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Fouling Behaviour and Radioactive Retention Properties of Inorganic Crossflow Microfiltration Membranes

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Fouling Behaviour and Radioactive Retention Properties of Inorganic Crossflow Microfiltration Membranes Fouling Behaviour and Radioactive Retention Properties of Inorganic Crossflow Microfiltration Membranes A Thesis Submitted for the Degree of Doctor of Philosophy of the University of London by Manouchehr Asaadi, B.Sc., M.Sc., D.I.C. Department of Chemical Engineering and Chemical Technology Imperial College of Science, Technology and Medicine London SW7 2BY February 1990 1 Abstract Variation of the filtration rate was examined for different types of tubular inorganic microfiltration membranes. The steady state filtration rate was examined with change in the membrane operating conditions such as, crossflow velocity, transmembrane pressure and feed concentration. A suspension of magnesia particles in water was used for the purpose of these experiments. When a run was started using a clean membrane the permeate declined sharply in the first few minutes of the operation and reached a near constant rate. The flux was related to the hydrodynamic properties of the flow and the feed concentration. The experimental results were successfully correlated by a mathematical model based on the resistance in series approach. The model may be used to estimate the flux for a given feed concentration, crossflow velocity and transmembrane pressure. An expression was also derived for the estimation of the period during which flux changes continuously in the initial stages of microfiltration. This model is particularly useful for estimation of the permeability of the fouling film. To examine the radionuclide retention characteristics of the membranes, a number of active runs were carried out using radioisotopes of interest. Apart from the membrane type other variables examined were the feed pH, the solute concentration and influence of absorbers in the feed. The resulting decontamination factors showed that in general the membranes were capable of retaining substantial amounts of radiocolloids such as Am-241, Eu-152 / Eu-154, Th-230, Pu-239, Co-60 and U-235 especially at high pH ranges. However, those species such as Sr-85, Cs-137 and Sb-125 which remained in aqueous phase were only retained partially or not at all even in the presence of magnesia suspension and high pH conditions. 2 Acknowledgements My sincerest thanks to Dr. D. A. White for his supervision, invaluable advice, guidance and interest throughout this project Thanks are also due to the members of staff, in particular Professor M. Streat for applying for my work permit, Dr. P. G. Clay for reading the manuscript and his useful suggestions and students at the Nuclear Technology Research Section for their friendship and advice in the course of this work. Valuable assistance was received from Mr. R. King ( departmental workshop) and Mr. P. Amrit ( postgraduate workshop ). Finally, the financial support of British Nuclear Fuels Pic. is gratefully acknowledged. 3 To m y Covingwife A zar and my son Aryan Table of Contents Page Title Page 1 Abstract 2 Acknowledgements 3 Table of Contents 5 List of Tables 10 List of Figures 13 CHAPTER ONE Introduction 17 1.1 Crossflow Microfiltration 17 1.2 Microfiltration in the Nuclear Industry 17 1.2.1 Type of Waste and Process Streams 18 1.3 Objectives 19 CHAPTER TWO Literature Survey 20 2.1 Introduction 20 2.2 Development and Application of Microfiltration 20 Membranes 20 2.2.1 Early Membranes 20 2.2.2 Inorganic Membranes 21 2.2.2.1 Manufacturing Methods 2.2.2.2 Application 2.3 Separation Properties of MF Membranes 22 2.3.1 Membrane Retention 22 2.3.2 Colloidal and Particulate Retention 22 5 2.4 Effect of Operating Parameters on Flux 25 2.4.1 Crossflow Velocity Effect 25 2.4.2 Transmembrane Pressure Effect 26 2.4.3 Feed Concentration Effect 26 2.5 Variation of Flux with Time 27 2.6 Temperature Effect 28 2.7 Influence of the Membrane Microstructure on Flux 28 2.8 Anti - fouling Measures 29 CHAPTER THREE Theory 31 3.1 Introduction 31 3.2 Fundamental Equations for Flow Through Porous Mass 31 3.3 Crossflow Microfiltration Process 33 3.3.1 Gel Polarisation - Formation of Gel Polarised Layer 34 3.6 Mathematical Models for Fouling 37 3.6.1 Semi - empirical Models 37 3.6.1.1 Exponential Relationship 3.6.1.2 Resistance in Series 3.6.2 Mechanistic Models 38 3.6.2.1 Hydrodynamic Resegregation Model 3.6.3 Aggregation Model 41 3.7 Retention Properties of Membranes 42 CHAPTER FOUR Experimental 44 4.1 Summary 44 4.2 Apparatus 44 4.2.1 Flow Rig 44 4.2.2 Filtration Module 45 4.2.3 Membranes 50 6 4.2.3.1 PALL Sintered Stainless Steel 4.2.3.2 DOULTON Ceramic 4.2.3.3 FAIREY Stainless Steel 4.3 Feed and Its Characteristics 53 4.4 Experiments 53 4.4.1 Determination of the Hydraulic Permeabilities of the Membranes 53 4.4.2 Preliminary Fouling Experiments 53 4.4.3 Experiments to Investigate Variation of Flux with Time and the Operating Conditions 56 4.4.3.1 Variation of Flux with Time 4.5 Radioactive Retention Experiments 57 4.5.1 MILLIPORE Tests 57 4.5.1.1 Feed Preparation and Experimental Technique 4.5.2 Retention Characteristics of M4 CARBOSEP Membrane 59 4.5.2.1 Apparatus and Membrane Used 4.5.2.2 Experiments 4.5.3 Radioactive Retention Properties of PALL, DOULTON 63 and CARBOSEP Membranes 4.5.3.1 Apparatus and Feed 4.5.3.2 Experiments CHAPTER FIVE Results and Discussion 65 5.1 Summary 65 5.2 Results 66 5.2.2 Hydraulic Resistance of the Membranes 6 6 5.2.3 Fouling Experiments 6 6 5.2.3.1 Variation of Flux with Time and Cross Row Velocity at Constant Pressure 7 5.2.3.2 Variation of Flux Time and Transmembrane Pressure at Constant Velocity 5.2.3.3 Further Investigation of the Variation of Flux with the Operating Variables 5.3 Model Development 74 5.3.1 Derivation of a Relationship Between Rf and Hydrodynamic Properties of Flow 75 5.3.2 Application of the Model to the Experimental Data 80 5.3.3 Further Points About the Model 85 5.4 Transient Filtration Period 88 5.4.1 Model Development 8 8 5.4.2 Application of the Model 93 5.4.2.1 Estimation of the Film Thickness 5.5 Results from the Active Experiments 98 5.5.1 MELLIPORE Filters 98 5.5.1.1 Effect of pH and Fouling Agent 5.5.1.2 Effect of Pore Size 5.5.2 M4 CARBOSEP Membrane 102 5.5.2.1 Retention of Nuclides at Different pH 5.5.2.2 Retention of Nuclides at Constant pH 5.5.2.2.1 Europium Run 5 5.2.2.2 Europium and Cobalt Run 5.5.3 M4,M6 CARBOSEP and PALL and DOULTON Membranes 109 CHAPTER SIX Conclusions and Recommendations 113 6.1 Conclusions 113 6.2 Recommendations for Further Work 115 8 Nomenclature 117 References 120 Appendices Appendix A 127 Operating Conditions and Steady State Flux Values from the Fouling Experiments at Different Crossflow Velocities and Feed Concentrations When Transmembrane Pressure is Kept Constant. Appendix B 130 Operating Conditions and Steady State Flux Values from the Fouling Experiments at Different Transmembrane Pressures and Feed Concentrations When Crossflow Velocity is Kept Constant. Appendix C 134 Application of the Schock Relationship to the Experimental Data Appendix D 140 Calculation of Transient Filtration Period, Cake Permeability and the Film Thickness 9 List of Tables CHAPTER 2 Table 2.1 Position of Microfiltration Process in Relation to Other Separation Techniques Where Porous Membranes are Employed. CHAPTER 4 Table 4.1 Characteristics of the Membranes Used in Fouling Experiments. Table 4.2 Characteristics of the Membranes Used in the Active Experiments. CHAPTER 5 Table 5.1 Hydraulic Resistance and Clean Water Flux of the Membranes. Table 5.2 Initial, 1 Hour and 2 Days Flux of Runs with Magnesia Suspension at Various Feed Concentrations, Crossflow Velocities and Transmembrane Pressures. Table 5.3 Summary of the DF Ranges for Different pH and Feed Conditions Using MILLIPORE Filters. Table 5.4 Variation of DF's with Feed pH for Different Elements in the Experiments with M4 CARBOSEP Membrane. Table 5.5 Variations of Activities and DF's with Time for Europium Feed at pH 11.5 Using M4 CARBOSEP Membrane. Table 5.6 Variations of Activities and DF's with Time for Europium and Cobalt Feed at pH 11.5 Using M4 CARBOSEP Membrane. Table 5.7 Summary of the DF Ranges of the Radionuclides of Interest for Different Membranes. Table 5.8 Ratio of Activity of Feed at the Beginning and the End of the Runs Using Different Membranes. 10 APPENDIX A Table A.l Variation of Steady State Flux with Crossflow Velocity and Feed Concentration for PALL Membrane at Constant Transmembrane Pressure. Table A.2 Variation of Steady State Flux with Crossflow Velocity and Feed Concentration for DOULTON and FAIREY Membranes at Constant Transmembrane Pressure. APPENDIX B Table B.l Variation of Steady State Flux with Transmembrane Pressure and Feed Concentration for PALL Membrane at Constant Crossflow Velocity. (Conc.6.0 and 18.5 % WAV) Table B.2 Variation of Steady State Flux with Transmembrane Pressure and Feed Concentration for PALL ( Cone. 28.5 % W/W ) and DOULTON ( Cone. 6.25 and 28.5 % WAV ) Membranes at Constant Crossflow Velocity. Table B.3 Variation of Steady State Flux with Transmembrane Pressure and Feed Concentration for DOULTON ( Cone. 17.5 % WAV ) and FAIREY (Cone. 13.0% WAV) Membranes at Constant Crossflow Velocity. APPENDIX C Table C.l Various parameters of the Runs with PALL Membrane for 6.0 % W/W Magnesia Suspension and Parameters Evaluated from Schock Equation, p = 1042.0 Kg m-3 , p =1.582e-3 Pa s Table C.2 Various Parameters of the Runs with PALL Membrane for 18.5 % W/W Magnesia Suspension and Parameters Evaluated from Schock Equation, p = 1128.0 Kg m-3, p = 4.837 e-3 Pa s, ty = 1.64 Pa Table C.3 Various Parameters of the Runs with PALL Membrane for 28.5 % W/W Magnesia Suspension and Parameters Evaluated from Schock Equation.
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