Some Aspects of the Aqueous Chemistry
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SOME ASPECTS OF THE AQUEOUS CHEMISTRY OF ZIRCONIUM AND RUTHENIUM IN RELATION TO NUCLEAR FUEL REPROCESSING A thesis submitted for the degree of DOCTOR OF PHILOSOPHY in the Faculty of Engineering of the University of London by M. AMIN ANJUM, BSc (Hops), MSc (Punjab), MSc (London), DIC, ARIC Department of Chemical Engineering and Chemical Technology, Imperial College of Science and Technology, London, S. W. 7. April 1972 ABSTRACT The ion-exchange behaviour of ruthenium IV, nitrosyl ruthenium III and zirconium IV has been investigated with a view to the utilization of anion-exchange resins for the separation of ruthenium and zirconium from plutonium solutions in nuclear fuel reprocessing. Both cation and anion-exchangers have been used for the removal of ruthenium IV. Increases in nitric acid concentration decreased the extent of removal by the cation-exchanger as did increases in ruthenium concentration at lower acidities. Studies of the anion-exchange behaviour -3 in nitric acid concentration range of 0.1 to 7.5 mol dm -3 showed that maximum adsorption occurs at 3.5 and 5 mol dm acid for ruthenium IV and nitrosyl ruthenium III respectively. From solutions of comparable strength nitrosyl ruthenium was adsorbed to a greater extent. When the nitrate ion concentration was kept constant a decrease in hydrogen ion concentration resulted in higher removal by the anion- exchanger. The results are discussed in terms of the species of ruthenium and the properties of the resin involved. The adsorbed ruthenium was found to be difficult -3 to remove. Thus 7.5 mol dm acid removed about 30% -3 of adsorbed ruthenium while 0.6 mol dm acid removed only about 10%. 3 The characterization of the species of ruthenium has not been completed. Although electrophoresis and ion-exchange data pointed to the presence of different complexes under different conditions, studies involving spectrophotometry failed to detect any such changes. The ion-exchange behaviour of zirconium was investigated -3 in the nitric acid range of 0.01 to 9 mol dm . At low acidities (e.g. 0.01 mol dm-3) both cation and anion exchange removed similar amounts. Increases in acidity decreased adsorption by the cation exchange. In the case of the anion-exchanger maximum adsorption was found 3 to occur at 0.1 and 7.5 mol dm acid. These maxima are explained in terms of the formation of polymers at lower acidities and of anionic complexes at higher acidities. The adsorbed zirconium was readily eluted with nitric -3 -3 acid stronger than 5 mol dm but removal by 0.6 mol dm acid was found to be difficult (i.e. <15%). A simple exponential equation C = J0.2241E- developed in this s work can predict the f' action of zirconium C/Co remaining on the resin after a contact time t (in minutes) of the -3 resin with the acid (>5 mol dm ). On the basis of results obtained a flow sheet for the removal of ruthenium and zirconium by an anion-exchange process has been developed. 4. ACKNOWLEDGEMENTS The author wishes to express his gratitude to Dr. P. G. Clay for his help and encouragement in the completion of this work. Thanks are also due to Professor G. R. Hall under whose guidance the earlier part of this work was completed. Many healthy discussions on the ion-exchange work with Dr. M. Streat are also acknowledged. Last but not the least, help given by Professor G. N. Walton in the preparation of this thesis is gratefully acknowledged. Thanks are also due to my friends and specially to P for making some very difficult times in London seem pleasant. Financial support from the British Council, made available in the form of a Colombo Plan Scholarship sponsored by the Atomic Energy Commission, Pakistan, is gratefully acknowledged. 5. CONTENTS Page Abstract 2 Acknowledgements 4 Chapter 1 GENERAL INTRODUCTION 11 1.1 Nuclear Fuel Reprocessing 12 1 1.1.1 Present Day Processing Techniques 13 1.1. 2 Fission Products in Solvent Extraction 14 1.2 Ion Exchange Resin and Nuclear Fuel Reprocessing 17 1.3 Present Work : Aims and Objects 18 Chapter 2 RUTHENIUM 22 2.1 General Chemistry 23 2.1.1 The Valency States of Ruthenium 23 2.1.1.1 The Oxidation-Reduction Potentials 34 of Different Valency States 2.1.1.2 Ion-Exchange Behaviour of Non- Nitrosyl-Ruthenium Compounds 36 2.1.2 Nitrosyl-Ruthenium Compounds 38 2.1.3 Behaviour of Ruthenium in Nuclear Fuel Reprocessing 43 2.1.3.1 Solvent Extraction of Nitrosyl- Ruthenium Compounds 45 2.1.3.2 Ion-Exchange Behaviour of Nitrosyl-Ruthenium 49 2.1.3.3 Waste Disposal of Ruthenium in Nuclear Fuel Reprocessing 51 2.2 Experimental 54 2.2.1 Materials Used 54 2.2,2 Preparations 56 6. Page 2.2.2.1 Ruthenium Tetroxide 56 2.2.2.2 Ruthenium IV 56 2.2.2.3 Preparation of Nitrosyl-Ruthenium Nitrates 58 2.2.3 Estimations 59 2.2.3.1 Ruthenium 59 2.2.3.2 Determination of the Valency of Ruthenium 66 2.2.3.3 Estimation of Copper and Chromium 67 2.2.3.4 Capacity and the Swollen Volume of Resin 68 2.2.4 Spectrophotometry 72 2.2.4.1 Instrument Used ' 72 2.2.4.2 Scan of the Spectra 73 2.2.4.3 Representation of the Data 76 2.2.5 Electrophoresis 77 2.2.6 Ion-Exchange : Adsorption and Elution 79 2.2.7 Paper Chromatography 79 2.3 Results 81 Z. 3.1 Properties of the Resins 81 2.3.1.1 Ultraviolet Absorption Spectra of Resin Washings 82 2.3.2 Ruthenium Tetroxide 86 2.3.3 Ruthenium IV Studies 89 Z. 3.3.1 Characterization of Ruthenium IVSolutions 89 2.3.3.1.1 UV Spectrum of Ruthenium IV 91 2.3.3.1.2 Reduction of Ruthenium IV 91 2.3.3.1.3 Presence of Chloride Ion in Ruthenium IV Solutions 94 2.3.3.1.4 Solutions of Ruthenium IV in Nitric Acid 94 7. pag e 2.3.3.2 Effect of Addition of Nitrate Ion to Ruthenium IV Solutions 95 Z. 3.3. Z. 1 Ultraviolet Spectra of Solutions 95 2.3.3.2.2 Polymerization of Ruthenium IV : Spectrophotometric Evidence 98 2.3.3.2.3 Infra-Red Spectrum 101 2.3.3.3 Electrophoresis 2.3.3.4 Ion-Exchange Studies 105 2.3.3.4. I Adsorption of Ruthenium IV by Zeokarb-225 105 .v/ 2.3.3.4.2 Use of Ion-Exchange for the Deter- mination of Charge 109 2.3.3.4.2.1 Cady' s Method 109 2.3.3.4.2.2 Application of the Method to Ions of Known Charges 112 2.3.3.4.2.3 Application of the Method to Ruthenium Species 112 2.3.3.4.3 Adsorption of Ruthenium IV by Ionac XAX- 1284: Effect of Shaking Time 118 2.3.3.4.3.1 Adsorption of Ruthenium IV by Ionac XAX- 1284: Effect of Ruthenium and Nitric Acid Concentration 120 2.3.3.4.4 Elution of Adsorbed Ruthenium by Nitric Acid 124 2.3.3.5 Solvent Extraction, Thin Layer and Paper Chromatography 127 2.3.3.6 Effect of Heat and Irradiation 129 2.3.4 Nitrosyl Ruthenium Nitrates 131 2.3.4.1 Anion-Exchange Behaviour of Nitrosyl Ruthenium Nitrates 135 2.3.4. 1.1 Adsorption 135 2.3.4.1.2 Elution 137 8 2.3.4.2 Paper Chromatography of Nitrosyl Ruthenium Nitrates 139 2.4 Discussion 147 2.4.1 Ruthenium Tetroxide 148 2.4.2 Preparation of Ruthenium IV 150 2.4.3 Ruthenium IV in Nitrate Ion Media 152 2.4.3.1 Ion Exchange Behaviour 153 2.4.3.1.1 Adsorption 153 2.4.3.1.2 Elution of Ruthenium IV from Ionac XAX-1284 157 2.4.3.7 Some Further Properties of the Nitrates of Ruthenium IV 161 2.4.4 Nitrosyl-Ruthenium Nitrates 162 2.4.4.1 Anion-Exchange of the Nitrosyl- Ruthenium Nitrates 163 2.4.4.1.1 Adsorption 163 2.4.4.1.2 Elution of Adsorbed Ruthenium 165 2.4.4.2 Paper Chromatography of the Nitrosyl Nitrates of Ruthenium 166 Chapter 3 ZIRCONIUM 167 3.1 General Chemistry 168 3.1.1 The Oxidation States 168 9. Page 3. I. 2 Aqueous Solutions of Zirconium IV 169 3. I. 3 Complex Formation 171 3. I.4 Ion-Exchange Studies of Zirconium IV 173 3. I. 5 Behaviour of Zirconium in Nuclear Fuel Solutions 175 3. I. 5. I Solvent Extraction of Zirconium 175 3. 2 Experimental 179 3. 2. I Materials and Apparatus 179 3. 2. 2 Resin Preparations 180 3. 2. 2. 1 Resin Capacities 181 3. 2. 3 Preparation of Solutions 181 3. 2. 4 Estimation of Zirconium 181 3. 2. 4. I Gravimetric 181 3. 2. 4. 2 Colourimetric Method 182 3. 2. 4. 3 Estimation of Zr-95 185 3. 2. 5 Adsorption of Zirconium by the Resin 188 3. 2. 5. 1 Equilibrium Experiments 188 3. 2. 5. 2 Column Experiments 188 3. 2. 6 Washing of the Loaded Resin 190 3. 2. 7 Elution of Zirconium 190 3. 3 Results 192 3. 3. I Adsorption from Nitric Acid 192 3. 3. 2 Effect of Change of Nitrate Ion Concentration at Constant H4 Ion Concentration 192 3. 3. 3 Effect of the Aqueous Phase Concent- ration of Zirconium on Adsorption 194 3. 3.4 Effect of Resin Cross-linking on the Adsorption of Zirconium 198 10 Page 3.3.5 Reproducibility of the Results on Adsorption from Dilute Acid Solutions 199 3.3.6 Column Loading 199 3.3.7 Adsorption of Zirconium by a Cation-Exchange Resin 202 3.3.8 Elution of Adsorbed Zirconium 205 3.4 Discussion 209 3.4.1 Adsorption of Zirconium from Nitric Acid 209 3.4.2 Effect of Change of Nitrate Ion Concentration on Adsorption 214 3.4.3 Effect of Aqueous Phase Concentration of Zirconium on Adsorption 216 3.4.4 Effect of Resin Cross-linking on Adsorption 218 3.4.5 Elution of Adsorbed Zirconium 219 Chapter 4 CONCLUSIONS 223 4.1 Ruthenium 224 4.2 Zirconium 228 4.3 Flow Sheet 229 References 231 Appendices 247 Appendix 1 Spectrum of Nd3 248 Appendix 2 Spectrum of Benzene in Cyclohexane 249 Appendix 3 Spectrum of Nitric Acid 250 Appendix 4 cyalues of Ru IV in Hc104 251 Appendix 5 Sample Calculations of Charge 253 Appendix 6 Values for RuNO-Nitrates 255 Appendix 7 Adsorption of RuNO-Nitrates by Ionac XAX-1284 256 11.