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The leaching of uranium from pitchblende ores by aqueous oxidation techniques Peters, Ernest 1951

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f\l„  /  OF  i"  C O F O . SE3;ES._/2L_  THE LEACHING OF -URANIUM FROM PITCHBLENDE ORES BY AQUEOUS OXIDATION TECHNIQUES by ERNEST PETERS  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department of Mining and Metallurgy  We accept t h i s thesis as conforming to the standard required from candidates for the degree of MASTER OF APPLIED SCIENCE  Members of the Department of Mining and Metallurgy THE UNIVERSITY OF BRITISH COLUMBIA September, 1951  Abstract  Uranium e x i s t s i n carbonate s o l u t i o n i n i t s hexavalent as the complex i o n U 0 ( C 0 3 ) 2  pitchblende  (U 0g).  3  .  state  I n most o r e s uranium o c c u r s as  I t has been found p o s s i b l e t o d i s s o l v e uranium i n  3  c a r b o n a t e - b i c a r b o n a t e s o l u t i o n s from these o r e s by l e a c h i n g them i n t h e presence o f oxygen. U3O8  The  +  \0  The o v e r a l l r e a c t i o n i s as f o l l o w s : Z  + 3C0 -= + 6 H C O 3 3  -* 3 U 0 ( C 0 ) 3 2  3  + 3H 0 2  o b j e c t i v e of t h e p r e s e n t r e s e a r c h was t o examine t h e k i n e t i c s  o f t h i s r e a c t i o n w i t h a view t o d e t e r m i n i n g t h e mechanism o f t h e r e a c t i o n and  t o e s t a b l i s h t h e v a r i a b l e s upon which t h e r a t e depends. Two s e r i e s o f experiments were conducted on two t y p e s o f  materials: (a)  Pitchblende  a solution containing  specimens o f measured s u r f a c e  a r e a were suspended i n  sodium carbonate and sodium b i c a r b o n a t e .  Above t h e  s o l u t i o n a d e s i r e d p r e s s u r e o f oxygen was m a i n t a i n e d . (b)  A p u l p o f low grade p i t c h b l e n d e  a g i t a t e d i n an a u t o c l a v e , desired  i n t h e presence o f oxygen m a i n t a i n e d a t t h e  pressures. The  analyzing  o r e i n carbonate, s o l u t i o n s was  r a t e o f s o l u t i o n o f uranium was measured b y sampling and  t h e s o l u t i o n s a t r e g u l a r time i n t e r v a l s . The  e f f e c t o f oxygen p r e s s u r e ,  temperature, and reagent concen-  t r a t i o n on t h e r a t e was s t u d i e d i n each s e r i e s . The  k i n e t i c r e s u l t s were examined by the methods o f t h e a b s o l u t e  reaction rate theory.  The f o l l o w i n g c o n c l u s i o n s w e r e d r a w n f r o m t h e (1)  The a b s o l u t e r e a c t i o n r a t e s  materials  about  the  same f o r a l l  tests: the  studied. The r e a c t i o n r a t e v a r i e s  (2) oxygen  are  leaching  as  the square r o o t o f  the  absolute  pressure. The a c t i v a t i o n e n e r g y i s  (3)  about  12,000 - 3000 c a l o r i e s  per  gram m o l e . (4) dissolve  M i n i m u m amounts  of  carbonate  the o x i d i z e d uranium.  amount r e s u l t  are  the r a t e  necessary  to  F u r t h e r i n c r e a s e s beyond t h i s minimum  i n only minor increases i n the rate of the  A mechanism f o r t h e oxidation is  and b i c a r b o n a t e  leaching rate i s  proposed  reaction. i n which  the  controlling step.  P  Acknowledgement  The author wishes to express his appreciation to the National Research Council f o r f i n a n c i a l aid i n the form of a research assistantship. Appreciation i s also expressed to Eldorado Mining and Refining  (1944)  Limited, who  supplied the pitchblende specimens and ore samples  used i n the research. The author i s indebted to Professor F.A. Forward and the s t a f f of the Department of Mining and Metallurgy f o r t h e i r encouragement and advice.  He i s e s p e c i a l l y indebted to Dr. J . Halpern who  directed the  research program, and who was of much assistance i n the w r i t i n g of t h i s thesis. The assistance of Ronald Dakers i n performing the analyses of the ores and residues i s also appreciated.  Contents page 1  Introduction General  1  Historical  2  Application of the Sodium Carbonate Leach to h  Pitchblende Ores Recent Research on Aqueous Oxidation at U.B.C. . .  5  The Chemistry of the Oxygen - Sodium Carbonate Leach  6  Side Reactions  7  Objectives of the Present Research  8 10  Materials Ores  . 10  Mineralogical Description  10  Pitchblende Specimens  12  Reagents  12  Equipment  13  Experimental Procedures  16  Pitchblende Specimens Ores A n a l y t i c a l Methods  16 1 6  17  Contents  (continued) page  Results  20 A. L e a c h i n g of P i t c h b l e n d e Specimens 1. R e p r o d u c i b i l i t y 2.  Proportionality  20  .  20  t o S u r f a c e Area  20  3. E f f e c t o f Sodium B i c a r b o n a t e C o n c e n t r a t i o n  . 21  4. E f f e c t o f Temperature  25  5. E f f e c t of Oxygen P r e s s u r e  28  6. E f f e c t o f Sodium Carbonate C o n c e n t r a t i o n  . . 30  7. E f f e c t o f Sodium S u l p h a t e C o n c e n t r a t i o n  . .  8. E f f e c t o f A g i t a t i o n  30 30  B. L e a c h i n g of Ores  32  1. R e p r o d u c i b i l i t y  32  2. E f f e c t o f Temperature  32  3. E f f e c t of Oxygen P r e s s u r e  35  4. E f f e c t o f M i l l i n g Time  35  5. E f f e c t o f Sodium Carbonate C o n c e n t r a t i o n 6. E f f e c t of R e c y c l i n g the Leach S o l u t i o n  . . 38  . . .  38  7. E f f e c t o f Pulp D e n s i t y  38  8. E f f e c t o f P r i o r Roast  . 40  9. E f f e c t o f P r i o r F l o t a t i o n o f S u l p h i d e s 10.  E f f e c t o f Sodium Sulphate  D i s c u s s i o n of R e s u l t s  *  Summary o f V a r i a b l e s .  Concentration  . . . . .  42 42  44 44  Contents  (continued) page Numerical Values o f R e a c t i o n Rates  .45  Comparison o f Absolute R e a c t i o n Rates of D i f f e r e n t Ores Z+6 Magnitude o f E r r o r s i n R e a c t i o n Rate E s t i m a t e s  . . 47  A c t i v a t i o n Energies  48  R e a c t i o n Mechanisms  49  Influence of Agitation  50  D e t e r m i n a t i o n o f the C o n t r o l l i n g S t e p  51  Mechanism  I  52  Mechanism  II  53  D i s c u s s i o n of Mechanisms Approximations  i n Theoretical  54 Rate C a l c u l a t i o n s  . 55  E f f e c t o f Leach Reagents  56  Change i n C o n t r o l l i n g Mechanism  57  Conclusions  . . . .  Appendix A  . . .  . . . . .  58  . . 59 3  Appendix B  61  Appendix C  62  Appendix D  . . . . . . . .  64  Contents  (continued) page  Appendix E  67  Appendix F  69  Bibliography  70  Illustrations  F i g . 1.  B o t r y o i d a l P i t c h b l e n d e i n AS-2 Ore . . . 11  F i g . 2.  No. 1 A u t o c l a v e  14  F i g . 3.  No. 2 A u t o c l a v e  14  F i g . 4.  Typical Calibration  F i g . 5.  E f f e c t o f S u r f a c e Area  22  F i g . 6.  E f f e c t o f Sodium B i c a r b o n a t e  23  F i g . 7.  L e a c h i n g Rate v s . Sodium B i c a r b o n a t e  F i g . 8.  P i t c h b l e n d e a f t e r a pure carbonate  F i g . 9.  Pitchblende a f t e r a carbonate-bicarbonate l e a c h  24  E f f e c t o f Temp, on a pure leach  26  .Fig.10.  F i g . 11.  Fig.12,  Fig.13.  Curves  18  . . 23  l e a c h 24  carbonate  E f f e c t o f Temp, on a % carbonate Ifo bicarbonate leach . ,  26  E f f e c t o f Temp, on a 5% carbonate bicarbonate leach  27  %  A r r h e n i u s P l o t s o f P i t c h b l e n d e Specimen Leaches  27  Contents  (continued) page Fig.14.  E f f e c t of Pressure  29  F i g . 15.  Rate v s . P r e s s u r e  29  Fig.16.  E f f e c t o f Sodium Carbonate  31  Fig.17.  E f f e c t o f Sodium Sulphate  31  Fig.18.  Comparison of Ore L e a c h i n g Curves  Fig.19.  E f f e c t of Temp, on Ore Leaching Curves . 34  Fig.20.  A r r h e n i u s P l o t o f Ore L e a c h i n g Rates . . 34  Fig.21.  E f f e c t o f Oxygen P r e s s u r e  Fig.22.  L e a c h i n g Rate v s . P r e s s u r e  36  Fig.23.  E f f e c t o f M i l l i n g Time  37  Fig.24.  L e a c h i n g Rate v s . M i l l i n g Time  37  Fig.25.  E f f e c t of Sodium Carbonate C o n c e n t r a t i o n  39  Fig.26.  E f f e c t of R e c y c l i n g  39  Fig.27.  E f f e c t of P u l p D e n s i t y  41  Fig.28.  E f f e c t of P r i o r Roast  41  Fig.29.  Effect of Prior Flotation  43  Fig.30.  E f f e c t of Sodium Sulphate  43  ...  . . . . . . .  33  36  THE  LEACHING OF URANIUM FROM PITCHBLMDE ORES BY  AQUEOUS OXIDATION TECHNIQUES  Introduction  General T r a d i t i o n a l methods f o r e x t r a c t i n g uranium from i t s o r e s  involve  s m e l t i n g o r l e a c h i n g w i t h an a c i d such as n i t r i c , h y d r o c h l o r i c , o r s u l p h u r i c . U n t i l r e c e n t l y t h e primary c o n s i d e r a t i o n has been t h e r e c o v e r y which n o r m a l l y o c c u r s and s e p a r a t e s w i t h t h e uranium.  o f t h e radium  The c o s t o f t h e s e  methods o f treatment has g e n e r a l l y been such t h a t o n l y f a i r l y h i g h ores or concentrates The  could be e c o n o m i c a l l y  grade  treated.  i n c r e a s e d importance o f and demand f o r uranium, coupled w i t h  the d i s c o v e r y o f c o n s i d e r a b l e  d e p o s i t s o f low grade o r e s have c a l l e d f o r  t h e development o f more e f f i c i e n t and more e c o n o m i c a l methods f o r e x t r a c t i n g uranium from such o r e s .  P r e l i m i n a r y work i n t h e s e l a b o r a t o r i e s and i n t h e  l a b o r a t o r i e s o f t h e Bureau o f Mines, Ottawa, suggested t h a t t h e most favourable  p o s s i b i l i t i e s i n t h i s d i r e c t i o n a r e o f f e r e d by a b a s i c  1  leach  2  u s i n g a l k a l i n e carbonate l e a c h s o l u t i o n s .  Among t h e advantages  of  t h i s leach are the f o l l o w i n g : (a) for  The a l k a l i n e carbonate s o l u t i o n i s a f a i r l y  uranium.  Most o t h e r metals  The reagent  solvent  ( e s p e c i a l l y i r o n , which i s commonly  p r e s e n t ) are not d i s s o l v e d and a f a i r l y (b)  specific  clean leach s o l u t i o n i s obtained.  ( i . e . sodium carbonate) i s r e l a t i v e l y cheap and  the  l e a c h s o l u t i o n s are n o n - c o r r o s i v e , p e r m i t t i n g the use o f i n e x p e n s i v e equipment. (c)  C a l c i u m carbonate, which commonly o c c u r s i n a s s o c i a t i o n w i t h  ( uranium, does not r e a c t w i t h the a l k a l i n e l e a c h i n g agent, whereas t h e presence o f c a l c i u m carbonate causes unduly h i g h reagent consumption i f an a c i d l e a c h i s used. (d)  The uranium  can be r e a d i l y and c o m p l e t e l y p r e c i p i t a t e d from the  l e a c h s o l u t i o n s by one o f s e v e r a l known methods, l e a v i n g t h e s o l u t i o n s i n a condition suitable f o r recycling.  Historical The for  sodium carbonate l e a c h has l o n g been r e c o g n i z e d as  the r e c o v e r y o f uranium  (and vanadium) from c a r n o t i t e  suitable  (K2O.UO3.V2O5.3H2O)  ores. The f i r s t mention  1,165,692,  awarded to R.B.  o f the carbonate l e a c h o c c u r s i n U.S. Moore.  1  Patent  No.  T h i s patent d e s c r i b e s a p r o c e s s f o r  the r e c o v e r y o f vanadium from c a r n o t i t e by a sodium carbonate - c a u s t i c leach.  The  c a u s t i c p r e v e n t s t h e uranium  from d i s s o l v i n g i n the  carbonate  1. Moore, R.B., ' E x t r a c t i n g Vanadium, Uranium, and Radium from Ore', U.S. P a t e n t s No. 1,165,692 and 1,165,693, Chemical A b s t r a c t s , Volume 10, 1916, page 561.  3  solution, thus effecting a uranium-vanadium separation.  Uranium is  subsequently recovered by the usual hydrochloric or nitric acid leach. H.L. Gibbs2 (U.S. Patent No. 1,999,807) proposes the use of an oxidizing agent such as H202 in the carbonate - caustic leach. A further method for the treatment of carnotite ores (K.B. Thews and F.J. Heinle)^ involves boiling the ore with a solution of sodium carbonate in an autoclave.  Sodium uranyl carbonate is subsequently  precipitated by evaporation. Mellor^ describes several methods for extracting uranium which involve the fusion of the ores with sodium carbonate or sulphate, or a mixture of sodium carbonate and nitrate.  The uranium is subsequently  extracted with hot water. Liddell^ describes a method for the treatment of pitchblende ores which involves fusion with sodium sulphate followed by a water leach to remove soluble salts, and a dilute sulphuric acid leach to extract the uranium sulphate. 2. Gibbs, H.L. 'Recovery of Values from Carnotite Ores', U.S. Patent No. 1,999,807, April 30, 1945, Chemical Abstracts Vol. 29, 1935, p.3916. 3. Thews, K.B., and Heinle, F.J., 'Extraction and Recovery of Ra, V, and U from Carnotite', Ind.Eng.Chem. 15, 1159-61 (Nov. 1923). 4. Mellor, J.W., 'A Comprehensive Treatise on Inorganic and Theoretical Chemistry1, Longmans (1932) Vol. XII. 5. Liddell, D.M., 'Handbook of Non Ferrous Metallurgy; Recovery of the Metals', McGraw-Hill, 1945, 2nd edition.  4  In  g e n e r a l , the methods of e x t r a c t i n g uranium have y i e l d e d  poor r e c o v e r i e s u n l e s s expensive n i t r i c as l e a c h i n g agents. r e s t r i c t e d almost  o r h y d r o c h l o r i c a c i d s were used  In the past t h e a l k a l i n e - c a r b o n a t e l e a c h has been  e n t i r e l y t o c a r n o t i t e o r o t h e r o r e s i n which the uranium  i s completely o x i d i z e d .  A p p l i c a t i o n of the Sodium Carbonate Leach t o P i t c h b l e n d e Ores Although uranium e x h i b i t s n e a r l y a l l the v a l e n c e s t a t e s r a n g i n g from 0 t o 8, i n i t s most s t a b l e compounds i t g e n e r a l l y has 4 o r 6 - c o r r e s p o n d i n g t o t h e o x i d e s U0  2  and U O 3 .  A c t u a l l y uranium forms  about f o u r d i f f e r e n t o x i d e s as w e l l as a continuous r a n g i n g i n composition from U 0 2  In  5  to  a valence of  s i n g l e phase s e r i e s  U0 . 3  i t s most common o r e , g e n e r a l l y known as p i t c h b l e n d e , uranium  o c c u r s as an o x i d e c o r r e s p o n d i n g c l o s e l y i n c o m p o s i t i o n t o the f o r m u l a U 0g 3  (sometimes c o n s i d e r e d (U0 .2U0 ) ). 2  3  T h i s oxide f a l l s w i t h i n t h e l i m i t s o f  c o m p o s i t i o n o f the s i n g l e phase s e r i e s noted above. In of  s o l u t i o n s i m i l a r v a l e n c e p r o p e r t i e s are e x h i b i t e d , t h e v a l e n c e s  4 and 6 b e i n g s t a b l e and v a l e n c e s o f 3, 5, and 8 b e i n g u n s t a b l e .  t e t r o v a l e n t compounds are i n s o l u b l e i n b a s i c ( i . e . c a u s t i c , carbonate, ammonia) s o l u t i o n s . carbonate  The h e x a v a l e n t  s o l u t i o n s but  as i n s o l u b l e In  or  compounds o f uranium are s o l u b l e i n  are p r e c i p i t a t e d from ammonia o r c a u s t i c  solutions  uranates. c a r n o t i t e o r e s the uranium i s a l r e a d y p r e s e n t i n t h e  s t a t e , and i s t h e r e f o r e r e a d i l y d i s s o l v e d by sodium carbonate T h i s e x p l a i n s why  the use o f the sodium carbonate  hexavalent  solutions.  l e a c h has g e n e r a l l y been  r e s t r i c t e d t o these o r e s . In  The  p i t c h b l e n d e o r e s , however, as noted above, the uranium i s  5  incompletely oxidized.  I t s h o u l d s t i l l be p o s s i b l e t o t r e a t t h e s e o r e s  by t h e sodium carbonate l e a c h , p r o v i d i n g an o x i d i z i n g agent i s p r e s e n t , t o c o n v e r t the uranium c o m p l e t e l y t o t h e h e x a v a l e n t s t a t e . The Bureau o f Mines, Ottawa, and E l d o r a d o M i n i n g and R e f i n i n g (1944) L i m i t e d , Port Hope, have conducted a s e r i e s o f s t u d i e s which have shown t h a t s u c c e s s f u l l e a c h i n g o f uranium from p i t c h b l e n d e o r e s can be a c h i e v e d w i t h o x i d i z i n g agents such as potassium permanganate.  The h i g h  c o s t o f such r e a g e n t s , however, d i s c o u r a g e s t h e i r use on low grade o r e s , particularly  when o t h e r o x i d i z a b l e c o n s t i t u e n t s such as s u l p h i d e s a r e  present. I t t h e r e f o r e appeared t h a t t h e use o f gaseous oxygen o r a i r , as the o x i d i z i n g agent, would be d i s t i n c t l y  advantageous.  Recent Research on Aqueous O x i d a t i o n a t U.B.C. The o x i d a t i o n o f c e r t a i n s u l p h i d e m i n e r a l s i n aqueous s o l u t i o n s  6 under oxygen p r e s s u r e has been s t u d i e d by R. C a r t e r , R.B.  Mcintosh,** J.F. Stenhouse,^ and J . E . A n d e r s e n . ^  7 W.K.A. Congreve,' These  investigators  found t h a t i n every case i t was p o s s i b l e t o o x i d i z e the s u l p h i d e m i n e r a l s w i t h gaseous oxygen under p r e s s u r e . 6. C a r t e r , R., ' I n f l u e n c e o f R o a s t i n g Temperature on Gold Recovery f r o m a R e f r a c t o r y G o l d O r e , M.A.Sc. T h e s i s , U n i v e r s i t y o f B r i t i s h Columbia, 1949. 1  7. Congreve, W.K.A., 'Use o f High P r e s s u r e Oxygen i n E x t r a c t i o n M e t a l l u r g y ; Report to t h e Research Committee', U n i v e r s i t y o f B r i t i s h Columbia, 1949. 8. M c i n t o s h , R.B., 'Recovery of C o b a l t from T a y l o r Gem Ore by Aqueous O x i d a t i o n , ' M.A.Sc. T h e s i s , U n i v e r s i t y of B r i t i s h Columbia, 1950. 9. Stenhouse, J.F., 'Humid O x i d a t i o n o f P y r i t e ' , M.A.Sc. T h e s i s , U n i v e r s i t y o f B r i t i s h Columbia, 1950. 10. Anderson, J.E., 'Aqueous O x i d a t i o n o f G a l e n a , M.A.Sc. T h e s i s , U n i v e r s i t y of B r i t i s h Columbia, 1951. 1  6  Two  o f the above i n v e s t i g a t o r s s t u d i e d t h e  fundamental o  mechanisms i n v o l v e d i n t h e o x i d a t i o n p r o c e s s .  Stenhouse  o x i d a t i o n o f p y r i t e by measuring the oxygen consumption. recording pressure  gauge was  attached  the oxygen f o r t h e r e a c t i o n .  7  studied A  continuously  t o a s m a l l c y l i n d e r which  A rocking autoclave  was  the  supplied  u s e d as a r e a c t i o n  vessel. Andersen s t u d i e d the o x i d a t i o n o f g a l e n a i n c a u s t i c s o l u t i o n s measuring the l e a d c o n c e n t r a t i o n  i n s o l u t i o n with a polarograph.  p ) A t i n u m e l e c t r o d e s of the p o l a r o g r a p h were p l a c e d w i t h i n the so t h a t the l e a d c o n c e n t r a t i o n  o f the  removing any o f the m a t e r i a l .  The  autoclave  s o l u t i o n c o u l d be measured  A s o f t i r o n a g i t a t o r was  by  without  r o t a t e d by  an  e x t e r n a l a l n i c o magnet. No  s t u d i e s had been made on t h e aqueous o x i d a t i o n o f  o x i d i z e d oxides. minerals  sulphide  prompted an i n v e s t i g a t i o n of s i m i l a r methods i n the o x i d a t i o n  pitchblende  The  However, the s u c c e s s of t h e s e t e c h n i q u e s on  incompletely  of  o r e s i n the presence o f a sodium c a r b o n a t e s o l u t i o n .  C h e m i s t r y of the Oxygen - Sodium Carbonate Leach U 0g i n the presence of oxygen d i s s o l v e s i n sodium carbonate 3  s o l u t i o n s as the complex i o n U 0 ( C 0 3 ) 2  as  .  3  The  r e a c t i o n may  be  written  follows: U 0 3  U0  3  8  + V  2  + H0 2  °2  -  3 U0  + 3C0 ~ 3  -*  I  3  U0 (C0 ) 2  3  3  + 20H"  II  H y d r o x y l i o n i s produced as a r e s u l t o f the s o l u t i o n o f uranium. In the presence of excess sodium h y d r o x i d e , uranium may the  p r e c i p i t a t e from  s o l u t i o n as sodium u r a n a t e , i n accordance with the f o l l o w i n g r e a c t i o n :  7  + 40H-  + 2 Na  Combining I, I I , and  I I I we  U0 (C0 ) 2  2U 0 3  3  3  + 0  8  2  + 9C0  +  3  6Na  ^=7  +  Na UO» + 3 C 0 " + 2H 0 insoluble 3  a  III  2  get 3 Na U0*. + 3U0a(C0.Oa  +  3  insoluble  soluble  A c c o r d i n g t o t h i s , o n l y h a l f the uranium o x i d i z e d appears i n solution.  I t i s l i k e l y t h a t t h i s s t a t e o f a f f a i r s i s approached i f t h e  s o l u t i o n o f s u f f i c i e n t l y l a r g e q u a n t i t i e s o f U 0g i n pure carbonate  solutions  3  i s attempted.  However, i n view of the f a c t t h a t the  e q u a t i o n I I I does not  equilibrium i n  l i e c o m p l e t e l y to t h e r i g h t , i t i s l i k e l y t h a t  amounts of U 0g can be d i s s o l v e d . 3  In the presence o f excess b i c a r b o n a t e  t h i s problem i s averted, w i t h t h e f o l l o w i n g r e a c t i o n t a k i n g +  U3O8  +  3C0 — 3  +  6  small  HC0 "  —  3  3U0 (C0 ) 2  3  place: + 3H 0  3  V  2  In e f f e c t the h y d r o x y l i o n t h a t i s formed by the s o l u t i o n o f uranium i s n e u t r a l i z e d by the  bicarbonate.  From t h i s equation i t can be seen t h a t the minimum reagent requirements f o r the s o l u t i o n o f 1 g . p . l . U 0g a r e :  0.02  3  0.38  g.p.l. Na C0 ; 2  3  0.60  g.p.l.  0; 2  g . p . l . NaHC0 . 3  Side Reactions Most p i t c h b l e n d e to form acids.  The  form s u l p h u r i c a c i d . o f the  ores contain m a t e r i a l s  most common examples are s u l p h i d e s This r e s u l t s i n the  carbonate t o b i c a r b o n a t e . 2FeS  2  + 7^  Only 0.114  which r e a c t w i t h water  The  + 8 C O 3 — + 7H 0 2  gms.  conversion  which o x i d i z e  to  of a c e r t a i n amount  f o l l o w i n g r e a c t i o n occurs with p y r i t e : —  2Fe(0H)  3  + 4 S 0 ~ + 8HC0 " 4  o f s u l p h u r per l i t r e i s n e c e s s a r y t o  3  VI  provide  s u f f i c i e n t b i c a r b o n a t e i n a pure sodium carbonate s o l u t i o n f o r the  complete  8  s o l u t i o n o f one 0.21  gram U 0g ( e q u a t i o n V) t o take, p l a c e .  An  3  additional  g . p . l . oxygen i s n e c e s s a r y t o o x i d i z e t h i s e q u i v a l e n t o f p y r i t e ,  and 0.47  g . p . l . o f sodium s u l p h a t e i s formed. d i s s o l v e as t h e s i l i c a t e i o n S i 0 3 — ,  In a d d i t i o n s i l i c a may  t h e r e b y c o n v e r t i n g some a d d i t i o n a l carbonate  to b i c a r b o n a t e .  The r e a c t i o n  i s as f o l l o w s :  Si0  2  + H20  + 2C0 ~  -*  3  S  i  0  3  ~  + 2HC0 "  VII  3  On the o t h e r hand, b a s i c o x i d e s such as CaO t o be present i n r o a s t e d ores) r e a c t w i t h carbonate  and MgO  (likely  s o l u t i o n s t o form  excess h y d r o x y l i o n s , as f o l l o w s : CaO  + H20  + C0 ~ 3  —  CaC0 + 20H~  VIII  3  Where t h i s o c c u r s s u f f i c i e n t b i c a r b o n a t e s h o u l d be p r e s e n t t o n e u t r a l i z e t h e h y d r o x y l i o n formed.  O b j e c t i v e s o f t h e Present  Research  P r e l i m i n a r y aqueous o x i d a t i o n - carbonate  leaching tests  performed i n t h i s l a b o r a t o r y showed t h a t uranium c o u l d be l e a c h e d f u l l y by the same t e c h n i q u e s  as;were developed  success-  f o r the o x i d a t i o n o f  11 sulphides.  The main o b j e c t i v e o f t h i s r e s e a r c h was  to study  the  c h e m i c a l and p h y s i c a l v a r i a b l e s i n v o l v e d i n t h i s l e a c h . To a c h i e v e t h i s o b j e c t i v e , two A.  s e r i e s o f experiments were made:  An i n v e s t i g a t i o n o f the k i n e t i c s of the o x i d a t i o n and  solution  of uranium u s i n g h i g h grade specimens o f p i t c h b l e n d e w i t h measured surface areas.  In t h i s way  i t was  hoped t o c a l c u l a t e a b s o l u t e r e a c t i o n  11. H a l p e r n , J . , 'Uranium Ore Treatment Research P r o j e c t ; Progress Reports No. 1 and 2', Department o f M i n i n g and M e t a l l u r g y , U n i v e r s i t y o f B r i t i s h Columbia, 1950-51.  9  r a t e s , and t o g a i n an i n s i g h t i n t o t h e mechanism of t h e B. low  leaching reaction.  An i n v e s t i g a t i o n of the l e a c h i n g c h a r a c t e r i s t i c s o f a t y p i c a l  grade p i t c h b l e n d e  leaching rate.  o r e , and  I t was  the e f f e c t o f v a r y i n g c o n d i t i o n s on  hoped t h a t a fundamental u n d e r s t a n d i n g o f t h e  l e a c h i n g process c o u l d be o b t a i n e d information  the  gained from t h e  by  comparing t h e s e r e s u l t s w i t h  s t u d i e s on p i t c h b l e n d e  specimens.  the  ore  10  Materials  Ores Two  o r e s of s i m i l a r o r i g i n , but of d i f f e r e n t  used i n the l e a c h i n g s t u d i e s . Ore  U„Qs  Fe  S  AS-1  0.18  4.0  0.59  AS-2  0.41  3.9  0.50  The  grades, were  a n a l y s e s are as f o l l o w s : Insol(Si0 )  As  P 0  86.5  0.01  0.10  5.0  85.9  0.01  0.10  6.0  9  a  C0  s  P  In a d d i t i o n i t i s l i k e l y t h a t t r a c e s o f l e a d , radium, and  other  m e t a l s u s u a l l y a s s o c i a t e d with uranium are p r e s e n t .  Mineralogical Description The AS o r e s c o n t a i n uranium as f i n e p a r t i c l e s of p i t c h b l e n d e which f o l l o w a f i n e network o f f i s s u r e s i n the main body of the o r e . M i c r o s c o p i c examination  ( f i g . l ) revealed a t y p i c a l laminated b o t r y o i d a l  f o r m present i n f i s s u r e s r a n g i n g from 10 microns An X-ray  mm.  i n thickness.  d i f f r a c t i o n p a t t e r n confirmed the u r a n i n i t e s t r u c t u r e , a f a c e  c e n t e r e d c u b i c l a t t i c e w i t h a u n i t c e l l dimension C a l c i t e appears  o f 5.49  angstroms.  to be t h e o n l y m i n e r a l p r e s e n t i n the ore which  i s d i r e c t l y a s s o c i a t e d with the pitchblende. magnetite  t o 0.5  Pyrite, ilmenite,  are a l l present i n the l a r g e r f i s s u r e s as d i s t i n c t  h a v i n g no apparent  a s s o c i a t i o n w i t h the p i t c h b l e n d e .  The  and  crystals  dominant  gangue m i n e r a l i s a v e r y hard red q u a r t z ( j a s p e r ) o f d i s t i n c t l y  primary  origin. The  o r e s were s u p p l i e d by Eldorado and were crushed,  and m i l l e d i n t h i s l a b o r a t o r y .  sampled,  11  Figure Botryoidal Pitchblende  occupying  1 f i s s u r e s i n AS-2  ore.  X75  12  P i t c h b l e n d e Specimens The  p i t c h b l e n d e samples used were hand-picked specimens o f  Great Bear Lake o r e , a l s o s u p p l i e d by E l d o r a d o . t h e i r h i g h grade and corresponded  fairly  They were chosen f o r  uniformly t o the f o l l o w i n g  composition: U-sOa  Insol (SiQ )  62.5^  19.4$  2  Specific Gravity 5.95  P i t c h b l e n d e i s t h e name given t o an i n t i m a t e but heterogeneous mixture  of t h e b l a c k uranium m i n e r a l u r a n i n i t e (U 0g) and v a r i o u s 3  i m p u r i t i e s , mostly  silica.  The specimens used, which were the b e s t  a v a i l a b l e , appeared homogeneous i n the f r e s h l y f r a c t u r e d o r ground s t a t e , but a f t e r l e a c h i n g showed areas h i g h i n s i l i c a , etching during the leach.  due t o d i f f e r e n t i a l  The l a c k o f homogeneity was r e f l e c t e d i n the  f a i l u r e t o achieve p e r f e c t r e p r o d u c i b i l i t y i n t h e measured l e a c h i n g r a t e s .  Reagents Sodium carbonate  and o t h e r reagents  used were commercial  products. D i s t i l l e d water was used i n a l l experiments.  CP.  13  Equipment  Two autoclaves were used i n the leaching and oxidation tests. The f i r s t (designated as No. 1 autoclave) consists of a two gallon stainless steel, v e r t i c a l l y stirred reaction vessel, heated by an internal steam c o i l .  The outward appearance i s shown i n f i g . 2.  The heating  c o i l , a thermometer well, and a sampling tube, i n addition to the propellor type agitator, formed the substructure of the removable autoclave top.  An  oxygen i n l e t tube, equipped with a pressure gauge, was attached to one side, about 1^2 inches from the top. . A plug at the bottom provided a simple method f o r removing the charge. The superstructure of the autoclave top, clearly v i s i b l e i n the photograph, consisted of a packed pressure gland, through which the s t i r r e r shaft passed, a pulley at the top end of the s t i r r e r shaft, an end bearing for the s t i r r e r shaft, and a sampling valve.  The end bearing was water  cooled, and provided cooling water to the main gland by means of a small copper tube extending through the hollow s t i r r e r shaft. The autoclave was designed f o r pressures up to 2 0 0 p . s . i . , well i n excess of the maximum pressure of 1 0 0 p.s.i. used during the course of the research. The second autoclave (designated as autoclave No. 2 and shown in f i g . 3) was of the same size and of similar design as the f i r s t .  The  substructures of the top (including the c o i l , sampling tube, thermometer w e l l , and thermal regulator well) were constructed more compactly, so that they would f i t inside a two l i t r e glass l i n e r .  The two l i t r e l i n e r was  held firmly i n place by a tripod of two fiberboard rings.  14  Figure  2  No. 1 A u t o c l a v e , r e a d y f o r a r u n .  Figure  3  No. 2 A u t o c l a v e . D e t a i l s of the substructure are v i s i b l e . The v a r i a c , t r a n s f o r m e r , and m e r c u r y s w i t c h a r e i n t h e background.  15  S i n c e i t was  d e s i r e d to use d i f f e r e n t temperatures  a u t o c l a v e , steam (which was heating.  a v a i l a b l e o n l y a t 212°F) was  not used f o r  I n s t e a d , heat v/as p r o v i d e d by a 2500 watt - 21 v o l t bare  r e s i s t o r , p l a c e d between t h e two l i t r e bottom.  i n this  The h e a t e r was  w i t h water when i n use.  g l a s s l i n e r and t h e a u t o c l a v e  i n s u l a t e d from t h e a u t o c l a v e , and One  end was  wire  connected  surrounded  to an i n s u l a t e d  p l u g i n t h e bottom o f the a u t o c l a v e , w h i l e the o t h e r was  copper  grounded t o  the autoclave. Power was  s u p p l i e d to the h e a t i n g c o i l by a 3KVA t r a n s f o r m e r  h a v i n g a 220 v o l t i n p u t and a 21 v o l t output r a t i n g . was  c o n t r o l l e d by a 220  volt  the e a r l i e r runs, was  operation.  input voltage  variac.  A mercury t h e r m o r e g u l a t o r , of  The  used f o r temperature  c o n t r o l i n some  abandoned because of i t s f r a g i l i t y and  I t was found t h a t b e t t e r temperature  inefficient  c o n t r o l c o u l d be  by s i m p l y s e l e c t i n g a s u i t a b l e v o l t a g e s e t t i n g on the v a r i a c .  achieved  16  Experimental  Pitchblende All  Procedures  Specimens  t h e w o r k p e r f o r m e d o n t h e p i t c h b l e n d e s p e c i m e n s was  i n no. 2 autoclave.  U s u a l l y two s p e c i m e n s w e r e w i r e d t o t h e  c o i l of the autoclave  a n d i m m e r s e d i n 1250 m i s . o f l e a c h s o l u t i o n .  done  internal  The p i t c h b l e n d e s p e c i m e n s w e r e p r e p a r e d i n e a c h c a s e b y clean f l a t  surfaces  o n a f i n e emery w h e e l .  grinding  Specimens were r e - u s e d  r e - g r i n d i n g the surfaces.  The s u r f a c e  and l a t e r c a l c u l a t e d , a f t e r  i t was e s t a b l i s h e d t h a t  after  a r e a was m e a s u r e d i n a f e w c a s e s , t h e a r e a was p r o p o r t i o n a l  t o t h e 2/3 p o w e r o f t h e w e i g h t . The a u t o c l a v e w a s c l o s e d a n d h e a t e d t o t h e d e s i r e d a f t e r which a desired pressure Samples  temperature  o f o x y g e n was i n t r o d u c e d a n d m a i n t a i n e d .  o f the l e a c h s o l u t i o n were withdrawn from t h e a u t o c l a v e  measured time i n t e r v a l s f o r u r a n i u m a n a l y s e s  and c a r b o n a t e  I n most c a s e s t h e specimens were w e i g h e d b e f o r e and a f t e r o b t a i n a m a t e r i a l balance The s u c c e s s i v e l e a c h s o l u t i o n samples due t o s a m p l i n g .  at  titrations. the run to  check. increments i n the uranium c o n c e n t r a t i o n of  the  were c o r r e c t e d f o r t h e change i n s o l u t i o n volume  The m e t h o d o f c a l c u l a t i o n i s  shown i n A p p e n d i x C .  Ores Both autoclaves t e m p e r a t u r e and p r e s s u r e a l l the other v a r i a b l e s  were used i n t h e o r e l e a c h i n g s t u d i e s . v a r i a b l e s were s t u d i e d i n n o . 2 a u t o c l a v e ,  i n no. 1  In no. 2 autoclave leach  s o l u t i o n was u s e d .  The and  autoclave.  a charge o f  500 grams o r e a n d 1000 m i s .  The o r e was p r e v i o u s l y m i l l e d f o r one h o u r i n  17  a rod m i l l .  Samples were withdrawn i n the same way as i n the study of  the pitchblende specimens. Since an amount of pulp proportional to the leach solution was withdrawn i n t h i s case, no correction of .solution analyses due t o the volume change was necessary.  Where d i s t i l l a t i o n of water from the inside  to the outside of the l i n e r occurred, a correction f o r the volume change was necessary, and could be calculated from carbonate t i t r a t i o n s and uranium analyses of the samples.  The method of c a l c u l a t i o n i s i l l u s t r a t e d  by the second sample calculation i n Appendix C. The procedure used i n No. 1 autoclave was similar except that a charge of 1500 grams ore and 3 or 4/2 l i t r e s of leach solution was used.  A n a l y t i c a l Methods Leach solutions were analyzed by a carbonate - peroxide method 12 s i m i l a r to those described by Rodden.  A f i v e ml. sample of leach  solution was d i l u t e d to 100 mis. a f t e r the addition of f i v e mis. 30$ hydrogen peroxide.  The o p t i c a l density of the resulting solution was  determined i n a Beckman model DV spectrophotometer at 370 millimicrons. D i s t i l l e d water was used as a standard.  The exact procedure was  altered  from time to time to suit the p a r t i c u l a r conditions of i n d i v i d u a l leaches. The o p t i c a l densities of standard solutions were determined i n most cases to obtain a c a l i b r a t i o n f o r each procedure.  Typical c a l i b r a t i o n curves  are shown i n f i g . 4. 12. Rodden, C.J., •Analytical Chemistry of the Manhatten Project', Nuclear Energy Series, Manhatten Project Technical Section, D i v i s i o n VIII V o l . 1, 1st ed., McGraw-Hill, 1951.  18  O U 0, 3  -10 CONTENT  -20 GRAMS PER  -SO LITER  Figure 4 T y p i c a l c a l i b r a t i o n c u r v e s showing the r e l a t i o n between Beckman s p e c t r o p h o t o m e t e r r e a d i n g s and t h e u r a n i u m c o n t e n t of the samples.  19  Ore head samples and  r e s i d u e s were a n a l y z e d f o r uranium by  13 the c e l l u l o s e column method.  In t h i s method elements t h a t i n t e r f e r e  i n the c a u s t i c - peroxide spectrophotometry  d e t e r m i n a t i o n are  from van e t h e r n i t r a t e s o l u t i o n by a c e l l u l o s e The  change i n carbonate  t h e l e a c h was  determined  0.1  The  N. HC1.  adsorbed  column.  and b i c a r b o n a t e c o n c e n t r a t i o n d u r i n g  by t i t r a t i n g samples o f the l e a c h s o l u t i o n w i t h  end p o i n t (pH = 80) f o r t h e c o n v e r s i o n o f C 0 " 3  and t h a t (pH = 4) f o r t h e c o n v e r s i o n o f HC0 ~ t o C 0 3  2  were  u s i n g p h e n o l p h t h a l e i n and methylorange, r e s p e c t i v e l y , as  t o HC0 "  determined indicators.  In l a t e r experiments more a c c u r a t e d e t e r m i n a t i o n s of t h e end p o i n t s were made w i t h a Beckman t i t r i m e t e r .  13. R a b b i t t s , F.T., et a l , 'The D e t e r m i n a t i o n of U 0 g i n Ores and Solutions; C e l l u l o s e Column Method', Mines Branch, Department o f Mines and T e c h n i c a l Surveys, Canada, Memo. No. 105. 3  3  20  Results  A.  Leaching of Pitchblende Specimens 1.  Reproducibility  In the work on the pitchblende specimens, a number of runs were repeated at various times to ascertain the r e p r o d u c i b i l i t y of the leaching rates.  The following effects were noted: (a)  Reproducibility f o r successive leaches on the same  specimens was good.  Maximum errors i n rate measurements were  probably no greater than ± 5%. (b)  Reproducibility f o r widely separated leaches on the  same specimens was r e l a t i v e l y poor due to a tendency f o r the rate to decrease with re-use of the  specimen.  In general, i n a series of f i v e runs, the l a s t would be about 15$ slower than the f i r s t under i d e n t i c a l condit ions.  In one case a  decrease i n rate of 35$ was noted i n two r e p r o d u c i b i l i t y runs separated by a series of eight runs. In general, successive leaches on one pair of specimens were used i n the study of each variable.  The r e s u l t s obtained i n t h i s way  were s u f f i c i e n t l y reproducible f o r meaningful i n t e r p r e t a t i o n .  The  r e p r o d u c i b i l i t y within a given s e r i e s was checked by repeating the f i r s t run a f t e r completion of the series.  The change i n rate was  generally  much smaller than the changes caused by the variable which i t was desired to  study i n the series. 2.  Proportionality to Surface Area  Since the pitchblende specimens decreased i n size with successive leaches, to obtain comparable rates i t was necessary to ascertain that the  21  l e a c h i n g r a t e was d i r e c t l y p r o p o r t i o n a l t o s u r f a c e a r e a .  T h i s would be  the case i n a t r u e heterogeneous r e a c t i o n . Two s u c c e s s i v e l e a c h e s were performed, the f i r s t u s i n g two specimens, and t h e second u s i n g o n l y one o f these two specimens.  The  t o t a l l e a c h i n g r a t e i s p l o t t e d a g a i n s t t h e measured s u r f a c e a r e a i n f i g . The  plot  5.  shows t h a t t h e l e a c h i n g r a t e i s p r o p o r t i o n a l t o t h e s u r f a c e a r e a . 3.  E f f e c t o f Sodium B i c a r b o n a t e  Concentration  S i n c e t h e c h e m i s t r y o f t h e sodium carbonate t h a t t h e presence  leach indicates  o f b i c a r b o n a t e i n the l e a c h s o l u t i o n i s n e c e s s a r y f o r  t h e o x i d i z e d uranium t o be d i s s o l v e d , a study was made o f t h e e f f e c t o f this  reagent. Fig.  and d i f f e r e n t  6 shows t h e l e a c h i n g curves a t f i v e p e r c e n t sodium c o n c e n t r a t i o n s o f sodium b i c a r b o n a t e .  carbonate  F i g . 7 shows t h e  change o f r a t e w i t h i n c r e a s i n g b i c a r b o n a t e c o n c e n t r a t i o n s . The f o l l o w i n g e f f e c t s o f b i c a r b o n a t e c o n c e n t r a t i o n s a r e noted: (a) . When one percent sodium b i c a r b o n a t e was added t o a f i v e p e r c e n t sodium carbonate more than (b)  leach s o l u t i o n , the leaching rate  doubled. The s u r f a c e o f the specimens was l e f t  a grey c o l o u r a f t e r  b e i n g s u b j e c t e d t o a l e a c h w i t h some b i c a r b o n a t e p r e s e n t . pure carbonate  l e a c h s o l u t i o n s were used, the s u r f a c e was  When left  a brown c o l o u r , presumably due t o t h e f o r m a t i o n o f some i n s o l u b l e sodium uranate  (see e q u a t i o n I I I page 7).  F i g s . 8 and 9 show  the t y p e s o f s u r f a c e etches produced on the p i t c h b l e n d e specimens w i t h a pure carbonate, (c)  and a carbonate b i c a r b o n a t e l e a c h .  A more n e a r l y l i n e a r l e a c h i n g r a t e i s produced when  b i c a r b o n a t e i s p r e s e n t i n the l e a c h s o l u t i o n .  In a s e r i e s o f  22  Figure The e f f e c t o f s u r f a c e Conditions: 100°C; Ifo N a E C 0 . 3  5  a r e a on t h e t o t a l l e a c h i n g r a t e . 60 p s i g . o x y g e n p r e s s u r e ; 5<?o N a C 0 ; 2  3  23  I  O  I  O  I  — I  30  I  60 TIME  -  90 MINUTES  Figure  1  L_  I20  ISO  6  The e f f e c t o f s o d i u m b i c a r b o n a t e on t h e l e a c h i n g o f u r a n i u m from p i t c h b l e n d e specimens. C o n d i t i o n s : 100°C; 60 p s i g . oxygen p r e s s u r e ; 5 $ NacCOg.  0  •10  1 I s  () •08  (  * •06 Ul  <0 9: &  5  •OJ  1  0  02  C  c>  1  1 2 PERCENT  /  r-  t...  3 Nai -/CC  •  Figure  h  -i  r  7  L e a c h i n g Rate v s . sodium b i c a r b o n a t e  concentration.  Figure  8  The a p p e a r a n c e o f t h e s u r f a o e o f a p i t c h b l e n d e s p e c i m e n a f t e r a n o x i d i z i n g l e a c h w i t h 5% s o d i u m c a r b o n a t e s o l u t i o n . T75  Figure  9  The a p p e a r a n c e o f t h e s u r f a o e o f a p i t c h b l e n d e s p e c i m e n a f t e r a n o x i d i z i n g l e a c h i n a s o l u t i o n c o n t a i n i n g 5$ s o d i u m c a r b o n a t e and 5$ s o d i u m b i c a r b o n a t e .  25  f i v e runs made w i t h pure carbonate s o l u t i o n s , two o f the r u n s showed a r a p i d s l o w i n g down i n t h e l e a c h i n g r a t e as t h e l e a c h proceeded, w h i l e t h e o t h e r t h r e e were much more n e a r l y l i n e a r . Carbonate t i t r a t i o n s r e v e a l e d t h a t t h e s o l u t i o n s i n t h e former two runs c o n t a i n e d a s l i g h t  excess o f c a u s t i c over t h e carbonate  content i n t h e l e a c h s o l u t i o n s .  I n the l a t t e r t h r e e runs which  showed more l i n e a r r a t e s , a s l i g h t excess o f b i c a r b o n a t e present.  was  F i g . 10 c l e a r l y r e v e a l s t h i s e f f e c t , c o n f i r m i n g t h e i  behavior a n t i c i p a t e d e a r l i e r  (see page 7) i n t h e d i s c u s s i o n  o f the c h e m i s t r y o f t h e l e a c h p r o c e s s . (d)  •  r  The r a t e o f l e a c h i n g i n c r e a s e d as t h e sodium b i c a r b o n a t e  c o n c e n t r a t i o n was i n c r e a s e d from one t o f i v e p e r c e n t , b u t showed a tendency to l e v e l o f f w i t h f u r t h e r i n c r e a s e i n b i c a r b o n a t e concentration. 'J; 4.  v  The  E f f e c t o f Temperature e f f e c t ' o f temperature on the l e a c h i n g r a t e was s t u d i e d a t  t h r e e d i f f e r e n t c o n c e n t r a t i o n s o f sodium b i c a r b o n a t e , as shown i n f i g s . 11, and 12.  F i g . 13 shows the A r r h e n i u s p l o t f o r each o f t h e s e  The r a t e o f l e a c h i n g i n c r e a s e d w i t h temperature.  10,  series.  Activation  e n e r g i e s o f 9 t o 12"^; k i l o c a l o r i e s per gram mole a r e c a l c u l a t e d f r o m t h e Arrhenius  plots. F o r subsequent c a l c u l a t i o n s , the l a s t s e r i e s , w i t h f i v e  percent  b i c a r b o n a t e , w i l l be c o n s i d e r e d the most a c c u r a t e f o r t h e f o l l o w i n g reasons: (a)  The f i r s t s e r i e s , without  b i c a r b o n a t e , does not have  l i n e a r l e a c h i n g r a t e s , and shows e v i d e n c e of incomplete of the o x i d i z e d p r o d u c t s .  solution  In t h i s case i t appears t h a t an  e q u i l i b r i u m r e a c t i o n i s involved.-  A unidirectional reaction i s  26  Figure  10  The e f f e c t o f t e m p e r a t u r e on t h e l e a c h i n g o f u r a n i u m f r o m p i t c h b l e n d e specimens. Conditions: 60 p s i g . o x y g e n p r e s s u r e ; 5fo N a C 0 . g  3  Figure  11  The e f f e c t o f t e m p e r a t u r e on t h e l e a c h i n g o f u r a n i u m f r o m p i t c h b l e n d e specimens. Conditions: 60 p s i g . o x y g e n p r e s s u r e ; 5$ N a C 0 ; l | NaHC0 . 2  3  3  27  /o  /  A  /  >  .c  I  >  <*  \,  ier  /  M_ o  £u Q w  ?/  X  i  g  5  r  A  <  i_r •  _  13  —  —t  ...  •  .90  120 Ho ~IME -MINU7  •  40  M 1  F i g u r e 12 The e f f e c t o f t e m p e r a t u r e o n t h e l e a c h i n g o f u r a n i u m f r o m pitchblende specimens. Conditions: 60 p s i g . o x y g e n p r e s s u r e ; 5% N a C 0 ; 5% N a H C 0 . 2  3  3  F i g u r e 13 Arrhenius p l o t s o f the temperature e f f e c t concentrations.  a t three  bicarbonate  28  d e s i r e d i n thfe c a l c u l a t i o n o f a b s o l u t e r e a c t i o n r a t e s . (b)  The  second s e r i e s , w i t h one  p e r c e n t sodium b i c a r b o n a t e  s o l u t i o n , c o n s i s t s o f o n l y t h r e e runs. b i l i t y o f these runs was  The  general reproduci-  too poor to permit use o f a s e r i e s o f  o n l y t h r e e runs f o r c o n c l u s i v e i n t e r p r e t a t i o n . (c)  The t h i r d s e r i e s , w i t h f i v e percent  bicarbonate,  c o n s i s t s o f f i v e runs, i n c l u d i n g one to t e s t the o f the s e r i e s .  A f a i r l y good A r r h e n i u s p l o t g i v e s an  energy of 12,300 c a l o r i e s per gram mole, w i t h e r r o r of t  reproducibility  1,000  probable  limits  5.  E f f e c t of Oxygen P r e s s u r e  The  e f f e c t o f oxygen p r e s s u r e was  c o n t a i n i n g f i v e percent sodium carbonate  series.  studied using a solution  and f i v e p e r c e n t sodium b i c a r -  The r a t e curves o b t a i n e d f o r runs a t d i f f e r e n t p r e s s u r e s  are  shown i n f i g .  14.  p r e s s u r e , and  a l s o as a f u n c t i o n o f the square r o o t o f the oxygen p r e s s u r e .  The t o t h e square  In f i g .  of  calories.  Subsequent c a l c u l a t i o n s a r e based on t h i s  bonate.  activation  15 t h e r a t e i s p l o t t e d as a f u n c t i o n o f oxygen  l a t t e r p l o t c l e a r l y i n d i c a t e s t h a t the r a t e i s p r o p o r t i o n a l root o f the oxygen p r e s s u r e , i n d i c a t i n g t h a t the oxygen  p a r t i c i p a t i n g i n the r e a c t i o n i s d i s s o c i a t e d . 14, The  same e f f e c t was  n o t e d by p r e v i o u s i n v e s t i g a t o r s  t h e aqueous o x i d a t i o n o f s u l p h i d e m i n e r a l s .  14.  Andersen, J.A.,  15.  Stenhouse, J.F.,  op.cit. op.cit.  15 in  29  zo (  /?£//V P-26 P-27 P-2B P-23 P-30  y'  •  £  1  TRA  u  ,*  t  PRESSURE IO oo 60  •  o  -4 -0  -  -+ —X  X j (  Et  \to  \ ° 0  H  fj  *:  l  n J%  i"  |  9  /<=  7"/ Arf C  o  Figure  Jl -  o  & to  MINUTEi  14  The e f f e c t o f p r e s s u r e on t h e l e a c h i n g o f u r a n i u m f r o m pitchblende specimens. Conditions: 100°C; 5% N a C 0 ; 5% N a H C 0 . 2  3  OXYGEN  PRESSURE  Figure Rate v e r s u s oxygen p r e s s u r e of oxygen p r e s s u r e .  -  PS.I.  15  and r a t e v e r s u s  square  root  3  30  6.  E f f e c t of Sodium Carbonate C o n c e n t r a t i o n  Two  s e r i e s of experiments  o f v a r y i n g t h e sodium carbonate was  were made t o determine  concentration.  The  the  effect  sodium b i c a r b o n a t e  kept constant a t f i v e p e r c e n t , and t h e carbonate v a r i e d between one  and f i v e p e r c e n t .  The  c o r r e s p o n d i n g d u p l i c a t e runs were averaged,  t h e l e a c h i n g curves o b t a i n e d i n t h i s way  a r e shown i n f i g .  16.  and  The  f o l l o w i n g e f f e c t s were noted: (a)  Only s m a l l i n c r e a s e s i n l e a c h i n g r a t e s o c c u r r e d w i t h  i n c r e a s e d carbonate c o n c e n t r a t i o n s . (b)  At low carbonate  c o n c e n t r a t i o n s , under t h e  temperature  c o n d i t i o n s e x i s t i n g i n t h e a u t o c l a v e , some o f t h e b i c a r b o n a t e was  c o n v e r t e d t o carbonate by e x p e l l i n g C 0 . 2  The r e a c t i o n i s  as f o l l o w s : 2HC0 3  C0 t 2  This i s probably a thermal  + H0 2  +  C0 — 3  effect.  7.  E f f e c t o f Sodium S u l p h a t e  Concentration  The  e f f e c t of a n e u t r a l s a l t ,  sodium s u l p h a t e , was  a s e r i e s o f two  runs, t o i n d i c a t e whether o r not a s a l t e f f e c t was  F i g . 17 shows t h e e x t r a c t i o n curves o f both No  studied i n  change i n the l e a c h i n g r a t e was  8.  E f f e c t of  One  run was  present.  runs. noted.  Agitation  attempted w i t h o u t a g i t a t i o n , except f o r t h r e e  minutes o f a g i t a t i o n p r i o r t o t h e t a k i n g o f each sample a t 30 minute intervals.  The l e a c h i n g r a t e was  agitation.  A p p a r e n t l y a g i t a t i o n has a s t r o n g e f f e c t , which may  c r i t i c a l under c e r t a i n c o n d i t i o n s . i n the temperature  about h a l f the normal r a t e w i t h  The h i g h a c t i v a t i o n energy  full  be revealed  study i n d i c a t e s t h a t the s t a n d a r d a g i t a t i o n c o n d i t i o n s  31  -  20  PUN  % P-/7->P~34-IV. P-/8*P33 P-/S->P-30 5%  »  -  o  —  — o  a.  15  S u  ^ *  P- a'.:  ^ K  '  .  I•JO  t  : _ i _  0  1  60  30  90 120 MINUTES  _l  F i g u r e 16 The e f f e c t o f s o d i u m c a r b o n a t e c o n c e n t r a t i o n o n t h e l e a c h i n g of uranium from p i t c h b l e n d e specimens. Conditions: 100°C; 60 p s i g . o x y g e n p r e s s u r e ; 5% NaHCO,,.  10  No Na.SCi /OY. Na.SO.  P35 P36  o -x-  «  o  |  c  |  _!_  30  60  TIME  90  /20 MINUTES  L 150  F i g u r e 17 The e f f e c t o f s o d i u m s u l p h a t e from p i t c h b l e n d e specimens. oxygen p r e s s u r e ; 5% N a C 0 3 ; 2  on t h e l e a c h i n g o f u r a n i u m Conditions: 100°C; 60 p s i g . Vfo NaHC03.  32  o f t h i s r e s e a r c h were not c r i t i c a l .  B.  L e a c h i n g of Ores 1.  Reproducibility  In t h e work on t h e o r e s , the r e p r o d u c i b i l i t y o f e x t r a c t i o n r a t e s was p e r f e c t l y s a t i s f a c t o r y on each o r e . o f o r e were used,  However, s i n c e two  comparable l e a c h i n g r a t e s were n e c e s s a r y  e f f e c t s s t u d i e d c o u l d be a p p l i e d t o both o r e s .  grades  i f a l l the  F i g . 18 shows t h a t t h e  l e a c h i n g r a t e s a r e i n f a c t v e r y c l o s e , p a r t i c u l a r l y i n t h e range o f 30 t o 70 p e r c e n t e x t r a c t i o n , the i n t e r v a l chosen as a measure o f t h e r a t e . 2.  E f f e c t o f Temperature  A s e r i e s o f s i x runs was made at f i v e d i f f e r e n t on AS-2 o r e .  The e x t r a c t i o n c u r v e s a r e shown i n f i g .  temperatures  19, and an A r r h e n i u s  p l o t , which corresponds t o an a c t i v a t i o n energy o f 9,700 c a l o r i e s per gram mole, i n f i g . 20.  F o r comparative  purposes,  Arrhenius plots are also  shown f o r two o t h e r p i t c h b l e n d e ores s t u d i e d i n t h i s l a b o r a t o r y . a r e Great Bear Lake (Hutch) c o n c e n t r a t e  (4.72$ U  3  0 g ) and B-C o r e (0.12$ U 0 g ) . 3  The two o r e s were found t o have s i g n i f i c a n t l y h i g h e r e n e r g i e s t h a n t h e AS-2 o r e . not  These  The r e a s o n f o r t h i s apparent  activation  discrepancy i s  c l e a r , but may be t h a t t h e a c c u r a c y o f the a c t i v a t i o n e n e r g i e s d e t e r -  mined f o r G.B.L. and B-C o r e s i s poor.  I n t h e c a s e o f B-C o r e the uranium  c o n c e n t r a t i o n was t o o low to permit a c c u r a t e d e t e r m i n a t i o n by the methods used.  The G.B.L. (Hutch) c o n c e n t r a t e was v e r y high i n s u l p h i d e s which were  oxidized during the leach. leach solutions.  Some copper was a l s o f o u n d t o d i s s o l v e i n t h e  I t i s possible that these f a c t o r s a f f e c t e d the rates of  uranium l e a c h i n g , o r i n t e r f e r e d w i t h t h e a c c u r a t e d e t e r m i n a t i o n o f t h e s e  rates.  33  too  cj  !  7 5  %.  5  '•50  A -s  1  ORE  Dec  o _X  25  1  o  i  SC  T/Mir  I  MJA///TJTC  /SO  F i g u r e 18 C o m p a r i s o n o f l e a c h i n g c u r v e s o f A S - 1 and AS-2 o r e s . Conditions: 100°C; 30 p s i g . o x y g e n p r e s s u r e ; 5% N a C 0 g  3  34  Figure  19  The e f f e c t o f t e m p e r a t u r e on t h e l e a c h i n g o f AS-2 o r e . Conditions: 30 p s i g . o x y g e n p r e s s u r e ; 5$ NagCOg.  O  \  ,  HUTCH B-L • ORE A -S2 • C. n & r c  '  M  • C) \ O V: >  in  RATE  ] _  " n  I  •  V  , ill;  • -2L  )-  • i 2-5  1  2 6  1  2 7  2  x/0  1  s  2 9  V  SO  3  Figure  20  A r r h e n i u s p l o t s o f t h e t e m p e r a t u r e e f f e c t on t h e rate of three ores.  leaching  35  I t s h o u l d be noted t h a t s m a l l e r r o r s i n t h e r a t e  determination  may l e a d t o l a r g e e r r o r s i n the e s t i m a t i o n o f t h e a c t i v a t i o n energy. general, a greater accuracy o t h e r ores  In  i s i n d i c a t e d f o r t h e A-S ores than f o r t h e  studied. 3.  E f f e c t o f Oxygen  Pressure  The e f f e c t o f oxygen pressure o f f o u r runs.  on AS-2 o r e was s t u d i e d i n a s e r i e s  The e x t r a c t i o n curves a r e shown i n f i g . 21.  r a t e i s p l o t t e d a g a i n s t t h e oxygen p r e s s u r e , o f t h e oxygen p r e s s u r e ,  i n f i g . 22.  The e x t r a c t i o n  and a g a i n s t t h e square r o o t  The r a t e i s seen t o be d i r e c t l y  p r o p o r t i o n a l t o t h e square r o o t o f t h e oxygen p r e s s u r e .  The same  relation  was o b s e r v e d i n t h e l e a c h i n g o f t h e p i t c h b l e n d e . 4.  E f f e c t o f M i l l i n g Time  The  e f f e c t o f m i l l i n g time was s t u d i e d o n AS-1 o r e i n a s e r i e s  of f i v e runs.  The e x t r a c t i o n curves are shown i n f i g . 23.  r a t e as a f u n c t i o n o f m i l l i n g time i s shown i n f i g . 24.  The l e a c h i n g  Screen  analyses  f o r each m i l l i n g time a r e g i v e n i n Appendix F. I t i s a w e l l known m i n e r a l d r e s s i n g p r i n c i p l e t h a t i n t h e m i l l i n g of coarse  homogeneous p a r t i c l e s , the t o t a l s u r f a c e a r e a o f the p a r t i c l e s  increases i n direct  proportion t o m i l l i n g time.  d i s t r i b u t e d throughout t h e ore i n f a i r l y coarse,  I f the pitchblende i s homogeneous p a r t i c l e s ,  t h e t o t a l s u r f a c e a r e a o f t h e p i t c h b l e n d e would t h e n i n c r e a s e i n p r o p o r t i o n t o the m i l l i n g t i m e .  F i g . 24, which c o n s i s t s o f a l i n e a r p l o t o f l e a c h i n g  r a t e a g a i n s t m i l l i n g time, thus i m p l i e s t h a t l e a c h i n g r a t e i s p r o p o r t i o n a l t o the surface area of the pitchblende  p a r t i c l e s i n the ore.  r e l a t i o n was observed i n t h e c a s e o f t h e p i t c h b l e n d e fig.  5).  & similar  (  specimens (page 22,  36  O  30  60  90  120  TIME  -  /50  /SO  2/0  240  MINUTES  Figure E l The e f f e c t o f o x y g e n p r e s s u r e o n t h e l e a c h i n g o f AS-2 o r e . Conditions: 1 0 0 C ; 5% N a C 0 . b  2  OK  i  3  YCE/V  PRESSURL  Iy  |  k  P S .1. /5  SO •  IO  s 3  •\-  < Ka  1  •  f m  •75  *§ ?| . in * -5" K kj  IP (a  A  > G  ay  O  o  . -r y ^  1 2-5 SQUARE  5 / ?007 OF OXYGEN  75 PRESS  yffE  F i g u r e £2 L e a c h i n g r a t e versus oxygen p r e s s u r e r o o t o f oxygen p r e s s u r e .  and r a t e v e r s u s  square  37  /oo  RUN MILLING TIME UL-46 90 MIN— 75 MIN — UL-50 60 M/N — UL5/ 45 MIA/ — UL-52 30 MIN — UL-53  TIME  90 /20 - M/NUTES  F i g u r e 23 The e f f e o t o f m i l l i n g t i m e on t h e l e a c h i n g o f A S - 1 o r e . Conditions: 100°C, 30 p s i g . o x y g e n p r e s s u r e .  O 1  1  15  1  30  1  45 MILLING TIME  I  I  60 75 - MINUTES  I  90  F i g u r e 24 Leaching r a t e versus  milling  time.  i  38  5.  E f f e c t of Sodium Carbonate  The  e f f e c t of sodium carbonate c o n c e n t r a t i o n was  s e r i e s o f f i v e runs on AS-1 i n the l e a c h s o l u t i o n . the  ore.  The  No  (a)  The  The  o t h e r reagent was  studied i n a  initially  present  e x t r a c t i o n curves f o r t h i s s e r i e s i n which  sodium carbonate c o n c e n t r a t i o n  are shown i n f i g . 25.  Concentration  was  v a r i e d between one  and  five  percent  f o l l o w i n g e f f e c t s are n o t e d :  leaching rate increases s i g n i f i c a n t l y with  increase  /  i n sodium carbonate c o n c e n t r a t i o n  i n the range o f low  t r a t i o n s ( l t o 3%).  s u r p r i s i n g s i n c e the  T h i s , i s not  concenuranium  i s i n s o l u b l e i n the absence o f carbonate. (b)  Only s m a l l i n c r e a s e i n l e a c h i n g r a t e , s i m i l a r t o  noted i n the work on p i t c h b l e n d e i s obtained  by i n c r e a s i n g the  specimens (page 31,  sodium carbonate  f u r t h e r , say up t o f i v e p e r c e n t . optimum c o n c e n t r a t i o n  The  i s reached and  that f u r t h e r increase  in  6.  E f f e c t o f R e c y c l i n g the Leach S o l u t i o n  The  e f f e c t o f r e c y c l i n g the l e a c h s o l u t i o n s was  leached  t h i s s e r i e s are shown i n f i g . 26.  e f f e c t on the  l e a c h s o l u t i o n was  each time.  concentration an  carbonate c o n c e n t r a t i o n  a f r e s h l o t of ore b e i n g  f i g . 16),  i n d i c a t i o n i s that  the  s e r i e s o f experiments i n which AS-1  has no  that  The  There does not  rate.  studied i n a  r e c y c l e d four times,  e x t r a c t i o n curves f o r appear t o be  any  s i g n i f i c a n t change i n r a t e as a r e s u l t of r e c y c l i n g t h e l e a c h s o l u t i o n . Minor v a r i a t i o n s i n r a t e may as the  be due  to i n c r e a s i n g b i c a r b o n a t e  concentration  solution i s recycled. 7.  E f f e c t of Pulp  Density  The  e f f e c t o f p u l p d e n s i t y was  studied i n a s e r i e s of three  runs.  39  O  30  60  TIME  90 /20 - MINUTES  /SO  F i g u r e £5 The e f f e c t o f s o d i u m o a r b o n a t e c o n c e n t r a t i o n on t h e l e a c h i n g o f AS-1 o r e . Conditions: 100°C; 30 p s i g . o x y g e n p r e s s u r e .  F i g u r e 26 The e f f e c t o f r e c y c l i n g l e a c h s o l u t i o n on t h e l e a c h i n g o f AS-1 o r e . Conditions: 100°C, 30 p s i g . o x y g e n p r e s s u r e ; 5fo NagCOg.  \  40  The  e x t r a c t i o n curves are  shown i n f i g . 27.  The  r a t e o f l e a c h i n g appears  t o be s l i g h t l y f a s t e r a t the h i g h e r p u l p d e n s i t y . are  The  f o l l o w i n g reasons  suggested: (a)  At the h i g h e r  sulphides i n the  i s present.  production  At h i g h e r  more f a v o u r a b l e .  The  concentration  o x i d a t i o n of these sulphides  o f a g r e a t e r amount o f b i c a r b o n a t e  subsequent i n c r e a s e (b)  pulp density a higher  of  results  with a  i n the l e a c h i n g r a t e . p u l p d e n s i t i e s a g i t a t i o n c o n d i t i o n s may Ho work was  done on the  be  agitation variable.  However, a g i t a t i o n i s known to have an e f f e c t on the  leaching  rate.  leaching.  8.  E f f e c t o f P r i o r Roast  One  b a t c h o f AS-2  The  ore was  r o a s t e d two  hours a t 700°C p r i o r t o  r e s u l t i n g l e a c h i n g curve i s shown, t o g e t h e r  with a  comparable l e a c h i n g curve f o r an u n r o a s t e d ore i n f i g . 28. The  l e a c h i n g r a t e o f the  t h a n t h a t of the  unroasted ore.  (a) present  The  roasted The  ore was  s u b s t a n t i a l l y slower  f o l l o w i n g reasons are  decomposition o f c a l c i t e  (CaCOs) known to  i n the ore r e s u l t e d i n t h e p r o d u c t i o n  (equation V I I I , page 8 ) , t h u s l i m i t i n g the The  leaching rate increased  a c i d and  sodium b i c a r b o n a t e  formed, but the  r a t e was  suggested: be  o f excess h y d r o x i d e  s o l u b i l i t y of uranium.  somewhat when s u f f i c i e n t  sulphuric  were added t o n e u t r a l i z e the  s t i l l w e l l below t h a t f o r an  hydroxide  unroasted  ore. (b)  The  pitchblende  r e a c t e d w i t h the  c l o s e l y associated  c a l c i t e d u r i n g the r o a s t t o form i n s o l u b l e c a l c i u m uranate  or  41  TIME  -  Figure  MINUTES  £7  The e f f e c t o f p u l p d e n s i t y on t h e l e e c h i n g o f AS-1 o r e . Conditions: 100°C; 30 p s i g . o x y g e n p r e s s u r e ; 5% NagCOg.  /OO  0  U/V/?OAST£ D  75  k k SO  <*  i  J  t  c  25 '/OOgms  NaHCO, a.<id.ecI  20/n/s 0 C1  j  1 200  /OO 1IML  Figure  300  J• 400  MINUTES  £8  The e f f e c t o f a p r i o r r o a s t on t h e l e a c h i n g o f AS-£ o r e . R o a s t i n g t e m p e r a t u r e = 700°C. Conditions of leach: 100°C; 30 p s i g . o x y g e n p r e s s u r e ; 5$ N a C 0 . 2  3  42  diuranate according to the f o l l o w i n g equation:  U 0 3  8  + 3CaC0  3  + \o  z  —  3CaU0 + 3C0 4  2  t  R e a c t i o n w i t h i r o n t o form i n s o l u b l e f e r r a t e s o r w i t h s i l i c a to form i n s o l u b l e s i l i c a t e s i s a l s o p o s s i b l e .  9.  E f f e c t o f P r i o r Flotation of  Sulphides  Most o f the s u l p h i d e s were removed f r o m one by f l o t a t i o n .  A f l o t a t i o n c o n c e n t r a t e weighing  uranium a n a l y s i s o f 0.50$ U 3 0 8 accounted o r i g i n a l 1500  gm.  sample of o r e .  The  t h a t o f an u n t r e a t e d sample i n f i g . The  23.7  sample o f AS-1  ore  grams and h a v i n g  a  f o r 4.4$ o f t h e uranium i n t h e  e x t r a c t i o n curve i s compared w i t h  29.  s m a l l d i f f e r e n c e between t h e two  e x t r a c t i o n curves i s p r o b a b l y  w i t h i n the l i m i t s o f r e p r o d u c i b i l i t y . 10. One  E f f e c t o f Sodium Sulphate sample o f AS-1  ore was  Concentration  l e a c h e d w i t h t e n p e r c e n t sodium  s u l p h a t e added.to t h e normal l e a c h s o l u t i o n . curve i s shown i n f i g .  30.  The  resulting leaching  As i n the case o f the p i t c h b l e n d e specimens  (page 30) no d i f f e r e n c e i s noted.  U3  /oo  TIME - MINUTES  F i g u r e 29 The e f f e c t o f p r i o r f l o t a t i o n o f s u l p h i d e o n t h e l e a c h i n g o f AS-1 o r e . Conditions: 100°C; 30 p s i g . o x y g e n p r e s s u r e ; 5% N a C 0 3 . 2  I  f /OO  j 75  \  I  -  r  h ^  i 50  L>L-66 UL 76  1 t  )  i  _  No NaiSOf /Of. Na SO,  —o —X  25  0 O  30  6(  TlMr  •?  1  120 ivii MI/-rrc  J /50  F i g u r e 30 The e f f e c t o f s o d i u m s u l p h a t e Conditions: 100°C; 3 0 p s i g .  o n t h e l e a c h i n g o f AS-1 o r e . oxygen p r e s s u r e ; 5 % NagCOg.  44  Discussion of Results  Summary o f V a r i a b l e s In the s t u d i e s on t h e l e a c h i n g o f p i t c h b l e n d e  specimens, and  o r e s , the f o l l o w i n g f a c t o r s a r e shown t o i n c r e a s e t h e r a t e o f l e a c h i n g markedly: (1)  Increasing  temperature.  (2)  I n c r e a s i n g oxygen  (3)  The presence o f some c a r b o n a t e i n i t i a l l y ,  pressure. i n the l e a c h  solution. (4)  The presence o f some b i c a r b o n a t e  initially,  i n the leach  solution. (5) The  Increased  m i l l i n g time ( o f o r e s ) .  f o l l o w i n g f a c t o r s s t r o n g l y r e d u c e d the l e a c h i n g r a t e :  (1)  Excess hydroxyl  (2)  Roasting  The  i o n i n the l e a c h s o l u t i o n s .  of the o r e s .  f o l l o w i n g f a c t o r s had o n l y a s m a l l e f f e c t on t h e e x t r a c t i o n  rates: (1)  Increasing bicarbonate  concentrations  beyond one t o two  percent. (2)  Increasing  (3)  Oxidation  carbonate c o n c e n t r a t i o n s beyond two  o f s u l p h i d e s , presence o f NagSO^, r e c y c l i n g and  o t h e r chemical  f a c t o r s i n f l u e n c i n g the concentration o f  carbonate and b i c a r b o n a t e The  percent.  by chemical  reactions.  f o l l o w i n g two f a c t o r s were n o t s t u d i e d c o n c l u s i v e l y :  (1)  Agitation.  (2)  Electrical Potential.  45  Each o f the f a c t o r s l i s t e d above may i n f l u e n c e t h e l e a c h i n g r e a c t i o n i n one o f two ways: (a)  By l i m i t i n g t h e e x t e n t t o which o x i d a t i o n o r s o l u t i o n  of t h e uranium can o c c u r ( i . e . by a f f e c t i n g t h e e q u i l i b r i u m ) . (b)  By i n f l u e n c i n g t h e r a t e of the l e a c h i n g  reactions.  An examination o f t h e c h e m i s t r y i n v o l v e d i n t h e l e a c h i n g (pages 6, .7 and 8) r e v e a l s t h a t c e r t a i n minimum c o n c e n t r a t i o n s carbonate, and b i c a r b o n a t e , amount o f uranium.  process  o f oxygen,  a r e n e c e s s a r y t o o x i d i z e and d i s s o l v e a given  I n a d d i t i o n , p r e c i p i t a t i n g agents such as h y d r o x i d e  must be absent. I f these c o n d i t i o n s a r e met, t h e n the l e a c h i n g unidirectionally  ( i . e . w i t h o u t r e - p r e c i p i t a t i o n o f t h e uranium o r t h e  s e t t i n g up o f an e q u i l i b r i u m ) or concentration Studies derive  r e a c t i o n proceeds  and any changes i n temperature,  pressure,  o f reagents, i n f l u e n c e o n l y t h e k i n e t i c s o f t h e r e a c t i o n . on t h e k i n e t i c s o f t h e r e a c t i o n can thus be used t o  a mechanism' ftor t h e r e a c t i o n by comparing t h e measured r a t e s w i t h  t h o s e c a l c u l a t e d f r o m fundamental p r i n c i p l e s .  Numerical V a l u e s o f R e a c t i o n Rates The  average a b s o l u t e  r e a c t i o n r a t e s measured f r o m t h e  specimens at 100°C and 60 p . s . i . g . oxygen p r e s s u r e a r e g i v e n following t a b l e f o r three bicarbonate  16.  The f i r s t  concentrations.  16  column c o n s i s t s o f averages f r o m Appendix A.  pitchblende  i n the  46  Na C0 percent 2  NaHC0 percent  3  Ratg mgms/cm. /min.  3  Rate molecules/cm. /sec. 2  5  0  .031  1.11 x 1 0  1 5  5  1  .080  2.86 x 1 0  1 5  5  5  .132  4.72 x 1 0  1 5  Comparison o f t h e Absolute L e a c h i n g Rates o f D i f f e r e n t The  Ores  a b s o l u t e r e a c t i o n r a t e s f o r t h e e x t r a c t i o n o f uranium from  t h e o r e s , l e a c h e d w i t h f i v e percent sodium carbonate,  have been  estimated  on t h e b a s i s o f t h r e e assumptions: (a)  The uranium o c c u r s as p i t c h b l e n d e p a r t i c l e s o f about  t h e same grade as t h e p i t c h b l e n d e specimens. (b)  The average s i z e o f t h e p i t c h b l e n d e p a r t i c l e s i s about  400 mesh, o r 37 microns,  a f t e r 50$ o f t h e uranium has been  e x t r a c t e d from t h e o r e s . (c)  The p a r t i c l e s are assumed t o be c u b i c i n shape.  17 The measured r a t e s ,  and t h e e s t i m a t e d a b s o l u t e r e a c t i o n r a t e s  f o r t h r e e o r e s , on t h e b a s i s of these assumptions, a r e : Ore  17.  17  E s t i m a t e d Rate mgms/cm. /sec.  E s t i m a t e d Rate molecules/cm. /sec.  (at 30 p s i g )  ( a t 30 p s i g )  ( a t 60 p s i g )  AS-2  .646  G.B.L.(Hutch)  .717  1  B-C  .96  1 8  Measured r a t e  19  Measured Rate, percent p e r minute  2  .030 8  2  1.5 x 1 0  .033  1.7 x 1 0  .044  2.2 x  for AS-2 ore i s an average  takenVrom  10  1 5  1 5  1 5  Appendix B.  18. P e t e r s , E., »The Leaching o f Uranium from P i t c h b l e n d e Ores; Progress Report No.3*, Department o f M i n i n g and M e t a l l u r g y , U n i v e r s i t y o f B r i t i s h Columbia, 1951. 19. F i n a l e s t i m a t e d r a t e s are based on a p r e s s u r e o f 60 p . s . i . g . f o r b e t t e r comparison w i t h the p i t c h b l e n d e specimens. The square r o o t r e l a t i o n s h i p between t h e l e a c h i n g r a t e and t h e p r e s s u r e was a p p l i e d .  47  The a b s o l u t e r a t e s f o r t h e t h r e e o r e s a r e seen t o be v e r y similar.  I n a d d i t i o n t h e y compare v e r y c l o s e l y w i t h the a b s o l u t e r a t e s  measured f o r t h e p i t c h b l e n d e specimens.  The i n d i c a t i o n i s thus v e r y s t r o n g  t h a t t h e s e p i t c h b l e n d e o r e s have s i m i l a r l e a c h i n g c h a r a c t e r i s t i c s .  Magnitude o f E r r o r s i n R e a c t i o n Rate The  Estimates  assumptions made i n t h e above a b s o l u t e r e a c t i o n r a t e s a r e  j u s t i f i a b l e o n l y i n t h e absence o f b e t t e r methods f o r e s t i m a t i n g s u r f a c e areas. 1.  The f o l l o w i n g e r r o r s are;.involved: The measured s u r f a c e area o f t h e p i t c h b l e n d e specimens i s based  on t h e i r macroscopic  measurements.  Chemical methods o f measuring a b s o l u t e  s u r f a c e areas o f p o l i s h e d s u r f a c e s i n d i c a t e t h a t t h e t r u e s u r f a c e a r e a may be  s e v e r a l times as l a r g e as t h e measured a r e a i n s u c h 2.  cases.  The assumption t h a t t h e p i t c h b l e n d e p a r t i c l e s i n the o r e are o f  t h e same grade a n d d e n s i t y a s the p i t c h b l e n d e specimens was made i n t h e absence o f any evidence on t h i s p o i n t . a f f e c t t h e e s t i m a t e d r a t e s by more t h a n 3.  The e r r o r i n v o l v e d would not 50$.  The assumption t h a t t h e average s i z e o f t h e p i t c h b l e n d e p a r t i c l e s  i s 400 mesh a f t e r 50$ uranium e x t r a c t i o n i s an e s t i m a t e based on t h e s c r e e n a n a l y s e s which show most o f t h e o r e to be -325 mesh. most o f the v e r y f i n e p a r t i c l e s w i l l have  At 50$ e x t r a c t i o n  disappeared.  An e r r o r n o t g r e a t e r than a f a c t o r o f two may be i n v o l v e d i n t h i s estimate. analyses 4.  T h i s e r r o r would be d i f f e r e n t f o r each ore, s i n c e t h e s c r e e n vary. The assumption t h a t t h e s u r f a c e area o f s m a l l p a r t i c l e s i s e q u a l  t o t h e s u r f a c e a r e a o f cubes o f t h e same mesh s i z e ,  i s i n error.  48  Gaudin  20  r e p o r t s t h a t i r r e g u l a r f i n e p a r t i c l e s may  (measured by a b s o l u t e c h e m i c a l methods) from 1.3 cubes o f t h e same s c r e e n  have a s u r f a c e a r e a  to 2.0  times t h a t of  size.  In g e n e r a l , t h e i n d i c a t e d a b s o l u t e r e a c t i o n r a t e s are  probably  c o r r e c t t o w i t h i n a f a c t o r of f i v e , and t h e r e l a t i v e r a t e s p r o b a b l y w i t h i n a f a c t o r of  two.  The  accuracy i s c o n s i d e r e d adequate f o r purposes o f comparison  o f the r a t e s w i t h each o t h e r and w i t h c a l c u l a t e d r a t e s .  A c t i v a t i o n Energies Temperature s t u d i e s on the p i t c h b l e n d e specimens and t h r e e o r e s produced a wide range of e x p e r i m e n t a l  activation energies.  The  activation  energy t e r m o f the r a t e e q u a t i o n i s t h e r e f o r e s u b j e c t t o a wide magnitude of e r r o r .  The f o l l o w i n g i s a summary of the n u m e r i c a l v a l u e s o f t h e  a c t i v a t i o n e n e r g i e s and the a c t i v a t i o n energy terms: (l)  P i t c h b l e n d e Specimens Na?C0.^ percent  NaHC0 percent 3  A c t i v a t i o n Energy A c t i v a t i o n Energy ( c a l o r i e s per gm.mole) Rate Term a t 100°C  £- E/RT  (2)  5  0  11,400  2.1  x lO"  7  5  1  9,150  4.3  x lO"  6  5  5  12,300  6.3  x  10-  8  B-C  14,600  2.8  x  10-9  G.B.L. (Hutch)  16,000  4.4  x  loAQ  Ores Ores  AS-2  20. 1939.  Gaudin, A.M.,  9,700  .  2.1 x l O "  ''Principles o f M i n e r a l D r e s s i n g ' , 1 s t ed.  6  McGraw-Hill,  49  I t can be seen from t h e above t a b l e t h a t t h e l e a c h i n g r a t e s a r e v e r y s e n s i t i v e t o changes i n the a c t i v a t i o n energy.  Since the l e a c h i n g  r a t e s f o r a l l the o r e s and t h e p i t c h b l e n d e specimens s t u d i e d agreed so c l o s e l y , i t i s c o n s i d e r e d v e r y u n l i k e l y t h a t t h e a c t i v a t i o n e n e r g i e s do, i n f a c t , v a r y over such a wide range o f v a l u e s .  I t i s more l i k e l y t h a t  some o f t h e a c t i v a t i o n energy v a l u e s determined  are i n c o n s i d e r a b l e e r r o r .  (An a c t i v a t i o n energy, based on two r a t e measurements 30°C a p a r t , and each  4000 c a l o r i e s i n  s u b j e c t t o 10% e r r o r , w i l l r e s u l t i n a p o s s i b l e e r r o r o f the r e s u l t i n g a c t i v a t i o n  energy.)  The v a l u e o f 12,300 c a l o r i e s p e r mole i s c o n s i d e r e d the most a c c u r a t e l y determined  o f a l l t h e v a l u e s , f o r reasons a l r e a d y g i v e n .  It  a l s o agrees w i t h t h e weighted average o f a l l t h e v a l u e s g i v e n i n t h e t a b l e . I t has t h e r e f o r e been chosen as t h e b a s i s o f subsequent  calculations.  R e a c t i o n Mechanisms  21 According to E y r i n g ,  a r e a c t i o n a t a s u r f a c e may be s e p a r a t e d  i n t o f i v e s t e p s , t h e slowest o f which w i l l d e t e r m i n e t h e o v e r a l l r a t e . The  steps a r e : (a)  Transport of reactants to the surface.  (b)  A d s o r p t i o n o f the r e a c t a n t s on the s u r f a c e .  (c)  R e a c t i o n on t h e surface..  (d)  D e s o r p t i o n o f t h e r e a c t i o n p r o d u c t s from the s u r f a c e .  (e)  T r a n s p o r t o f t h e products away f r o m t h e s u r f a c e .  In t h e a l k a l i n e - carbonate  leach of pitchblende, the o v e r a l l  21. G l a s s t o n e , S., L a i d l e r , K., and E y r i n g , H., 'The Theory o f Rate P r o c e s s e s * , McGraw-Hill, New York and London, 1941.  50  l e a c h r e a c t i o n has been given as  30g + \q  + 3 C 0 ~ + 6HCO3- -* 3U0 (C0 3 )3  u  z  3  +  2  3H 0 2  In t h e l i g h t o f t h e above s t e p s , t h i s r e a c t i o n can be w r i t t e n i n the f o l l o w i n g  steps:  1.  \p  (gas) -*• ^fcO ( s o l u t i o n )  2.  V g2 ( s o l u t i o n ) -»• ^ 0  3.  U3O*  4.  U0  5.  U0 (0H)  z  ( s o l u t i o n of oxygen)  z  2  + %>0  2  3U0  2  2  2  2  (near surface)  ( d i f f u s i o n through s o l u t i o n ) (adsorption - r e a c t i o n )  3  + H 0 -* U 0 ( 0 H )  3  2  (hydration - desorption)  2  + CO3— + 2HCO3- — U 0 ( C 0 ) - 2  3  + 2H 0  3  (complexing  2  o f uranium as a homogeneous r e a c t i o n i n s o l u t i o n U0 (C03)3  6.  2  The  (near s u r f a c e )  slowest step  U0 (C0 ) 2  3  (diffusion)  3  i n t h i s s e r i e s w i l l determine t h e r a t e o f t h e  overall reaction.  Influence  of A g i t a t i o n  In t h e above s e r i e s , steps 1, 2, and 6 a r e i n f l u e n c e d by a g i t a t i o n i n the f o l l o w i n g way: 1. interface.  Increased a g i t a t i o n i n c r e a s e s  Step 1, which i s a heterogeneous r e a c t i o n a t t h i s i n t e r f a c e ,  would i n c r e a s e 2.  the t o t a l a r e a o f the g a s - l i q u i d  i n r a t e p r o p o r t i o n a l l y w i t h the i n t e r f a c e  The t o t a l d i s t a n c e  necessary f o r reactants  d i f f u s e would decrease w i t h i n c r e a s e d  agitation.  d i f f u s i o n , r e p r e s e n t e d by t h e c o n c e n t r a t i o n greater, with a r e s u l t i n g increase  area.  and p r o d u c t s t o  The d r i v i n g f o r c e f o r  g r a d i e n t , would be  correspondingly  i n the r a t e .  Although one t e s t was performed on t h e e f f e c t o f a g i t a t i o n (page 30) t h e f o l l o w i n g f e a t u r e s  i n d i c a t e t h a t none o f t h e s t e p s a f f e c t e d by  51  a g i t a t i o n represents described i n t h i s 1.  the c o n t r o l l i n g mechanism under t h e c o n d i t i o n s  research:  A s i n g l e t e s t with a g i t a t i o n present o n l y t e n percent  of the  time showed a r e a c t i o n r a t e n e a r l y h a l f as f a s t as t e s t s i n which f u l l time a g i t a t i o n was employed. 2.  D i f f u s i o n and s o l u t i o n mechanisms have much lower a c t i v a t i o n 22  e n e r g i e s t h a n any o f those observed. d i f f u s i o n mechanisms  Eyring  i n d i c a t e s t h a t aqueous  have a c t i v a t i o n e n e r g i e s no greater, t h a n 5,000  c a l o r i e s p e r mole. In c o n c l u s i o n , the evidence  i n d i c a t e s t h a t none o f steps  1,  2, and 6 a r e t h e c o n t r o l l i n g mechanism under t h e c o n d i t i o n s d e s c r i b e d in this  research.  Determination  o f t h e C o n t r o l l i n g Step  Of t h e t h r e e remaining  steps, the f i f t h  can a l s o be e l i m i n a t e d  as .the r a t e c o n t r o l l i n g s t e p , due t o i t s homogeneous n a t u r e . evidence  Conclusive  o f a heterogeneous c o n t r o l l i n g step i s g i v e n by the p r o p o r t i o -  n a l i t y o f the r e a c t i o n r a t e to s u r f a c e a r e a .  The remaining  two  steps  are: 1.  The a d s o r p t i o n , o r o x i d a t i o n s t e p , expressed u  2.  "^0 -*3U0  +  2  U 0 3  8  + H 0-> U 0 ( 0 H )  Glasstone,  2  2  equation:  (Mechanism I)  3  The h y d r a t i o n , o r d e s o r p t i o n s t e p , expressed .  22.  30g  by the  2  S., e t a l , i b i d .  by t h e e q u a t i o n :  (Mechanism II;)  52  Mechanism I S i n c e i n t h e o x i d a t i o n s t e p o n l y t e t r a v a l e n t uranium atoms a c t u a l l y take p a r t , the e q u a t i o n o f the s t e p can be U0 The  + ^0  2  —  2  U0  written  3  u n i t process i n v o l v e s the r e a c t i o n of d i s s o c i a t e d ( i . e .  atomic) oxygen as i n d i c a t e d by the p r o p o r t i o n a l i t y o f the r a t e t o the square r o o t of t h e oxygen The  pressure.  r a t e equation f o r t h i s step i s given  rate(molecules/cm. /sec.) = 3 C  C  2  Q  2  where C Q ^ i s the  experimental  U  2  h  concentration  Cyo^is the c o n c e n t r a t i o n  . KT  O  as  . f  0  2  . .  %>  concentration  R T  2  o f oxygen  of uranium atoms on the  surface  K  i s Boltzman's  T  i s the a b s o l u t e  h  i s Planck's  f*  i s t h e p a r t i t i o n f u n c t i o n o f the a c t i v a t e d complex  f  i s t h e p a r t i t i o n f u n c t i o n of oxygen  n  constant temperature  constant  f y o ^ i s the p a r t i t i o n f u n c t i o n o f s u r f a c e U0  The  - */ H  e  e  i s the base o f n a t u r a l  H*  i s the enthalphy o f a c t i v a t i o n  R  i s the gas  concentration  molecules  logarithms  constant  o f t e t r a v a l e n t uranium atoms i s e q u a l to  o f a l l uranium atoms on the s u r f a c e ,  i s capable o f r e a c t i n g .  2  The  the  s i n c e any uranium atom  f a c t o r o f t h r e e t a k e s i n t o account  the  f a c t t h a t t h r e e atoms are a c t u a l l y d i s s o l v e d f o r each atom o x i d i z e d .  53  The n u m e r i c a l v a l u e of t h e r e a c t i o n r a t e i s c a l c u l a t e d  from  t h i s e q u a t i o n , u s i n g an a c t i v a t i o n energy o f 12,300 c a l o r i e s per gram mole, i n Appendix D.  The  calculated theoretical reaction rate for  t h i s mechanism corresponds  to 4 x 1 0 ^  molecules/cm. /sec., a f a c t o r 2  o f e i g h t f a s t e r t h a n the measured r a t e on p i t c h b l e n d e specimens i n a f i v e percent  carbonate,  five  percent b i c a r b o n a t e l e a c h s o l u t i o n .  Mechanism I I The  d e s o r p t i o n s t e p has been e x p r e s s e d by t h e U0  + H0  3  —  2  U0 (0H) 2  equation  2  The r a t e e q u a t i o n f o r t h i s r e a c t i o n can be w r i t t e n as rate =  C ,C„ . KT . ft. U0 '°H 0- £± U0 *% 0 T t n  rt  3  " * H  e  /  R  T  2  h  f  3  2  where C J J Q ^ i s the c o n c e n t r a t i o n of h e x a v a l e n t  uranium atoms  on the s u r f a c e ^H 0  ^  2  fU"0  ^  s  c o n c e n t r a t i o n °f water  e  the p a r t i t i o n f u n c t i o n o f hexavalent  3  uranium % 0 2  ^  s  t  n  e  P  surface  molecules a r t ,  i t i o n f u n c t i o n o f l i q u i d water.  The o t h e r symbols have the same s i g n i f i c a n c e as i n t h e r a t e e q u a t i o n o f mechanism I . The  c o n c e n t r a t i o n s and p a r t i t i o n f u n c t i o n s a r e based on a  standard s t a t e o f 1 molecule  per cm.  o r per cm.  .  The t h e o r e t i c a l v a l u e f o r t h e r a t e o f t h i s mechanism a t and  100°C  an a c t i v a t i o n energy o f 12,300 c a l o r i e s per gram mole i s c a l c u l a t e d  54  i n Appendix E.  The c a l c u l a t e d r a t e i s e q u a l t o 1.2  per square c e n t i m e t e r per second.  x 10  This i s a factor of  than t h e measured r a t e on p i t c h b l e n d e specimens  molecules  3000  slower  i n a f i v e percent  carbonate, f i v e percent b i c a r b o n a t e l e a c h s o l u t i o n .  D i s c u s s i o n o f Mechanisms With an a c t i v a t i o n energy o f  12,300  c a l o r i e s per "'gram mole,  t h e r e i s a s t r o n g i n d i c a t i o n , from t h e c a l c u l a t i o n o f t h e o r e t i c a l r a t e s , t h a t t h e o x i d a t i o n s t e p (Mechanism I ) i s t h e c o n t r o l l i n g s t e p i n t h i s reaction.  No allowance has been made f o r the e f f e c t o f w i d e l y s c a t t e r e d  e x p e r i m e n t a l a c t i v a t i o n e n e r g i e s , such as t h o s e l i s t e d p r e v i o u s l y .  The  f o l l o w i n g t a b l e shows t h e c a l c u l a t e d r a t e f r o m b o t h mechanisms through a . range o f a c t i v a t i o n e n e r g i e s covered by t h o s e o b t a i n e d by A c t i v a t i o n Energy. ( c a l o r i e s p e r gram mole)  C a l c u l a t e d Rate Mechanism I (molecules/cm ./ sec.)  C a l c u l a t e d Rate Mechanism I I (molecules/cm?/ sec.)  3.3 x 1 0  1 8  9.3 x 1 0  1 3  10,000  8.7  x  10  1 7  2.6  x  10  1 3  11,000  2.2  x  10  17  6.7  x  10  1 2  12,000  5.9  x  10  1 6  1.8  x  10  1 2  13,000  1.5  x  10  1 6  4.7  x  10  1 1  14,000  4.0  x  10  1 6  1.2  x  10  1 1  15,000  1.0  x  10  15  3.1  x  10  1 0  16,000  2.8  x lO ^  9,000  1  8.3 x 10  experiment. Measured Rate,., (molecules/cm./sec.  1.11  x  10  15  10  1 5  to  4.72  x  9  The above t a b l e shows t h a t t h e r e i s b e t t e r agreement w i t h mechanism I f o r a l l a c t i v a t i o n e n e r g i e s above  10,000  c a l o r i e s per gram  55  mole.  Good agreement between mechanism I I and t h e measured r e a c t i o n  r a t e would be o b t a i n e d i f the a c t i v a t i o n energy were about 7,000 c a l o r i e s p e r gram mole. 23 Andersen  found t h a t a d e s o r p t i o n  mechanism such a s  mechanism I was the c o n t r o l l i n g s t e p i n the aqueous o x i d a t i o n i n galena.  of lead  He found an e x p e r i m e n t a l a c t i v a t i o n energy o f 6,820  c a l o r i e s p e r gram mole i n t h i s case.  In t h e l e a c h i n g o f  pitchblende,  an a c t i v a t i o n energy o f t h e same o r d e r o f magnitude would be expected f o r a s i m i l a r c o n t r o l l i n g mechanism. 2.L.  In c o n t r a s t t o both t h e s e mechanisms, Stenhouse  found an  a c t i v a t i o n e n e r g y o f 1,840 c a l o r i e s p e r gram mole i n t h e o x i d a t i o n o f iron i n pyrite.  He proposed a c o n t r o l l i n g mechanism i n v o l v i n g t h e  d i f f u s i o n o f oxygen through a l a y e r o f i r o n o x i d e - an i n s o l u b l e product o f the r e a c t i o n . impurities  In t h e o x i d a t i o n o f p i t c h b l e n d e ,  such as l e a d and s i l i c a  insoluble  c o u l d b u i l d up on t h e r e a c t i n g  s u r f a c e , t o t h e p o i n t where a s i m i l a r mechanism c o u l d No e v i d e n c e o f t h i s t y p e o f e f f e c t was Approximations i n T h e o r e t i c a l Rate  play a r o l e .  noticed. Calculations  In a d d i t i o n t o t h e p o s s i b l e e r r o r i n v o l v e d  i n the a c t i v a t i o n  energy, c e r t a i n o t h e r approximations were made i n c a l c u l a t i n g t h e theoretical reaction  rates:  23.  Andersen, J . E . , op. c i t .  24.  Stenhouse, J . F . , op. c i t .  56  (a)  The p a r t i t i o n f u n c t i o n s o f s o l i d r e a c t a n t s were  equal to u n i t y .  They c o u l d be c a l c u l a t e d f r o m t h e E i n s t e i n model f o r  s p e c i f i c heat o f s o l i d s , were known.  considered  i f the s p e c i f i c heat e q u a t i o n  f o r the s o l i d  I n no case i s the p a r t i t i o n f u n c t i o n o f a s o l i d  reactant  a t the normal b o i l i n g p o i n t l i k e l y t o be g r e a t e r t h a n t e n . (b) considered  The p a r t i t i o n f u n c t i o n o f t h e a c t i v a t e d complex was equal to u n i t y .  I t i s l i k e l y t o be o f t h e same o r d e r as  the s o l i d r e a c t a n t , and would t h e r e f o r e c a n c e l most o f t h e e r r o r i n v o l v e d i n (a). (c)  The r a t e equation  o f t h e l e a c h reagents,  does not take i n t o account t h e p a r t i c i p a t i o n  which a r e known t o have an e f f e c t on t h e l e a c h i n g  rate.  E f f e c t o f Leach Reagents In t h e steps o u t l i n e d f o r the o x i d a t i o n - l e a c h i n g of uranium from p i t c h b l e n d e , completely  only step f i v e involves the reagents.  I f step f o u r i s  u n i d i r e c t i o n a l , as i t i s b e l i e v e d t o be, changes i n the  concentrations  o f t h e reagents would have no e f f e c t on t h e r a t e .  I f the i n d i c a t e d steps a r e c o r r e c t , t h e r e a g e n t s must have xome i n f l u e n c e on a s t e p p r i o r t o the u n i d i r e c t i o n a l s t e p f o u r .  This  i n f l u e n c e may not n e c e s s a r i l y be caused by d i r e c t p a r t i c i p a t i o n o f t h e reagents. Thermodynamically, t h e most s t a b l e s u r f a c e any uranium can present t o atmospheric oxygen i s a U3O8 s u r f a c e . reagents c o n t r i b u t e t o t h e s t a b i l i t y o f t h e U0 the l e a c h s o l u t i o n .  t?  3  oxide  Possibly the  surface i n contact  with  57  Change i n C o n t r o l l i n g Mechanism The h e r e i n may  c o n t r o l l i n g mechanism i n a r e a c t i o n such as  change from one  s t e p t o another by t h e  described  a l t e r i n g of  the  25 p h y s i c a l or c h e m i c a l c o n d i t i o n s  o f the  experiment.  Stenhouse  and  26 Andersen the  both found t h a t the  caustic concentration  was  rate of oxidation increased  dropped r a p i d l y when  beyond a c e r t a i n maximum.  26 Andersen r a t e was  showed t h a t at the h i g h e r c a u s t i c  h i g h l y dependent on a g i t a t i o n , w h i l e a t the  concentration, the  a g i t a t i o n p l a y e d no  r o l e at a l l .  He  oxygen.  the  reaction  lower c a u s t i c pointed  reduced oxygen s o l u b i l i t y i n h i g h e r c o n c e n t r a t i o n s o f  r e s u l t e d i n a c o n t r o l l i n g s t e p i n v o l v i n g the 25  not  concentration  out  caustic,  solution or d i f f u s i o n of  Stenhouse ' suggested t h e same p o s s i b i l i t y , though he  study the  did  agitation variable.  These aqueous o x i d a t i o n r e a c t i o n s c o u l d c o n c l u s i v e l y by a d j u s t i n g t h e c o n d i t i o n s c o n t r o l l i n g mechanisms are  be  studied  so t h a t the d i f f e r e n t  dealt with separately.  The  the t y p e of mechanism i n v o l v e d . t h i s out  25.  Stenhouse, J.F.,  26.  Andersen, J.E.,  However, not enough work has  conclusively.  ibid. op. c i t .  possible  order of  magnitude" of the a c t i v a t i o n energy i s sometimes s u f f i c i e n t to  done to p o i n t  that  indicate been  58  Conclusions  1.  Theoretical considerations indicate that the  controlling  mechanism i n the a l k a l i n e carbonate l e a c h i n g of uranium from p i t c h blende ores under t h e c o n d i t i o n s d e s c r i b e d h e r e i n i s the step.  oxidation  Most o f the e f f e c t s on the r a t e o f l e a c h i n g noted i n t h i s  study are e x p l a i n e d by t h i s mechanism. 2.  At an a c t i v a t i o n e n e r g y of 12,000 c a l o r i e s per gram mole  ( a p p r o x i m a t e l y the v a l u e observed i n t h i s s t u d y ) , the l e a c h i n g r a t e can be doubled by r a i s i n g t h e temperature 1 5 ° C must be n e a r l y d o u b l e d t o achieve 3.  The  4. become the  m i l l i n g time  a s i m i l a r increase i n leaching rate.  optimum reagent c o n c e n t r a t i o n s  sodium c a r b o n a t e and f i v e percent  The  sodium  are about f i v e  percent  bicarbonate.  Under c o n d i t i o n s of v e r y poor a g i t a t i o n , d i f f u s i o n c o n t r o l l i n g mechanism, w i t h  a correspondingly  may  lower  a c t i v a t i o n energy. 5.  The  l e a c h i n g r a t e v a r i e s i n p r o p o r t i o n t o t h e square r o o t  o f the oxygen p a r t i a l 6.  pressure.  There i s no apparent d i f f e r e n c e i n l e a c h i n g b e h a v i o r  low grade p i t c h b l e n d e o r e s , the  h i g h grade c o n c e n t r a t e ,  blende specimens t h a t were examined i n t h i s  research.  of  the  or the p i t c h -  59  Appendix A E x p e r i m e n t a l L e a c h i n g Rates from P i t c h b l e n d e Specimens  Run  Variable Reagents under NaHC0 Na C0 study Percent Percent 3  Temp.  Nil  2  5  3  Conditions Temp, P r e s s . °C. psig.  Remarks  Standard  75  11  11  i»  P-8  11  11  11  P-9  11  it  11  100 110 121 90 100  1  5  100  60  1 1  5  85 115 100 100 100  50 70  5  5 5 5 Nil  60 60 60  5  1  100  60  P-5  P-6 P-7  11  11  11  60 68 52  60  Rate mgms/cm. per minute 2  Reprodu-  .0294 .0392  .0666 .0194 .0385  cibility P-10  Temp.) NaHC0 )  —  .0685  3  P-L2 P-13 P-14 P-15  P-16  11 11  NaHC0  3  i•  Na C0 2  3 5  3  Drove o f f C0 Drove o f f C0 less severely  .048 .125 .102 .107 .083  2  P-17  11  .064  2  P-18  11  P-19  None  1  P-20 P-21 P-22 P-23 P-24 P-25  Area Temp.  1  P-26 P-27 P-28  P-29  I  11 11  11  t ?  Pressure 11  t» 11  5  5 5  5 5 5  3 5 5 5  5 5  5 5  5  5  5 5  5 5  5  5  100 100  60 60  100 100 84 70 115 100  60  100 100 100 100  60 52 50 70 60 60 30 10 100  -  .122  -  .0622 .165 .056 .031  Reproducibility Standard  -  Reproducibility Standard  —  .067  .235 .120  .116 .0862 .0282 .144  60  Appendix A (cont)  Run  Rea eents Variable NaHC0 Na C0 under Percent Percent study3  2  3  Conditions Press. Temp °C. psig.  Remarks  Rate £ mgms/cm. per min.  P-30  Pressure  5  5  100  60  Reproducibility  .103  P-31 P-32 P-33 P-34 P-35 P-36 P-37  NaHC0  3  3 1  10$ Na S0,  .101  3  100 100 100 100 100 100 100  60 60  Na C0  5 5 3  «t 2  11  Na S0 2  4  Agitation  5 5 5 5 5  1 1 1 1  60  60 60 60  60  2  Agitation on 10$ o f time  .074 .094 .093 f  .090 .090 .037  61  Appendix B E x p e r i m e n t a l L e a c h i n g Rates f r o m A-S Ores  Run  UL-35  Ore  AS-2  Na C0 Percent 2  5  3  Percent Solids  25  C y c l e Temp. Press °C. p s i g .  1  100  30  Remarks  Rate Percent per min.  Roasted 2 0.067 hrs.800°C. 1$ NaHC0 added. M i l l e d 90 min. 1.18 1:1 P u l p 1.01 Density M i l l e d 75 1.27 min. M i l l e d 60 0.74 min. M i l l e d 45 0.55 min. M i l l e d 30 . 0.33 min. M i l l e d 60 0.67 min. Recycle 0.59 Recycle 0.845 Recycle 0.67 S t d . Run 0.50 Prior flo0.76 tation of Pyrite ' (Effect of) 0.46 (Na C0 ) 0.41 3  UL-46  UL-48  5 5  25 50  1 1  100 100  30 30  UL-50  5  25  1  100  30  5  25  1  100  30  UL-52  5  25  1  100  30  UL-53  5  25  1  100  30  UL-51  AS-1  '  1  UL-56  AS-2  5  25  1  100  30  UL-59  AS-1  UL-62  11  UL-63 UL-66  11  5 5 5  33 1/3 33 1/3 33 1/3 33 1/3 33 1/3  2 3  100 100 100 100 100  30 30 30 30 30  100 100 100 100 100 101  30 30 •' 30  81 61 115 100  22 18  11  UL-70  11  UL-72  1?  UL-73 UL-74  Tt t t  11 UL-75 » f UL-76 Ul-109 AS-2 UL-110 UL-111 UL-112 UL-113 UL-114 UL-115 UL-116 UL-117  11 • t 11 11 11 ? t 1 • 11  5 5  4 3  4  1 1  2 1 5 5  33 1/3 33 1/3 33 1/3 33 1/3 33 1/3 33 1/3  5  33 1/3  33 1/3  1 1  33 1/3 33 1/3 33 1/3 33 1/3 33 1/3 33 1/3  1 1 1 1 1 1  5 5  5 5  5 5 5  1  1 1 1 1 1  71 100 100 100  30 30 30  2  3  11  2  r t 11  11  30 20  1 t  60  0.26  10$ N a S 0 No.2 Autoclave  40  l\  0.37  11  1 t 1t 1 t 1 t  if  0.55  0.645  0.288  0.149 1.07 0.698  0.217  0.448 . 0.326 0.760  62  Appendix C Sample C a l c u l a t i o n s (a)  C o n v e r s i o n o f o r i g i n a l d a t a to a b s o l u t e u n i t s i n t h e e x t r a c t i o n  o f uranium from p i t c h b l e n d e  P-25  • Specimen weight  specimens:  = 14.6- grams.  Wt. l o s s = 0.2838 gmsf^  -v 2 S u r f a c e Area = 14.5 fimV '.  Sample  Time  D  Grams U 3 0g per l i t r e  B  -  1 2 3 4; 5 6' 7 8  9  20 40 60  0 min.  ..009 .019 .029 .0:39  .009  100 ' 120 140 160  .064 .077 .090 .101  .049  Standard;, Standard  .058  .059 • ..069 1079 .087 =  A  .-  .130  0  .026 . .053 f. .079  .028 .037  .053  80  >  .019  r  .114 .143 .172'; .201 .224 • .140  Grams U 3 0g Total  Milligrams per cm. 2  0 .033 .066 .099 ' .143 .179 .215  14.8  .280  17.3 • 19.3  w  0 2.3 4.4 6.8  9.9 12.3  • .350  O p t i c a l D e n s i t y f r o m Beckman  Spectrophotometer.  A  B  -  (a) -  (b)  D  c o r r e c t e d f o r volume change due t o sampling,  Note m a t e r i a l . b a l a n c e check i n t h i s r u n .  C o n v e r s i o n o f o r i g i n a l d a t a to p e r c e n t  U 0g 3  extracted i n the  l e a c h i n g o f A-S ores i n A u t o c l a v e number 2.  UL-117.:  Residue A n a l y s e s =  .031$ U 0g. 3  Final-extraction =  92.2$.  63  Appendix C. (Contd.)  Sample  1 2 3 4 5 6 7 8 9 10  B  Time  0 5 10 20 30 45  Diff.  E  D  13.5  27.1 26.35  13.4  .106  13.45  26.95  13.8 14.1 14.35 14.7  .137 .159 .188  12.65 12.9 12.8 12.75 12.8 12.85 12.7 13.9  .373  90 120 150  c"  M.0.°  .113 .147 .175 .211 .244 .287 .324  60  1  Phenol.  .430 .483  14.75  27.25 27.5 27.95 28.4 29.15 31.9 34.25  Percent U 0 g Extracted 3  30.2 39.0 45.3 53.5 61.0 69.8 77.2 84.3 88.9 92.2  .214 .245 .271 .296 .312 .324  15.05 15.85 17.3 18.7  A  -  Optical Density  from Beckman Spectrophotometer.  B  -  Phenolphthalein  end  w i t h 0.1 C  -  -  N.  f o r 3 ml.  sample t i t r a t e d  HC1.  M e t h y l Orange end 0.1  D  N.  p o i n t i n mis.  p o i n t f o r a 3 ml.  sample t i t r a t e d  with  HC1.  D i f f e r e n c e between p h e n o l p h t h a l e i n  and m e t h y l orange.end  l e s s h a l f the t o t a l c a l c u l a t e d t i t r a t i o n f o r the up as t h e uranium complex i o n U 0 ( C 0 ) 2  be a c o n s t a n t  i n the  3  3  .  points,  carbonate t i e d  T h i s column would  absence o f d i s t i l l a t i o n w i t h i n the  auto-  clave . E  -  O p t i c a l Density from  readings  corrected f o r d i s t i l l a t i o n calculated  D.  P e r c e n t e x t r a c t i o n i s based on the r e l a t i o n between r e s i d u e a n a l y s i s and the  o p t i c a l d e n s i t y o f the f i n a l  sample.  the  64  Appendix D C a l c u l a t i o n o f Rate f r o m Mechanism I  From t h e r e a c t i o n U0  + j£0  U0  3  2  2  3  the r a t e e q u a t i o n can be w r i t t e n as  ' Ik rate(molecules/cmf/sec.) = 3 . C Q . C ^ Q 2  2  2  . KT . h  f*  Hf  .e  -H*/RT 1  f  where t h e symbols have t h e same s i g n i f i c a n c e as on pages 52 and 53. At e q u i l i b r i u m , t h e c o n c e n t r a t i o n related to the concentration C  0 2  CQ  (Uq)  o f oxygen i n s o l u t i o n i s ,  i n t h e gas phase by the f o l l o w i n g  = fQ (liq) . e -  equation:  H l / R T  2  (gas)  f  Q  (gas)  where f r e p r e s e n t s  II  the p a r t i t i o n f u n c t i o n o f t h e m a t e r i a l  d e s i g n a t e d b y t h e s u b s c r i p t , and  represents  the enthalphy o f  s o l u t i o n o f oxygen. We can now s u b s t i t u t e f o r C Q  i n I, obtaining  2  the f o l l o w i n g  equation: rate =  3  C  *  C  • ^  -  •  I f t h i s i s t h e c o n t r o l l i n g mechanism, a c t i v a t i o n energy i s e q u a l t o (H]_  +  H*)-RT.  III  the experimental  S u b s t i t u t i o n , the r a t e  2~ becomes: rate -  3e-CQ  C  • )r-pHr J  -e  "  At 100°C (373°K) the f o l l o w i n g s u b s t i t u t i o n s may be made:  i»  Appendix D  U 0 3  8 ; (  65  (continued)  1.  e = 2.72  2.  ^U0 "  (base o f n a t u r a l l o g a r i t h m s ) . ^  2  t h e r e a r e 6.02  a  x 10  P  s  e  c  i  m  e  x 6.0 842  h a v i n g a d e n s i t y o f 6.0  n  x  2 3  .625  =  2.68  x 10  a t 62.5$  molecules  2 1  U 0 3  8  21 per c c , o r 8.05 no way  x 10  atoms uranium per c c .  t o d i f f e r e n t i a t e between t e t r a v a l e n t and h e x a v a l e n t uranium  atoms, a l l o f them must be The The  Since there i s probably  c o n s i d e r e d capable o f r e a c t i n g .  s e p a r a t i o n o f 100  p l a n e s i n the U 0 g l a t t i c e i s 2.7  s e p a r a t i o n o f 111 planes i s 3.12  e q u a l l y e a s i l y on t h e s e two  A°.  3  A°.  Assuming the c r y s t a l s e p a r a t e s  p l a n e s , the average  s e p a r a t i o n of planes  r e p r e s e n t e d by the s u r f a c e i s 2.91 A". The number o f p l a n e s per cm. 8 7 a t t h i s s e p a r a t i o n i s 10 = 3.44 x 10' planes per cm. The number o f 2.91 atoms uranium on 1 cm. atoms/cm. .. * .  3.  C  U  Q  2  =  2  ^Og^  3.44  o f s u r f a c e i s then 8.05  2.34  x  •'  2,  1  ne  ^  4.  =  2  KT h  =  c o n c e n  5.  f*  =  6.  f  7.  f  = 6.02  x 10  23 x  273  y  60  373  =  per cc  8.03  x  10  1 9  14.7  Q y  x  10 .  1.38  x  10"  16  x  373 = 7.76  x  10  12  (~1 )  x lO-X'f  sec  p a r t i t i o n f u n c t i o n o f the  s o l i d reactant ~  1 1  2  .  A  l O ^  p a r t i t i o n f u n c t i o n o f the a c t i v a t e d complex — =  U0  x  t r a t i o n o f oxygen i n m o l e c u l e s  8.96  6.62  2.34  14  22400 C Q  =  2  10 .  at 60 p s i g . and 100°C i s C A  .%  x 10^ x 10"*"  The p a r t i t i o n f u n c t i o n o f gaseous oxygen can  be  2  26  3/2 s p l i t up i n the f o l l o w i n g way:  fQ ( t r a n s l a t i o n ) = (2frmKT)  = 2.46  x  10  66  Appendix D ( c o n t i n u e d )  f f  (vibration)  n u  2 2  .*.  1  ( r o t a t i o n ) = 8 TT^IKT 2"  n  (J  —  f  8.  Q  e  =  (2.46 x 1 0  .  2 6  =  177  x 177)  =  2.085 x l O ^ . 1  T h i s i s the a c t i v a t i o n energy t e r m .  At an  a c t i v a t i o n energy o f 12,300 c a l o r i e s per gram mole, t h i s term i s e q u a l t o 6.3 x  10~ . 8  S u b s t i t u t i n g t h e s e v a l u e s i n t o e q u a t i o n IV, we get r a t e = 3 x 2.72  x 8.96 x 1 0  x a.34  9  x 10  x 7.76  1 4  x 10  x  1 2  x 2.085 x =  6.37  x 10  =  4 x 10  16  3  x 6.3 x  10"  molecules U0  Observed r a t e = 4.72  x 10^  Factor of difference  =8.5  2  10  6.: 10-*  1Lv  8  per cm.  2  per second.  molecules/cm. /sec. 2  The t h e o r e t i c a l r a t e i s somewhat f a s t e r than the observed r e a c t i o n r a t e , b u t t h e agreement i s r e a s o n a b l e , i n view o f the e s t i m a t e s involved i n the c a l c u l a t i o n s .  67  Appendix E C a l c u l a t i o n o f t h e Rate f r o m Mechanism I I  From t h e h y d r a t i o n e q u a t i o n : U0  + H 0 -* U 0 ( 0 H ) t h e  3  2  2  2  r a t e e q u a t i o n c a n be w r i t t e n a s : r a t e = C„ . C . KT . H o U0 — n  f*  T T n  2  —  3  n  1  H 0  , 1  2  U0  . e' 11*^ 7  I  3  where t h e symbols have the same s i g n i f i c a n c e as on pages 52 and 53. The f o l l o w i n g r e a c t i o n s w i l l have reached e q u i l i b r i u m i f t h i s i s the c o n t r o l l i n g mechanism: (1)  0  gas -» 0  (2)  U0  2  + \o  2  solution  2  -  z  U0  3  From t h e s e e q u i l i b r i a , the f o l l o w i n g e q u a t i o n s c a n be drawn: 0 (soln)  f =  (gfe)  (soln)  •  C  C U0  f  Q  2  (  g  - C ft " U0 ' °0 * (soln)  a  s  )  f  u  2  e  °  C  3  ^ -H]_/RT  2  n  3  =&  2  U0  0  2  2  e  *  6  -H /RT 2  m 1  1  1  soln  where H-^ i s t h e e n t h a l p y o f s o l u t i o n o f oxygen H  i s the enthalpy o f o x i d a t i o n of U0  2  2  i n solution.  S u b s t i t u t i n g t h e s e v a l u e s , the r a t e e q u a t i o n becomes: -(Hi+ H rate = C « . C . C ^ Q . KT . f* . e T h _ _ 0  J  8  U 0 2  2  + H*)/RT IV  0 - U0 - H 0 1  1  2  2  2  In terms o f t h e e x p e r i m e n t a l a c t i v a t i o n energy, t h i s e q u a t i o n becomes: 1/2 rate - e . C ^ . C ^ . C ^ .  -E/RT  A  f  0 ' U0 f  2  , f 2  H 0 2  •  6  V  Appendix E ( c o n t i n u e d )  68  Comparing t h i s e q u a t i o n w i t h mechanism I, we r a t e  (mech.II)  "  r a t e  find:  5fe2  (mech I)• i •  1  i  H 0  V  i  2  The f o l l o w i n g s u b s t i t u t i o n s may be made: • (l) W  r a  ^ ( m e c h I)  C  e  H 0  =  6.02  =  2  S  ^ x  x  m  10  °l  =  2 3  e c u  l  f  Q  H  =  2  3.34  x  10 . 2 2  ^  H p O where S t R s t a n d a r d s t a t e o f 1 molecule per cm. '"(3)  / c n i . / sec.  e s  M  R  i s the e n t r o p y o f water i n a  Q  2  S  H 2  '. *'  Q f  =  121.55 '  .« H 0 2  2 7  2 3  „ 121.55 £ ft  .  a t 100°C ( c a l c u l a t e d f r o m data) q  =  j  2 7 ,  v  '  x  i  n i  D  U  *  The c a l c u l a t e d r a t e i s t h e r e f o r e : r a t e = 4 x 10  16  x 3.34 x 10  3 x 3.7 x Observed Rate = 4.72  10 x  22  =  1.2 x 10  12  2 molecules/cm. / s e c .  2 6  10 . 1 5  3 Factor of d i f f e r e n c e  4 x 10 .  The t h e o r e t i c a l r a t e based on t h i s mechanism and an a c t i v a t i o n energy o f 12,300 c a l o r i e s per gram mole i s about 4,000 t i m e s too slow, compared w i t h the observed r e a c t i o n r a t e .  27. Hougen, O.A., and Watson, K.M., I I , W i l e y and Sons, New York, 1947.  Chemical Process P r i n c i p l e s , P a r t  28. K e l l e y , K.K., C o n t r i b u t i o n s to the Data on T h e o r e t i c a l M e t a l l u r g y , B u l l e t i n 476, U.S. Govt. P r i n t i n g O f f i c e , Washington, 1949.  69  Appendix F Screen Analyses o f AS-1 Ore  RUN NO.  UL-46  —  MILLING TIME •*+ SCREEN SIZE I  UL-50  UL-51  UL-52  UL-53  90  75  60  45  -  -  -  0.3$ .  -  2.0$  -  1.3$  32.5$  trace  0.4$  11.4$  17.-4$  0.5$  6.0$  18.9$  10.1$  30  -100 +150  "  -  -150 +200  "  trace  -200 +270  "  1.0$  6.1$  15.4$  13.8$  6.5$  -270 +325  "  0.1$  1.3$  5.3$  4.5$  2.7$  98.9$  92.1$  72.9$  50.1$  28.5$  + 48 mesh  -48 + 65  "  -65 +100 *•  -325 TOTALS  100 $  100 $  100 $  MILLING CONDITIONS : Rod Charge  =  60 l b s .  Ore Charge  =  1500 grams.  L i q u i d Charge  =  1 l i t r e water.  M i l l Speed  =  40 r.p.m.  100 $  100 $  70  Bibliography  Gaudin, A.M. ' P r i n c i p l e s o f M i n e r a l D r e s s i n g ' , 1st ed., M c G r a w - H i l l ,  1939. Gibbs, H.L., 'Recovery o f Values from C a r n o t i t e Ores', U.S. Patent 1,999,807, A p r i l 30, 1935, Chemical A b s t r a c t s 29, 3916, 1935. G l a s s t o n e , S., L a i d l e r , K., and E y r i n g , H., 'The Theory o f Rate P r o c e s s e s ' , McGraw-Hill, 1941. H a l p e r n , J . , 'The Chemistry o f t h e A l k a l i n e Carbonate Leach', GR-1 Memo. , Department o f M i n i n g and M e t a l l u r g y , U n i v e r s i t y o f B r i t i s h Columbia, 1951. H a l p e r n , J . , 'Uranium Ore Treatment Research P r o j e c t ; P r o g r e s s Reports No. 1 and 2, Department o f M i n i n g and M e t a l l u r g y , U n i v e r s i t y o f B r i t i s h Columbia, 1950-51. L i d d e l l , D.M., 'Handbook o f Non F e r r o u s M e t a l l u r g y ; M e t a l s ' , 2nd ed., McGraw-Hill, 1945.  Recovery o f the  M e l l o r , J.W., 'A Comprehensive T r e a t i s e on I n o r g a n i c and T h e o r e t i c a l Chemistry, V o l . X I I ' , Longmans, London, 1932. Moore, R.B., ' E x t r a c t i n g Vanadium, Uranium, and Radium f r o m Ores', U.S. P a t e n t s 1,165,692 and 1, 165,693, Chemical A b s t r a c t s , 10; 561, 1916. P a u l i n g , L., 'The Nature o f the Chemical Bond', C o r n e l l U n i v e r s i t y P r e s s , I t h a c a , New York, 1948. R a b b i t t s , F.T., Guest, R.J., Jordan, J.E., K o r n e l s e n , E.D., P r o u l a , E., La Chance, G.R., and R i c e , W.B., 'The D e t e r m i n a t i o n o f U 0 i n Ores and S o l u t i o n s ; C e l l u l o s e Column Method', Mines Branch, Department of Mines and T e c h n i c a l Surveys, Canada, Memo. 105. 3  8  Rodden, C.J., ' A n a l y t i c a l Chemistry o f t h e Manhattan P r o j e c t ' , N u c l e a r Energy S e r i e s , Manhattan P r o j e c t T e c h n i c a l S e c t i o n , D i v i s i o n V I I I V o l . 1, 1st ed., McGraw-Hill, 1951. Thews, K.B., and H e i n l e , F . J . , ' E x t r a c t i o n and Recovery o f Ra, V, and U from C a r n o t i t e ' , Ind.Eng.Chem. 15, 1159-61, November, 1923. W e l l s , A.F., ' S t r u c t u r a l I n o r g a n i c Chemistry', 2nd ed., Oxford U n i v e r s i t y P r e s s , London, 1950.  

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