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Studies on the depressive action of chromate and dichromate salts on galena Okada, Susumu 1970

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STUDIES ON THE DEPRESSIVE ACTION OF CHROMATE AND DlCHROMATE SALTS ON GALENA  by SUSUMU OKADA B.A.Sc. (Mining E n g i n e e r i n g ) Kyoto U n i v e r s i t y , Japan,  19 67  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE  i n the Department of Mineral Engineering  We accept t h i s t h e s i s as conforming required  t o the  standard.  THE UNIVERSITY OF BRITISH COLUMBIA January,  19 70  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the  requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference  and study.  I further  agree  t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s .  I t i s understood  that  copying o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l  gain  s h a l l not be allowed without my w r i t t e n  permission.  SUSUMU OKADA  Department o f M i n e r a l  Engineering  The U n i v e r s i t y o f B r i t i s h Vancouver 8, Canada  Columbia  ABSTRACT  In the c o u r s e o f the e x p e r i m e n t a l work c o n d u c t e d i t was found t h a t when g a l e n a was t r e a t e d w i t h chromate s a l t s o r d i c h r o m a t e s a l t s i n an aqueous s o l u t i o n , l e a d chromate i d e n t i f i e d by i n f r a r e d s p e c t r o s c o p y was t h e main s p e c i e s a d s o r b e d on the g a l e n a s u r f a c e . The f o r m a t i o n o f chromium h y d r o x i d e o r chromium o x i d e was not observed.  Thermodynamic c o n s i d e r a t i o n s o f the P b - C r - S - r ^ O b u l k  system i n d i c a t e the v e r y s t a b l e c h a r a c t e r o f l e a d chromate as shown i n t h e p o t e n t i a l - p H d i a g r a m c o n s t r u c t e d i n t h i s s t u d y .  It  i s a l s o seen t h a t no s t a b l e domain o f l e a d d i c h r o m a t e e x i s t s . The a d s o r p t i o n r a t e as w e l l as a d s o r p t i o n amount o f d i c h r o m a t e a t the p s e u d o - e q u i l i b r i u m c o n d i t i o n i n c r e a s e s w i t h the d e c r e a s e i n pH v a l u e .  T h i s phenomenon s u p p o r t s the f a c t e x p e r i e n c e d i n g a l e n a  f l o t a t i o n t h a t a d i c h r o m a t e s a l t i s a much more e f f i c i e n t d e p r e s s a n t than i s an e q u i v a l e n t chromate  salt.  The d e s o r p t i o n o f x a n t h a t e from g a l e n a s u r f a c e s c o v e r e d w i t h more than a monolayer t h i c k n e s s o f x a n t h a t e was found t o be p o s s i b l e by a d d i n g chromate s a l t t o the system, whereas chromate d e s o r p t i o n from g a l e n a s u r f a c e s due t o x a n t h a t e a d d i t i o n was not j  observed. I t was f o u n d t h a t under comparable c o n d i t i o n s x a n t h a t e a d s o r b e d on l e a d chromate s u r f a c e s o x i d i z e d t o dixan'thogen much more r e a d i l y t h a n x a n t h a t e a d s o r b e d on g a l e n a s u r f a c e s .  TABLE OF CONTENTS Page INTRODUCTION LITERATURE SURVEY  ,  -  1  . . . . . . .  5  EXPERIMENTAL  11  Materials  11  A n a l y t i c a l Equipment  12  E x p e r i m e n t a l Procedures  13  (1) A d s o r p t i o n and D e s o r p t i o n T e s t s  13  (2) B u f f e r A c t i o n T e s t s  14  (3) I d e n t i f i c a t i o n by I n f r a r e d Spectroscopy EXPERIMENTAL RESULTS  . .  14 16  A. E f f e c t o f pH on the C o n c e n t r a t i o n s o f Chromate and Dichromate Ions  16  B. Changes i n pH o f the S o l u t i o n s C o n t a i n i n g Galena  19  (1) Changes i n pH o f Aqueous S o l u t i o n s C o n t a i n i n g Galena . . . .  19  (2) Changes i n pH o f a Chromate C o n t a i n i n g Galena  23  Solution  C. A d s o r p t i o n Rates o f Chromate and Xanthate Ions by Galena  26  D. A d s o r p t i o n o f Chromate Ion and Xanthate Ion on Galena S u r f a c e  29  E. Enhanced A d s o r p t i o n o f Chromate Ion by Galena i n the Presence o f Oxygen  34  F. E f f e c t o f pH on Chromate A d s o r p t i o n on Galena  37  V  Page G.  H.  I.  Desorption of Xanthate from Galena Surface  Ion  Adsorption Chromate  I o n s by  of Xanthate  o r Chromate I o n . . . . . . . Lead  43  Thermodynamic C o n s i d e r a t i o n s o f the I n v o l v e d i n the System Pb-Cr-S-H 0  Reactions 44  2  J.  K.  I d e n t i f i c a t i o n o f R e a c t i o n P r o d u c t s on t h e Surface of Galena Treated with Potassium C h r o m a t e or,; P o t a s s i u m D i c h r o m a t e Identification X a n t h a t e on  DISCUSSIONS A.  C.  of Adsorption  Lead  Products  Changes i n pH  of  Chromate  53  c  o  t  of the t  c  b  o  57  Solutions c  e  <  •  C h e m i s o r p t i o n o f Chromate o r I o n s on G a l e n a S u r f a c e  Containing •  •  •  •  •  (1) C o m p e t i t i v e (2) A d s o r p t i o n Lead  REFERENCES APPENDIX  •  Products  Chromate  of Xanthate  . . . . . . . .  FUTURE WORK  . . . . . . . .  . . . . . . . . . . . . .  «  «  57  59 of 60  Adsorption  . . . . . . . . .  SUGGESTIONS FOR  •  Dichromate  I n f l u e n c e o f Chromate on t h e A d s o r p t i o n X a n t h a t e on G a l e n a S u r f a c e -  CONCLUSIONS  46  . . . . . . . . . .  G ci ~L 6 n 3,  B.  37  60 on 62 64 66 67 69  LIST OF TABLES Table I. II.  III. IV o V. VI. VII.  Page A d s o r p t i o n o f Chromate Ion and/or Xanthate Ion on Galena Surface  .33  A d s o r p t i o n o f Chromate Ion on Galena Surface i n the Presence o r Absence o f Oxygen  36  D e s o r p t i o n o f Chromate Ion from Galena S u r f a c e Due t o Xanthate A d s o r p t i o n  39  D e s o r p t i o n o f Xanthate Ion from Galena Surface Due t o Chromate A d s o r p t i o n (1) . . . .  40  D e s o r p t i o n o f Xanthate from Galena Surface Due t o Chromate A d s o r p t i o n (2) . . . .  42  A d s o r p t i o n o f Xanthate Ion on Prec i p i t a t e d Lead Chromate  45  R e a c t i o n s and E q u i l i b r i u m f o r the System Pb-Cr-S-H 0  49-50  LIST  OF  FIGURES  Figure  . 1  2  3  4  5  6  7  8  9 10  11  12  Page  A b s o r p t i o n S p e c t r a o f (a) Potassium Chromate S o l u t i o n (pH 11.5) a n d ( b ) P o t a s s i u m D i c h r o m a t e S o l u t i o n (pH 4.3)  18  S t a b i l i t y o f Chromate a s a F u n c t i o n o f pH  20  Ion and  Dichromate Ion  A b s o r p t i o n Spectra o f J^CrO^, K.Et.X., T h e i r M i x t u r e i n an Aqueous S o l u t i o n ( p H 9.8) Time Dependence Suspension  o f pH  o f r^O  with  24  T i m e D e p e n d e n c e o f pH Containing Unoxidized  of the Galena  Solution 25  T i t r a t i o n Curves (a) O x i d i z e d Galena, U n o x i d i z e d G a l e n a , and (c) Water Only  (b) 2 5a  T i m e D e p e n d e n c e o f pH o f 2.0 x 1 0 M / L P o t a s s i u m Chromate S o l u t i o n C o n t a i n i n g Galena .  27  -4 T i m e D e p e n d e n c e o f pH o f 2.0 x 10 M/L P o t a s s i u m Chromate S o l u t i o n C o n t a i n i n g Unoxidized Galena . .  28  Titration  30  _ i |  Curves  o f Chromate  A d s o r p t i o n Rates o f Chromate on G a l e n a a t 25°C Effect Galena  o f pH  on  Chromate  Solutions and  Xanthate 31  Adsorption  on 37a  Potential-pH Cr-H 0 .  Diagram f o r the  System 47  Potential-pH Diagram f o r the Pb-S-H 0 . . . . .  System  Potential-pH Pb-Cr-S-H 0  System  48  2  14  22  Galena  2  13  and  2  Diagram f o r the  51  viii  Figure 15  16  Page Infrared Spectra of (a) Synthetic PbS Treated with K^CrC^, (b) Synthetic PbS Treated with K C r 0 7 , (c) Galena Treated with K C r 0 7 , (d) PbCrOLi .  54  Infrared Spectra of (a) PbCrCv treated with K . E t . X . , (b) PbS treated with K C r 0 , then K . E t . X . , (c) P b ( E t X ) , (d) X „ , and (e) Cr 03  56  E f f e c t of the Concentration of Potassium Chromate on the Rest Potential of Galena Electrode  73  E f f e c t of pH on the Rest Potential of Galena Electrode i n 1.0 x 10-3 M / L K CrO Solution  74  E f f e c t of pH on the Rest Potential of Galena Electrode i n 1.0 x IO" M/L K C r 0 Solution  75  Anodic P o l a r i z a t i o n Curves for Galena Electrode  76  Cathodic P o l a r i z a t i o n Curves for Galena Electrode  77  2  2  2  2  2  2  7  2  2  A-l  A-2  A-3  3  2  A-4 A-5  2  7  ACKNOWLEDGEMENT  The author wishes t o express h i s s i n c e r e a p p r e c i a t i o n t o Dr. H. Majima f o r h i s guidance and encouragement g i v e n throughout the p e r i o d o f study.  Thanks a r e  a l s o extended t o the f a c u l t y , s t a f f and graduate students of the M i n e r a l E n g i n e e r i n g Department f o r many h e l p f u l discussions. F i n a n c i a l support from the Mines  Branch,  Department o f Energy, Mines and Resources, Ottawa i s a l s o appreciated.  INTRODUCTION In the f l o t a t i o n o f complex s u l f i d e ores c o n t a i n i n g g a l e n a , chromate o r dichromate as d e p r e s s a n t s . o f chromate  s a l t s a r e commonly used  The h i s t o r y o f s t u d i e s i n v o l v i n g the use  i n f l o t a t i o n c i r c u i t s date t o 1912, when  Lowry and Greenway [ 1 ] i n t r o d u c e d what would now be termed a "depressant" f o r the l e a d m i n e r a l by u s i n g one p e r cent sodium  dichromate. The  dezincing operation f o r lead concentrates i s  important as a method o f improving and  lead concentrate  quality  i n c r e a s i n g zinc e x t r a c t i o n i n t o zinc concentrate i n  z i n c l e a d ore f l o t a t i o n . C o n c e n t r a t o r , dichromate  F o r example, a t the S u l l i v a n s a l t had been used  f o r the  d e p r e s s i o n o f galena i n the s e l e c t i v e f l o t a t i o n  circuit.  A c c o r d i n g t o the example a t the S u l l i v a n C o n c e n t r a t o r , the l e a d c o n c e n t r a t e was c o n d i t i o n e d w i t h dichromate, l i m e , xanthate, f r o t h e r and copper depressed heated  5 8.1%  Galena was  under these c o n d i t i o n s when the m a t e r i a l was  t o 30-35°C,  results  sulphate.  [ 2 ] were:  One o f the examples o f o p e r a t i o n the grade o f i n i t i a l  lead  concentrate,  Pb, 9.19% Zn, 9.7 2% Fe, the grade o f z i n c  product  then w i t h  froth  29.3% Pb, 34% Zn, 9.7 2% Fe and those f o r f i n a l  lead concentrate  62.45% Pb, 5.55% Zn, and 9.72% Fe.  Even though t h i s type of reagent'? has almost p r a c t i c a l importance  i n m i l l i n g operations, i t i s s t i l l  lost  2  one  o f t h e most i n t e r e s t i n g  sulfide with  minerals.  the  salts on  summarized  galena  by  and  the  galena  result ( 2 ) The  chromate  main  previous researches  solution, i s lead  or  results are  ions  suggest  the h y d r o p h i l i c  the  o f an  oxide  chemical  The  c h r o m a t e a d s o r p t i o n on  The with  the  solution  above t h i s  t o pH pH  6 and  flotation.  ion  place i n a  differ-  surface i s  galena  increases  concentration of becomes a l m o s t  the  constant  value.  i n c r e a s e of the  proportional  mineral  Freundlich equation.  i n c r e a s e i n the up  a  chromate  of xanthate  the m i n e r a l  a d s o r p t i o n o f c h r o m a t e on an  as  at the  attachment of  apparently takes  area.  by  formed  film.  irregularly  ent  described  film  However, some  to m i n e r a l i s independent  a t t a c h m e n t , and  a  that depression occurs  chromate i s adsorbed and  a chromate o r  chromate.  of formation  surface,  ( 5 ) The  The  of  concerned  pyrite with  i s treated with  researchers  (H)  depression  as f o l l o w s :  dichromate  (3)  the  have been p r e s e n t e d .  ( 1 ) When g a l e n a  on  on  l a r g e number o f p a p e r s  depression of galena  dicromate obtained  A  topics  chromate a d s o r p t i o n c r e a t e s  decrease  i n the  yield  of galena  a by  ( 6 ) Dichromate  i s a much more e f f i c i e n t  f o r galena than chromate. also said that  depressant  On the c o n t r a r y i t i s  galena d e p r e s s i o n i s most  e f f e c t i v e at pH 5 - 6 and above 8 . ( 7 ) Galena d e p r e s s i o n occurs when a depressant  adsorp-  t i o n l a y e r , approximately e q u a l t o a monolayer, i s formed;  a t t h i s p o i n t a d s o r p t i o n of xanthate  remains  the same as without the d e p r e s s a n t .  ( 8 ) The p o t e n t i a l o f a galena e l e c t r o d e decreases when xanthate i s added and the a d d i t i o n of d i c h r o mate causes an i n c r e a s e i n p o t e n t i a l  proportional  t o the l o g a r i t h m o f i t s c o n c e n t r a t i o n .  A galena  e l e c t r o d e t r e a t e d w i t h c o n c e n t r a t e d dichromate s o l u t i o n shows no s i g n i f i c a n t p o t e n t i a l change by the a d d i t i o n of xanthate. As mentioned  above, i n the d e t a i l e d mechanisms o f  g a l e n a d e p r e s s i o n w i t h chromate or dichromate problems are y e t u n s o l v e d .  s a l t , some  F i r s t l y , i t seems t h a t t h e r e i s  a d i s c r e p a n c y i n the prq,posed r e a c t i o n product which galena depression.  causes  Secondly, P l a k s i n e t a l . [ 3 ] s t a t e d  t h a t the i n c r e a s e of the chromate a d s o r p t i o n c r e a t e d the p r o p o r t i o n a l decrease i n f l o t a t i o n y i e l d , and i t i s a l s o w e l l known t h a t dichromate than chromate.  i s much more e f f e c t i v e f o r galena  On the o t h e r hand Bagdanov and Podnek [ 4 ]  showed t h a t galena d e p r e s s i o n by chromate s a l t was e f f e c t i v e at pH 5 - 6 and above 8.  Furthermore,  most  i n the  system  4 o f g a l e n a , x a n t h a t e , and chromate, t h e b e h a v i o r s o f x a n t h a t e and chromate s p e c i e s on g a l e n a s u r f a c e a r e n o t fully  understood. C o n s i d e r i n g t h e s e p o i n t s , i n t h e p r e s e n t work  some e x p e r i m e n t a l s t u d i e s and a thermodynamic i n v e s t i g a t i o n were made i n o r d e r t o g e t a b e t t e r u n d e r s t a n d i n g o f t h e depression of galena.  F o r t h e s e purposes  an .  s p e c t r o m e t e r as w e l l as u l t r a v i o l e t s p e c t r o p h o t o m e t e r used t o i d e n t i f y t h e s u r f a c e p r o d u c t s on g a l e n a .  were  The  p r i n c i p a l e x p e r i m e n t s were t h e a d s o r p t i o n t e s t s o f chromate, d i c h r o m a t e , and/or x a n t h a t e i o n s on t h e g a l e n a s u r f a c e . B e s i d e s t h e s e e x p e r i m e n t a l s t u d i e s , thermodynamic s t u d i e s were made o f t h e p o s s i b i l i t y o f t h e f o r m a t i o n s o f l e a d chromate and chromium o x i d e . -pH  F o r t h i s purpose, a p o t e n t i a l  diagram was c o n s t r u c t e d f o r t h e system o f Pb-Cr-S-ri^O,  and t h e s t a b l e domains o f l e a d chromate and chromium o x i d e were p r e s e n t e d  graphically.  i  LITERATURE SURVEY  ,f  As mentioned b e f o r e , the h i s t o r y o f s t u d i e s i n v o l v i n g the use o f chromate o r dichromate  salt i n  f l o t a t i o n c i r c u i t s date t o 1912, when Lowry and Greenway [1] i n t r o d u c e d what would now be termed "depressant" f o r the l e a d m i n e r a l s by u s i n g one p e r cent sodium  dichromate.  Gaudin and h i s co-workers [ 5 ] s t u d i e d the system, i n which galena was depressed w i t h potassium i n the presence  o f iso-amyl xanthate.  They a l s o s t u d i e d  the s e p a r a t i o n o f galena from s p h a l e r i t e . experiment  was performed  dichromate  The f l o t a t i o n  w i t h the s y n t h e t i c mixture o f  galena and s p h a l e r i t e both s i z e d t o be -100+600 mesh. Galena was w e l l depressed, w h i l e s p h a l e r i t e was n o t . They assumed t h a t galena was depressed  by dichromate  salt  because the i n s o l u b l e c o a t i n g o f l e a d chromate was formed on the galena s u r f a c e .  C o a t i n g may be r e s p o n s i b l e f o r the  f a i l u r e to float, A few years l a t e r , however, Wark and Cox [ 6 ] showed t h a t l e a d chromate, the m i n e r a l c r o c o i t e , f l o a t e d by e t h y l xanthate,  was  i n d i c a t i n g t h a t the i n t e r p r e -  t a t i o n g i v e n by Gaudin e t a l . was not s a t i s f a c t o r y . P l a k s i n and Myasnikova [ 7 ] , [ 8 ] employed  radio-  51 a c t i v e chromium, Cr  , f o r the study o f the e f f e c t o f  chromate on the f l o t a t i o n o f galena and p y r i t e . r e s u l t s a r e summarized as f o l l o w s :  Their  (1) The chromate  .  adsorption accuracy  on t h e m i n e r a l  surface  by t h e F r e u n d l i c h e q u a t i o n :  chromate amount,  k = constant  PbS a n d 2.12 f o r F e S ,  f o r PbS a n d 0.83 f o r F e S . 2  the  o f 2.9 5 f o r  with value  of  ( 3 ) The a d s o r p t i o n  increase of the concentration  increased  mineral  surfaces, taking probably  crystal  lattice.  From t h e s e  at t h i s value  and  form o f chemical  values on t h e  the free places  experimental  that the depressive  with  o f t h e s o l u t i o n up t o  ( 4 ) The c h r o m a t e i s a d s o r b e d i r r e g u a l r l y  concluded  0.42  ( 2 ) The i n c r e a s e o f t h e c h r o m a t e  pH 6 a n d becomes a l m o s t c o n s t a n t  the  (a = adsorbed  n  creates a p r o p o r t i o n a l decrease of the y i e l d of  by f l o t a t i o n .  above.  with the value  1/n = c o n s t a n t  2  adsorption  a = ~kC^^  sufficient  C = e q u i l i b r i u m concentration of the  chromate s o l u t i o n ,  mineral  i s given with  i n the  results,  they  e f f e c t o f chromate i o n s  attachment t o the mineral  as a r e s u l t o f w h i c h t h e m i n e r a l  s u r f a c e became  hydrated;  c o n d i t i o n s , s u r f a c e h y d r a t i o n was s o g r e a t  the m i n e r a l  c o u l d no l o n g e r be f l o a t e d  presence of a xanthate  adsorption  a d e n s i t y up t o 30-33 p e r c e n t The d e p r e s s i v e  from  i n spite of the  l a y e r on i t s s u r f a c e o f  e f f e c t o f p o t a s s i u m chromate and  on t h e s u r f a c e  a s due t o a d s o r p t i o n o f  of galena  and p y r i t e ;  a t t a c h themselves chemically t o the mineral  According  to the r e s u l t s  studying  that  of a complete monolayer.  potassium dichromate i s regarded  anions  took  surfaces,  under these  chromate anions  6  obtained  the depressive  these  surfaces.  by P l a k s i n and M y a s n i k o v a  a c t i o n o f chromate i o n s  on  .7 p y r i t e and galena by means o f t r a c e m i c r o r a d i o g r a p h y , the c h e m i c a l attachment o f chromate ions t o m i n e r a l i s independent  o f xanthate  i o n s attachment and a p p a r e n t l y  takes p l a c e i n d i f f e r e n t areas [ 3 ] .  The study o f the  d e p r e s s i v e a c t i o n o f chromates on galena and p y r i t e , which was c a r r i e d out a t the Mekhanobr I n s t i t u t e o f U.S.S.R. [ 9 ] , supports the h y p o t h e s i s g i v e n by P l a k s i n e t a l . P l a k s i n and Myasnikova [10] s t u d i e d the d e p r e s s i v e 51 a c t i o n o f chromate on galena and  p y r i t e by u s i n g Cr  i s o t o p e , w i t h e t h y l x a n t h a t e as the f l o t a t i o n agent oil  as the foaming agent.  and pine  They found t h a t the maximum  chromate i o n a d s o r p t i o n on the s u l p h i d e m i n e r a l s u r f a c e resulted  i n a minimum o f t h e i r e x t r a c t i o n .  In the c o n t r a s t  t o r e f e r e n c e s [7] and [8] the chromate a d s o r p t i o n was a f f e c t e d by the pH o f the s o l u t i o n , was zero a t pH 0, and reached  0.2 mg/g a t pH above 6, a f t e r which i t remained  constant.  They h y p o t h e s i z e d t h a t the d e p r e s s i v e a c t i o n o f  chromate i o n was a t t r i b u t e d t o the f o r m a t i o n o f very slightly  s o l u b l e normal o r b a s i c chromates on the m i n e r a l  surface. Bogdanov and Podnek [ 4 ] a l s o examined the e f f e c t of potassium Experiments  chromate on galena and copper s u l p h i d e s . on galena f l o t a t i o n w i t h v a r i a b l e chromate  salt  consumption showed the t o t a l galena d e p r e s s i o n occurs when a depressant  a d s o r p t i o n l a y e r , approximately  equal t o a  monolayer, i s formed; a t t h i s p o i n t a d s o r p t i o n o f b u t y l x a n -  8 t h a t e remains  the same as without a d e p r e s s a n t .  o f g a l e n a by potassium chromate was  Depression  e x p l a i n e d by the hydro-  p h i l i z a t i o n e f f e c t o f chromate i o n , which covers the hydrop h o b i l i z a t i o n e f f e c t of xanthate i o n s on the  surface.  Galena d e p r e s s i o n appeared most e f f e c t i v e a t pH 5-6 above 8. pH  8 was  The  sharp impairment  and  of g a l e n a f l o t a t i o n a t above  e x p l a i n e d as due t o the f a c t t h a t i n t h i s r e g i o n  potassium chromate i s i n s o l u t i o n w i t h chromate i o n s , forming l e a d chromate, and t o the d e p r e s s i v e a c t i o n of h y d r o x y l ions. M i t r o f a n o v and Kushnikova  [11] s t u d i e d the adsorp-  t i o n of chromium compounds on s u l p h i d e m i n e r a l s by u s i n g 51 r a d i o a c t i v e i s o t o p e Cr  i n the form of dichromate.  e f f e c t o f v a r i o u s f a c t o r s , such as pH, dichromate  temperature,  c o n c e n t r a t i o n , c o n t a c t time, e t c . on the  t i o n o f chromium compounds on s u l p h i d e m i n e r a l s .  The potassium adsorpThey  found t h a t the a d s o r p t i o n of chromium compounds on galena i n c r e a s e s w i t h the i n c r e a s e i n temperature, c o n c e n t r a t i o n o f potassium dichromate  and c o n t a c t time.  t h a t the a d s o r p t i o n of dichromate connected w i t h HCrO^ and CrO", because s o r p t i o n was e r a l s washed w i t h  i o n was  They  suggested  evidently  r a t h e r than w i t h CrCOH)^  reduced by a p p r o x i m a t e l y h a l f on min-  HC1.  C o n t r a r y t o the c o n c l u s i o n of M i t r o f a n o v e t a l . , Stepanov and Nagirnyak  [12] suggested t h a t the d e p r e s s i o n  of galena and p y r i t e occurs as a r e s u l t of f o r m a t i o n of  9 oxide f i l m s on t h e i r s u r f a c e s .  In the i n t e r m e d i a t e pH  range, both dichromate and chromate ions are p r e s e n t i n the s o l u t i o n , r e g a r d l e s s o f which chromate s a l t i s added t o t h e p u l p ; the e f f e c t o f each o f these i o n s i s determined by i t s c o n c e n t r a t i o n i n the p u l p , and depends on the pH of the s o l u t i o n .  They made the thermodynamic c a l c u l a t i o n s  f o r t h e o x i d i z i n g r e a c t i o n s o f chromium s a l t s on xanthates. A c c o r d i n g t o t h e i r c a l c u l a t i o n , under standard c o n d i t i o n s the lower xanthates  are o x i d i z e d , and the h i g h e r  xanthates  are not o x i d i z e d . M i t r o f a n o v and Kushnikova [ 1 3 ] , [14] have s t u d i e d the e f f e c t o f .potassium  dichromate and sodium  s u l p h i d e on a d s o r p t i o n o f an amine on s u l p h i d e s o f heavy metals  i n c o n n e c t i o n with t h e i r f l o a t a b i l i t y .  t o the experiments u s i n g potassium  According  dichromate and t r i -  14 decylamme l a b e l e d w i t h C  , potassium  dichromate i n c r e a s e d  the a d s o r p t i o n o f t r i d e c y l a m i n e on s p h a l e r i t e and p y r i t e a t a l l pH v a l u e s ; however, on g a l e n a , t h i s i n c r e a s e was s h i f t e d toward a l k a l i n e pH v a l u e s , w i t h a maximum a t about pH  10.  Then, the f o l l o w i n g c o n d i t i o n s f o r t h e s e p a r a t i o n  of s p h a l e r i t e from galena were determined: dichromate 3-5 kg/ton,  amine consumption 20 g/ton, pH 7.2,  e x t r a c t i o n o f z i n c i n t o the zinc c o n c e n t r a t e and  use o f potassium  t h a t i n t o Pb c o n c e n t r a t e  68.0-72.0%  26.0-33.0%.  Yamasaki e t a l . [15] s t u d i e d the a c t i o n o f potassium  chromate on galena by means o f e l e c t r o n d i f f r a c -  10 tion.  They observed the f o r m a t i o n o f l e a d chromate  on the galena s u r f a c e when the g a l e n a specimen 2mm x 2mm x 1mm  was t r e a t e d w i t h 0.2 M/L  chromate s o l u t i o n f o r 24 hours.  film  having  o f potassium  An aggregate o f f i n e  p o l y c r y s t a l l i n e l e a d chromate was.suggested  as the s u r f a c e  product. An e l e c t r o c h e m i c a l survey o f g a l e n a f l o t a t i o n was done by Pomianowski and Czubak-Pawlikowska [ 1 6 ] .  They  observed t h a t the r e s t p o t e n t i a l o f galena e l e c t r o d e decreased when potassium e t h y l xanthate was added, and t h a t an a d d i t i o n o f dichromate  caused the i n c r e a s e o f the  p o t e n t i a l p r o p o r t i o n a t e t o the l o g a r i t h m o f i t s c o n c e n t r a tion.  Solov'eva and Khokhlova  [17] a l s o measured the  e l e c t r o d e p o t e n t i a l o f g a l e n a i n dichromate  solutions.  They found t h a t the treatment o f e l e c t r o d e w i t h c o n c e n t r a t e d dichromate  solution  (1 g/L) r e s u l t e d i n the c o v e r i n g o f  e l e c t r o d e w i t h a l e a d chromate f i l m and no decrease o f p o t e n t i a l was observed a f t e r a d d i t i o n o f x a n t h a t e . of dichromate  A t 2 0 mg/L  s o l u t i o n , the a d d i t i o n o f xanthate caused the  decrease o f p o t e n t i a l , and i t was e s p e c i a l l y l a r g e a t pH around  7. Poole r e p o r t e d the e f f e c t o f dichromate i n  f l o t a t i o n a t the S u l l i v a n m i l l a t the year o f 1920 [ 1 8 ] .  EXPERIMENTAL Materials The g a l e n a , from Galena, Kansas  was s u p p l i e d  by Ward's N a t u r a l Science E s t a b l i s h m e n t I n c . The m i n e r a l specimen  grade o f galena was ground  and screened i n t o s i z e f r a c t i o n s . for  a l l the runs was ground  vacuum d e s i c c a t o r .  i n a mortar and p e s t l e Enough o f the m i n e r a l  initially  and s t o r e d i n a  Only - 200 + 270 mesh, - 270 +325 mesh  and - 325 + 400 mesh" s i z e f r a c t i o n s were used f o r a d s o r p t i o n tests.  Galena samples f o r i n f r a r e d s p e c t r o s c o p y , were p r e -  pared by a f u r t h e r g r i n d i n g i n an agate mortar f o r 3 0 minutes. Pure potassium e t h y l xanthate was s y n t h e s i z e d by a s t a n d a r d method u s i n g potassium h y d r o x i d e , methanol and carbon d i s u l p h i d e and p u r i f i e d t h r e e times by r e c r y s t a l l i z a t i o n w i t h e t h y l a l c o h o l and e t h y l e t h e r [ 3 2 ] . s o l u t i o n was always Dixanthogen  prepared j u s t b e f o r e every  Xanthate experiment.  p r e p a r a t i o n was a c h i e v e d by o x i d i z i n g the  aqueous s o l u t i o n o f pure xanthate w i t h i o d i n e ,  extracting  the product w i t h e t h y l e t h e r and then d r y i n g i t under reduced p r e s s u r e [ 3 3 ] . Potassium  chromate, potassium  dichromate,  potassium h y d r o x i d e , l e a d s u l p h i d e o f reagent grade  supplied  Mesh s i z e s r e f e r t o T y l e r standard s c r e e n s .  12 from the F i s h e r S c i e n t i f i c Company were used. A l l s o l u t i o n s were made w i t h d i s t i l l e d water. a c i d was Baker and Adamson, 6 0%. the  The p e r c h l o r i c  Lead chromate  used f o r  a d s o r p t i o n t e s t o f xanthate was p r e c i p i t a t e d by the  r e a c t i o n between l e a d n i t r a t e and potassium chromate o f r e a g e n t grade, f o l l o w e d by f i l t r a t i o n ,  r i n s i n g with  d i s t i l l e d water and d r y i n g under reduced p r e s s u r e . F o r the  p u r g i n g o f d i s s o l v e d oxygen from aqueous s o l u t i o n s ,  h e l i u m o r n i t r o g e n gas  s u p p l i e d by Canadian L i q u i d A i r  Company L i m i t e d , was used without f u r t h e r  Analytical  purification.  Equipment A P e r k i n - E l m e r Model 450 UV-VIS-NIR R e c o r d i n g  Spectrophotometer and matched 1.0 cm Corex c e l l s were used for  t h e d e t e r m i n a t i o n o f x a n t h a t e , chromate  ion  concentrations.  of  and dichromate  The s p e c t r o p h o t o m e t r i c d e t e r m i n a t i o n  xanthate i o n was based on i t s a b s o r p t i o n peak a t the  wave l e n g t h o f 301 my. Chromate and dichromate i o n s were q u a n t i t a t i v e l y a n a l y z e d by measuring  the o p t i c a l d e n s i t i e s a t 370 my and  345 my, r e s p e c t i v e l y . The i d e n t i f i c a t i o n o f adsorbed s p e c i e s o f chromate or  dichromate i o n s on g a l e n a , s y n t h e t i c l e a d s u l p h i d e and  xanthate i o n s o f l e a d chromate "Helium:  was a c h i e v e d by means o f  99.995% , moisture <10 P.P.M., D.P. -76°F.  s'c ii  G Grade N i t r o g e n : 99.5 t o 99.8%, argon content i n c l u d e d , oxygen 2-5000 P.P.M., moisture 128 P.P.M., D.P. -40°F.  i n f r a r e d spectroscopy. Spectrometer,  t r o d e was  A P e r k i n - E l m e r Double-beam I n f r a r e d  Model 5 21 was  used f o r t h i s  purpose.  The measurements of r e s t p o t e n t i a l of galena  elec  done w i t h a Beckman E l e c t r o s c a n Model 30 and  a  matched e l e c t r o d e assembly.  The measurement of pH were  u s i n g the same equipment, but a combination  mad  e l e c t r o d e was  used.  Experimental  Procedures  (1) A d s o r p t i o n and D e s o r p t i o n T e s t s A d s o r p t i o n and d e s o r p t i o n t e s t s were conducted a c y l i n d r o c o n i c a l g l a s s v e s s e l whose diameter was and the l e n g t h o f c o n i c a l p a r t was f o r n i t r o g e n gas or a i r flow was bubbles  7.0  cm.  4.5  in  cm.  A bubbling t i p  i n s e r t e d to allow  t o a g i t a t e the galena samples g e n t l y .  gas  Some adsorp-  t i o n t e s t s were c a r r i e d , out i n a glove box under a c o n t r o l l atmosphere.  A c e r t a i n amount of galena was  put i n t o  g l a s s v e s s e l , and the n e c e s s a r y amount of s o l u t i o n added.  Then the apparatus  temperature  was  was  Some  when i t was  experiments  necessary.  a c e r t a i n p e r i o d o f a g i t a t i o n , the s o l u t i o n was  Then the s o l u t i o n was  After  filtered  u s i n g a M i l l i p o r e f i l t e r o r s e p a r a t e d from galena by a c e n t r i f u g e .  was  put i n a water bath whose  kept a t 25 ± 0.5°C.  were done .at room temperature  the  particles  subjected to a  s p e c t r o p h o t o m e t r i c d e t e r m i n a t i o n o f the c o n c e n t r a t i o n s of  14 x a n t h a t e , chromate or dichromate i o n s .  Dixanthogen i n a  s o l u t i o n o r formed on s o l i d p a r t i c l e s was a l s o determined spectrophotometrically  when i t was n e c e s s a r y , a f t e r f i r s t  e x t r a c t i n g i t with hexane. was sometimes checked  The amount o f dixanthogen  by p y r i d i n e c o l o r i m e t r i c method [ 1 9 ] .  •  (2) B u f f e r A c t i o n  Tests  In order t o study the b u f f e r a c t i o n o f g a l e n a , f i v e grams o f galena one  powder (- 200 + 270 mesh) was put i n  hundred m i l l i l i t e r s  v a r i o u s pH v a l u e s . in adsorption was r e c o r d e d electrode.  tests.  o f d i s t i l l e d water a d j u s t e d a t  The same g l a s s v e s s e l was used as used Then the change i n pH o f the s o l u t i o n  f o r t h i r t y minutes u s i n g a combination F o r pH adjustment, p e r c h l o r i c a q i d and potassium  h y d r o x i d e s o l u t i o n s were used. used t o a g i t a t e the galena  A i r and n i t r o g e n gas were  powders g e n t l y .  (3) I d e n t i f i c a t i o n by I n f r a r e d Spectroscopy i  I d e n t i f i c a t i o n of adsorption and  p r o d u c t s o f xanthate  o f chromate o r dichromate on n a t u r a l g a l e n a ,  synthetic  l e a d s u l p h i d e , and l e a d chromate was made by i n f r a r e d spectroscopy. with  Extremely f i n e powder o f galena was made  an agate mortar t o i d e n t i f y the a d s o r p t i o n  dichromate on the galena  surface.  products o f  One gram o f the sample  The s u r f a c e products on the s u r f a c e o f f i n e powder may b e . d i f f e r e n t fromthose on the s u r f a c e o f l a r g e p a r t i c l e s , because the c o n d i t i o n s o f t h e s u r f a c e a r e d i f ferent. -  15 powder was  immersed i n  one  hundred  milliliters  of  -2 1.0  x 10  M/L  hour a t 25°C.  potassium dichromate After f i l t r a t i o n  a vacuum d e s i c c a t o r .  s o l u t i o n f o r one  the sample was  stored i n  S y n t h e t i c l e a d s u l p h i d e was  also  used t o i d e n t i f y the s u r f a c e products of chromate and dichromate  on g a l e n a .  Lead chromate and  l e a d s u l p h i d e were exposed  to a  1.0  chromate-treated  x 10  M/L  xanthate  s o l u t i o n t o i d e n t i f y the a d s o r p t i o n products of xanthate on l e a d chromate. sample  One  t o two m i l l i g r a m s of these d r i e d  were then ground w i t h f i v e hundred  m i l l i g r a m s of  potassium bromide and p r e s s e d i n t o p e l l e t s a t f i v e psi,  and s u b j e c t e d t o IR  identification.  thousand  EXPERIMENTAL RESULTS  A.  E f f e c t of pH on the C o n c e n t r a t i o n s of Chromate and Dichromate Ions, and the E f f e c t of the A d d i t i o n of Chromate on Xanthate  Stability  In the f l o t a t i o n of s u l p h i d e ores c o n t a i n i n g g a l e n a , both chromate and dichromate  are used as  However, the r e l a t i o n s h i p between chromate and i o n s can be expressed  2CrO^  The  +  2H  =  +  depressants  dichromate  as,  2HCrO~  =  Cr 0 2  ?  +  H0 2  e q u i l i b r i u m c o n d i t i o n of the r e a c t i o n  c a l c u l a t e d as E q u a t i o n  . . . .  (4-1)  (4-2) can be  (4-3), u s i n g the necessary thermo-  dynamic data g i v e n i n Latimer's book [ 2 0 ] .  2CrO~  +  2H  pH = 7.3  +  =  +  Cr 0^ 2  log (CrOp  S i m i l a r l y the r e a c t i o n  +  H0 2  - 0.5  log (Cr 0^) 2  (4-4) has the e q u i l i b r i u m  . . . .  (4-2)  . . . .  (4-3)  condition  which can be expressed by E q u a t i o n (4-5).  CrO^  +  pH = 6.46  H  +  =  HCrO"  - l o g (HCrO")  +  log (CrCO  . . . .  (4-4)  . . . .  (4-5)  In order t o c o n f i r m photometry  such a r e l a t i o n s h i p , s p e c t r o -  d e t e r m i n a t i o n s were made f o r chromate  dichromate i o n c o n c e n t r a t i o n s . s p e c t r a of chromate  Figure 1  shows a b s o r p t i o n  s o l u t i o n as w e l l as dichromate s o l u t i o n .  The peak o f a b s o r p t i o n band of chromate the wave l e n g t h o f 37 0 my 345 my,  i o n and  ions was  found a t  and t h a t o f dichromate i o n s a t  thus the c o n c e n t r a t i o n s  o f each s p e c i e s can be  determined by measuring the o p t i c a l d e n s i t i e s a t the wave l e n g t h o f 345 my  A  345  =  e  'c c  A  370  =  e  c  C  C  c  and 370  +  +  e  e  my.  . . . . (4-6)  d d C  . . . . (4-7)  'd d C  Where A ,, 0  c  and A  370 my  o n r  O  OHO  respectively, C  c  are- absorbance a t 345 my  and  /U  and  are c o n c e n t r a t i o n s  o f chromate  #>  ion  and dichromate i o n , e amd e' are the molar e x t i n c t i o n '• c c c o e f f i c i e n t o f chromate a t 37 0 my and 345 my, and and e'; d 345 my  are the molar e x t i n c t i o n c o e f f i c i e n t o f dichromate a t and 37 0 my.  The c o n c e n t r a t i o n s  o f chromate  and  dichromate i o n s were determined a t the d i f f e r e n t l e v e l s o f pH and were d e p i c t e d i n F i g u r e  2.  The s t a b i l i t y  ican be shown g r a p h i c a l l y as i n F i g u r e  o f each i o n s  2, and i n the n e u t r a l  s o l u t i o n , both i o n s c o e x i s t i n s o l u t i o n , r e g a r d l e s s o f which s a l t i s used. *e ""E  i s 0.482xl0 /M  and e'  i s 0.315xl0 /M  and e'd i s 0.112xl0 /M.  4  c  4  d  i s 0.240xl0 /M. 4  c  4  The molar e x t i n c t i o n c o e f f i c i e n t s o f chromate at pH 9.5 and d i chromate at pH 1.0 were determined s t a t i s t i c a l l y u s i n g 1 cm Corex c e l l s .  Figure 1  Absorption Spectra of (a) P o t a s s i u m Chromate S o l u t i o n (pH 11.5) and' (b) P o t a s s i u m D i chromate S o l u t i o n (pH 4.3). j .  The a b s o r p t i o n s p e c t r a o f p o t a s s i u m e t h y l xanthate  p o t a s s i u m chromate, and t h e i r m i x t u r e  aqueous s o l u t i o n a r e shown i n F i g u r e 3.  The  i n an  concentration  _5  of potassium e t h y l xanthate -4 o f chromate was 2.0 x 10  was 6.0 x 10  M/L.  M/L, and t h a t  The spectrum o f t h e m i x t u r e  was t a k e n f o r t y minutes a f t e r m i x i n g , and t h e pH o f t h e s o l u t i o n was 9.81. of the mixture Equation  A t any wave l e n g t h , t h e o p t i c a l d e n s i t y  s a t i s f i e d the r e l a t i o n s h i p expressed  by  (4-7).  A = C  e  xx  +  C  . . . .  e  c c  (4  where A i s t h e absorbance o f t h e m i x t u r e , C concentration ' x o f x a n t h a t e i o n s , C c o n c e n t r a t i o n o f chromate i o n s , e t h e ' c ' c m o l a r e x t i n c t i o n c o e f f i c i e n t o f chromate s o l u t i o n , and e ' x the m o l a r e x t i n c t i o n c o e f f i c i e n t o f x a n t h a t e Therefore,  solution.  the r e s u l t i n d i c a t e s the s a t i s f a c t o r y  of t h e m i x t u r e  o f chromate and x a n t h a t e  stability  i o n s under  these  conditions. B.  Changes i n pH o f t h e S o l u t i o n s C o n t a i n i n g  Galena  (1) Changes i n pH o f Aqueous S o l u t i o n s C o n t a i n i n g  Galena  An attempt was made t o d e t e r m i n e t h e s t o i c h i o m e t r y o f t h e a d s o r p t i o n r e a c t i o n o f chromate i o n s on g a l e n a by a n a l y z i n g chromate i o n c o n c e n t r a t i o n and measuring pH. However, t h e change i n pH o f t h e s o l u t i o n c o n t a i n i n g  galena  0 Figure 2  2  4  6  8 10 pH S t a b i l i t y of Chromate Ion and Dichromate Ion as a of pH  12 Function  14  21  a l o n e was  found t o be v e r y l a r g e i n the p r e s e n c e o f oxygen.  Both the changes i n pH and the amount of chromate i o n s adsorbed on g a l e n a  s u r f a c e were l a r g e r when oxygen  was  present  i n s o l u t i o n t h a n i n the absence of oxygen as mentioned  later.  From t h e s e o b s e r v a t i o n s  i t would appear t h a t  r e a c t i o n system i s r a t h e r c o m p l i c a t e d .  the  I n f a c t , because  the r a t i o s between chromate i o n s adsorbed and hydrogen i o n s consumed were not found t o be a c o n s t a n t  f o r the  different  l e v e l s o f i n i t i a l pH and o f i n i t i a l c o n c e n t r a t i o n o f chromate i o n s , the s t o i c h i o m e t r i c d e t e r m i n a t i o n  of adsorption r e a c t i o n  o f chromate i o n s on g a l e n a  unsuccessful.  Therefore, f i r s t c o n t a i n i n g g a l e n a was galena  (- 270  s u r f a c e was  of a l l , the change i n pH of water  studied.  Five  gram  q u a n t i t i e s of  + 325 mesh) were put i n one hundred  milliliters  o f d o u b l e d i s t i l l e d w a t e r o f v a r i o u s pH a d j u s t e d by  per-  c h l o r i c a c i d , and the changes i n pH w i t h time were measured continuously during gentle a g i t a t i o n .  Figure 4  shows the  changes o f pH o f w a t e r c o n t a i n i n g g a l e n a i n the p r e s e n c e o f oxygen.  The  i n i t i a l pH.  v a l u e o f pH s h i f t e d toward 7, r e g a r d l e s s o f the S i m i l a r e x p e r i m e n t s were c a r r i e d out under the  same e x p e r i m e n t a l  c o n d i t i o n s but w i t h g a l e n a p r e p a r e d  g l o v e box under a n i t r o g e n atmosphere. deaerated  by n i t r o g e n gas b u b b l i n g .  are shown i n F i g u r e 5. pH were s i m i l a r t o those  The The  in a  w a t e r used  result  was  obtained  I n the a c i d i c r a n g e , the changes i n i n the p r e s e n c e o f oxygen, but  changes i n the a l k a l i n e r e g i o n were not so l a r g e .  the  In order t o o b t a i n a b e t t e r understanding way i n w h i c h g a l e n a  of the  i s r e s p o n s i b l e f o r t h e pH o f t h e  s o l u t i o n , t i t r a t i o n experiments m i l l i l i t e r s o f double  were d e s i g n e d .  One hundred  d i s t i l l e d w a t e r c o n t a i n i n g f i v e grams  o f g a l e n a was a d j u s t e d t o pH 3 by p e r c h l o r i c a c i d , and was t i t r a t e d w i t h 0.01 N sodium h y d r o x i d e . shown i n F i g u r e 6.  Curve (a) shows a t i t r a t i o n i n t h e p r e -  sence o f oxygen, w h i l e curve w i t h o u t oxygen. the  The r e s u l t s a r e  (b) shows c o r r e s p o n d i n g  results  The former has a s i m p l e shape compared t o  latter. A l l experiments  mentioned above were c a r r i e d o u t  w i t h o u t r e m o v a l o f oxygen c o n t a i n e d i n t h e n i t r o g e n gas used. S i n c e t h e o x i d a t i o n o f a g a l e n a s u r f a c e by oxygen c o n t a i n e d i n n i t r o g e n gas might o c c u r , one must l e a v e room f o r some variation.  I t would be v e r y i n t e r e s t i n g t o examine t h e  change i n pH o f t h e s o l u t i o n a v o i d i n g oxygen  contamination  as c o m p l e t e l y as p o s s i b l e , however, f u r t h e r e x p e r i m e n t s  were  not done i n t h i s work. (2) Changes i n pH o f a Chromate S o l u t i o n C o n t a i n i n g Galena S i m i l a r experiments -4 out u s i n g 2 x 10  as mentioned above were c a r r i e d  M/L p o t a s s i u m  r e s u l t s o b t a i n e d i n t h e presence  chromate s o l u t i o n .  The  and absence o f oxygen a r e  shown i n F i g u r e 7 and F i g u r e 8, r e s p e c t i v e l y .  In the pre-  sence o f oxygen, when s t a r t i n g pH v a l u e s were 9.9 and 10.9, pH v a l u e s d i d n o t change s i g n i f i c a n t l y a f t e r t h i r t y minutes  Figure 4  Time Dependence o f H„0 w i t h Galena  Suspension  Figure 5  Time Dependence o f pH o f t h e S o l u t i o n U n o x i d i z e d Galena  Containing  0  3  1 - 2  0.01N Figure 6  T i t r a t i o n Curves (a) O x i d i z e d Galena '(b) U n o x i d i z e d Galena (c) Water Only  4 NaOH (ml.)  5  " 6 •  7  26 a g i t a t i o n , b u t when i n i t i a l pH was below 9, pH o f t h e s o l u t i o n increased with time.  In the previous experiments,  pH o f t h e s o l u t i o n s w h i c h d i d n o t c o n t a i n chromate changed  from 3 t o 3.5 and 4 t o 5.6 a f t e r t h i r t y  salt  minutes  s t a n d i n g , b u t i n t h o s e e x p e r i m e n t s , pH s h i f t e d from 3 t o 4.5 and from 4 t o 7, r e s p e c t i v e l y .  This indicates that  pH s h i f t o f t h e s o l u t i o n s c o n t a i n i n g chromate  s a l t was  l a r g e r t h a n t h a t o f t h e s o l u t i o n s w i t h o u t chromate  salt.  S i m i l a r phenomena were o b s e r v e d when t h e oxygen was e x c l u d e d . The pH v a l u e s o f t h e s o l u t i o n s which d i d n o t c o n t a i n  chromate  s a l t i n c r e a s e d g r a d u a l l y , whereas t h a t o f t h e s o l u t i o n s c o n t a i n i n g chromate was 3.  s a l t i n c r e a s e d r a p i d l y , when i n i t i a l pH  F i g u r e 9 shows a t i t r a t i o n c u r v e s f o r a chromate  s o l u t i o n and f o r a chromate  C.  s o l u t i o n containing galena.  A d s o r p t i o n Rates o f Chromate and X a n t h a t e Ions by Galena P l a n k s i n and M y a s n i k o v a [ 4 ] , and Bogdanov and  K a k o v s k i i [ 9 ] r e p o r t e d t h a t t h e c h e m i c a l attachment o f chromate  i o n s t o m i n e r a l s , such as p y r i t e , g a l e n a , e t c . ,  was independent o f x a n t h a t e i o n attachment and a p p a r e n t l y took p l a c e i n d i f f e r e n t areas. In o r d e r t o o b t a i n an u n d e r s t a n d i n g o f t h e ads o r p t i o n o f chromate and x a n t h a t e on g a l e n a s u r f a c e , i n t h e system o f g a l e n a - x a n t h a t e - c h r o m a t e e x p e r i m e n t s were conducted t o i n v e s t i g a t e t h e c o m p e t i t i v e a d s o r p t i o n between  chromate  27  Figure 7  Time Dependence'of pH o f 2.0 x 10 M/L P o t a s s i u m Chromate S o l u t i o n C o n t a i n i n g Galena ,• .  11*  61  I  1  1  0  5  10  15 • TIME,  '  Figure 8  •  I  \  I  20  25 •  minute -h  Time Dependence o f .pH o f 2.0 x 10 M/L Chromate S o l u t i o n C o n t a i n i n g U n o x i d i z e d  Potassium Galena  I  -3 0  and x a n t h a t e  i o n s , t h e d e s o r p t i o n o f chromate i o n s  the a d s o r p t i o n o f x a n t h a t e  from g a l e n a p r e t r e a t e d w i t h  chromate, and t h e d e s o r p t i o n o f x a n t h a t e p r e t r e a t e d w i t h xanthate  due t o  from g a l e n a  d u r i n g t h e chromate  surface  adsorption  test. P r i o r to proceeding s o r p t i o n experiments, xanthate  w i t h such a d s o r p t i o n and de-  t h e a d s o r p t i o n r a t e s o f chromate and  i o n s on g a l e n a were s t u d i e d .  The r e s u l t s  obtained  -4 f o r t h e s o l u t i o n s c o n t a i n i n g 1.6 x 10  M/L  xanthate  and  -4 4.0 x 10  M/L  chromate r e s p e c t i v e l y a r e shown i n F i g u r e  Though t h e c o n c e n t r a t i o n o f chromate i o n s was than t h a t of xanthate  higher  i o n s t h e a d s o r p t i o n o f chromate i o n s  i s f a i r l y slow compared t o t h a t o f x a n t h a t e p r e d i c t e d from t h e s e r e s u l t s t h a t x a n t h a t e  ions.  i n a s o l u t i o n c o n t a i n i n g both xanthate  It is  adsorption i s  completed b e f o r e chromate a d s o r p t i o n when g a l e n a  D.  10.  i s immersed  and chromate i o n s .  A d s o r p t i o n o f Chromate Ions and X a n t h a t e Ions on Galena Surface In order t o understand the a d s o r p t i o n s t a t e of  xanthate  and chromate i o n s on g a l e n a , a c o m p e t i t i v e  t i o n s t u d y may p r o v i d e u s e f u l i n f o r m a t i o n .  adsorp-  Three k i n d s  o f s o l u t i o n s , one c o n t a i n i n g p o t a s s i u m chromate a l o n e , c o n t a i n i n g potassium xanthate i n g b o t h chromate and x a n t h a t e obtained  a r e shown i n T a b l e I .  one  a l o n e , and t h e o t h e r c o n t a i n i o n s , were used.  The  results  0  5  10  15 0.01N  Figure 9  20  NaOH (ml.)  T i t r a t i o n Curves o f Chromate S o l u t i o n s ( I ) Chromate S o l u t i o n Only ( I I ) C o n t a i n i n g Galena  31  10 bO  0  10 .  20  30  40  TIME, minute F i g u r e 10 • A d s o r p t i o n ' Rates o f Chromate and X a n t h a t e on • . G a l e n a a t 25°C. ' G a l e n a (-325 + 400 mesh) 10 g. K CrO (4.0 x ' 1 0 M/L) ' 50 m i s . , I n i t i a l pH 7.2 >  - 4  2  )4  • K.Et.X.(1.6  x IO  - 4  M/L)  50 m i s . , I n i t i a l pH 7,4  F i r s t o f a l l , t e n grams o f g a l e n a (- 325 + 400 -4 put i n t o f i f t y m i l l i l i t e r s o f 4.0 x 10 M/L  mesh) was  p o t a s s i u m chromate s o l u t i o n and a e r a t e d f o r t h i r t y  minutes  at  pH  25°C.  I n i t i a l pH o f t h e s o l u t i o n was  7.35,  and  i n c r e a s e d s l i g h t l y t o 7.56 a f t e r t h i r t y minutes r e t e n t i o n . The amount o f chromate i o n s adsorbed by g a l e n a was 1.24 x 5 10 moles p e r gram g a l e n a . The  a d s o r p t i o n o f x a n t h a t e by g a l e n a was s t u d i e d _5 u s i n g a n e u t r a l pH s o l u t i o n . When 8.0 x 10 M/L and 1.6 -4 x 10 M/L x a n t h a t e s o l u t i o n s were u s e d , x a n t h a t e i o n s -7 -7 adsorbed were 3.5 x 10 /g g a l e n a , r e s p e c t i v e l y .  moles/g g a l e n a and 7.7  x 10  I t i s seen t h a t t h e amount absorbed  a l m o s t doubled when the i n i t i a l c o n c e n t r a t i o n o f the was  moles  solution  doubled. -4  In a s o l u t i o n c o n t a i n i n g 1.6 x 10 M/L potassium -4 x a n t h a t e and 4.0 x 10 M/L p o t a s s i u m chromate, the -7 a d s o r p t i o n o f x a n t h a t e i o n s was 3.65 x 10 moles/g o f g a l e n a _g  w h i l e the chromate a d s o r p t i o n was galena.  0.79  x 10  The pH v a l u e changed from 7.2 5 t o 7.91  agitation.  The  a d s o r p t i o n o f b o t h chromate and  moles/g o f d u r i n g the xanthate  were a l t e r e d c o n s i d e r a b l y under the c o m p e t i t i v e c o n d i t i o n s . The  d e c r e a s e measured i n the a d s o r p t i o n o f chromate  36 p e r c e n t , but i n x a n t h a t e  53 per c e n t .  was  33  TABLE I A d s o r p t i o n o f Chromate I o n and/or Ion on Galena  Surface  Galena:  -325+400 mesh  Xanthate  and/or Chromate S o l u t i o n s :  R e t e n t i o n Time: Temperature:  Initial CrO"  0 0  5 0 mis.  25°C. .  Concentration  -4  10.0 grams  30 minutes  (M/L) EtX  4.0 x. 10  Xanthate  (M/L)  0 8.0 x 1 0 "  Initial pH  7 .35 5  1.6 x I O " -4 , ~ -4 4.0 x 10 1.6 x 10 4  Amount o f A d s o r p t i o n Cr0  (m/g) EtX  4  1.2 x 10  6 .85  0  7 . 01  0  7 . 26  -6  Final pH  (m/g)  0 3.5 x 1 0 ~  7 .56 7  7.7 x 1 0 " -7 -6 0.8 x 10 3.7 x 10  7  6.98 7 .03 7.73  S i n c e t h e r e s u l t s o b t a i n e d by U.V. spectrophotometer a r e a c c u r a t e t o w i t h i n ±1 %. Considering the experimental a c c u r a c y , t h e c o n c e n t r a t i o n s o f CrO^", Cr 0^~, EtX", and d i xanthogen, d e r i v e d from U.V. absorbance d a t a and p r e s e n t e d i n Tables I t o V I , a r e c o r r e c t e d t o two s i g n i f i c a n t f i g u r e s . 9  the a d s o r p t i o n t e s t , h e l i u m b u b b l i n g was a g i t a t i o n purpose.  The  continued  for  c o n c e n t r a t i o n o f the chromate  -4  s o l u t i o n was  4 . 0 x 10  the s o l u t i o n was i t was  M/L.  A f t e r t h i r t y minutes r e t e n t i o n  s e p a r a t e d from the g a l e n a p a r t i c l e s  subjected to spectrophotometric The  and  analysis.  o t h e r f r a c t i o n , w h i c h weighed e x a c t l y the  same as the f i r s t , was  t a k e n out from the g l o v e box i n  o r d e r t o i n v e s t i g a t e the oxygen e f f e c t .  T h i s sample  was  t r e a t e d i n a chromate s o l u t i o n w i t h a i r b u b b l i n g f o r a g i t a t i o n purpose.  The  e x p e r i m e n t a l c o n d i t i o n s were a l l the  same except f o r the a i r b u b b l i n g . experiment  Completion  o f the same  t w i c e gave s i m i l a r r e s u l t s and the averages o f  t h e s e r e s u l t s are shown i n T a b l e I I . 7.6 0 ( i n  I n i t i a l pH o f a chromate s o l u t i o n was air  atmosphere).  g a l e n a s u r f a c e was  The  amount o f chromate i o n s adsorbed  1 . 2 7 x 10  on  —6  moles per gram o f g a l e n a i n — 6  h e l i u m atmosphere and i n c r e a s e d t o 1 . 7 4 x 10 gram o f g a l e n a i n a i r . a t m o s p h e r e . for  the l a t t e r case i s about 1 . 4  former.  The  moles per  a d s o r p t i o n o f chromat  t i m e s o f t h a t o f the  T h i s f a c t s u p p o r t s the p r e d i c t i o n t h a t oxygen  be i n v o l v e d i n the f o r m a t i o n o f l e a d chromate on surface.  may  galena  Such a phenomenon i s r e a s o n a b l e from the thermo-  dynamic p o i n t o f view w h i c h w i l l be d i s c u s s e d  later.  36  TABLE I I A d s o r p t i o n o f Chromate  Ion on G a l e n a S u r f a c e  i n t h e P r e s e n c e o r Absence o f Oxygen  Galena:  -270+325 mesh  P o t a s s i u m Chromate R e t e n t i o n Time:  Solution:  4.0 x 10  M/L  50 m i s .  3 0 minutes  I n i t i a l Temperature:  Atmosphere  5.0 gram  Initial pH  2 5°C.  Adsorption of CrO"  (moles/g)  x  He  7 .60  1.2  Air  7 .60  1.7:  x  10" i o  -  6  6  Ratio  Final pH  1.0 '  7.72  1.4-  7 .80  37 F.  E f f e c t o f pH on Chromate A d s o r p t i o n on  Galena  F i g u r e 11 shows the e f f e c t o f pH on chromate a d s o r p t i o n on g a l e n a .  Ten grams o f g a l e n a (- 325 + 400 —2  mesh) was  put i n one hundred m i l l i l i t e r s  o f 1.0  x 10  M/L  p o t a s s i u m chromate s o l u t i o n s which had v a r i o u s i n i t i a l values.  pH  A f t e r g e n t l e a g i t a t i o n f o r t e n minutes a t 25°C,  t h e s o l u t i o n s s e p a r a t e d from s o l i d p a r t i c l e s were used f o r s p e c t r o p h o t o m e t r i c d e t e r m i n a t i o n s and pH measurements.  In  F i g u r e 11, the amount o f chromate i o n s consumed are g i v e n i n terms o f b o t h i n i t i a l and f i n a l pH v a l u e s .  At  pH  below 9 chromate a d s o r p t i o n d e c r e a s e d l i n e a r l y w i t h pH, and above pH 9 i t remained c o n s t a n t . G.  D e s o r p t i o n o f X a n t h a t e Ions o r Chromate Ions From Galena S u r f a c e As mentioned  b e f o r e , the a d s o r p t i o n and d e s o r p t i o n  e x p e r i m e n t s were c a r r i e d out i n o r d e r t o u n d e r s t a n d the adsorbed  s t a t e s o f x a n t h a t e and chromate on g a l e n a .  Table  I I I and T a b l e IV show the r e s u l t s o b t a i n e d f o r the d e s o r p t i o n t e s t s o f chromate i o n s and x a n t h a t e i o n s , r e s p e c t i v e l y . Ten grams o f g a l e n a (- 325 + 400 mesh), which was -4 p r e - t r e a t e d w i t h 4.0 x 10 M/L p o t a s s i u m chromate f o r f o r t y m i n u t e s , was 10 -4 M/L  taken i n t o t w e n t y - f i v e m i l l i l i t e r s  o f 1.6  x  p o t a s s i u m e t h y l x a n t h a t e and a g i t a t e d f o r t h i r t y  minutes a t 25°C.  The amount o f x a n t h a t e i o n s adsorbed  37a  2'  F i g u r e 11  3  ' 4•  .•  •  5 . 6  7  8  9  10  pH  E f f e c t o f pH on Chromate A d s o r p t i o n on Galena  11  on g a l e n a was 3.56 x 10  moles p e r gram o f g a l e n a .  v a l u e was l e s s than h a l f o f t h e amount adsorbed treated galena. of  This  on un-  I n t h i s e x p e r i m e n t , no d e t e c t a b l e amount  chromate i o n s from g a l e n a s u r f a c e was desorbed  balancing the xanthate a d s o r p t i o n .  counter-  This i s true f o r a l l  the other xanthate a d s o r p t i o n t e s t s . _5 Then, t e n grams o f g a l e n a p r e t r e a t e d w i t h 8 x 10 M/L  x a n t h a t e s o l u t i o n were p u t i n t w e n t y - f i v e m i l l i l i t e r s -4  of for  4.0 x 10  M/L  t h i r t y minutes  p o t a s s i u m chromate s o l u t i o n and a g i t a t e d a t 25°C.  The v a l u e o f pH o f t h e s o l u t i o n  moved from 7.3 2 t o 7.9 3 d u r i n g t h e a g i t a t i o n .  The amount  of  chromate i o n s adsorbed on x a n t h a t e - t r e a t e d g a l e n a was —6 0.96 x 10 moles p e r gram o f g a l e n a and was about 77 p e r cent o f t h a t adsorbed on t h e f r e s h g a l e n a . No x a n t h a t e i o n s were d e t e c t e d i n t h e r e s u l t i n g s o l u t i o n . However, -7 1.12 x 10 x a n t h a t e moles p e r gram o f g a l e n a were d e t e c t e d , -4 when t e n grams o f g a l e n a p r e t r e a t e d w i t h 1.6 x 10 M/L -2 x a n t h a t e s o l u t i o n were immersed i n a 1.0 x 10 s o l u t i o n f o r t h i r t y minutes.  M/L  chromate  Other e x p e r i m e n t s w i t h more  c o n c e n t r a t e d s o l u t i o n s were performed.  The r e s u l t s o b t a i n e d  were s i m i l a r t o t h e above, and t h e r e s u l t s a r e a l s o shown i n T a b l e s I I I and IV. I t i s expected t h a t dixanthogen i s i n v o l v e d i n t h i s g a l e n a , chromate and x a n t h a t e system.  In f a c t , Table V  shows t h a t about 40 p e r cent o f t o t a l x a n t h a t e i o n s consumed s t a y s as d i x a n t h o g e n on t h e s u r f a c e and i n a b u l k s o l u t i o n .  39  TABLE I I I D e s o r p t i o n o f Chromate I o n from Galena S u r f a c e Due t o X a n t h a t e A d s o r p t i o n  Galena:  -325+400 mesh  10.0  Potassium E t h y l Xanthate: R e t e n t i o n Time: Temperature:  grams  25 m i s .  30 minutes  25°C.  I n i t i a l pH o f X a n t h a t e S o l u t i o n s :  Cone.  6.3-7.8  of  CrO = Ads.  I n i t i a l Cone.  CrO^ Des. EtX  CrOJJCM/L)  (mol es/g)  of  (moles/g) (moles/g)  4.0 x IO "  1.2  x IO  - 6  1.0 x 1 0 "  2  N.D.  3.6\-  -4  1.1  x IO  - 6  1.0 x 1 0 ~  2  N.D.  1.4- x 10 -6  1.6 x 1 0 ~  4  N.D.  3.2 x 1 0 "  4  N.D.  3.5 ^ x 10 -7 -7 6 .6 x 10  1.0 x 1 0 "  2  -  1.0 x 1 0  - 1  N.D.  =  Not D e t e c t a b l e  Ads.  =  Adsorbed  Des.  =  Desorbed  Cone. =  -7  4  -  4.0 x IO"  EtX"(M/L)  Ads.  Concentration  x 10  TABLE IV D e s o r p t i o n o f X a n t h a t e I o n from G a l e n a S u r f a c e Due t o Chromate A d s o r p t i o n (1)  Galena:  -325+400 mesh  10.0  grams  P o t a s s i u m Chromate S o l u t i o n : R e t e n t i o n Time: Temperature:  25 m i s .  30 minutes  2 5°C.  I n i t i a l pH o f Chromate S o l u t i o n s :  Cone. o f EtX"(M/L)  EtX Ads. (moles/g)  8.0 x 1 0 " 1.6 x 1 0  I n i t i a l Cone, E t X " Des. o f CrO (M/L) (moles/g)  CrO~ Ads (moles/g)  1.0  =  5  3.5  x 10~  7  4.0 x 1 0 ~  4  - 4  7.6  x 10~  7  1.0 x 1 0 "  2  1.0 x 1 0 "  2  1.0 x 1 0 "  2  -  N.D.  =  Not D e t e c t a b l e  Ads.  =  Adsorbed  Des.  =  Desorbed  Cone. =  5.3-7.4  Concentration  N.D. 1.1  0 8.0 x 1 0 ~  x 10~  7  2.4-  x 10~  -6  1.4-= • x 10-6  N.D. 4  x 10  0 7  1.2.  x 10  -6  T h i s e x p e r i m e n t f o r x a n t h a t e d e s o r p t i o n was made u s i n g twenty grams o f g a l e n a (- 270 + 325 mesh), one  hundred  -4 milliliters  o f 1.0  x 10  M/L  potassium xanthate.  After  s e p a r a t i n g s o l i d s from the s o l u t i o n , d i x a n t h o g e n was tracted with f i f t y m i l l i l i t e r s  ex-  o f hexane, and s u b j e c t e d t o  a spectrophotometric determination. i o n s s t a y i n g as l e a d x a n t h a t e was  The amount o f x a n t h a t e  c a l c u l a t e d from the  d i f f e r e n c e between t o t a l x a n t h a t e i o n s consumed and d i xanthogen  on g a l e n a s u r f a c e .  e t h y l x a n t h a t e was s o l u t i o n was  7.60.  5.92  I n i t i a l pH o f p o t a s s i u m  and t h a t o f p o t a s s i u m chromate  These r e s u l t s show t h a t 66 p e r c e n t o f  l e a d x a n t h a t e and 40 p e r c e n t o f d i x a n t h o g e n  initially  p r e s e n t were desorbed from g a l e n a s u r f a c e due t o a d d i n g potassium  chromate. I t i s seen from t h e s e s i m p l e e x p e r i m e n t s  that  the a d s o r p t i o n o f x a n t h a t e on c h r o m a t e - t r e a t e d g a l e n a  was  much more a f f e c t e d t h a n t h a t o f chromate onto x a n t h a t e treated galena.  I t i s a l s o seen t h a t x a n t h a t e d e s o r p t i o n  from g a l e n a s u r f a c e i s p o s s i b l e when the m i n e r a l i s t r e a t e d w i t h a c o n c e n t r a t e d s o l u t i o n o f chromate, w h i l e no sorption  de-  o f chromate i o n i s o b s e r v e d due t o x a n t h a t e  adsorption.  These r e s u l t s agree w i t h t h o s e o b t a i n e d i n t h e  c o m p e t i t i v e a d s o r p t i o n t e s t s o f chromate and x a n t h a t e i o n s on g a l e n a and w i t h the r e s u l t s o b t a i n e d from the a d s o r p t i o n e x p e r i m e n t o f x a n t h a t e i o n s on l e a d  chromate.  I t would have been v e r y i n t e r e s t i n g t o  investi-  gate t h e d e s o r p t i o n o f x a n t h a t e , which i s l e s s t h a n mono-  TABLE V D e s o r p t i o n o f X a n t h a t e from Galena S u r f a c e Due t o Chromate A d s o r p t i o n (2) Twenty grams o f g a l e n a (-270+325 mesh) were w i t h 100 m i s . o f 1.0 x I O "  4  treated  M/L p o t a s s ium e t h y l  x a n t h a t e s o l u t i o n f o r t e n minutes a t 25°C. (as x a n t h a t e i o n ) X a n t h a t e adsorbed on g a l e n a  - 6  moles  as l e a d x a n t h a t e  7. 7 " x I O 4. 1 ' x I O  - 6  moles  as d i x a n t h o g e n D i x a n t h o g e n i n an aqueous  3.6 . x I O 1.2- x I O  - 6  solution  - 6  moles moles  Then g a l e n a mentioned  above was t r e a t e d w i t h 5 0 mis . o f 1.0 x 10 M/L p o t a s s i u m chromate s o l u t i o n f o r t e n minutes a t 25°C. X  10" 6 moles  4. 2A  X  10" 6 moles  2 .7  X  10" 6 moles  1. 5  X  10" 6 moles  0 .2  X  10" 6 moles  3 .3  X  10" 6 moles  Chromate adsorbed on g a l e n a  1.  X a n t h a t e remained on g a l e n a as l e a d x a n t h a t e as d i x a n t h o g e n D i x a n t h o g e n desorbed i n t o s o l u t i o n X a n t h a t e i o n desorbed i n t o s o l u t i o n  .  3<<  43 l a y e r c o v e r a g e , from g a l e n a s u r f a c e .  However, t h e s e n s i t i v -  i t y o f a n a l y t i c a l t e c h n i q u e used i n t h i s s t u d y was i n s u f f i c i e n t f o r such a purpose.  H.  A d s o r p t i o n o f X a n t h a t e Ions by Lead Chromate In  o r d e r t o examine whether chromate i o n s a r e  r e l e a s e d o r n o t t o a s o l u t i o n from l e a d chromate when x a n t h a t e i o n s a r e adsorbed on i t , a d s o r p t i o n t e s t s o f x a n t h a t e on l e a d chromate were  conducted.  One gram o f  p r e c i p i t a t e d f i n e l e a d chromate was p l a c e d i n an Ehrenmyer f l a s k which c o n t a i n e d one hundred m i l l i l i t e r s o f x a n t h a t e s o l u t i o n and a g i t a t e d m e c h a n i c a l l y f o r t h i r t y minutes.  The s o l u t i o n was t h e n s u b j e c t e d t o s p e c t r o p h o t o -  m e t r i c d e t e r m i n a t i o n o f x a n t h a t e i o n s as w e l l as chromate ions.  T h i s was done f o r s o l u t i o n s o f d i f f e r e n t  concentrations.  xanthate  The r e s u l t s o b t a i n e d a r e shown i n T a b l e  VI. When t h e i n i t i a l x a n t h a t e c o n c e n t r a t i o n was 1.0 _2  x 10  M/L,  t h e amount o f x a n t h a t e i o n s adsorbed p e r one -4 gram o f l e a d chromate was 1.8 x 10 moles w h i l e t h e amount _5 of chromate m t h e s o l u t i o n was found t o be 3.9 x 10 _3  moles a f t e r t h i r t y minutes  agitation. _5  x a n t h a t e s o l u t i o n was used 1.4 x 10  When 1.0 x 10  M/L  moles o f x a n t h a t e  i o n s were adsorbed p e r one gram o f l e a d chromate.  This i s  a p p r o x i m a t e l y one t e n t h o f t h e amount adsorbed when 1.0 x  10  M/L  x a n t h a t e s o l u t i o n was used.  The amount o f chrom_5  a t e i o n s r e l e a s e d i n the l a t t e r case was  4.7  x 10  moles.  :0n the o t h e r hand, when no x a n t h a t e was added, 5.8 x 10 ^ moles o f chromate were found i n the s o l u t i o n a f t e r minute a g i t a t i o n .  thirty  By u s i n g hexane as a s o l v e n t f o r  d i x a n t h o g e n , i t was a l s o found t h a t more t h a n 80 p e r c e n t o f t o t a l x a n t h a t e consumption s t a y e d as d i x a n t h o g e n i n t h i s system. These r e s u l t s show t h a t t h e r e l e a s e o f  chromate  i o n s from l e a d chromate was d e c r e a s e d s l i g h t l y by x a n t h a t e a d s o r p t i o n on l e a d I.  chromate.  Thermodynamic C o n s i d e r a t i o n s o f the R e a c t i o n s I n v o l v e d I n The System Pb-Cr-S-H 0 2  I n o r d e r t o get i n f o r m a t i o n on t h e adsorbed s p e c i e o f chromate  o r d i c h r o m a t e s a l t on g a l e n a , i t might be use-  f u l t o i n v e s t i g a t e the system Pb-Cr-S-I-^O  thermodynamically  F o r t h i s p u r p o s e , the p o t e n t i a l - p H diagram f o r the system Pb-Cr-S-H 0 a t 25°C 2  was  constructed.  Thermodynamic d a t a  used were c i t e d from L a t i m e r [20] and P o u r b a i x [ 2 1 ] . The p o t e n t i a l - p H diagrams f o r the system Cr-I^O and Pb-S-H 0 a r e shown i n F i g u r e 12 and 13 r e s p e c t i v e l y . 2  The e x p e c t e d r e a c t i o n s and t h e i r e q u i l i b r i u m c o n d i t i o n s a r e given i n Table V I I .  The p o t e n t i a l - p H diagram f o r the  system Pb-Cr-S-H 0 i s shown i n F i g u r e 14. 2  In these f i g u r e s  the s o l i d l i n e s r e p r e s e n t the u n i t a c t i v i t y o f the d i s s o l v e d  45  TABLE VI A d s o r p t i o n o f X a n t h a t e I o n on Precipitated  Lead Chromate  Lead Chromate ( p r e c i p i t a t e d ) :  1.0 0 gram  Potassium E t h y l Xanthate S o l u t i o n : R e t e n t i o n Time: Temperature:  X a n t h a t e (M/L)  1.0 x I O 0  30 minutes  2 5°C.  I n i t i a l Cone, o f  1.0.x 1 0 "  100 m i s .  Adsorption of Xanthate  CrO~ i n  Pb  (moles/g) S o l n . ( m o l e s )  2  1.8  x 10"  4  3.9  x IO"  - 3  1.4  x 10"  5  4.7  -x 1 0 "  0  5.8. x 1 0 "  Soln.  1 P.P.M.  5  5  in  5  2 P.P.M. 1 P.P.M.  i o n s and  the b r o k e n l i n e s an a c t i v i t y o f 10  .  The  dynamic d a t a f o r l e a d t h i o s u l p h a t e and b a s i c l e a d were not a v a i l a b l e , t h e r e f o r e l e a d s u l p h a t e sulphate  thermo-  thiosulphat  and b a s i c  lead  were used i n s t e a d . I t i s seen from t h e s e f i g u r e s t h a t g a l e n a i s  o x i d i z e d to lead sulphate  o r b a s i c l e a d s u l p h a t e , and  that  beyond t h a t p o t e n t i a l l e a d chromate i s formed, i g n o r i n g the k i n e t i c f a c t o r s . s t a b l e domain.  F u r t h e r m o r e , l e a d chromate has  T h i s i n d i c a t e s t h a t even i n the pH  where d i c h r o m a t e i o n i s s t a b l e , f o r example pH 1, formation  o f l e a d chromate i s f a v o r e d  and  there  a large range  the  i s no  lead  d i c h r o m a t e s t a b l e domain.  T h i s i s e a s i l y checked by  t h e d i c h r o m a t e s o l u t i o n and  lead n i t r a t e dissolved i n a  d i l u t e d n i t r i c a c i d whose pH formation favored  i s 1.  mixing  As mentioned above the  of l e a d chromate i n t h e b u l k system i s v e r y much  and  l e a d chromate once formed has  a very  stable  domain.  J.  I d e n t i f i c a t i o n o f R e a c t i o n P r o d u c t s on the S u r f a c e o f G a l e n a T r e a t e d w i t h P o t a s s i u m Chromate o r P o t a s s i u m Dichromate As mentioned p r e v i o u s l y , many i n v e s t i g a t o r s exam-  i n e d the s u r f a c e p r o d u c t s on g a l e n a t r e a t e d w i t h a chromate o r d i c h r o m a t e s o l u t i o n by e l e c t r o n d i f f r a c t i o n and  reported  t h a t l e a d chromate was  They  formed on g a l e n a s u r f a c e .  used a s i n g l e c r y s t a l o f g a l e n a and  treated i t with a  con-  F i g u r e 12  Potential-pH  diagram f o r the system Cr-H-O  H S 2  pH F i g u r e 13  Potential-pH  diagram f o r the system Pb-S-H„0  49 TABLE V I I R e a c t i o n s and E q u i l i b r i u m Formulae F o r The  1.  Pb0  + C r O ^ + 4H  2  System Pb-Cr~S-H 0 2  + 2e = PbCrO^ + 2H 0  +  2  E = 1.919 - 0.1182pH + 0.0295 l o g [ C r O ^ ] 2.  2Pb0  + Cr 0  2  + 6H  =  2  y  + 4e = 2 P b C r 0  +  + 3H 0  4  2  E = 1.704 - 0.0886'pH + 0.0148 l o g [ C r 0  =  2  3.  Pb0  + H Cr0  2  2  + 2H  4  y  ]  + 2e = PbCrO^ + 2H 0  +  2  E = 1.706 - 0.0591pH + 0.0295 l o g [ I ^ C r O ^ ] 4.  Pb0  + HCrO^" + 3H  2  + 2e = P b C r 0  +  + 2H 0  4  2  E = 1.729 - 0.0886 pH + 0.0295 l o g [ H C r O ^ ] -  5.  PbCrO^ + S 0  + 8H  = 4  + 3e = P b S 0  +  + Cr  4  + 4H 0  3 +  2  E = 1.318 - o.l576 pH + 0.0197 l o g [ S O ^ ] - 0.0197 l o g [Cr 6.  2PbCr0  4  ]  3 +  + 2S0  = 4  '+ 10H :  + 6e = C r 0  +  2  + 2PbSC> + 5H 0  3  4  2  E = 1.153 - 0.0985 pH + 0.0197 l o g [ S 0 ] =  4  7.  PbSO^'PbO + 2 C r 0  + 2H  = 4  +  = 2PbCr0  + S0  4  = 4  + H0 2  pH + | l o g C S 0 ] - | l o g [ C r 0 ] = 11.053 =  =  4  8.  2PbCr0  4  + S0  = 4  + 8H  4  + 6e = C r ^ + PbSO^'PbO + 4H 0  +  2  E = 1.094 - 0.0788 pH + 0.0098 l o g C S 0 ] =  4  9.  Pb0  + H S 0 " + 3H  2  +  4  + 2e = P b S 0  4  + 2H 0 2  E = 1. 626 - 0.0886 pH + 0.0295 l o g [HS0 *~] 4  10.  Cr 0 2  = 7  +  H 2  °  +  = 2H Cr0  2 H +  2  4  pH + l o g [ H C r 0 _ l - | l o g [ C r 0 ] = -0.091 2  11.  2Cr0  = 4  + 2H  +  4  = Cr 0 2  2  y  + H0  = 7  2  pH + | l o g [ C r 0 2  = 7  ] - l o g [ C r 0 ] = 7.296 =  4  50 12,.: P h 0  + 2H  = 3  = Pb0  +  2  + H0 2  pH - | l o g [ P b 0 ] = 15.660 =  3  12.-  2Pb0  + S0^~ + 6H  2  +  + 4e = PbSO^'PbO + 3H 0 2  E = 1.593 - 0.0886 pH + 0.0148 l o g [ S 0 ] =  4  14.  2Pb0  = 3  + S0  + 10H  = 4  + 4e = PbSO^'PbO + 5H 0  +  2  E = 2.518 - 0.1480 pH + 0.0296 l o g [ P b 0 ] + 0.0148 l o f =  3  [so 15.  2Cr0  = 4  + 10H  = 4  +  ] + 6e = C r 0 2  3  + 5H 0 2  E = 1.310 - 0.0985 pH + 0.0197 l o g [ C r 0 ] =  4  16.  H Cr0 2  4  + 6H  +  + 3e = C r  + 4H 0  3+  2  E = 1.330 - 0.1182 pH - 0.0197 l o g [ C r  3 +  ] + 0.0197 l o g  [H Cr0 ] 2  17.  4  PbSO^'PbO + S 0  = 4  + 2H  = 2PbS0' + H 0  +  4  2  pH - j l o g [ S 0 ] = 3.02 =  4  18.  Cr 0 2  3  + 6H  +  = 2Cr  3 +  pH + j l o g [ C r 19.  PbSO^ + 8H  +  + 3H 0 2  3 +  ] = 2.80  + 6e = P b  + S + 4H 0  + +  2  E = 0.280 - 0.0788 pH - 0.0098 l o g [ P b ] + +  20.  Pb  + S + 2e = PbS  + +  E = 0.354 + 0.0295 l o g [ P b J + +  21.  PbSO^ + 8H  +  + 8e = PbS + 4H 0 2  E = 0.299 - 0.0591 pH 22.  PbS0 'PbO + S 0 4  = 4  + 18H  + 16e = 2PbS + 9H 0  +  2  E = 0.321 - 0.0667 pH + 0.0037 l o g [ S 0 ] =  4  23.  PbS + 2H  +  + 2e = Pb + H S 2  E = -0.301 - 0.0591 pH - 0.0295 l o g [ H S ] 2  50a 24,.  Cr  9+  + e = Cr  ++  E = -0.408 - l o g [ C r 25.  Cr 0 2  + 6H  3  + 2e = 2 C r  +  + +  + +  ] + log [ C r  3 +  ]  + 3H 0 2  E = 0.088 - 0.1773 pH - 0.0591 l o g [ C r 26.  PbCr0  4  + S0  = 4  + 2H  = PbSO^ + H C r 0  +  2  + +  ]  4  pH - | l o g E S 0 ] + | l o g [ H C r 0 ] = -0.415 =  4  2  4  51  F i g u r e 14  Potential-pH  diagram f o r t h e system  Pb-Cr-S-H-0  ..centrated chromate o r d i c h r o m a t e  solution.  In a f l o t a t i o n  •-.•condition, t h e same p r o d u c t i s e x p e c t e d t o be formed on :  :galena s u r f a c e when a chromate o r d i c h r o m a t e  s a l t i s used  as a d e p r e s s a n t ; b u t t o prove t h i s , i t i s n e c e s s a r y t o i n v e s t i g a t e whether t h e same r e a c t i o n p r o d u c t i s o b t a i n e d ;when g a l e n a i s t r e a t e d w i t h a d i l u t e s o l u t i o n which c o n t a i n s t h e same l e v e l o f chromate o r d i c h r o m a t e p e r u n i t s u r f a c e area.  .The a u t h o r used a n a t u r a l g a l e n a powder and a l s o  s y n t h e t i c g a l e n a t r e a t e d w i t h a chromate o r d i c h r o m a t e  solu-  t i o n and t r i e d t o i d e n t i f y t h e p r o d u c t s formed on g a l e n a s u r f a c e by making p e l l e t s f o r use i n a i n f r a r e d spectrophotometer. To make a p e l l e t , an e x t r e m e l y f i n e g a l e n a powder was p r e p a r e d a c c o r d i n g t o t h e p r o c e d u r e mentioned  before.  F i v e hundred m i l l i g r a m s o f t h e powder was immersed i n f i f t y _2  m i l l i l i t e r s o f 1.0 x 10  M/L  dichromate  s o l u t i o n whose pH  was 4.2 and was m e c h a n i c a l l y s t i r r e d f o r one hour a t room temperature.  A f t e r f i l t e r i n g and d r y i n g t h e sample i n a  vacuum d e s i c c a t o r , t h e p e l l e t was made w i t h KBr.  The same  p r o c e d u r e was a p p l i e d f o r l e a d s u l p h i d e which was t r e a t e d i n a d i c h r o m a t e and a chromate s o l u t i o n , and t h e pH v a l u e s were 4.2 and 7.6 r e s p e c t i v e l y . w h i c h were scanned  The s p e c t r a o f t h e s e t h r e e p e l l e t s  on a P e r k i n - E l m e r Model 521 a g a i n s t KBr  b l a n k s a r e shown i n F i g u r e 15 - ( a ) , (b) and ( c ) .  As a  c o m p a r i s o n , a spectrum o f l e a d chromate i s shown i n F i g u r e 15 - ( d ) . The spectrum o f l e a d s u l p h i d e t r e a t e d w i t h a  -:chromate s o l u t i o n a t pH 9,8  was  S p e c t r a ( a ) , (b) and  the same as ( c ) . (c) show the a b s o r p t i o n band  v a t 848 cm ^ which i n d i c a t e s the f o r m a t i o n o f l e a d chromate on g a l e n a s u r f a c e .  The a b s o r p t i o n bands f o r chromium o x i d e  chromium h y d r o x i d e , l e a d d i o x i d e , o r l e a d h y d r o x i d e were not  K.  found,  I d e n t i f i c a t i o n of A d s o r p t i o n Products of Xanthate on Lead Chromate The  same•IR s p e c t r o s c o p i c t e c h n i q u e , which  was  employed f o r t h e i d e n t i f i c a t i o n o f l e a d chromate on g a l e n a s u r f a c e , was  used i n o r d e r t o i d e n t i f y t h e a d s o r p t i o n  p r o d u c t s o f x a n t h a t e on l e a d chromate. mentioned  As the a u t h o r  b e f o r e t h e s p e c t r a o f powdered n a t u r a l g a l e n a  t r e a t e d w i t h a chromate o r d i c h r o m a t e a v e r y c l e a r a b s o r p t i o n band.  s o l u t i o n d i d not g i v e  Therefore i n t h i s case, lead  chromate p r e c i p i t a t e d and s y n t h e t i c g a l e n a t r e a t e d w i t h potassium dichromate  s o l u t i o n were used i n s t e a d o f n a t u r a l  g a l e n a t r e a t e d w i t h a chromate o r d i c h r o m a t e In  solution.  o r d e r t o t r e a t l e a d chromate w i t h x a n t h a t e ,  one gram o f l e a d chromate and s y n t h e t i c g a l e n a p r e t r e a t e d w i t h a potassium dichromate  s o l u t i o n whose pH was _2  placed m  o f 1.0  fifty milliliters  e t h y l x a n t h a t e whose pH was for  6.8  x 10  M/L  were  potassium  r e s p e c t i v e l y and  one hour a t room t e m p e r a t u r e ;  5.6  stirred  the m a t e r i a l s were  I n f r a r e d • S p e c t r a o f (a) S y n t h e t i c PbS t r e a t e d w i t h K C r 0 (pH 7.6), (b) S y n t h e t i c PbS t r e a t e d w i t h K Cr„0 (pH 4-. 2 ) , ( c ) G a l e n a t r e a t e d w i t h K Cr 0 (pH'4.3), (d) PbCrO^. 2  4  ?  2  2  7  washed w i t h d i s t i l l e d water and d r i e d i n vacuum.  After  making p e l l e t s w i t h K B r , s p e c t r a were o b t a i n e d .  They a r e  •shown i n F i g u r e 16 - (a) and ( b ) . S p e c t r a o f l e a d (c) and chromium o x i d e  xanthate  (e) a r e a l s o shown i n t h e same  figure. Spectra  (a) and (b) have f o u r s i g n i f i c a n t a b s o r p -  t i o n bands r e s p e c t i v e l y a t 1200 cm ^, 1106 cm ^, 1016 cm and  84 8 cm ^.  dixanthogen, obtained.  The a b s o r p t i o n bands due t o chromium lead d i o x i d e , or lead hydroxide  oxide,  c o u l d n o t be  The band a t 848 cm ^ i s c o n s i d e r e d t o r e p r e s e n t  l e a d chromate and o t h e r s r e p r e s e n t  lead xanthate.  However,  t h e s e t h r e e a b s o r p t i o n bands i n s p e c t r a (a) and (b) do n o t agree e x a c t l y w i t h t h o s e  i n spectrum ( c ) .  Leja studied the surface products  on d e p o s i t e d  t r e a t e d w i t h potassium e t h y l xanthate photometer and suggested a  lead  by i n f r a r e d  sulphide  spectro-  r a d i c a l i n t h e f i r s t mono-  The d e v i a t i o n o f a b s o r p t i o n peak f o r x a n t h a t e  a d s o r p t i o n products p o s s i b i l i t y of  on l e a d chromate may i n d i c a t e t h e  1:1 c o - o r d i n a t i o n between  l e a d i n t h i s system. later.  and  1:1 c o - o r d i n a t i o n between t h e  s u r f a c e m e t a l atom and x a n t h a t e layer.  Poling  x a n t h a t e and  However, t h i s m a t t e r w i l l be d i s c u s s e d  WAVENUMBER, 1400  F i g u r e 16  1200  1000  CM 800  600  I n f r a r e d S p e c t r a o f (a) PbCrCv t r e a t e d w i t h K.Et.X. (pH 7.2), ( b ) PbS t r e a t e d w i t h K Cr2_0 (pH 6.3), t h e n K.Et.X. (pH 7.2), (c) P M E t X ) , (d) X , and (e) C r 0 9  7  3  56  DISCUSSIONS  A.  Changes i n pH of the S o l u t i o n s C o n t a i n i n g As  shown i n F i g u r e s  4 and  5, the  Galena  explanations  f o r b u f f e r a c t i o n can be g i v e n i n s e v e r a l ways. when oxygen was  Firstly  e x c l u d e d , i n a l k a l i n e s o l u t i o n s , no  i c a n t l a r g e s h i f t i n pH was  o b s e r v e d , whereas the  i n pH were f a i r l y l a r g e i n a c i d i c s o l u t i o n s . the o x i d a t i o n o f g a l e n a by oxygen c o n t a i n e d  signif-  changes  Neglecting i n nitrogen  gas  used i n t h e s e e x p e r i m e n t s , the s h i f t of pH t o the a c i d i c s i d e might be due  t o a d i s s o l u t i o n o f g a l e n a i n the  c h l o r i c a c i d used t o a d j u s t pH and  the p r e f e r e n t i a l  adsorption  The  o f hydrogen on g a l e n a .  g a l e n a i s e x p r e s s e d by the n e x t  PbS  +  2H  +  =  Pb  + +  +  d i s s o l u t i o n of  equation:  HS  ....  2  S e c o n d l y , when oxygen i s p r e s e n t , the o x i d i z e d p r o d u c t of g a l e n a i s t h o u g h t t o be l e a d or b a s i c lead t h i o s u l p h a t e .  per-  (5-1)  initial thiosulphate  A number o f i n v e s t i g a t o r s  s t u d i e d the o x i d a t i o n r e a c t i o n of s u l f i d e m i n e r a l s i n aqueous s o l u t i o n s i n the c o n n e c t i o n w i t h the f l o t a t i o n or h y d r o metallurgy  of s u l f i d e o r e s .  the f o r m a t i o n  H a g i h a r a e t a l . [22]  of lead sulphate.  s u g g e s t e d the f o r m a t i o n  L e j a , L i t t l e and  of l e a d t h i o s u l p h a t e  and,  indicated Poling  [23]  Eadington  58 and  Prosser  •„:sulphate.  [24] reported  the formation  of basic lead  thio-  In the leaching o f p e n t l a n d i t e or galena i n  ammonical s o l u t i o n s a t e l e v a t e d t e m p e r a t u r e ,  Forward  e t a l . [ 2 5 ] found t h a t t h e i n i t i a l o x i d i z e d p r o d u c t was m e t a l l i c s a l t s o f t h i o s u l p h a t e , and t h a t t h e f i n a l p r o d u c t was m e t a l l i c s a l t s o f s u l p h a t e . of f l o t a t i o n are considered,  Therefore,  i f the conditions  the r e s u l t s obtained  e t a l . , and E a d i n g t o n e t a l .  by L e j a  seem t o be more r e a s o n a b l e  t h a n t h a t by H a g i h a r a e t a l . [ 2 2 ] and by Abramov [ 2 6 ] . pH o f a s o l u t i o n i s i n c r e a s e d , to basic thiosulphate. species  i s discussed,  must be used.  l e a d t h i o s u l p h a t e may  As convert  When t h e d i s s o l u t i o n o f adsorbed s o l u b i l i t y d a t a o f adsorbed  species  S o l u b i l i t y d a t a , however, a r e n o t a v a i l a b l e  f o r t h e adsorbed s p e c i e s o f l e a d t h i o s u l p h a t e o r b a s i c t h i o s u l p h a t e on g a l e n a .  The s o l u b i l i t y o f l e a d  lead  thiosulphate  _ 3  i s reported  t o be 0.94 x 10  M/L, w h i l e no d a t a i s g i v e n on  the s o l u b i l i t y o f b a s i c l e a d t h i o s u l p h a t e .  When t h e  d i s s o l u t i o n o f t h o s e o x i d i z e d s p e c i e s proceeds i n an a c i d i c s o l u t i o n , hydrogen i o n i s consumed.  Therefore,  i n the  a c i d i c s i d e , hydrogen i o n consumption by t h e d i s s o l u t i o n o f g a l e n a i t s e l f and t h e o x i d i z e d p r o d u c t s o f g a l e n a  surface  may cause t h e i n c r e a s e i n pH, and a t t h e same t i m e , t h e p r e f e r e n t i a l hydrogen i o n a d s o r p t i o n  [ 2 7 ] may cause t h e pH t o  increase. I n a l k a l i n e s o l u t i o n s , t h e n , t h e s h i f t o f pH i s explained  by t h e f o r m a t i o n  o f l e a d h y d r o x i d e adsorbed o r  -deposited on t h e g a l e n a s u r f a c e as w e l l as t h e p r e c i p i t a t i o n A  .of l e a d h y d r o x i d e  i n a bulk s o l u t i o n .  As b u l k l e a d  . s u l f i d e i s l e s s s o l u b l e i n comparison t o b u l k l e a d h y d r o x i d e , and assuming t h i s tendency i s t r u e f o r adsorbed  species,  .the f o r m a t i o n o f l e a d h y d r o x i d e on f r e s h g a l e n a s u r f a c e i s not f a v o r e d .  T h i s a s s u m p t i o n seems r e a s o n a b l e because t h e  s h i f t o f pH i n t h e a l k a l i n e s i d e was n o t l a r g e when oxygen was a v o i d e d .  When an o x i d i z e d f i l m i s formed on g a l e n a  s u r f a c e , t h e f i l m i s d i s s o l v e d by i n c r e a s i n g pH, f o l l o w e d by the r e a c t i o n of lead ions d i s s o l v e d w i t h h y d r o x y l i o n s .  Thus  P M O l D g i s p r e c i p i t a t e d on t h e g a l e n a s u r f a c e and i n a b u l k s o l u t i o n as w e l l .  T h i s e x p l a n a t i o n can be s u p p o r t e d by  the f a c t t h a t s l i g h t l y o x i d i z e d g a l e n a , o r a t l e a s t when oxygen i s p r e s e n t i n t h e system, g a l e n a can be f l o a t e d by s u l p h y d r y l c o l l e c t o r s , whereas no f l o t a t i o n i s observed strong a l k a l i n e B,  ina  solution.  C h e m i s o r p t i o n o f Chromate o r Dichromate Ions on Galena Surface As mentioned i n t h e p r e v i o u s s e c t i o n , from t h e  thermodynamic p o i n t o f v i e w , t h e f o r m a t i o n o f l e a d chromate on g a l e n a s u r f a c e i s v e r y much f a v o r e d when g a l e n a i s t r e a t e d w i t h chromate s a l t o r dichromate  salt.  The s o l u b i l i t y o f l e a d h y d r o x i d e and t h a t o f g a l e n a i s 1.2 x 1 0 M / L . _6  In a c i d i c  i s 6.4 x 10  M/L  60 •region, where dichromate 1*8 a l s o v e r y  i o n i s v e r y s t a b l e , l e a d chromate  stable.  Furthermore,  as seen from the i n f r a r e d s p e c t r a  'given i n F i g u r e 15, a l l s p e c t r a have an a b s o r p t i o n band a t 848 cm  w h i c h i s a s s i g n e d t o Cr-0  symmetrical  However, the weak peaks a t 7 95 and 935 observed.  Both peaks may  s t r e t c h , and may  cm ^ are a l s o  be a s s i g n e d t o Cr-O-Cr asymmetric  i n d i c a t e the f o r m a t i o n o f l e a d  on g a l e n a s u r f a c e .  stretch [28].  dichromate  Anyway i t i s o b v i o u s t h a t the main  p r o d u c t on g a l e n a s u r f a c e i s l e a d chromate when g a l e n a i s t r e a t e d w i t h chromate o r dichromate  salt.  On t h e o t h e r hand, as shown i n F i g u r e 11, the amount o f chromate uptake on g a l e n a i n c r e a s e d almost w i t h dichromate  concentration.  o f chromate a d s o r p t i o n was  In a c i d i c  r e g i o n , the amount  v e r y l a r g e , and t h i s i n d i c a t e s  the h y d r o p h i l i c p r o p e r t y o f g a l e n a s u r f a c e . i s very understandable e f f i c i e n t depressant  C.  linearly  t h a t dichromate  Therefore, i t  s a l t i s a more  than chromate s a l t i n f l o t a t i o n .  I n f l u e n c e o f Chromate on the A d s o r p t i o n o f  Xanthate  on G a l e n a S u r f a c e CD  Competitive  Adsorption  I t has been shown t h a t l e a d chromate i s formed on the g a l e n a s u r f a c e when g a l e n a i s t r e a t e d w i t h a chromate solution.  Due  t o the h y d r o p h i l i c p r o p e r t y o f t h i s f i l m ,  f l o a t a b i l i t y of galena i s suppressed.  However, Wark and  the  61 sCox [ 6 ] r e p o r t e d t h a t c r o c o i t e ,  PbCrO^,  x a n t h a t e , and P l a k s i n and h i s co-worker the c h e m i c a l attachment  was  floated  by  [ 4 ] suggested t h a t  o f x a n t h a t e i o n and t h a t o f chromate  i o n took p l a c e i n d i f f e r e n t a r e a s . I n t h e p r e s e n t work, t h e a d s o r p t i o n r a t e s o f x a n t h a t e i o n s and chromate i o n s on g a l e n a , t h e c o m p e t i t i v e a d s o r p t i o n o f t h e s e two s p e c i e s , the d e s o r p t i o n o f x a n t h a t e i o n s o r chromate i o n s from g a l e n a s u r f a c e due t o chromate o r x a n t h a t e t r e a t m e n t were completed.  Furthermore  the  r e s t p o t e n t i a l o f g a l e n a e l e c t r o d e i n a chromate s o l u t i o n , and t h e p r o d u c t s on g a l e n a s u r f a c e were examined t o i n v e s t i gate t h e d e p r e s s i o n o f g a l e n a w i t h chromate o r  dichromate  i o n and t h e p o s s i b i l i t y o f f l o t a t i o n o f c h r o m a t e - t r e a t e d g a l e n a by x a n t h a t e . Under the c o n d i t i o n s d e s c r i b e d i n F i g u r e 10, x a n t h a t e i s adsorbed more r a p i d l y than chromate.  Neverthe-  l e s s , i n c o m p e t i t i v e a d s o r p t i o n t e s t s , as shown i n T a b l e I , x a n t h a t e a d s o r p t i o n i s more suppressed t h a n chromate adsorption.  I t might be p o s s i b l e t o e x p l a i n such a phenomenon  i n s e v e r a l ways.  However, i t i s r e a s o n a b l e t o c o n s i d e r t h a t  t h e a d s o r p t i o n r a t e o f x a n t h a t e i s r e t a r d e d , even i f i t s i n i t i a l r a t e i s f a s t , by the i n h i b i t i o n due t o the h y d r o p h i l i c f i l m o f chromate adsorbed  s p e c i e s on g a l e n a .  O x i d a t i o n o f x a n t h a t e by chromate i o n i n an aqueous s o l u t i o n i s e x p e c t e d t o be v e r y slow from the f a c t t h a t the U.V.  spectrum o f the m i x t u r e o f chromate and  x a n t h a t e s o l u t i o n s i s v e r y s t a b l e as shown i n F i g u r e 1. Such a slow o x i d a t i o n o f x a n t h a t e i n chromate s o l u t i o n i s q u i t e u n d e r s t a n d a b l e from the e l e c t r o n t r a n s f e r t h e o r y o f chromium r e d u c t i o n [ 3 0 ] .  However, i f a s e m i c o n d u c t o r  like  g a l e n a i s i n v o l v e d i n t h e system, the enhanced o x i d a t i o n r a t e o f x a n t h a t e by a c a t a l y t i c e f f e c t due t o g a l e n a i s predictable.  Pomianowski and P a w l i k o w s k a  [16] showed t h a t  the r e s t p o t e n t i a l o f g a l e n a was r a i s e d s t r o n g l y by the chromate a d d i t i o n .  T h i s phenomenon i n d i c a t e s  the  p o s s i b i l i t y o f o x i d a t i o n o f x a n t h a t e t o d i x a n t h o g e n by chromate i o n s i n t h e p r e s e n c e o f g a l e n a .  In f a c t , the  f o r m a t i o n o f d i x a n t h o g e n amounted t o about  80 p e r c e n t o f  t h e t o t a l x a n t h a t e adsorbed.  T h i s was  d e t e c t e d by  analyzin  t h e r e s u l t a n t s o l u t i o n o f x a n t h a t e a d s o r p t i o n t e s t w i t h the a i d s o f U.V. formed  spectrophotometry.  i n t h e p r e s e n c e o f chromate i n the system i s much  h i g h e r than t h a t without (2)  The amount o f d i x a n t h o g e n  chromate.  A d s o r p t i o n P r o d u c t s o f X a n t h a t e on Lead Chromate I t has been shown t h a t l e a d x a n t h a t e and d i x a n t h o  gen are formed when l e a d chromate i s t r e a t e d w i t h a x a n t h a t s o l u t i o n , as shown i n F i g u r e 13 and T a b l e V. shown i n F i g u r e 13, t h e one a b s o r p t i o n band x a n t h a t e i s l o c a t e d a t 1200  However, as of lead  cm ^ and t h i s i n d i c a t e s a  c e r t a i n s h i f t from the a b s o r p t i o n band  a t 1210  cm  for  l e a d x a n t h a t e which can be f o r m u l a t e d by P b C E t X ^ .  Leja  e t a l . [29] o b t a i n e d an i n f r a r e d spectrum o f l e a d  sulfide  t r e a t e d w i t h a x a n t h a t e s o l u t i o n and suggested a 1:1 c o • o r d i n a t i o n between t h e s u r f a c e m e t a l atom and t h e x a n t h a t e ^ r a d i c a l i n t h e f i r s t monolayer  from the s h i f t i n C-O-C  band f r e q u e n c y from about 1210 t o 1195.  As t h e same type  of s h i f t i n f r e q u e n c y was observed i n t h i s e x p e r i m e n t , a 1:1  c o - o r d i n a t i o n between t h e s u r f a c e l e a d atom and the  x a n t h a t e r a d i c a l may be suggested on l e a d chromate As mentioned  surface.  b e f o r e , t h e f o r m a t i o n o f d i x a n t h o g e n can be  e x p l a i n e d i n terms o f t h e h i g h r e s t p o t e n t i a l o f l e a d chromate.  (Cf. Figure A - l . )  CONCLUSIONS In order to o b t a i n a b e t t e r understanding 'depressive a c t i o n o f chromate o r d i c h r o m a t e s a l t on some e x p e r i m e n t a l  work was  were c o n s i d e r e d .  The  of  the  galena,  performed and the thermodynamics  main r e s u l t s o b t a i n e d under the  c o n d i t i o n s employed i n t h i s study are as f o l l o w s : (1) Galena shows a b u f f e r a c t i o n i n an aqueous s o l u t i o n . However i n the absence of oxygen a t a l k a l i n e r a n g e , no s i g n i f i c a n t pH change was (2) The  observed.  a d s o r p t i o n amount of chromate on g a l e n a  almost constant  above pH 9 and  stays  i t increases  with  the i n c r e a s e i n d i c h r o m a t e c o n c e n t r a t i o n i n solution. (3) When g a l e n a  i s t r e a t e d w i t h chromate s a l t o r -dichro-  mate s a l t , l e a d chromate i s formed on the  galena  s u r f a c e as the main adsorbed s p e c i e s . (4) The  p o t e n t i a l - p H diagram o f P b - C r - S - ^ O  a t 25°C. was  constructed.  system  This i n d i c a t e s that  l e a d chromate i s a v e r y s t a b l e s u b s t a n c e whereas lead dichromate i s very  unstable.  (5) X a n t h a t e can adsorb on c h r o m a t e - t r e a t e d s u r f a c e and  galena  a l s o on l e a d chromate s u r f a c e .  65 (6) X a n t h a t e adsorbed on c h r o m a t e - t r e a t e d g a l e n a o r l e a d chromate appeared m o s t l y as d i x a n t h o g e n . (7) The d e s o r p t i o n o f chromate from g a l e n a s u r f a c e due to xanthate a d d i t i o n i s very s l i g h t . (8) The d e s o r p t i o n o f x a n t h a t e from g a l e n a s u r f a c e which i s c o v e r e d w i t h more t h a n a monolayer  thick-  ness o f x a n t h a t e , due t o chromate a d d i t i o n i s possible.  However  t h e desorbed amount o f x a n t h a t e  i n such a case i s o n l y 10-20% o f t h e amount o f chromate adsorbed. (9) When x a n t h a t e - t r e a t e d g a l e n a i s s u b j e c t e d t o d e s o r p t i o n t e s t by chromate,  i t i s found t h a t b o t h  x a n t h a t e i o n s and d i x a n t h o g e n were desorbed.  SUGGESTIONS FOR FUTURE WORK  I n t h i s s t u d y , when much x a n t h a t e was adsorbed on g a l e n a s u r f a c e , x a n t h a t e i o n s were desorbed by a d d i n g chromate s a l t .  However, i t may be v e r y h e l p -  f u l t o i n v e s t i g a t e the p o s s i b i l i t y of the desorption o f x a n t h a t e when t h e amount o f x a n t h a t e a d s o r p t i o n i s much l e s s .  F o r t h i s p u r p o s e , t o use x a n t h a t e  i n c l u d i n g r a d i o a c t i v e s u l f u r may be v e r y u s e f u l . The mechanism o f d e p r e s s i o n o f g a l e n a by chromate or dichromate  s a l t i s n o t c l e a r enough.  v e r y u s e f u l t o s t u d y more about  I t may be  galena-chromate-  x a n t h a t e system and t o i n v e s t i g a t e t h e r o l e o f dixanthogen i n t h i s  system.  REFERENCES  1.  Lowry, A. and Greenway, H.H., (1912).  2.  G l e m b o t s k i i , V.A., K l a s s e n , V . I . , and P l a k s i n , I.N., F l o t a t i o n , P r i m a r y S o u r c e s , New Y o r k , 49 9 (1963).  3.  P l a k s i n , I.N. and M y a s n i k o v a , G.A., ( 1 9 5 8 ) , 2.  4.  Bogdanov,.0.S. and Podnek, A.K., T r . Vses. N a u c h n . - I s s l e d . i . P r o e k t n . I n s t . Mekhan. O b t r a b o t k i P o l e z n . I s k o p . , No. 135, 54-62 (1965).  5.  G a u d i n , A.M., G l o v e r , H., Hansen, M.S., and O r r , C.W., U n i v . o f Utah and U.S. Bur. M i n e s , Tech. Paper No. 1 (1928).  6.  Wark, I.W. 189 .  7.  P l a k s i n , I.N. and M y a s n i k o v a , G.A., A120, ( 1 9 5 9 ) , 5-15.  8.  P l a k s i n , I.N. and M y a s n i k o v a , G . A. , Obogashchen. P o l e z n . Iskoraemykh, Akad. Nauk S.S.S.R., I n s t . Gorn. D e l a , ( 1 9 6 0 ) , 71-77.  9.  Bogdanov, O.S.  and Cox, A.B.,  A u s t r a l i a n P a t e n t 5065  Trans.  Tsvetnye M e t a l l y .  AIME, 112. (19 3 4 ) , Freiberger  Forschungsh.  and K a k o v s k i i , I.A., M e t a l l u r g i z d a t  (1955).  10.  P l a s k i n , I.N. and M y a s n i k o v a , G.A., S.S.S.R., 117, 864-6 (1957).  Doklady Akad. Nauk  11.  M i t r o f a n o v , S.I. and K u s h n i k o v a , V.G., No. 6 ( 1 9 6 4 ) , 15.  12.  Stepanov, B.A. and N a g i r n y a k , F . I . , T r . N a u c h n . - I s s l e d . i . P r o e k t n . I n s t . Uralmekhanobr., ( 1 9 6 1 ) , 31.  13.  M i t r o f a n o v , S.I. and K u s h n i k o v a , V.G., I z v . Akad. Nauk. S.S.S.R., Met. i . Gorn. D e l a , ( 1 9 6 4 ) , 167.  14.  M i t r o f a n o v , S.I. and K u s h n i k o v a , V.G., U.S.S.R. 155, 766, Aug. 13, 1863; A p p l . A p r . 28, 1962.  Tsvetn. Metally.  68 i.5.  Yamasaki, T. , S a s a k i , H., and Matsuoka, I . , Nippon Kogyo K a i s h i , 84 ( 1 9 6 8 ) , 338.  16.  Pomianowski, A n d r o z i j and Czuback-Pawlikowska, J . , Z e s z y t y Nauk. U n i v . J a g i e l . , S e r . Nauk. Mat. P r z y r o d . , Mat., F i z . , Chem. No. 4 ( 1 9 5 0 ) , 171.  17.  S o l o v ' e v a , L.R. and K h o k h l o v a , N.E., Obogashch. Rud. i . U g l e i , Akad. Nauk S.S.S.R., I n s t . Gorn. D e l a , ( 1 9 6 3 ) , 121.  18.  P o o l e , H.W.,  19.  Mamiya, M. and Majima, H., p r i v a t e  20.  L a t i m e r , W.M., O x i d a t i o n P o t e n t i a l s , P r e n t i c e - H a l l , Inc. Englewood C l i f f s , N.J., (1952).  21.  P o u r b a i x , M. and R y s s e l b e r g h e , P.V., C o r r o s i o n , 5, 313 (1950).  22.  H a g i h a r a , H., J o u r n a l o f P h y s i c a l C h e m i s t r y , 5 6 616 .  23.  L e j a , J . , L i t t l e , L.H., and P o l i n g , G.W., 414 .(1963 ) .  24.  E a d i n g t o n , P. and P r o s s e r , A.P., I n s t . M i n i n g and M e t a l l u r g y , T r a n s a c t i o n s . , 28, 74-82, (June 1969).  25.  S h e r r i t t Gordon Mines L t d . (By Frank A Forward and Andrew I . V i z s o l y i ) Can. 701, J a n . 5, 1965.  26.  Abramov, A.A., U.S. Bur. o f M i n e s , Rept. I n v e s t . No. 6816 (1966).  27.  S.C. Sun and G. P u r c e l l , M i n e r a l I n d . Penn. S t a t e U n i v . 2_9, No. 1 , 1-5 (1959 ).  28.  J.A. C a m p b e l l , S p e c t r o c h i m i c a A c t a , 1965, V o l . 2 1 , pp. 1333-1343.  29.  P o l i n g , G.W. and L e j a , J . , J . o f P h y s i c a l 6 2 , 2121 (1963). ;  30.  H a l p e r n , J . , Canad, J . Chem., 1956 , 34_; 1419.  31.  B r o d i e , J.B., The E l e c t r o c h e m i c a l D i s s o l u 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 o f B r i t i s h Columbia, 1968.  Eng. M i n i n g J . 1_24 ( 1 9 2 4 ) , 140. communication.  (1952),  I b i d . , 7J2  Chemistry,  F o s t e r , L.S., M i n e r a l and M e t a l l u r g i c a l R e s e a r c h T e c h n i c a l P a p e r , No. 2, U n i v e r s i t y o f U t a h , 1927. D e w i t t , C C , and Roper, E.E., 1932, 54, 445.  J . AM Chem. Soc.  A P P E N D I X  ELECTROCHEMICAL  STUDY  E l e c t r o c h e m i c a l Measurements on  Natural  G a l e n a Specimen  E l e c t r o c h e m i c a l measurements were made on n a t u r a l .galena specimens, mounted i n p l a s t i c and m e c h a n i c a l l y  pol-  i s h e d t o expose a measured s u r f a c e a r e a t o s o l u t i o n s , chromate, d i c h r o m a t e , and  1M HCIO^.  .because i t i s c o m p l e t e l y  T h i s a c i d , HCIO^, was  chosen  i o n i z e d a t t h i s d i l u t i o n and  p e r c h l o r a t e i o n i s v e r y s t a b l e and  does not  the  significantly  complex m e t a l c a t i o n s . P o l a r i z a t i o n s t u d i e s were performed w i t h a Beckman model TM30 E l e c t r o s c a n i n s t r u m e n t stat. calomel  A three-electrode  equipped w i t h a p o t e n t i o -  system was  used i n v o l v i n g a  e l e c t r o d e i n a L u g g i n c a p i l l a r y w i t h the  point  l o c a t e d v e r y c l o s e t o the specimen t o e l i m i n a t e as much as p o s s i b l e of the IR p o t e n t i a l drop i n the s o l u t i o n . p o t e n t i a l between the c a l o m e l c o n t r o l l e d and  e l e c t r o d e and  The  the specimen  was  c o u l d be scanned w i t h the p o t e n t i o s t a t , w h i l e  c u r r e n t passed o n l y between the specimen and an  auxiliary  electrode. The  s o l u t i o n was  by b u b b l i n g w i t h h e l i u m  u s u a l l y kept almost oxygen-free  i n a covered c e l l .  the c e l l c o u l d be passed t h r o u g h a gas  The  helium  from  t r a i n t o absorb  gases such as I^S, which are g i v e n o f f under c e r t a i n cond i t i o n s by the specimen.  The  normal k i n d of e x p e r i m e n t  71 "that was performed c o n s i s t e d o f d e t e r m i n i n g t i o n curve.  the p o l a r i z a -  The p o t e n t i a l between t h e specimen and t h e  r e f e r e n c e e l e c t r o d e was v a r i e d a t a s e l e c t e d scan r a t e and the c u r r e n t was r e c o r d e d . anodic  T h i s curve  c o u l d be d i v i d e d i n t o  and c a t h o d i c r e g i o n s c o r r e s p o n d i n g  t o the d i r e c t i o n  ;of c u r r e n t i n t h e specimen, and t h e p o t e n t i a l d i v i d i n g t h e a n o d i c and c a t h o d i c r e g i o n s i s known as t h e " r e s t "  potential  o f t h e specimen. The  r e s t p o t e n t i a l o f g a l e n a e l e c t r o d e was measured  i n a chromate s o l u t i o n a t pH 10.8, as chromate i o n i n a s o l u t i o n . A-l.  where chromate s a l t  stays  The r e s u l t i s shown i n F i g u r e  I t i n c r e a s e d by a d d i n g chromate s a l t and s t a y e d  almost  _3  constant  a t c o n c e n t r a t i o n 1.0 x 10  M/L.  I t may be s a i d t h a t t h e r e s t p o t e n t i a l w h i l e l e a d chromate i s formed on g a l e n a  increases  specimen.  F i g u r e A-2 shows pH dependence o f t h e r e s t  potential  _3  o f g a l e n a e l e c t r o d e i n 1.0 x 10 As  M/L chromate  solution.  seen from t h e f i g u r e , pH dependence i n a c i d i c r e g i o n i s  d i f f e r e n t from t h a t i n a l k a l i n e r e g i o n . An i n c l i n a t i o n i n a c i d i c r e g i o n was 46mV/pH and i n a l k a l i n e r e g i o n 66my/pH. _3  When 1.0 x 10  M/L  l^C^O,., s o l u t i o n was u s e d , an i n c l i n -  a t i o n was 46mV/pH i n a l k a l i n e and 7 0mV/pH i n a l k a l i n e solution. These r e s u l t s i n d i c a t e t h a t t h e r a t i o H /e +  4/5 i n a c i d i c r e g i o n and 9/8 i n a l k a l i n e r e g i o n .  is  However  i t must be emphasized t h a t t h e r e s t p o t e n t i a l o f g a l e n a e l e c t r o d e i n aqueous s o l u t i o n s o f v a r i o u s pH v a l u e s changes.  also  72  F i g u r e A-4 shows a example o f a n o d i c  polarization  ..vcurves o f g a l e n a e l e c t r o d e i n v a r i o u s s o l u t i o n s .  The  ^ p o l a r i z a t i o n curve o f g a l e n a e l e c t r o d e i n 1M HCIO^ was s t u d i e d by B r o d i e [ 3 1 ] .  When chromate  or  dichromate s a l t  added, t h e c u r r e n t d e n s i t y was s u p p r e s s e d  was  significantly.  T h i s may i n d i c a t e t h e f o r m a t i o n o f p a s s i v e f i l m on g a l e n a surface. galena  F i g u r e A-5 shows c a t h o d i c p o l a r i z a t i o n curve o f  electrode.  120  L  i  i  • 0  •  4  .8  i  i  i  ,1  12  16  CONCENTRATION o f K C r 0 , 2  Figure A - l  4  (lO  - 4  i  i  20  24  M/L)  E f f e c t of the Concentration of Potassium Chromate on-the Rest P o t e n t i a l o f Galena Electrode . ( I n i t i a l pH o f t h e S o l u t i o n : 10.8)  76  0.  0.2  0.4  0.6 Eh  F i g u r e A-4  0.8  1.0  1.2  (Volt)  A n o d i c P o l a r i z a t i o n Curves f o r Galena E l e c t r o d e in (a) IM HC10„ (b) 4.0 x 10 M/L K C r C \ (pH 10.0) (c) 4.0 5 I O " M/L K Cr^ (pH 2.9) scan r a t e 2.8 mV/sec. He'bubbled 4  2  4  2  7  -0.6  -0.4  ' •0  -0.2  0.2  0.4  Eh (v) C a t h o d i c P o l a r i z a t i o n Curves f o r Galena E l e c t r o d e in (a) 1M HClOh (b) 4.0 x I O " M/L K CrOLi (pH 10.0) ( c ) 4-.0 x I O - M/L K Cr 0 (pH 2 . 9 ) scan r a t e ' '2.8 mV/sec. He b u b b l e d 4  2  4  2  2  7  

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