THE THERMODYNAMIC PROPERTIES OF NEODYMIUM HYDROXIDE IN ACID, NEUTRAL, AND ALKALINE SOLUTIONS AT 25°C.: AN INTERPRETATION OF THE IONIC SPECIES PRESENT IN AQUEOUS SOLUTIONS OF NEODYMIUM SALTS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By RUSSELL STUART TOBIAS, B. Sc. 4 \ «V St i't The Ohio State University 1956 Approved by: Adviser Department! of Chemistry AC KNOWLEDGEMENT The author wishes to express his sincere appreciation to Professor A. B. Garrett for his encouragement and counsel during the course of this investigation. I also wish to thank him for his interest in my welfare while I have been a student at The Ohio State University. I also wish to thank The Ohio State University for the assistant ship granted to me and the Visking Corporation, the General Electric Corporation, E. I. du Pont de Nemours and Company, and the Allied Chemical and Dye Company for financial assistance during the course of my studies. Finally, I would like to acknowledge the assistance of Mr. G. W. Leddicotte, of the Oak Ridge National Labora­ tory, who performed the activation analyses described in this work. TABLE OF CONTENTS Subject Page INTRODUCTION ............................................. 1 HISTORICAL REVIEW ........................................ 3 The Basicity of the Rare Earth Oxides ............ 3 The System Neodymium Oxide-Water ................. 4 The Hydrolysis of Neodymium Solutions .......... 9 The Analyses of Solutions of Neodymium ........... 11 EXPERIMENTAL . .. 18 General Procedure ................................... 18 Preparation of the Reagents ....................... 18 Neodymium Oxide ................................. 18 Hydrochloric Acid Solutions ................... 20 Sodium Hydroxide Solutions .......... 20 Perchloric Acid Solutions ........... 21 Neodymium and Praseodymium Perchlorate Buffers 22 Sodium Chloride Solutions ..................... 22 Sodium Perchlorate Solutions ................. 22 Distilled Water ............................ 23 Hydrolysis Studies .................................. 23 Experimental Method ............................ 23 Electrochemical Cells ..................... 25 Electrical Circuits ................. 34 Details of the Experimental Procedure ....... 37 Analysis of the Free Acid Concentration of the Rare Earth Buffers ......... 4 1 iii TABLE OF CONTENTS (Cont'd.) Solubility Studies .................................... 42 Preparation of Samples ............ ............. 42 Equilibration ..................................... 43 Sedimentation ................................. 44 Transfer of the Solutions for Analysis .......... 44 Measurement of the Hydrogen Ion Concentration . 46 Spectrophotometric Analyses ..................... 47 Activation Analyses .............................. 55 Analysis of the Solid Phase in theEquilibria . 56 THE DATA .... a . ..................................... 65 AN ANALYSIS OF THE DATA OBTAINED FROM THE DISSOLUTION OF METALLIC HYDROXIDES IN DILUTE ACIDS AND FROM A STUDY OF THE RESULTING EQUILIBRIA ..................... 104 AN ANALYSIS OF THE DATA OBTAINED FROM THE DISSOLUTION OF METALLIC HYDROXIDES IN BASIC SOLUTION AND FROM THE WATER SOLUBILITY .................................... 125 AN ANALYSIS OF THE EXPERIMENTAL DATA FOR NEODYMIUM HYDROXIDE ................................................. 129 Equilibria with Hydrochloric Acid.................... 129 Equilibria with Perchloric A c i d ............... 147 Equilibria with Water and with Sodium Hydroxide Solutions ...................................... 148 Hydrolysis of the Tri-valent cations of Neodymium and Praseodymium .............................. 154 CONCLUSIONS................................................. 166 iv LIST OP TABLES Table Page 1. A Comparison of the E.M.F. of the Glass and Quinhydrone Electrodes in the Presence of 0.01 C Pr+3 ................................................... 32 2. A Comparison of the E.M.P. of the Glass and Q,uinhydrone Electrodes in the Presence of 0.025 C Nd+3 ..................................................... 33 3. Powder Photograph Data for the Water Equilibrated Sample of Neodymium Oxide ............................ 61 4. Powder Photograph Data for the Anhydrous Oxide of N e o d y m i u m ........................................ 63 5. Hydrolysis of Neodymium Perchlorate, c » 24.45 mC, Standardization of Electrodes ........................ 66 6. Hydrolysis of Neodymium Perchlorate, c = 24.45 mC, Titration of Buffer Solution ......................... 67 7. Hydrolysis of Neodymium Perchlorate, c = 24.45 mC, Calculation of Average Ligand Number ............... 68 8. Hydrolysis of Neodymium Perchlorate, c = 9.79 mC, Standardization of Electrodes ................... 70 9. Hydrolysis of Neodymium Perchlorate, c » 9.79 mC, Titration of Buffer Solution ........................ 71 10. Hydrolysis of Neodymium Perchlorate, c = 9.79 mC, Calculation of Average Ligand Number ................ 72 11. Hydrolysis of Neodymium Perchlorate, c ** 4.895 mC, Standardization of Electrodes ........................ 73 v / LIST OP TABLES (Cont'd.) 12. Hydrolysis of Neodymium Perchlorate, c = 4.895 mC, Titration of Buffer Solution ...................... 74 13. Hydrolysis of Neodymium Perchlorate, c = 4.895 mC, Calculation of Average Ligand Number ................ 75 14. Hydrolysis of Praseodymium Perchlorate, c = 25.00 mC, Standardization of Electrodes .................. 78 15. Hydrolysis of Praseodymium Perchlorate, c = 25.00 mC, Titration of Buffer Solution .......................... 79 16. Hydrolysis of Praseodymium Perchlorate, c = 25.00 mC, Calculation of Average Ligand Number ................ 81 17. Hydrolysis of Praseodymium Perchlorate, c = 12.50 mC, Standardization of E l e c t r o d e s .............. 83 18. Hydrolysis of Praseodymium Perchlorate, c = 12.50 mC, Titration of Buffer Solution ......................... 84 19. Hydrolysis of Praseodymium Perchlorate, c = 12.50 mC, Calculation of Average Ligand Number ............. 85 20. Hydrolysis of Praseodymium Perchlorate, c =< 10.24 mC, Standardization of Electrodes ........................ 86 21. Hydrolysis of Praseodymium Perchlorate, c = 10.24 mC, Titration of Buffer Solution ........ 87 22. Hydrolysis of Praseodymium Perchlorate, c = 10.24 mC, Calculation of Average Ligand Number ................ 88 23. Hydrolysis of Praseodymium Perchlorate, c «= 5.00 mC, Standardization of Electrodes ........................ 90 vi i LIST OP TABLES (Cont'd.) 24. Hydrolysis of Praseodymium Perchlorate, c « 5.00 mC, Titration of Buffer Solution ......................... 91 25. Hydrolysis of Praseodymium Perchlorate, c *> 5.00 mC, Calculation of Average Ligand Number ............... 92 26. Solubility of Neodymium Hydroxide in Hydrochloric Acid at 25°C............................................. 94 27. Data on the Equilibrium between Neodymium Hydroxide and Hydrochloric Acid at 25°C......................... 96 28. Studies on the Completeness of the Reaction between Hydrochloric Acid and Neodymium Oxide ........ 99 29. Data on the Equilibrium between Neodymium Hydroxide and Perchloric Acid at 25°C'......................... 100 30. The Water Solubility of Neodymium Hydroxide at 25°C...................................................... 101 31. The Solubility of Neodymium Hydroxide in Sodium Hydroxide Solutions at 25°C.............. 101 32. Data on the Equilibrium between Mercuric Oxide and Nitric A c i d ............................................. 116 33. Data on the Equilibrium between Beryllium Hydroxide and Hydrochloric Acid ................................. 119 34. Data on the Equilibrium between Thorium Hydroxide and Perchloric A c i d ............................ 123 35. Summary of Data on Neodymium Hydroxide ............. 171 vil LIST OP FIGURES Figure Page 1. Hydrolysis C e l l ........................................ 27 2. A Comparison of the Glass and Quinhydrone Elec­ trodes in a 0.01 C Pr+3 Solution .................... 35 3. A Comparison of the Glass and Q,uinhydrone Elec­ trodes in a 0.025 C Nd+^ Solution ................... 36 4. Apparatus for Transferring the Filtering Samples ,. 45 5. Standard Curve for Neodymium Analysis-10 cm Cells . 50 6. Standard Curve for Neodymium Analysis-1 cm Cells .. 51 7. Molar Extinction versus Wave Length-1 cm Cells .... 52 8. X-Ray Powder Patterns of Oxide Samples ............ 59 9. Determination of the Free Acid in the Neodymium Buffers, c => 24.45 and 9.79 mC ................. 69 10. Determination of the Free Acid in the Neodymium Buffers, c => 4.90 mC .................................. 76 11. Hydrolysis of Neodymium Perchlorate ................ 77 12. Determination of the Free Acid in the Praseodymium Buffers, c = 25.0 and 12.5 m C ........... 82 13. Determination of the Free Acid in the Praseodymium Buffers, c = 10.24 and 5.00 mC ................. 89 14. Hydrolysis of Praseodymium Perchlorate ............. 93 15. Solubility of Nd(0H)3 in Dilute Hydrochloric Acid . 95 16. as a Function of the Equilibrium Hydrogen Ion A c t i v i t y ........................ 98 viii LIST OP FIGURES (Cont'd.) 17. Solubility of Nd(OH)g in Sodium Hydroxide Solutions. 102 18. Solubility of NdCOHjg in Sodium Hydroxide and Hydrochloric Acid Solutions ........................... 103 ix INTRODUCTION The purpose of this investigation was to obtain data on the equilibria between crystalline neodymium hydroxide and hydrogen ions and hydroxyl ions in aqueous solution at 25°C. and to study the hydrolysis