A Thesis submitted to the School of Graduate Studies.. in partial fulfilment of the requirements for the degree Doctor of Philosophy

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1 STUDIES ON THE GROWTH, DISSOLUTION AND EQUILIBRIUM SOLUBILITY OF Sa, Pb AND Ra SULFATES IN AQUEOUS SULFATE MEDIA: WITH APPLICATIONS TO THE SULFURIC ACID LEACHING PROCESS FOR URANIUM MIWNG. By CHRISTOPHER ROBIN PAIGE, B.Sc., M.Sc. A Thesis submitted to the School of Graduate Studies.. in partial fulfilment of the requirements for the degree Doctor of Philosophy McMaster University Copyright Christopher Robin Paige June 1990

2 STUDIES ON THE GROWTH, DISSOLUTION AND EQUIUBRIUM SOLUBIUTY OF Ba, Pb AND Ra SULFATES IN AQUEOUS SULFATE MEDIA =,.,. tl " o t.' \\ ;' - ",.

3 STUDIES ON THE GROWTH. DISSOLUTION AND EQUIUBRIUM SOLUBIUlY OF Ba. Pb AND Ra SULFATES IN AQUEOUS SULFATE MEDIA: WITH APPLICATIONS TO THE SULFURIC ACID LEACHING PROCESS FOR URANIUM MILLING. By CHRISTOPHER ROBIN PAIGE. B.Sc. M.Sc...:.. A Thesis submitted to the Department of Chemistry, ~ in partial fulfilment of the requirements for the degree Doctor of Philosophy!) McMaster University Copyright Christopher Robin Paige June 1990 i'\

4 DOCTOR OF PHILOSOPHY (1990) McMASTER UNIVERSITY Hamilton, Ontario TITLE: Studies on the growth, dissolution and equilibrium solubility of Ba, Pb and Ra sulfates in aqueous sulfate media: with applications to the sulfuric acid leaching process for uranium milling AUTHOR: Christopher Robin Paige, B. Sc. (London) M. Sc. (Brock) SUPERVISOR: Professor O. E. Hileman, Jr. NUMBER OF PAGES: 217, xxix. ",.' '.' " '_.. 11

5 '.: Abstract The formation of hetero-epitaxial deposits of Sa, Pb and mixed Ba/Pb and Ba/Ra sulfates on quartz and mica surfaces has been demonstrated. The kinetics of their growth and dissolution has been established. The importance of the formation and dissolution of these deposits is found in the observation that they are all host solids for the formation of solid solutions of 228-radium (and by extension 226-radium). Desorption studies caried out on Ba 2 +, ea2 + and S from quartz and mica surfaces into water indicate that these ions are strongly retained by mica surfaces, with retention times which are of sufficient duration to permit the formation of the potential host solids required by the National Uranium Mine Tailings model. The equilibrium solubility of PbS04 in Na2S04 solutions and in H2S04 solutions from 0 to 6m has been measured experimentally at' 600C with subsequent modelling by means of the Pitzer formulation for ion activities at high ionic strength. The equilibrium solubility of BilS04 in H2S04 solutions from 0 to 6m has been measured experimentally at both 250 C and 600C with subsequent modelling. Such data are a necessary iii

6 requirement for the modelling of the evolution of uranium mill wastes by the National Uranium Mine Tailings model and for understanding the fate of radium during the milling and leaching processes. '.',- c.~,; c iv

7 Acknowledgements The author would like to express his thanks and appreciation to Professor O. E. Hileman, Jr. for his supervision, sense of humor, enthusiasm for chemistry and for creating the atmosphere of shared learning which is so important for true learning. In addition. thanks are offered to all the other members of the department for their invaluable assistance and attention. especially for the wide ranging discussions which are so valuable a part of the activities of a University. Finally, the greatest thanks are due to my wife, Valerie Elizabeth ( Freeman ) Paige. who for many years has accepted this rather curious person, who has such a persistent scientific interest. as a husband "I.t., {) v

8 Never let success hide its emptiness from you, achievement its nothingness, toil its desolation. And so keep alive the incentive to push on further, that pain in the soul which drives us beyond ourselves. Whither? That I don't know. That I don't ask to know. Dag Hammarskjold Youth, to live, must have some great aspiration. Gaston Rebuffat I! "::C '.' vi

9 Table of Contents Page Abstract Acknowledgements Table of Contents List of Figures List of Tables Symbol Table J i i v vii x ii xxv xxvii -/- Chapter 1. Introduction Outline of the milling and processing of uranium ore Fate of radium during ore processing Laboratory work on radium precipitation 3 in the leach tanks The Hileman-Snodgrass model of leach tank processes The Hileman-Snodgrass model of uranium. ml'11 waste t al'1' Ings ~. ;;-;;;-:;. --~6 1.S Components of the precipitation/dissolution model Purt10se of this research 12 r- --' vii

10 Page Chapter 2. Background information Review of Activity Coefficient Modelling. c using the Pitzer equations Supersaturation and Activity Nucleation Growth of crystals (i) Growth by two-dimensional nucleation (ii) Growth by a spiral growth mechanism (iii) Growth in the presence of Impurities ~~ 34 Perfection of crystals. 35 (J Chapter 3. Solubility of sparingly soluble sulphates In H ',: 3.1 Solubility of PbS04 in H2S04 and Na2S04... "., from 0 to 6m at 6(jJ C by ICP/MS analytical methods Experimental procedure used for the determination of the equilibrium solubility of PbS04 in both Na2S04 - H20 and H2S04 - H2 0 mixtures : 48 Modelling of solubility equilibria using the Pitzer equations for activity coefficients 49 viii

11 Page Modelling of the available literature data for the solubility of PbS04 in H2S04 and Na2S04 along with the experimental data obtained in this research Solubility of BaS04in H2S04 and Na2S04 tram a to 6m at 250C and 600C Experimental procedure 53 3'.2.1.i Preparation of mixed 133Ba/BaS04 crystals ii Solubility Measurements Discussion aris~ing from the experimental procedures used for the determination of the solubility of PbS04 and BaS04 in sulfate media i The effect of labelling on the,\ solubility of the barium sulfate...l...~ ii The effect of particle size on the ':0' solubility of substances :~58.' iii The nature of the filters used for the radio labelled material 59 ~ 3.3 Results of the modelling of the available literature data for the solubility of RaS04 in H2S04 at 298K and the prediction of the solubility at 333K 60 ix F /'

12 Page Chapter 4. Kinetics of the exchange process at the faces of large single crystals of barium sulphate and lead sulphate Introduction Kinetics of isotope exchange limited by the rate of surface reactions ~ i 4.4.ii 4.4.iii 4.4.iv 4.4.v 4.4.vi Experimental procedure 96 Experimental results and data analysis 98 Calculation of jump frequencies 102 Comparison with data obtained from crystal growth and exchange experiments 105 Exchange for 133Sa on SaS04 at 298K 106 Exchange for 133Sa on SaS04 at 333K 107 Exchange for 133Sa on BaS04 at 298K in the presence of Pb2+ions Chapter 5. Kinetics of growth and dissolution of epitaxial films on quartz and mica surfaces Objectives of this phase of the research Kinetics of desorption of ions, involved in the Hileman-Snodgrass model, from quartz and mica surfaces 13a 5.2.i Introduction ii Design and construction of the desorptio/dissolution cell iii Results and discussion Growth of potential host solids on quartz and mica surfaces G x

13 Page 5.3.i Experimental procedure ii Results Kinetics of the growth of potential host solids on model surfaces as a function of solution concentration i Experimental ii Results and discussion Kinetics of the dissolution of potential host solids, including 228Ra as amico-component, from model surfaces i The preparation of carrier-free 228Ra from thorium, using cation ".~.. exchange columns 144,, 5.5.ii Discussion iii Dissolution of the host matrix. as followed by radiotracer techniques iv Results and discussion v Dissolution of BaS04 labelled with 5.5.vi 228Ra 149 Results of the dissolution or BaS04 labelled with 228Ra 150 Chapter 6 Summary and Conclusion for Entire Thesis i Contributions to knowledge ii Contributions to the Iiterature iii Suggestions for further research 193 Appendix I 1 96 Appendix II 198 xi

14 References ,\.'.- xii ~.'

15 Table of Figure Captions Page Figure 1 Uranium mill process streams for the sulfuric acid leach process 14. Figure 2 Variation of the ionic strength I and the ion and complex concentrations in a solution containing 50mmol/L (NH4)2S04 and NaH2P04. The ph is adjusted by ammonia, [N]t being the total ammonia (NH3 + NH4+) in the system; calculations based on data from (21) and (22) 40 Figure 3 Activation free energy for nucleation as a function of the nucleus size. The critical value ag* must be reached for creating a nucleus of critical radi us r* 41 Figure 4 Cap shaped nucleus of radius r forming on a solid substrate, with which it forms the contact angle a 42 Figure 5 Schematic representation of a crystal exhibiting flat (F), stepped (5) and kinked (K) faces. Front face exhibits a polygonized growth spiral. whereas the top face exhibits a twodimensional nucleus 43 Figure 6 Birth and spread model; several twodimensional nuclei spread across the crystal face (taken from S9) 44 xiii

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