BIOSORPTION of URANIUM by Nuru A. Yakubu, M.Sc., D.I.C., a Thesis
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BIOSORPTION OF URANIUM by Nuru A. Yakubu, M.Sc., D.I.C., A thesis submitted for the degree of Doctor of Philosophy of the University of London Department of Mineral Resources Engineering Mineral Technology Section, Royal School of Mines, Imperial College of Science and Technology University of London. April 1986 ABSTRACT A review of uranium history and industry has been carried out with emphasis on processing and the need for improved processes to control heavy metal effluents. Industrial ion exchange applications of Spirogyra and similar microorganisms are discussed in comparison with the more conventional techniques of resin and liquid ion exchange (solvent extraction). Preliminary experimental work indicated relatively great similarities between microorganisms and resins. Work on solvent extraction led incidentally to new insight into the equilibria involved in the uranium-Alamine 336-sulphu- ric acid-kerosene system and the results are reported in Chapter 2 of the thesis. In particular, semi-quantitative modelling of parallel 'competing' reactions has been applied to uranium equilibria and their relative contributions to the overall equilibria are discussed. The interactions of uranium with the microfilamentous fungus Aspergillus niger and the bacterium Methylophilus methylotrophus (in the form of ICI Pruteen) have been studied. Comparative adsorption isotherms as functions of pH and ionic strength in the presence of interfering ions are presented. Conditions for optimum uptake and elution of uranium have been established. Uranium biosorption is essentially reversible and pH control may be used to efficiently adsorb and desorb uranium. This property was used to determine breakthrough and elution curves for uranium with A. niger and Pruteen. Mechanistic studies of uranium adsorption onto A, niger and Pruteen have been undertaken by X-ray fluorescence, Fourier transform infrared spectrometry, electronmicroscopy and microelectrophoresis. An ion exchange mechanism has been proposed and a biological ion exchange model has been developed for the adsorption of uranium onto A. niger mycelium. Experimental evidence supporting the model is presented and discussed. A semi-continuous biological ion exchange column was tested under different conditions with fluidised, compart mentalised and packed beds of specially grown A, niger 'pellets'. The physical properties of these 'pellets' - specific gravity close to unity and a non-rigid structure- facilitated semi-continuous (interrupted) countercurrent operation of the column. Comparative loading curves are presented and a possible effluent control process discussed. 11 ACKNOWLEDGEMENTS I would like to express my sincere gratitude to my supervisor Dr. A.W.L. Dudeney for his guidance and continued support over the past three years. I gratefully acknowledge the assistance given by the following: The Department of Pure and Applied Biology, especially Dr. M. Carlile, Dr. S. Archer, Dr. J. Gay and Mr. R. Hartley for their advice and assistance with micro biological techniques. Imperial Biotechnology Ltd., for use of their Fermentation pilot plant. Dr. M. Streat of the Department of Chemical Engineering for his valuable suggestions. The Department of Chemistry, University College London, especially Mr. J. Hill for assistance with Fourier transform infrared spectroscopy. Mr. D. Shillam, Mrs. J. Heeley and Mr. V.G. Harris for their technical assistance. I would also like to acknowledge the financial support given by my employer, Abubakar Tafawa-Balewa College, Ahmadu Bello University, Bauchi, Nigeria. Lastly, but not the least, I would like to thank my wife, Rabi, for her patience and understanding during the difficult period of this study. iii LIST OF CONTENTS Page ABSTRACT i ACKNOWLEDGEMENTS ii LIST OF CONTENTS iii LIST OF FIGURES ix LIST OF TABLES xiv CHAPTER 1 LITERATURE SURVEY 1 1.1 HISTORY AND INDUSTRY 1 1.1.1 Geochemistry and occurrence 1 1.1.2 Uranium industry 8 i) Development 8 ii) Present trends 11 1.2 PROCESSING 19 1.2.1 Mining and pretreatment 19 1.2.2 Leaching 28 i) Acid leaching 30 ii) Alkaline leaching 32 iii) Recent advances in uranium leaching technology 34 1.2.3 Solution purification 37 i) Fixed bed ion exchange (FBIX) 38 ii) Continuous ion exchange (CIX) 41 iii) Resin-in-pulp (RIP) process ing 43 iv) Solvent extraction (SX) 44 v) Precipitation 48 1.3 ION EXCHANGE FUNDAMENTALS 50 1.3.1 Resin ion exchange 50 1.3.2 Liquid ion exchange 58 1.3.3 Biological ion exchange 63 i) Industrial processes 63 ii) Studies 65 iii) Mechanism 67 1.3.4 Conclusion 70 iv Page CHAPTER 2 TECHNIQUES AND PRELIMINARY WORK 71 2.1 ANALYTICAL METHODS 71 2.1.1 Spectrophotometric determination or uranium(VI) 71 i) Determination of U(VI) in complex solutions 72 ii) Direct determination of uranium(VI) 74 2.1.2 Atomic absorption/emission spectro metry 76 i) Atomic absorption spectro metry 76 ii) Inductively coupled plasma atomic emission spectrometry 78 2.1.3 X-ray fluorescence spectrometry (XRFS) 79 i) Sample preparation 81 ii) Analysis conditions 81 iii) Spectrum processing 82 2.2 BIOCHEMICAL METHODS 85 2.2.1 Selection of biological materials 85 2.2.2 Preparation and handling of Aspergillus niger and Pruteen 86 i) Fungal spore production and propagation 86 ii) Spore counting procedure 87 iii) Morphology and medium selection 88 2.2.3 Fermentation procedures and production of stock mycelium 94 i) Pilot scale fermentation 94 Unrestricted growth 94 Restricted growth 96 Stationary/declining phases 98 Lag/acceleration phase 98 V Page ii) Production of 'pellet * mycelium 98 iii) Disruption and homogenisation of mycelium 100 iv) Freeze drying of mycelium 101 2.3 A STUDY OF URANIUM SOLVENT EXTRACTION EQUILIBRIA 103 2.3.1 Introduction 103 2.3.2 Experimental 107 i) Reagents and analytical methods 107 ii) Procedures 108 Factorial experiment 108 Sulphuric acid extraction 109 Uranium extraction 110 2.3.3 Theoretical 112 i) Sulphuric acid solvent extraction 112 ii) Uranyl sulphate solvent extraction 116 2.3.4 Results and discussion 118 i) Factorial experiment 118 ii) Sulphuric acid extraction 118 iii) Uranyl sulphate extraction 123 CHAPTER 3 THE MECHANISM OF BIOSORPTION OF URANIUM BY A. NIGER .AND PRUTEEN 128 3.1 INTRODUCTION 128 3.2 EXPERIMENTAL PROCEDURES 130 3.2.1 Equilibrium adsorption isotherms 130 i) Effect of pH 131 ii) Effect of co-ions and counter -ions 131 iii) Adsorption/desorption characteristics 132 vi Page 3.2.2 Electron microscopy 132 3.2.3 Infrared spectrometry 133 i) Near Infrared 133 ii) Mid and far infrared 134 iii) Diffuse reflectance 134 3.2.4 Microelectrophoresis 135 3.2.5 Rate of uranium uptake 135 3.3 THEORETICAL MODEL FOR BIOLOGICAL ION EXCHANGE OF UO^* AT THE CELL WALL OF A. NIGER 137 3.4 RESULTS AND DISCUSSION 140 3.4.1 Equilibrium adsorption isotherms 140 i) Preliminary experiments 140 ii) The effect of pH on uranium adsorption 144 iii) The effect of co-ions and counter-ions 154 iv) Adsorption and desorption characteristics 161 3.4.2 Electron microscopy 163 3.4.3 Microelectrophoresis 166 3.4.4 Infrared spectrometry 169 3.4.5 Ion exchange equilibrium 179 3.4.6 Kinetics of uranium biosorption 179 3.5 CONCLUSIONS 189 CHAPTER 4 SEMI-CONTINUOUS FLUIDISED BED BIOSORPTION 191 4.1 INTRODUCTION 191 4.2 THEORETICAL 193 4.3 PRELIMINARY EXPERIMENTS 197 4.3.1 Procedures 197 i) Breakthrough curves 197 Vll Page ii) Elution curves 197 iii) Batch simulation of counter- current decantation 198 4.3.2 Discussion of preliminary work 200 i) Breakthrough and elution curves 200 ii) Batch simulation of counter- current biosorption on A. niger 207 4.4 FLUIDISED BED OPERATION 211 4.4.1 Review 211 i) Aggregated cells 211 ii) Adsorbed cells 212 iii) Entrapped cells 213 4.4.2 The fluidised bed ion exchange equipment 215 i) Fluidised column 215 ii) Solution feed pump 217 iii) Mycelium recirculation pump 218 4.5 EXPERIMENTAL 219 4.5.1 Production of fungal pellets 219 4.5.2 Equipment commissioning 219 4.5.3 Procedure for column biosorption 222 4.5.4 Uranium elution 224 4.6 RESULTS AND DISCUSSION 225 4.7 CONCLUSIONS AND RECOMMENDATIONS 237 REFERENCES 239 Ill age 2.1 275 2.2 276 2.3 277 2.4 280 2.5 282 2.6 284 2.7 288 3.1 291 3.2 300 3.3 306 ix LIST OF FIGURES Page CHAPTER 1 Fig. 1.1 Distribution of uranium resources by deposit type 6 Fig. 1.2 (a) Uranium prices 10 (b) World uranium production and production capacity 10 Fig. 1.3 Map of Nigeria showing areas of uranium anomaly 15 Fig. 1.4 Nuclear fuel cycle showing some effluent waste discharges 17 Fig. 1.5 Simplified flowsheet of Panel mine and mill 20 Fig. 1.6 A view of the Margnac Mine in France, an underground ore train, a specimen of pitchblende and autunite 22 Fig. 1.7 (a) Ascending cut-and-fill ('overhead') sloping method 23 (b) Descending stoping method using concrete slabs 23 Fig. 1.8 Simplified geologic cross section of solution mining 25 Fig. 1.9 Summary of leaching techniques 29 Fig. 1.10 Acid and alkaline uranium extraction circuits 33 Fig. 1.11 The main methods of purifying uranium leach solutions 39 Fig. 1.12 A 3-column fixed bed ion exchange system 38 Fig. 1.13 A diagram of a two-column loading and elution NIMCIX contactor 43 Fig. 1.14 Three stage mixer-settler arrangement for the extraction of uranium 45 Fig. 1.15 Generalised flowsheet of the AMEX process for uranium allowing for a choice of stripping methods 46 Fig. 1.16 Eh-pH diagram for U-S-H2 O system at 25°C 51 Fig. 1.17 Typical and ideal breakthrough and elution curves 56 X Page Fig. 1.18 Equilibrium isotherm for uranium adsorpt ion from an acidic leach liquor by Amberlite IRA-430 resin 57 Fig.