chemical and physical properties of reactants and byproducts. Consideration was given to construction materials and their contribution of impurities to the metal products. Yttrium or rare -earth chlorides, fluorides, bromides or iodides were investigated as intermediates for metal production. Emphasis was placed on the development of methods for pre- paring these halides and for refining them to a high state of purity. Rare -earth chlorides were prepared either by slow dehydration of hydrated salts while in contact with ammonium chloride, or by a more rapid technique involving the direct chlorination of mixtures of rare -earth oxides and carbon. In either case, chloride salts were purified by vacuum distillation or by filtration of molten salts. Lithium, sodium, potassium and calcium were tested as reductants for anhydrous halides. These metals were compared as reductants on the basis of operating characteristics, purity of metal product, and yield of product. Yttrium and rare -earth metals prepared in this study were consolidated, usually by inert -atmosphere arc melting, and the consolidated metals were evaluated on the basis of chemical analyses and mechanical workability. Of the many systems studied, best results were obtained by the lithium reduction of rare -earth chlorides in Inconel or molybdenum apparatus. Metal made by this procedure was freed of byproduct lithium chloride by vacuum distillation, and the rare -earth metal, which appeared as a sponge, was consolidated by arc -melting. Yttrium was prepared by this technique on a scale of 15 pounds of metal per batch. Metal recoveries were greater than 95 percent and the major impurity, oxygen, was usually present in amounts less than 500 ppm. Samarium and europium cannot be prepared by reduction of their halide salts. These metals were produced by reduction of their oxides in a high vacuum employing lanthanum, cerium, or zirconium as reductants. Yields were usually over 90 per- cent during tests conducted at 900 to 1450°C. PREPARATION OF YTTRIUM AND RARE -EARTH METALS BY METALLOTHERMIC REDUCTION by FRANK ELMER BLOCK A THESIS submitted to OREGON STATE UNIVERSITY in partial fulfillment of the requirements for the degree of CHEMICAL ENGINEER June 1963 APPROVED: Professor of Chemical Engineering Head of Department of Chemical Engineering Chairman of School Graduate Committee MIMEDean of Graduate School / __ Date thesis is presented s , - 4__) , ) Typed by Grace Danton Bernice Wirowek ACKNOWLEDGEMENT The work on which this thesis is based was performed at the Albany Metallurgy Research Center of the U. S. Bureau of Mines. It was supported by funds authorized by the Bureau of Mines and by the U. S. Atomic Energy Commission. The author is grateful to the Bureau for the opportunity to present this work. Special thanks are due his colleagues, Thomas T. Campbell, Ralph E. Mussler, and Gabriel B. Robidart who participated in the project upon which this thesis is based. Credit is also acknowl - edged to the many other associates who contributed to this broad project. The author is also grateful to Dr. Charles E. Wicks and other members of the Staff of the Department of Chemical Engineering for their encouragement and help in furthering the chemical engineering profession within the metallurgical industry. TABLE OF CONTENTS Page INTRODUCTION 1 THEORETICAL CONSIDERATIONS 5 Free -Energy Changes 5 Physical Properties of Reactants and Products 17 Purity of Reactants 25 EXPERIMENTAL PROCEDURES AND RESULTS 28 Preparation of Rare -Earth Fluorides by Reaction of Rare -Earth Oxides With Ammonium Bifluoride -- 28 Preparation of Rare -Earth Chlorides 30 Reaction of Rare -Earth Oxides With Ammonium Chloride 34 Dehydration of Hydrated Rare -Earth Chlorides in Presence of Ammonium Chloride 38 Direct Chlorination of Rare -Earth Oxides 39 Purification of Rare -Earth Chlorides 44 Vacuum Distillation 44 Filtration of Molten Chlorides 47 Materials of Construction 49 Preparation of Yttrium Bromide and Iodide by Reaction of Yttrium Carbide with Hydrogen Halides 52 Metallic Reduction of Rare -Earth Halides 55 Bomb Reduction of Rare -Earth Chlorides 57 Calcium Reduction of Rare -Earth Halides 58 Reduction of Rare -Earth Chlorides 64 Reduction of Yttrium Bromides and Iodides 75 Metallic Reduction of Samarium and Europium Oxides in Vacuo 77 Consolidation of Rare -Earth Metals by Arc - Melting 85 Page Impurity Analysis of Rare -Earth and Yttrium Metal - - -- 86 Mechanical Working of Rare -Earth Metals 96 CONCLUSIONS 98 BIBLIOGRAPHY 102 LIST OF FIGURES Figure Title Page 1. Free -Energy Change for Metallic Reduction of Rare -Earth Oxides 7 2. Free -Energy Change for Metallic Reduction of Rare -Earth Oxides 8 3. Free -Energy Change for Metallic Reduction of Rare -Earth Fluorides 9 4. Free -Energy Change for Metallic Reduction of Rare -Earth Fluorides 10 5. Free -Energy Change for Metallic Reduction of Rare -Earth Chlorides 11 6. Free -Energy Change for Metallic Reduction of Rare -Earth Chlorides - 12 7. Free- Energy Change for Metallic Reduction of Rare -Earth Bromides - - -- 13 8. Free- Energy Change for Metallic Reduction of Rare -Earth Bromides 14 9. Free -Energy Change for Metallic Reduction of Rare -Earth Iodides 15 10. Free -Energy Change for Metallic Reduction of Rare -Earth Iodides 16 11. Vacuum Dehydration and Ammonium Halide Sublimation Unit 35 12. Rare -Earth Chlorination Apparatus 42 13. Rare -Earth Halide Purification Assembly 46 14. Halogenation Apparatus for Preparing Yttrium Bromide or Yttrium Iodide 54 15. Inert Atmosphere Reduction Assembly 62 16. High -Vacuum Reduction -Distillation Assembly - -- 66 17. Metallic -Reduction. Assembly 72 18. Large Scale Reduction -Distillation Assembly 80 19. Split- Graphite Re sistor Furnace Assembly 84 20. Photomicrographs of Rare -Earth Metals 95 LIST OF TABLES Number Page 1. Rare -Earth Halide Melting Points and Estimated Temperatures for 2 mm and 760 mmHg Vapor Pressure 19 2. Fusion and Vaporization Temperatures of Reduc- tants and Their Halide Salts 23 3. Analysis of Metallic Reductants 26 4. Preparation of Rare -Earth Fluorides by Reaction of Rare -Earth Oxides with Ammonium Bifluoride 31 5. Preparation of Rare -Earth Chlorides by Reaction of Rare -Earth Oxides with Ammonium Chloride 37 6. Preparation of Rare -Earth Chlorides by Dehydra- tion of Hydrated Chlorides in the Presence of Ammonium Chloride 40 7. Preparation of Rare -Earth Chlorides by Chlorina- tion of Rare -Earth Oxides 43 8. Results of Yttrium Chloride Corrosion Tests - - -- 51 9. Preparation of Yttrium Iodides and Bromides 56 10. Bomb Reduction of Lanthanum and Cerium Chlorides 59 11. Inert -Atmosphere Crucible -Reduction of Rare - Earth Fluorides 65 12. Inert -Atmosphere Crucible -Reduction of Rare - Earth and Yttrium Chlorides 71 13. Sodium Reduction of Yttrium Chloride 75 14. Metallic Reduction of Yttrium Bromides and Iodides 77 15. Metallic Reduction of Samarium and Europium Oxides - 82 16. Semiquantitative Spectrographic Analysis of Rare -Earth Metals Prepared by Bomb Reduction 88 17. Chemical and Semiquantitative Spectrographic Analysis of Rare Earth Metals Prepared by Calcium Reduction 89 18. Chemical and Semiquantitative Spectrographic Analysis of Rare -Earth Metals Prepared by Lithium and Sodium Reduction of Anhydrous Chlorides 90 19. Chemical and Semiquantitative Spectrographic Analysis of Yttrium Metal Prepared from Yttrium Bromides and Iodides - 91 20. Chemical and Semiquantitative Spectrographic Analysis of Samarium and Europi um Metal - 92 PREPARATION OF YTTRIUM AND RARE -EARTH METALS BY ME TALLOTHERMIC REDUCTION INTRODUCTION The group of 16 1/ elements which comprise yttrium and the rare earths, or lanthanides, are always found closely associated in nature. Chemists have long sought ways to separate these elements and although complex fractional precipitation techniques had been employed with partial success for over 150 years, only during the last 15 years have methods been developed for preparing individual rare -earth oxides in high purity form. Spedding and co- workers at Iowa State University (40,41) developed ion exchange techniques by which rare -earth ions can be selectively eluted from cation exchange resins to separate these elements in any required state of purity. During the last 10 years high - purity rare -earth oxides have become available commercially and tonnage quantities of yttrium oxide have been produced for government contract research. Rare -earth metals have been prepared on a gram scale by reduction of anhydrous halides, notably chlorides, almost as long as rare -earth compounds have been separated. As long ago as 1827 Mosander prepared metallic cerium by reducing cerous chloride with 1/ Element 61, promethium, does not exist in nature as a stable element. 2 potassium (36). Since that time most experimenters have employed metallic reduction of halide salts as a method for metal
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