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Kinetics of the dissolution of copper in aqueous aliphatic amines, and catalytic reduction of nickel.. Sircar, Sisir Coomar 1959

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KINETICS OF THE DISSOLUTION OF COPPER IN AQUEOUS ALIPHATIC AMINES  And  CATALYTIC REDUCTION OF NICKEL ION BY MOLECULAR HYDROGEN  by  SISIR COOMAR SIRCAR  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE  REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  i n t h e Department of MINING AND METALLURGY  We a c c e p t t h i s t h e s i s a s conforming  t o the  standard required from candidates f o r t h e degree o f MASTER OF  SCIENCE.  Members o f t h e Department o f M i n i n g and M e t a l l u r g y .  THE  UNIVERSITY OF BRITISH COLUMBIA May  1959  ABSTRACT  K i n e t i c s o f t h e D i s s o l u t i o n o f Copper i n Aqueous A l i p h a t i c Amines.  An i n v e s t i g a t i o n was made o f t h e d i s s o l u t i o n o f c o p p e r m e t a l i n aqueous s o l u t i o n s o f m e t h y l , e t h y l and n - b u t y l amine and aranonia, as w e l l as i n s o l u t i o n s o f t h e i r aminium and ammonium i o n s , under oxygen pressure.  S t u d y o f t h e k i n e t i c s o f t h e d i s s o l u t i o n was c a r r i e d out o v e r a  wide range o f c o n c e n t r a t i o n s .  I t was observed t h a t  o f oxygen p r e s s u r e dependency o f t h e r a t e .  t h e r e a r e two r e g i o n s  The range o f oxygen p r e s s u r e ,  where r a t e i s independent o f oxygen p r e s s u r e , was i n v e s t i g a t e d  The r a t e p r o c e s s has been e s t a b l i s h e d  kjJAV 1  L  i n detail.  t o obey t h e r e l a t i o n  J  .  f o r a l l t h e systems s t u d i e d .  A mechanism f o r t h e d i s s o l u t i o n r e a c t i o n has been p r o p o s e d .  ABSTRACT  C a t a l y t i c R e d u c t i o n of N i c k e l Ion b y M o l e c u l a r Hydrogen.  The r a t e o f p r e c i p i t a t i o n o f n i c k e l from s a l t by m o l e c u l a r hydrogen  solution  i n t h e p r e s e n c e o f c a t a l y s t has been i n v e s t i -  g a t e d o v e r a wide range o f c o n c e n t r a t i o n s . The v a r i a b l e s  studied  are c o n c e n t r a t i o n o f n i c k e l , hydrogen p r e s s u r e , amount o f c a t a l y s t , c o n c e n t r a t i o n of- hydrogen  i o n and t e m p e r a t u r e .  The r a t e o f r e d u c t i o n  i s found t o obey an e q u a t i o n o f t h e form:  dt The a c t i v a t i o n energy i s f o u n d t o be 25*2 k c a l / m o l .  The Ni° + 2 H  +  equilibrium constant k f o r the r e a c t i o n N i  i s found t o be  4.65  x  10"  6  atm"  1  at  140°C.  + +  +  H  2  In the  presenting  requirements  this for  of  British  it  freely available  agree for  that  Columbia,  copying  gain  shall  by or  not  of  M  l  n  n  g  and  study,  I  extensive  copying  be. g r a n t e d  n  d  of  this  without  my  Notallurgy  The U n i v e r s i t y of B r i t i s h V a n c o u v e r S, Canada.  Columbia,  by  of  the  It  thesis  is  make  further this  Head  of  thesis my  understood  for  written  of  University  reference  representatives.  a  the  shall  allowed  l  at  Library  publication be  degree  fulfilment  the  for  his  partial  that  p u r p o s e s , may  or  that  Department  for  in  advanced  I agree  permission  scholarly  Department  an  thesis  financial  permission.  TABLE OF CONTENTS  K i n e t i c s o f t h e D i s s o l u t i o n o f Copper i n Aqueous A l i p h a t i c Amines.  Page INTRODUCTION  1  Scope o f Present Work  3  EXPERIMENTAL Preparation  6 o f Copper Sample  6  Apparatus  6  Temperature C o n t r o l  8  C h e m i c a l Reagents  6  A n a l y t i c a l Procedure  9  E x p e r i m e n t a l Procedure Preliminary Results  11 •  RESULTS AND DISCUSSION  11 16  F r e e Amines  16  E f f e c t of Acid  2k  Ammonia  31  R e a c t i o n Mechanism  31  REFERENCES  39  :  APPENDIX I  67  D a t a P e r t a i n i n g t o t h e D i s s o l u t i o n o f Copper by Aqueous A l i p h a t i c Amines  67  C a t a l y t i c R e d u c t i o n o f N i c k e l I o n by M o l e c u l a r Hydrogen kO  INTRODUCTION  k2  Scope o f t h e Work EXPERIMENTAL  43  Catalyst Reagents .  ^ •  3  k3  Table of Contents (cont»d.)  Analysis  Page  .  Experimental Procedure  ..  45  . . . . . . . . . .  45  Preliminary Experiments RESULTS AMD  • .  DISCUSSION  .  47 52  (a)  Dependence of the r a t e on n i c k e l concentration  .....  (b)  E f f e c t of the amount of catalyst  52  (c)  E f f e c t of hydrogen pressure  57  (d)  Dependence of the rate on hydrogen i o n concentration  (e)  Temperature dependence  .  Use of Equilibrium N i c k e l Concentration  52  • .  57  •  57  f o r C a l c u l a t i o n of 61  the Thermodynamic Equilibrium Constant REFERENCES  66  APPENDIX II  73  Data Pertaining t o the Reduction of N i c k e l Ion Molecular  Hydrogen  by 73  •FIGURES  Kinetics of the Dissolution of Copper in Aqueous Allphatio Amines, No, 1,  Page ,  *.•.,  7  2, Calibration curve for copper analysis  •  10  3, Typical curve for the dissolution of copper  .  12  Schematic diagram  of the autoclave  4, Pressure dependence plot for ethyl amine  14  5, Pressure dependence plot for n-butyl amine  15  6, Typical family of rate curves for methyl amine  17  t  7, Plot of rate vs concentration for methyl amine  18  8, Plot of rate vs concentration for ethyl amine 9, Plot of rate vs concentration for n-butyl amine  19 ,,,,,,,  20  10. Plot of QAJ /R VS [A] for methyl amine  21  11.  22  Plot of [ A ]  2  / R VS  12, . Plot of [ A ] 13,  2  CA] for ethyl amine  / R VS [A]  for n-butyl amine  ,  23  Plot of rate vs concentration of methyl amine at constant pH ,  25  14,. Relation between the rate and methyl aminiura ion concentration,  27  3.5, Relation between the rate and ethyl aminlum ion concentration ,  28  3.6, Relation between the rate and n-butyl aminium ion concentration 17,  Plot of £ A ]  2  ..  / R VS [[A]  ..,,.,,,,*»  for methyl amine at constant pH  ,.,.  18• Plot of rate vs concentration of ammonia 19.  Plot of [ A ]  30 32  ,,,,.  33  20, Relation between the rate and ammonium ion concentration , , ,  34  2  / R VS [A]  for ammonia  29  FIGURES  Catalytic Reduction of Nickel Ion by Molecular Hydrogen, No. 1.  Page Schematic diagram of arrangements for holding catalyst and f i l t e r i n g under pressure  ..........  44  2.  Calibration  curve for the determination of nickel  . . . . . . .  3.  Typical plot showing two types of rate curves  4.  Typical family of rate curves  5.  Effect of i n i t i a l concentration on the i n i t i a l rate  6.  Plot of log ( i n i t i a l rate) vs log ( i n i t i a l concentration)  7.  Effect of amount of catalyst on the i n i t i a l rate  8.  Effect of hydrogen pressure on the i n i t i a l rate  . . . . . . . .  56  9.  Effect of i n i t i a l hydrogen ion concentration on the i n i t i a l rate.  58  10,  Plot of log ( i n i t i a l rate) vs reciprocal of temperature  ....  59  11,  A plot showing approach to equilibrium concentration from ....  60  50 . , . . . . . .  51 53 54 55  Plot of equilibrium nickel concentration vs reciprocal of hydrogen pressure  13,  ... . .  "dissolution and reduction of nickel 12,  46  .....  62  Plot of equilibrium nickel concentration vs square of f i n a l hydrogen ion concentration  63  TABLES  Kinetics  of the D i s s o l u t i o n  Aqueous A l i p h a t i c  o f Copper i n  Amines.  No.  Page  1,  A c i d d i s s o c i a t i o n c o n s t a n t s f o r aminium i o n  2,  V a l u e s of t h e c o n s t a n t s k^ and k studied.  2  . . . . . . . . .  4  i n E q u a t i o n 1 f o r t h e amines  . . . . . . . . . . .  .*  24  3,  Values obtained f o r k  4,  Values o f c o n s t a n t s f o r ammonia  31  5,  S e l e c t e d values o f constants  36  3  ,  26  ACKNOWLEDGEMENTS  The author i s grateful t o the National Research Council f o r the f i n a n c i a l aid which enabled t h i s project to be carried out. The author i s g r a t e f u l t o the members of the Department of Mining and Metallurgy f o r t h e i r assistance, and i s e s p e c i a l l y g r a t e f u l to Dr. D.R. Wiles, under whose guidance and supervision t h i s work has been c a r r i e d out. The author takes pleasure i n expressing gratitude to Dr. W.C. L i n f o r suggesting the part of work on the reduction of n i c k e l , and taking i n t e r e s t i n the problem. are g r a t e f u l l y acknowledged.  Suggestions made by Mr. I.H. Warren  KINETICS OF THE DISSOLUTION OF COPPER IN AQUEOUS ALIPHATIC AMINES,  INTRODUCTION  The  c o r r o s i o n o f m e t a l s has a t t r a c t e d t h e a t t e n t i o n o f s c i e n t i f i c  i n v e s t i g a t o r s f o r o v e r a hundred y e a r s .  The main e f f o r t and i n t e r e s t i n  t h i s problem, however, have been d i r e c t e d towards p r e v e n t i o n o f c o r r o s i o n . In the p a s t few decades, t h e a t t e n t i o n o f i n v e s t i g a t o r s has been f o c u s s e d ^ more on t h e n a t u r e and causes o f c o r r o s i o n  processes.  Up t o t h e p r e s e n t t i m e ,  however, d e t a i l e d u n d e r s t a n d i n g o f t h e k i n e t i c p r o c e s s i n v o l v e d has  been g a i n e d i n o n l y a v e r y few  instances,  2 3  ix  i n corrosion  5  Among t h e systems which have been s t u d i e d w i t h a view t o d e t e r m i n i n g the  k i n e t i c a s p e c t s o f t h e c o r r o s i o n p r o c e s s , t h e d i s s o l u t i o n o f copper has  been t h e most t h o r o u g h l y  investigated,  Yamasaki^ was one o f t h e f i r s t t o s t u d y t h e problem o f d i s s o l u t i o n o f copper i n ammonia s o l u t i o n i n t h e presence o f p u r i f i e d a i r . the d i s s o l u t i o n r a t e t o be independent of t h e c o n c e n t r a t i o n  He observed  o f ammonia.  He  concluded ^moreover, t h a t t h e d i s s o l u t i o n p r o c e s s i s a u t o c a t a l y t i c , t h e c u p r i c ammonia complex a c t i n g as c a t a l y s t .  From s t u d i e s  o f t h e d i s s o l u t i o n o f copper i n ammonium compounds,  Z a r e t s k i i and Akimov'' concluded t h a t t h r e e important s t e p s a r e i n v o l v e d i n the d i s s o l u t i o n process.  The s t e p s a r e ( i ) e l e c t r o c h e m i c a l  copper w i t h f o r m a t i o n o f cuprous ammonia,(ii) o x i d a t i o n the  c u p r i c ammonia complex and ( i i i ) e l e c t r o c h e m i c a l  ammonia complex a t t h e m e t a l  surface.  dissolution of  of t h i s species t o  reduction  of the cupric  - 2 More recent work of Lane and McDonald  8  on d i s s o l u t i o n of copper i n  ammonia solution led them to believe that no autocatalytic e f f e c t i s present and that the d i s s o l u t i o n rate i s i n f a c t dependent on the concentration o f ammonia. A l l of these investigators have observed that the rate of d i s s o l u t i o n i s strongly dependent on the s t i r r i n g r a t e . A detailed study of d i s s o l u t i o n of copper i n ammonia and i n o mixtures of ammonia and ammonium ion has been made by Halpern,  7  He found  two regions i n the dependence of rate o f d i s s o l u t i o n of copper on the oxygen pressure.  In the range of low oxygen pressure, he observed that the r a t e of  d i s s o l u t i o n of copper i s dependent on the oxygen pressure and that the rate of d i s s o l u t i o n i s independent of oxygen pressure at higher pressure. a c t i v a t i o n energies found by him f o r the oxygen pressure oxygen pressure independent rate are 1.33  and 5.54  The  dependent rate and  kcal/mol r e s p e c t i v e l y .  From the low activation energy f o r rates at low oxygen pressure, he concluded that the rate c o n t r o l l i n g step i s a p h y s i c a l process, oxygen from the bulk of solution to the metal surface. energy for the oxygen pressure  independent rate  such as d i f f u s i o n of The higher a c t i v a t i o n  has been taken as i n d i c a t i n g  that some chemical step i s involved i n the rate c o n t r o l l i n g process.  From his  work i n the region of chemically-controlled rate, he has proposed the following mechanism: 1.  Adsorption of dissolved oxygen on the  surface.  fast Cu + 1/2 0  2.  2  * Cn - 0  Reaction of ammonia or ammonium ion with, the copper-oxygen complex  - 3 on t h e s u r f a c e , f o l l o w e d  by d e s o r p t i o n slow  Cu - 0 + NH  ->  3  or  ^NH  Studies  fast  3  Cu ^ +  on t h e  -+ i,Cu  +  ++  + KOH  -*  Product  r a t e , to e l u c i d a t e t h e the s t a b i l i t y constants another.  Due  + 0H  fast -»  Product  i n the  +  range of  k i n e t i c process f u r t h e r . of  to the  chelate  His  complexes and  chelating  chemically-controlled studies indicated that  d i s s o l u t i o n r a t e are  related  s m a l l number of systems s t u d i e d , the exact  l a t i o n o f c o m p l e x i t y constants mechanism of t h e  H  k i n e t i c s of t h e d i s s o l u t i o n o f copper by  agents were c a r r i e d out by M i l a n t s , ^  The  complex  r  Cu - 0 + NH^  t o one  o f the  and  d i s s o l u t i o n r a t e s has  k i n e t i c p r o c e s s was  corre-  not been e s t a b l i s h e d .  found t o be analogous t o t h a t  of  ammonia.  Scope o f Present Work  I n the l i g h t  of the  by c h e l a t i n g agents, i t was the  attack of the  r e s u l t s obtained  considered  copper s u r f a c e by n o n - c h e l a t i n g  work to l o o k f o r p o s s i b l e d i f f e r e n c e s i n the case of ammonia and  aliphatic  copper  w o r t h w h i l e t o s t u d y the k i n e t i c s o f  a l i p h a t i c amines, t o e l u c i d a t e the mechanism.  The  f o r d i s s o l u t i o n of  agents, such as  I t was  the  a l s o a purpose o f  k i n e t i c processes involved  be c o n t r o l l e d by one  more o f s e v e r a l p h y s i c a l o r c h e m i c a l p r o c e s s e s ( a d s o r p t i o n o f gaseous of d i s s o l v e d reactants  s u r f a c e , r e a c t i o n on the s u r f a c e , and present  work was  in  amines.  r a t e o f a heterogeneous r e a c t i o n may  i n solution, transport  this  from b u l k o f s o l u t i o n t o  desorption  of r e a c t i o n p r o d u c t ) .  planned p r i m a r i l y t o f i n d out the  chemical processes  or reactant the The  involved  i n t h e d i s s o l u t i o n o f copper b y a l i p h a t i c amines.  agents used i n t h i s work were m e t h y l ,  Present  The complexing  e t h y l , and n - b u t y l amines, and ammonia.  knowledge o f t h e nature  o f t h e complexes formed i n aqueous  s o l u t i o n between a l k y l amines and copper i o n i s not w e l l advanced. i s known t o form s e v e r a l d i f f e r e n t amine complexes w i t h copper,^"  Ammonia and 12  indications  f o r complex f o r m a t i o n w i t h a l k y l amines have been n o t e d .  The  constants f o r t h e d i s s o c i a t i o n RNH K  where  xi  + 3  =  M  RNH  2  + H+  faNHj]  R = H, o r an a l k y l group,  are g i v e n i n Table I .  i  Table I ' A c i d d i s s o c i a t i o n c o n s t a n t s f o r aminium  ions.  K (M)  The  Ammonia  5.68  x 10"°  (13)  M e t h y l amine  2.30  x IO  - 9  (14)  E t h y l amine  1.80  x 10  - 9  (14)  n - B u t y l amine  2.L6 x 1 0 "  9  (14)  o r d e r o f s t a b i l i t y o f copper complexes may be c l o s e l y r e l a t e d t o t h e  s t a b i l i t y of t h e R N H  + 3  species.  S i n c e t h e main aim o f t h e p r e s e n t work was t h e s t u d y o f t h e chemical aspects o f the r e a c t i o n , t h e v a r i a b l e s of  studied  were  concentration  r e a c t a n t s (amine and aminium i o n c o n c e n t r a t i o n ) and hydrogen i o n concen-  tration  .  Some o b s e r v a t i o n s were made o f t h e e f f e c t o f v a r i a t i o n o f oxygen  p r e s s u r e i n o r d e r t o ensure t h a t t h e experiments were not c a r r i e d out i n t h e range of oxygen p r e s s u r e where d i f f u s i o n o f oxygen i s r a t e  controlling.  - 6EXPERIMENTAL  P r e p a r a t i o n of t h e Copper Sample.  In t h i s work were used t h e same copper specimens Milants.^  as were used by  These specimens were p r e p a r e d f r o m c o n d u c t i v i t y copper, by  m e l t i n g and c a s t i n g i n a s p e c t r o s c o p i c g r a p h i t e c r u c i b l e and g r a i n by c o l d w o r k i n g and a n n e a l i n g . l e a v i n g one exposed  refined  F i n a l l y t h e y were mounted i n b a k e l i t e  f a c e whose s u r f a c e a r e a was about 2 cm. .  The p u r i t y ( i n t h i s c a s e  99.99$)  by M i l a n t s not to i n f l u e n c e the r a t e . used i n t h i s work was 0.12  mm.  and the. g r a i n s i z e were found  The average g r a i n s i z e o f t h e specimen  (A.S.T.M. n o n f e r r o u s g r a i n  size standard).  Before e a c h experiment, t h e specimen was p o l i s h e d w i t h 4/0  emery  paper, and was l i g h t l y e t c h e d w i t h a sodium p e r s u l p h a t e ammonia m i x t u r e . The g e o m e t r i c a r e a o f t h e exposed  s u r f a c e was measured by means o f a  microscope w i t h a c a l i b r a t e d eye p i e c e  ( c a l i b r a t e d t o 0.01  was computed f r o m t h e mean o f s e v e r a l measurements.  mm.).  The a r e a  In p r a c t i c e , the  specimens were always etched j u s t b e f o r e t h e experiment, and when not i n use, were s t o r e d i n a d e s i c c a t o r .  Apparatus.  The experiments were c a r r i e d out i n an a u t o c l a v e , shown i n F i g u r e 1, d e s i g n e d f o r w o r k i n g a t p r e s s u r e s up t o S atmospheres. c l a v e was made from 316  stainless steel.  The a u t o -  A t i t a n i u m l i n e r was used t o  c o n t a i n t h e s o l u t i o n t o a v o i d c o r r o s i o n of t h e s t e e l  by the r e a g e n t s used.  The b a k e l i t e - m o u n t e d copper specimen was h e l d i n p l a c e by means o f a s t a i n l e s s s t e e l r o d , t h i s b e i n g screwed i n t o t h e l i d o f t h e a u t o c l a v e .  H  A B C D E  = = = = =  shaft thermoregulator w e l l cooling c o i l sampling tube copper sample  F i g . 1,  F G H I J  = = = = =  impeller pump relay heater thermostat  Schematic diagram o f t h e a u t o c l a v e and temperature c o n t r o l system.  - 8 -  A g i t a t i o n was p r o v i d e d by a double t u r b i n e - t y p e swept a c y l i n d r i c a l volume 8 cm. i n d i a m e t e r . a l l t h e experiments.  i m p e l l e r which  I t was d r i v e n a t 750 RPM f o r  I t was f o u n d ^ t h a t under t h e e x p e r i m e n t a l  used, t h e s t i r r i n g r a t e had no e f f e c t  Oxygen, o b t a i n e d  conditions  on t h e r a t e o f d i s s o l u t i o n o f copper.  from Canadian L i q u i d A i r Company, was s u p p l i e d  t o t h e a u t o c l a v e from a c y l i n d e r through a p r e s s u r e - r e g u l a t i n g gauge. a d d i t i o n a l pressure the  An  gauge was mounted on t h e oxygen s u p p l y l i n e t o check  pressure.  Temperature C o n t r o l .  The  temperature o f t h e r e a c t i o n s o l u t i o n was h e l d a t 25-0.1°C  by f o r c i n g c o n t r o l l e d - t e m p e r a t u r e into the autoclave.  water through a s t a i n l e s s s t e e l c o i l  fitted  The temperature o f t h e c i r c u l a t i n g water was c o n t r o l l e d  by a m e r c u r y - c o n t a c t t h e r m o r e g u l a t o r .  The water c i r c u l a t i o n was  maintained  w i t h t h e h e l p o f a c e n t r i f u g a l pump.  C h e m i c a l Reagents.  The m e t h y l , e t h y l and n - b u t y l amines as w e l l as t h e carbamate were Eastman Kodak white l a b e l grade.  Ammonia and sodium hydroxides  c h e m i c a l l y pure q u a l i t y s u p p l i e d by N i c h o l s Chemical Company. reagent  were  Anhydrous  grade sodium p e r c h l o r a t e was s u p p l i e d by t h e G. F r e d e r i c k Smith  Chemical Company.  The  experimental  s o l u t i o n s were prepared  known s t r e n g t h t o t h e r e q u i r e d c o n c e n t r a t i o n . by t i t r a t i o n  a g a i n s t standard  by d i l u t i n g s o l u t i o n s o f  A l l t h e s o l u t i o n s were checked  s u l p h u r i c a c i d t o t h e m e t h y l - r e d end p o i n t .  In  9 o r d e r t o a v o i d changes i n t h e s a l t  e f f e c t a t low c o n c e n t r a t i o n s ,  mol/1. o f sodium p e r c h l o r a t e was added t o a u t o c l a v e  solution.  0.1 o r 0.2  The volume o f  - 9 the  s o l u t i o n was  s h o w n ^ t o have no e f f e c t  on the  rate of d i s s o l u t i o n .  A n a l y t i c a l Procedure.  D e t e r m i n a t i o n o f copper was yellow chelate  compound  formed by  done c o l o r i m e t r i c a l l y by means of  sodium d i e t h y l t h i o c a r b a m a t e .  has been d e s c r i b e d by s e v e r a l a u t h o r s ^ > ^ » - ^ authors t h a t the  s t a b i l i t y o f the  a f f e c t e d by d a y l i g h t .  the  T h i s method  I t has been r e p o r t e d by  these  c o l l o i d a l copper carbamate complex i s  To a v o i d t h i s e f f e c t , gum  a r a b l e was  added t o  stabilise  17 the  colour.  way:  0*2  The  gms.  carbamate-gum a r a b i c s o l u t i o n was  of carbamate was  t h i s s o l u t i o n was  d i s s o l v e d i n 200 m l of d i s t i l l e d water  s u b s e q u e n t l y added t o 500 ml o f 1% gum  r e s u l t a n t s o l u t i o n was was  d i l u t e d t o 1000  f i n a l l y f i l t e r e d i n t h e dark and  a n a l y t i c a l work was  the chelate  done i n an  t o 9.2.  ml and  1 ml o f t o l u e n e was  The  stability  added  to  9.0  by a d d i t i o n of 1:1  mate s o l u t i o n was 50 m l .  I t was  perchloric acid.  added, and t h e m i x t u r e was  mixed c a r e f u l l y and  the  To  an  the pH was  adjusted  Then 10 ml of  d i l u t e d i n a volumetric  i t s o p t i c a l d e n s i t y was  The  f l a s k to  determined w i t h  s o l u t i o n s were found t o obey Beer's law over a  range of c o n c e n t r a t i o n f o r convenient a n a l y s i s . g i v e n i n F i g u r e 2. t o w i t h i n *0.5%. :  The  I t was  The  to  carba-  Beckman model-Dk2 r a t i o - r e c o r d i n g spectrophotometer, at a wave l e n g t h o f millimicrons.  9»0.  5 ml o f 20% ammonium c i t r a t e  complex a c c i d e n t a l t r a c e s o f i r o n and ammonia o r 1:1  of  were c a r r i e d out at pH  Samples f o r a n a l y s i s were p r e p a r e d i n the f o l l o w i n g way:  was  It  A l l the  t o be independent of pH o n l y w i t h i n  a l i q u o t o f the sample t a k e n from the a u t o c l a v e ,  The  added.  s t o r e d i n a c o l d , dark p l a c e .  For t h i s r e a s o n , a l l a n a l y s e s  and  arabic solution.  a r t i f i c i a l l y l i g h t e d room. 17  complex i s r e p o r t e d  range o f 7.5  p r e p a r e d i n the f o l l o w i n g  a 437  sufficient  c a l i b r a t i o n curve i s  r e s u l t s from t h i s method were found t o be  reproducible  a l s o observed t h a t t h e p r e s e n c e of t h e amines used  - 10 -  Copper concentration (mg/l). Calibration ?urve for analysis of copper.  - 11 -  i n t h i s work does not have any e f f e c t on t h e o p t i c a l d e n s i t y .  Experimental Procedure.  The procedure used f o r measuring t h e r a t e o f d i s s o l u t i o n o f copper i n d i f f e r e n t s o l u t i o n s was  as f o l l o w s :  The a u t o c l a v e was  first  charged w i t h  t h e d e s i r e d s o l u t i o n and, w i t h the copper sample i n p l a c e , the s o l u t i o n a l l o w e d t o s t a n d under a n i t r o g e n atmosphere was  reached.  Then the a u t o c l a v e was  u n t i l the r e q u i r e d  temperature  f l u s h e d several t i m e s v e r y q u i c k l y w i t h  oxygen and t h e oxygen p r e s s u r e r a i s e d t o t h e f i n a l d e s i r e d v a l u e . was  t a k e n as z e r o t i m e .  was  This  last  To f o l l o w t h e course o f t h e r e a c t i o n , measured  volumes o f s o l u t i o n were removed from t h e a u t o c l a v e by means of a sampling t u b e , at v a r i o u s time i n t e r v a l s .  These samples were a n a l y s e d f o r copper.  U s i n g t h e s e r e s u l t s , t h e known s u r f a c e a r e a of t h e copper and the volume o f the s o l u t i o n at t h e time cf sampling, the t o t a l amount o f copper d i s s o l v e d p e r u n i t a r e a f o r each sampling time was l a s t e d about 75 m i n u t e s . d i s s o l v e d was  computed.  The experiments  usually  I n a t y p i c a l experiment, the amount of copper  u s u a l l y between 0,5  and 2.0  x 10~^ mol/1.  This i s too s m a l l a  q u a n t i t y t o cause any s i g n i f i c a n t decrease i n t h e c o n c e n t r a t i o n of the complexing a g e n t s .  Preliminary Results.  I n a s e r i e s o f p r e l i m i n a r y e x p e r i m e n t s , i t was ( i ) the nature o f t h e r a t e p l o t s , and  hoped t o determine  ( i i ) t h e n a t u r e o f t h e dependence o f  t h e r a t e on the oxygen p r e s s u r e .  A t y p i c a l r a t e p l o t i s shown i n F i g u r e 3.  The  l i n e a r form o f  9 this  plot  i s i n agreement w i t h the f i n d i n g s o f H a l p e r n  10 and M i l a n t s  i n d i c a t e s t h a t t h e r e a c t i o n i s o f zero o r d e r i n d i s s o l v e d copper.  and  I t was  - 12 -  •»  !  1  1  •  ,  r  Time (minutes) Conditions:  F i g . 3,  0.801 (M) methyl amine; s t i r r i n g rate 750 RPMj Temperature 25°Cj NaClO^ 0.1 M; oxygen pressure 7.9 atm. T y p i c a l curve f o r the d i s s o l u t i o n of copper.  - 13  found t h a t t h e r a t e s , as determined reproducible to b e t t e r than  from t h e s l o p e of t h e r a t e p l o t s , were  *2%,  if)  q E a r l i e r work ' 7  -  showed t h a t f o r t h e r a t e of d i s s o l u t i o n ,  e x i s t s two s e p a r a t e r e g i o n s o f p r e s s u r e dependence.  there  In t h e low p r e s s u r e r e g i o n ,  t h e r a t e i s p r o p o r t i o n a l t o the p r e s s u r e o f oxygen, w h i l e a t h i g h p r e s s u r e , the r a t e i s independent o f oxygen p r e s s u r e . i n t h i s work and shown i n F i g u r e s 4 and  R e s u l t s o f experiments performed  5 show c o n f o r m i t y w i t h those  of  9 previous observations.  T h i s type o f behaviour  has  bean shown  t o be  the  r e s u l t o f a t r a n s i t i o n f r o m d i f f u s i o n c o n t r o l t o c o n t r o l by the r e a c t i o n on  the  surface. S i n c e i n the p r e s e n t work, the main aim was  t o s t u d y the  a t t a c k on t h e copper s u r f a c e , a l l experiments were c a r r i e d out a t h i g h p r e s s u r e s o f oxygen t o e l i m i n a t e d i f f u s i o n  control.  chemical  sufficiently  - 14 -  F i g . 4«  P r e s s u r e dependence c u r v e . f o r  e t h y l amine.  \  - 15 -  P r e s s u r e o f oxygen (atm.) Conditions; F i g . 5»  Temp. 25°C; s t i r r i n g r a t e 750 RPM; NaClO* O.IM.  P r e s s u r e dependence curve f o r b u t y l amine.  - 16 -  RESULTS AND DISCUSSION  Free  Amines  The v a l u e s o f t h e r a t e s measured f o r m e t h y l , e t h y l and n - b u t y l amines a r e g i v e n i n Table IA, I I A and I I I A i n t h e Appendix. of  r a t e curves  i s g i v e n f o r m e t h y l amine i n F i g u r e  The r e l a t i o n between t h e r a t e and the  A typical family  6.  amine c o n c e n t r a t i o n i s g i v e n  i n F i g u r e s 7, 8, and 9, f o r m e t h y l , e t h y l and n - b u t y l amines r e s p e c t i v e l y . The s i m i l a r i t y among t h e s e  curves i s q u i t e e v i d e n t .  i n d i c a t e s a r a t e dependence a p p r o x i m a t e l y t i o n and approaching suggests  first  The form o f t h e s e  second-order a t low amine  order at higher concentration.  This  t h a t some a d s o r p t i o n p r e - e q u i l i b r i u m may be important  the r e a c t i o n r a t e .  curves  concentra-  behaviour i n controlling  I t was found t h a t t h e d a t a can be b e s t f i t t e d  by an  e x p r e s s i o n o f t h e form  [cu ] ++  d  -  R  =  dt  k  l^.-(k LA3)  (1)  2  k$'J+ 1  where R stands f o r r a t e o f d i s s o l u t i o n , tAjstands f o r c o n c e n t r a t i o n o f amines and  k]_ and k  Equation  2  a r e c o n s t a n t s , t h e s i g n i f i c a n c e o f w h i c h w i l l be d i s c u s s e d  ( l ) can a l s o be e x p r e s s e d  [£= W R  k  i n t h e form  +  2  j  i n F i g u r e s 10, 11, and 1 2 t h a t E q u a t i o n 2  ( )  _ k^  2  2  from w h i c h i t i s p o s s i b l e t o e v a l u a t e t h e c o n s t a n t s  values of k  later,  and k . 2  I t i s seen  (2) f i t s t h e data q u i t e w e l l .  The  f o r t h e t h r e e amines were e v a l u a t e d from the s l o p e s o f l i n e a r  p o r t i o n o f t h e curves 7, 8 and 9, and f r o m t h e s l o p e s o f t h e l i n e a r p l o t s o f Equation  ( 2 ) .  The constant  k i was e v a l u a t e d  i n e a c h case from t h e i n t e r c e p t  - 17 -  28  24  20  g  Cone, o f m e t h y l amine  • o o A  •  0  o X  0.195 0.396 0.568 0.600  M  M M M  0.801 M 1.117 M  1.492 M 1.492 M 1.490 M  7.9 atm. i t  11  11  i t  r  t I t t I l i  11 i t  t t i t  t t  11  5.5  '»  16 ©  o  (to0  •H X)  12 h  ,o  40  30  50  Time (minutes) Conditions:  F i g . 6.  Temperature 25°Cj NaCIO* 0.1 Mi  s t i r r i n g r a t e 750 RPMj  T y p i c a l f a m i l y o f r a t e c u r v e s f o r m e t h y l amine  7b-  - IS -  Concentration Conditions:  F i e . 7.  o f m e t h y l amine  (M)  Temperature 25°C; s t i r r i n g r a t e 750 RPM; NaClOi,. 0.1 M; oxygen p r e s s u r e 7.9 atm.  Plot of  r a t e vs c o n c e n t r a t i o n f o r  m e t h y l amine  - 19 -  0  0.50 C o n c e n t r a t i o n p f e t h y l amine  1.00 (M)  C o n d i t i o n s : Temperature 25°C; s t i r r i n g r a t e 750 RPM; NaClO^ 0.1M; oxygen p r e s s u r e 7.9 atm.  F i g . 18 ,  P l o t o f r a t e v s c o n c e n t r a t i o n o f e t h y l amine  '  ••••  ""  •  1  i  1  •  y  9Y ^ XT  / •  0  0.50 Concentration Conditions:  F i g . 9.  1.00 o f n - b u t y l amine  1.30  (M)  Temperature 25°C; S t i r r i n g r a t e 750 RPM. NaCIO*,. O.IM; oxygen p r e s s u r e 6.9 atm.  P l o t o f r a t e vs c o n c e n t r a t i o n o f n - b u t y l  amine  - 21 -  0  1.00  0.50  C o n c e n t r a t i o n o f m e t h y l amine Conditions;  Fig. 1 0 .  (M)  Temperature 2 5 ° C ; s t i r r i n g r a t e 7 5 0 RPMj NaClO^ O.lMj oxygen p r e s s u r e . 7 . 9 atm.  2 P l o t o f j A j /R.vs [_AJ f o r m e t h y l amine.  - 22 -  Fig. 11.  Plot  of  |jQ /R vs 2  00  for  ethyl  amine.  0.10  •  0.05c.  1.00  0.50 Concentrate Conditions;  F i g . 12.  o f n - b u t y l amine  (M)  Temperature 25°Cj s t i r r i n g rate 750 RPM. NaClO^ 0,10Mj oxygen p r e s s u r e 6.9 atm.  P l o t o f [ A l / R VS 2  [A] f o r n-butylamine  1.50  - 24 of the  straight  l i n e i n F i g u r e s 10,  11,  and  12.  The  of k± and  values  k  are  2  given i n Table I I . Table Values  o f the c o n s t a n t s  Equation  Complexing agent  II k]_ and  in  2  ( 1 ) , f o r the amines s t u d i e d .  k ( E i g . c i i r h - M - - " ) k^mg.cm-^h-lM- )  k^M" ) 1  2  1  3  1  2  from i n t e r c e p t s o f F i g s . 10, 11 and 12.  from F i g s . 7, 8, and 9.  from F i g u r e s 10, I I and 12.  M e t h y l amine  1.86  18.20  20.8  E t h y l amine  2.27  19.20  20.0  n - B u t y l amine  1.85  20.00  23.0  I t i s e v i d e n t from a comparison o f t h e two that  k  curves  i n F i g u r e s 7,  8,  t h e v a l u e s from F i g u r e s 10,  and 11,  9 had and  sets of values f o r k  2  - \  not y e t become q u i t e l i n e a r , so t h a t  12 are l i k e l y t o be the more c o r r e c t .  I t i s apparent f r o m t h e v a l u e s g i v e n i n T a b l e I I f o r t h e  constants  t h a t t h e t h r e e amines a r e v e r y n e a r l y i d e n t i c a l i n t h e i r b e h a v i o u r . d o u b t f u l whether any r e a l s i g n i f i c a n c e can be  attached  It i s  to the small d i f f e r -  ences o b s e r v e d .  i Effect of Acid.  The  e f f e c t o f a c i d was  at constant  pH,  at  f r e e amine c o n c e n t r a t i o n .  constant  The F i g u r e 13  constant  s t u d i e d i n two  waysj f o r m e t h y l amine o n l y ,  r a t i o o f aminium t o amine and  f o r a l l three  r e s u l t s o f e x p e r i m e n t s performed a t constant  (the r a t e v a l u e s  on t h e q u a l i t a t i v e nature  pH a r e shown i n  are g i v e n i n t h e Appendix, T a b l e  indicates that the v a r i a t i o n of the of the  IB).  hydrogen i o n c o n c e n t r a t i o n has  r a t e dependence.  amines  This no  effect  - 25 -  l  :  i  r  C o n c e n t r a t i o n o f m e t h y l amine Conditions;  F i g . 13o  (M)  Temperature 25°C; s t i r r i n g r a t e 750 Oxygen p r e s s u r e 7.9 atm.  RPM;  P l o t o f rate; vs c o n c e n t r a t i o n o f m e t h y l amine a t c o n s t a n t pH e  - 26 The r e s u l t s o f experiments a t constant amine c o n c e n t r a t i o n a r e shown i n F i g u r e s 14, 15 and 16 f o r methyl, ively  e t h y l and n - b u t y l amines r e s p e c t -  (see T a b l e s I C , I I B , and I I I B i n t h e Appendix f o r r a t e v a l u e s ) .  l i n e a r r e l a t i o n s h i p between r a t e and aminium i o n (AH ) c o n c e n t r a t i o n +  that Equation  ( l ) be m o d i f i e d  R  k  =  The suggests  slightly:  l V ^  k  2  +  k aj  (3)  3  kltA>l where  ^-MSiD.  a =  CAT  Cjf = R  T h i s r e l a t i o n c a n a l s o be e x p r e s s e d as  k  l  +  + k a  2  3  k^k  2  (4) + k a) 3  A l i n e a r p l o t i s shown f o r m e t h y l amine i n F i g u r e 17.  The v a l u e s o f k  3  o b t a i n e d f o r t h e t h r e e amines a r e g i v e n i n T a b l e I I I .  Table I I I Values obtained f o r k  Values o f k^(mg.cm }r M'" ')  Complexing Agent  g2  From F i g u r e s 13. 14. 15. Methyl  amine  E t h y l amine n - B u t y l amine  ft  3  From Equation  140, 153  160  93  x  103  (4)  1  1  C a l c . from . E q u a t i o n (3) 146 93 94  These v a l u e s o f k a r e mean v a l u e s . Values o f a l l c o n c e n t r a t i o n s s t u d i e d a r e g i v e n i n Tables ID, I I B , and I I I B i n t h e Appendix. 3  The v a l u e s f o r k  3  agreement w i t h each o t h e r .  determined  b y d i f f e r e n t methods a r e i n good  The v a l u e o f k  3  f o r m e t h y l amine i s s t r i k i n g l y  d i f f e r e n t f r o m t h e v a l u e s f o r t h e o t h e r amines.  - 27 -  C o n c e n t r a t i o n o f m e t h y l aminium i o n (M) Conditions;  Fig.  H  Temperature 25°Cj s t i r r i n g Oxygen p r e s s u r e 7 . 9 atm.  rate  7 5 0 RPM;  R e l a t i o n between the r a t e and m e t h y l aminium ion concentration.  -  F i g . 15  Relation between the rate and e t h y l aminium ion concentration.  28  - 29 -  Conditions:  F i g . 16.  Temperature 25°C; stirring Oxygen p r e s s u r e 6.9 atm.  r a t e 750  RPM;  R e l a t i o n between r a t e and n - b n t y l aminium i o n concentration.  - 30 -  A  l AH 3 = 0.10 +  0.04  & Pi  and  are c a l c .  values.  0.03  0.02  O 0.25  0.50  Concentration o f methyl amine (M) Conditions;  . 17.  Temperature 25°C; s t i r r i n g r a t e 750 RPM; Oxygen pressure 7.9 atm. P l o t o f [AjP/R VS [Xj f o r methyl amine at constant pH.  - 31 Values o f t h e r a t e s o b t a i n e d a t constant h i g h m e t h y l amine concent r a t i o n and at d i f f e r e n t  amounts o f aminium s p e c i e s are g i v e n i n Appendix.I.  These r a t e v a l u e s observed i n h i g h e r range o f c o n c e n t r a t i o n do not appear t o follow Equation  ( 3 ) . The reason f o r t h i s i s n o t y e t c l e a r .  Ammonia. I t was found t h a t t h e ammonia system showed a p a t t e r n o f a k i n e t i c b e h a v i o u r v e r y s i m i l a r t o t h a t d e s c r i b e d f o r t h e a l i p h a t i c amines.  The  e x p e r i m e n t a l data are p r e s e n t e d i n F i g u r e s 16, 19, and 2 0 and Tables IVA, IVB, and IVC i n t h e Appendix.  The v a l u e s of the c o n s t a n t s f o r ammonia a r e  g i v e n i n Table IV. Table IV. Values o f c o n s t a n t s f o r ammonia.  klClT ) 1  k (mg. c m 2  From F i g u r e IB  x  69.5  From F i g u r e 19  4.65  77.0  From F i g u r e 2 0  x  x  From E q u a t i o n ( 3 ) , Mean v a l u e  assumed 4 . 6 5  - 2  ^ ^ ) 1  1  assumed 7 7 . 0  k (mg, c n f ^ ^ ) 2  3  3  2445,  2420  2450  84  From R e f . 9.  From a l l t h e e x p e r i m e n t a l r e s u l t s , i t i s found t h a t t h e n a t u r e o f the k i n e t i c p r o c e s s f o r d i s s o l u t i o n a l i p h a t i c amines. quite different  o f copper  i s the same f o r ammonia and  However, t h e v a l u e s o f t h e c o n s t a n t s f o r ammonia are .  from t h o s e o f t h e amines.  R e a c t i o n Mechanism.  The form o f E q u a t i o n  (3) suggests t h a t the t o t a l r e a c t i o n  may  i n v o l v e a n a d s o r p t i o n e q u i l i b r i u m f o l l o w e d by t w o p a r a l l e l independent  first  1  - 32 -  0T2I 0T50 Concentration of ammonia (M) Conditions:  Temperature 25°C; s t i r r i n g rate 750 RPM; NaClO^ 0.10; oxygen pressure 7.9 atm.  F i g . IB. Plot of rate vs concentration f o r ammonia.  - 33 -  0.010  cv 0.005 .  0  0.25  0.50  C o n c e n t r a t i o n o f ammonia (M) Conditions:  F i g . 19.  Temperature 25°C; s t i r r i n g r a t e 750 RFM; MaClO^ 0.10; oxygen p r e s s u r e 7.9 atm.  P l o t o f [ T J /R v s \ A 3  f o r  ammonia.  - 34 -  Cone, o f ammonia.  30. -  •  0.202M  A  0.303 M  O  0.404 M  0  0.005 C o n c e n t r a t i o n o f ammonium i o n (M)  Conditions;  Temp. 25°C; s t i r r i n g r a t e 7 5 0 RPM; N a C 1 0 F i g . 20.  4  0.10-j Oppress. 7 . 9 atm.  R e l a t i o n between t h e r a t e and ammonium I o n concentration.  order steps.  These s t e p s may  be f o r m u l a t e d  as f o l l o w s (S stands f o r copper  atom on t h e s u r f a c e ) .  Step I. ; '  fast  S + A . . (a)  Step I I .  SA;  slow ^  SA + A  k  SA  slow SA + AH+ -—v SA k  (b)  x  r  =  S A  fast —>  2  1  L  „ Product  ^ fast + K+ >  2  Product  3  I n a d d i t i o n t o t h e s e s t e p s , t h e oxygen a d s o r p t i o n e q u i l i b r i u m must considered. i s no way  T h i s i s assumed t o be f a s t and  essentially  be  complete.  There  of d e c i d i n g unambiguously whether oxygen a d s o r p t i o n s t e p precedes  o r f o l l o w s t h e amine a d s o r p t i o n s t e p .  However, i t i s thought  likely.this  s t e p precedes the amine a d s o r p t i o n step under the c o n d i t i o n s used i n t h e present  study.  adsorption of AH  The +  occurrence  of a p a r a l l e l e q u i l i b r i u m step i n v o l v i n g  s p e c i e s i s not  i n d i c a t e d by the o b s e r v a t i o n s t h a t  d i s s o l u t i o n of copper does not proceed  i n the presence o f aminium or ammonium  i o n alone and t h a t t h e p l o t s o f r a t e v s ^ A H ^ a r e l i n e a r and  the  ( F i g u r e s 14,  15,  16  20).  From c o n s i d e r a t i o n o f t h e above mentioned s t e p s , the r a t e law be g i v e n by the  will  expression  R  =  k  2  [SA^fjO  C o n s i d e r i n g t h e s u r f a c e balance  S  D  + k (SAl(AH+l 3  = S  +  the f i n a l r a t e e x p r e s s i o n can be f o r m u l a t e d  R =  K  J ~^ A  k$jl where R i s e x p r e s s e d  (k£k\+  SA, and  the e q u i l i b r i u m S t e p 1,  as,  kJAH+)3 3  (5)  (°)  L  i n rate per u n i t area.  This i s i d e n t i c a l with  - 36 -  Equation  (3) d e r i v e d from t h e k i n e t i c  data.  Selected values f o r t h e constants k , k f  2  and k  f o r methyl,  3  ethyl,  n - b u t y l amine and ammonia a r e g i v e n i n T a b l e V,  T a b l e V. Selected values c f constants.  Complexing agents  k^M" ) 1  ^(mg.cnr ^ ^ ) 2  4.65  77  1.86  E t h y l amine n - b u t y l amine  Ammonia Methyl  amine  1  1  k (mg. cm- h""lM-l) 2  3  k /k 3  2  2450  31.80  20.8  146  7.00  2.27  20.0  93  4.65  1.85  23.0  94  4.10  I t i s e v i d e n t from t h e v a l u e s o f t h e c o n s t a n t s t h a t t h e l e n g t h o f t h e carbon  chain exerts v e r y l i t t l e  q u i t e apparent  i n f l u e n c e on t h e r a t e .  I t i s , however,  t h a t t h e e f f e c t due t o a d d i t i o n o f a p r o t o n t o form t h e A H  +  i o n i s v e r y pronounced i n a l l t h e cases s t u d i e d .  S i g n i f i c a n c e o f k]_: A c c o r d i n g t o t h e proposed scheme f o r t h e r e a c t i o n , k^ i s t h e e q u i l i b r i u m constant f o r t h e a d s o r p t i o n p r o c e s s . v a l u e s t h a t ammonia i s much more s t r o n g l y adsorbed a d s o r p t i o n c h a r a c t e r i s t i c s of m e t h y l ,  I t i s apparent  from t h e k^  t h a n t h e o t h e r amines.  The  e t h y l and n - b u t y l amines appear t o be  e s s e n t i a l l y t h e same. S i g n i f i c a n c e of k : 2  The s i g n i f i c a n c e o f t h e v a l u e s o f k o f s u r f a c e adsorbed  species by those  2  i s as an i n d i c a t i o n o f a t t a c k  i n the s o l u t i o n .  The v a l u e s o f k f o r 2  t h e amines a r e almost t h e same f o r t h e t h r e e amines and w i d e l y d i f f e r e n t  from  - 37 -  t h a t o f ammonia.  It is difficult  d i f f e r e n c e between t h e k  2  t o draw any d e f i n i t e c o n c l u s i o n about t h e  v a l u e s o f amines and ammonia.  I t may be  perhaps  l a r g e l y due t o a s t e r i c f a c t o r ; t h e ammonia has a s m a l l e r chance o f u n s u c c e s s f u l c o l l i s i o n w i t h t h e r e a c t i o n s i t e t h a n have t h e amines.  S i g n i f i c a n c e of k : 3  The v a l u e o f k AH  +  3  i n d i c a t e s t h e a t t a c k o f s u r f a c e adsorbed s p e c i e s by  o r NHV " s p e c i e s from s o l u t i o n .  The d i f f e r e n c e o f v a l u e s i n k  1  t h e amines and ammonia i s perhaps  a l s o due t o a s t e r i c  The d i f f e r e n c e i n s u r f a c e a t t a c k by A and A H from t h e d i f f e r e n c e i n v a l u e o f k  2  and k .  Perhaps  3  3  between  effect.  +  species are evident  f o r the l a t t e r  species,  t h e e l e c t r o n exchange i s much f a c i l i t a t e d due t o presence o f charge on t h e AH  +  species.  In t h e l i g h t o f t h e f o r e g o i n g d i s c u s s i o n , i t appears  l i k e l y that the  d i f f e r e n c e i n o r d e r o f r e a c t i o n observed i n t h e case o f c h e l a t i n g a g e n t s ^ and t h a t i n t h e case of amines and ammonia may a r i s e from t h e d i f f e r e n c e i n t h e number o f f u n c t i o n a l groups  p r e s e n t i n t h e s e two t y p e s o f compound.  For the  c h e l a t i n g a g e n t s , c o n s e q u e n t l y , i t appears t o be a u n i m o l e c u l a r r e a c t i o n , ' t h e a d s o r p t i o n s t e p b e i n g the o n l y o b s e r v a b l e s t e p .  The r e a c t i o n can be  r e p r e s e n t e d b y the f o l l o w i n g sequence o f s t e p s : fast Step I  Step I I  S +  S — x — —x—  S slow —  Si>x  x fast ~* Product  - stands f o r b i d e n t a t e c h e l a t i n g  agent.  These steps a r e e s s e n t i a l l y s i m i l a r t o t h o s e proposed f o r amines except t h a t t h e slow step does not i n v o l v e a second  molecule.  -38 In view o f the p r e s e n t r e s u l t s , i t appears t h a t f u r t h e r work ought t o be done t o extend the same work t o o t h e r complexing systems.  In  t h i s sense i t would be i n t e r e s t i n g t o i n v e s t i g a t e the f o l l o w i n g :  (1) (^A"\  Rate measurements w i t h m i x t u r e s o f amine and aminium i o n  + ^AH"^  (2)  =  c o n s t a n t ) over a wide range of  pH.  Rate measurements w i t h m i x t u r e s o f primary amines and  secondary  amines. (3) diamines.  I n v e s t i g a t i o n o f t h e r a t e p r o c e s s w i t h 3- and 4-carbon c h a i n  - 39 REFERENCES  1.  Evans, U.R., Introduction  2.  King, C.V. and H i l l n e r , E,, J . Elec. Chem. Soc. 103. 261 (1956),  3.  Gatos, H.C., J . E l e c . Chem. Soc. 103. 286 (1956).  4.  C r e t e l l a , M.C. and Gatos, W.C., J . E l e c . Chem. Soc. 105. 487 (1958).  5.  Smith, Tennyson and H i l l , R. George, J . E l e c . Chem. Soc. 105. 117 (1958).  6.  Tamasaki, E., Science r e p r i n t ; Tohuku Imperial University, 9_> 169 (1920).  7.  Z a r e t s k i i , E. and Akimov, G., J . Appl. Chem. USSR 11, 1161  8.  Lane, R.W. and McDonald, H.J., J . Amer. Chem. Soc. 68,  9.  Halpern, J . , J . E l e c . Chem. Soc. 100. 421 (1953).  10.  to Corrosion, Edward Arnold and Co, (1951).  (1938).  1699(1946),  Milants, H.Y., M. Sc. Thesis, Department of Mining and Metallurgy, University of B r i t i s h Columbia (1958).  11.  Bjerrum, J . , Metal Amine Formation i n Aqueous Solution.  Copenhagen (1941),  12.  Sidgewick, N.V., The Chemical Elements and Their Compounds. V o l . I  f  Oxford University Press (1950). 13.  Conway, B.E.., Electrochemical  14.  Kolthoff, I.M. and Stenger, V.A., Volumetric Analysis Interscience  data. E l s e v i e r Publishing Co. (1952). Vol.1,  (1942).  15.  Hoar, T.P., Analyst. 62, 657 (1937).  16.  High, T.H., Analyst 72, , 60 (1947).  17.  Sandell, E.B,, Colorimetric Determination of Traces of Metals, Interscience  (1950).  V  CATALYTIC REDUCTION OF NICKEL ION BY MOLECULAR HYDROGEN  INTRODUCTION  The p o s s i b i l i t y o f r e d u c t i o n o f m e t a l i o n s from s o l u t i o n b y m o l e c u l a r hydrogen has been recognize'd f o r a l o n g t i m e .  Among e a r l y  12 3 i n v e s t i g a t o r s , Ipatiew ' ' has perhaps made t h e g r e a t e s t  contribution.  I n r e c e n t y e a r s , more d e t a i l e d s t u d i e s o f t h e s e r e d u c t i o n p r o c e s s e s have  k  been made b y S h a u f e l b e r g e r , and Sussmuth.^  5 Mackiw, L i n and Kunda, and Knacke,  Fawlek  An e x c e l l e n t r e v i e w o f h y d r o m e t a l l u r g i c a l p r o c e s s e s a t h i g h  p r e s s u r e i s by Forward and H a l p e r n .  7  E a r l y attempts of I p a t i e w t o d i s p l a c e metals from s o l u t i o n s a t h i g h p r e s s u r e s and temperatures met w i t h v a r y i n g degrees o f s u c c e s s . H i s work was u s u a l l y done a t h i g h temperature and f o r t i m e s as l o n g as s e v e r a l days.  (300°C) and p r e s s u r e (7000 p s i )  He succeeded i n p r e c i p i t a t i n g by  hydrogen r e d u c t i o n , e i t h e r a s t h e m e t a l o r a s a b a s i c s a l t , t h e f o l l o w i n g m e t a l s ; p l a t i n u m , i r i d i u m , copper, n i c k e l , c o b a l t , l e a d , t i n ,  arsenic,  antimony and b i s m u t h .  S h a u f e l b e r g e r ^ has i n v e s t i g a t e d t h e p o s s i b i l i t y o f r e d u c t i o n o f -  copper and n i c k e l by m o l e c u l a r hydrogen.  From examination o f t h e thermo-  dynamic d a t a , he concluded t h a t s u c h r e d u c t i o n i s p o s s i b l e a t h i g h temperat u r e (•vr200°C) and a t s u i t a b l e hydrogen i o n c o n c e n t r a t i o n . hydrogen  The e f f e c t j o f  i o n c o n c e n t r a t i o n and complex f o r m a t i o n were i n v e s t i g a t e d b y him  t o a r r i v e a t a s u i t a b l e system f o r t h e complete removal o f t h e m e t a l i o n from  solution.  -uThe k i n e t i c s of t h e r e d u c t i o n o f n i c k e l i n ammoniacal  solution  was  s t u d i e d by Mackiw, L i n and Kunda.5  The c o n d i t i o n s under w h i c h t h i s work  was  done were s i m i l a r t o t h o s e adopted by S h e r r i t t Gordon Mines L t d . , f o r  recovery of n i c k e l .  Knacke, Pawlek and Sussmuth  0  i n v e s t i g a t e d the k i n e t i c s of t h e homo-  geneous r e d u c t i o n o f s i l v e r and copper and  heterogeneous c a t a l y t i c  reduction  of n i c k e l , from t h e i r s u l p h a t e s o l u t i o n s .  Tho r e s u l t s f o r p r e c i p i t a t i o n o f 8  s i l v e r and copper  are n o t in agreement w i t h t h o s e found by l a t e r  The r a t e o f r e d u c t i o n o f copper and  s i l v e r was  t h e square root o f hydrogen p r e s s u r e . o f the a c t i v a t i o n energy was  found  0  -  on the  co-workers, i t depends on  For the reduction of n i c k e l , the value  t o be 4.12  k c a l / m o l , which suggests t h a t  i n h i s work, the r e d u c t i o n r a t e was d i f f u s i o n c o n t r o l l e d . proposed by t h e s e workers • v - Jk  workers. '  f o u n d t o be dependent  p r e s s u r e o f hydrogen w h i l e a c c o r d i n g t o Pawlek and  9  _ 5.59 x 10 C 2  2  N 1 + +  P  1/2 H 2  e  The r a t e e q u a t i o n  -4.12  does not suggest t h a t hydrogen i o n has e f f e c t on t h e r a t e o f r e d u c t i o n . 8  H a l p e m and P e t e r s  have i n v e s t i g a t e d the homogeneous a c t i v a t i o n  o f hydrogen by c u p r i c i o n , and t h e r e d u c t i o n o f copper from t h e s o l u t i o n . The product can be copper o r cuprous o x i d e depending on t h e pH o f t h e s o l u t i o n and t h e temperature o f t h e r e a c t i o n .  I t has  a l s o been found from a  s t u d y o f t h e copper s u l p h a t e s y s t e m , ^ t h a t t h e r e a c t i o n p r o c e s s i s r e v e r s i b l e . This r e v e r s i b i l i t y i s strongly hydrogen-ion-concentration  dependent.  R e d u c t i o n o f t h e m e t a l s , copper, s i l v e r and mercury has been found t o be homogeneously c a t a l y s e d by t h e m e t a l i o n s and by t h e i r complex  ions.  But f o r r e d u c t i o n o f n i c k e l or c o b a l t , i t has always been n e c e s s a r y t o add a  heterogeneous c a t a l y s t .  Among c a t a l y s t s  sulphate, c o l l o i d a l graphite  used are n i c k e l powder, f e r r o u s  and h y d r o q u i n o n e , ^  I n t h e work r e p o r t e d h e r e ,  n i c k e l powder i s used as a c a t a l y s t .  Scope o f t h e Work,  In t h e p r e s e n t work an attempt was made t o e l u c i d a t e o f r e d u c t i o n o f n i c k e l from s a l t  solutions  presence o f n i c k e l powder c a t a l y s t .  the k i n e t i c s  b y m o l e c u l a r hydrogen i n t h e  I n t h e l i g h t o f p r e v i o u s work, i t was  thought worthwhile t o s t u d y t h e r e d u c t i o n o f n i c k e l from a b u f f e r e d and  a few u n b u f f e r e d s o l u t i o n s .  the  equilibrium  temperature.  solution  I t i s a l s o an aim o f t h i s work t o e v a l u a t e  constant f o r t h e e q u i l i b r i u m  Ni  + +  +  H f=^ N i ° 2  + 2 H , at high +  EXPERIMENTAL  Apparatus. The reaction studies were conducted i n a one-gallon stainless-steel 12 autoclave manufactured by Autoclave Engineers inc.  Additional fittings  included an arrangement to drop the catalyst from a sealed glass capsule and an arrangement i n the sampling tube t o collect the sample under pressure. These are shown i n Figure 1.  Since for the system studied, the stainless  steel autoclave may act as a catalyst, a glass liner with a titanium baffle was used to contain the solution.  The impeller,  sampling tubes were also made of titanium.  thermocouple well and  The autoclave was heated by a  gas ring burner, and the temperature was controlled to within i l . 5 ° C using a Leeds and Northrup micromax controller. A l l pH measurements were made at room temperature, using a Beckman model GS pH meter. Catalyst. The catalyst used i n these experiments was standard *A» carbonyl nickel powder, prepared by the Mond Nickel Company, Ltd. These are spherical particles, and of 100% -350 mesh.  The surface area was found* to be 1.85 nrVgm.  Reagents. The nickel acetate, acetic acid, and anhydrous sodium acetate used i n these experiments were a l l r  -rent grade, obtained from the Allied Chemical  and Dye Company and the Niclyls Chemical Company. Other incidental chemicals were also reagent grade.  Hydrogen gas supplied by the Canadian Liquid Air  Company was used without further purification.  A l l the solutions for  •k The author i s grateful to Mr. Peter Hennes for surface area determination.  - hk  A B C D E  = = = = =  glass capsule 0 • r i n g arrangement sampling t u b e autoclave w a l l gas i n l e t s t o push t h e Fig.  1.  F G H I  = = = =  w i r e gauge g l a s s wool asbestos total filtering  capsule  Schematic diagram f o r h o l d i n g c a t a l y s t and f i l t e r i n g under p r e s s u r e .  device.  - 45 experiments were prepared by diluting solutions of known strength. Measured volumes of sodium acetate, acetic acid and nickel acetate were transferred to a 2000 ml volumetric flask and diluted up to volume to get a solution of the desired concentration.  Distilled water was used for preparation of a l l the  solutions. Analysis. Determination of pickel was done colorimetrically using dimethyl glyoxime. '  A Beckman Model DK -2 ratio-recording spectrophotometer was  used for measurement of optical density.  Measurements were made at a wave-  length of 450 millimicrons. The analysis was performed in the following way: To an aliquot of the sample were added 2 ml of saturated bromine water 4.5 ml of concentrated ammonia, 7 ml of 1% solution of dimethyl glyoxime in alcohol, and 5 ml of alcohol, and the whole was diluted to 25 ml. made within 10 minutes of mixing.  Measurements were  Beer's law i s obeyed, as seen from Figure 2,  over a sufficient range of concentration to permit analysis following appropriate dilution. Experimental Procedure, The experiments were done i n the following way; the required amount of catalyst was weighed and placed in a glass capsule and the capsule was f i l l e d with d i s t i l l e d water and sealed.  Then i t was placed in the autoclave  as shown i n Figure 1, The autoclave was charged with the required solution. After the autoclave was sealed, i t was flushed several times with hydrogen and was heated under hydrogen at a pressure of about 200 p s i . It was flushed again at about 80°C, and f i n a l l y heated up to the required temperature under 200 psi of hydrogen pressure.  Samples were removed after attainment of the  f i n a l temperature to ascertain the zero time concentration.  The capsule of  -  U6 -  -47catalyst was injected by hydrogen pressure into the autoclave where i t was smashed by the impeller. required value. as zero time.  The hydrogen pressure was then adjusted t o the  The time when the catalyst was dropped into solution was taken Samples were collected through the sampling device  which samples are f i l t e r e d  out  (through  from s o l u t i o n under hydrogen pressure), at  suitable time i n t e r v a l s f o r n i c k e l analysis by the method already described. Preliminary Experiments. Preliminary experiments were conducted t o examine ( i ) the nature of the reduction process i n unbuffered  solutions (solutions of n i c k e l sulphate  and n i c k e l perchlorate), ( i i ) the v a r i a t i o n of the pH of the s o l u t i o n r e s u l t ing  from the reduction of n i c k e l ion, ( i i i ) the v a r i a t i o n of the reduction  rate using d i f f e r e n t types of c a t a l y s t s and (iv) the nature of the rate curve. (i)  Reduction from n i c k e l sulphate and perchlorate solutions: Experiments using n i c k e l perchlorate and sulphate solutions were  found t o give only a very small amount of reduction (10% of a 0.1 M s o l u t i o n at  160°C).  I t was observed that during t h i s process, the pH of the s o l u t i o n  f e l l to about 2.4 and the reaction stopped. less reduction was found.  For perchlorate solutions s t i l l  For t h i s reason, further work described i n t h i s  thesis was done with buffered s o l u t i o n s .  (ii)  Variation of pH: A l l the pH measurements were done at room temperature.  I t was found  that the i n i t i a l and f i n a l pH of the buffered system a f t e r reduction d i f f e r e d only s l i g h t l y (for example, from pH 4.25 to 4.15). as the amount of n i c k e l reduced increases.  This difference increases  In spite of the small change i t  was.felt desirable to use only the i n i t i a l rate i n studying the mechanism since only i n the i n i t i a l part can the conditions f o r reaction be known with  - 48 -  any  certainty. (iii)  Different types of c a t a l y s t : Three types of n i c k e l powder were t r i e d as c a t a l y s t . (a)  Dense n i c k e l powder:  These were dense granular n i c k e l powders  obtained from S h e r r i t t Gordon Mines Ltd. were 20-30 microns i n diameter. before use.  The p a r t i c l e s used f o r t h i s test  These were annealed i n a hydrogen atmosphere  I t was found that t h i s catalyst was not active enough t o make  the reduction of n i c k e l ion from solution possible. n i c k e l powder continued f o r a few hours.  Instead, d i s s o l u t i o n of  It was found that s t a r t i n g with two  d i f f e r e n t i n i t i a l concentrations of n i c k e l , the d i s s o l u t i o n approaches a type of pseudoequilibrium.  This powder was not used because of i t s lack of  catalytic activity. (b)  'Nucleating powder':  This powder, obtained from S h e r r i t t Gordon  Mines Ltd., was less than three microns i n diameter and of i r r e g u l a r shape. This catalyst was found to be very active, but r e p r o d u c i b i l i t y of rate measurements was poor. (c) described). bility.  Carbonyl n i c k e l powder: (This catalyst has already been It was found to be quite active and as w e l l gave good reproduci-  The difference i n the r e p r o d u c i b i l i t y of rate measurements f o r  catalyst (b) and (c) i s perhaps due t o the nature of the catalyst surface and i t s shape. described (iv)  The carbonyl n i c k e l catalyst was used f o r a l l the experiments hereafter.  Nature of the reduction curves: The rate curves i n which n i c k e l concentration i s plotted against  time, were found to show an induction  period of variable length.  curves were of two types, (a)'at high s t i r r i n g rate  These  (75° RPM), the n i c k e l  concentration i n solution was found t o increase considerably and then to  - 49 d e c r e a s e , (b) at lower s t i r r i n g r a t e remained constant  (400 RPM), t h e n i c k e l  f o r a few minutes and t h e n d e c r e a s e d .  In a l l cases,  however, n e i t h e r t h e measured r e d u c t i o n r a t e , n o r t h e f i n a l c o n c e n t r a t i o n was dependent on t h e s t i r r i n g r a t e . curve a r e shown i n F i g u r e r a t e s were e v a l u a t e d  The ascertained.  3.  concentration  equilibrium  The two t y p e s o f r a t e  I t i s a l s o made c l e a r i n F i g u r e  3 how t h e  from t h e d a t a .  r e a s o n f o r t h e r e b e i n g two t y p e s o f r a t e curves was not However, i t may be c o n j e c t u r e d  t h a t the cause may l i e i n t h e  presence o f an o x i d e l a y e r on the c a t a l y s t s u r f a c e , which i n one case i s being  d i s s o l v e d before  situ.  b e i n g reduced and i n t h e o t h e r  case i s reduced i n  I t seems i n c o n s i s t e n t , however, t h a t pre-treatment o f the c a t a l y s t  (the powder was t r e a t e d w i t h warm a c e t i c a c i d , washed w i t h a l c o h o l , d r i e d a t 60°C) d i d not appear t o a f f e c t the d u r a t i o n or the n a t u r e o f t h e i n d u c t i o n period.  T h i s may s i g n i f y t h a t  e i t h e r t h e oxide f i l m r e s i s t s t h i s  treatment  o r forms a f t e r t h i s treatment a t a v e r y r a p i d r a t e .  I t was found t h a t a l t h o u g h t h e d u r a t i o n was  v a r i a b l e , measured v a l u e s  i n t h e Appendix g i v e s v a l u e s e f f e c t o f chemical  period  o f t h e i n i t i a l r a t e s were c o n s i s t e n t .  Table I  showing s t i r r i n g e f f e c t , r e p r o d u c i b i l i t y and  treatment.  curves ( a l l a t 400 RPM).  of the i n d u c t i o n  Figure  4 gives a t y p i c a l f a m i l y of rate  Independent e v a l u a t i o n o f r a t e s from these  curves  gave values which, though d i f f e r e n t by as much as 20%, were c o n s i s t e n t among themselves.  Time (minutes) Conditions: Temperature 140°C; Catalyst 10 gms/1400 ml; Hydrogen 13.55 atm; Acetic acid 0.2 M; Total acetate 0.06 M; Initial, nickel 0.005 M. Fig. 3.  Typical plot showing two types of rate curves.  - 51 -  Conditions:  F i g . 4.  Time (minutes) Temp. 140°C; C a t a l y s t 10 gms/1400 ml; Hydrogen 13.55 atm; A c e t i c a c i d 0.2 (M); T o t a l a c e t a t e 0.06 (M); S t i r r i n g r a t e 400 RPM; i n i t i a l pH 4.25.  Typical family of rate  curves  RESULTS AND DISCUSSION  The  v a r i a b l e s s t u d i e d i n an attempt t o e l u c i d a t e t h e mechanism o f  r e d u c t i o n o f n i c k e l from s o l u t i o n by molecular  v  - \ i r o g e n i n t h e presence o f a  n i c k e l c a t a l y s t were (a) i n i t i a l n i c k e l c o n c e n t r a t i o n , (c) p r e s s u r e o f hydrogen, (d) i n i t i a l r e a c t i o n temperature.  (b) amount o f c a t a l y s t ,  hydrogen i o n c o n c e n t r a t i o n and (e)  The e x p e r i m e n t a l d a t a a r e g i v e n i n T a b l e s  I t o VTII i n  Appendix I I .  (a)  Dependence o f t h e r a t e on n i c k e l The  concentration.  i n i t i a l r a t e f o r any c o n c e n t r a t i o n was o b t a i n e d  p l o t s as shown i n F i g u r e 4.  from t h e r a t e  These runs were made a t 140°C, 13.55 atm. hydrogen  p r e s s u r e , 10.00 gms o f c a t a l y s t . i n 1400 m l s o l u t i o n and. s o l u t i o n pH o f 4.25 and v a r y i n g i n i t i a l c o n c e n t r a t i o n o f n i c k e l .  The v a r i a t i o n i n i n i t i a l  w i t h i n i t i a l n i c k e l c o n c e n t r a t i o n i s shown i n F i g u r e 5.  This plot  l i n e a r dependence o f t h e r a t e on t h e n i c k e l c o n c e n t r a t i o n .  rate  shows a  The p l o t passes  t h r o u g h t h e v a l u e o f the e q u i l i b r i u m n i c k e l c o n c e n t r a t i o n f o r t h e c o n d i t i o n s used.  The f i r s t  o r d e r dependence on n i c k e l c o n c e n t r a t i o n  p l o t of l o g (cone, o f n i c k e l ) vs l o g ( i n i t i a l  i s confirmed  by a  r a t e ) shown i n F i g u r e 6. The  measured s l o p e o f t h i s l i n e , 0.93 i s s a t i s f a c t o r i l y c l o s e t o 1.  (b)  E f f e c t o f t h e amount o f c a t a l y s t .  A number o f runs were done v a r y i n g t h e amount o f c a t a l y s t , a t a constant initial  n i c k e l c o n c e n t r a t i o n o f 0.005 (M)  same as given above.  w i t h other c o n d i t i o n s b e i n g t h e  F i r s t o r d e r dependence o f t h e r a t e o n t h e c a t a l y s t  i s shown by t h e l i n e a r i t y o f t h e p l o t g i v e n i n F i g u r e 7. straight  area  The f a c t t h a t t h e  l i n e passes t h r o u g h t h e o r i g i n i s c o n s i s t e n t w i t h t h e o b s e r v a t i o n  t h a t no r e a c t i o n occurs  i n t h e absence o f a  catalyst.  - 53  I n i t i a l nickel concentration Conditions;  Fig.  5.  (M)  Temperature 140°C; C a t a l y s t . 1 0 gms/1400 ml; Hydrogen 13.55 atm; A c e t i c a c i d 0.2 (M); T o t a l a c e t a t e 0.06 (M); I n i t i a l pH 4.25.  E f f e c t o f i n i t i a l c o n c e n t r a t i o n on t h e rate.  initial  -4.31  -  -2.9  — i -2.7  — J  log Condition's;  Fig.  6.  1  -2.5  -2.3  1 -2.1  1 —  -1.9  C i++ N  Temperature 1 4 0 C ; C a t a l y s t 10 gms/1400 ml; Hydrogen 1 3 . 5 5 atm; A c e t i c a c i d 0 . 2 (M); T o t a l a c e t a t e 0 . 0 6 (M); I n i t i a l pH 4 . 2 5 . P  P l o t of l o g ( i n i t i a l r a t e ) vs l o g ( i n i t i a l  cone).  5  10  15  Amount of catalyst (gms/1400 ml) Conditions; Temperature 140°C; Hydrogen 13.55 atm; Acetic acid 0.2 (M); Total acetate 0.06 (M); I n i t i a l nickel concentration 0.005 (M); I n i t i a l pH 4.25. Effect of amount of catalyst on the i n i t i a l rate.  - 56(c)  E f f e c t o f hydrogen p r e s s u r e . R e s u l t s o f experiments conducted at d i f f e r e n t hydrogen p r e s s u r e s ,  showed t h a t t h e r a t e i s d i r e c t l y p r o p o r t i o n a l to t h e square r o o t o f the hydrogen p r e s s u r e .  The d a t a are p r e s e n t e d i n Figure 8.  At s u f f i c i e n t l y h i g h  p r e s s u r e s , t h e r a t e i s seen t o d r o p from t h i s dependency, which may saturation of catalyst surface. r a t e - d e t e r m i n i n g s t e p may  (d)  indicate  T h i s t y p e o f dependence suggests t h a t t h e  be one i n v o l v i n g atomic  hydrogen.  Dependence o f the r a t e on hydrogen i o n c o n c e n t r a t i o n .  Experiments d e s i g n e d t o t e s t the dependence o f t h e r a t e on  hydrogen  i o n c o n c e n t r a t i o n were performed under the same c o n d i t i o n s as d e s c r i b e d but w i t h d i f f e r e n t i n i t i a l hydrogen i o n c o n c e n t r a t i o n s .  above,  The r e s u l t s shown  i n F i g u r e 9 show t h a t the r a t e d e c r e a s e s i n an a p p r o x i m a t e l y l i n e a r  fashion  w i t h i n c r e a s i n g c o n c e n t r a t i o n o f hydrogen i o n .  (e)  Temperature  dependence.  Temperature  v a r i a t i o n was  s t u d i e d t o determine the a c t i v a t i o n  energy  and t h e r e b y perhaps t o be a b l e t o make some d e c i s i o n as t o the n a t u r e o f t h e rate limiting step. 130  t o l60°C.  Figure  10  The measurements were.made o v e r the temperature  range  The a c t i v a t i o n energy determined f r o m A r r h e n i u s ' p l o t shown i n  appears t o be  25*2  kcal/M.  This value f o r the a c t i v a t i o n  energy  s t r o n g l y s u p p o r t s t h e view t h a t t h e r a t e p r o c e s s measured i s not one which i s c o n t r o l l e d by d i f f u s i o n .  From the above e x p e r i m e n t a l r e s u l t s , the r a t e e q u a t i o n can be e x p r e s s e d as  iMlil4t  -k^M^tNi^.kaCs]  (V)  - 57 -  Conditions?  Fig.  8.  Temperature 140°C; C a t a l y s t 10 gms/L400 ml; I n i t i a l n i c k e l c o n c e n t r a t i o n 0.005 M; A c e t i c a c i d 0,2 (M); T o t a l a c e t a t e 0.06 M; I n i t i a l pH 4.25. E f f e c t o f hydrogen p r e s s u r e  on t h e i n i t i a l r a t e .  Fig,  9«  Effect of i n i t i a l hydrogen ion concentration on the i n i t i a l rate.  - 59 -  l/T x 10  Gondii ions:  Fig. 10.  3  Catalyst 15 gms/1400 ml; Hydrogen 13,55 atm; I n i t i a l concentration of nickel 0,005 M; Acetic acid 0.2 (M); Total acetate 0.06 (M); I n i t i a l pH 4,25. Plot of log ( i n i t i a l rate) vs reciprocal of temperature.  I n i t i a l pH 4.25. F i g . 11.  A plot showing approach to equilibrium from d i s s o l u t i o n of n i c k e l and reduction of n i c k e l .  - 61 -  where ^ N i ~ ] and [H ]are: concentrations and Qsl ++  +  i s the catalyst surface area.  Although the mechanism of the reduction reaction can not be deduced assurance from the above presented  with any  information, i t i s now clear that the  ,Ni activated complex is of the form surface £ . The reverse reaction H n i c k e l d i s s o l u t i o n appears to go through an activated complex of the type + +  N  surface / / H+ , The form of the rate equation i s s i m i l a r t o that found by HN ii Pawlek; but i n t h i s work, importance of hydrogen ion is c l e a r l y shown t o be X  involved i n the k i n e t i c s of rate of reduction. Use of the equilibrium n i c k e l concentrations f o r c a l c u l a t i o n of the thermodynamic equilibrium constant; The experiments from which the nature o f the dependence of the rate on the pressure of hydrogen and on the hydrogen ion concentration has been derived, were usually prolonged equilibrium n i c k e l concentration.  f o r a s u f f i c i e n t time t o obtain the  A plot showing the approach t o equilibrium  n i c k e l concentration from reduction of n i c k e l as w e l l as d i s s o l u t i o n of n i c k e l i s shown i n Figure 11. From the values of the equilibrium n i c k e l concentration and corresponding hydrogen pressure and hydrogen ion concentrations, an attempt was  made t o evaluate the equilibrium constant f o r the reaction ;  •Ni  + +  + H ^ 2  M  where  Ni° + 2 H  +  2  (^Ni"""^  i s -the equilibrium n i c k e l concentration  £H ~\  i s the hydrogen ion concentration  ^PH ~\  i s the' pressure of hydrogen  1  +  2  - 62 -  1/P„  (atm ) x -1  10  2  Conditions; I n i t i a l pH 4.25; temperature 140°C; i n i t i a l n i c k e l concentration 0.005. F i g . 12.  Plot of equilibrium n i c k e l concentration vs r e c i p r o c a l of hydrogen pressure.  k  0  6  8  Concentration of (H ) +  Conditions; Fig. 13.  (M) x 10  10  12  8  Temp. 140 C; catalyst 15/gms/1400 ml; Hydrogen 13.55 atm.; i n i t i a l concentration of nickel 0.005 (M). C  Plot of equilibrium nickel concentration vs final hydrogen ion concentration.  - 64 A plot of the equilibrium concentration of nickel in solution against reciprocal of hydrogen pressure (at constant \^H ]) i s given i n +  Figure 12,  It i s seen to be a straight line passing through the origin in  agreement with expectation,. The equilibrium nickel concentration was found to be a linear function of the square of hydrogen ion concentration as is seen i n Figure 13. The straight line does not pass through the origin, since the values used for the hydrogen ion concentrations are those measured at room temperature.  The  difference w i l l be a constant factor related to the intercept.., Hydrogen ion concentration from the plot was found to be 1.6 x 10"^  a  t 140°C (the room  -5 temperature value being 7 x 10  ).  The valuejof constant k calculated with  the help of corrected hydrogen ion concentration and slopes of plots 12 and 13, are 4.7 x 10"^ and 4.6 x 10"^ respectively. calculated from thermodynamic data  The value of constant k was  available for room temperature (extra-  polated to 140°C, using relation A F  = AF T-z  - (T - T n ) A S )  T  2  0  The value  l  x  obtained from this calculation i s 7.6 x 10"^  The agreement between experi-  0  mental and calculated values i s satisfactory, since validity of extending thermodynamic data to higher temperature, and of the assumption of the activity of nickel to be equal to that of total nickel present are very uncertain. agreement indicates, however, that the assumptions used are not grossly incorrect. £  Refs. 15 and 16.  Ni++ = -11.53 kcaly^ H ++ = -15.3 kcal/^y  F  Ni  S S  N  i  +  +  ~ -38.1  H (gas) 2  =  +  cal/degree  31»2 cal/degree  % i ( s o l i d ) ^ 7.1 cal/degree +  The  - 65 I t i s apparent t h a t b e f o r e f u r t h e r work i s done on t h i s p r o b l e m , the nature of the c a t a l y s t  s u r f a c e must be s t u d i e d i n an attempt t o  u n d e r s t a n d and e l i m i n a t e t h e v a r i o u s u n c e r t a i n t i e s and a n o m a l i e s w h i c h p e r s i s t e d throughout t h e present work.  After e l i m i n a t i o n of the  a r i s i n g out o f u n c e r t a i n t y i n t h e n a t u r e o f catalyst s u r f a c e ,  troubles  f u r t h e r work  may be e n l i g h t e n i n g i n o b t a i n i n g a more q u a n t i t a t i v e approach t o t h e r e a c t i o n mechanism.  REFERENCES  1.  Ipatiew, V. and V e r k h o v s k i i , V., Ber. dtsch. Chem. Ges 4Jt, 1755 (1911).  2.  Ipatiew, V., J . S o c . Phys. Chem (Russ.) 43_, 1746 (1911).  3.  I p a t i e w , V. and Ipatiew, V.V. ( J r . ) , Ber. c t s c h . Chem, Ges. 62B. 386 (1929)  4.  S h a u f e l b e r g e r , F.A., J . Met. 8,  5.  Mackiw, V.N., L i n , W.C. and Kunda, W,, J . Met. 9, 786 (1957).  6.  Knacke, 0, Pawlek, F. and Sussmuth, E , , Z . f . Erzbergbau u , M e t a l l h u t t e n w s ,  695 (1956).  2, 566 (1956). 7.  Forward, F.A. and H a l p e m , J , , T r a n s , I n s t , M i n , and Met., 66, P a r t 5, 191  (1956-57).  8.  P e t e r s , E , and H a l p e m , J . , Can, J . Chem, 3Jt» 554 (1956).  9.  Webster, A.H, and H a l p e m , J , , J , Amer, Chem, S o c , 60, 280 (1956).  10.  Macgregor, E.R. and H a l p e m , J . , T r a n s . A.I.M.E. 212. 244 (1958).  11.  Kaneko, Thomas M. and Wadsworth, M.E., J . Phys. Chem, 60, 457 (1956),  12.  P e t e r s , E , , Ph.D. 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, 1956,  13.  M i t c h e l l , " A.M. and M e l l o n , M.G.,  14.  S a n d e l l , E.B,, C o l o r i m e t r i c D e t e r m i n a t i o n o f Traces o f M e t a l s .  Ind. Eng. Chem, A n n a l , E d , 17., 380 (1945)  I n t e r s c i e n c e , 2nd E d . (1950), '15,  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 , 2nd Ed., P r e n t i c e H a l l  16,  Kubaschewski, 0. and Evans, E.L., M e t a l l u r g i c a l Thermochemistry. Butterworth S p r i n g e r  (1951),  (1952).  - 67 APPENDIX I Experimental data pertaining to dissolution of copper Table I A Methyl amine  (Atm. ).  Ionic Strength (M)  Amine £AJ concentration (M)  7.9  0.10  0.568 1.117 0.801 0.600 0.396 0.195 1.492  Oxygen pressure  Run No. 1" 2 3 4 5 6  11 11 •t t • 11 11 11  7 7R  »»  11 11  »»  5.5  23  Rate (R)  [A)  2  (Mg.cm~ h" )  R  5.80  0.05560 0.07998 PJD6290 0.05450 O.O4613 0.03169 0.09850 0.09800 0.09700  2  :L  15.60 10.20 6.60 3.40 1.20  22.60  22.70 22.90  Table IB Methyl amine Oxygen pressure - 7.9 atm. . . Run No. 16 17 18 19 25 26 27 29  I o n i c s t  $|  ., n g t h  0.10 0.20 " " 0.1 »t •» , f  Free amine [A] Conc'n. (M) 0.192 0.384 0.576 0.480 0.600 0.400 0.700 0.500  Aminium C&H+J Conc'n. (M) 0,040 0.080 0.120 0.100 0.060 0.040 0.070 0.050  Rate (R) (Mg.cm-V ) 1  2.10 7.80 16.70 12.60 11.60 6.20 15.20 8,60  [j^j R 0,0176 0.1880 0.1980 0.183 0.0310 0.0258 0.0322 0,0291  -  68 -  Appendix I (cont'd.) Table IC M e t h y l amine Oxygen p r e s s u r e - 7.9 atm.  Run No.  Ionic strength  25 28 30 20 21 17  0.10 11 11  0.600 _ft  0i20 t • 11  0^384 11  Free amine CKJ C o n c e n t r a t i o n (M)  m  Aminium I o n [ \ F J ' C o n c e n t r a t i o n (M) +  0.060 0.100 0.030 0.120 0,040 0.080  t f  t ?  Rate (Mg.cmSh- ) 1  11.60 15.20 9.20 10.30 5.70 7.80  Table ID M e t h y l amine Oxygen p r e s s u r e - 7,9 atm. . Run No.  Ionic strength (M)  25 28 30 26 27 29 20 21 17 16  0.100  18 19  F r e e amine, C o n c e n t r a t i o n (M)  Aminium i o n QtHf) C o n c e n t r a t i o n (M)  0.600  0.060 0.030  II  II  f t  ft  0.100  0,400 0.700 0.500 0.384 11 11 0.192  0.040 0.070 0.050 0.120 0.040 0,080 0.040  0.200 11  0.576 0.480  0.120 0.100 .  0.200 11 11  1  2  ••»•»  11 1f  kaOng.cm^h-^-M- ) where ki=1.86,k =20.8 .140 160 137 156 124 136 140 . " ' 142 135 100(excluded from mean) 169 167  - 69 Appendix I  (cont'd.) Table IE M e t h y l amine.  I o n i c s t r e n g t h - 0.20(M) Oxygen p r e s s u r e = 7 . 9 atm. •  Run No.  Free amine Concentration  8 9 10 11 12 13 14 15  0.800 »» *» •» •" " " "  ,  Aminium i o n Concentration  (M)  Rate (mg.cm~ h~l)  (M)  2  50.0 18,0 52.0 15.0 17.0 55.6 48.8 18.0  0.195 0.050 0.125 0.025 0.040 0,100 0.075 0.05  Table I I A E t h y l amine I o n i c s t r e n g t h = 0.10(M)  Run No.  1 2 3 4 5 6 O.R.  11  Oxygen pressure (atm.)  7.9  11 11  t» 1.71  2.74 7.90 11  Amine £k) Concentration  0.203 0.400  0.757 0.916 11 11  0.535 1.040  (M)  •Rate (R) (mg.cm h ~ l ) .  1.30 3.60 9.00 12.60 6.90 11.00 6.40  16.60  C a  1H  2  6-0316 0.0445 0.0636 0.0666 :  0.0447 0.0650  - 70 Appendix I  (cont'd.) Table I I B E t h y l amine  Oxygen p r e s s u r e = 7.9 atm.  Run No.  8 9 10  Ionic Strength (M)  Free amine Conc'n. (M)  0.350 0.200 0.200  Rate  Aminium i o n Conc'n. (M)  k  mg. cm'~ h ~ l 2  (mg.cm^h where 3  x  0.210 0.210 0.210  0.100 0.050 0.150  4.50 2.80 5.80  I o n i c s t r e n g t h = 0.10  IIIA  1 2 3 4 5 6 7R 8 9  6.9 »»  (M)  Amine [£) Concentration  0.326 0.958 »»  •« «» »« •»  1.71 2.74  0.630 0.187 1.641 1.293 11 »t  (M)  Rate (R) (mg.cm~ h~l) 2  2. 80 14.30 15.00 7.60 1.10 32.30 20.70 10.20 15.80  2  97.0 90.0 92.  n - B u t y l amine  Oxygen pressure (atm.) .  ^ ) 1  k =2.27, k =20.0  Table  Run No,  - 1  [JJ2 ~  .0381 O.064I 0.0620 0.0523 0.0318 0.0844 0.0809  -  71  -  Appendix I (cont'd.) Table  IIIB  n - B u t y l amine I o n i c s t r e n g t h = 0 . 2 0 (M) Oxygen p r e s s u r e = 6 . 9 atm.  Run No.  Free amine Concentration  Aminium i o n Concentration  (M)  (M)  Rate (R) (mg.cm'^h" ) 1  k (mg.cm- h" M- ) where lq.-l.85; k =23.0 1  1  1  3  2  2.60 1.80 5.00  0.050 0.025 0.025  0.202 0.202 0.398  12 15 17  98.0 80.0 105.  T a b l e IVA Ammonia Oxygen p r e s s u r e = 7 . 9 atm, I o n i c s t r e n g t h = 0.10(M)  Run No.  Ammonia [£\ Concentration  1 2 3 4  (M)  Rate (R) (mg.cnr^h !)  0.65 0.655 0.310 0.086  -  5.45 38.00 14.10 2.10  C'A3 R  2  0.00500 0.01130 0.00680 0.00352  Table IVB Ammonia Oxygen p r e s s u r e = 7 . 9 atm. I o n i c s t r e n g t h = 0 . 1 0 (M) Run No. 5 6 7 8 9 10  .  F r e e ammonia 00 C o n c e n t r a t i o n (M) 0.404 11 0.303 0.202 11 o  Ammonium i o n CNH^^ C o n c e n t r a t i o n (M) 0.0040 0.0080 0.0030 0.0060 0.0020 0.0040  Rate (R) (mg.cm^h"-'-) 26.40 32.80 17.80 22.20 10.00 12.60  R 0.00615 0.00495 0.00515 0.00414 0.00407 0.00322  Appendix I (cont'd.) Table IVC. Ammonia  Run No.  F r e e ammonia Concentration  (M)  Ammonium i o n Concentration  k  (M)  (mg.cm ^ ^ ) where •kj- 4.65, k = 77 - 2  3  2  5 6 7 8 9 10  0.404 0.303 _ 11  0.202 11  0.0040 0.0080 0.0030 0.0060 0.0020 0.0040  2350 2410 2340 2420 2600 2540  1  1  APPENDIX I I  Experimental data pertaining  to catalytic  r e d u c t i o n o f n i c k e l i o n by hyrirogen.  Table I T e s t on r e p r o d u c i b i l i t y , s t i r r i n g and treatment o f c a t a l y s t .  Run No.  S t i r r i n g rate RPM  R  I n i t i a l conc'n. o f n i c k e l (M)  400  R  2  R  3  7  4  I n i t i a l rate (M.min- ) x 10 1  0 . 0 0 5  6  "  1.85  0  1.80 1.80  4 0 0  R^  Remarks  h  1.95  550 R  effect,  »  »•  »  1.90  0.3 gms.FeAc  "  1.95  added Catalyst treated with acetic acid.  Conditions; Concentration of a c e t i c  acid  -  0.2M  Concentration of t o t a l acetate  - 0.06M  Temperature  - 140° ±1.5  Catalyst  -  PH  2  Initial  pH  •  .  10 gms/1400 m l .  - 13.55 atm. -  4.25  .  3  -7kAppendix I I (cont'd.) Table I I Values o f i n i t i a l r a t e and i n i t i a l  Run No.  R, R  R R R  I n i t i a l concentration o f n i c k e l 00  I n i t i a l rate (M.min- ) x 10^ 1  0.005  1.95 1.85 1.20 0.65 3.90  '»  2  0.003 0.0015 0.010  5 7 8  concentration.  Conditions; Concentration o f a c e t i c a c i d Concentration of t o t a l acetate P r e s s u r e o f hydrogen Temperature I n i t i a l pH Catalyst Stirring rate  -  0.2M 0.06M 13.55 atm.  -  4.25 10 gms/1400 m l . 400 RPM.  -  uo°c  ,"  Table I I I I n i t i a l r a t e and amount o f c a t a l y s t  Run No.  I n i t i a l rate (M.min ) x 10^ -1  6  RR]_ RR 2  RR3  R]_ and R  Amount o f c a t a l y s t i n gms. f o r 1400 ml. of s o l u t i o n  2  1.00 4.00 2.70 1.95, 1.85  20 15 10  Conditions: Concentration o f a c e t i c a c i d Concentration o f t o t a l acetate Temperature P r e s s u r e o f hydrogen I n i t i a l c o n c e n t r a t i o n of n i c k e l I n i t i a l pH S t i r r i n g rate  -  0.2M 0.06M 140°C 13.55 atm. 0.005M 4.25 400 RPM  - 75 Appendix I I (cont'd.) T a b l e IV I n i t i a l r a t e and hydrogen  Run No.  P  ?  2  P R]_ and R  I n i t i a l rate ( I L a i n " ) x 10  PH i n Catm») .  P, 3  2  27.2 6.70 3.30 13.55  pressure  1  5.22 2.59 1.82 3.68  4  2.20 1.30 0.90 1.95, 1.85  Conditions: C o n c e n t r a t i o n cf a c e t i c a c i d Concentration of t o t a l acetate Temperature Catalyst S t i r r i n g rate I n i t i a l pH  0.2H 0.06M 140° C' lOgms/1400 m l . 400 RPM 4.25  Table V I n i t i a l r a t e and i n i t i a l hydrogen i n c o n c e n t r a t i o n .  Run No  H  H  RR  Conctn. o f a c e t i c a c i d (M) 0.80 0.40 0.60 0.20  2  3 3  I n i t i a l conc'n. o f hydrogen i o n (M)  3.16 x ICrh 1.60 x 10-^ 2.40 x 1 0 5.6 x 10-5 - 4  I n i t i a l rate (M.min-1) x 1 0 0.65 1.60 1.10 2.70  Conditions: Catalyst Temnerature  %  I n i t i a l concentration o f n i c k e l T o t a l concentration of acetate  15 gms/1400 m l . 140°C 13.55 atm, 0.005M 0.06M.  4  -  76  -  Appendix II (cont'd.) Table VI I n i t i a l rate and temperature Run .No.  Ti  Temperature °C. 160 151  T RR Hi 3  3  Conditions:  130 140 140  1 x 10 T  00  2.31 2.36 2.48 2.42 2.42  log ( i n i t i a l rate)  3  (M.min-1) 1.1 x 10"? 5.1 x 10"* 1.4 x 10"f 2.5 x 10"? 2.7 x 10"*  Concentration o f acetic acid Concentration of total acetate — Catalyst I n i t i a l pH I n i t i a l concentration of nickel Pressure of hydrogen  -2.96  -3.29 -3.85  -3.60  - 3 . 5 7 (rate converted to 15 gm/HC0 ml)  0.2M 0.06M  15gms/1400 ml. 4.25 0.005M 13.55 atm. '  Table VII Final hydrogen ion concentration and corresponding equilibrium nickel ion concentration. . Run No,  pH I n i t i a l Final  CH (final) +2  Equilibrium nickel Concentration (M) x 10  3  - 77 -  Appendix I I (cont'd.) )  :  Table VIII Hydrogen pressure and corresponding equilibrium n i c k e l concentration. Run No.  P, P P RR 2  3  2  Pressure of H (atm.).  27.2 6.70 3.30 13.55  1  2  P  x 10  H  3.67 14.90 30.30 7.40  2  Equilibrium concentration. of n i c k e l (M) X 103  0.30 0.85 1.55 0.35  S i s i r Coomar SIRCAR  PUBLICATIONS: 1.  Studies on the behaviour of bi-univalent s a l t s i n aqueous s o l u t i o n , Part VII, Copper Acetate, (with S. Aditya and B. Prasad), J . Indian Chem. S o c , 50, 655, 1955-  2.  Studies on the behaviour of bi-univalent s a l t s i n aqueous s o l u t i o n , Part X, Zinc Perchlorate, (with B. Prasad), J . Indian Chem. S o c , 31, 483, 195^.  3.  Determination of s o l u b i l i t y product of copper oxide, (with B. Prasad),.J. Indian Chem. Soc,.1955-  h.  Studies on the behaviour of uni-bivalent s a l t s i n aqueous solution, .Part I I , Na S0 , (NEL4) S0 , (with B. Prasad), J . Indian Chem. S o c , (in press). 2  5>  4  2  4  Studies on the behaviour of uni-bivalent s a l t s i n aqueous solution, .Part I I I , N a C 0 , (with B. Prasad), J . Indian Chem. S o c , (in press). 2  2  4  6.  Studies on the behaviour of bi-bivalent s a l t s i n aqueous s o l u t i o n , .Part I I , ZnSC-4, (with B. Prasad), J.. Indian Chem. S o c , (communicated).  7-  Studies on the behaviour of bi-bivalent s a l t s i n aqueous s o l u t i o n , Part IV, MnS0 , BeS0 , CuS0 ,.(with B. Prasad), J . Indian Chem. Soc,(communicated). 4  4  4  

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