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Reduction of thio-molybdate in aqueous solutions Okita, Yoshiaki 1969

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THE R E D U C T I O N OF T H I O - M O L Y B D A T E AQUEOUS  IN  SOLUTIONS  by YOSHIAKI OKITA B. E n g . , T h e U n i v e r s i t y  o f T o k y o , 1962  M.  o f T o k y o , 1964  E n g . , The U n i v e r s i t y  A THESIS  SUBMITTED I N P A R T I A L  THE REQUIREMENTS  F U L F I L M E N T OF  FOR THE DEGREE  OF  DOCTOR OF P H I L O S O P H Y  in  the Department of METALLURGY  We  accept  required  this  thesis  as c o n f o r m i n g  to the  standard  THE U N I V E R S I T Y OF B R I T I S H December, 1969  COLUMBIA  In  presenting  requirements British freely that  this  available  permission  Department  in partial  f o r an a d v a n c e d  Columbia,  scholarly  thesis  I agree  degree  that  f o r reference f o r extensive  purposes  may  be  f u l f i l m e n t of the at the U n i v e r s i t y  the L i b r a r y  shall  and s t u d y .  I further  copying  granted  by  of t h i s t h e Head  o r by h i s r e p r e s e n t a t i v e s .  that  copying  gain  shall  or p u b l i c a t i o n  n o t be a l l o w e d  of t h i s  without  my  of  Metallurgy  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, C a n a d a  Columbia  make i t agree  thesis for of  my  I t i s understood thesis  for financial  written  YOSHIAKI  Department  of  OKITA  permission.  ii  ABSTRACT  The (VI)  high  -sulphur  ammoniacal  temperature  (-II) -water  b u f f e r was  At  150°C.  system  a l lspecies  to e x i s t  tri-,  and  tetra-thiomolybdate  M." ,  2.7  x  were  strong  Mo(SH)g,  and  10  7.0  3  the  molybdenum  i n the presence  of  the s t a b i l i t y  M." ,  8  of  o f an  studied.  shown  2  behaviour  indications  1 0  MoO. S 4-x x o f mono-,  constants  were  x 10  of  the form  2.3  M.~ ,  x  10  2 - 1 M.  were d i - ,  , 3.5  respectively.  4  the f o r m a t i o n  i n solutions containing  low  Application  gases  x  species,  of  free  system  pro-  ammonia.  duced  a mixture  whose  composition  the  of a s u l p h i d e depended  on  and  an  to t h i s  oxide  the i n i t i a l  o f molybdenum , composition  of ,  solution. Under  catalytic, hydrogen rate  of reducing  hydrogen,  rate  being  pressure.  determining  hydrogen paths,  on  one  was  dependent  higher  The  step  was  being  produced.  proposed  of  of  and  i n which  followed  and  auto-  amount  of p r e c i p i t a t e s  the s o l u t i o n  the c o n c e n t r a t i o n  sulphide  i n product  activation  the s u l p h i d e  distribution  r e a c t i o n was  heterogeneous  proportion  on  order  A m e c h a n i s m was  to produce  oxide.  fractional  first  the s u r f a c e s  the  the r e d u c t i o n  the other  by  two produce  the s u l p h i d e  to the  composition,  the higher  tetra-thiomolybdate  of hydrogen  the  of  to  5  There  of protonated  concentration  10  oxide  and  the  i o n , t h e more  the  the  Under found  carbon  monoxide  to  have  an  solution  then  followed a  with  time.  dependence A  mechanism  was  a  bdates  slow and  precipitate  The on  induction  slope  both  was  of  decomposition carbon which  period.  linear this  molybdenum  proposed  of  The  plot  molybdenum  showed  the  Langmuir  rate  complex  adsorbed  the  in  type  between on  of  pressure.  determining  strongly  during  was  in concentration  c o n c e n t r a t i o n and  some  produced  reduction reaction  decrease  i n which  monoxide was  the  step  thiomolycatalytic  induction  period.  iv  ACKNOWLEDGEMENT  I patience  am  grateful  and encouragements  this  thesis.  ment  of Metallurgy  fields  grants  Council  I wish  during I  for  t o D r . I.H. Warren  my  am  to thank  f o r their  thankful  countless  of  of the Depart-  assistances  to the people  through  and f o r f e l l o w s h i p s  and t h e U r a n i u m my  a l l members  and i n d e b t e d  i n a i d of research  To  the preparation  i n various  stay.  o f Canada  Foundation  also  throughout  forhis direction,  wife  Research  the National through  Research  the Lead-Zinc  Foundation.  I say thank you.  o f Canada  V TABLE  OF  CONTENTS  Table  Page  INTRODUCTION  1  1  General  2  L i t e r a t u r e survey 2-1 2-2 2-3 2-4  1  2-4-b 2-4-c 2-4-d 2-4-e 2-4-f  3  PART  Scope  2  T e c h n o l o g y o f molybdenum i n d u s t r y H y d r o m e t a l l u r g i c a l treatments o f molybdenum o r e s Reduction of aqueous molybdenum solutions The molybdenum ( V I ) - s u l p h u r ( - I I ) -water system 2-4-a  2-5  .  Salts of tetra- substituted species Salts of d i - substituted species . . S a l t s o f mono- a n d t r i - s u b s t i t u t e d species Species other than those of the f o r m MoO, S 2~ H — X X Studies of the e q u i l i b r i u m between the complex s p e c i e s A c i d d e c o m p o s i t i o n o f t h e complex species . .  Synthesis  o f molybdenum  of present  di-sulphide  . . . .  work  1 - STUDY OF E Q U I L I B R I U M I N THE MOLYBDENUM ( V I ) -SULPHUR ( - I I ) -WATER S Y S T E M 1 2  3  2 4 6 8  10 14 15 16 17 17 21 24  26  P r i n c i p l e of experiment Experimental  26 30  2-1 2-2 2- 3  30 32 33  A p p a r a t u s and p r o c e d u r e s Reagents A n a l y t i c a l methods  Results 3- 1 3-2 3-3  3-4  and c a l c u l a t i o n s  Observed spectrogram C a l c u l a t i o n of formation f u n c t i o n and free sulphide concentration Conversion of free sulphide concentration to aqueous h y d r o g e n sulphide concentration C a l c u l a t i o n of s t a b i l i t y constants from formation curve  36 36 37  42 44  vi Table  Page  3-4-a 3-4-b 3-4-c 3-4-d  3-5  4  PART  Numerical constants  calculation (2)  OF R E D U C T I O N  -SULPHUR  51  stability 53 60  I N THE MOLYBDENUM ( V I )  ( - I I ) -WATER  SYSTEM  . .  72  Experimental  72  1-1 1-2  A p p a r a t u s and p r o c e d u r e s A n a l y t i c a l procedures  72 74  1-2-a 1-2-b  74 75  Analysis Analysis  of solutions of precipitates  2  Precipitation  i n an i n e r t  3  Precipitation  i n hydrogen  3-1  3-2  3- 3 4  of  44 47 49  D i s c u s s i o n and c o n c l u s i o n s  2 - STUDY  1  Bjerrum's H a l f - n Method Two-parameter Approximation . . . . Calculation of Numerical c a l c u l a t i o n of s t a b i l i t y c o n s t a n t s (1)  Reduction  Aqueous  3-1-b  Precipitates  81 87 87  phase  87 87  study  105  3-2-a  Effect  of pressure  3-2-b 3-2-c 3- 2-d  Effect Effect Effect  of temperature 109 of catalyst 121 o f s o l u t i o n c o n d i t i o n s . . . . 123  D i s c u s s i o n and C o n c l u s i o n  Precipitation 4- 1 4-2  .  products  3-1-a  Kinetic  atmosphere  i n carbon  monoxide  Reduction products K i n e t i c study 4- 2 - a Induction period 4-2-b Growth  107  133 137 137 1  4  1  1^5 1  4  8  vii  Table  Page  4-2-b-l  4-3  GENERAL  SUMMARY  SUGGESTED  148  4-2-b-2  Effect  of p r e s s u r e  4-2-b-3  Effect bdenum  of t o t a l molyconcentration.  Discussion  AND  E f f e c t of sulphide concentration  and C o n c l u s i o n s  CONCLUSIONS.  F U T U R E WORK  . . .  . .  148  150 154  161 163  REFERENCES  165  APPENDICES  170  A  Experimental  B  Spectrogram  C  Rate  data of s o l u t i o n s  of e q u i l i b r a t i o n  171 184 191  LIST  Technology  o f molybdenum i n d u s t r y  Pressurized Plot  OF F I G U R E S  solution  of equation  Calculation  injection  . . . . .  system  . . .  (10)  of n  n v s . S^ Conversion  o f S. t o [H„S] r z aq. Formation curve of thiomolybdate 150°C. . . Calculation  o f k^ , 1 5 0 ° C .  Calculation  o f k^ , 120°C  Numerical (2) Plot  calculation  of numerical  system at  .  .  of s t a b i l i t y  calculation  (2)  Schematic  diagram  Variation  of c o n c e n t r a t i o n s under  First  order plot  X-ray  diffraction  constants  of thiomolybdate  patterns of  system  .  nitrogen  precipitates  T.G.A. o f p r e c i p i t a t e s  from  runs  . . . .  D.T.A. o f p r e c i p i t a t e s  from  runs  . . . .  Composition of p r e c i p i t a t e s , solution composition r ( r  dependency S  +  r  H  2  ~  3  )  vs. initial  on a c i d i t y V  S  '  r  S  P  .T.G.A. r e s u l t s , w e i g h t  l  0  loss  t  '  vs. r  M O j v s . S^ a n d t i m e Variation  of Mo  T  v s . time,  under  ' ' S  ix Figure  Page  24  Log  25  Slope  26  Two-stage  27  Plot in  (Mo  H  - Mo)  Q  and  vs.  time  intercept  I l l  vs.  pressure  112  run  o f a~  114  v s . a,  during  precipitation  . . . . .  2  28  Variation  29  Plot  30  Effect  of  catalyst  31  Effect  of  solution  condition,  Mo^  32  E f f e c t of variation  solution  condition,  (NH^)^  of  of  116  ln  total  (P/(a +  Po  - P))  118 vs.  time  120  .'  122 variation SO^  .  . .  124  amount 126  33  Plot  of  slope  34  Slop  v s . ct [ N H  vs. a  35  Plot  of  36  Effect  4  + 4  1/slope of  pressure  and  ] / [NH vs.  solution  3  [NH^ ]/[NH^J , 1 5 1 . 6 ° C . +  .  J , combined  130  1/ ( a ^ [NH^"*"] / [NH^ ] ) condition,  S  129  130  variation,  T  158.8°C  132  37  Variation  o f Mo^  38  D.T.A.  39  Variation  o f Mo^  under  CO,  high  40  Variation  o f Mo^  under  CO,  low  41  Variation  o f Mo^,  under  CO,  high  42  Induction  period  vs.  43  Induction  rate  44  Growth  rate  45  Effect  of Mo  46 47  Growth 1/rate  u n d e r CO, vs. 1/P  48  Integral  results  of  under  T  on  rate plot =  139  from Mo  T >  Mo^, Mo^,,  CO  run  .  P varies P varies S varies  .  .  140  .  .  142  .  .  143  .  .  144  pressure  rate,  Y  CO  precipitates  vs.  induction  C 0  plot,  S ,  constant  vs. T  and  147  S^  147  period  149  158.8°C  149  vs. pressure  l n Mo  +  at.  . . . . . . . . .  151 15? 155  X Figure  Page  B-l  Spectrogram  of s o l u t i o n s ,  Equilibrium  B-2  Spectrogram  of s o l u t i o n s ,  Equilibrium  NH  186 low 187  3  B-3  Spectrogram  of s o l u t i o n s ,  Run  under  ^  . . . .  188  B-4  Spectrogram  of s o l u t i o n s ,  Run  under  CO  . . . .  188  B-5  Spectrogram  of s o l u t i o n s ,  Run  under  B.^  . . . .  189  B-6  Spectrogram  of s o l u t i o n s ,  equilibration  . . . .  190  C-l  Variation room C  vs. time, S  C-3  C /Mo S  C-4  Plot  3  concentration,  temperature  C-2  3  of complex  T  T  T  193 varied  194  v s . time  of rate  vs.  196 concentration  (normalized)  197  C-5  Test  of i n t e g r a l equation .  200  C-6  Plot  f o r C,,  200  Equation  (C-5)  xi LIST  OF  TABLES  Table 1  Page Summary o f s t a b i l i t y by  2 3  4  various  calculated  methods  61  E f f e c t of temperature constants  on  consecutive 69  P r o p e r t i e s of v o l a t i l e materials heating the p r e c i p i t a t e s X-ray  diffraction  from v a r i o u s 5  Composition  6  Analysis  7  Variation  8  constants  data  for  by 88  and  precipitates  conditions  90  of p r e c i p i t a t e s  of oxygen of r  g  96,  97  i n the p r e c i p i t a t e s  and r  by  R  reaction  2  Effect  on  of temperature  study  M0S2  produced  A-l  The  of e q u i l i b r i u m  A-2  P r e c i p i t a t i o n under  A-3  P r e c i p i t a t i o n under  H  A-4  P r e c i p i t a t i o n under  CO  the extent  97 of 106  the rate  120a 171 175 6  1 7 2  1  8  1  1  INTRODUCTION  1.  General Molybdenite,  lubricant, It  particularly  is usually  mineral  to  of  acid  by  a  remove  known  be  many  an  process  materials  attempts  excellent  applications^. involving  c o n c e n t r a t e and  abrasive  demand,  to  temperature complex  molybdenite  to  increasing  is well  for high  manufactured  dressing  hydrofluoric Owing  M0S2,  have  leaching  with  such  as  silica  been  made  2  to  3  produce have  molybdenite  involved  sulphur, from  an  direct  with  of  state to was  of  reduction  undertaken  containing of  study  molybdenum  sulphide  developing  to  ion with a  and  but  no  of  the  reported  attempts  compounds  attempts  is a  to  except  As  compound  the  usual  p r o d u c t i o n of  sulphidization. the  i n the the  Most  and  produce in  some  reduction  of  hexa-valent  object  recovery technique  of  of and  tetramost  molybdenite The  state  subjects  are  the  literature  reviewed:-  survey  below,  the  likely  work  solutions  i n the  producing M0S2  f o r molybdenum  is  present  aqueous  stable  and  from  presence of  process  solutions. In  i t  interest.  sulphur.  i s +6,  .  molybdenum  been  molybdenite  with  molybdenum  involve  have  geochemical  molybdenum  of  results,  system  Nominally valent  fusion  varying  aqueous  experiments  synthetically  following  2 1.  The  technology  2.  The  hydrometallurgical  and  o f the molybdenum treatment  industry. o f molybdenum  ores  intermediates.  3.  The  reduction  4.  The M o ( V I )  5.  The  -  of aqueous s o l u t i o n s S(-II)  synthesis  of  2.  Literature  Survey  2-1  Technology  of  - water  molybdenum.  system.  MoS2-  the molybdenum  Molybdenum  of  i s known  industry  to improve  the q u a l i t y of  iron  4 and  steel  and  i t s use  ness of  alloys  i n nature  compounds  as an  summarized sent  o f molybdenum  limits  and  i n F i g . 1, forms  traded  as  a by-product  to  the f a c t  from  that  molybdenite,  of copper no  more  industry,  the  reagents  have  o f modern  of which  concentrate purification  established  industry.  production  is  underlined  than  90%  about  production i s done  corros-  molybdenum  the percentages More  use  lubricating of  materials with  scarce-  usefulness  o f molybdenum  material  the major  the s p e c i a l  element  of the s p e c i f i c a t i o n .  comes  steel  c a t a l y s t s and  i n which  a strategic  Although  metal,  indispensable  as  of i t s r e l a t i v e  the chemical  technology  the product  produced  and  as p i g m e n t s ,  The  the  i s i n the i r o n  of M0S2  molybdenum  i n spite  (3/10,000 of iron)"*.  resistance  properties  It i s classified  i s increasing  molybdenum  ion  .  of  reprelisted  molybdenum  half .  as  comes Owing  f o r the  majority  oxidized  molybdenite(MoS ) 2  CaMo0 , FbMo0 , F e ( M o 0 ) , e t c .  copper b y - p r o d u c t s O.OI-O.O5/0M0S2  primary ore 0.2 - l.C$MoS  grade:  2  ores  4  4  2  4  3  above 0.1#Mo  mineral dressing molybdenite concentrates above 85%MoS , below lfoCu 2  Hydrometallurgical : treatments  roasting t e c h n i c a l molybdic oxide(M0O3) above 55</oMo, below lfoCu and 0.25$S purification leaching with HF s o l u t i o n s  briquetting with p i t c h  pyrometallurgy  reaction w i t h CaO  sublimation : pure m o l y b d i c oxide above 99.5$>Mo0 3  pure MoS above99.9$MoS no s i l i c a t e s : 2  lubricant  use:  2  M0O3 b r i q u e t t above 52$Mo~ below 12$C, below 0.5#Cu  ferromolybdenum 58-6^Mo  reaction reaction w i t h NaOH w i t h WH3  CaMo0  4  Na MoQ 2  hydrogen r e d u c t i o n  ammoniummolybdenum m e t a l molybdate powder : above 95%Mo, below : 2.5f Fe, 1 . 5 $ S i , 0.5#Cu.  4  0  f e r r o - a l l o y s and f o u n d r i e s  catalysts reagents  pigment fertilizer  sheet, rod, w i r e , nonferrous a l l o y s  85.Cf  0  io-v.se i s i n terms o f molybdenum c o n t e n t , i n lT.S .A. i n I966. r e f . " M i n e r a l Yearbook" r  F i g . 1. Technology o f molybdenum, ( u n d e r l i n e d a r e commercial forms w i t h s p e c i f i c a t i c e s below)  4 of  uses,  molybdenite  requirements. is  termed  with  c o n c e n t r a t e must meet  Although  the m i n e r a l d r e s s i n g of  simple , several 7  cleaning  i n t e r m e d i a t e low temperature  grinding  are necessary,  stringent  sometimes  molybdenite  and r e - c l e a n i n g  roasting  purity  steps  or steaming  at the expense  and  of recovery,  8 in  order  cations or  t o meet  a r e n o t met  other  gical ores  after  these  .  processing i s essential o f molybdenum. stringent  Hydrometallur-  i n the treatment  of  molydbenite  requirements  a l l abrasives, particularly  specifi- .  hydrometallurgical  be u s e d .  L u b r i c a n t grade purity  If purity  treatments,  p r o c e s s i n g t e c h n i q u e s must  e v e n more of  the s p e c i f i c a t i o n s  silica,  since which  oxidized must  meet  i t m u s t be  free  i s normally  2 removed  by  treatment  molybdenite the  and  production cation by ing  molybdic  foundries without of metal  oxide  further  and c h e m i c a l s  .  Sulphur  molybdenum the desired  trioxide,  i s used  and o t h e r  which  Hydrometallurgical treatment  step  of  s u l p h u r and mainly  of  in ferro-  For purifi-  impurities  a r e removed  t r e a t m e n t s , thus i s further  end products"''' ^ '  Majority  purification.  another  s u b l i m a t i o n or h y d r o m e t a l l u r g i c a l  produce 2-2  technical  i s necessary.  pure  acid  c o n c e n t r a t e s a r e r o a s t e d t o remove  resulting  alloys  with hydrofluoric  produc-  processed  to  .  of molybdenum  ores  and  intermediates. Hydrometallurgical in  the p u r i f i c a t i o n  processing  methods a r e c u r r e n t l y  of t e c h n i c a l  of o x i d i z e d  ores.  The  molybdic former  oxide  employed  and t h e  involves  1)  disso-  lution other  i n dilute  ammonia  insolubles  metals  such  t o remove  2) p r e c i p i t a t i o n  as copper  as s u l p h i d e s  hydrosulphide  3) p r e c i p i t a t i o n  acidification  4) r e e r y s t a l l i z a t i o n  to  molybdic  metallurgy oxidized bodies iron 2)  oxide'''"'". which  ores  recent  minerals.  adsorption  of heavy  by a d d i t i o n  ammonium  and  m o l y b d a t e by  5) c a l c i n a t i o n i n -  i s i n the processing overlaying  ferric-molybdates  I t involves on c h a r c o a l  of  sulphide ore etc.,  mostly i n  1) d i s s o l u t i o n i n a c i d 3) s t r i p p i n g  4) c r y s t a l l i z a t i o n  of  a p p l i c a t i o n of hydro-  o f molybdenum, found dispersed  s i l i c a and  and f i l t r a t i o n  o f ammonium  The s e c o n d  i s more  as f i n e l y  ammonia  sulphides,  with  o f ammonium  an aqueous  m o l y b d a t e and 12  5)  calcination The  to produce leaching  to  be a s u b j e c t  of  processing  purification (a)  of molybdenite  of interest  lower  grade  methods.  i n acid  t e c h n i c a l grade  media:  H„S0.+Mn0 2 4 2  because  concentrates  i toffers  concentrates  The l e a c h i n g HN0 +H SC> 3  2  '  1  4  oxide h a s come  the p o t e n t i a l  and g i v e s  methods 1 3  4  molybdic  a choice  of  proposed a r e : -  , H S0 +NaC10 2  4  ,  1 4 3  1 5  o  (b)  i n alkaline (high  (c)  Although found  temperature)  bacterial  leaching  costly.  media:  Na C0 +HC10 2  3  1 6  '  1  7  '  1  8  , KOH+C>  2  19  leaching.  was s u c c e s s f u l ,  the oxidants  employed  were  6 Various the  leached  stripping  solution  ferricmolybdate  13  were  and c o n c e n t r a t i o n methods  suggested,  14 ' , molybdenum  e.g. p r e c i p i t a t i o n  as  20 tri-hydroxide a n d ammonium  17  molybdate 18,24,25  21 23 ' ' , i o n exchange , . and s o l v e n t e x t r a c t i o n  from  using  anion exchange r e s i n s 26 , ,12 TBP , charcoal and  using  2 7  others 2-3  Reduction  o f aqueous  Reduction  solution  o f molybdenum  o f molybdenum complexes  i n acid  solution  28 is  known  t o be p o s s i b l e  , although  i ti s reported  that 29  molybdate An  i o n i s reduced  industrial  method  infinitely  has been  slowly  suggested  i n alkaline  f o r recovery  molybdenum from a c i d s o l u t i o n s as Mo(OH)^ a f t e r Mo w i t h •i r o n m e.t a..20 l 30 6  media  of  reducing  +  M  Paal ous  hydrogen  and Buetter  studied  at atmospheric  pressure  the absorption and a t room  in  s o l u t i o n s (-0.05M.) o f ammonium m o l y b d a t e  of  a very  active  Absorption 30  palladium  was n o t e d  complete also  f r o m +6  until  reduction being  reported  reaching  duction  50~60%  that  initially  very  only  overpressure  the t h e o r e t i c a l  stage,  process, ,  three  further,  days. when  They heat  o f h y d r o g e n was a p p l i e d ,  value  equivalent  to tri-valent. they  (within  value of  slow  after  presence  catalyst.  rapidly  of the t h e o r e t i c a l  achieved  temperature  i n the  as a  the r e d u c t i o n proceeded  of hexa-valent  the i n i t i a l  added  t o +4, f o l l o w e d b y a v e r y  (~60°C.) a n d s l i g h t  in  to occur  m i n . ) up t o a b o u t  reduction  hydrosol  of gase-  could, after  From  to the r e -  the p r e c i p i t a t e  careful  drying,  7 obtain  Mo(OH)  MoO(OH)  4'  Lyapina duction  in acid  reduction  by  "primed" to  form  by  for  the the  seed  hydrogen  were  7.0,  60  atm.  and 38.3  even the  an  pH  in  initial  pH  The  of  and  hours,  11.7% of  2  as  in  40,  70 20  and and  fast  initial  pH  of  hours  34%,  (final At  5  200°C,  and  At  7  atm.  78%  when i n i t i a l  concentra-  from  5.33  to  99%  tions  molybdenum were d e c r e a s e d  43.6  one  under  2 0 0 ° C . , 60  increased  in  gave  100°C.  precipitation and  at  respectively,  atm.  3,  respectively. 41%  amount)  molybdenum  respectively).  only  when  four  10  re-  batch  stoichiometric  82,  recovery of  from  times  the  43.62 g . / l . of  60,  an  hydrogen  that  recoveries  2.67,  gave  At  of  99,  recovery,  same c o n d i t i o n .  four  (7%  2 were  the  reported  containing  of  successively.  2 '  studied  to  powder  3.94  four  and  two  pressure  6.56,  31  They  crystal.  solutions  initial  pH  81.1,  solution.  molybdenum  M0O2  MoO  Zelikman  h y d r o g e n was  200°C. f r o m with  and  and  to  hour,  the  g./l.  32 In  a  subsequent  of  tungsten  bdenum.  W at  0.5  from  When a  5 g.W/1. a t 20 a t m . for and  paper a  reported  the  containing  containing  selective  tungsten  41.0  reduction  and  g.Mo/1.  moly-  and  i n i t i a l pH o f 2 was r e d u c e d a t 200°C. and P 90 m i n . , t h e s o l u t i o n c o n t a i n e d 38.9 g.Mo/1.  g.W/1. a n d  200°C. and  accelerator, respectively. are  solution  solution  respectively.  data  they  the  precipitate  When t h e  P  =  2  the  60  atm.  solution  As  difficult  the to  solution  pH  with  Mo  contained value  analyse.  was  47%  was  reduced  powder 0.3  varied  and  40%  2  i n Mo  and  subsequently  added  as  an  g . / l . of  Mo  and  considerably  their  W  A somewhat  different  approach  to the reduction i n 33  an  acid  s o l u t i o n was a d o p t e d  photolysis  of acidified  sodium  pH = 2 b y H C l a d d i t i o n ) H ,  under  CO, C 0 , H e , v a c u u m , H  2  by Dodonova  2  molybdate various  + 0  2  who s t u d i e d t h e  2  solutions  atmospheres  a n d CO + 0^.  (made such as  He n o t e d t h e  6+ appearance  of blue  Mo^  H  +  under  2  c o l o r due t o t h e r e d u c t i o n  a n d CO a n d n o a p p e a r a n c e  attributed  the l a t t e r  photolysis  products  with  H  blue  o f Mo  colour  .  by  Kunda and Rudyk  and  initial  linear  4  centrations  of  o f molybdenum w i t h  .  combine  the rapid + 0  2  2  mixture,  hydrogen  found  solution  very  2  of the rate  of precipitation  and g r a p h i t e ,  deter-  (added as  found  23 a t m . ) ,  a t 177°C.,  1 M.Mo, 1~1.5  an a p p r o x i m a t e  of precipitation  with  were  as w e l l as m e t a l l i c  o f c a t a l y s t s and (NH^^SO^ (below  and temperT  effective  for a solution containing They  ammonium  pressure  of precipitation  palladium  i n ammoniacal  a p p l i c a t i o n i n mind,  The e f f e c t s o f c a t a l y s t ,  and e x t e n t  of hydrogen  the rate  i nH  hydrogen  an i n d u s t r i a l  a n d 1.5~2 M.NH^•  increase  pressure  was i n c r e a s e d  powder, m e t a l l i c n i c k e l  24.5 atm. H  M.(NH ) S0  2  s o l u t i o n ) as a c a t a l y s t ,  2  molybdenum  2  When 0  avoiding  partial  They a g a i n  4  2  molybdenum,  mined.  and  H 0 a n d HCHO t h u s  otherwise  o f ammonium i o n , f r e e  on t h e r a t e  PdCl  would  concentrations  ature,  0.5%  He  +  was s t u d i e d , w i t h g  recycling,  the others.  disappeared.  Reduction solution  to  t o t h e o x i d a t i o n o f Mo"' b y t h e  of water, which  a n d CO t o f o r m 5+  2  reoxidation the  fact  under  o f Mo  with  and w i t h  partial  and a l i n e a r  the i n i t i a l  the con-  decrease  concentration  of  molybdenum.  Increase  rate  of  reduction.  rate  of  p r e c i p i t a t i o n at  studied  with  PdCl^  both  cases  16.4  Kcal./mole.  and  4-5%  partly  2-4  the  NH^, to  The  The  and  of  apparent Their  metal  of  powder  as  a c t i v a t i o n energy precipitates that  the  state  Mo  system  In  system,  Mo(VI)-water  in  the the  variables  was  the  catalyst.  was  found  reduction  (67%  of  contained  Mo(VI)-S(-II)-water the  decreased  dependence  c e r t a i n values  Mo  trivalent  ammonium  temperature  suggesting  the  free  to  60-65%  had  be Mo  proceeded  Mo(0H> ). 3  under  weak  acid  con-  4ditions,  large  and  a  and  non-metallic  r v  [X  n+  large  M  rt  Mo,0 6  isopoly  family  of  ions  But  ions,  complex  ions  under  sulphide  e.g.,  ions  with  _ 2+ , Co  , Mn  34  Mo^C^^  many  metallic  e.g.,  =  ...2+ Nl  sufficiently  decompose  When  formed,  heteropoly  ,m(2x-36-n)„ ] , X x m  35 etc. .  are  In  into ion,  alkaline  the S  2-  simple ,  is  2+  , Cu  2+  , Se  conditions molybdate  introduced  4+  3+ ,P ro  these  ion,  MoO^  into  the  2-  2Mo(VI)-water  system,  sulphide  can  these  ion  the  Most  expected  following  of  of  because  oxide of  ion,  the  0  ,  with  similarity  of  t h e s t u d i e s o f t h i s s y s t e m up t o 1928 36 w e r e r e v i e w e d by M e l l e r a n d up t o 1963 by t h e Chemical 37 S o c i e t y of London . The m o r e r e c e n t s t u d i e s a r e r e v i e w e d in  ions.  be  interchange  order:  ,  .  10 (a) s a l t s  of t e t r a - s u b s t i t u t e d  2_  s p e c i e s , MoS^  ,  2(b)  salts  of d i - s u b s t i t u t e d  (c)  salts  o f mono- a n d  Mo0 S ~,  MoOS  2  3  2 3  species,  M0O2S2  tri-substituted  ,  species,  ~, 9  (d) s p e c i e s o t h e r (x  of the form  MoO,  S  = 1-4),  (e)  studies  (f)  acid  2-4-a  than  Salts  of the e q u i l i b r i a between  decomposition  of the complex s p e c i e s .  of t e t r a - s u b s t i t u t e d  Salts  the complex s p e c i e s ,  species,  of the t e t r a - s u b s t i t u t e d  MoS^  2-  species  (or tetra-  2thiomolybdate) *  MoS^  , have been  claimed  by a n u m b e r  of  36  workers  .  The  blood-red, ating  ammonium s a l t  needle-like  crystal  ( N H ^ ^ M o S ^ was b y Kruess  i n 1884  a n a m m o n i a c a l ammonium p a r a m o l y b d a t e  hydrogen  s u l p h i d e gas.  similarly Alkali  for their  metal  salts  Tridot  visible  and  by  solution 39  Bernard  a n d U.V.  prepared  also  as a satur-  with  ,  prepared i t  spectroscopic study.  have been o b t a i n e d ^ .  Spacu and  3  co-worker ^ 4  p r e p a r e d t h e s a l t s o f c o m p l e x m e t a l l i c a m i n e o f Cu a n d C r : [Cr(NH ) ][MOS ]N0 |H 0,[Cr(NH ) Cl][MoS ],[Cr (OH) en ] 3  6  4  IMOS ] S0 , 4  and  2  stated  alkali  4  3  3  6  [Cr (OH) en ][MoS ] Cl 4  that these  metal  2  salts.  6  6  4  salts They  2  4  2  and  [Cu  were more s t a b l e  also  prepared  4  6  6  en ][MoS ]|H 0. 2  than  the s a l t s  4  the  2  simple  of organic  bases  such  as  those  of  methylenetetramine  aminopyridine,  and  ethylenediamine ,  1,10-phenanthroline.  hexa-  Perel'man  and  41 co-workers  employed  the  sodium  system.  After  salts  NaOH a t  60-70°C.  of M o  =  6 +  were  of  27%  the  25°C.  t o make up  f o r 24  They  and  hours  reported  2  4  lattice.  compound,  a solution  the  Na^oO^, Na S  and  2  composition  NaOH = 5 ~ 4 0 % , t h e and  solid  and  that Na^oS^  and  due  Langrock  range  mixtures  liquid  d i d not  to the 42  tetra-thiomolybdic acid,  Ni(II),  tures  of  Leroy  and  by  the  The a  phases exist  instability  prepared  an  H M o S , by 2  4  MoS^  days  the  by  Cu(II)  co-workers  reaction  formed  at  of  was  -5°C.  reaction  45  metric  and  Zn(II), metals  prepared  molybdic  acid  +  stating  of  They of  the  w i t h NX^OH  and  prepared  with  complex.  the  salts or E t , ) . after  were  and  (AsPh^^  chloride  S a x e n a and  of a + K  mix-  s u l p h i d e and  (NEt^^MoS^  pass-  trisulphide  (X = Me  (PPh^^MoS^  ammonium s a l t  tetrapheriyl  t o be  q u a r t e r n a r y ammonium  (NMe^^MoS^ also  them  w i t h molybdenum  saturated w i t h hydrogen  crystals  corresponding  workers  ammonium s a l t  s u l p h i d e s of these 44  solution  few  the  to  through the H form 43 c a t i o n exchange r e s i n . C l a r k and D o y l e confirmed the a n d NH"!" s a l t s b u t d e n i e d t h e e x i s t e n c e o f t h e s a l t s o f 4 Co(ll),  of  Bock  study  the  NaOH c o n c e n t r a t i o n p e r h a p s  Na MoS  unstable ing  at  method  dissolving  = 6~13%  2  analysed.  below  i n water  3~30%, S "  were kept  solubility  of.  co-  46 '  confirmed  titration  of  the  Pb(N0,j)  f o r m a t i o n of 2  and  PbMoS^ by  thiomolybdate  ampero-  solution.  Crystallographic thiomolybdates molybdate  and  ion  study  of  spectroscopic  in solution  the  salts  study  of  of  the  have been r e p o r t e d  tetra-  tetra-thioby  several  3 8 workers.  Kruess  K^MoS^ a n d planes,  grew l a r g e  from  the  Haushofer  crystals  measurements  reported  of  them as  of  (NH^^MoS^  and  angles  between  habit  having  w i t h ;a:b-:c = 0 . 7 8 4 6 : 1 : 0 . 5 6 9 2 study  of  the  reported a  =  9.599, b  be NH^  be  =  orthorhombic  12.288,  c =  and  Gattow  MoS^  with A,  with  K^SO^  tetrahedral ion  2  the  7.000  - Pnam, i s o - m o r p h o u s ion  .  ammonium t e t r a - t h i o m o l y b d a t e  i t to  rhombic  symmetry  made a n  X-ray  crystal  and  / 7  op  unit  and  length  as  group  to  i t s space  type  are  cell  crystal,  packed  in  rather  which  loosely  +  +  G a t t o w a n d F r a n k e s u m m a r i z e d t h e i r X - r a y d a t a f o r K , Rb , + + 49 50 Cs a n d NH^ s a l t s . Schaeffer et a l . r e p o r t e d t h e same 2experiment  and  stated  t h a t MoS^  t e t r a h e d r a are  slightly  distorted. The  Mo-S  bond  Raman s p e c t r o s c o p y . t h e I.R. s p e c t r a + + + Rb , Cs NH^ the  band  Gattow,  has  Franke  and  I^MoS^ c r y s t a l s , +52 and Tl , and  ally  unchanged  by  460,  480,  195  observed  the  various  and  280  for  1  v  v  a n  by  Mueller^ M  +  that  anions  first  v i b r a t i o n of the c r y s t a l s  and  K , are  Bands were the  I.R.  measured  =  reported  complex  c m . " , and  studied  where  cations.  these were a s s i g n e d to ^ » 3 ^ 43 hedra. C l a r k and D o y l e studied + NH^  been  of  frequencies  155,  strength  practic-  found  at  t h r e e of 2MoS^ tetra+ of K and  2salts  along  with  MoO^  salts  and  reported  the  existence  4 8  of  discrete by  S  2-  quencies . workers Mo-S did  2-  4  ions  to approximately  The  theoretical  revealed  Kaufman  much  shift  i n I.R. s p e c t r a  the change The  of the s i z e electronic  ion  c a n be s t u d i e d  the  aqueous  and  of  between  fre-  and c o -  character  44  stated  of  that  nor appearance  quarternary  they  o f new  ammonium  salts,  cation.  state  of the tetra-thiomolybdate  by t h e v i s i b l e  solution.  bonding  Charlionet  i n bands  of  the v i b r a t i o n a l by M u e l l e r  double  of t h e i r  of s u b s t i t u t i o n  halve  treatment  the higher  Leroy,  not observe  spectrogram  and t h e e f f e c t  was  bonds.  bands by  53  MoS  Tridot  a n d U.V.  and B e r n a r d  200 a n d 5 0 0 my  spectroscopy  39  studied  o f t h e aqueous  of  the solutions,  -4 (1.25x10  M.), o b t a i n e d  by d i s s o l v i n g  salt  they  by K r u s s ' s  the  which  absorption  molar  prepared peaks  extinction  1 0 , 8 0 0 M.  - 1 - 1 cm.  crystals  method.  of  They  a t 2 1 0 , 2 4 0 , 325 a n d 465 my  coefficients  a t 392.5  , respectively.  a n d 465 my  Yatsimirski  and  ammonium reported  and t h e a s 700 a n d Zakharova  54  39 did  not observe  in  their  by  mixing  solution. the  rate  Bernard. peaks ion  the peaks,  stated  by T r i d o t  and B e r n a r d  study  of d i l u t e  solutions  spectrophotometric ammonium This  molybdate  disagreement  of approach Companion  as t h e c h a r g e  to a molecular Mueller,  solution may  and sodium  noted  a n d Mackin"'"' i n t e r p r e t e d transfer  obtained  sulphide  be due t o t h e s l o w n e s s  to the e q u i l i b r i u m  o f an e l e c t r o n  ,  by T r i d o t  of and  the absorption on t h e s u l p h i d e  o r b i t a l l o c a l i z e d o n 56t h e m e t a l i o n . R i t t e r and N a g a r a j a n compared t h e  2electron that  TT-bonds  Mueller on  absorption  MX^  t^  anions  where  that  t o a weak  -bonding  7  M  molecular  anti-bonding  stated  summarized  their  W  the non-bonding  on  molecular  the metal  orbital  le  to  S,  Se.  molecular  atom,  They  t ^ -»- 2 e ,  orbital  which i s  and t h a t by  orbital  trans-  orbital  2e  i s stabilized  character of molecular  Later  s p e c t r o s c o p i c study  a n d X = 0,  corresponded  anti-bonding  localized  and  i n the thioanion.  = V, Mo,  from  a n d MoS^  be assumed  t h e band  of e l e c t r o n  essentially  in  also  and E k k e h a r d ^  interpreted ition  must  s p e c t r a o f MoO^  2-  the s t r o n g l y the increase  2e. 2-  2-4-b  Salts The  of d i - s u b s t i t u t e d ammonium  M0O2S2  di-thiomolybdate same  procedure  except  that  ammonium which  , was  on e x p o s u r e  prepared  i t by  or  " 3 8 by K r i i s s by t h e  having  used.  He  to a i r .  a slightly obtained  Recently  t h e same m e t h o d .  the e x i s t e n c e  of a s o l u b i l i t y  prepared  species,  of the tetra-thiomolybdate  solution  c o n c e n t r a t i o n was  postulated results  2—  MoO^S^  of the d i - s u b s t i t u t e d  as f o r t h e s a l t  a chilled  reddened  Gattow^  salt  species,  o f Na2Mo02S2 investigation  higher  yellow  crystals  Hofmeister  Perel'man  to e x p l a i n  al. "'' 4  their  at low Na S 2  et  and  and  NaOH  39 concentration.  Tridot  salt  method,  by K r u s s ' s  chloride  to f a c i l i t a t e  spectrogram  and B e r n a r d except  that  prepared they  added  the c r y s t a l l i z a t i o n .  o f the aqueous  t h e ammonium  From  t h e ammonium t h e U.V.  s o l u t i o n they r e p o r t e d the molar 2e x t i n c t i o n c o e f f i c i e n t of Mo0 S i o n a t 290 my o f 6,950, -1 -1 54 M. cm. . Y a t s i m i r s k i i and Zakh'arova proved the e x i s t e n c e 2  2  of  M0O2S2  tion,  2-  Ion from  when s o d i u m  greater  than  a spectrographic  sulphide  study  of d i l u t e  t o ammonium m o l y b d a t e  4 t o 1 i n 2 x 10  M. Mo  4  solution.  solu-  ratio i s Mueller and  59 Gattow salt  investigated  and r e p o r t e d  t h e I.R. s p e c t r o s c o p y  the fundamental  800,  o f t h e ammonium  frequencies  t o be 8 3 6 ,  4 8 8 , 305 and 200 cm." . They compared t h e s e w i t h t h e -2 s p e c t r u m o f MoO^ s a l t a n d s t a t e d t h a t t h e e n t r y o f two . 2s u l p h u r a t o m s i n t o MoO^ d e c r e a s e d t h e M-0 b o n d s t r e n g t h . 60 L e r o y and Kaufman o b s e r v e d t h e Raman s p e c t r u m o f t h e ammonium s a l t u s i n g a He-Ne l a s e r a s t h e e x c i t a t i o n s o u r c e . 1  The  recorded  lines  were  indexed  on t h e a s s u m p t i o n  that  2M0O2S2  has  symmetry.  2S a l t s o f mono- a n d t r i - s u b s t i t u t e d s p e c i e s , M o O „ S 2and MoOS Few s t u d i e s o f t h e mono- a n d t r i - s u b s t i t u t e d salts,  2-4-c  3  22mono- a n d t r i - t h i o m o l y b d a t e MoO^S a n d MoOS^ , have 38 been r e p o r t e d . Kruess claimed t o have p r e p a r e d t h e sodium or  41 salt  of mono-thiomolybdate,  postulated  both  mono—and  Na2Mo0.jS.  Perel'man  tri-thiomolybdate  et a l .  to explain  their  61 stability triof  data.  Hofmeister  and Glemser  and m o n o - t h i o m o l y b d a t e were  t e t r a - and d i - t h i o m o l y b d a t e , 62  Bernard  studied  alkaline solutions cluded  molybdate  that  of hydrogen  s o l u t i o n and f r o m  mono-thiomolybdate  thiomolybdate  the product  that the  of h y d r o l y s i s  respectively.  the absorption  at d i f f e r e n t degrees  stated  T r i d o t and sulphide  the spectrograms  of s u l p h i d i z a t i o n , they d i d not exist  e x i s t s and has t h e a b s o r p t i o n  but that peak  by of the contri-  a t 392.5  my  with of  the molar  extinction  9 , 8 5 0 a n d 4 0 0 M.  coefficients  cm.  a t 392.5  ^, r e s p e c t i v e l y .  and 465  my  Y a t s i m i r s k i i and  54 Zakharova and  studied  more  dilute  c l a i m e d to have proved  solutions  the existence 2-  in  the s o l u t i o n  of  (Mo) +  (S  by J o b ' s of  method  mono-thiomolybdate  -3 ) - 1 x 10  M.  Leroy,  Kaufman  44 and  Charlionet  quarternary They of  also  prepared  spectrum  2  i n preparing  ammonium s a l t s ,  (NH ) Mo0 S 4  succeeded  2  2  o f MoOS^  392.5  a n d 4 6 5 my  three  strong  first  two and  (NX^^MoOS^ where X = E t and  the cesium  with 2-  salt  revealed I.R.  absorption the l a s t  Species other — ( x = 1-4) 1  Their  spectrum  U.V.  than  •  and  as Me.  the  reaction  and  visible  bands a t 317,  of the c r y s t a l s  b a n d s a t 467 , 477 were  by  three s i g n i f i c a n t  857  gave cm.  .  The  attributed  vibration, respectively. I t was has symmetry i n t h e c r y s t a l . 2-4-d  Cs^oOS^  C s C l a t -5°C.  and  tri-thiomolybdate  those  t o Mo-S a n d Mo-0 63 2— proven l a t e r t h a t MoOS^ 2o f t h e f o r m MoO. S 4-x x —  2o t h e r t h a n MoO^ ^ S ^ 36 ( x = 1~4) h a s b e e n c l a i m e d b y v a r i o u s w o r k e r s . Recently 64 Srivastava and Ghosh s t a t e d t h a t , a t l o w e r pH v a l u e s , 42y e l l o w (HgMoSg) and o r a n g e (HgMoSg) were formed i n s o l u t i o n s o f [Mo] = 0 . 0 2 5 M. a n d [ M o ] : [ S ] ratio greater than A form  of ionic  species  54 1:8.  Yatsimirskii  Mo 0,S  2-  o  te D  tion at  from  (0.1M.) S:Mo  and Z a k h a r o v a  the f a c t  that  a t 4 6 5 , 500  = 1:2,  which  suggested  the absorbance  a n d 5 2 0 my  i s rather  passed  dubious  the presence;of of isomolar through  because  solu-  a maximum of the high  molarity  and  chosen.  Saxena,  of  sodium  also  polymerized of  p o s s i b l e inadequacy  Jain  and  thiomolybdate  measurements  pH  the  and  Mittal^~\ studied  with  suggested  species  Studies A  complex  of  the  of  by  pH  , (Mo S > 2  wavelength acidification  conductometric  of ~  7  the  the  and  formation  (Mo^S^)  detailed  species  HCl  the  8 . 5 - 7 . 5 , 5.3-4.2 and  2-4-e  of  three  and  different  (Mo^S^)  ~  at  3.3-2.8, r e s p e c t i v e l y .  e q u i l i b r i u m between  study  of  the  the  complex  species  e q u i l i b r i u m between  M o ( V I ) -S £-II)_water s y s t e m  has  not  the been  61 performed.  Hofmeister  and  reaction  tetra-  di-thiomolybdate  of  equations  MoS  2 4  " +  Mo0 S 2  at was  (a)  2 2  H0  -*• M o O S  2  ~  +  H 0  20  independent  of  the  to  9.  hydrolysis 26.5  available  They  to  Real./mole, from  the  hydrolysis  according  their  •> e t c .  2  HS  60°C.  the  tetra-  +  2  etc.  They  hydrogen  gave  r e a c t i o n of  HS  +  2  3  of  7  +  2 3  •*• M o 0 S  2  studied  to  the  (b):-  temperatures  of  and  and  and  Glemser  ion  reported  (a)  .  (b)  that  . . .  the  rate  c o n c e n t r a t i o n between  activation and  . . . .  energy  for  di-thiomolybdate  r e s p e c t i v e l y , but  no  pH  the as  19.7  further details  are  report. 6 2  Bernard  and  work.  They measured  at  atmospheric  one  Tridot the  performed  absorption  pressure  and  at  of 19°C.  the  most  hydrogen during  extensive  sulphide certain  gas time  18 intervals, and  0.06  by M.  10 m l . o f a s o l u t i o n or  0.12  M.  spectrophotometrically tri-,  ammonia  0.06  i n a closed  determined  and d i - t h i o m o l y b d a t e  containing  M.  vessel,  the c o n c e n t r a t i o n s  using  the values  (NH^J^MoO and of  of molar  tetra-,  extinc-  39 tion  coefficients  also  calculated  free  sulphide  they  had p r e v i o u s l y d e t e r m i n e d  the concentration  concentration  by  t h e mass  mono-thiomolybdate  d i d not e x i s t .  containing  (NH ) Mo0 S  did  0.06  not report  calculated  M.  4  2  2  They  and  the data  (a)  thiomolybdates  (b)  in alkaline sulphur  M.  di-thiomolybdate  tatively,  especially  pH  =  that  solution  could  They have  been  that:-  7,  of oxygen  i n three  i o n forms,  at sulphide  o f S/Mo  a  ammonia.  the s u b s t i t u t i o n  i s q u a n t i t a t i v e and o c c u r s  to the l i m i t  total  assuming  used  that  a r e not s t a b l e below  solution  They  the c o n c l u s i o n  initially  up  also  0.06  but reached  and  balance  the e q u i l i b r i u m constants  from  i)  2  of molybdate  .  by  steps:  quanti-  concentrations  = 2 i n 0.001  M.Mo  solu-  tion; ii)  second bdate tion  iii)  being  i o n , marked peak  the formation by  a t 3 9 2 . 5 my  which  as s u l p h i d i z a t i o n  thirdly  tetra-thiomolybdate  Their  end p r o d u c t  data  was  the consecutive  of  goes  o f an  through  absorpa  proceeds; i o n occurs  as t h e  sulphidization.  processed  constants  of t r i - t h i o m o l y -  the appearance  maximum  final  obtain  step  by  using  the present  author  the l i t e r a t u r e  to  values  for  the d i s s o c i a t i o n  hydrogen that b)  sulphide  a) t h e r e  constants  o f ammonium  and h y d r o s u l p h i d e  i s a doubt  about  ion.  their  ion,  aqueous  The r e s u l t s  showed  equilibrium condition,  i f e q u i l i b r i u m i s assumed, m o n o - t h i o m o l y b d a t e must be  assumed stants  to exist (in M.  (Mo0 S  2  2  2  (Mo0 S  and t h e l o g a r i t h m s  ),k  4  =  (MoS  ~ ) (H S) , k  2  =  (Mo0 S  _ 1  2  2 -  3  )/(Mo0  2 4  2 4  ~)/(MoOS  2  ~)(H S)  of the consecutive  2 2  2 3  " ) (H S) , k 2  ) /(Mo0 S  2 _  3  ) (H S)-  =  (MoOS^ )/ -  and ^  2  a r e 2 . 7 , 3 . 4 , 4.4  2  3  a n d 5.5  con-  =  respectively.  54 Y a t s i m i r s k i i and Z a k h a r o v a solution. secutive the  But t h e i r constants  complex  equilibrium range and  with  exist  from  2-4-f  Job's  i n which  each  many  other.  and w a v e l e n g t h s  a small  a rather  d a t a are n o t p r o c e s s a b l e  because  system  used  method  f o r t h e con-  i s not r e l i a b l e i n  species  Around  dilute  are existing i n  their  e m p l o y e d , mono- a n d  concentration di-thiomolybdate  amount o f t r i - t h i o m o l y b d a t e c a n be e x p e c t e d Tridot's  Acid  data.  decomposition  Acid  to  of the complex  decomposition  species  of thiomolybdates  was  observed  36 to  occur  .  solution, hydrogen  When  acid  molybdenum sulphide  was a d d e d  trisulphide  gas.  to a  tetra-thiomolybdate  precipitated,  liberating  However, a d i - t h i o m o l y b d a t e  solution  38 yielded  no h y d r o g e n  sulphide  . 66  Zvorykin, equilibrium tions system  Perel'man  composition  of p r e c i p i t a t e s  (made pH = 4.5 w i t h by t h e s o l u b i l i t y  and T a r a s o v  studied the  with  HC1) o f t h e N a M o 0 2  method.  acidified 4  -  solu-  Na^-water  The p r e c i p i t a t e d  phases  in  relation  found  to the s t a r t i n g  molar  ratio,  were  r _> 3  3  2MoS '5Mo0 , 3  and  3  last  2 > r > 1  3  MoS '5Mo0  0.67 j> r >^ 0.50  3  two c a n be w r i t t e n t e n t a t i v e l y  3M0SO2*3Mo0 ,  respectively,  3  ment  (S)/(Mo),  to be:-  MoS  The  r =  of 0 with  suggesting  S i n molybdic  oxide,  as 3MoS20*4Mo0 the simple  3  and  replace-  Mo0 « 3  61 Hofmeister position  reactions,  MoS, 4  2-  Mo0 S 2  step  + H 2-  +  equation  the acid  decom-  ( c ) and ( d ) , between  2  ^ ^ +  1  " H Mo0 S 2  2  and s t a t e d t h a t  2, t h a t  studied  HMoS. + MoS„ + HS 4 3  1  + 2H  2  pH = 1 a n d 4 were  and G l e m s e r  . . . . (c)  2 2  + MoO S x  y  + H S 2  . . . . (d)  the rate determining  the decomposition  r e a c t i o n s were  steps  of the 1  first rate  order,  and t h a t  constants  t h e pH d e p e n d e n c e o f t h e f i r s t  suggested  reaction  products  equation  (d) as H S  p r e - e q u i l i b r i u m step  suggested 2  i n equation  are contrary  1.  ( c ) a s HS  to previous  order  The  and i n 38 knowledge  Srivastava of  molybdenum  molybdate  by  itation  was  as  M.  0.05  proposed He  could  sulphide the  NaHS  be  from  form  by  solution 2N  the  only  decomposed  studied  7  HCl  when  exceeded  that  a  of  only  possible  stated  Ghosh*'  addition  complete  the  also  and  the  the  and  found  ratio  of of  0.025  that  Mo:S  give  of  the  =  added  1:8.  He  3MoS^iH^S  form  molybdenum  M.  precip-  sulphide  p r e c i p i t a t e as  thiosalt to  precipitation  containing  amount  molar  of  acid  the  the  H,MoS 4 8  'H^O.  6 —  n  sulphide.  65 Saxena,  Jain  decomposed 2-5  and  into  stated  bdate  was  then  of  many  that  pH  of  tetra-thiomolybdate  less  than  2.5.  molybdenum'disulphide synthesis  when  boiled  precipitated  at  3  first  that  stated  MoS *H20  Synthesis The  he  Mittal  an  in  along  a  aqueous closed  with  syntheses  was  of  made  solution  vessel,  other  by  of  sulphides  have  in  1826;  tetra-thiomoly-  molybdenum  complex  molybdenite  Berzelius  been  disulphide 36  .  Since  made.  Arutyunyan  6 8 and  Khurshudyan  reviewed  and  the  information  their  following  reported  gated  methods is  reported  abstracted  up  partly  to  1966  from  <  work Most  is  the  of  to  the  be  bi-molecular  having  a  of  molybdenum the  unit  rhombohedral  disulphide  hexagonal cells  modification  except  structure  found  with  for a  a  few  in  nature  with rare  elonexamples  tri-molecular  69 hexagonal in  M0S2  prisms  cell  are which  at  . the  share  The  sulphur  corners vertical  of  atoms right  edges  surrounding equilateral  with  one  molybdenum trigonal>  another  to  build.  up  complete  M  °S2  layers  hexagonal  modification  ing  complete  these  alternating in  a  requirements  layer  positions with  slashes  capital  and  the  indicate  of  the  the  the  distance  between  the  to  be  (3.66A  bonding  the  between  source  of  the  material^.  The  cations  reported  can  be  were other  of  The  and  Reaction are  be  hexagonal  methods  Arutyunyan 1.  to  of  and  in  a  the  result  6 8  gaseous  reacting  M  into  o$2  a  trigonal  layers of  is  said  this  two modifi-? 71 same . There  from a l t e r n a t i n g packings  72  classified  groups:-  the  chlorides at  than  modification)^  were  four  medium:  sulphur.  the  rhombohedral  molybdenum  gas,  may  synthesizing  Khurshudyan  volatile  sulphide  essentially  of  the  properties of  the  where  larger  forming  double  of  as  ,  i n hexagonal  qualities  which  is  and  positions  layers  atoms  lubricating  lubricating  68  the  sulphur  described  double  sulphur  to  those  molybdenum  atoms  2.98A  the  modifications  combinations  by  sulphur  against  to  denoting  be  sulphur  repeat-  close-packing,  By  of  by  the  according  according  can  positions these  weak  another  In  up  ' ' AbA/BcB/CaC/A I I  as  between  axis.  is built  and  former  latter  CQ  hexagonal  letters  distance  The  crystal on- one  The  bi-pyramids  the  close-packing.  letters,  I I AbA/BaB/A I I  to  modification,  cubic  with  small  the  layers  rhombohedral  three  normal  initial and  components  hydrogen  temperature  of  700-  800°C. 2.  Reaction may  be  i n molten  Mo0  3  +  S,  salts:  CaMoO^ +  the Na C0 2  initial 3  +  S,  components or  Mo0  3  +  Na2CC>  3  ranges 3.  +  S.  The  from  700° t o  R e a c t i o n between phase w i t h at  4.  5.  method  Thermal  7 3  ''  Almost subjected except  f o r a few  gas  are  a  high  atmosphere).  is decomposition  8  molybdenum  of  disulphides  r e p o r t e d t o be  examples  prolonged  inert  at  salts.  synthetic  analysis  or a f t e r  i n an  or h y d r o t h e r m a l ^  hexagonal  solid  sulphide  trisulphide  added  thio-complex  to X-ray  conditions  s h o u l d be  a l l the  in  700-800°C.  ( o v e r 500°C.  7 4  molybdenum  of  compounds  or hydrogen  of molybdenum  which  of s y n t h e s i s  900°C.  the molybdenum  a temperature  Decomposition  further  temperature  s u l p h u r vapour  temperature, A  usual  prepared  rhombohedral  under  annealing at high  extreme  temperatures. 6 8  This  p o i n t was  from  their  study  molybdates. solutions, 8-12 for  made c l e a r of  by  the hydrothermal  Their experiments containing  those  of  hours. the  bottle  Their results  other workers,  0.5  as  and  were  and  Khurshudyan  decomposition  consisted  maximum o f  w i t h NaOH, i n a g l a s s 1~100  Arutyunyan  M.  of  sealing 2-  MoS^  follows:-  thio-  aqueous  w i t h pH  h e a t i n g at summarized  of  of  300-700° along  with  C.  24  Crystal  Modification  Temperature  amorphous  They  pH<6~7  200-300°  rhombohedral  250-900°  short duration of heating  hexagonal  600°C  22  hexagonal  1300°C  demonstrated  Scope  the t r a n s i t i o n  by  days  2 hours i n s i l i c a t e melt  to the h i g h e r  the use of X-ray  of Present  From seem  20-300°C  colloformic  crystallization  3•  Conditions  level  of  diffraction.  Work  a review  of  the l i t e r a t u r e ,  the f o l l o w i n g  points  clear:-  1.  The a  2.  demand  f o r molybdenum  search f o r processes  i s growing,  to t r e a t  Hydrometallurgical  methods  sulphide  to produce  oxide  ores  leading  lower  grade  can t r e a t  low  pregant  to  ores.  grade  molybdenum  solution. 3.  Reduction hydrogen with  of aqueous s o l u t i o n s gas  A  at elevated  the a i d of c a t a l y s t s  tri-valent 4.  can proceed  fairly  molybdenum  extensive  Mo(VI)-S(-II)-water aration  and  of molybdenum  to produce  with  temperatures tetra-  or  compounds.  study  has been  system  performed  especially  characterization  of  of the  f o r the  thio-complex  prepsalts.  25 The  study  of  incomplete vated 5.  equilibrium  and  no  mostly  of  performed  process  used  was  prior  In as  the  1.  of  of  at  present  plex 2.  To  media  been and  and  the  hydrothermal  positive  the  when  material,  molybdenum  facts  ele-  in  effort  has  solution  sulphide.  the  following  was  taken  the  Mo(VI)-S(-II)-water  work:-  of  temperatures  equilibrium  with  the  constants  object  between  of com-  species.  investigate  water to  the  has  starting  of  at  reported.  thermal  equilibrium  elevated  establishing  as  is  system  disulphide  the  above  system  the  been  simple  reduce  the  on  T h e r e f o r e , no  the  the  study  system  used  precipitation  view  scope  To  to  to  the  i n non-aqueous  was  decomposition. made  have  molybdenum  thiomolybdate  been  studies  temperatures  Synthesis  in  system  analyse  the  with  r e d u c t i o n of hydrogen  and  reduction products  the  Mo(VI)-S(-II)-  carbon and  monoxide  kinetics.  and  26 PART  I:  STUDY  OF  EQUILIBRIUM  I N THE Mo ( V I ) - S ( - 1 1 ) - W A T E R  SYSTEM  1.  Principles  of the experiment  From the  a review  following  (a)  facts  o f t h e p r e v i o u s works  seem  In c r y s t a l s  t o have  been  and i n a l k a l i n e  on t h i s  system,  established:-  solutions  thio-complex  2species  of the form  MoO,  S  ( x = 1-4)  exist.  t ™" X . 3C  (b)  Predominant near  MoS  U.V.  2 4  MoOS  2  Mo0 S (c)  (d)  bands  o f t h e above  and  2 2  condensed  forms.  there  c a n be v a r i o u s  Establishment of equilibrium in alkaline  temperature i s highly  dilute  when  at higher  solutions  between  complex  the complex  i s rather  slow a t  but the formation of the favoured  concentration  Therefore, solution  species are:-  "—290my. solutions,  anion  and  315my,  In a c i d i c  room  i n the v i s i b l e  ~—392.5my,  species  acal  range  "—465  3  2  absorption  i n the presence  thio-  of a very  of sulphide i o n .  conducting experiments temperatures,  i n an ammoni-  the f o l l o w i n g  simple 2-  equilibrium (x  = 1-4)  between  can be  the species  expected:-  of the form  Mo0 _ S 4  x  x  27 2-  MoO. 4  + H„S 2  Mo0 S ~  + H S  2  3  Mo0 S  2  MoOS  ~  2  where  ~  + H S 2  + H.S 2  MoO.S 3  =  Mo0 S  =  MoOS  2  =  MoS  k's a r e t h e c o n s e c u t i v e  In ion,  2  3  2  2  =  M,  ,  T  constants,  8 M  T  system  or f r e e  8^  2 3  ~ 4  ~  + H 0  : fc  2  " + H 0  :  2  + H_0 2  2  k  :  k,  3  4  with  one c e n t r a l  metal  of t o t a l  metal,  M  T  ,  total  .  IT k .  j=l  2 2  k, 1  l i g a n d , L , and by a s e t o f s t a b i l i t y  i =  :  o  c o - o r d i n a t i o n number o f N i s f u l l y  by t h e c o n c e n t r a t i o n s  L  + H 0 2  constants.  a complex  a n d a maximum  described ligand,  general,  2-  ,  i  =  1~N  J  =  [M] +  [ML] +  =  [M][l  +  BjL  [ML ] + 2  +  8 L 2  2  +  .  . +  .  . +  [ML  N  ]  8 L ] N  N  L = L + [ML] + 2[ML ] + . . . + N[ML ] T  2  = L + [M][ An the  system,  N  BjL + 26 L +...' + N8 L ] 2  N  2  alternative n, d e f i n e d  of  l i g a n d s p e r atom when  L,  and i s u n i q u e  as  a function of L , 8  N  i s to use the formation  by B j e r r u m " ' as t h e a v e r a g e  number  7  the concentration  for a particular n  function of  can i n turn  system.  of free Once  ligand i s ri-is  be c a l c u l a t e d by  obtained  several  28  n  =  (L -L)/M T  N (E n3 n-1  =  T  L )/(1 n  n  methods  N + E B n=l  described  by  a^,  from  equation  n  the f r e e  and  7  (1) shows  distribution  ligand  of  that  n is  the s p e c i e s  concentration,  L,  by  ML  c >  the  ( 2) : -  c - (d l n a /d l n L )  =  . . (1)  Rossotti ^.  of equation  the f r a c t i o n a l  against  . .  n  Rossotti  Consideration given  L )  n  . . . .  (2)  c  where  The L  a  c  usual  = L^,  =  [ML  1/M c i  method  followed  differentiations however,  =  B ,L /(l c C  f  to use by  successive  ML  , a r e known,  of  (2) i s a t f i r s t  sets  o r some  two  n  approximations  final  the c o n c e n t r a t i o n s  the c o n c e n t r a t i o n s  N E B L ) j}=in  equation  to o b t a i n  to  +  of n  and  properties  and L.  by  graphical If,  proportional  successive  s p e c i e s , ML . and ' m-1 f u r t h e r s i m p l i f i e d by r  m  substituting  equation  ( 2 ) c a n be  the e q u i l i b r i u m  r e l a t i o n s h i p between  species, i . e .  ML  By  , + m-1  L  =  differentiation  ML  , k m m  = a  m  /a  putting  _L m-1  these  29  d  I n L = - d l n (k  a m  Therefore  n  = c-  equation  by  measuring  using and  n  (2) w i l l  (d l n a ) / ( d c  For  Mo^  and  - d ln a  system,  equation  = 4 - 1/(1 - d l n a_/d  of  against  log a  liminary at  3  and  log  -  n  -  = 3 - l/(l-d  by  4 6 5 my by  and  Bernard  . . . . (4)  31 5  the slopes  of the  the breakdown o f equation equation  ( 5 ) was  Pre(4)  used:-  l n a^)  /d  plot  graphical differentiation.  cases  ln  given  obtained  (4) a p p l i e s .  c a l c u l a t e d from  f o r such  and  (3)  4  c a l c u l a t i o n s showed  low  a t 3 9 5 my  l n a.)  3  n c a n be  c a n be  coefficients  (3)  . . . .  and  absorptions  Thus  Therefore  ,) m-1  m  extinction  39 62 ' .  be r e w r i t t e n a s e q u a t i o n  ln a  the present  the molar  Tridot  - /a ) = - d l n a . + d ln a m-1 m m-1 m  . . . .  (5)  "315 where and  will  i s a specific be d i s c u s s e d  approximation  was  absorption  later.  a l s o used  From n v a l u e , S^,  was  and  s u l p h i d e , Mo^, a n d  by  Equation when  species (2) w i t h  was  the c o n c e n t r a t i o n  calculated using S^,  total  ML^  a t 315  successive  too low t o o b t a i n of f r e e  concentration  by e q u a t i o n ( 6 ) : -  of  my  n.  sulphide, molybdenum,  30  S  2.  =  f  S  - n Mo  T  Apparatus  and  Experiments autoclave, equipped room  were  conducted  a titanium liner  temperature)  couple  Procedure  were  and a s t a i n l e s s  attached:  system,  a gas i n l e t  contact  with The  was p r o v i d e d  a ring  activated  measured another  system,  two  thermo-  a sampling  A l l the parts i n  titanium.  by t h e e.m.f.  for rapid  c o n t r o l l e d by a s o l e n o i d temperature  well.  of a Alumel-Chromel  well with  ice-water  motorheating  valve  controller,  Co.) i n c o n j u n c t i o n  i n one t h e r m o c o u p l e  thermocouple  l i d to which the  by a Bunsen b u r n e r  Instrument  probe  Ltd.,  was b e l t - d r i v e n b y a n e l e c t r i c  by a T h e r m i s t e m p  thermistor  steel  1990 m l . a t  mechanism,  and a gas o u t l e t .  type burner  (Yellowsprings  Co.  volume  steel  a stirrer  t h e s o l u t i o n were stirrer  by P a r r  (inside  wells, a solution injection  Heating  i n a stainless  s e r i e s 4500, manufactured  with  following  and  (6)  Experimental  2-1  and  . . . .  T  with  Model  71  a  Temperature  was  thermocouple i n  as a c o l d  junction  was u s u a l l y w i t h i n ± 0 . 5 ° C . o f t h e s e t v a l u e . As  above  the temperature  the b o i l i n g  injection  system  point was  selected  of water,  constructed  f o r experimentation,  a pressurized with  Type  316  solution, stainless.  was  31 steel  parts  as  positioned  shown  system with 2  and  sucked  B  into  closed higher  w h i c h was scale  the  and  10  was  the  a  system.  was  (-10  By  ml.)  sample  existing  at  drop  of  sequence: solution Teflon  a  of  was  1/16  room  packing  system  .  was  Then  pressure autoclave,  gauge w i t h solution  surface  of  was  solution  the  of  measured the  a was  tubing, of  the  solu-  injection i n the  was  gas  injection  approximately  process  constant  injected. reactions  temperature were quenched  system  to  consisted  freeze  to  of  titanium tubing  autoclave,  attached  with  trap  of  tetra-  reportedly . the  equilibrium  temperature.  i n . O.D.  i n s i d e the  an  and  stainless  the  cycle  decomposition at  of  completion  one  the  a nitrogen  the  pressure  flushing  opening  opening  above  method  elevated  sampling  By  The  and  the  psi. helicoid  s o l u t i o n was  the  and  apply  through  s o l u t i o n s were the  The  a 1500  this  ,  and  to  slightly  di-thiomolybdate  slow,  system  first  S,  closed  division.  closed  by  inside pressure  autoclave  Although and  whole  a s u i t a b l e vacuum  autoclave.  completed.  amount  with  sharp  out  closing  the  w h i c h was  by  then  opened  than  i n s i d e the  detected  was  S by  p s i . per  into  t i p of  tion  The  through  attaining  measured  of  flushed  was  from  value  carried  water  closed. After  of  were  distilled  evacuated.  was  2.  vertically.  Injections  V  in Figure  the  a  stainless  l i d and  a  the  following  immersed steel  in  valve  cooling coil  the with of  31a  T V|,V ,\^,V 2  « high pressure valves, 3I6SS.  4  A  > autoclave.  B  :  T  ' trap.  S  F i g . 2.  A  :  high pressure bottle, 316SS. container of solutions to be injected, glass.  SOLUTION  INJECTION SYSTEM.  1/16  in.  water line  O.D.  bath from  (7~10°C.). end  temperature its  stainless  to  end  section  The was  of  Operations sodium  100  ml.  for  of  bdenum was  was  the  were  replaced  the  volume  system  then  molybdenum  solution  prepared was  was  injected  to  equilibrium  between  the  withdrawn  solution  quenched  subsequently (Pyrex glass  10  "Fine" bottle  sampling  while  of  in  a  the  cold  sampling  1.5  ml.  The  about  a  quarter  was  high  were  gas  the  stored  repeated  described NH^  of  in  (NH > 4  the  SO^  2  same  stock  the  was  30  system  The  cooling  system,  the  was  through  any  5  a  The  solution solution-  attain solution  ml.  of  the  discarded dry  glass  precipitates,  analysis.  Moly-  sealed,  the  sample  first  system  to  and  atmosphere  Sulphide  minutes  and  buffer  solutions.  and  for  One.litre  buffer  the  stirring.  injected.  below.  autoclave,  species,  for  -  injection  remove  were  the  filtered  to  sulphide  from  in  stand  the  grade) and  a  stirring.  by  ml.  in  while  through  allowed  are  fresh  nitrogen  equilibrated  or  solution  charged  was  then  case  sulphide  with  and  mixture  was  sample and filter  into  injection  a  dry  and ,  successively.  Reagents The  solutions 0.4  inside  immersed  approximately  latter  sodium  solution  heated  of  molybdate  composition  2-2  tubing  length. Solutions  of  steel  M.Na.S  experimental  of  1 M.Na^oO^  (stored  in  a  solutions (stored  dark  glass  were  in  a  made  from  polyethlene  bottle),  10  M.NH  stock bottle), and  4  M.  (NH^^SO^ All  grade used  and  using  the  were  reagent  reagents  used  as  grade  used  chemicals.  in analysis  purchased.  were  of  reagent  De-ionized water  was  f o r a l l purposes. The  n i t r o g e n gas  commercially  in a  was  cylinder  the  and  low  used  oxygen  without  grade  supplied  further  purif-  ication.  2-3  Analytical The  phide,  c o n c e n t r a t i o n s of  total  solution  ammonium  were  a  and  total  complex  molybdenum,  species  in  total  the  sul-  sample  determined.  Total using  methods  molybdenum  Beckman  Model  B  was  determined  spectrometer  colorimetrically  according  to  Buchwald  77 and of  Richardson's the  solution  solution  at  was  420  mu  (pH = 5.2) w i t h ( a f t e r oxidizing NaOH  alkaline,  HNO^  to  drive  nitrogen  system done  a  calculated by  from  complexing  the  molybdenum  content  the  absorbance  of  in a  0.05  M.  acetate  a buffer  n  adding  Na2S0.j  o f f excess and  to  modified  to  SO2,  reduce  boiling  neutralizing  analysis  i s known  by  , i n which  s o d i u m -2 , 3 - d i h y d r o x y - n a p h t h a l e n e - 6 - s u l f o n a t e sulphide i n a s a m p l e s o l u t i o n w i t h #2^2 ^  oxide, The  method  of  be  total  to  to  H2O2,  expel  the  pH=5.2 w i t h  sulphide in  difficult.  Volhard  excess  In  Part  method,  which  aliquot  of  the 1  was  adding lower  NaOH). thiomolybdate  the  analysis  also  ,was  employed  41 by  Perel'man  added  to  et  a known  al.  .  excess  An  amount  of  sample  AgN0„  solution  standard  was  solution  in  ammoniacal solution were  solution  to  precipitate  sulphide  heated  to  agglomerate  Ag S  was  filtered  off  after  ammonium s o l u t i o n . and  acidified  the  solution  by  The  5N  titrated  HNO^  washed  and  a  Ag^S.  with  a  the  Ag  standard  which  combined  remaining  +  The  dilute  washings were  and  with  as  precipitates  2  and  filtrate  adding  was  cooling  ion  in  KCNS s o l u t i o n  using  3+ Fe  solution  calculated  by  as the  Total lation into  solution into  2  waiting  a  the from  the few  to  The  with  remaining to  pH  =  by  solution  contained to  f i x the  an  a  fed  ammonia. and  NaOH was the  acid  with  titrated B e c k m a n pH  calculated  by  ,  sulphide  a known amount of was  *  aqueous  oxidation  concentrated  distil-  was  oxidize free  the  5 using  was  was  the  added standard a  meter  and  difference  blank.  ;  concentration  colorimetrically. taken  trometer  into  ammonium c o n t e n t  The  was  completed,  NaOH s o l u t i o n  total the  be  determined  allow  amount  blank.  former  to  to  the  sulphide  sample  which  minutes  the  was  a  latter  distilled  solution.  standard  from  of  apparatus,  a m m o n i a was  H SO^  aliquot  and  neutralization and  and  KMnO^ i n H^SO^, t h e  sulfate  After  difference  An  Kirk's of  indicator,  ammonium c o n t e n t  method.  the  an  between using  distilled  gave m o l a r  a  The 600 0.1  water  extinction  thiomolybdate  at  19°C.  of  complex  spectrogram and cm. as  260  my  quartz a  with cell,  reference.  coefficients as  of  follows:-  of  species the a  was  sample  determined solution  B e c k m a n DK-2  spec-  without  dilution,  Bernard  and  the  tetra-  and 39 6 2  Tridot and t r i -  '  35  392.5  e  3  e  4  e  =  Q  . 2 98.5 x 10  392.5  _  where  i s a molar  a  i  species  the of  2—  and C  (7) assuming  -  3  =  . ,2 108 x 10  4  (1.018  A  3  9  2  ,  3  h  coefficient  ) at wavelength A, A \  the concentrations  thiomolybdate,  C  . 465 e  at wavelength  the s o l u t i o n ,  equations  . __2 4 x 10  extinction  (MoO^^S  absorbances  =  3  . _2 x 10  7  ^ 465 e  of t e t r a -  , respectively,  -  0.066  A  4  6  78 A(my) .  (A = 392.5  were  no i n t e r f e r e n c e  5  (M.^cm.  5  )  10~  ) of  From  a n d 4 6 5 my)  and  t r i -  calculated  by t h e o t h e r  x  - 1  by  ions.  M,  3  (7)  C  The  =  4  (0.928  A  concentration  from  4  6  by B e r n a r d  -  0.038  A  3  9  2  ,  5  )  of di-thiomolybdate  the absorbance  given  5  a t 290 my  and T r i d o t  62  x  was a d o u b t  Instead  of di-thiomolybdate  portional was  to the f r a c t i o n a l  calculated  A  3  1  2  ~315 where  A  discussed  5  e  315  a t 315 my, A ^  distribution  about  the s p e c i f i c -  absorbancy  M.  3  was n o t c a l c u l a t e d  as t h e r e .  10.  , which  i s pro-  of di-thiomolybdate,  by e q u a t i o n ( 8 ) .  = A  3  1  5  -  2.01. x  10 a  .  4  4  .  .  . (8)  315 = A later).  /Mo^, a  4  = C^/Ko^,  (the  constant  will  be  analysis The  For  most  was  performed  s p e c t r o g r a m was  slight was  c h a n g e was  taken  3.  and  Observed  at  Tridot  the  peak at  as  the  is  true  as  sulphide  for  In  (=  absorption  Appendix  no  395,  and my  315  other  395  tration  of  added.  The  and  reported  290 54  my '  my.  reached and  my  C)  exists  at  was  shows  that  decreases  The 465  success-  Bernard  a maximum a n d  peak  series  other  by  increases.  The  a  same  my  increases  increases. the  465  ,  concentration  my,  of  decreased also  reaching  observed  at  as  shown  a as  small more  smaller.  in Figure to  total  The  peak  a new  sulphide  ammonium  B2  the  concen-  sulphide  a maximum a n d higher  free  magnitude  corresponding  maximum a t  m a g n i t u d e was after  of  etc. " . I t also  reaches  observed  peak at  sulphide  degenerated 380  p e a k was  The  thiomolybdate,  sample  injected  peak  concentration at  example  ( S e r i e s D ) , v a r i a t i o n i n p o s i t i o n and  B.  a  a  Appendix  absorption  increases,  peak  shows an  authors  s e r i e s where  the  of  l a t e r ) , (see  s o l u t i o n was  sulphide  concentration  small  minutes  Only  spectrogram  where  the  a  the  for  withdrawal.  10=20 m i n u t e s .  when  10  ammonia  sample  B  sulphide  was  around  observed  465,  290  total  within  and  Rl i n Appendix  3962 '  and  my  immediately.after  I t i s clear that  those  sulphide  Spectrogram  spectrograms  than  of  Calculations  Figure  ively.  fixing  taken  repeatedly  Results  3-1  of  cases  of  in tetra.  .  :  was at  395  peak  at  concentration.  A new  p e a k was  this  was  this  wavelength  peak  than  a l s o observed  obscured  the  one  of  no  p e a k was  the  new  3-2  the  at  At  give  resulting had  210  my,  high  my  due  free  considered  low  and  my,  although  showed to  no  free  around  other  sulphide ion.  ammonium was  kept  high,  sulphide concentration,  t o be  caused  by  protonated  S^.  and  were  calculated  obtain n values  too  i n the  too  of n  first  s c a l e to  to  to  230  at  270  thiomolybdate.  Calculation  found  around  increase in absorption  scan  t h a t when  observed  of  log-log  A  around  fact  peaks were  species  a general  range.  In view such  by  at  large values  graphically.  of  n at  i n c o n s i s t e n c y of  a value,  the  and  low  plotted This  values  was  of  material balance.  equation  ( 4 ) was  not  in  Because  meaningful.  39 Bernard 315  my  giving A  If  the  and  Tridot  stated that  the  absorption  i s caused  by  d i - and  tetra-thiomolybdate  the  extinction  coefficients, i.e.,  3 1 5  molar = le  3 1 5  2  equilibrium  thiomolybdate,  C  0  2  + le  C.  3 1 5  4  i s assumed  equation  (9)  4  ; I',  can  be  without  path l e n g t h ,  between  . . . .  d i - , tri-  rewritten  at  and  as  (9)  tetra-  equation  (10):  A  3 1 5  c /c 4  2 3  =  (£e  3 1 5 2  k /k ) + £ 4  3  e  3 4  1  5  (c /c ) 4  3  2  . . . .  (10)  Thus  from  the  plot  of  A  315  2  C^/C^  against  9  (C^/C^)  ,  315 can a  plot  be  of  others  obtained.  S e r i e s A.  giving  the  £  A  £  4  MT  1  1 .96  cm. x  -1  10  2 .04  x  10  4  C  1 .95  x  10  4  this  an  was  example  found  of  for  such  the  below:k  Temperature °C.  cm. x  10  x  10  2  44.6  x  10  2  the  150  2  40.5  table  shows  linearity  3 1  41.4  4  3  2 V 3  M .  B  From  Good  results  315  Series  Figure  Nominal Concentrations NH„ 3  =  1.0,  NH*  150  NH  =  0.5,  NH*  120  NH  =  1.0,  NH  molar  3  3  extinction  =  4  »  +  4  at  315  taken  as  201  x  Then  to  di-thiomolybdate  at  315  my  by  equation &  315  =  2  due  of  -1  10  M. is  -1 cm...  given-  (11): &  315  ~  201  x  10  2  I  Z  C  .  4  .  .  .  Dividing  1.0  coefficient  tetra-thiomolybdate absorption  was  1.0 =1.0  2 my  M.  this  with  Mo^  gives  the  specific  (11)  315  absorption  315 =  A^  /Mo , T  tribution by  of  equation  which  di-thiomolybdate,  the  , needed  fractional in n  dis-  calculation  (5).  Figure -  i s p r o p o r t i o n a l to  4  shows  a^.  By  an  example  of  the  plot  of  and  :  315 against  smoothly  fitting  curves  graphical differentiation and  by  using  equations  of  (4)  the and  (5)  f o r h i g h and low v a l u e s o f r e s p e c t i v e l y , n was calculated p l o t t e d i n F i g u r e 5 a n d l i s t e d i n A p p e n d i x A, T a b l e A - l - 1 f o r each e x p e r i m e n t a l p o i n t . The c a l c u l a t e d n and are  Fig. 3  PLOT  OF  EQUATION (10) TO OBTAIN  ^'  OQZO  Fig. 4  0.050  T3I5 XIO 0.100 0.200  CALCULATION OF  4  M: cm? 0.500 1  n , I50°C., SERIES A  1  1.000  41  42 3-3  Conversion hydrogen  of f r e e  sulphide  The f r e e to  sulphide  sulphide  the c o n s e c u t i v e  constants. hydrogen  Since  concentration  temperatures,  constants  the  and f r e e  mass b a l a n c e  [ H  2 ^aq  Usually  pK 2  sulphide  (  1  < sl  +  K  i s estimated  g  consequently  be  great  was  converted  i n order  to  stability of aqueous  accuracy  employed  for calculation.  aqueous h y d r o g e n  concentration  f o r high  sulphide  i s given  by  equation,  " V  S  between  the  constants  the f o l l o w i n g method  concentration  and  a r e n o t known w i t h  The r e l a t i o n s h i p  must  concentration  the d i s s o c i a t i o n  sulphide  to aqueous  concentration  the aqueous h y d r o g e n s u l p h i d e  calculate  concentration  the l a s t  / [ H + ] )  ( s l s 2 t  +  K  K  to be l a r g e r  term  /  H  +  ] ^ 2  than pK ^  by 3.5  g  and  i n the d e n o m i n a t o r i s n e g l i g i b l e  37 i n weak a l k a l i n e proportional free  solution  .  to the r a t i o  Hydrogen i o n concentr.ation i s  o f ammonium i o n c o n c e n t r a t i o n  ammonia c o n c e n t r a t i o n .  Therefore  t h e above  and  equation  isreducedto,  [ H  2  S ]  aq  =  f  S  /  ( 1  +  M  INH. J/[NHJ])  . . . .  3  (12) i  or  where  [NH+]/[NH ] = ( 1 / I H S ] 3  m  Therefore  is a  2  ) ( S [NH*] / [NH ] f  ) -m  3  constant.  by p l o t t i n g  [NH ]/[NH ] +  4  3  against  S [NH ]/[NH ] +  f  4  3  for  the  constant  the  intercept. At  ium of  ion the  for  first  were  series  ammonium  equilibrium  where room a  T  =  K  M  is  of  of  the  the  smaller. sampling  of  and  not  amount  of  (Ammonia line  was  were  values.  Since  plex  free  system,  [H„S] 2 aq  at  be  obtained  ammonia total  150°C.  the  material  and  as  ammon-  ammonium,  temperature,  From  added.  [NH ]  read the  ligand  the  ion  to  [NH  plot  ion  knowing same  N , T  that  amount  balance  found free  and  of  and ,  with  due  and  to  io  of  ammonium  ion  10  =  p H  ammonia  sulphide  flushing'at  gives  the  ammonia.  The  obtained  considering  were the  be  p I  thus  temperature  at  10 * would  0  free  p H  a  magnitude  outlet  of  at  constant  negligible).  Figure  formation  concentrations 5  for  for  is equivalent case.  different  function is a  concentration n  vK^)\  +  against  at  free  sulphide  from  i ([NH^]  consequently,  change  loss  ] +  of  intercept  and,  present r  the  4  constant  molybdenum  constant the  =  3  ammonium  n-values  the  and  was  Thus  Secondly  of  pH  room  dissociation  ammonium  considered  that  the  free  at  ] +  4  line  proportion  from  can  of  experiments  temperature.  value  was  concentrations  m  equations,  [NH  straight  [H_S] , z aq  s o l u t i o n s at  sulphate  N  of  calculated  quenched  the  value  the to  the  [NH  unique  + 4  ]/[NH ]  function  mono-nuclear constant  3  com-  44  F i g u r e s 6a and 6b show t h e p l o t s o f and  [NH ]/[NH ] vs.  S [NH ] / [ N H ] ,  +  4  respectively,  +  3  4  v s . 10^^  3  Table  A - l - 2 i n Appendix A g i v e s the r e l e v a n t data.  Figure  6b  m  [H„S]  was o b t a i n e d  by e q u a t i o n  t o be  (12).  5.8  and  was  and F  r  converted  o  m  to  F i g u r e 7 shows t h e p l o t o f n  3. Q  vs.  [H„S] a t 150°C. 2 aq  sulphide  n values  of S e r i e s D at high  free  6  c o n c e n t r a t i o n s were n o t i n c l u d e d i n t h i s  figure  since  the i n t e r f e r e n c e by t h e a p p e a r e n c e o f new p e a k s became l a r g e and  of the d e t e r m i n a t i o n of a  accuracy  3-4  C a l c u l a t i o n of s t a b i l i t y  constants  4  became  less.  from the f o r m a t i o n  curve 3-4-a  B j e r r u m ' s H a l f - n Method Bjerrum  suggested  t h e use o f t h e r e c i p r o c a l  concentration at a l l h a l f - n values  f o r consecutive  ligand  constants,  namely, k where k  n ML  and  L  =  n  l/L  n  i s the c o n s e c u t i v e n-1 n  + L  =  i s the l i g a n d n  ML  constant  f o r the step-n: r  n  concentration at  • n  =  The p r i n c i p l e  n -  1/2  i s b a s e d on t h e f a c t  that a s o l u t i o n with a  n - v a l u e o f (n - 1/2) must c o n t a i n a p p r o x i m a t e l y o f t h e ML ,- and ML - c o m p l e x e s ^ . n-1 n ^  equal  T h i s method was a p p l i e d t o t h e p r e s e n t  case.  f o l l o w i n g v a l u e s were r e a d  from F i g u r e  7:-  amount The  45  1.4  TOTAL AMMONIA  0.8  2  3  antilog(pH- 9 )  /  (NH^/uNHj)  ( 6b)  4  n = 0.85  O  1.42  •  , 1 0  S [NH4)/(NH ) f  Fig. 6a, 6b  CONVERSION  OF  3  S  f  TO  15  _ 20 MJCIO 3  (HgS^ , PLOT FOR m  5 Curve  method  Fig. 7 THE FORMATION CURVE OF THE THIOMOLYBDATE SYSTEM, 150°C.  47 rt  The  calculated  When n - v a l u e s stability with in  1/2  0 . 35  X  io-  3  M.  3/2  1.4  X  lO"  3  M.  5/2  2. 3  X  io"  3  M.  7/2  8.0  X  io"  3  M.  stability  constants  were  the observed 7  Bjerrum's  condition  was  neighbouring ent  enough  thus  with  obtained,  values  except  are given equation  i n Table  1.  (1) u s i n g t h e  the r e s u l t  d i d not  a t the mid p o i n t  agree  as shown  line-1.  Rossotti the  calculated  constants  Figure  L  and R o s s o t t i ^  H a l f - n method k  and c o n c l u d e d  ../k > 10 . n-1 n  Since  4  consecutive  to s a t i s f y  discussed  constants  none  were  the condition,  the v a l i d i t y that  the necessary  o f t h e two  found  this  of  t o be  method  differ-  was n o t  adequate. 3-4-b  Two-parameters A  degree  system  all of  c o n t a i n i n g many  of complexing  parameters.  constant  the neighbouring Dyrssen  R  n  may  gives  and S i l l e n  consecutive  assume  R  =  i n terms  different of only  two  of the over-  and t h e o t h e r  the r a t i o  constants^.  constants  =  of  the magnitude  of the system  consecutive  = . k /k ,, n n+1  complexes  be d e s c r i b e d  One p a r a m e t e r  stability  neighbouring  approximation  that  the r a t i o  i s constant:  constant  of the ;  48 Bjerrum  assumes  R  where  =  n  depends  unique  factor",  parameter  mid-point  slope For  four,  on n i n a s t a t i s t i c a l  ( (N - n + l ) ( n +  N i s t h e maximum  "spreading  is  that  c o o r d i n a t i o n number  defined  by B j e r r u m  f o r a complex  system  of the formation  the case  the above  1)/(N - n)n )  where  2 x  and x i s t h e  as a c o n s t a n t and r e l a t e d  and  to the  curve.  t h e maximum  two m e t h o d s  way:  lead  coordination  number  to the f o l l o w i n g  equations:Dyrssen  ii  =  (R a +  and  2R a  3  4  Sillen:  +  2  3R a 3  /(l  B  a  = VL,  x  = R  3  v:  v, 3  + 4a )  3  4  + R a + R a 3  4  + R a  2  3  + a )  3  . . . . (13)  4  constant  = R  2  4 2  v , 3  3 3 = R v , J  3  3  = v  A  4  Bjerrum:  n  =  3 (4x b +  4 2 12x b +  /(l b  0  X  = kL,  k:  3 = 4x k,  3  + 4x b  +  3  4 4b )  6x b 4  2  +  4x b 3  3  + b  4  ) . . . (14)  constant  2  Families were  3 3 12x b +  constructed  4 2 = 6x k ,  3  3  3 3 = 4x k ,  of normalized f o r various  3  4  diagrams  values  = k  4  o f n - a a n d n-b  o f R and x,  respectively,  49 and  the best  abjove  them.  results by  f i tvalues  sought  by p l a c i n g  The f o l l o w i n g  values  gave  and t h e c a l c u l a t e d  values  of s t a b i l i t y  equation  (13) and (14) a r e g i v e n  \  Dyr'ssen  Bjerrum:  Both method  were  v  and S i l l e n : .  the Dyrssen  stants.  The l i n e  t h e most  i n Table  satisfactory constants  1.  3 - 1 M,  R  =  1.05,  v  =  0.57  x 10  x  =  0.65,  k  =  0.57  x 10  and S i l l e n  gave a p p r o x i m a t e l y  Figure 7  method  t h e same v a l u e s  2 i n Figure  and t h e  M.  Bjerrum  of s t a b i l i t y  7 represents  3  the values  conof n  i i  calculated given the  by t h e D y r s s e n  above.  Clearly  H a l f - n Method  and S i l l e n  this  although  method the  method  using  the values  gave a b e t t e r f i t than  fits  at the highest and,the  i lowest 3-4-c  values  of free  Calculation From  ligand  c o n c e n t r a t i o n s were  poor.  o f k, 4  the equilibrium  relationship  between  tetra-  i and  t r i - t h i o m o l y b d a t e , the r a t i o  of the c o n c e n t r a t i o n of  I  the is  tetra-thiomolybdate  to that of the t r i - t h i o m o l y b d a t e  p r o p o r t i o n a l to the c o n c e n t r a t i o n of the aqueous hydrogen  sulphide:  L . r if)  C /C 4  Figure linearity  was  3  =  k  8 shows  considered  4  [H S] 2  the plot good.  a q  of the data The s l o p e  a t 150°C.  gives  The  the value  _ 1  for  k, a s 2 , 6 . x 1 0 4 2 Figure  120°C,  9 shows t h e s i m i l a r  w h e r e C^/C^  concentration hydrogen tained  2 - 1 M.  were p l o t t e d  plot  against  sulphide  since  the conversion  experimentally at this  a l s o good  data  are  available  factor  temperature.  sulphide  was n o t o b -  The  linearity  -1  ( s l o p e : 0 . 4 3 ^ x 10  o f K„, t h e a c i d N  ion,  the free  at  i n s t e a d of the c o n c e n t r a t i o n of the aqueous  2 was  f o r the data  M.  dissociation  ).  Fairly  constant  i n the l i t e r a t u r e s  reliable  o f t h e ammonium  a n d a t 120°  and  150°C.  37 pK^  a r e 7 . 0 g a n d 6.6^,  conversion constant  equation  i s the r a t i o  of the aqueous  1 5 0 ° C . was  calculated  the  value  was  estimated  120°C.  respectively  a t 25°C.  t o b e 6.0,..  This  as 10.^ and combined  Numerical  with  the least  where  Y  =  n/Z, X  and  Z  =  (3-ii)  program"  7  ,  e  3  making  + 3 x 2  -  2  L  +  2  3  of s t a b i l i t y  pK  g l  at  with  at  120°C.  for  m  at  Figure  constants  ( 1 ) c a n be  e x 1  9,  (1) handled  i t as f o l l o w s  1  (2-ii) L / Z , X 2  ±  +  , pK  r  s q u a r e s method by t r a n s f o r m i n g  -=  By  3  y i e l d e d the value  i s known, t h e e q u a t i o n  Y  to  the slope from 2 - 1 5 . 3 x 10 M. 5  calculation  When k^  dissociation  By i n t e r p o l a t i o n  with  as  i n the  acid  g  i n the l i t e r a t u r e  Q  m  s u l p h i d e , K ^,  t o be 5.8^.  (7.0 )  Since  of the f i r s t  hydrogen  k. a t 1 2 0 ° C . w a s o b t a i n e d 4 3-4-d  .  (4-n) L  =  (l-ii)  4  use of the " m u l t i p l e l i n e a r  o f t h e HP9100A c a l c u l a t o r ,  L/Z  the best  regression  f i t values  of  the  consecutive  tained three  i n section values  sulphide became  the  3-5  of  Numerical  ical  method  entiation  shows  thus  1. t o n and f r e e  i n Table  The  obtained  constants  (2) made u s e  by t h e g r a p h i c a l  differ-  distributions  The f o l l o w i n g  to e l i m i n a t e  dotted  1.  so f a r d e s c r i b e d  of the f r a c t i o n a l  derived  curve  and  the c a l c u l a t e d  of s t a b i l i t y  and t r i - t h i o m o l y b d a t e . was  concentrations.  C, 1 2 0 ° C .  are listed  methods  function  of the p l o t s  tetra-  C, 1 2 0 ° C .  calculation  3-^  deviated  performed  f o r the Series  calculation  the formation  the  of  semi-numer-  the g r a p h i c a l  differ-  process. From  of  c a l c u l a t i o n s were  and 3 - v a l u e s  hydrogen  f o r the c a l c u l a t i o n  i n Table  ob-  lowest  consideration,  the formation  are l i s t e d  5, S e r i e s  curve  entiation  at the  o f the aqueous  into  neglected  concentrations  The  k^ v a l u e s  of the l i g a n d  7 shows  3-values  Similar  formation  the points  taken  values  were  3 i n Figure  i n Figure  using  and t h e c a l c u l a t e d n - v a l u e s  points  calculated.  sulphide  sought  When  7 were  at the higher  line  line  3-4-c.  i n Figure  these  were  of the concentration  negative  greatly Thus  constants  the d e f i n i t i o n  the mono-nuclear  complex  of the f r a c t i o n a l  distribution  system,  i a. i  =  3.L /U, i 1  U  =  1 +  N Z . ,  3.L x  1  a./a.  and  Defining  a  ,  -  k. L i  function  as  i-1 F  =  Q  i  a i  Substitution  of  •  where  For  g  =  0  the above  "  k=0  ±  where  0  =  k  4  /  k  a  l  =  k  4  /  k  l  2 3 k  k /k  a  3  -  a  4  =  a  6  =  etc.  relationships  yields  d  k  a  f c  =  (  6  k  /  8  i - i  )  k  i  (  a  i  ^  4,  3  B  0  =  6  1  =  1  /  a  )  k  0  6  2  =  (a /a )k  1  6  =  (l/a )k  3  3  1  3  =  (l/a )k  4  4  4  k  2  k  =  k  ) U  i-1  8  =  2  =  n  a 1  a  5  i  k  i  a  a  k  a  * /<* _  the case  i  / B  k  E  ±  (B  i-1  N  F  i-1  =  / a  5  /  k  4  6 5 k  3  /  B  k  4  3  5  =  6  =  2  Q  Q  Q  (a /a )k 5  (  etc  a  6  Q  /  a  0  )  k  FQ values  and  g c a n be  of the f r a c t i o n a l  species.  By  of  a value  g,  lated  and  finding  without  definition,  following,  , stability  a^  working  were  F  and  F  l  H  =  h  diverge  were  any  ation plot  of  of  0  "  8  H  constants  the  polynominal  c a n be  calcu-  F ^ and  H,  defined  as  Q  +  a g  - g  1  J  3  2  0  +  into  +  a g  (Mo  a-h + 1  - C  +  3  N Z  a g  -  C )/C  E  a, h k  fc  4  .  k=5  i n the f u n c t i o n H  infinity  h  T  a„h 0  o f h,  as  amount  h  c  c a n be  contains  3  the p l o t  of complexes  used  a l l the  of H  approaches z e r o  the t e t r a - s u b s t i t u t e d vs.  2  +  1/g.  the inverse  appreciable  than  complex  species. as  against  h  i f there  of higher  coordin-  Therefore  the d e t e c t o r  poly-  of  the  higher  formation. Figure  h  =  the summation  will  of  V g ' a  forms  neighbouring  used  4  nominal  the  i n the f u n c t i o n F ^ are u n i t y  a^  (C /C )  Since  of  experimental  differentiation.  functions  a  where  the  a set of c o e f f i c i e n t s  of  that  from  distributions  the g r a p h i c a l  Noting by  obtained  f o r the data  1 0 shows of s e r i e s  the plots B where  of  F^ v s . g  the nominal  and  ratio  H vs. of  free  ammonia  to  ammonium  150°C.  As  the  need  a  higher  the  of  was  low  in  sulphide  the  as  protonated  the  when  was  2  that  F  =  ±  The ally the of  using  the  free  2H  +  a ^  +  was  of  free  mated)  Mo(SH)  F  was  Fronaeus  values  and  func t i o n  bands  tetra-  although that  the  the  total  new  peaks  increased,  values  the  c  6  +  4H.0 2  a g  . . . .  &  of  a's  were  similar  treatment  obtained in  of  =  of  CF  and  a  2  (16)  graphic-  principle  n  as  a  to  function  of  slope  g,  F^  a^.  tends After  to a^  a was  straight known  line  (or  function  2  a  concentration^.  Q  c a l c u l a t e d and  intercept  +  2  for  from  concentration  the  was  the  6  a g  e x t r a p o l a t i o n method  low  a^  the  fitting  ligand  At intercept  Q  values,  Judging  to  and  was  postulated:  =  +  h  ammonia  increasing  Mo(SH)g  +  low  absorption  concentration  6H.S 2  best  the  method the  a  at  new  2 Then  temperature  indicated.  increased  sulphide  MoO " + 4  the  corresponding  stopped  species  is  3-2  peaks  species  and  concaves-up  section  concentration  increased  0.5  term  spectrum  that  substituted  H  complex in  the  and  was  function  observation  appeared  ion  as  - a )/g Q  plotted the  =  a  x  against  limiting  + a g 2  +  g,  to  give  slope.  a g  5  6  a^  as  Similarly  an the  of  esti-  58  F  =  3  (F  -  2  a  ) / g  i  =  a  +  2  a g  4  6  4 was  calculated  intercept  and  and p l o t t e d a^ as  Since  the  against  g  to give  a  as  2  an  slope.  the e r r o r  accumulates  i n the value  of  a,,  6 calculation ting  a  procedure  was  reversed  by  c a l c u l a t i n g and  plot-  function l  G  =  F  1 S 7  6  =  l  F  h  6  =  a  6  +  2  a  h  4  +  a  l  h  5  +  a  0  h  6  4 against  h  to obtain  a^ as t h e i n t e r c e p t .  Subsequently  func tions G  G  were  =  2  3  =  ( G  calculated  ag.  Then sets  and  refined,  value  2  2  ~  and  of a's.  the data  Equally  a  g  6  2  a  )  /  After  good  f i t was  l  a  + a^h  2  +  a  against  0  +  a h  2  Q  h  h to obtain  approximation  was  a , 2  used  a^  and  to match  a_ , a . , a„ a n d 2, w e r e o b t a i n e d 0 1 2 6 c o n s t a n t s were c a l c u l a t e d u s i n g the  11a and  0.072,  a  i n section  of Series  were  =  4  "  h  plotted  o f k. o b t a i n e d 4  and  )/h  a  stability  Figures  a  -  1  the successive  two  for  (G  B.  3-4-c.  l i b show t h e e x a m p l e The  best  0 . 0 3 7 , 0.68 obtained  by  f i t values  and  0.27  putting  of such of a^,  plots a^,  respectively.:  a^ as  zero,  or  59  assuming  that  mono-substituted for a . 0  the  values  and  0.27^  respectively.  are  given  i n Table  these 4.  stability  Good  poor  obtained  and  nominal  1:1,  indicated  Series  C,  a  The  and  best  A  0.085,  0.025,  values  of s t a b i l i t y  n stability values  4 .  numerical  by  not  Since C./C  and  "  f i t was  or  150°C.  ion being formation.  formation and  0.58  of a^  and  The  the values  higher for  0.30,  and  calculated o f k^ i n  for Series  obtained  and  compared  compared w i t h line  C using with  the the  method.  t h e one  i n Figure  The  obtained 5,  by  C)  Conclusions  by  a good  against  line  1.  (1). (Solid  1 shows  obtained  no  respectively.  calculated  good  3 but  A,  graphical differentiation so  7 as  complex  0.045,  using  from  concentration.  o f a ^ , a ^ , a^  i n Table  thus  method  Discussion  constants  0.00  constants  were  i n Figure  of higher  0.105,  constants  of n  t o ammonium  indicated  C were  constants  was  ammonia  1:1,  and  values  and  0.70„ 8  stability  f o r the S e r i e s  amount  are given  values  Table  of  0.87  obatined  agreement the  Series  3-4-c  of l i g a n d  f i t values  Series  section  and  of f r e e small  0.080,  b e t w e e n n o f 1 and  calculation  120°C.  complex.  calculated calculated  low v a l u e s  ratio  were  6  are plotted  observed  Similar and  The  constants  f i t was  at high  The  d i d not e x i s t  a,  a„ a n d 2  n  1.  species  t h e summary the v a r i o u s linearity  of the c a l c u l a t e d methods  was  aqueous hydrogen  already  observed  sulphide  stability  described.  f o r the  plot  concentration i n  61 TABLE Summary  of S t a b i l i t y By  1  Constants  Various  Calculated  Methods  150°C .  B  MT  Method  MT  1  xl0~  3  xl0~  9  M:  4  xlO"  1 2  M:  6  xlO"  Line i n  4  xlO  1 8  Figure  1  -  3  0 .13  1  0.40  0 .22  0.11  -  0.49  2  0 . 35  0 .21  0.11  -  0 .52  -  -  0.262  -  0.262 (set)  3  0 .66  Two-parameter Bj e r r u m  0.63  -  (2)  - 6  M:  3  k  -  Two-parameter Dyrssen  Numerical  M:  h  0 . 11  2  ( 1 ) 0.23  2  h  0 .89  2.9  Numerical  h  xlO  Half-ii  k. c a l c n . 4  2  '°6  -  -  -  0. 35  0.27  0.070  Series  B  0.13  0 .65  0 . 25  0.065  Series  B  0.61  0.22  0.059  Series  A  0.00 (set) 0. 11  0. 38  0.-17  0. 045  —  0 . 0 0 1 2 0.262 (set) 0 . 0 0 1 1 0 . 262 (set) 0 . 0 0 0 9 0.262 (set)  4  4  120°C.  Numerical  (1)  Numerical  ( 2 ) 0. 16  k^  Calculation  Line  i n Figure  4  ' 6 2  -  ' o  3-S  1.8  2. 9  1. 8  0.96  9  8  -  -  -  ?  0. 0 (set)  -  0 .53 (set) 0 .53 (set)  dot solid'  0. 53 5  5.  k^ was o b t a i n e d b y u s i n g t h e e s t i m a t e d v a l u e o f d i s s o c i a t i o n c o n s t a n t of aqueous hydrogen s u l p h i d e a t 120°C.  7  the  calculation  general molar  method  of  i n s e c t i o n 3-4-c  of c a l c u l a t i o n  ( F i g u r e 8 ) , the  o f n, and t h e e s t i m a t e s  extinction coefficients  of t e t r a -  of  and t r i -  39 thiomolybdates  given  to be c o r r e c t . sion  by T r i d o t and B e r n a r d  Therefore  Figure  used  considered  f o r t h e compar-  o f methods e m p l o y e d . No s i m p l e  fitting  the t o t a l  method  of c a l c u l a t i o n  range of the l i g a n d  Calculated  values  est  values  o f aqueous h y d r o g e n  too  low a t the l o w e s t  sulphide  values  o f n.  obtained rather  values  concentration  sulphide  slope  However  i t was  at lower v a l u e s  concluded  trapolated  from  The already,  values  the h i g h e r  validity  fit",  obtained  of l i g a n d  This  of  values  n  t h e same values  method  were  region  of aqueous  i s p l a u s i b l e since i n Figure  and may  4 was  f o r the present  were  discussed  system o u t l i n e d .  t h e Two-parameter A p p r o x i m a t i o n  t h e c a l c u l a t e d k^ v a l u e s  ex-  be t o o l a r g e .  o f t h e H a l f - n Method has b e e n  and i t s i n a d e q u a c y Although  that  i n the lowest  concentration.  a t the lowest  and  o f t h e aqueous h y d r o g e n  i n e r r o r and t o o l a r g e  twice  gave a  ;  the v a l u e s  i n s e c t i o n 3-4-c as shown i n t h e column 7 i n T a b l e  Therefore sidered  sulphide  at the h i g h -  a l l t h e methods gave a p p r o x i m a t e l y Therefore  result  concentration.  by t h e g r a p h i c a l d i f f e r e n t i a t i o n  hydrogen  "good  yielded a  o f n were g e n e r a l l y t o o h i g h  concentration.  concentration,  the  7 was  were  t h e Two-parameter A p p r o x i m a t i o n method was  n o t t o be a d e q u a t e  to d e s c r i b e  this  system.  con-r  1  In in  the numerical  the section  using  the s t a b i l i t y  fairly  well  entiation line the  3 - 4 - c was  with  the values  i t was  observed  thiomolybdate  was  concentration,  and  (around  range  simple  where  same a m o u n t .  obtained  the dominant  From  the  absorption  -  were  differ-  7.  ; When  calcu-  ( b ) mono-  i n a l l range  of the l i g a n d were  fairly  concentration  and t e t r a - t h i o m o l y b d a t e  of di-thiomolybdate  agreed  m o l y b d a t e and  the ligand  distribution specific  3 i n Figure  species,  the c a l c u l a t e d  by  dotted  and d i - t h i o m o l y b d a t e  20%) a r o u n d molybdate  by a  species  (a) simple  significant  method  by t h e g r a p h i c a l  of various  that  obtained  calculated  by t h i s  C and by t h e l i n e  (c) t r i -  significant  value  3-2, a s c a n b e s e e n  were  less  (1),  The n v a l u e s  obtained  distributions  tetra-thiomolybdate  the  constants  5 curve  fractional  lated,  used.  i n the section  i n Figure  calculation  values  were o f  of f r a c t i o n a l -  and t h e measured v a l u e s  of the di-thiomolybdate  a t 315  of  my,  315 ,  the molar  extinction  coefficient  of the d i - t h i o m o l y -  4 bdate  a t 315 my  (Table  postulate  which  the numerical a protonated  was n o t n e c e s s a r y  of  experiment  of  this  an  explanation  the  was  t o b e 0.9,. x 10  calculation species  M.  enough  However  this  f o r the observation  ( 2 ) i t was  of higher  i n the other  not high  assumption.  concentration  short  calculated  -1 cm.  A - l - 1 i n Appendix A ) . In  to  was  -1  expected  from  coordination,  methods.  The  accuracy  to confirm  the v a l i d i t y  protonated  species  i n S e r i e s D,  of t e t r a - s u b s t i t u t e d  of the values  necessary  species  the other  offers  i n which stopped f a r  series  and  also  new of  peaks total  appeared sulphide  constant the  of the hydrogen  i n proportion  concentration, concentration high  value  i n intensity  was i n c r e a s e d .  f o r the protonated  square  increase  and i n c r e a s e d  ammonia  ratio,  Mo(SH)^  ion concentration,  to the square  to free  the s t a b i l i t y  species  or to the square  of this  Since  contains $, o  would  of the hydrogen i o n  of the r a t i o  o f ammonium i o n  concentration,  t h e term  a s t h e amount-  and a t a  containing  B,.  very  would  6  dominate  the whole  distribution the  complex  of a l l the other  protonated  were  the f r a c t i o n a l  which  agrees  with  rejected  on t h e g r o u n d  2  MoO 4 2  + 4H„S 2  concentrations the fourth plot  + 2H  H  calculation  (2) would  zero,  i s contrary  The  +  H.MoS. 2 4  that  by t h e e q u i l i b r i u m  =  HMoS. + 4H.0 4 2  =  H.MoS. + 4H.0 2 4 2  species  of the ligand  of function  which  +  of these  power  o f t h e forms  and  M o O " + 4H.S + H 4 2  the  species,  species  HMoS. 4  to  decreasing  observation. The  the  system  against  not concave  protonated  would  be p r o p o r t i o n a l  concentration. h  i n the  up a s  equations  h  Therefore  numerical  approaches to  to the observation. species  proposed  by Ghosh  et a l .  64  ,  65  4HgMoSg  2HgMoSg  and  equilibrium  , were  2  +  8H„S 2  =  H,MoS " + 6 8  concentration  ion  be  adversely  proposed  HgMoSg  of these affected  with  HC1^"\  acid  side.  solution necessity  might  by Saxena  experiments  by t h e  +  species by  +  +  4H„0 2  4H 0 2  would  n o t be a f f e c t e d o r  the increase  of hydrogen  where  be a f o r m a t i o n  of p o l y n u c l e i  et a l . to e x p l a i n  the r e s u l t s  thiomolybdate  However,  i n their  The p r e s e n t  appear  of p o s t u l a t i n g  system  action  of the f o l l o w i n g  species  may  A  molybdate varies  polynuclei  two  *\  X  2X  representing  i o n and t h e p r o t o n a t e d  with  S  ,  the hydrogen  their  titrated on t h e  i n ammoniacal without  the  species. (VI)-  sulphur  (-II)  of the  inter-  curves:  the e q u i l i b r i a  ion concentration.  curve  data  species of  was  as a r e s u l t a n t  formation  MoO,  pH  explained  representing  of the form  A  the  experimental  be d e s c r i b e d  curve  the hydrogen (b)  work  t h e molybdenum  -water  (a)  s o l u t i o n s were  t o be a d e q u a t e l y  Consequently  with  since  concentration. There  the  2H  4  =  would  rejected  equations  Mo0 ~ 4  the  also  which  does  (Curve  between not  1)  the e q u i l i b r i u m species,  vary  between  Mo(SH)^,which  ion concentration.  (Curve  2)  Figure  12  shows  the  schematic  d e s c r i p t i o n of  the  above  statement. Therefore centration,  or  in  a  will  be  completely  tion  of  the  expected.  when  a  3,  to  room  was  The  sulphide  low  high  the  and  confirmed  a  high MoO.  by  following  an  4-x  hydrogen  fractional 2x  S  would  concentrations  were at  C  (NH.).SO. 4 2 4  0.49  M.  C. 4  0.0005 6  Na S 2  0.33  Mo^  0.00067  appearence  of  peaks"  observed  no  calculated values concentration  the of  with  "new n  and  2  realized 150°C.  M.  M.  2  be  0.86  1  curve  i n Part  autoclave  con-  distribu-  20  3  ion  solution,  experiment  shaking  temperature  of  alkaline  form  in  value  within  NH  D.  the  of  r e a c t i o n mixture  quenched  There  very  suppressed  was  where  a  fairly  species This  section  at  was  minutes.  0.00012  3  aqueous  M.  2  5  _•M.  M.  in  Series  hydrogen  the  method  described  in  section  M.,  r e s p e c t i v e l y , assuming  _3 3-3  were  3.82  the  high  temperature  shown  and  in Figure  considered  27  x  10  e q u i l i b r i u m was  7 with  a  double  frozen.  circle.  The  This  that  point  agreement  is was  good.  The  actual  be  a  colloidal  of  a  molecule  to  molybdenum  structure  molybdenum i n which atom,  of  the  protonated  trisulphide,  MoS *3H S,  six hydro-sulphide since  (a)  the  species  3  ions  2  are  experimental  may  instead coordinated mixtures  h i g h e r CH ) +  Curve I n Curve 2  Log (H2S) Fig. 12 SCHEMATIC DIAGRAM OF THIOMOLYBDATE SYSTEM Curve I  1  MoQ^sf  + HgS  =  MoO^sf", + H 2 0 (i»0,l,2,3)  Curve 2  s  Moo|"  + 2H + + S^S = Mo(SH)6 + 4 h ^ 0  in  Series  (Pyrex)  D  to  give  originally peaks  did  passed  120°  not  are  and  lation  the  charged,  In stants  through  seem  Table listed  150°C.  method  but  (b)  the  absorption  follow  the  Beer's  logarithm  for various from  (1).  of  grade  amount  the  are  finest  same  to 2  the  The  the  glass  molybdenum  of  of  values  at  19°C.  the  The  experimental  estimates of  oxide  were 5  of  by  enthalpy  ion with  performed  and  data  Tridot  and  entropy  sulphide  using  and  ion  these  data  are  calculated  changes  and  decreased  enthalpies  i n magnitude  of as  the the  exchange  .  from  The  the  in  were  the  rough  exchange species  column -  i s reported  that  "step-wise  enthalpies  for  association  with  ionic  solution  are  as  large  as  or  mercury  usually -10  between  kcal./mole,  (II) with  usually  between  0  dendate  l i g a n d s , but  neutral  multi-dendate the  negative ion  values  value and  for  and may  for the  0  and  for  cyanide -5 be  or  as  iodide  large 79 .  as  The  decrease  one  ion  i n aqueous . but  e.g.  ions.  may  be  silver  The  (I)  values  for neutral uni-20  kcal./mole  present  neutral ligands. of  sulphide  kcal./mole,  kcal./mole  exchange  subsequent  ligands  ±5  and  ligantional  r e a c t i o n s of  ligands" the  negative  c o o r d i n a t i o n of  It  phide  '  thiomolybdate  increased.  within  calcu-  62  for  listed  at  6. The  are  values  numerical  Bernard  i n the  con-  the  39 the  new  consecutive  temperatures. of  concentration  Law.  the  results  filter  The  oxygen  i n magnitude  values  with  were  large  ion with as  more  sul-  69  TABLE Effect  of Temperature  on  Temperature  k  ±  log  k  2  log  k  3  log  k  4  (°C.)  Constants  120  150  5 . 20 5 . 81  3 . 63  2.36  -11.  4 . 08 4 . 74  3 . 36  3.18  3.30 3 . 51  2 .55  2 . 89  2.68 2 . 76  2 .73  2.41  k v a l u e s a t 19°C. were by T r i d o t a n d B e r n a r d , k v a l u e s a t 120° method ( 1 ) . The e f f e c t i v e one.  the Consecutive  AH Kcal. / mole  19 log  2  and  figures  calculated r e f . 39.  150°C.  of  were  log k  from  from  and  "  " -  5  3  AS  9  "  '4  "  5  '5  "  9  -9  0.8  the r e s u l t s  AS  10 .  '5  Q  the experimental  AH,and  e.u.  would  of  be  3  '4  data  numerical  two  and  oxygen of  ions  were  stronger  exchanged  covalent  decrease  in  effect  trend  is  in  good  first  absorption  exchange ted  to  the  bonds  as  the  by  peaks  cause  with  moved  The of  the  the  of  saturated. that  wavelength  covalent  appearance  formation  subsequent  observation  longer  formation  the  and  becomes  the  to  clearly  exchange  exchange  agreement  advanced.  be  indicates  of  the  as  bonds  This  the is  absorption  attribu-  peaks  2in  the  visible  range  when  ions  ClO^,  CrO^  and  MnO^  ,80 were  compared The  advanced. species,  If the  difference  sulphide, for  the  close step  to  of  entropies there  step this  be  value  the  in  the  the  of  water  decreased  This would  as  the  bdenum-ligand molecules .  and  The  entropies  molecule  since the  as  of  step  entropy  the  to  be  of  exchange  approached• as  the  thiomolybdate  the  sulphide  In  as  ions  the  other  words  thiomolybdate ion 8 2  "iceberg" nature  the  hydrogen  interpreted  covalent  increases,  would  increased  of  exchange  thiomolybdate  aqueous  hydration.  bound  the  the  tetra-molybdate  s u b s t i t u t i o n of  bonds  each  d i f f e r e n c e was  as  from  difference  entropies  smaller  for  water  .  the the  i s understandable become  exchange  t r i - and and  decreased  contribution  e.u.  Since  difference  exchange  between 80  -12.5  between  similar,  amount  of  entropy  decreased.  would  i s no  entropy  namely  of  advanced.  around of  r e l e a s i n g more  ions  the water  the  ions  moly- .  71 In  conclusion  1. of  the  species  constants 0.23  x  0.070  The  10 x  of  12  M.  bdenum  MT  and 1  indicated  by  MoO._  f ™ X  S  10  M.~ ,  6  2-  and  X  the  the  existence  stability  tetra-thiomolybdate 0.27  2  showed  x  10  M." ,  9  were  and  3  respectively.  were  species  Molar  strong  indications  Mo(SH) may  6 >  be  extinction  di-thiomolybdate  cmT  >  1  4.  and  150°C.  as the  the  pH  of  the  formation  of  the  solution  colloidal  form  of  moly-  trisulphide.  tetra4  ,  at  d i - , t r i - , and  species,  This  3.  x 10  -4  There  protonated  form  0.35.x  1  decreased.  the  mono-,  2. of  of  M." ,  3  10  experiments  entropy sulphide  were  at  estimated  315  to  be  my  of  2.01  and  respectively.  A  the  coefficients  calculation compensating  for ion.  the  of  thermodynamic  effect  step-wise  of  parameters  enthalpy  substitution  of  oxide  ion  0.95  PART  2:  STUDY  OF  Hydrogen ing  gases  were  made  under  H  2  i n solution  a n d CO  reaction  will  case.  1.  Experimental  A apparatus  series  the  introduced  was  was  autoclave.  resumed  with  of experiments  equilibrated, Agitation  was  The  constant  was  stage  measured  pressure  the case was  temperatures  this  latter  and c a r b o n  the three  of  condition. monoxide  gases,  Products were  noted  a sample stopped  was  N , 2  o f any  studied  then  samples  gases stage  with  in  on.  t h e same  After  the  withdrawn  and r e d u c i n g  pressure.  from  1.  The  at c e r t a i n  from  g a s was  Agitation  i n t h e a u t o c l a v e was  o f two by  performed  i n Part  partial  by a d m i t t i n g more In  first  total  was  described  f o l l o w e d by w i t h d r a w i n g  vals.  under  studies  decrease  of the r e a c t i o n s  to the d e s i r e d  and t i m e  Some  some  hydrogen  reduc-  f o r any  at high  under  as  procedures  and p r o c e d u r e s  temperature  noted  the r e a c t i o n s  and  chosen  be d e v e l o p e d .  2  was  SYSTEM  availability  (N ) because  and t h e k i n e t i c s  Apparatus  were  be d i s c u s s e d s e p a r a t e l y .  each  1-1  ready  i n the system  processes  to d i f f e r ,  monoxide  might  atmosphere  reduction  appear  that  of s t a b i l i t y  molybdenum Since  of their  process  an i n e r t  I N THE Mo-S-H^O  and c a r b o n  because  industrial  REDUCTION  was  reaction  time  inter-?-  maintained,  manually. runs,  t h e end o f t h e  the disappearence  o f a n o r a n g e - .,  73 yellow  color  molybdenum A  sample  to  from  the s o l u t i o n .  solution  was  was  withdrawn  injected  was  the  i n cold  series  of batch  reducing  g a s was  was  stopped  the i n j e c t i o n  and a g i t a t i o n  and  system.  was  resumed  A t t h e end o f t h e r u n t h e a u t o -  quenched A  with  immediately  continue the r e a c t i o n .  clave  Agitation  water. experiments  performed  using  hydrogen  in a stainless  steel  as  shaking  84  autoclave  described  were  prepared  some  cases  added  by McAndrew  a t room  sodium  temperature  sulphide  solution  flushed  with  desired  temperature  while  stopped  temporarily  and h y d r o g e n  reaction  was  pressure  change  reading filled the  of a h e l i c o i d with  silicone  bration  was  o f a known  variations  applying the  reaction  sealed,  was  the shaking  system  was  t h e dead  more  and m e a s u r i n g  to the then The  and t h e  followed  (0 - 1 5 0 0 p s i . , 10  by i n t r o d u c i n g  cooling  was  introduced.  the p r e s s u r e drop  by t h e  psi./div., volume).  ceased, hydrogen  At  califrom  a  the pressure  and t h e b o t t l e .  calibration  a water  of the exper-  Agitation  g a s was  In  s u l p h a t e was  and e q u i l i b r a t e d  o i l to minimize  volume  solutions  solutions.  the system  shaking.  gauge  of the system  After  then  by r e s u m i n g  r u n when  performed  ammonium  gas, heated  o f the whole  end o f each  bottle  charged,  initiated  stock  A c o n s t a n t volume  imental  nitrogen  Experimental from  and/or  i n c r y s t a l l i n e form. was  .  t h e a u t o c l a v e was  coil  i n the middle  around  quenched  i t shead.  o f t h e r u n was  by  Quenching  performed  by t h e  same to  cooling  120°C.  method.  in  less  After the  slurry  than  the  was  with  in  dryer,  for  vacuum  reduction  the  was  and  cooled the  dried  to  room  precipitate  overnight  stored  each  tion  a  or  time  dilute By  the  the  solutions  in  a  the  run  was  except  160°C.  at  bottle  temperature, was  washed  room in  a  temperature desiccator  was  boiling  found of  with  to  the  a  catalyze  autoclaves  dilute  nitric  hydroxide-hydrogen employed  starting  the  the  the were  acid  peroxide  thermal  reduction  solu-  solution.  history  reaction  of was  same.  procedure  of  the  analysis  performed for  were  surfaces  procedure  Analysis The  by  sodium  Analytical  1-2-a  the  before  approximately  1-2  precipitates  reaction,  cleaned  by  of the  sulphide,  solution sample same  where  solutions  procedure  in  some  taken  during  described  in  cases  the  the  Part  following  1,  method  employed:A  into  a  suitable  beaker  N.NaCIO  added,  followed  solution  around  and  aliquot  containing  0.05  the  and  from  minutes.  system  water,  dropped  analysis . As  of  temperature  5  filtered  thoroughly a  The  10  and  by  of  10  ml.  of  Kl  the  ml.  solution,  approximately  lg.  of  2.  crystals  of  100 2  sample 1  N.NaOH.  ml.  of  N.I^SO^ The was  solution  distilled to  make  solution added.  Then  was  The  the  was  taken  25  ml.  water pH  was  of  swirled resulting  I„ -,  was  titrated  by  0.05  immediately  before  The  content  sulphur  from  the  from  -2  reagent t o +6 In  quartz that  they  the  of  assuming  the  light  path  spectrogram  of  the  not  1-2-b  show  rapidly  Several precipitates,  the  methods  were  was  oxidized  taken  samples the  the  with  were  scale. made  and  time  with  a  diluted  so  Although up  at  dilution,  reduction  employed  and  room the  experiment  dilution.  f o r the  analysis  of  namely,  b)  Thermogravimetric  c)  Differential  d)  X-ray  e)  Optical  f)  Infrared  spectroscopy.  g)  Magnetic  susceptibility  h)  Others.  analysis  f o r Mo,  S,  analysis  thermal  NH^,  and  i n both  analysis  Ar  i n both  Na. and a i r . Ar  and a i r .  diffraction.  Chemical  and  electron  microscopy.  measurements.  analysis  Molybdenum: Br  difference  precipitates  Chemical  -  solution.  s u l p h u r was  time  from  a)  KBr  on  with  solutions  of  the  Mo-S-R^O m i x t u r e  a p p r e c i a b l e change  • Analysis  from  that  and  accommodated  the  standard  spectrogram  be  of  standardized  state.  could  spectrogram  with  KIO^  calculated  cases  changed  a)  was  1cm.  solution,  3  against  blank  temperature  did  use  valence  some  cell  N.Na2S20  0  A  weighed  solution  and  amount HN0„  of and  sample then  was  heated  oxidized to  drynes  after in  concentrated  water  and  the  phenolphthalein 5%  by  able the  volume. amount  solution  2%  washed  (filtrate  dried,  and  The  taken  as  was  was  acidified  cooled  to  with  precipitate  at  were kept  and  i n weight  the  amount  of  the  o f Mo  HCl  to  was  suit-  added, was  and  filtered,  for S analysis)  525°C. i n a w e i g h e d  increase  to  5~10°C., a  a-benzoinoxime washings  dissolved  neutralized  solution  and  MoO^  then  r e s i d u e was  a-benzoinoxime  ignited  crucible.  The  solution  w i t h NaOH a n d The  of  addition.  resulting  r e s u l t i n g Mo-  was  HCl  porcelain porcelain  i n the  crucible  sample  was  calculated. Sulphur: analysis heated  The  were n e u t r a l i z e d  to near  boiling,  BaSO^ p r e c i p i t a t e s precipitate furnace  at  was  into The to  HCl pH  ence  hot  after  solution after  and  H2S0  cooled,  After  4 >  diluted  N.HC1  solution  ignited  remaining  = 5.2 i n HCl  using  was  complete  apparatus  titrated  Beckman  consumption  zeromatic  from  and  adding with  the  the  sulphur  blank.  :  and  sample  digested with the  charged the  ammonia  standard pH-meter. blank  0.01 The gave  hot  solu*-  into  concentrated  reagent  The  muffle  dissolution,  with water,  and.the  (= 20mg.) o f  and  Mo  N.HC1,  in a  and  amount  the  overnight.  s u b t r a c t i n g the  after  from  added,  aging  weighed;  A measured  micro-distillation  0.01  BaC^  and  washings  in a micro-Kjeldahl flask  concentrated  Kirk's  and  NaOH t o make 0.1  washed, d r i e d ,  calculated  placed  was  10%  filtered  Nitrogen:  tion  with  800°C., c o o l e d  a m o u n t was  was  filtrate  a distilled  NaOH. N.NaOH... differthe  NH^  77 amount,  hence  the  N%  Sodium; metrically  after  ing  to  Atomic their  Mev.  (San  bottle, with  gamma-ray  was  Oxygen  Inc.  irradiated  sample.  dissolving  description  polyethylene was  the  Sodium  Oxygen: General  of  determined the  analysis  was  with  hot  performed  was  with  compared For  phere of  using  procedure,  the  of  with  the  and  and N"^  was  to  cipitates.  a  sealed  the  sample  by  the  intensity  , which  was  For run,  The  precipitate  sample  distilled  water  were  in  left  weight  was  dissolved filtrate  and  customer,  of  the  formed  (n,p)  6.13  by  N  stayed  was  under  where  the  reaction,  hydrogen  the  mostly  added  sulphate,  molybdenum  chemical  to  total  on  after  and  analysis  weight  was  on  fritted  the  atmosphere  measured.  and  autoclave,  (~50ml.).  the  with  a  16  0  experiments  free of  in  the  atmosamount  autoclave  thorough  dissolve sulphur  washing  the was  preperformed  solutions.  the  the  of  solution  Analysis  the  Accord-  standard.  small  remove  leached  via  the  shaking  NaOH-H202  water  the  neutrons  series  precipitate  walls,  on  a  Gulf  of  neutrons  against  by  C a l i f o r n i a , U.S.A.).  16 interaction  i  HNO^.  Diego,  prepared  photopeak  sample  flame-photo-  KBr-B^  washings  The  the  determined  The  glass  funnel  dry  precipitate  set  and  precipitates  i n d i r e c t l y as  precipitate  until  solution being  of  and on  HNO^,  aside  for  was  follows:  washed  and  the  the  overall  the  Mo  with  funnel  funnel  and  during  was  y  washed,  and  S  analysis.  The  funnel  difference sample used the  from  cribed  I n some  was  instances  much  determined  was  treatment  taken  filter  Subsequent  lower  measured.  was  a normal  the p r e c i p i t a t e .  i n the a n a l y s i s  gravimetrically  as  paper  was was  cases.  spectrophotometrically  of the sample  as  treatment  i n these  The  solution,  as  des-  and s u l p h u r  BaSO^.  Thermogravimetry A  from  sample  was  mounted  one arm o f a c h e m i c a l  fibre  i n a Vycor  a vertical  sample  was  ( 3 0 mm.  electric  recorded  I.D.)  on a c h a r t  flow,  and d e o x y g e n a t e d  (500°C.) least  tube  containing  one h o u r  before  t h e f u r n a c e was  temperature reading  Vycor  tube  vessel. scale, time  with  lag.  ± 2 ~ 3 mg.  mm.  linearly was  calculated  was  recording  was  due  was  to a  calibrated  of the  through  was  a  argon  gas  a heated . (  passed  The  from  f o r at  temperature and t h e  t h e e.m.f.  i n a quartz  exactly  the bottom  vibration  The b a l a n c e  change  (~6°C./min.)  thermocouple  from  change  at the centre  Constant  turnings,  hung  quartz  by p a s s i n g t h r o u g h  the t i p of which  The w e i g h t  tube  the h e a t i n g s t a r t e d .  raised  a n d 2~4  thin  time  mechanism.  of a Chromel-Alumel tube,  a  The w e i g h t against  copper  of the sample  couple  with  furnace  furnace.  zero-balancing  dried  i n a quartz vessel,  balance  photometric  of  and w e i g h t  before  b u t a c c u r a c y was  determined  b)  as b e f o r e  the value  to c o l l e c t  Molybdenum  of  dried  weight.  same  was  was  centered  thermo-  i n the:  of the quartz o n -80 mg.  full  zero-balancing  each  time  by  placing  known  weights  on  the  other  side  of  the  arm  of  the  chemical  balance. After ature with  i n Ar the  flow.  same  of  dry a i r .  c)  D.T.A.  the  run  the  The  subsequent  procedure  Differential was  performed  sample  was  with  in a  argon  atmosphere  place  of  corroded raised  by  a  Pt-Pt  gas  deoxygenated passed  ing  was  by  After  room  temperature  i n the  test  i n a i r was  d)  X-ray  with  the  argon by  compared the  run  was  which  furnace  the  against under  was  in  found  temperature  copper one  The  used  Argon  0  least  flow  precipitates  11.6 C./min.)  at  run  performed  was gas,  turnings,  hour  before  heat-  f u r n a c e was  cooled  to  atmosphere allowing  and  free  a  subsequent  access  of a i r .  analysis  X-ray tional  of  heated  temper-  constant  thermocouple  at  room  department.  and  case  to  the  in this  (The  system  performed  of  thermocouple  linearly  started.  i n a i r was  the  Rh  evolved.  the  run  powder  passing through  through  cooled  passing a  made  10%  was  analysis  In  Alumel-Chromel the  by  A^O^  cell.  approximately  was  thermal  with  reference  the  except  apparatus  diluted  Al^O^  sample  X-ray  a nickel  diffraction  diffractometer filter.  The  pattern using  was a  samples  taken  copper were  Ka  with  a  conven-  radiation  mounted  on  silicone  80 grease  Three but  packed  sharp  i n a window of  peaks  the b l a n k  peaks e)  and  run  thus  at  2.14,  of  the  an  1.85  electron  sheet 0  and  A.  silicone  1.56  grease  sample h o l d e r .  were  showed  they were d i s c a r d e d from  observed the  same  consideration.  Q  Micrographs A  aluminum  Zeiss  metallurgical  microscope  were  used  microscope to  and  a  Hitachi  take micrographs  of  pre-  cipitates . Samples not  to g r i n d  or  optical  f)  on  of  or e l e c t r o n  Infrared  ground  Magnetic  i n the  a small  matic cation  dried  microscope,  and  mixed  dropped  on  and a  for inspection  shape.  microscope with  an  respectively.  w e r e made u s i n g t h e K B r  with  I.R. KBr  spectrometer crystals  in a  disc 621.  mortar  conditions.  susceptibility  Chemistry  Pyrex  balance. of  and  size  care  susceptibility  Magnetic  in  film  spectrograms  atmospheric  balance  s u s p e n s i o n was  a Perkin-Elmer grating  Samples were  g)  in particle  taking  spectroscopy  Infrared  under  d i s p e r s e d i n water  a change  the  a carbon  method w i t h  first  to cause  Then a p o r t i o n glass  were  glass The  was  measured w i t h  Department.  Samples were  tube  weight  the magnetic  hanging  on  the  arm  c h a n g e b e f o r e and  field  was  measured  and  of  after  a  Gouy  placed the  auto-  appli-  magnetic  susceptibility reading.  Mr.  h)  B.  cobaltate  Califord  Other  the  the  Chemistry  employed  i n v a r i o u s media  Precipitation  icant  decrease  solution  centration Series  and  A,  was  of  tween  of  (II)  the  blank  tetrawas  supplied  Department.  were  will  be  digestion  of  the  discussed elsewhere  in  Figure  13  nitrogen change  8.]  regular  and  extent  the  was  the  the  total  [See  down  some  signif-  at  con-  Appendix the  A-l-1,  high  equilibria  demonstrated  a batch  i n transmission with  room  temperature,  spectrogram  from  to  time of  indicating the  run  i n Appendix  corresponding  shows  temperature.  of  F i g u r e B-3  complexing  s m a l l but  concentration in  where  slowed  is clearly  line  of  a  be-  precipitate.  result  the  1,  increased.  decrease  spectrogram  decrease  at  series  sulphide indicating  atmosphere.  broken  mixture  The  i n Part  molybdenum  i n the  equilibration  which  i n the  total  noted  of  Atmosphere  experiments  the  solution The  Inert  s u l p h i d e i o n was  No.  the  i n an  the of  concentrations  the  mercury  ( I I ) , Hg(Co(NCS)^) , which  methods  During  The  made w i t h  subtraction  text.  2.  the  of  was  after  me t h o d s  Other samples  calculated  Calibration  thiocyanate by  was  solutions  under B  this  a  shows  the  run.  A  is clearly  the the  in  initial  seen. solution  difference at  high  in  I  0  Fig.13  1  20  —I  r  40  1  60  1  —I  80 100 TIME min. VARIATION OF CONCENTRATION UNDER N 2 158 8°C  I  120  I  140  I  160  Apparently [X-Xe] X  i s ' p'l'o'tted  a n d Xe  Xe's fit  a good  against  linearity time  are instantaneous  were  assumed.  values"of  k  Table  a n d Xe  as  i s obtained  shown  when l o g  i n Figure  14,  where  and  equilibrium  concentrations,  A-2  i n Appendix  A  calculated  by  using  lists  the  best  the i n t e g r a t e d  form:  X  ,' \'  ) When  \ A  Xe  +  k  x  . . . . (17)  t  x  the c a l c u l a t e d  k  the  which  showed  shown  was  roughly  constancy  i n Table  A-2  empirical rate  and  when  by  Q  line  13-16  Xe,  a  number  equation  was  assumed  -k jMo] [S] ([Mo]  d  [X]/dt  =  -k [X]  ."  From  M  y  S  T'  C  4'  the molar  precipitate  was  ratio  calculated  ^tS] /A[Mo] T  T  ([ ] -  calculated, A.  Thus  [Mo] )  . . . .  e  (18)  [X] )  X  °3  of by  =  was  t o be  -  e  the e m p i r i c a l equation  molybdenum,  =  e  f o r [Mo]^,  i n the Appendix  =>  T  except  k^. / [ M o ] [ S ]  [Mo] /dt  calc  divided  constant,  d  X  s  was  x  found  which  r  a e  •• )  was  as  =  (17) f o r s u l p h u r  sulphur equation  ( [ S ] Q  and molybdenum  and i n the  (19)  [S])/([Mo]  Q  -  [Mo])  ( X -Xe )  M*I0 3  0 Fig.14  40  80 120 T J M E min.  FIRST ORDER P L O T  160  = (a /a s  substituting  was  The  The sulphur  s )/(l t  of time, line  The  - e ^o )  . . . .  1  t, at  of Table  t h e end  A-2  agreement w i t h  (19)  of the  i n Appendix  A  the observed  values  good.  found  was  t o be  constants  almost  gives  =  f o r molybdenum  t h e same.  a stoichiometric  d[S]/d[Mo]  Integration  _ k  empirical rate  were  there  - e  last  the r e s u l t s .  considered  that  )(l  the values  experiments. shows  M o  This  and  implies  precipitation, i.e.  (d[S]/dt)/(d[Mo]/dt)  =  k ([S]  -  =  ([S] -  [ S I )/([Mo] e  s  [S] )/k e  M o  ([Mo]  -  [Mo] ) e  [Mol ) e  f o r the instantaneous  values  of  [SJ )  [Mo] ) +  [S] and  [Mo];  log  ([SJ -  =  e  l o g ([Mo] -  g  constant  Therefore  [S]  where  -  q  u is a  [S]  fairly  bdenum  and  u([Mo]  o  -  [Mo]),  constant.  Chemical that  =  large sulphur  analysis amounts were  of  the p r e c i p i t a t e s  of substances  present.  The  other  X-ray  revealed than  moly-  analysis  showed  broad  diffraction  observed  for  the  atmospheres. weight 12%  loss  between  precipitates  property  and  of  [-10%] a t  tests  thio-oxy  and  around  thus  in  the  the  C.  was  about  is reported i s most  carbon  a  rapid  and  330°  to  also  and  showed  i n argon  a i r at  precipitate  which  hydrogen  analysis  280°  compound  60°,  both  Thermogravimetric  i n subsequent  molybdenum  26=30°  have  likely  another C.  No  this a  mixture  89 of  a  sulphide  and  an  From  the  concentrations  bdate  ions  secutive  coupled  constant  oxy-  with k, 4  conversion  factor  was  estimated  as  Part  1,  value  section  at  150° The  atmosphere  Literature  the  concentration  a  slow  reduction  a  part  of  -  of  molybdenum  in  the  in  aqueous  slightly.  C.  in  158.8°  the  same  3  the as  M. )  various  acid  sulphide might  be  The  (12)  in  in  in  with  the  (See  However the  taking  the  inert  large  Introduction  since  place  there  of  that  was  was  (18),  consuming the  valency  sulphur  unaccounted  molybdenum  of  equation  calculation  form  that  equation  decomposition  assuming  indicated  con-1 M.  fair.  precipitates the  the 3 10  described  authors  2-4-f).  and  the  precipitation the  data,  i n magnitude  was  - 1  tri-thiomoly-  0.29,. x 5  method  agreement  10  and  analytical  at  sulphide.  the  tetra-  be  section  hydrosulphide  hydroxide,  by  reaction  divalent  of  of  compound  to  same  observed  survey  x  of  other  The 2  hydroxy-  estimated  with  (0.26  be  a  were  4.9  mechanism  may  thiomolybdate  m  3-4-c.  C.  the  was  The  or  was  residuals  reduced  87 3.  Precipitation  3-1  Reduction  3-1-a  phase  absorption  reduction  were  in  (Study  Part  peaks  1  were  Appendix 700  my  of  a  reduction  i n lower  those  No  new  my  as  absorption shown i n  210-260 those  described  my  and  observed  above i n the  concluded  oxidation  intermediate  that  state  existed  soluble  than  t o be  complexes  6 was  detected  i t must  be  not and  short  prothat i f  lived.  Precipitates  appearence  fine  black.  a white  volatile  identification  of  this  the q u a l i t a t i v e i t was  some  Optical showed  were  to carbon  atmosphere,  that  as  concentration  Precipitates  but  260  regions  t h e same  i t was  in sufficient  3-1-b  and  as  during  study.  molybdenum  duced  t h e same  700  The  also  Therefore of  of the s o l u t i o n s  the e q u i l i b r i u m ) .  B5.  found  equilibrium  t o be  between  Figure  were  spectrograms  observed  evident  B,  Hydrogen  products  Aqueous The  with  When  observations  and  powders  they  material  volatile  compound  black  were  heated  evolved.  m a t e r i a l , was listed  of sulphide  similar  and  e l e c t r o n micrographs  i n Ar  A  total  not  i n Table  in  attempted 3  suggest  nitrogen. of  precipitates  that:  (a)  Particle ation  shapes  seemed  were  very  extensive.  irregular  and  agglomer-  83 Table Properties  (a)  of  the v o l a t i l e  Produced  i n Ar  Solidifies in  a  cold  (b)  material  atmosphere  a t room trap  Evaporates  3  at around  temperature  (around  slowly  produced  and  easily  resulting  solution  heating  150°C. trapped  completely  -10° C . ) .  i n t h e a i r a t room  Dissolved  by  i n 0.1  N  HCl  reduced  temperature.  solution  an  and  ^-starch  the  solution,  2+ oxidized Nesler  a Fe  reagent  different  solution to give  absorption  and  reacted  a similar  spectrum  but  from  with  the  slightly  that  given  by  ammonium. (c)  Corroded Ar  an A l u m e l - C h r o m e l  atmosphere  at around  thermocouple C.  The  i n the a i r i n d i c a t i n g  that  not  occur  was  not produced  300°  in oxidizing  wire i n  corrosion did this  atmosphere.  material  (b)  There with  (c)  was  was  no  When  < 2, a n d / o r  ±  as t h e ( [ S ] / [ M o ] ) ^  to  t o be  from  smaller  the d u p l i c a t e  completion,  during  X-ray  diffraction  the p r e c i p i t a t e s  were  noted  i n this  roughly  was  particle  an was  The  halfway of  size was  particles  allowed  t o go  growth  were  area  correspond o f M0S2  There  heated  a  a n d 1.56  to those  A).  (Figure  did  general and,  i n A r , two d i s t i n c t  developed  reported  was  26 = 30 a n d 60 d e g r e e s  ( d = 2.68 was  of the p r e c i p i t a t e s  peaks.  between  a t d = 6.4A  modification  were  products  decreased.  which  patterns  defined  when  peaks  [NH*],  the s i z e  indicating  of r e f l e c t i o n  peak  runs  shape  the run.  any s h a r p l y  broad  low  interrupted  than  and  conditions  of the f i n a l  runs  particles  ([NH^~ ] ) .  observed  particles  i n size  the i n i t i a l  i n the s i z e  from  increase  change  and l a r g e  ([S]/[Mo])  found  give  when  of  pressure.  increase  of  not  change  of hydrogen  > 2  i  size  apparent  particles,  ([S]/[Mo]) (d)  apparent  variation  There of  no  Also  15).  peaks a  These  of the rhombohedral  by s e v e r a l  authors  (See Table  83 4).  ^°^3 synthesized  reflection. completely of  by C h i y a ' s  The d i f f r a c t i o n different.  the p r e c i p i t a t e s  Some  showed  method  patterns electron  d i d not give  of  (NH^^MoS^  diffraction  a hexagonal  symmetry,  any  were  pictures which i s  90 TABLE X-ray  D i f f r a c t i o n Data  Rhombohedral MoS  4  f o r MoS„  (2)  (1) A  I  hkil  d  A  I  6. 2 3.05 2.72 2 . 64 2 . 359  100 3 19 14 18  0003 0006 1010  6. 1 3 . 02 2 .77  10 1 9b  6. 0  1014  2 . 345  4  -  -  2 .254  2 . 205 2 .051 1.857  20 11 9  1015 0009 1017  2 . 198 2 . 053 1.874  5 6 4  2 . 050  1.766 1. 704 1.586 1.524 1.429 1. 360 1.314 1. 253 1.228 1. 217  5 1 15 18 1 2 2 5 3 2  1018 1019 1120 000 ,12 Oil,11 2022 2022 1129 000,15 2027 112,12 000,18  1.754  -  -  -  -  -  -  -  -  -  -  -  -  Rhombohedral  Precipitates  P r e c i p i t a t e s by H y d r o t h e r m a l Decomposition of Thiomolybdate  2  d  and  -  MoS ; 2  3  -  -  1.578 1.528  -  -  2 .72  -  1.824  -  d  10  A  -  5b  -  2  -  4b  -  -  1.362  7 1  Bell  1.097 1.034  --  -  -  and H e r f e r t ,  2 .68  b  1.56  b  -  -  ,-  -  - .  -  2  r e f . 71. and  P r e c i p i t a t e s by h y d r o g e n : 1 5 8 . 8 ° C , 500 p s i . , [Mo] = 0.01 M. , [ S ] [ N H ] = 1.0 M., [NH+] = 1.0 M., t i t a n i u m P r e c i p i t a t i o n c o m p l e t e d w i t h i n one h o u r .  -  10b  3  1.033  Hydrothermal decomposition; A f t e r Arutyunyan r e f . 68. Conditions: ( 1 ) 6 4 0 ° C , 20 h o u r s . (2) 5 5 0 ° C . , 3 hours. (3) 3 8 0 ° C . , 4 hours.  3  w  -  •-  -  -  8 4  6.4  -  -  -  -  I  -  -  -  A  -  -  -  2 2 5  -  -  -  1. 361 1.297 1. 248  5  10b  -  -  1  -  5  2 .71  9b  d  -  —  1.568  -  I  6.0  10 8  -  1. 094 1.029  -  I  1.578 1.529  -  1. 246  A  2  (3)  8 8  -  1. 353  A f t er  -  d  ppts by H  Khurshudyan,  = 0.05 M., autoclave.  -  -  1.  SILICONE  3. C O , H E A T E D  5. H , H E A T E D 2  2. C O  6.  40  F i g . 15 •  2© X-RAY DIFFRACTION PATTERNS OF  No  30  PRECIPITATES  92 reported in  both  t o be  the c h a r a c t e r i s t i c of M0S2.  modification  that  the s u l p h i d e form  very  fine  particle A  an  0.32  unpaired  disulphide and  weak  MoO^  heated  o f t h e molybdenum  electron  a weak  disappeared  i n Ar atmosphere  M0S2  specific ually  as t h e f r e q u e n c y  parent  a t around  650  when  M0S2  1  to  approximately  weak  The  natural  diamagnetism,  The o b s e r v e d  para-  the p r e c i p i t a t e s  were  were  compared  d i d n o t show a n y  I t s absorption decreased  decreased  cm.  r e d u c t i o n showed  of p r e c i p i t a t e s  The n a t u r a l  a b s o r p t i o n band.  is a  300°C.  spectrum  a n d MoS^-  a very  paramagnetism.  at  suggested  products  o f molybdenum.  completely  seen  disulphide.  amounting  t o have  network  i t was  by h y d r o g e n  p e r mole  i s reported  Infrared with  produced  paramagnetism  a n d MoO^  magnetism  Therefore  i n the p r e c i p i t a t e d  precipitate  apparent  o f t h e Mo-S  .  until  MoS^  i t was  almost  s y n t h e s i z e d by  gradtrans-  decompo-  83 sition  of  (NH^^MoS^  absorption The  around  precipitates  absorptions: 1395(s,sh), strong,  Therefore the  under  1600(b),  when  hydrogen  gave  atmosphere  and 3 4 5 0 ( b ) ,  was  observed  where  heated  were  gave  1020(sh),  respectively.  the sample  i n Ar  considered  cm." . 1  the  following  1115-1190(b),  s, s h , b They  weak  means  disappeared atmosphere. t o be due t o  material.  F i g u r e 16 s h o w s analysis  acid  880-935(s),  and b r o a d  the peaks  volatile  with  1 6 5 0 , 1 4 2 5 , 1 1 2 5 , 9 5 0 , a n d 900  620(sh),  sharp,  completely  solution  of p r e c i p i t a t e s  the r e s u l t s from  of the  a series  thermogravimetric  of experiments  where  I  0  I  100  I  200  I  300  I  400  I  500  Temperature °C. Fig. 16 TGA OF PRECIPITATES, WEIGHT LOSS vs. TEMPERATURE. CONDITIONS OF PRECIPITATION ; I58.8°C, 600psi., NH =0.8M., NH4 = I.OM., Mo =0.1 M., S = varies (( S/Mo * I) 0.66,2) 0.97 3) 1.30 , 4) 2.01 , 5) 2.84 , 6) 5.77, Initially )) 3  the  initial  weight  loss  starting samples weight loss  concentration of sulphide i n Ar atmosphere  at around which  gain  had been  at 350°C.  a t around  peaks  analysis  at higher  cipitates for ence  17  MoS^  D.T.A.  shows  was  of peaks  performed a n d when  apparently  place  Chemical composition  Tables  analysis,  i n which  i n nature  from  5 a , 5b results  n i t r o g e n and c a r b o n In  molybdenum nitrogen  a l l cases and s u l p h u r  and s o d i u m  constituents.  show  monoxide  amount  indicated  in  Therefore the  low  that  material  temperature.  revealed  that  of the  atmosphere  these  were  j  were  of  precipitates  were  residual  subtracted.  the  of the  precipitates  a large  was  peak a i r  of the r e s u l t s  of analysis  t h e r e was  no  the composition  some  differ-  When t h e  volatile  those  observed  and 5 0 0 ° C . i n -  disappeared.  which  gave  but the  repeated  of p r e c i p i t a t e s  weight  and t h e p r e -  t h e r e was  at a comparatively  on  M0S2  i s involved.  was  and a  The p e a k s  350°C.  a  differential  MoS^  similar,  i n Ar to produce  depending  solutions  obtained.  were  a t around  analysis  varied  experimental  synthetic  The  inair.  The n a t u r a l  the experiment  reaction  took  of the  experiments.  at 350°C.  cases)  re-heated  i n Ar atmosphere  t h e peak  decomposition  were  than  i n these  difference  successively  showed  the r e s u l t s  and t h e p r e c i p i t a t e s  some  i n Ar atmosphere ([Sj/lMo]^  The  magnitude  350°C.  they  temperature  produced  observed,  from  when  and  a t around  of p r e c i p i t a t e s .  i n the r a t i o  dicates  heated  varied.  in position  and e n d i n g  ( f o rlow  450°C.  Figure thermal  150°C.  varied  i o n was  included. when t h e  Analysis for only  minor .  100 1.17  J  200  I  300  I  _J  400  500  Temperature DTA OF PRECIPITATES FRQM H  2  600  °C. RUNS  Curve I. natural molybdenite, in air 2. synthetic molybdenum tri sulphide, in air 3. precipitate under hydrogen, in air  4. 5.  I  H  , in Ar  II  , in air after Ar  96  TABLE 5a Compositions  No .  46  Gas  N  2  of Precipitates  Compositions Mo%  S%  X%  44.9  39 .8  15 .3  Main  Other  Variables  ;  -  Conditions  (Mo  = 0.020M.,  T  0.056M.,  H  2  H  86 85 83  H  2  H  2  H H  2  48 . 0 47 . 7 47 . 2  32 . 7 34.4 36.8  19 . 3 17 . 9 16 . 0  47.4 50.2 53.9  33 . 3 20 . 8 14.4  19 . 3 29 . 0 31 . 7  P = 500psi. 300 100  S  T1  0.195M. 0 . 096 0 . 065  =  =  T  NH„ = NH. 3 4 158.8°C.)  l.OM., 40 42 44  S  =  +  _  (Mo = 0.020M., S „ = T T 0.056M., NH = NH. = 3 4 l.OM., 1 5 8 . 8 ° C . , ) T  (Mo _ = 0.1M. , N H „ = T 3 0.9M., N H = 1.OM., 158.8°C. , P = '600psi. 2 4  u  H  106 108  H H  2  49.8 53 . 4  32.5 29 . 4  17 . 7 17 . 2  =  0.98M. 0 . 39  (Mo  = 0.1M. , S ' = l 1 0.2M., n o N H , 1 5 1 . 6 ° C . T  T  3  P CO  61  33 . 4  22 . 2  44 . 4  Mo  =  T  0.001M.  (S P  u H  2  CO CO CO  49 . 0 48.6 44.7  30 . 7 33.6 33 . 7  20 . 3 17 .8 21 .5  S  T1  =  0.011M. 0 .033 0.089  = 700psi.,NH  c o  (Mo  880psi.)  = 0 . 023M. , 1 5 1 . 6 ° C . ,  T  NH 23 25 26  =  + 4  T  =  X%  =  100  -  Mo% -  S%.  l.OM.);.  = 0.020M.,  500psi. , NH l.OM.)  =  3  3  P  C  = NH  =  Q  + 4  =  97 TABLE Detailed  Analysis  5b of a  Precipitate  Conditions of p r e c i p i t a t i o n s : Run 6 4 . Mo = 0.010M., S = 0.049M., N H = N H t = 1. OM. , P two-stage run i n titanium a u t o c l a v e , no c a t a l y s t T  T  3  as  precipitated  Mo S N Na difference  equivalent/mole %Mo  a b c d  -  3  = 500 p s i . , addition  H  after  47.1% 32.7 2.5 0.0 17.7  heating* 59.0% 32.8 0.3 0.0 7.9  100.0  100.0  15.0  15.6  Mo  dissolved^ by 0.2M NH C l b y ( 1 + 1) H C l by w a t e r b y 2 N NaOH  18.5 33.7 19.3 83.  n.d, n.d, n.d, n.d,  washed w i t h w a t e r and vacuum dried, 3 0 0 ° C , 2 hours i n Ar. reducing equivalent w i t h NaClO. 60°C., 1 hour i n A r .  TABLE Analysis Sample  No.  o f Oxygen Mo  6  i n the  Precipitates  S  X  0  64  47.1  32 . 7  64d  59 . 0  32.8  102  50.1  32 . 3  17 . 6  20.0  105  5 8.3  17 .6  24.1  23.2  106  49.8  32.5  17 . 7  22 . 8  108  53.4  29.4  17 . 2  24.9  C o n t e n t i n %, X = 100 - Mo a n d 0 b y G.G.A.  - S , Mo a n d  20 . 2 8. 2  S a r e by  28.1 12 . 6  the  author  3  The activation ornia, in  6.  chemical  general,  exactly  performed  depended  sulphide shows  agreed.  precipitate, centrations solution, Clearly  b c  than  limiting  2  of  above  =  that  the r a t i o  in  concluded  i n the  precipi-  of molybdenum solutions.  o f molybdenum  ;  and  Figure  to sulphur  18  i n the  when  2 a n d when  t h e s o l u t i o n was  (dotted  larger  line)  than  2,  well  when  buffered.  ([S]/[Mo]). i s x  rg approaches  some  value. o f t h e pH  (NH.)-SO. 4 2 4  addition  f o r the h i g h l y  to the mixture  a variation  of r g .  the p r e c i p i t a t i o n amount  buffered  consumption  the r a t i o  o f t h e s o l u t i o n by v a r y i n g  addition  the p r e c i p i t a t i o n  The with  oxygen.  to sulphur  100%) d i d  values  predominantly  above  and  from  i t was  ([S]/[Mo]). x  the e q u i v a l e n t  sulphide,  Calif-  c  solution yielded  (NH^^SO^  neutron  = (S/Mo) , against the r a t i o of the conb pp t o f molybdenum and s u l p h i d e i n t h e i n i t i a l  Variation amount  results  higher  i n the i n i t i a l  ([S]/[Mo])_^, r  smaller  r  Atomic,  Therefore  the r a t i o  the  the r e s i d u a l stated  gave  o f molybdenum  concentration of  with  General  (by t h e d i f f e r e n c e  p r i m a r i l y on  the p l o t  Gulf  the former  t h e r e s i d u a l s were  tates  analysis with  activation analysis  and  ratio  by  compared  results  the trend  The  Na S  of the oxygen  Although  analysis  agree  that  method  U.S.A., w e r e  Table  not  results  was  of  (NH^^SO^  was  complete  solution  of hydrogen  of the c o n c e n t r a t i o n  the  o f N a „ M o O . and 2 4  At  low  level  not complete  pf  but  to n e u t r a l i z e and  rg  (Figure varied  approached  19).  also  of sulphide  primarily and  molybdenum  99  2.5  i  2.0  o  •  /  ;  -  / i «  •  • /  y  1 / fIf s  1.5  1.0  •  —  NH T p Mo S 0.1 M. varies 0.80 M. LOOM. 158.8^. 600psi 3  varies  0.21 M. 0.86  O total 0.016 M. 0.5 h  0.0  Fig.18 r  860  II  1677  530  II  l 2  i 3 (CS)/[Mo))  i 4  i 5  i 6  |nrtja|  COMPOSITION OF PRECIPITATES BY 8  151.6  j  i 1  D  0.98  REDUCTION  DEPENDENCE ON THE INITIAL SOLUTION COMPOSITION  i 7  100 in  the  (r  + n  initial r  -  3)  solution. is plotted  against  r„  i.e.  r  i s the  n u  no  ratio  state.  r  The  =  n u  Assuming sulphide  1 +  that  H x z  and  clearly  shown  when  in Figure  20,  MoS  r  when  r  and/or  empirical  0.18r  to  molybdenum  approaches  hypothetically,  i n oxide  the  zero,  r ^ approaches  hydroxide  equation  was  was  given  oxide  ( o r h y d r o x i d e ) and  i n the  precipitate  y  and  r„ S  are have  1.  in by:  . . . .  b  c  H , r e s p e c t i v e l y , r„ y u ' H  n  =  y[MoS  R  =  ((3 -  S  [MoS  [ r  r  consumption  (20)  the expressed the  relationships:  r  or  that  (or hydro sulphide)  following  Then  hydrogen  formation  words m o l y b d e n u m  tetra-valent  MoO  of  It is clear  sulphide  other  by  as  more  b  consumption.  By  i s shown  o  where  In  This  R  H  +  r  =  [3  comparing  relationships  g  -  3]  =  - x +  with were  x +  1/2  z)[MoO  H ])/([MoO H ] + y u x z  -[x -  1/2  the  H ]/([MoS H ] + y u y u  1/2  z] +  [([x -  empirical  derived;  z] +  [MoO  H  ] +  [MoS  [(x -  1/2  equation  z]  1/2  -  (20)  H ]) x z  (3  - y +  1/2  u)  H ]) y u  z +  1/2  u)/y]r  [y -  1/2  u])/y]r  the  following  g  s  2.0  (Value from Nr^=.9aNHj=l)-  °-  &  1.8 ~  O  O  1.6 0.2  0.0 Fig. 19  h  (NH^SQi  0.4  M.  0.6  r DEPENDENCE ON ACIDITY s  O  Mo+S constant S varies Mo varies  A  I  (NhL^C^ varies P varies  ro  -I  -2 0 Fig.20  0.5  1.0  (r + r - 3 ) H  s  vs.  1.5 r  §  2.0  2.5  x -  1/2  y  1/2  -  z  u  =  2  =  2 - 0.18  y  =  1.6.'-  0.07, u  y This  indicates  sulphide)  has  and  that  and  trivalent  u  3,  =  sulphide,  chemical  tates were  close  analysis.  tion  depending  on  the  average,  of a mixture  on  to the v a l u e  the r e s u l t s Figure  i n gram  m e a s u r e d by  the v a l u e  of  tetra-  o f u.  o f molybdenum  If  tri-hydro  21  p e r mole  T.G.A.,  was  o f T.G.A. w i t h  shows  the plot  o f molybdenum  against  r  g  .  of  further those  various  i n the  Three  from  precipi-  weight  losses  considered:  and  AW  reactions the  composed  3.4  composition of the p r e c i p i t a t e  AW.^ :  weight  loss  i n Ar  at  200°C.  AW^:  weight  loss  i n Ar  at  650°C.  AW^:  weight  loss  i n a i r at 550°C.  ing  AW^  be  than  (or hydro-  .  comparing  loss  may  molybdenum  Mo(SH)  by  i n the s u l p h i d e  the v a l e n c y of l e s s  2.92,  The  weight  molybdenum  the s u l p h i d e  y =  studied  that  o  2  are expected i n the i n e r t  oxidation was  T.G.A.  t o show  the e f f e c t  atmosphere.  i n inert  perform-  i n Ar.  characteristics  complete  after  AW^  i s expected  o f the sample  atmosphere.  of decomposition  after  to  show  decomposi-  103  40  Fig.2l  T6A RESULTS, WEIGHT LOSS IN  WEIGHT LOSS vs. r  8  g./mote Mo in precipitates  104 Although was  greater  dependences  AW  showed  2  than  1.7, a l l t h r e e  on r  .  behaviours  agree  well  fairly  shown  Weight Loss  AW  2  AW  3  Found g./mole  sulphur  The at  the  36  Mo(0H)  4  -* M o 0  2  Mo0  3  Mo0  increased  3  o f oxygen  amount  with  weight  smaller  agreed  between  than  must  dioxide  Weight Loss g . / m o l e Mo  r  18  H 0  36  - | o  the value  o f a mole  i n the p r e c i p i t a t e s yield  the d i f f e r -  and o x y g e n ,  observed.  the p a r t i a l  consumption.  the simple  molybdenum  namely  Therefore  to t r i v a l e n t ,  of hydrogen  of X-ray  -16  2  i n the p r e c i p i t a t e .  sulphur  well with  2  addition  should  molybdenum  fairly  the observation  2  be a s s o c i a t e d w i t h  dioxide with  AW_ , b e l o w  + 2  sulphur  o f molybdenum  addition  molybdenum  2  o f molybdenum  the observation  with  and  H 0  2  by 1 8 g . f o r e a c h  ment  value  Reaction  -> M o ( O H ) 0 +  of t e t r a v a l e n t  ment  molybdenum  4  reduction  of  of hydrated  Mo(0H)  slightly  sulphur  gross  (or hydroxide)  Decomposition  i n molecular  with  g  linear  Mo  to a mole  constant  16g.,  when r  = 0 give the  16  replacement  ence  those  -19  AW of  with  showed  at r  of the oxide  scatter  below.  X  AW  values  The i n t e r c e p t s  hypothetical  as  a considerable  i n agreeBut the  replacement  d i s u l p h i d e i n agree-  pattern.  = 1.7, a n d AW.,  decreased  b y 12 a n d  4g.,  respectively,  to  mole  a  the  of  simple  r  g  =  r  s  =  1.7,  for  each  molybdenum  replacement and  in of  production  addition the  r  conditions,  with  volatile  o  and  r  varied  ri  variation  of  r  with and  pected.  which  d u p l i c a t e runs  was  at  was  the  When  runs  allowed  stopped  allowed  results.  to  to  to  low,  r  larger  than  those  of  the  facts  molybdenum other  to  and  whereas  indicate  oxide,  high  [NH^]  until  under  the  above  the  The  and  But the  one that  paths  the  the  run  compared  initial  was  susone  with  other  7  the  shows  high,  when  r . and  those  of  stopped to  two  go  to  r„  sulphide  was  ([S]/[Mo]).  2  faster ion  <  runs 2 was  paths  and  of  the  ([S]/[Mo])^  in a  precipitation  H  completion.,  (or more)  followed  <  halfway  conditions  sulphide  the  ([S]/[Mo])^  form  the.  b  with  under were  was  i n which  H  are to  Table  [NH*]  allowed  proceeded  d e p l e t i o n of  of  conducted  runs  there  condition path  change  and  agreed  runs  molybdenum  the  Kinetic  section  of  that  both  sulphide  completing  in  suggests  material  completion.  precipitation:  form  proportion  to  completion.  was  These  were  halfway  halfway  [NH^]  3-2  This  below  during  u  ( [ S ] / [ M o ] ) . > 2 and 'i  stopped go  go  an d / o r  [NH^]  sulphur  rl  Several  experiment  2  of  sulphur  the  r  b  >  mole  1.7. As  of  a  precipitate.  oxygen of  of  certain  complete,  and/or  than  the  from  the  low oxide  path  solution.  study investigation  3-1  indicated  of  that,  the  final  products  apparently,  the  described  reactions  106  TABLE 7 • Variation  o f S and H r  by t h e E x t e n t o f R e a c t i o n  r  Initial [Mo] M.  Condition  No .  %  102 111  100 57  1.93 1.98  113 112  100 81  2 . 03 1.45 1.98 1.52a  160 . 0 0.100 0 .195 0.86 0 . 100 0 . 195 0 .86 160.0  r  s  R  H  T  °C. 1.22 1.37a  151. 6 151. 6  0 .099 0.097  [s]  T  M. 0 .211 0.195  85 114  97.5 71  1.23 1.42  1.39 1. 46a  158 . 8 0 .098 0.096 0 . 100 0.097 160.0  110 115  85 51  1.66 1.83  1. 35 1.70a  151. 6 0.097 160 . 0 0.098  % - P e r c e n t o f molybdenum d i s a p p e a r e d a -  [NH ] 3  [NH{]  P  0 .86 0 . 98 858 0 . 86 0 .98 865 0.98 821 0 . 98 826 600 824  0.85 0.97 0 . 86 0.98  0 . 211 0 . 00 0 . 98 884 0 . 195 0 . 00 0 . 98 840  from  solution.  H f o r t h e r u n s i n t e r r u p t e d i n h a l f w a y were o b t a i n e d by e x t r a p o l a t i n g t h e p r e s s u r e d r o p c u r v e s u n t i l t h e t i m e s when t h e t e m p e r a t u r e s o f t h e s y s t e m d r o p p e d 20° C .  b - [ N H ] was added as ammonium s u l p h a t e . +  «i psi .  M.  M.  |  could  be  classified  concentration  into  ratio  ammonium  sulphate  of  sulphide  to molybdenum  duction value  giving  no  reaction  of sulphur  sulphide  and  oxide  and/or  Analysis conforming variation  solution.  Figure  rapidly solid  The type  mechanism stancy  of  was  expected  above.  concen-  a  the r e limiting,  (2) - r a t i o l o w NH^  followed  that  of  concentra-  by t h e  shows total  the p l o t sulphide  was  there  was  the  runs  i n fact  of molybdenum process  of t o t a l  of  good  depletion  to the open  and  pre-  i n the  i n view  as  no  molybdenum,  concentration  considered  correspond  during  the whole  of the p a r t i a l  first  of the r a t i o  discussed  NH^  shown  of the by t h e  triangle.  pressure  effect  ( 1 ) was  first  of the consumption  linearity  t r i a n g l e s which  Effect  2 and/or  (1) showed  a c c e l e r a t i n g molybdenum  3-2-a  the  22  against  The  type  of the s o l u t i o n produced  the s o l u t i o n during  concentration  ratio  hydroxide.  i n the r a t i o  cipitation.  than  the sulphide  to the type  from  ratio;  t h e amount  during  having  initial  (1) -  2 and h i g h  products  t o molybdenum  precipitating  than  the  and  type  i n the product  the f i n a l  on  to molybdenum  larger  less  depending  in solution:  variation  tion,  sulphur  present  to molybdenum  the  types,  of sulphide  of  tration,  two  investigated during  pressure since  no  of hydrogen f o r change  the run c o n s i d e r i n g  of comsumption of molybdenum  of  the and  consulphide  o  00  109 Figure tration  was  this  order  a  good  as  of r e a c t i o n  this  removed  was  i n Figure  pressure  as  the r e a c t i o n  on m o l y b d e n u m  The  was  except  concen-  158.8°C. of  molybdenum  proceeded.  concentration  the logarithm  observed  at  of disappearence  solution  24.  of the t o t a l  No describes  o f t h e amount  plotted  of  against  time,  f o r the i n i t i a l  parts  integrated equation  describing  removal i s : -  log  where cussed shown  s and  ([MoJ  pressure  25.  were  ([Mo]  =  st +  and  intercept  -  [Mo])  of  Therefore  =  . . . .  of the p l o t s  and  of s v s . pressure  c o n c e n t r a t i o n was  Q  log i  dependence  Linearity  observed.  the molybdenum  log  [Mo])  are slope  The  i n Figure  -  0  log i  above.  1/(pressure) for  from  constant  rate  B u t when  linearity  shown  The  increased  phenomenon.  molybdenum  the v a r i a t i o n  under  varied.  the s o l u t i o n  simple  shows  o f molybdenum  Pressure from  23  c Vt ±  given  are  and  i vs.V formula  by  log (c  +  dis-  i  the e m p i r i c a l  (21)  0  +  c /P) 3  . . . .  Differentiation stant  pressure  of this  equation  with  respect  to time  (22)  at  con-  yields:  -d[Mo]/dt  =  c P([Mo] 1  0  -  [Mo])  . . . .  (23)  Ill  Fig. 24  Log(Moo-Mo)  vs. Time  112  xlO  200  Pressure  psi.  400  Intercept  M. xlO  Fig.25  3  xlO? SLOPE S INTERCEPT vs. PRESSURE H  2  psi  113 The  equation  autocatalytic trations  do  molybdenum aspect,  and  not  stage  was  being  detected  as  and  second  the  first  second while  which  stage.  stage was  of  shows  was  both  found  end  of  The  of  of  this  t h e end  the c o l o u r  molybdenum  of molybdenum  of  i n which  the  point  of  thio-  solution  depletion  the  were  was  was  of  were  This  acting The  the f i r s t found  constant  by  stage.  5.3-fold This  the a c t i v a t i o n  of  p s i . of  the  completion  precipitates that  as a  i n the  substrate  of d e p l e t i o n of  stage  t o be  of  i n the  indicates  rates  500  until  of  simply  In the other  kept  time  to molybdenum  2.6  and  at the  and  6.2  r u n where  a t 500  d e p l e t i o n at the i n i t i a l  by  the pressure  p s i . from  against  constant.  to i n c r e a s e  where  t o 200  linear  reduced.  stage  results,  d e p l e t i o n o f molybdenum  almost  a t t h e end  the f i r s t  caused  more  conducted,  a fresh  of s u l p h u r  easily  stages  was  to c l a r i f y  is  concen-  process  to c o m p l e t i o n ,  decreased  , respectively.  molybdenum  be  the r a t e  sulphide  the r a t e  were  t o go  molybdenum  the second  min.  order  Then  practically  molybdenum of  was  the r a t i o  second  into  the disappearence  26  stage  stage  remained  and  the r e a c t i o n  before.  Figure the  In  allowed  complexes.  injected  followed  directly  experiments  by  that  molybdenum  depletion.  first  was  that  come  two-stage  molybdate  (23) i m p l i e s  part  x  the  beginning 10  M.  pressure  p s i . , the r a t e of  compared  i n c r e a s e was  the second with  that  from  stage  at the  interpreted  the p r e c i p i t a t e  of  the  to first  Tig. 26  TWO  STAGE  RUN,  H 2 , 500psi., I58.8°C.  stage  by  tween  the  the  dissolved two  equation  hydrogen  stages. (23)  of  stage  calculated  of  was  the  close  The  stage  Figure of  other  the  tional of  also The  the  the  includes  given  1  shows  results  by  the  same  equilibrium produced. ing  the  lie  in  obtained  in  Although  close  were  plex  the  Part  there  of  is  at  agreement  and  tendency  e q u i l i b r i u m with  were  and not  exchange rate  end  ^  in  changes  similar  during  plotting (ot^)  to  the  with  run  the  concluded each  reactions  controlling.  27  the  at  are  re-,  represent158.8°C.  equilibrium  that  other  same  indicated  points  the  that  Figure  120°C.  reactions with  frac-  the  are  representing and  the  against  scale  same  150°  reduction  in  the  mentioned  equilibrium).  scatter,  i t was  at  min.  was  species  the  the  Therefore  of  variation.  lines 1  M.  rate second  change  time  log-log  from  the  concentration  with  during  reaction  species  the  (Study  data  Also  samples  reduction  where  symbol.  relationship. species  Part  the  in  value.  tri-thiomolybdate  reasoning  of  10  be-  constant  depletion  i n v e s t i g a t e d by  (oi^) i n  the  part  x  complex  thiomolybdate in  rate  activity  concentration  of  interval  pressure,  of  5.5  variation  r e a c t i o n was  the  to  rate  was  of  time  initial  observed  distribution  distribution  tetra-  the  molybdenum The  reduction  from  with 26  that  the  correcting  species.  total  at  calculated value  agreement  the  proportional  molybdenum  first  above.  Assuming  was  depletion  during  the  during  between  complex the the  ; com-  0.40  line  l  line  2=  :  Equilbrium at ..  I20°C. I50°C.  0.30 h  0.20 h log scale  I58.8°C. 0.15  NH3 = I M. NH* = I M.  0.10 0.05  0.07  0.10  ±  ±  0.15  0.20 o<  Fig. 27  PLOT OF rf3  vs. c<4 , DURING  4  JL  0.30  0.50  log scale  PRECIPITATION IN HYDROGEN ATMOSPHERE  Since towards a  the  end  convenient  fore  followed  in by  of  the  of  discussed  above  the  rate  the  form  where  y  to  in  a  the  the  total as  with  in  rate  equation  in  -dP/dt  =  and  6  are  of  kP(Y(P  constants  between  Q  as  the  28,  system,  of  the  the  reaction  as  equation  +  to  and  the time  rate  (23)  applies,  would  . . . .  the  of  proceeded.,  pressure  6)  was  system.  similar  the  P)  the  reaction  namely  representing  molybdenum  c o n d i t i o n of  were  There-  autoclave  the  drop  hydrogen  -  obtain  concentration with  equation  terms  to  i n which  volume and  rapidly  reaction.  employed  time  Figure  If  difficult the  pressure  molybdenum  shown  same  was  section  increased  the  follow  constant  total  decreases  accelerated  i t was  method  consumption  relationship initial  method  experimental  reading  decreases  reaction  reaction,  conducted  Pressure  hydrogen  the  experimental  was  described  reduction  sampling  another  experiment  the  be  of  (24)  stoichiometric  hydrogen,  respectively.  and  the  Upon  integration,  [P/(a  ln  +  P  Q  -  P)]  =  -ky(P  Q  +  a) t +  ln(P /a) Q  . . . .  where  a_  =  6  /y.  (25)  QI u  Fig.28  1  50  1  100  1  1  150 200 Time min. VARIATION OF TOTAL PRESSURE, H 2 dbns.  1 250  119 Figure equation  (25)  Fluctuation  of  of  and  slopes  predicted Figure  was  rates  by  to  were  the  hold by  pressure  The for  21.-titanium  (B)  120ml.  the  reaction  8  the  linearity  (PQ  in  the  equation of  reduced -  P).  smoothly  fluc-  was (Po  observed +  a)  as  inserted  (24)  was  con-  experimental  rate  -dP/dt,  psi.  temperature  shown  temperature  experimental  shows  are  the  for  (B)  the  slope  the  10  of  data  (1/P)(-dP/dt)  The were  instantaneous obtained  fitting  curves  by of  the  on  the  methods  reaction  employed,  pressure  maintained  autoclave,  pressure  was  com-  namely constant  varied  and  as  proceeded.  (A)  that  the  as  side  time.  autoclave,  for  slope of  consumed. methods  activation  of  stainless-steel  Table  imental  of  taken  hand  temperature  two  (A)  hydrogen  the  against  effect  the  as  consumption,  of  by  analysis  consumption,  readings  a. was  left  p r o p o r t i o n a l to  Therefore further  the  Good  be  (25)  differentiation  Effect  pared  to  plotting  hydrogen  graphical  3-2-b  and  where  of  0.3°C.  found  29.  plot  caused  equation  hydrogen  of  was  approximately  performed  against  the  time  points  in Figure  sidered  shows  against  tuation the  29  and  energies  same  rate  the of  the In  results  the  reduced  spite  the were  plot  of  i n which of  the  rate the  controlling  almost step  against  range the  was  rate  equation the  difference  concentration found  the  in  (23)  and  amount the  employed,  same,  constants  of  experthe  indicating  operating  and  >  the  120  Fig. 29  PLOT OF  Time min. ln( P/ (a + Po- P ) ) vs. TIME  120a  TABLE Effect  A.  t  N  H 3  PH  J  = =  2  No.  of Temperature  1  -°  M  27.2  [MoJ  T  8  -»  on  the Rate  I(NH ) S0 ] 4  atm.  2  Initial  = 0.020  M.,  =  4  [ S ] = 0.056  k  158.8°C.  3.03  x  45  151.6°C.  2.03  x 10~ min.  I  N H 3  J  =  Initial  °-  M  >>  10" min. 2  2  I(NH ) S0 ] 4  2  =  4  _ 1  E = 20 k c a l /mole  _ 1  0.45  M.,  conditions:  [Mo]_ = 0.10 T No.  9  M.  T  Temperature  M.,  concentrations:  41  B.  0.5  M.,  [ S ] „ = 0.20  Temperature  M.,  P  v u  2  =  57  atm.  k  111  151.6°C.  1.12  x 10~  3  atm." min." 1  1  112  16-0.0°C.  1.74  x IO  3  atm.~ min.~  1  -  1  E A  = 21 k c a l . /mole  121 step and  d i d not depend sulphide  3-2-c  in  Effect By  (26)  was  P/dt  i n only When  the  was  against  pressure,  equation  the bracket  t o draw  linearity  i n fact  would  from  in total  hand  be  side  under  Addition expected  were  fitted best  added  the other  (26)  corre-  t h e same  of  catalyst  to cause  a  shown  The  were  plotted  30.  ( 2 0 0 mg.)  against 30.  was and  hydrogen amount A  (26)  c o n d i t i o n of  f o r s o l u t i o n s of the  of  good  6 i n the equation  to the i n i t i a l  rates  (no a d d i t i o n )  of Figure  as  parallelism  i n t e r c e p t s at zero  Therefore  identical  of reduced  i n Figure  t o t h e r u n 117  i n the i n s e r t  correspond  good  t o t h e r u n 118  f i t lines  observed.  as  a  added,  of hydrogen  the p l o t  showed  matched  well  r u n were  consumption  However  consumptions  a n d y was  compositions.  the runs  f o r t h e r u n 118  was  . . . .  existing,  composition.  (400 mg.).  precipitates  5)  i n the r i g h t  of c a t a l y s t  increased.  points  that  r u n 116  of  - P) +  6 .  hydrogen  slope  catalyst  (24) w i t h  k(y(Po  precipitates  was  consumption  did  =  increase  t h e end  taken the  an  amount  when  equation  of s o l u t i o n  the beginning  there  molybdenum  catalyst  t o t h e amount  change  The  of  inside  conditions at  of  derived.  value  sponds  the c o n c e n t r a t i o n s  solution.  dividing  -din  The  on  same  122  123 The sidered and  initial  t o be  caused  Effect From  cipitates Since from  steps  i t was  varied  with  shown  solution  was  and  this  31  sulphide  and  ammonium  sulphate.  whereas after  section the  3-1  of molybdenum  the  hydrogen  there  appear  were  t o be  step  of the  which  precipitates.  performed  to  of the v a r i a t i o n  of  S/Mo  when S/Mo,  to zero  were  less  t h e maximum  consumption. where  at constant  concentrations Clearly  sharply  resulting  pre-  depletion  controlling  the e f f e c t s  t o molybdenum,  reaching  hydrogen  by  the nature  of  conditions.  o f molybdenum  of experiments  shows  at high  when  solution  controlled  and  described  the composition  f o l l o w i n g the r a t e  concentration  dropped  (20).  products,  of p r e c i p i t a t e ,  series  precipitates.  aspect.  Figure  rate  that  the rate  the composition  sulphide  i n the  conditions  the i n i t i a l  that  con-  precipitates  the e m p i r i c a l equation  found  t h e amount  Several c l a r i f y  sulphide  primarily  (or a step)  determine  of  with  30 w e r e  of  the a n a l y s i s of the f i n a l  i t was  pressure  i n Figure  the d i s s o l u t i o n  of s o l u t i o n  s e c t i o n 3-1,  the  values  i s i n agreement with  3-2-d  of  by  exchange of oxide  This  in  high  was  were  above  reaching  2,  tails  From  of  ammonia  and  molar  ratio  2,  the  reduced  t h e maximum,  were  at approximately  t h e r u n was  solution  the i n i t i a l  after than  of free  amount  observed  t h e same  the experiments  described  i n t e r r u p t e d i n halfway  analyzed,  i t was  amount  found  and  that  in  Reduced rate  M.mia' atm"  xlO  10  Fig. 31  . 1 5 _. Hydrogen consumed M. xlO EFFECT OF SOLUTION CONDITION, Mo TI VARIATION , IN  H, NJ  sulphide fore  depleted  the portions  correspond  ammonium  alent were  namely  observed, rate  indicated  was  with  There-  considered  two  above  salts.  was  to  series  was  of the than  long  was  ratio  Molybdenum  There  less  of  molar  2.  a  vari-  ammonium  the  equiv-.  induction  the equivalent  consumption  the compositions  of the p l o t  effect  a t above  the equation  2.  the i n i t i a l  sulphide  the d i s t r i b u t i o n  determining  than  of the v a r i a t i o n  t h e amount  t h e amount  the above  were  slightly  value,  periods high  observed.  of r e s u l t s ,  of various  o f t h e s o l u t i o n seemed  From  the  when  less  where  as sodium  curves  whereas  that  t h e pH  slope  added  of hydrogen  From  in  the e f f e c t s  concentration  were  was  precipitation.  to n e u t r a l i z e the sodium  initial  and  32 s h o w s  i n the rate  sulphate,  S/Mo  t h e maximum  to molybdenum  sulphide  ation  before  sulphate  sulphide  and  when  to the sulphide Figure  of  first  to play  i t was  complex  species  important  roles  of the p r e c i p i t a t e s .  (25), i t i s suggested  that  o f - d i n P / d t v s . (Po - P) w o u l d  of s o l u t i o n conditions  the  represent  on t h e c o m p o s i t i o n  of  precipitates. Initial by  using  compositions  the r e s u l t s Formation  n  =  n  o f the s o l u t i o n were  obtained  i n Part  f u n c t i o n was  (L) ,  L  1, a s  calculated  follows:-  assumed a s :  =  [H S] Z  . . . . aq  (27)  126  Fig. 32 EFFECT OF SOLUTION CONDITION, IN H 2 (NH4)2S04 AMOUNT VARIATION  127 The  material balance  = nM  +  T  S  for sulphide  = nM  f  +  T  The  charge  balance  equation  for  a l l molybdenum  species,  [Na ]  +  +  [H ] +  [NH+]  +  + By  the other  2M  , OH  +  2  +  2[S0  2 _  [S ~] 2  noting  ]  +  t h e same  [OH ]  +  -  [HS  charge  ] +  2[S ~] 2  2and  ionic  [H S]  yielded,  T  -  neglecting H  with  =  yielded  S  ,  species  as b e i n g  and  small  substituting  in the  comparison relation-  ships :  the of  [H S] 2  =  S /(1 +  m[NH ]/[NH+])  [HS~]  =  [H S]m(N  f  2  3  T  -  following equations the c o n c e n t r a t i o n  n  =  S /M  L  =  (N  T  1  T  -  -  2M  from  of  to s a t i s f y  sive  derived  o f ammonium  T  -  T  applies also  lated  were  for n  ion,  and  L as  equation  2[S0 "] 2  was  made  [Na ]) +  that  at 151.6°C. (28) and  the equation  approximations  . . . .  1  +  N^m  (N^ -  the formation Then n  and  (29) s e l e c t i n g (27) by  functions  ;  (1 - m + m N / N ) L/M^  Assumption 150°C.  [NH+])/[NH+]  f o r a set of values  of  . . (29)  f u n c t i o n at  L were  calcu-  a suitable  t h e method  (28)  of  , S^,  value  succes,  128 + [Na  2] , and  obtained the  [SO^  i n Part  aqueous  fractional were in  ]. 1.  ratio  Since at  of  31  be  and  combined  and  33b  plotted  33b  or  were  as  of  L, t h e species  constants  obtained  be  (section  B-2-3)  and  the  and  error,  combined  32  from  and  respectively. were  these  conducted two  appropriate  the r a t i o  i t was  only  series function  of the  , with  The  i o n to free  added  increase  assumption.  effect  i n the case  i n the slopes seen  were  •  i o n concenammonia,  by  where  to the i n i t i a l  of hydrogen  Figures  distribution  of the slopes  t o t h e same  observed  The  that  the slopes  the hydrogen  low v a l u e s  due  r u n were  when  found  of the f r a c t i o n a l  o f ammonium  of consumption  support  and  an  slopes  ammonia.  the products  34.  31  of the  distributions  ammonia,  by  distributions  as were  a previous  amounts  value  the p l o t s  the slopes  expressed  considered  precipitates from  5.8  thiomolybdate  fractional  of Figures  the r a t i o  i n Figure  show  i o n to f r e e  and  trial  could  against  tration,  series  as  concentration,  the s t a b i l i t y  tetra-thiomolybdate,  shown  the  of various  against  i o n to f r e e After  to  32  and  temperature,  the f r a c t i o n a l  ammonium  of  33a  o f ammonium  t h e same  33a  using  the experiments  could  obtaining  taken  1.  Figures  the  o f m was  sulphide  distributions  c a l c u l a t e d by  Part  value  After  hydrogen  Figures of  The  as  i n the the  initial  precipitates  solution, at  pH  large  i n Figure  32  seem  129  Slope psr'mirn1 x IO% )  0.2  Q Mo VARIED.  (a) o •  0.4 AND  a , + a,  a2  8  0  0.6 (NH+)/(NH3)  i  U •  a,  0.8  a  (NH+)/(NH3)  7  | 0  (NHj)/(NH3)  T psir1 min.1  xlO  (b). Fig.33  (NH4) 2 S0 4  PLOT OF  SLOPE  VARIED. vs. (2 AND  (NH+)/(NH 3 ).  o  Mo  - A  varied  I5I.6°C.  (NH^SC^ «  Slope 1 psir1 min" nnir xlO 5  — —  o—  A  0 Fig. 34  1  0.05 SLOPE vs.  0.10 0.15 0.20 a4(NHj)ANr%) CX4(NHj)/(NH3) , COMBINED  0.25  O  1/Slope 2psi. mm. r 4 xlO I o  0 Fig. 35  PLOT OF  40  i  Mo  1  varied  80 120 160 1/lQ (NHj)/(NH3)) I/Slope vs. 1/( a4(NH4)/(NH3)  Figure large of a  value  indicates  of the product  the slope good  34  was  plotted  linearity  was  a saturation  stated  above.  against  observed  effect When  the i n v e r s e  as shown  at the  the  of  inverse  the  i n Figure  product,  35,  namely,  1/slope  where  and  slope  Noting  =  A  =  + A /(a [NH ]/[NH ])  ±  2  constants.  4  4  3  [NH ]/[NH ] 4  concentration,  3  i  4  3  Therefore  (a [NH J/[NH ])/[A  that  4  s  2  + A (a^  [NH+]/[NH ])]  ±  3  proportional  [ H ] , the above +  to hydrogen i o n  r e l a t i o n s h i p c a n be  written  as  slope  This it  was  +  4  treatment  applied  sodium of  = k'[a [H ]/(k''  molybdenum,  Figure where  35a  product  Figure  be:  +  4  while  keeping and  of slope  constants  at 150°C.  36b  the p l o t  o f t h e two  shows  was  also  successful  o f a s e r i e s where  sulphate  the p l o t  Therefore to  varied  ammonium  shows  stability  lation.  was  a [H ])]  of the data  to the r e s u l t s  sulphide  +  the  constant.  against  and  used  of slope  of  concentrations  ammonia  were  amount  when  [NH ]/[NH ] 4  f o r the  against  3  calcu-  the  variables. the e m p i r i c a l  rate  equation  was  assumed  0.02 Fig.36  EFFECT  OF  0.04 0.06 0.08 0.10 a 4 (NHj)/(NH 3 ) SOLUTION CONDITION , S VARIED.  133  -d  l n P/dt = k [ a [ H ] / ( k +  + a [H ])](Po  1 1  - P) +  +  4  4  k'''  . . . .  3-3  Discussion The  1.  The  and  conclusions  experimental  precipitates  bdenum  (30)  results  obtained  tetra-hydroxide  a r e s u m m a r i z e d as f o l l o w s :  were  mixtures  and p o s s i b l y  of moly-  molybdenum  tri-  hydrosulphide. 2.  The in  molar  the f o l l o w i n g  r„  The  of hydrogen  the p r e c i p i t a t e s ,  with  3.  ratios  to the molybdenum  and  sulphur  were  related  equation:-  = 1 + 0.18  empirical rate  consumed,  . . . .  r  equations  were  f o r the  (20)  molybdenum  consump t i o n : -  -d and  [Mo]/dt  f o r hydrogen  -d  = k P ([Mo]  0  - [Mo])  . . . .  c o n s u m p t i o n :.-  In P/dt = k ( a [ H ] / ( k +  4  1 1  + a [H ])(Po  - P) +  +  4  . . . . 4.  The v a r i o u s solution  (23)  complex s p e c i e s  are i n rapid  of molybdenum  equilibrium  with  (30)  i n the  each  k'  other.  1 1  5.  The  activation  depletion  The following  (1)  from  above  solution  the was  rate  of  around  are  molybdenum  20  kcal./mole.  consistent with  the  mechanism:  Precipitation  of  catalytic  reaction  as  the  Rapid  path  and  various  ...  on  the  one  material  observed  adsorption  thiomolybdate each  other  in  the  adsorption  of  hydrogen  (4)  Activation mining  of  in  the  the  the  the  same  inert  catalyst  which  the  of  Weak  on  species  surfaces  (3)  through  initiation.  strong  equilibrium  (5)  of  observations  atmosphere. (2)  energy  were  solution  of  in  as  well  as  catalyst.  adsorbed  on  the  catalyst  hydrogen.  ...  surfaces.  rate  deter-  step.  Consumption  of  the  a c t i v a t e d hydrogen  through  two  paths ; (a)  Reaction to  with  produce  hydrogen  the  the  per  protonated  sulphide,  mole  of  catalyst (b)  Reaction the  oxide  gen  per  The slow  with  reduction  or  mole  initiation at  the  consuming  1.5  mole  of  molybdenum.  generation.  simple  molybdate  hydroxide of  tetra-thiomolybdate  adsorbed  consuming  one  to  mole  produce of  hydro-  molybdenum.  step  was  beginning  of  necessary reaction.  to  explain Since  the this  slow  part  disappeared  surfaces  t o be  homogeneous  due  step  t o an  added  not cleaned,  inherent  (2) a s s u m e s  of v a r i o u s  solution  were  were  o r when  the  the delay  slowness  of  was  any  reactions.  The  rium  precipitates  of the a u t o c l a v e  considered  bution  when  and  on  between  that  thiomolybdate  the s u r f a c e s  the f r a c t i o n a l  i s t h e same  of  both  the c a t a l y s t .  tetra-thiomolybdate  and  distrii n the .  The  equilib-  i t s protonated  form  g i v e s :-  MoS ~ 2  4  or  +  H  [HMoS~]  rium  +  =  =  K  2  , (Where  +  K  i s the  equilib-  constant). the f r a c t i o n  molybdate  on  y'  where  pressure  =  a  s  [ H  4  +  ] / ( k  1  +  a  4  [ H  concentrations  The  (3)  step  of  protonated  surfaces  contains  [ H  C  of adsorbed  the c a t a l y s t  the s u r f a c e s  where  ,  4  [MoS ~][H ]  Therefore  on  HMoST  assumes  +  by  ] )  of a l l the other  that  of the c a t a l y s t  i s given  tetra-thio-  t h e amount  of  species. hydrogen  i s p r o p o r t i o n a l to the  partial  hydrogen.  2 ads ]  =  k  2 s C  i s t h e number  • • • '  P  of a c t i v e  sites,  (  3  1  )  136 The expressed  step  (4) assumes  that  the r a t e equation i s  by  -dP/dt  Substitution  =  ' • ' •  of equation  •dP/dt  The  =  step  (31) i n t o  k k C 2  3  g  equation  (32)  P  (5) assumes  yields  . . . .  that  t h e amount  of  i s p r o p o r t i o n a l t o t h e p r o d u c t o f t h e amount  hydrogen  consumed  thiomolybdate  the f r a c t i o n  on t h e c a t a l y s t  dC  /dt  =  ey  l  of protonated  surface  existing.  (33)  catalyst  produced  with  <32)  of  tetraNamely  (-dP/dt)  . . . .  (34)  s where £ drop by  into  mole/1, when  mole molybdenum  sion. the  i s the conversion  I f Y'does  equation  catalyst  the a c t i v e  relate  site  i n the p r e c i p i t a t e  not vary  ( 3 4 ) c a n be  s  =  substitution  (26) .  to  much d u r i n g  number  the  pressure  is  per l i t e r  expressed of  the r e d u c t i o n  i n t e g r a t e d to give  suspenreaction,  t h e amount  of  as  c  and  factor  E ' (P Y  into  0  -  P)  +  C S  0  the equation  (33) y i e l d s  the  equation  y  When tion  of  equation  itatively this two  varies  1  the  (34)  of  As  reaction  (33)  of  the  making  the  pH  also  decrease  of  The  (5)  becomes  proceeds  34  can  depletion  of  molybdenum  of  be  the  y'would  and  be  consumed  solution  the  difficult  Figure  ammonium i o n w o u l d  balance, the  the  and  variation  mechanism. mole  as  integra-  but  qual-  explained  to  proceeds  keep  larger.  become  with  the  This  charge causes  increasingly  smaller. step  also  indicate  that  r  and  u  r  H related  to  y  R  =  1.5  =  3 y<  r  r  hence  s  r  =  1  by  1 +  coefficient  equat i o n  f o r the  catalyst  4.  4-1  -  =  Y')  1 +  0.5  y'  i s in close  agreement  with  the  one  in  activation  energy  heterogeneous  of  20  kcal./mole  activation  of  is  hydrogen  reasonon  various  surfaces  Precipitation  Reduction The  the  (1  (20). The  able  y' +  0.16-. r / S  H  The  are S  with  Monoxide  Atmosphere  products  absorption  experiments  experiments  i n Carbon  were  spectra  the  hydrogen  same as  as  of  the  those  shown  solutions observed  in Figure  B-4  during in in  the  Appendix visible  B.  No  range.  of  molybdenum,  of  very  small As  was  the  considered  possible  only  corresponding  But  be  seen  to  the  initial  reaction, indicating  process.  For  the  varied,  curve  the  but  Variation is  also  where around  shown  total 550°  by  in  the  sulphide C.  37,  .  complex  molybdenum,  No  is  precipitate  molybdenum as  was  [ S ] ^ , was  during  the  small.  stoichiometry  precipitation  conditions,  was  reaction  through-  of  the  [Mo]^  plotted  observed  existence  the  was  T  the  slope  of  observed.  results  to  87  [S] /[Mo]^,  concentration  corresponds  1  both  composition  D.T.A.  of  decreased  initial  linearity the  of  where  the  sulphide  different  precipitate  observed.  linearity  and  the  (discussed  i t s synthesis  conditions:  ratio,  Figure  of  carbonyl  solution  out  molybdenum  be  precipitates  since  concentrations  [Mo]  between  to  insoluble carbonyl  form  anhydrous  good  the  complexes  considered  those  simple  The  against the  a  to  form.  in  in  carbonyl  the  no  [S]^, in the  of  similar  to t h i s c a r b o n y l was  when  can  be  observed  short-lived.  curves  expected  total  was  soluble  reduction,  under  sulphide,  as  to  not  The  proceeded  and  D.T.A. to  the  peak  e x i s t e d , were  quantity  hydrogen  was  and  i f they  found  Mo(CO)g,  absorption  Therefore  the  below) were from  new  of  the  shown was  precipitates  in Figure  varied.  oxidation  of  38,  The the  peak molybdenum 89  compound  to  form  The  at  around  peak  MoO^  i n agreement  390°  C.  with  increased  as  literature the  values  sulphide  .  concen-  Fig. 37  VARIATION OF (Mo)T AND (S3 T  UNDER  CO  All curves are  in the exothermic scale.  Precipitation  S/Mo of precipitates  ro  Conditions  />\ / \  500 psi., 160° C , (Mo) = 0.0 2 M. (S) = 0.033 M.  1  /» I / ' \ / * \  Tj  2.23  T i  CO  Jni 1 \ i i i \ / \  h\  500 psi., I60°C. fMo) = 0.020 M. CSJ , » 0.01 1 M.  /  /.  TI  T  V  1.67  V  1.87  CO 500 psi, 160° C. (Mo) = 0.020 M. [S) = 0.023 M.  /  /  T |  CO  / /'  \  /' \ / * / '  500 psi., I 6 0 ° C . (Mo) | = 0.020M. CSJJ, ' 0 . 0 3 3 M ^ ^ _—  I  I  200  i  \  i  400  TEMPERATURE a i A. RESULTS :  /  \ I  \  I-is  T  Fig. 38  V  /—i  Ti  i  600 °c.  tration  increased,  of  ratio  S/Mo  sulphide  4-2  which  i s i n agreement w i t h  o f p r e c i p i t a t e s and s u g g e s t s  and h y d r o x i d e  Kinetic  stated  i n section  condition  against of the  Figure  [Mo]^^  and  initial the  time  [ S ] ^ , where varied.  induction  Figure [Mo]^_^ a n d h i g h  tion  was  periods  concentration  The  40  clear  and  of  by l i n e a r  high sulphide,  carbon  approximately  t h e same  decrease  until  shows  ,  p!  the r e s u l t s  of a s e r i e s at low  the p a r t i a l  by t h e d e p l e t i o n  with  curves  a steady  41 s h o w s  show  decrease  curves  followed  concentration. the l i n e a r  the experimental  by  rather  of  short  of t o t a l  carbon indue-;  molybdenum  slope.  o f a s e r i e s a t h i g h ,,,  pressure  The  pressure  of the  the r e s u l t s  partial  varied.  studied,  within  show  followed  [ S ] ^ where  molybdenum  sulphide  of  initial  complete.  the i n d u c t i o n period  total  curves  pressure  followed  T  to the  of a series at  The  [ S ] ^ was  concentration  o f molybdenum  the p a r t i a l  period  [Mo]^,_^ a n d c o n s t a n t  of  the r e s u l t s  varied.  Figure  where  according  concentrations  d e p l e t i o n was  monoxide  of  3-1.  of the t o t a l  varied  39 s h o w s  of i n i t i a l  was  the mixture  solution.  values  monoxide  increase  study  T h e mode o f d e c r e a s e molybdenum  the  of carbon  monoxide,  showed  large  linear  decrease  At lowest  decrease period.  part  variation of  concentration was  not even  of  Fig. 40 VARIATION OF CONCENTRATION UNDER CO ,  LOW (MoU, P VARIES M  Lo  • CS) = O.OIIM. T  A  0  Fig.4l  40  80  «  TIME  VARIATION OF CONCENTRATION UNDER CO,  0.023"  min.  • (S) =0.033M. T  A  120  «  0.0 56 "  HIGH (Mo)T , ( S ] T VARIES  160  145 The induction  kinetics  period  the i n i t i a l  part was  was n o t c l e a r ,  4-2-a  against  portion.  The  the induction  induction  the l i n e a r  concentration.  by t h e method  Induction When  i n two s e c t i o n s , t h e  by e x t r a p o l a t i n g  molybdenum  calculated  analyzed  and t h e l i n e a r  t i m e -was o b t a i n e d to  were  When  reaction  discussed  portion  back  the l i n e a r  rate  constant  below.  period  [Mo]^ values  the square  i n the i n i t i a l  of time,  a good  [Mo]  ( k t )  part  linearity  were  was  plotted  observed,  i.e.  [Mo]  and  0  the inverse  proportional  «  constant, time,  k, was  x,  found  obtained  t o be  by t h e  l/k  f o r the cases  enough  constants  of the rate  . . . . (35)  2  method.  x  clear  =  to the i n d u c t i o n  extrapolation  Therefore  -  where  the l i n e a r  to use the e x t r a p o l a t i o n  were  used  f o r the analysis  portion  method,  was n o t  these  rate  of the i n d u c t i o n  reaction. The shown  i n Figure  pressure tion  pressure  i n the range  period  reaction  42.  dependence of the i n d u c t i o n There  investigated.  i s concluded  by c a r b o n  was no a p p a r e n t  monoxide.  d e p e n d e n c e on t h e  Therefore  n o t to depend  time i s  on t h e  the  induc-  reduction  146 The period  greatly  roughly  as  shown  under  (18).  Thus  nitrogen of  is  T  time  At  At  is  same  given  =  0  at  this  43.  the  induction  This  showed  initial by  rate  M  e  to  yield  rate  is  e  a  =  {A[Mo]_/k [Mo] ([Mo] I M e U  same  by  reaction  the  form  the slow  stated  con-  as  -  equation  2,  e  amount  [Mol  period  p r e c i p i t a t i o n of Part  [Mo] )  A[Mo]  of  0  n  induction  in  initial  by  T  o  -  Q  constant  given  T  the  the  namely,  k [Mo] [S] ([Mo]  M  follows  of p r e c i p i t a t i o n  substituting  A[Mo] /(-d[Mo] /dt)  of  . . . . (36)  T  atmosphere  =  Therefore caused  the  required  precipitate  nitrogen  molybdenum,  (-d[Mo] /dt)  which  Figure  T  centration  The  in  varied  ex [ S ] , o r T oc l/[s]  p r e c i p i t a t i o n under  equation  be  is  concentration  that  k  The  sulphide  section  e  )}/[Sl  e  -  1/[S]_ Te  (36). is  concluded  catalyst with 2.  to the  0  147  10  induction time 5fmm. 0  I  o  1  Fig.42 INDUCTION PERIOD,  0  1 2 0  i  1 p  co  a t m  '  4 0  VS. PRESSURE  10 20 30 40 (Sl T ml. ot the stock solution added Fig.43 INDUCTION PERIOD, k vs. (S) T  148 4-2-b  Growth  4-2-b-l  slope  Effect  of  the  linear  rate  rate  constant,  centration  was k,  was  portion,  words,  determining  4-2-b-2  the  the  rate  slopes  linear  sulphide  of  effect was  of  of  the  slopes  tration  of  sure  carbon  expected  But  reaction  the  sulphide  observed, that  con-  as the  amount  and  quality  induction  period  and  has  does  i . e . , the  not  of  the  molybdenum  come  shown to  in  follow  rate  were  =  Figure  various of  into  the  of  no  growth  a  of  the  plotted  and low  46.  of  part.  rate  monoxide  carbon  sulphide initial  When  the  high and  the  concenpartial  dependence  value  at  high  type  of  curves  This  monoxide  series with  against  non-linear limiting  carbon  conditions.  the  molybdenum  series  some  of  pressure  portion  of  monoxide,  approaching  pressure  under  linear  initial  as  was  the  the  partial  studied  concentration  region  ion  only  varied  curve.  concluded  portion,  partial  initial  observed  the  i t was only  rate  induction  linearity  varies  during the  Effect  of  good  the  also  step.  The on  a  Therefore  produced  other  the  s e r i e s where  the  catalyst  In  of  for  44..  on  rate,  against  concentration  effect  concentration  plotted  varied,  Figure  concentration  sulphide  sulphide  direct  portion)  sulphide  initial  the  in  of  The  when  shown  (linear  pres-  was pressure may  be  the r e l a t i o n s h i p ,  B^/Cl  +  B P) 2  (37)  149  RATE  0 Fig.  44  10 RATE  o IMOIT  RATE  vs.  k  20  INDUCTION  minT  30  PERIOD  o  £ = 200 psi. 0  Q  400  A  700  •  A  mm.r l x 10 A — " " A "  0  Fig.45  0.2  0.4  1  " ~  I  0.6 0.8 3 (McOj M.x|0 EFFECT OF [Molj ON RATE , I60°C.  1.0  150  thus 1/rate  Figure  47  shows  linearity of  the  given B  2  is  rate in  are  on  also  When in  of  free  ing  does  not  the  effect  gated  under  sulphide. change the  C  of  dition  stated  above  was  at  =  atm.  The from  was  interpolated value the  0 . 0 0 1 0 M.,  results is  A-4  A  indicating carbon  a  large  not  of  the  such  molybdenum  B^  and  A.  to  [Mo]^,  appreciably  in  as  concentration  compared  change  good  dependence  monoxide  i n Appendix  molybdenum  i n Table  pressure  20.4  of  1/P.  the  degree a  a  concentra-  of  case.  slight  complexTherefore  concentration  was  investi-  conditions.  =  c o  ( l / B ^  calculated values  appreciably  0.022 M. , a n d . [ M o ]  P  +  against  Consequently  total  Series  partial  The  i s very does  )(i/P)  plot,  pressure  total  [ S ]^  such  In the  of  ] L  1/rate  i n Table  [Mo]^  of  2  this  (37).  listed  (B /B  of  in  partial  Effect  variation  plot  observed  equation  4-2-b-3  tion  the  =  of  a  compared  A-4-1  carbon  0.0010  i n Appendix  monoxide  ~  0 . 0 0 0 8 M.  fulfilled. the of  result the  series in  the  was  The from  initial of  initial [Mo]  rate  below.  where  varied,  Hence,  experiments  table  A,  = at  [S]^, =  the  con-,,  rate  determined  0.0008 P^  with  =  M.  20.4  [Mo]^  atm. =  Fig.46  GROWTH UNDER CO,  RATE vs. PRESSURE  152  0 Fig.47  5 I/RATE  vs.  1/ P C Q  I/Prn  10 PLOT  atrrc' x IO2  15  153  [Mo]  M.  x  Initial  T  10  m i•n . -  M.  3  0.8  1 . 44  1.0  1 . 81  where  k'  =  (Initial  Fair constant  1  the  when  the  rate  k'  5  min.  ^  (found)  the  sulphide  10^  1.81  T  i s noted  on  x  1. 80  (interpolated)  Rate)/[Mo]  agreement  of  i10n  x  calculated, indicating  dependence tration  Rate  for the  total  the  first  pseudo  order  first  molybdenum  concentration  was  rate  order concen-  in  large  excess. The centration of  the  dependence  was  series  ([MoJ^/Rate) where  further  [Mo]^  of  high  was and  Rate  good  various  pressures  was  45.  assumed  to  the  to  molybdenum  against  [Mo]^  for  -d[Mo]/dt  the  the  are  was  observed  with  constant  intercept  the  a  rate  the  equation  T  =  =C[Mo] /(a T  a +  +  b  b  [Mo]  [Mo] ) T  P  concurves  When  series,  instantaneous  a l l the  for  T  rate  ratio.  (-d [Mo ] ^,/dt)  be  T  molybdenum  sulphide  [Mo] /(-d[Mo] /dt)  or  on  analyzing  having  Therefore  rate by  =  linearity  the  studied  plotted  values,  Figure  of  as  this  lines  at-  shown  in  series  154 The  Integration  Y  The  ln  left-hand  obtained the  =  The to  at  =  45,  and of  [Mo]  plotted the  inverse  48 .  -b  c a l c u l a t e d by  values  the  in Figure  +  was  Figure  b.  proportional shown  [Mo]  side  from  slope  gives  of  +  T  constant  putting  a  against  [Mo]^  to  obtain  found  to  be  slope  b  were  pressure.  Therefore  the  rate  The  =  0.11  min.  plottings  equation  is  are  given  by,  -d  where For  b  1  the  [Mo] /dt T  is a  =  [Mo] /[a T  +  (b'/P)[Mo] ]  . . . .  T  (38)  constant.  initial  rate  equation  (38)  i s reduced  to  equation  (39). (-d[Mo] /dt) T  4-3  to  [Mo]  T i  P/(aP  +  b'[Mo]  T ±  )  . . . .  (39)  growth (i)  experimental  observations  are  shown  by  equation  (38). A  for  =  Discussion The  (35)  i  mechanism  consistent  i s proposed  Fast  as  with  the  above  observations  follows:  e q u i l i b r i u m between  various  molybdenum  plexes MoO  S~ 2  n  4-n  + H„S t 2  MoO  ,S ~ , v 4-(n-l) 2  n-1  f  +  H_0 2  com-  155  156 (ii)  Fast  and  strong  molybdenum  complex  catalyst surfaces,  C  +  bc  C_ s (iii)  +  CO  2S. 4-n  [MoO  CO  aq  CO  , ads  decomposition  of  S~ 2  4-n  Rapid  on  n  2S. ] 4-n J  , ad s  , ads adsorbed  species  to  adduct  2S. ] , 4-n a d s  n  monoxide  a  g  an  [MoO  of  C ,  form  n  equilibrium  carbon  e q u i l i b r i u m between  Slow  (v)  n  and  Fast  [MoO  (iv)  MoO  adsorption  •••  +  [MoO  the  n  CO]  C ~ s  +  the  growth  2  ads  n e u t r a l i z a t i o n to  •••  . ads  adduct  i  CO]  2S. 4-n  cause  C0 2 o  of  the  precipitates .  The the  above  of  assumption  -d  The  strong  and  [MoO  n  rate  [Mo]  T  /dt  adsorption  S?~ 4-n  .  .  molybdenum  precipitation  given  from  is  =  k  [MoO  n  S? 4-n  •••  CO]  e q u i l i b r i u m between  . CO]  , ads  yields  ads  . . . .  (40)  2^ ds'^°^n^4-n^ads a  157  [MoO S^- • • • C 0 ] n  a d s  = C e s  M C O  [MoONS4?n  /(WCO  +  —CO]  n [MoO S^?n 1 +niC0  [ M o 0  n  M  n U-n  ••• °])  s  C  ...»  assuming  the  adsorption and  (iii)  K  Using  the  related  n  S. 4-n  •••  adsorption,  The  to  the  n  CO]  where  e q u i l i b r i u m at  =  equilibrium  fractional  [MoO  total  S  4-n  K  [MoO  1  n's  the  are  step ( i i )  of  concentration  ] =  a  [Mo]  n  of  n  S. ] P 4-n co  . . . .  (42)  constant.  distribution  Substitution (40)  of  gives  i s an  1  type  coefficients.  [MoO  where  Langmuir  (hi)  of  species,  [MoO  molybdenum  n  S,  4-n  by  . . . .  1  equations  (41),  (42)  and  (43)  ] is .  (43)  into  yields:  -d [Mo] /dt = k C T  s  M C 0  Ka [Mo] P  Aacopco  n  +  T  C 0  n' °nf ^ Mo  M  +  nM^a [Mo] P ) n  T  C0  ..(kk)  158 For  large  ator  which  versus  others  term  and  = (kc e  [Mo] /dt  s  T  I C 0  K)P /(ri C 0  +  [Mo]^,  the l a s t  others  -d  i n the  equation  denomin-  (44)  n coKP ) M  M  CO  i s e q u i v a l e n t to the equation  versus  and  [ M o ] / d t T  term  £ s  (44) r e d u c e s  0^n) C0 P  M C  combination production  actual of  [ M o ]  [MoJ^-time  the molybdenum  process,  the c a t a l y t i c  F o r low  i n the denominator  equation  = (kC  (37).  n  which  will  MV  MO]  T)  (38),(39). i s the r e s u l t  depletion  reduction process  is negligible  + N  p  curve  be  values  to  T/( C0 C0  i s e q u i v a l e n t to the equation The  b)  [Mo]^ the f i r s t  to  -a  which  of  is negligible  reduces  of  values  by  a)  denoted  of the  the  , and  which  will  be  catalyst by  denoted  M. 2  i.e.,  initial  total  molybdenum  =  f  M  ]  = T  i  I ] M  +  [M-^]  +  t 2 M  The  rate  equations  obtained  for  (a)  and  (b)  are  in  simplified  forms ,  dM  1  dt  dM  =  k  (M  =  k_  we  P  +  k  i  )  [M] [M]  3  =  y  "  equations  equation  dt  =  w  h  (45)  for  d[M]  the  +  k^  [M]  .  ( 4 6 )  .  .  .  P  dM  e  and  r  e  (46)  -  dM  +  dt  y"=  can  be  shape  concentration  (M  in  V  1  1 0  [M]  1  ) + k  - M J  2  M  1 0  e  _  k  l  t  +  k  large is  the  aqueous  rate  phase:-  P  +  k  P [M]  3  ( 1  1 0  -  +  k  [M]  P  P  +  k  3  [M]  +  k  4  e'^) and  4  2  P  Y"M  give  -  [M] l  to  dt  1  k  factor  combined  Y'M  (47)  ( 4 5 )  P  molybdenum  k  For  . . . .  assume  Cs  the  M  C  2  dt  If  -  iu  values  of  [M]  reduced,  on  expansion,  [M]  .  small to  values  of  t,  P  .  .  .  equation  ( 4 7 )  160  d  [M]  P -  dt  This  l10  k  M  +  k  X  l 10 M  1  i s t h e same  i  form  ( k  2  U  Z  k  + k P  as e q u a t i o n  Y"-  k  l  }  t 1  (35), i f the f i r s t  term,  -ki t i.e.,  k^,  i s small.  For large  values  of t, e  - 0,  1  thus , d  [M]  [M] P y-'M.  = k„ d  in  t  2  P + k  agreement w i t h The  and view  carbon  [M] + k  3  4  the observed  assumption  monoxide  [M] P  rate  of adsorbed  i n the step  1  0  equation. adduct  (iii)  of  thiomolybdates  i s reasonable i n  of the e x i s t e n c e of v a r i o u s organq-molybdenum  complexes  87 containing  carbon  postulated  the  carbon  monoxide  monoxide  adsorbed  as a l i g a n d  adduct  i n h i s study  .  of cobaltic  solution  with  carbon  ammine  of the r e d u c t i o n  88 sulphate  Halverson  monoxide  of  also  with  cobaltic  161 GENERAL 1. (-II)  form  and  4,  at  that ion  although  of  exchange causes  the  bond  and p o s i t i v e by  less  hydrogen  system  equilibrium.  was  was  1  indicated i o n with  sulphide  yielding  negative  production  which  difference in  sulphide  and  water.  at elevated  temperature  n o t s t a b l e and decomposed  There  by s u l p h i d e  formation  atmosphere  of  concentration.  parameters  entropy  Species  significant  sulphide  the negative  In t h e . i n e r t  (VI) -sulphur  of x between  i o n i n the molybdate  aqueous  thiomolybdate  was  hydrogen  covalent  compensated  molybdenum  f o r a l l values  of thermodynamic  a strong  between  approach of  aqueous  of oxide  2.  o f molybdenum  a t 120° and 150°C.  existed  of exchange  n o t be  made  CONCLUSION  mono-thiomolybdate  estimation  entropy  was  2MoO. S 4-x x  enthalpy may  system  a l l ranges  Rough  AND  E q u i l i b r i u m study  -water  the  SUMMARY  an i n d i c a t i o n  to  of reduction  i o n i n the ammoniacal  alkaline  solution.  3. reaction order  Under  was  found  i n t h e amount  and  hydrogen  the  rate  hydrogen  alternative molybdenum  of molybdenum  step  was  one  which  A mechanism was  the s u l p h i d e paths,  atmosphere  t o be a u t o c a t a l y t i c ,  pressure.  determining on  hydrogen  rate  precipitates,  first solution  suggested  i n which  of the  followed  sulphide  and the o t h e r  being  has l e f t  the a c t i v a t i o n  to produce  tri-valent  was  the r e d u c t i o n  adsorbed  by  two  i n which  to produce  oxide  162 in  which  by  the  the  molybdenum  former  proportion  termined  by  reduction followed  reaction by  a  decomposition  lyst  and  linear  i s then of  carbon  produced  active was  and de-  conditions.  found  the  monoxide  to have  decrease  an  atmosphere  period  f o r a main  between  rate  was  considered  not  to change  the main  reaction.  period A  mechanism  produces  reaction  strongly  was  the  induction  i n concentration.  induction  active  adducts  sulphide  i n the product  monoxide  amount  during  was  The  catalytically  to o x i d e  the carbon  i n which  catalyst  bdates  considered  sulphide  Under  suggested  This  of  was  tetra-valent.  the s o l u t i o n  4.  is  path  was  where  adsorbed  determining.  a  catalyst. slow  thiomolyThe  significantly  cata-  163 SUGGESTED  1. as  an  Use  indicator  (a)  of  of  the  aqueous is  possible  in  Part  1,  by  elevated the  adding  gen  and  for  their  natures  method  potential industry  ling  of can  found  this be  a  of  system  be  metal  heavy  s u l p h i d e s at  hydrogen to  of  metal  produced  reduction  may  be  be  molybdenum  worth  Thus  f o r the  from the  measur-  sulphide the  by  solutions.  required.  during  general hydrogenation  of  by  co-precipitation  may  material  the  temperatures.  determined  molybdenum  complete.  Reduction  extent  can  described  accurately  various  heavy  temperatures  method  more  of  the  study  processing in  the  hydro-  investigation catalyst.  solution of  by  the  molybdenum  worthwhile.  tri-valent  the  as  Stripping was  4. and/or  monoxide  elevated  investigation  with  Catalytic  at  aqueous  s m a l l amount  molybdenum  carbon  of  of  the  properties  experimental  determining  activity  of  3. the  the  temperatures  case  sulphide concentration  s u l p h i d e at  products  this  tetra-thiomolybdate couple  hydrogen  c o n s t a n t k^  In  2.  and  WORK  thermodynamic  after  Solubility  ing  of  hydrogen  consecutive (b)  tri-  aqueous  Determination  FUTURE  of  was  of  found  hexavalent to  reduction,  molybdenum  proceed. molybdenum  Thus  by  to  tetra-  control-  disulphide  may  be  p r o d u c e d . 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A 29^ p t . 2 , ( 1 9 6 0 ) 1 8 1 ; CA 55. 1 0 1 7 2 1 .  65.  S a x e n a , R . S . , J a i n , M.C. a n d M i t t a l , M.L., A u s t . J . Chem., 21 ( 1 ) ( 1 9 6 8 ) 9 1 ; CA 68 72831y.  66.  Z v o r y k i n , A. Y a . , P e r e l ' m a n , F.M. a n d T a r a s o v , V . V . , R u s s i a n J . I n o r g . Chem., j6 ( 9 ) ( 1 9 6 1 ) 1 0 2 1 .  67.  S r i v a s t a v a , M.H.N, a n d G h o s h , S., P r o c . N a t l . A c a d . S c i . I n d i a , S e c . A 29 p t . 2 , ( 1 9 6 0 ) 178 ; CA 55. 1 0 1 7 2 1 .  68.  A r u t y u n y a n , L.A. and K h u r s h u d y a n , I n t e r n a t i o n a l , 1966, 479.  K.B. a n d Z a k h a r o v a , L . A . , 8 (1) (1963) 48.  G.,  Russian J .  P h y s . h2_  8 (5) (1968)  G., N a t u r w i s s . ,  Bull.  4_7 ( 1 9 6 0 )  Chem. 348  Chem., 7JL  S c i . Chim.  E.Kh.,  France,  Geochem.  169 69.  Traill,  R.J.,  Canad. M i n e r ,  70.  Wyckoff,  71.  B e l l , R.E. a n d H e r f e r t , (13) (1957) 3 3 5 1 .  72.  Z e l i k m a n , A . N . , C h i s t y a k o v , Yu.D.', I n d e n b a u m , G.V. a n d K r e i n , 0.E., K r i s t a l l o g r a f i y a , 6 ( 3 ) ( 1 9 6 1 ) 3 8 9 ; CA 57 5391e.  73.  S p e n g l e r , G. a n d W e b e r , A . , Chem. B e r . , 9\2 ( 1 9 5 9 ) CA 5_4 873e.  R.W.G., I b i d . ,  7 4 . ° R o m a n o v s k i , W., CA 60 6467f.  7_ ( 3 ) ( 1 9 6 3 )  524.  v . 1, p . 2 8 0 . R . E . , J . A m e r . Chem. S o c , _79  Roczniki  Chem., 3_7 ( 9 ) ( 1 9 6 3 )  2163 ;  1077 ;  75.  B j e r r u m , J . , " M e t a l Ammine f o r m a t i o n i n A q u e o u s S o l u tion," P. H a s s e a n d S o n , C o p e n h a g e n , ( 1 9 5 7 ) p . 1 4 .  76.  R o s s o t t i , F . J . C . a n d R o s s o t t i , H., "The D e t e r m i n a t i o n of S t a b i l i t y C o n s t a n t s , " M c G r a w - H i l l , New Y o r k , (1961), C h a p . 5.  77.  B u c h w a l d , H. a n d R i c h a r d s o n ,  78.  M u e l l e r , A., R i t t e r , W., a n d N a g a r a j a n , G., Z. P h y s . Chem. N . F . , 5_4 (1967) 229. T h i s work g i v e s a d i f f e r e n t value of molar e x t i n c t i o n c o e f f i c i e n t of t e t r a t h i o m o l y b d a t e a t 467 my. i  79.  R o s s o t t i , F.J.C., "Modern C o o r d i n a t i o n C h e m i s t r y " Ed. b y L e w i s , J . a n d W i l k i n s , R.G., I n t e r s c i e n c e , New Y o r k , (1960) C h a p t e r 1.  80.  Wolfberg, 837 .  81.  L a t i m e r , W.M., "Oxidation Potential", H a l l , N.Y. ( 1 9 5 2 ) .  82.  Frank, 133 .  83.  C h i y a , T., p. 8 6 2 .  84.  M c A n d r e w , R.T., P h D . T h e s i s , T h e U n i v e r s i t y Columbia, (1962).  M.  and H e l m h o l z ,  H.S. a n d Wen, W.Y.,  E . , T a l a n t a , 9_ ( 1 9 6 2 ) 6 1 3 .  L. ,  J . Chem. P h y s . ,  20_ ( 1 9 5 2 )  2nd e d . P r e n t i c e -  D i s c . Faraday  S o c , 2j4, ( 1 9 5 7 )  " M u k i k a g a k u " v . 2, S a n g y o t o s h o .  Tokyo,(1959)  of  British  169a 85.  Halpern, J . , Quart. (1956) 463.  Rev.  Chem. S o c . ,  86.  B e e c k , 0.,  87.  C o a t e s , G.E., "Organometallic Compounds' 2nd e d . J o h n W i l e y a n d S o n s , New Y o r k ( 1 9 6 0 ) p. 268. Z e i s s , H. ed . ' O r g a n o m e t a l l i c C h e m i s t r y ' Reinhold P u b . C o . , New Y o r k (1960).  88.  H a l v o r s o n , H., PhD. Columbia, (1966) .  89.  Duval, C, " I n o r g a n i c Thefomogravimetric Analysis," E l s e v i e r P r e s s , Inc., Houston, Texas, (1953).  D i s c u s s . Faraday  Thesis.  Soc,  The  (London)  8> ( 1 9 5 0 )  University  1_0  118.  of  British  170  A P P E N D I X  APPENDIX  A  Experimental Table  A-l  The  Table Series No .  Mo M. xlO  A.  150°C,  T M. xlO S  3  22 3 4 5  0 . 49 .97 1.47 2 .13  32 3 4 6  0 .50 1.05 1.61 2 . 69  42 3 4 5  0.50 1.01 1.54 2 .07  72 3 82 3 4 5 6 •7 8 9  a  [NH 3  A-l-1  ] = 1 M., a  Study  4  Data  o f Eq u i l i b r i u m  Analytical  Data  [NH. ] = 1 M. , A  3  1  2  5  (nominal  n  "I M. ,cm. x l O -4 M - l  3  12. 73 12 . 26 12 . 23 12 .13  f M. xlO S  Concentration) [H S] M? xlO 3  3  2 calcd. a  q  0 . 233 . 216 . 201 . 181  0.105 .091 .076 . 060  0 .221 . 208 .208 .188  1.54 1.47 1.41 1.32  11 .98 10 .83 10 .16 9 . 32  1.89 3 1. 711 1. 605 1.473  0 . 231 .234 .234 . 231  36 87 90 03  0 . 098 . 088 .073 . 060  0.020 .014 .012 .008  0 .148 .138 .125 .113  0 . 84 . 78 .69 .59  4.94 5 .05 4 .79 4.44  0.781 .798 . 757 . 702  0 .138 . 142 . 132 .119  23.81 24 . 38 24 . 28 24 .14  0.329 . 334 .323 .314  0.327 . 311 . 291 . 256  0 .110 .123 .132 . 151  3 ,16 3.10 3.03 2.93  22.23 21 . 25 19 .61 18 .07  3 .512 3 . 358 3.098 2 .855  0. 152 . 159 . 172 . 185  2 . 008 1.973  2 .82 5 . 84  0.017 . 063  0.001 .010  0.054 .115  0.4 7 .60  1. 88 4 .66  0.297 .736  0. 028 . 127  0 . 998 .930 .880 .871 .854 .828 .821 .817  2 .49 5 . 39 7 . 38 • 10.47 14 . 37 16 .93 19.84 22.44  0 .017 . 065 . 125 . 207 . 282 .319 .334 . 340  0.001 .011 . 031 . 079 .145 .199 . 250 . 286  0.052 . 121 . 171 .212 . 229 .224 . 195 . 172  0 .47 .61 1.06 1.42 2.07 2.52 2.82 2.99  2 .02 4.82 6 .45 9.23 12 .60 14.84 17 .52 20 . 00  0 .319 . 762 1.019 1.458 1.991 -2.345 2 .768 3 . 160  0 .032 . 134 .186 .230 . 228 . 212 . 189 . 169  5 5 5 6  . . . .  172  SERIES B 150°C,  [ N H ] = 0.5 M. ,  (Nominal No . [Mo] M. xlO 92 3 4 5 6 7 8 9  [s]  a  T  a  3  1  0. 995 . 916 .946 .956 . 944 . 912 .910 .882  [NH*] = 1 M.  3  '3 xlO  Concentrations) 315 _ 2 _ M. cm. xl0-4 7 A  4  2  x  M  2.41 0.043 0 . 003 0.098 5.40 .163 . 194 .044 8.44 .253 . 104 . 237 11 .38 . 301 .172 .226 . 327 .235 . 203 14.26 17 . 23 . 337 . 295 . 172 . 322 19 . 80 .326 .146 22 . 16 .316 .355 .124  n  0.57 1.13 1.79 2 . 58 2.80 3 .10 3.21 3 . 29  [S] M xlO  1.84 4.37 6.75 8 .91 11.62 14 .40 16 .88 19 . 26  SERIES C 120°C,  [ N H ] = 1 M., 3  (Nominal No . [Mo] M. xlO 52 3 4 5  0.465 . 865 1.407 2 .000  62 3 4 5  0.498 1. 019 1.494 2 . 000  122 3 4 5 6 7 8  1.036 1.068 1.028 . 967 . 852 . 742 .671  [s]  M. xlO  T  a  3  a  8.16 0 . 215 0 .060 6 . 30 . 116 .029 4.68 - .053 . 008 .038 4 . 38 .004 _  -  0.319 .322 .324 .320  [NH*] = 1 M.  Concentrations)  4  -315 M. cm. xl0-4  n x  '3 xlO 1.83 1 .28 .89 . 84  0 . 285 0 .136 .279 . 151 . 262 .172 . 242 . 200  2.61 2 .61 2 . 51 2.43  0 . 018 0.004 3.44 6.64 .095 . 027 . 178 .073 10 . 39 14 .10 .130 .246 . 193 17 . 21 . 295 20 .78 .328 .257 . 331 24 . 28 . 351  0.065 . 139 .186 . 201 .191 .175 . 133  [S] M  0.192 . 170 . 108 .089  0. 81 1.15 1.62 1.97 2 .33 2 .50 2.66  <*  f  7 .31 5 .19 3 .43 2 . 70 _  -  2 .60 5.41 8.73 12 .20 15 .22 18 .93 22.50  2  xlO  3  calcd .  0 . 440 0.057 1.044 . 196 1.613 .234 2 .129 . 22 3 2 .777 . 189 3.442 .155 4 .034 . 130 . 110 4 .603  173 TABLE Study  A-l-1  of E q u i l i b r i u m (continued)  SERIES 150°C. No .  Mo M. xlO  Nominal  a  3  0.095 0.201 0 .195  112 3 4 5 6a 7a 8  1 .024 1. 015 1 .009 0.990 0 . 988 0 .985 0.985 0 .985  2 . 58 3 .76 7 .61 9 .76 12.06 14 .80 16.00 18.76  0.100 0 . 206 0 . 198  a  -  a  4  A  315 2  =  0.1/1  n  -  -  0 . 013 0.076 0 .114 0.138 0.136 0 .133  0.177 0.255 0 . 266  0 . 018 0.080 0. 114 0. 138 0 .133 0. 130 0 . 127 0 . 124  0. 186 0.258 0 . 242  -  -  M ' 3 xlO" 2  ' 3 xlO  2 . 34 4.75 7.17 9 .32 13.48 11.59?  a  3  J  1.054 1.051 1.044 1.031 1. 0 2 1 1.010  9.a  (NH )/(NH+) x  T M. xl0 S  102 3 4 5a 6a 7a  a  Ratio  D  3  3  0.82 1.48 1.42 3 .26 3.97 3.06 3.93 5 . 27 4 .18 9 . 21 4.26 10.40  0 . 75 1.66  0 . 88 1.68 1.42 2 . 32 2 . 98 4.60 5.81 3 .99 4 . 10 8 .10 4 .14 10 .73 4.15 11.92 4 .17 14.66  0.85 1.18  -  -  T o o much i n t e r f e r e n c e was o b s e r v e d p r o b a b l y d u e t o t h e a p p e a r a n c e o f p r o t o n a t e d s p e c i e s , a n d 0:3 a n d A ^ ^ could n o t be o b t a i n e d . Therefore n was c a l c u l a t e d b y u s i n g 014 a n d Srn w i t h s u c c e s s i v e approximation. But the v a l u e s obtained f o r n w e r e r a t h e r d o u b t f u l s i n c e a4 m i g h t a l s o contain the i n t e r f e r e n c e s t a t e d above. 3  2  q  174 TABLE Calculation  1.  N  T  v s . lCr  plot,  of  Figure  Temperature °C.  [NH ]/[NH ;  150  1/1  8-h 8-c  0.5/1  was  the Conversion  6a  [NH ] MT  [NH ]  9 . 61 1.557 9.62 1. 5 8 1  4.07 4.17  0 . 746 0.770  0 .811 0.811  9-h 9-c  9 . 38 1. 256 9 . 39 1.270  2.40 2.46  0 . 445 0.459  0 . 811 0. 811  0.1/1  10-h 11-h  8 . 82 0. 946 8.89 0 .938  0 .66 0.78  0 .135 0 .125  0 . 811 0.811  1/1  5-h 5-c 6-h 6-c 12-h  9.46 9 .43 9 .62 9 .66 9 . 70  0.542 0.524 0 .745 0 . 840 0 .88  0 . 821 0.851 0 .780 0 . 800 0 .77  No .  pH  P H  T M. N  M./M.  measured  a t room  9  -  n  [NH ]/[NH ]  vs.  [NH J/[NH ]  !S]  (nominal) M./M.  M. xlO  4  3  3  4  —  +  M.  temperature.  [S] [NH,, ] / [ N H ] £  f  _ -  1.363 1.375 1. 525 1. 640 1.65  ' h ' a n d ' c ' i n c o l u m n 3 mean t h e s a m p l e t e m p e r a t u r e s and t h e s a m p l e t a k e n a f t e r room t e m p e r a t u r e , respectively.  2  Factor  10 o xlO"  +  3  120  pH  A-l-2  3  [NH ] 3  M.  taken from e x p e r i m e n t a l systems were c o o l e d to  plot,  [NH+]  Figure  [NH ]/[NH ] 4  3  6b.  'S  f  [NH ]/[NH ] 4  M. xlO  M.  3  3  1.42  1/1 0.5/1 0 . 1/1  9.2 5. 3 2. 8  0 .746 0.445 0 .135  0 .811 0 .811 0 . 811  1.09 1. 82 6 . 0  10.0 9.6 16 . 3  0.85  1/1 0.5/1 0 .1/1  5.5 3.3 1.6  0 . 746 0.445 0 .135  0 .811 0.811 0.811  1.09 1. 82 6 . 0  6.0 6 . 0 9.4  174a  3.  Conversion  Equation  [  From  the  A:  Nominal  B:  Nominal  D:  Nominal  2  H  plots  S  ]  aq  =  [  S  ]  (1) and  f  /  (  1  +  (2),  I  m  m  =  H  t  ]  '  )  5.8,  [NH J/[NHj]  =  1/1  [NH ]/[NH ]  =  0.5/1;  [H S]  [NH J/[NH^]  =  0.1/1;  [H S]  3  3  3  4  ;  N  [  H  2  S  ]  aq  2  2  and  a q  consequently: °-  =  1  5  8  [  S  ]  f  =  0.23 [S]  F  =  0.50 IS]  f  9  8  175 TABLE Precipitation Temperature  158.8°C  Sulphide  Under [NH  was  A-2 Nitrogen  ] = 1.0  added  as  a  M,  X. X  X 6  [S],  k/X  k  M  Mo  e  for  /[Mo]  e  Composition  M.xlO  3  M.xlO  3  k  mm.  4  X. l X e k  M.xlO  3  M.xlO  3  • mm.  X. l X  M.xlO  3  M.xlO  3  k  • mm.  X. l X  M.xlO  3  M.xlO  3  k  • mxn.  [S],  M.  C  4  C  3  [S]  ratio  -  -  1  1  x li On  x li On  x li On  3  . -1 mm . -1 . -1 M. mxn. -1 . -1 M. mm. (M.  -2  of p r e c i p i t a t e s  S/Mo  Observed Calculated  )  =  0.5  M,  solution Run  47  Run  46  16 . 0  14.5  3. 2  11. 3  8.9  27 . 5  51. 5  53.5  20 . 4  42 . 6  38.5  5.8  10 . 7  8 . 8  1.11  2.97  3 27  0. 68  1. 28  1  18 .0  27  22 . 2  2 .93  4.55  3 78  1. 63  2 . 34  3 ,35  22 .  5  4  8 . 6  0 .28  . -1 mxn . xlO  2  2  19 . 4  10 . 0  3  4  19 .1  15.4  3  -1  Mo S difference  Molar  -  1  49  11. 2  xlO  (NH ) S0  (NH > S Run  [Mo  Atmosphere  12 . 9  0 .25 14.  19. 9  0 .23 18.  6 .1  5 . 5  5.9  1.8  1 . 7  1.6  (%) 40 .1 41.4 18 . 5  45.0 39.9 15 .1  44.9 39 . 8 15 . 3  100 . 0  100.0  100 . 0  = r. 3 .10 4 . 20  2 .65 3 .08  2.65 2.83  176 TABLE A-3-1 Series  A  Series  Mo M. 0 . 049 0 . 099 0.148 0 . 198 0. 247  B  Series  T M. S  0 . 646 0 . 616 0.327 0 . 235 0. 154 0 . 116 0 .079  C  100  4 . 28 2 . 14 1.4 2 1.07 0 .85  r  s  7 .0 6.6 3.41 2 .42 1.59 1. 18 0 .81  Mo M.  S  T  . 014  M., Mo  N H 4 = 0.97 M., = 0.097 M., P  2 . 30 n.d. 2 . 08 2 .10 1.53 1.23 0 .80  S ) , 167.7°C,  NH  = 0.86  M.,  S/Mo  r  s  r  "  1.00  1.02  1. 2  0  .60 0 . 33 0.17  0.61 0 .32 0 .15  1.2  . 008 . 006 0 .004 0 .002  NHT 4  0  0.010  = 600  p s i .  1. 35 1. 24 1.23 1.41 1.29 1.3-9 1. 23  0  0 .010  . 014  1.29 1 .22 1. 20 1.16 1. 15  2.45 2 .16 1.62  0.012  0  M., P = 860 p s i .  7. 0 3. 0 1.67  0  . 004 0 . 006 0 . 008 0 . 012  H2  s  M:  0 .002 0  and r„  '-a  0.91  r  b  M., NH," = 0.98 S = 0 . 2 1 1 M.,  2 .14 1.93 1.45 1.11  S/Mo  C o n s t a n t (Mo + P = 530 p s i  No .  94 95 96 . 97 98 99  S/Mo  S variation 1 5 8 . 8 ° C , NH = 0.84 Initial conditions:  No .  79 72 80 86 81 85 83  of P r e c i p i t a t e s , r  Mo v a r i a t i o n 1 5 1 . 6 ° C , NH = 0.86 Initial conditions:  No .  101 102 10 3 104 105  Analysis  A-3  2  2.5? 1.6 1.6  1. 3 1.1  = 0.98  M.  177  Series  D  P variation . 158.8°C, NH = 0.84 M., NH* = 0.96 I n i t i a l concentrations: Mo = 0.097 3  No .  P  initial p s i .  2 86 87 88 89  P  final 2psi .  R  602 441 310 228  1 5 8 . 8 ° C ,  Initial  NH  =  420 220 95 16  1.00  M.,  concentrations:  titanium  r  autoclave,  NH*  =  0.99  M.,  =  0.020  M.,  T  pressure  maintained  No .  r  = 0.194  s  2 . 10 1.83 1.96 1.96  Mo  M. , M., S  ST  1.41 1.51 1.47 1.45  =  0.054  M.  constant.  s  psi. 44 43 42 41 40  Series  100 200 300 400 500  E  2 2 2 2 2  . 33 .09 .16 . 06 . 04  n .d . n. d . n. d . n .d . n. d .  pH v a r i a t i o n 1 5 1 . 6 ° C . , no N H , Initial concentrations: Na MoO, N a S = 0.211 M., I n i t i a l p r e s s u r e 880 p s i . 3  ?  = 0.097  M.,  2  No .  (NH ) S0 4  2  4  r  s  M. 106 109 107 110 108  0.490 0 .392 0.294 0.245 0 . 191  1.96 1.93 1.85 1.66 1.65  Mo in final s o u t i o n s , M. T  ^2 1.28 1.26 1.26 1. 35 1.48  nil. nil. nil. 0 .014 0.039  M.  178 TABLE Analysis  of  T.G.A.  A-3-2 Precipitates Results  We i g h t No .  r  Loss  i n g./mole AW  s  Mo AW  2  3  83  0 .80  13 . 4  25 . 6  -5 . 2  85  1. 23  11. 7  23 . 3  3.4  81  1.53  9.8  17 . 6  9.3  86  2 .10  7 .1  25 . 9  17 . 2  80  2 . 08  7. 4  26 . 8  18 . 5  79  2 . 30  9. 2  29 . 3  31. 3  87  1. 83  5. 3  21.6  13 .1  88  1. 96  .7 . 8  21.9  16 . 2  89  1.96  7. 3  14.3  17 . 3  90  1. 64  16.9  12 . 4  91  1. 98  18.3  17 . 7  92  1.99  28.0  18 . 5  r^:  molar  ratio  11. 1 7. 9 11.6  of sulphur  t o molybdenum  AW^ : w e i g h t  loss  i n Ar at  200°C.  AW :  weight  loss  i n Ar a t  650°C.  : weight  loss  i n a i r a t 550°C.  2  AW  after  i n precipitates  T.G.A.  i n Ar.  179 TABLE  A-3-3  Kinetic 3-1 1.  P Dependence  Constant Pressure 1 5 8 . 8 ° C , NH = 1.00 M., I n i t i a l Concentrations: Titanium Autoclave,  No .  P  NH Mo  T  Slope  100 200 300 400 500  and  intercept log  2.  P  n u  o  z  were  (Mo  Slope  Q  - Mo)  obtained ln  where  a. was  taken  by  D  S  = 0.054  T  NH, Mo T  3  2.57 1.34 1. 25 0.90 0 . 32  plotting  the  = 0.96 M., = 0.097 M.,  S  = 0.194  T  x  P  0  10 p s i .  the  equation:  - P)) = -  equation:  log I  slope • -1 mxn.  plotting  M.  intercept M.xlO  0 . 086 0.061 0.053 0 . 029  (P/(a + as  by  = -St +  602 441 310 228  was  = 0.99 M., = 0.020 M.,  obtained  initial pS 1 .  86 87 88 89  Series  -0 . 0057 -0 . 0 1 4 0 -0.0214 -0.0301 -0 . 0 3 2 1  Constant Volume 1 5 8 . 8 ° C , NH = 0.84 M., I n i t i a l Concentrations:  No .  —  slope^ min .  H2  psi. 44 43 42 41 40  Study  St +  l n P /a 0  M.  180 3-2  Effect  of S o l u t i o n  Conditions  151. 6°C . No .  Slope psi.-Imin. xlO  Fractional  Distribution  1  5  a  o  a  l  a  a  2  (NHJ) 3  a  /(NH )  4  3  101 102 103 104 105  8. 3 7. 3 5. 7 4.8 3.5  0 . 020 0 . 246 0 .438 0 .532 0 . 606  0.019 0.093 0 . 117 0.120 0 .118  0 . 123 0 .235 0 . 206 0 .179 0 . 153  0.400 0 .298 0 .184 0 .135 0 . 100  0 .439 0 .128 0 .055 0 .034 0 .022  0.515 0 .460 0 .455. 0 . 450 0.448  106 109 107 110 108  3.9? 4 .6? 7. 0 6.2 3. 2  0 . 208 0 .220 0 . 243 0 .277 0 .389  0 . 086 0 .088 0 . 093 0.099 0 . 113  0 . 233 0 . 234 0 . 234 0 .233 0 . 217  0 . 323 0 . 315 0 . 300 0.279 0 . 211  0 . 150 0 .142 0 . 129 0 .112 0 . 069  1.444 0.975 0.466 0 .266 0 .110  158 . 8 ° C . No . atm.  79 72 80 86 81 85 83  Slope min. xl03 x  1.5  6  l-7 2.4 2. 0 0  8  I.74 1.74  l-7  3  7  Fractional  Distribution  (NHJ)  x  a  o  0 . 134 0 .106 0 . 085 0 . 183 0 . 364 0 .478 0 .694  a  a  l  a  2  0 .221 0 .211 0 .199 0 .231 0 .222 0 .195 0. 119  0 . 067 0 . 058 0 . 051 0.080 0 .111 0 . 119 0 . 112  3  0 . 370 0 .387 0 .398, 0.339 0 . 22.6 0 . 163 0.064  S l o p e s were o b t a i n e d by p l o t t i n g r e d u c e d against hydrogen consumption, ( P - P ) .  rate,  a  4  calculated by u s i n g i n P a r t 1.  stability  3  0 . 208 0 .239 0 . 267 0 . 167 0 .077 0 .046 0 .012  (-d  G  a's were obtained  /(NH )  constants  at  0 .030 0 .037 0.250 0 . 4 0.8 0.590 0 .696 0 .815  In  P/dt), •  150°C.  181 TABLE  Series  A  Precipitation  Under  Table  A -4-1  A-4  Carbon Monoxide Effect  of  Atmosphere  Pressure  1 5 8 . 8 ° C , [ N H J = 1 . 0 M., [ (NH,) S 0 ] = 0.5 M., I n i t i a l Concentrations: [Mo] = 0 . 0 2 0 M., [ S ] = 0.056 M. i 3  4  m  No .  Pressure (atm.)  39 38 37 35 30  Induction period(min.)  6 . 8 13 . 6 20.4 27.2 34 . 0  Series  B  T  Growth r a t e (M.min. )xl0 _ 1  6 . 1 4.2 4 . 3 5.5 5 . 3  4  2.33 4 .13 5 . 85 7.46 8.65  1 5 8 . 8 ° C , [NH ] = 1.0 M. , [ (NH. ) SO. ] = 0.5 M., I n i t i a l Concentrations: [Mo] = 0 . 0 0 1 M., [ S ]  No .  Pressure (atm.)  Induct ion period(min.)  = 0.022  Growth r a t e (initial slope (M.min. !) xlO -  5  56 54 53 52 51 57  6 . 8 13.6 20.4 27 . 2 34.0 40.8  Series  C  (short) (short) (short) (short) (short) (short)  0 .98 1.63 2.54 3 .12 3.21 3 .63  1 5 1 . 6 ° C , [NH^] = 1.0 M. , [ ( N H ) S 0 ] = 0.5 I n i t i a l Concentrations: [Mo] = 0 . 0 0 1 M., [S] = 0.022 M. 4  4  M.,  T  No .  63 62 60 59 58 61  a:  Pressure (atm.)  13 . 6 20.4 27 . 2 34.0 40.8 47.6  a  .[Mo]  Induction period(min.)  =  0.0008  (short) (short) (short) (short) (short) (short)  M.  Growth slope)  rate (initial (M.min. 1) xl05 -  1.34 1.44 2.26 2 . 36 2.85 5 .06  M.  182 TABLE  A-4-1  E f f e c t of Pressure (continued) Series  D  1 3 9 . 1 ° C , [NH^] = 1.0 M., [NH C l ] = 1.0 M., I n i t i a l Concentrations: [Mo] = 0.010 M. , [SJ = 1.0 M. T  T  No .  Pressure (atm.)  Induction period(min.)  Growth r a t e (M.min. )xl0 _ 1  4  "  6 . 3 10 . 9 17.5 23 . 3  12 13 11 14  20? 16? 7 10  TABLE Effect Series  E  of Sulphide  [s]  T  (M.)  Growth r a t e (M.min. )xl0  0.011 0.023 0. 033 0.033 0.056 0.089  1.3 3. 2 4. 3 5. 5 8. 3 14 . 4  The s u r f a c e s acid.  of autoclave  Series  F  Concentration  3  _ 1  a:  A-4-2  1 5 8 . 8 ° C . , [ N H J = 1.0 M. , [ ( N H ) SO ] = 0.5 P = 3 4 .0 a t m . CO I n i t i a l Concentrations: [Mo] = 0.020 M.  No .  34 33 31 32a 30 29  0.73 1.24 1.37 2 . 45  Induction period(min.)  4  Induction rate constant(minT^)  10. 9 9.0 8. 2 8.7 5. 3 3. 2  were  139.l'C, [NH ] = 1.0 P = 34.0 atm.  7.1 11. 7 14. 7 13 . 2 24.4 40.6 <  not treated with  M.,[(NH  ) SO 1  M.,  ] = 0.5  nitric  M.,  4  C Q  No .  Initial  Concentrations:  [ M o ] _ = 0.020  [s]  Growth r a t e (M.min. )xl0  Induction period(min.)  T  - 1  23 24 25 22 26  0.011 0 . 023 0.033 0.056 0.08 9  0. 30 0.52 1. 26 2 . 87 5 .39  A  n.d. n.d. 40 13. 2 7.5  M. Induction rate^ cons t a n t ( m i n . ) 0. 9 2.6 3.3 8.9 15 .9  183 TABLE Effect  Series  No . 27 28  G  of Sulphide Concentration (continued)  120°C,  [NH  Initial  Concentrations:  [s]  T  l  0.056 0.089  A-4-2  ] = 1.0  M. , [ ( N H ) SO.]  Growth r a t e (M.min.~ )xl0 1  0.22? 1. 28  [Mo]  4  = 0.5  = 0.020  Induction period(min.) n.d. 42.  M. ,  M.  Induction rate c o n s t a n t (min. -'-) -  1.3 3.3  184 Appendix  B  Spectrogram  Spectrograms transmission without  a  tungsten  and  1,  some  2,  were  lamp)  the l i g h t  and  source  was  the  transmission values  the  tungsten  spectrum  100%  readings  lamp  were  taken  using  are reproduced  taken  In  Figures  the scan  at was  was  were  t h e 0 and  to the s c a l e  the  here  4,  performed  line  observed  made  f o r the c a l c u l a t i o n  a t 600  t h e ones  my.  Finally  my  t o 315  i n such  with  350  (using  my. lamp  a way  that  obtained a  and  with  further  and  i t h e 0%  with  100%  taken  100% t r a n s m i s s i o n  my.  3 and my  was  adjusted  agreed  t o 260  700  6,  changed to the hydrogen  at around  was  adjusted  5 and  the spectrum  0%  and  o f them  adjusted  the  were  Solution  of the s o l u t i o n  and  Figure  the s o l u t i o n s  Then  the  alteration. In  of  scale  of  and  100% t r a n s m i s s i o n s  the tungsten  t o 300  my.  A  the necessary  of  lamp  light  linear  source  drift  correction  of the  was  t h e c o n c e n t r a t i o n s o f complex.;  species.  • The  for  use  calibration  mission value  was  was  justified  by  maximum  at around  700  observed The  solutions  of the wavelength  for distilled  following  whose  table  spectrum  were  a t 600  the f a c t my  and  my  and  that also  700  the close  my  transto the  water. shows  the c o n d i t i o n s of the  taken.  •  185 Figure  1  Part  1,  The  150.0°C, nominal  Figure  2  4  A,  Part  1,  study  The  Part  2, C,  [NH ]  =  (See  Figure  Part  2,  5  3  [NH_] 3 Figure  6  of  1 x  the 10~  =  Appendix  =  10"  =  1  M.  2  -  20  [NH^] A,  =  x 1  No.  10~  M.  3  M.  8,  2-9).  [S]  0.1  =  M.,  2 -  D,  10~  =  1  M.  No.  a nitrogen M.,  x  [NH*]  Series  3  20  [S]  11,  M.  3  2-9).  atmosphere  =  52  x  10~  M. ,  3  13).  =  n  under  20  x  [NH ]. = 4 I  M.,  B,  =  ±  1 x  [NH ] 4 +  The  [Mo]  =  1 x  10~  [NH ]  =  1 M.,  4  [NH*]  10  =  3  1.0  of  [S] »  1  M.,  _ 3  M.  [S]  =  6.4  54  x  10~  3  atm.  hydrogen  M.,  [S]  M.,  P„ H  the  =  monoxide  P_„ = ' C O  under  study  M.,  carbon  1 M.,  +  [Mo]  10  reaction,room  3  =  Series  M.,  3  x  +  1 M.,  0.7  1 M.,  under  Precipitation  =  =  19  [NH ]  [Mo]  C,  [S]  A-l-1,  Precipitation  2,  M.,  equilibrium  [NH^]  Table  [Mo]  C,  150.0°  A,  1 M.,  ]. = l  Part  =  3  A-l-1,  Precipitation  158.8°  [NH  10~  equilibrium  {NH^j  compositions  Appendix  the  Table  [Mo]  (See  158.8°  Figure  1 x  Appendix  3  Figure  =  T  (See  nominal  3  [Mo]  of  compositions  150.0°C,  Figure  study  =  ±  =  14  8.3  equilibration  x  10~  3  M.,  10~  atm.  2  temperature, 19  x  3  M,  M.,  191 Appendix  C  Rate  The in  rate  t h e Mo-S-H^O  comparison the  rate  of equilibration  system  with  method  An  used  species  f o r two r e a s o n s : reduction  2) t o c h e c k  f o r the study  1) f o r  to  check  the v a l i d i t y  of equilibrium  of the  between  complexes. at high  temperature  but d i f f i c u l t y  the o p e r a t i o n  temperature  studied  between v a r i o u s  o f molybdenum  step  experiment  the high  department,  was  the rate  thio-molybdenum  made  Equilibration  controlling  quenching  using  of  spectrocell  Thus  was  attempted  developed  i n the i n j e c t i o n  impossible.  experiments  temperature  i n this  of the s o l u t i o n  the r e s u l t s  are presented  o f room  here.  Experimental Solutions solutions. buffer The  placed cell as  Suitable  solution  mixed  solution  placed  scan  was  t o make  poured  when  repeatedly  they  of the absorbancy  smooth  fitting  i n buffer  i n a beaker  a spectrocell,  Distilled  curves  B6  with  i n Appendix  10 m i n u t e  were  a t each  were  was  read  wavelength  used  B ) , wave  DK-2  intervals.  recorded.  a t the time  [10 m l . ] .  and t h e  water  a Beckman  and  a l i d was  e v a p o r a t i o n and o x i d a t i o n ,  at approximately  the time  fresh  a c o n s t a n t volume  into  a t 4 6 5 , 3 9 5 , 315 a n d 290 my  against  made  taken  In a run (Figure  was made  Spectrometer  values  added  were  i n the l i g h t - p a t h .  the r e f e r e n c e .  length  the  was  and S were  portions  on t o p t o a v o i d  was  peaks  o f Mo  and  The  plotted  The i n s t a n t a n e o u s were  desired  read  from  and t h e c o n -  centrations were  made w i t h  lengths moment The  were  calculated.  a Beckman  Model  o f 395 a n d 465 my. when s u l p h i d e  mixing  was  Temperature  In the other  Time  was m e a s u r e d  of the c e l l  readings  a t t h e wavefrom the  s o l u t i o n s were  t o be p e r f e c t  within  mixed.  half  a  minute.  was n o t c o n t r o l l e d , b u t i t s t a y e d  between  2 6 ° a n d 3 2 ° C. d u r i n g  cases.  When  high  36° C. t o w a r d s  as  B Spectrometer  and molybdenum  expected  runs  t h e DK-2 was  the whole  used,  experiment  the temperature  i n most  went  up a s  t h e end o f t h e e x p e r i m e n t .  Results Figure of  the spectrogram  peaks  points  2t o MoS^  seen  i n Figure 2-  to the stepwise  C - l , where  and M o O „ S 2 2 b  for calculation  29  B shows  t h e time  variation  Steady  increase  of the  and d e c r e a s e  2. The e x i s t e n c e  MoO^  MoOS_  of a mixture.  a t 465 a n d 395 my  clearly  1  B-6 i n A p p e n d i x  shift  are plotted  a t 290 my  of composition  of equilibrium  calculated  methods.]  o f t h e peak  i s more  concentrations  against  The r a p i d  from clearly 2o f MoS^  time.  [See Part  reaction  to M0O2S2  2and is  subsequent  relatively  slower  shift  t o MoOS^  22-  a n d MoS^.  observed. Figure  C-2  shows, v a r i a t i o n  of the concentration  of  2species stant  MoOS^  , C^, a g a i n s t  a n d [ S ] ^ was v a r i e d .  time  where  [ M o ] ^ was k e p t  con-  These s e r i e s were measured with 315 t h e B e c k m a n M o d e l B, t h u s k^ was n o t m e a s u r e d . I t was 2f o u n d t h a t t h e c o n c e n t r a t i o n o f s p e c i e s MoS^ was l e s s t h a n 25% o f t h e c o n c e n t r a t i o n o f MoOS^ . In a d d i t i o n , t h i s range  193  Fig. C l . VARIATION OF  COMPLEX CONCENTRATIONS  195 of  time  corresponds  to  the  initial  rapid  increase  seen  in  2Figure  C-l.  Therefore  the  effect  of  MoS^  was  considered  insignificant. When approximately between  20  sulphide in  the 3  and  initial  to 30  7 minute minutes  concentration  both  cases  linearity  and  [Mo]^,.  Thus  initial  rapid  the  the  part  were  good  slopes,  in  and  the  the  linearity turn  was  subsequent  average  against  was  showed  molybdenum  mechanism  [corresponds  and  plotted  , a  total  same  slope  range],  [S]  their  against  maximum  a  to slope  total observed  good  concentration  suspected slower  for  part  both  of  the  the  curves. When of  [Mo]  T  and  time,  the  had  ratio  a  almost  values  [S] ,  of  into  [S ]^  to  experimental  ratio  was  but  their  Figure  smaller  shows  represented  by  rates, was  than  the  C-4 T  c a l c u l a t e d by  equations  around  In  the  results,  in  plots as  the  the  ratio  i n which  the  plots  cases of  the  against which  scale]  were  products  runs  26,  the the  the  plotted  than  For  decreased  were  for  the  where  the  the  same  shape  decreased. first  group  are  values.  shows T  the  point  plot  against  approximating the  ^  range.  d(C /[Mo] [S] )/dt, 3  M.  by  and  T  groups.  ±0.1  26,  averaged  Figure  [S ] ,  [Mo]^, g r e a t e r  time  magnitudes  C-3  two  [within  whole  normalized  3  fell  identical  were  i . e . , C /[Mo]  T  data  of  in  the  of  the  instantaneous  C /[Mo] [S] . 3  T  plots  to  question.  T  The  quadratic  rate  Y(=C 3 /Mo T S T ) M: PLOT OF RATE v s . CONCENTRATION 1  Fig.C4  198 Good same  slope  region  as  where  initial  linearity shown  was  found  i n Table  C /[Mo] [S] 3  T  approximately  C - l i n column was  T  with  small  3,  except  corresponding  the f o r the  to the  regions.  TABLE C - l  No .  Intercept M.  mm  7,8,9,10  0.67  11  Slope  S/Mo  S  -1  .  -0 .075, 4  26  0.56. 4  -0.072  0  17 . 3  12  0.43  -0.078  1  13  0 .38  -0.079  3  14  0.32, 4  Thus  3  ?  -0.081  the e m p i r i c a l r a t e  equation  -3 . -1 mm . k  M.X  mm.  2  T 10  3  13 . 0  k ayS 3  . -1 mxn .  8 . 7  0.066, 0 0 . 067^^  0.0049  8,7  4.3  0.076  0.0019  4.3  4. 3  0.077, 6  0.0017  2. 2  4.3  0.079^ 6  0.0014  c a n be w r i t t e n  as  2  0.0087  equation  Cc-i).  -dX/dt  where of  I and  =  I -  the above p l o t  respectively  Integration (C-2).  SX  S are the i n t e r c e p t  . . . . (C-l)  and n e g a t i v e and  of equation  f  X  =  C  3  of the  slope  / [Mo ] ^, [ S ] ^ .  (C-l) gives  equation  X  Where  =  [I/S]  where  very  f o r the averaged  data  ) > 26 a n d t h e d i f f e r e n c e s  the observed  was  (C-2)  constant.  calculated  ( [ S ] .j,/[Mo ]  from  ment  exp[-St]  B i s the i n t e g r a t i o n B was  X  - B  good  values [less  a r e shown  than  of  calculated  i n Figure  1% d i f f e r e n c e ]  of the case  C-5.  Agree-  except  at the 2-  initial is  and f i n a l  expected  parts,  to r a i s e  where  the e f f e c t  the observed  value  of species  larger  MoS^  than the  calculated. Discussion  The model  results  i n which  species  MoO  S.  obtained  a rapid 2-  which  above  equilibrium further  are consistent  i s established  reacts  t o form +H S,k  +H S  2  0  MoO  2-  MoCKS  4  rapid  then  = k C 3  2  3  23  (C-3)  [H S] - k_ C 2  ([Mo] T  3 ^ are s t a b i l i t y  aqueous  form  2-  MoOS  3  C ) 3  ,  hydrogen  constants,  [ H  2  S ]  IH SJ  +  2  a = 1  of  MoOS„  2-  3 = a  where  to  a  equilibrium  dC /dt 3  2-  with  +  [H S]  s u l p h i d e and, at  2  e  1  2  B  2  [ H  2  S ]  2  i s the c o n c e n t r a t i o n  constant  temperature  200  7  Y o b s  -i  8 * " e.5 r  AY  -O.lh  Time  mm. Fig.C5  TEST  OF  INTEGRAL EQUATION, A Y = Ycjjg ~ X;alc Y =C  /Mo S  3  T  Fig.C6 C  T  PL0T FOR  EQUATION  4 t  C-5  Mo = I x ICT  4  T  S  =196  T  M.  ii  NH =NH+ = 1.0 M. 3  C4/C3  201 and  pH, i t i s r e l a t e d  sulphide  species,  [H S]  = Y  2  where of  K^,  Kg  aqueous  Y = 1/[(1 +  f  are the f i r s t  2  concentration  of  free  S^, b y t h e e q u a t i o n :  S ,  hydrogen The  to the t o t a l  (K  /[H ])  +' ( K  +  s l  and second  S  1  K  /[H ] )] +  S  2  dissociation  2  constant  sulphide.  equation  (C-3) b e c o m e s  equation  (C-4) b y  substitution.  dC =  [Mo]  [k aY 3  T  S ] f  -  [k aYS 3  f  + k_ ] C  . . . .  3  (C-4)  dt  Dividing  by  [Mo] [S] T  T  d(C /[Mo] [S] )/dt 3  T  T  yields  =  [k ayS /[S] ] 3  f  T  -  [k a S 3  Y  f  + k_ ] 3  (C /[Mo] [S] ) 3  At  high  Thus  a  f  «[ S ]  T  1  -  the f i r s t  term  concentration  which  fficient  also  tration  T  sulphide concentrations  S  and  T  will i f  k„ay[S]  will  be i n d e p e n d e n t  agrees  with  of the sulphide  the observation.  be i n d e p e n d e n t  of the sulphide  i s insignificant  compared  The  coe-  concenwith  k „.  202 k_  and  3  the  k^aytSj^were  inter.cept  equation Table  I,  and  C-l.  the .  calculated  slope results  and  are  the  observed  [ S ] ^ , by  seen  magnitude  of  i n c o l u m n s '6 l a n d  7  of  •  [k a S ]  =  I  • [S]  k_  =  S  -  found  The  values  the f o l l o w i n g  '  3  The  S  from  Y  f  3  justifies  second  order  the  rate  I  T  • [S]  above  T  argument.  constant,  k  , was  estimated  i  for  the  the  literature  H^S.  first  The  group  by  values  value  of  found  Similar  putting  a  =  1,  dissociation  was  2.3  x  calculation  10  was  2  [S]^  =  [S]  constants  M.  -1  min.  performed  -1!  T  and  f o r NH^  by  and  (Note)  f o r the  variation  2of  the  tion  concentration  reaction  MoOS  of  species  mechanism  +  2  3  also  H S 2 ,  -  0  k  dC /dt  =  4  (Note)  -  The NH. 4  k [H S] 4  2  seemed  MoS. 4  C  3  following values =  H  +  H S 2 aq  -  H  +  HS~  =  H  +  0  -4  +  +  NH  +  HS~  3  + s -  MoS^  -  and to  the  equilibra-  apply:  2  .,  k_ C 4  were  4  used  for  calculation  P N  =  9 .50  P S1  =  6  .97  12  .89  K  R  2  P K  S2  =  ref .  37  203 Division  by  gives  (dC /dt)/C A  The  plot  of  The  linearity  calculated  (d.C /dt)/C 4  seems  For [NH C  2  /  C  + 4  ]  3  = =  ~  1  The  error  the  rate  A  A  C  C  3  /  4  /  The  C  C  3  =  4  =  1 0  by  k  3  [  of  k_  =  4  4  =  70  of  2  rate  was  ~  H  2  4  relatively  M.  in  fact  that  shift  S  ]  of  at  room  would  obtained  C  2  2  /  C  3  3  error  general  of  rate  temperature,  not  were  poor.  equilibrium  x  equilibrium  ~  10~  M. ,  3  c i  i  in Part /  =  c 3  0.1  1, ~  "  k_ ]  k A  min. of  CH  At  4  10  was  interfere  the of  order  2  S3 +  *  in  amounts  molybdenum  of  10  equilibration  the  by  using  k_ C /C ] 4  reduction  4  At  3  =  0.05At  0.02At  equilibration the  estimated  above, i . e . ,  -3  -  4  in  k  disappearance  the  C-6  min.  the 20  (C-5)  in Figure  constants  to  maximum  at  -2 was  . . . .  3  i s shown  3  the  k. 4  T  (C /C )  4  [C /C ]  study  [S]  [k [H S]C /C  the  -  -  equation  [  S ]  and  ^,  the  1 M.  the  estimated  rate  ] =  3  of  2  accuracy  min.  most  [ NH_  hold  the  0.03  [ H  4  against  3  to  although  k _ . = -4  k  =  3  50%.  The  high  temperature  .  view  -1 min. was  of  In the  reaction reaction.  same at  of  the  order 150°C.  1,  

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