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Hydrothermal treatment of nickeliferous laterite with ferric chloride solutions Munroe, Norman Donald Hollingsworth 1981

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HYDROTHERMAL TREATMENT OF NICKELIFEROUS LATERITE WITH FERRIC CHLORIDE SOLUTIONS by NORMAN DONALD HOLLINGSWORTH MUNROE B.Sc. (Chemistry, Physics), University of Dar Es-Salaam. 1973 M.Phil (Mineral Process Engineering), University of Leeds, 1977  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES The Department of Metallurgical Engineering  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA October, 1981 (c) Norman Donald Hollingsworth Munroe, 1981  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the  requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make it  f r e e l y a v a i l a b l e f o r reference  and study.  I further  agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by t h e head o f my department o r by h i s o r h e r r e p r e s e n t a t i v e s .  It i s  understood t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l gain  s h a l l n o t be allowed without my  permission.  Department o f  L  Mf^LUJ(LCHOB  The U n i v e r s i t y o f B r i t i s h 2075 Wesbrook P l a c e Vancouver, Canada' V6T 1W5 Date  Mil.  /VqV.  Columbia  1981  Nfe^HiNG-  written  ABSTRACT  The e x t r a c t i o n of n i c k e l laterite,  and c o b a l t , from  together with the hydrothermal  hematite has been i n v e s t i g a t e d .  nickeliferous  p r e c i p i t a t i o n of  In order to emphasize the  relevance and s i g n i f i c a n c e of t h i s process, an a p p r a i s a l i s made of the s t a t e of the n i c k e l , c o b a l t and A c o m p i l a t i o n of the annual on the world market  aqueous s o l u t i o n  i s included with an examination of the and  cobalt.  r e l a t i o n s h i p s f o r iron are reviewed  p o s i t i o n and temperature. elevated temperatures  in terms  ( I I I ) compounds in of pH, s o l u t i o n com-  The thermodynamic data used at  between 60°C (333°K) and 200°C (473°K)  have been estimated by using the "Entropy p r i n c i p l e " method of C r i s s and Coble. i s shown in Appendix  c o n c e n t r a t i o n , (c) h y d r o c h l o r i c acid pulp d e n s i t y were studied  temperature  correspondence  A sample  calculation  A.  The e f f e c t s of (a) temperature;  conditions.  industries.  production of the r e s p e c t i v e ores  f u t u r e uses and demand of n i c k e l  Solubility  iron  chloride  c o n c e n t r a t i o n and  (d)  in order to evaluate e x t r a c t i o n  G e n e r a l l y , metal and f e r r i c  (b) f e r r i c  extraction  increased with  chloride concentration.  over 90 percent of the n i c k e l ii  was  At 423°K,  e x t r a c t e d with a f e r r i c  c h l o r i d e c o n c e n t r a t i o n g r e a t e r than  1M.  Since  appreciable  amounts of gangue d i s s o l v e d under most c o n d i t i o n s , thereby consuming a c i d , a d i s c u s s i o n on the recovery acid  is  presented.  Filtration ficult,  of h y d r o c h l o r i c  of the p r e c i p i t a t e d  hematite has  because of the very f i n e nature  An overview of the n u c l e a t i o n and supersaturated  s o l u t i o n s has  of the  proved  dif-  particles.  growth of p a r t i c l e s in  t h e r e f o r e been i n c l u d e d .  This  phenomenon i s used to d e s c r i b e the phase changes which occurred  during l e a c h i n g experiments, and  proach by which coarser p a r t i c l e s might be  iii  to propose an achieved.  ap-  TABLE  OF CONTENTS Page  Abstract  1 1  Table o f Contents  i  L i s t of Tables  1 X  L i s t of F i g u r e s  x  Acknowledgements  .  '  v  i l  X 1 V  Chapter 1  INTRODUCTION  1  1.1  General  1.2  Mineralogy of L a t e r i t e 1.2.1  1.3  1.4  1.5  Ore D e p o s i t s  D e f i n i t i o n and Nature o f N i c k e l i f e r o u s  3  Limonites.  5  E c o n o m i c s , Market Survey and Mine P r o d u c t i o n o f N i c k e l . .  6  1.3.1  S t a t e o f the N i c k e l  Industry  1.3.2  Marketed N i c k e l P r o d u c t s  1.3.3  S t a t e o f the N i c k e l M a r k e t ,  1.3.4  Prices,....  1.3.5  Resources - Reserves o f N i c k e l  1.3.6  Uses  6  1 2  14 1 4  19 1 9  Economics, Market Survey and Mine P r o d u c t i o n o f C o b a l t . .  21  1.4.1  S t a t e o f the C o b a l t Market and I n d u s t r y  21  1.4.2  Resources - Reserves o f C o b a l t  22  1.4.3  Production of Cobalt  25  Iron Ore - Market Relevance t o I r o n Residue  26  1.5.1  26  The S t a t e o f S t e e l P r o d u c t i o n  iv  Chapter  Page 1.5.2  The Role of the Iron Residue from Nickel-" •• Laterites in the Direct Reduction of Iron  1.5.3 1.6  2  (DRI) Industry  26  Outlook for the Future Use of the Iron Residue ..  31  Review of Existing Methods of Nickel Extraction from  1  Laterites  32  1.6.1  Laterite Processing Methods - General  32  1.6.2  Pressure Acid Leaching  34  1.6.3  Matte Smelting  35  1.6.4  Ferronickel Production  36  1.6.5  Selective Reduction Roast/Ammoniacal Leach  36  A REVIEW OF PREVIOUS INVESTIGATIONS ON DIRECT ACID LEACHING..  38  2.1  Direct Acid Leaching of Nickeliferous Laterites  38  2.1.1  Direct Leaching of Goethite  39  2.1.2  Mechanisms of Leaching of Goethite  43  2.1.3  Direct Leaching of Low Magnesium Limonites  46  2.2  Hydrothermal  Precipitation in Solutions Containing  Mainly Ferric Ions 2.2.1  47  Hydrolysis of Metal Species at Elevated Temperatures  47  2.2.2  Precipitation of Iron as Ferric Oxide  48  2.2.3  Hydrothermal  53  2.2.4  Hematite-Goethite Relations in Acid Solutions ...  2.2.5  The Effect of pH on the Solubility of Iron III  Precipitation of Iron III Compounds.  Compounds Without Complexing v  54  54  Chapter  Page 2.2.6  Considering the Ferric Ion--Hematite Equilibrium.  55  2.2.7  Considering the Ferric Ion--Goethite Equilibrium.  58  2.2.8  Considering the Ferric Ion--Ferric Hydroxide Equilibrium  2.3  58  Thermodynamic Considerations Underlying the Hydros'i. thermal Treatment of Nickel Laterite with Ferric  3  69  2.3.1  The Effect of Chloride Complexing  70  2.3.2  Temperature/pH Consideration  70  EXPERIMENTAL  72  3.1  72  Mineralogical Investigation 3.1.1  Energy D i s p e r s i v e  X-ray A n a l y s i s  3.1.2  X-ray Diffraction Analysis  v i a SEM .  72 73  3.2  Quantitative Chemical Analysis  73  3.3  Apparatus Design  74  3.4  Pressure Leaching Experiments  74  3.4.1  Experimental Procedure  74  3.4.2  Liquid/Solid Separation  78  3.5  4  Chloride  Analytical Methods  79  3.5.1  Atomic Absorption Analysis  79  3.5.2  Determination of "Free Acid"  80  RESULTS 4.1  84  The Leaching of Nickel iferous Laterite in Aqueous Ferric Chloride  84 vi  Chapter  Page  4.2  4.1.1  Effect of Temperature  84  4.1.2  Effect of Concentration  87  4.1.3  Effect of Pulp Density  87  The Leaching of Nickel iferous Laterite in Ferric Chloride/Hydrochloric Acid Solutions  4.3  4.4  90  Leaching of Nickeliferous Laterite in the Presence of Ferrous Chloride  93  Acid Consumption During a Batch Leach (423°K)  94  4.4.1  The Effect of Hydrolysis on Acid Consumption  96  4.4.2  "Free Acid" Concentrations  in Ferric Chloride  Solutions  1  99  4.5  The Determination of Leaching Equilibrium  99  4.6  Simulation of a Continuous Leaching Circuit  102  4.7  Morphology of the Iron Residue  103  4.7.1  Hematite from the Hydrolysis of Ferric Chloride..  103  4.7.2  Iron Residue from the Hydrothermal Treatment of Nickeliferous Laterite with Ferric Chloride  4.7.3  Solutions  107  Iron Residue from the Hydrothermal Treatment of  110  Nickeliferous Laterite with Ferric Chloride/ Hydrochloric Acid Solutions 4.8  Comparison of Nickeliferous Laterite and the Iron Residue by Electron Microanalysis  4.9  110  110  Comparison of Particles Found in Nickeliferous Laterite and the Iron Residue by Electron Microanalysis vii  114  Chapter 5  Page DISCUSSION  1 1 9  5.1  Review of Leaching Results  5.2  The Significance of Acidity During Hydrolysis  120  5.3  Nature of the Iron Residue  121  5.4  Hydrothermal Precipitation of Hematite in Super-  5.5  H  9  saturated Ferric Chloride Solutions  123  5.4.1  Homogeneous Nucleation  123  5.4.2  Growth of Nuclei  125  The Degree of Supersaturation for Hematite in a Goethite Saturated Solution  127  6  CONCLUSION  131  7  SUGGESTIONS FOR FUTURE WORK  133  7.1  133  Improvement in Experimental Procedure  REFERENCES APPENDICES A B  134  Criss and Cobble Calculations X-ray Diffraction Results  vi i i  138 1 5 1  LIST OF TABLES Table  Page  1.1  Distribution of Major Elements in Nickel i f erous Li.monites ...  7  1.2  Principal World Nickel Producers  9  1.3  World Nickel Mine Production, 1977, and Capacity 1977, 1978.. and 1980  11  1.4  Commercial Forms of Primary Nickel  13  1.5  Identified World Nickel Resources  20  1.6  Western World Cobalt Market Consumption Shares  23  1.7  World Raw Steel Production by Region  27  1.8  Direct-reduced Iron Processes Applied Commercially up to the End of 1979  28  1.9  Growth of World DRI Capacity  30  2.1  Activation Energies for Direct Dissolution of Hematite and Goethite  42  2.2  Equilibrium Data for the F e  2.3  The pH Corresponding to Various Activities of Ferric  3 +  — F e ^ — H 0 System 2  Ion in Equilibrium with Hematite  59  2.4  Equilibrium Data for the Fe —FeOOH—H 0 Metastable System..  2.5  The pH Corresponding to Various Activities of Ferric Ion  3+  2  in Equilibrium with Goethite 2.6  60  61  Equilibrium Data for the Fe —Fe(0H) —H 0 Metastable 3+  3  2  System 2.7  57  62  The pH Corresponding to Various Activities of Ferric Ions in Equilibrium with Ferric Hydroxide ix  63  Table 2.8  Page Theoretical Equilibrium pH at Various Temperatures and Activities for the F e  2.9  3 +  — F e ^ — H 0 Metastable System  64  2  Theoretical Equilibrium pH at Various Temperatures and Activities for the F e — FeOOH—H 3 +  n  2  Metastable System  65  3.1  Chemical Analysis of the Nickeliferous Laterite  75  3:2  pH values of Hydroxides in Equilibrium with their Metal Ions.  81  4.1  Metal Extraction from Nickel ferous Laterite with Aqueous FeCl y.  86  4.2  Leaching results in the Presence of "Free Acid" at 423°K  4.3  Leaching Results in the Presence of FeCl at a Pulp Density 94  Acid Consumption During a Batch Leach at 423°K with a Pulp Density of 400 g/1  4.5  95  Comparison of "Free Acid" Concentration in Filtrates with Acid Concentration Due to the Hydrolysis of FeCl  3  4.6  Iron Precipitation from FeCl Solutions at 423°K  4.7  Percentage Nickel Extraction from Nickeliferous Laterite  3  in the Presence of High Concentrations of Nickel 4.8  92  2  of 400 g/1 4.4  .  97 100  102  Percentage Metal Extraction in a Simulated Continuous Leaching Circuit  104  4.9  Chemical Analysis of the Iron Residue for Each Stage  106  5.1  Comparison of Raw Materials used in the Iron and Steel Industry  A.l  122  Best Values of a^, b^, a^., 3^. and S^ (H ) at Several Temperatures  144  x  Table A.2  Page Standard Free Energies, Entropies and Partial Molal Ionic Heat Capacities Adopted for Species Participating in 3+ Reactions Considered in the Fe —H^O System  A.3  145  Summary of Average Heat Capacities Over the Ranges of 298°K to Upper Limits of 333°, 373°, 423° and 473°K (Estimated by  A. 4 B. l  the Correspondence Principle)  149  Summary of Computations of the Free Energy of Hydrolysis 3+ Reactions Considered in the Fe — H,,0 System X-ray Diffraction Patterns of Goethite Using K Radiation ...  150 152  a  B.2  X-ray Diffraction Patterns of Hematite Using K Fe a  Radiation B.3  153  X-ray Diffraction Patterns of Chromite Using K Fe a  Radiation  xi  154  LIST OF FIGURES  Figure  Page  1.1  Chemical composition of nickel laterite ore zones  4  1.2  Nickel producer inventories, 1967-1980 (Noncommunist World)..  1.3  Refined nickel production and producer deliveries, 1967-1980  1 5  (Noncommunist World),  ^  1.4  Noncommunist world nickel consumption  /  ^  2.1  The structure of diaspore and goethite (after Bragg)  -  41  2.2  Experimental temperature vs p H  2g8  diagram for the  F e — F e 0 — H 0 system 3+  2  2.3  3  ;  Free energy versus temperature for iron (III) hydrolysis 66  reactions 2.4  4 9  2  Influence of pH on the solubility of iron (III) hydroxides and oxide at 423°K  6 7  3+  2.5  Temperature versus pH diagram for the Fe  —Fe^O^—H^O 68  system 3.1  The l e a c h i n g apparatus  "  76  3.2  The  '  7 7  3.3  pH titration curves of metal chlorides in hydrochloric  pressure f i l t r a t i o n , device  82  acid versus sodium hydroxide 4.1  Effect of temperature on nickel extraction from 85  nickeliferous laterite 4.2 4.3  Effect of FeCl concentration on nickel extraction at 448°K..  8 8  3  Effect of pulp density on nickel extraction with 1M FeCl at 423°K  3 8 9  xi i  Figure 4.4  Page Effect of "Free Acid" strength at several FeCl  3  concentra-  tions on nickel extraction at 423°K, and a pulp density of 400 g/1 4.5  91  "Free Acid" concentration and percentage iron precipitation versus iron (III) concentration at 423°K  4.6  101  Metal extraction versus lixiviant composition at 423°K and a pulp density of 400 g/1  ' 105  4.7  Hematite particles precipitated from FeCI_ at 423°K  4.8  Iron residue obtained from the hydrothermal treatment of nickeliferous laterite with FeCl  4.9  108  3  109  3  Iron residue obtained from the hydrothermal treatment of nickerliferous laterite with FeCl /HCl  /  3  4.10  Main nickel-bearing particles (goethite)  4.11  SEM x-ray analyser spectra for nickeliferous laterite and  112  iron residue  113  4.12  Silicate particles after leaching in HC1/HN0  4.13  Magnetic particles found in nickeliferous laterite and  115  3  the iron residue 4.14  115  SEM x-ray analyser spectra for silicate and magnetic particles  4.15  —  ,"''117  SEM x-ray analyser spectra for magnetic particles in the iron residue  5,1  HI  • 118  Free energy of formation of spherical embryos as a function of the diameter for a series of temperatures  xi i i  126  ACKNOWLEDGEMENTS  I am p a r t i c u l a r l y Peters  f o r h i s s u p e r v i s i o n , keen i n t e r e s t  criticism -for  of t h i s r e p o r t .  h i s continuous  but s p i r i t u a l  Special  Dr. E.  and c o n s t r u c t i v e  I s i n c e r e l y thank him, not only  guidance  i n matters  of an academic  nature  as w e l l .  mention must be made of my w i f e , E l e i s e , who  gave me moral and  indebted to my S u p e r v i s o r  support  and i n s p i r a t i o n when d i f f i c u l t i e s  arose;  b e l i e v e me, there were many.  Thanks are a l s o extended to a l l members of the Department of .Metal 1 u r g i c a l Engineering f o r t h e i r cooperation and unendingassistance.  The  author  i s grateful  of Canada f o r f i n a n c i a l  to the National Research  support  As s i s t a n t s h i p.  xiv  Council  i n the form of a Research  1  Chapter 1  INTRODUCTION  1 .1  General The  m a j o r i t y of the world's known and a n t i c i p a t e d reserves  of n i c k e l  ores  are l a t e r i t i c  deposits.  Nickeliferous limonites,  which c o n s t i t u t e one of three zones of a t y p i c a l p o s i t , a r e a l s o f u t u r e sources  Laterites  u l t r a m a f i c rock. present  of c o b a l t , chromium and i r o n .  are near-surface  formed by extreme weathering  production  l a t e r i t e de-  deposits of o x i d i z e d m a t e r i a l  (or " l a t e r i z a t i o n " ) of parent  In c o n t r a s t , the m a j o r i t y of the world's of r e f i n e d n i c k e l  d e p o s i t s , which tend  i s from primary  to extend deep i n t o the e a r t h .  s u l p h i d e ores are r e l a t i v e l y easy to process combination of o r e - d r e s s i n g  sulphide Although  ( u s u a l l y by a  and p y r o m e t a l 1 u r g i c a l  techniques),  mining costs are e s c a l a t i n g and e s t a b l i s h e d mines are g e t t i n g deeper and o b t a i n i n g lower grade o r e . L a t e r i t e s , however, are q u i t e abundant and are much l e s s expensive to mine.  It i s an e s t a b l i s h e d f a c t laterites  that processing  costs f o r  are higher than sulphide ores, because of the  2  n e c e s s i t y of chemical ore.  and/or thermal  treatment  However, improved processing technology,  of the  entire  increased world  demand f o r n i c k e l , and d e p l e t i n g sulphide r e s e r v e s , i n d i c a t e the f u t u r e importance  of l a t e r i t e  ores.  At p r e s e n t , t h i s m a t e r i a l i s being t r e a t e d f o r n i c k e l c o b a l t recovery at Nicaro and Moa new  Bay,  Cuba,^ and  i n s t a l l a t i o n s are p r o j e c t e d f o r A u s t r a l i a ,  Caledonia and the Phi 1ippine- I s l a n d s . and chemical striking  of m a t e r i a l s from  s i m i l a r i t i e s , the methods used  of n i c k e l ferent. world  composition  and other d e s i r e d metal  duction of f e r r o n i c k e l  in an  the  New  mineralogy  these c o u n t r i e s show  f o r the e x t r a c t i o n  values can be q u i t e d i f -  Those which are i n commercial  i n c l u d e , pressure a c i d  a number of  Indonesia,  Although  and  o p e r a t i o n around the  l e a c h i n g , matte s m e l t i n g , proel ec.tr i c.:: or  b l a s t f u r n a c e , and 2  selective  The  r e d u c t i o n roast/ammoniacal  o b j e c t of t h i s r e p o r t i s to i n v e s t i g a t e the  of l e a c h i n g n i c k e l i f e r o u s tions.  In l i g h t  in l a t e r i t e s thermal  leach.  values.  solu-  present  s o l u t i o n with g o e t h i t e , hydro-  of the ore i s a useful method of s e p a r a t i n g Using a p p r o p r i a t e techniques, n i c k e l  c o b a l t can be recovered from  the leach s o l u t i o n .  other hand, i s hydrolyzed to hematite iron residue.  chloride  of the f a c t that most of the n i c k e l  occur i n s o l i d  treatment  i t s metal  l a t e r i t e with f e r r i c  chemistry  and  and  Iron, on the  is referred  to as the  3  1.2  Mineralogy All  of L a t e r i t e Ore Deposits  laterites  are formed by weathering  in areas of abundant r a i n f a l l . in t r o p i c a l  Deposits are t h e r e f o r e found  i n more temperate zones.  The  i n the u l t r a m a f i c rock u s u a l l y occurs as an ion r e p l a c e -  ment i n the s i l i c a t e  lattice  or as an a s s o c i a t e d s u l p h i d e .  Surface waters c o n t a i n i n g carbon the u l t r a m a f i c rock, c a r r y i n g of the metal of n i c k e l parent  rock  r e g i o n s , al though.'-some 1 a t e r i te  or s u b t r o p i c a l  d e p o s i t s are known to e x i s t nickel  of the parent  d i o x i d e leach n i c k e l  i t downward.  out of  Reprecipitation  deeper i n the ore d e p o s i t may cause an  enrichment  i n the range of 5 to 20 times the content o f the  rock.  Magnesia and s i l i c a  may be leached from  the parent  rock,  l e a v i n g varying c o n c e n t r a t i o n s of n i c k e l , c o b a l t , chromium, iron and aluminium i n the r e s i d u a l r e s u l t of the " 1 a t e r i z a t i o n " three d i s t i n c t chemical  process  zones o v e r l y i n g each other and varying i n  in chemical  for a typical  composition  Figure 1.1 d e p i c t s  and ore type  ,  with  3 4  deposit. '  The three zones of a t y p i c a l  laterite  d e p o s i t a r e : the  leached or canga zone, the i r o n oxide or l i m o n i t i c the s a p r o l i t i c  The end  i s the formation of  and m i n e r a l o g i c a l composition.  the v a r i a t i o n depth  s u r f a c e mantle.  or m a g n e s i u m - s i l i c a t e - r i c h zone.  zone, and Below the  Increasing Metal Content Figure 1 Chemical composition of nickel laterite ore zones. :  5  saprolitic  zone l i e s  the remaining  u n a l t e r e d parent  Any of the three zones may be extremely the t h i c k n e s s of i n d i v i d u a l meters. one  rock.  t h i n or absent,  while  zones may vary as much as 30-plus  Some d e p o s i t s may even be composed e n t i r e l y of almost  zone.  1.2.1  Definition  and Nature of N i c k e l i f e r o u s  Limonites  5  The  term  nickeliferous  nate, the i r o n oxide r i c h  limonite  amounts of other hydrous oxides.  varying  to d e s i g -  zone of a l a t e r i t e d e p o s i t .  s i s t s of a c r y p t o c r y s t a l 1 i n e mixture  chromite  i s used  I t con-  of g o e t h i t e , with minor  Hematite,  are accessory minerals commonly  maghemite and  present, along with  subordinate amounts of n i c k e l i f e r o u s p h y l 1 o s i 1 i c a t e s  of the montmori11onite and s e r p e n t i n e type. silicates  has  a significant  impact  The presence of  on the e f f i c i e n c y  of the  e x t r a c t i v e procedures, even though they contain l e s s than a tenth of the t o t a l  nickel.  Most l i m o n i t e s c o n t a i n at l e a s t 90 percent g o e t h i t e . Three-quarters  of the ore's n i c k e l  content occur i n s o l i d  and h a l f of i t s chromium  s o l u t i o n with the i r o n m i n e r a l s .  ever, more than 90 percent of the c o b a l t occurs t i o n with manganese  The  How-  in associa-  oxides.  only s p e c i f i c  nickel  mineral  detected i n l a t e r i t e s  6 is g a r n i e r i t e . an e q u i v a l e n t  I n v e s t i g a t i o n has of 15 mol  percent  amounts of adsorbed water. ing between 383°K and 685°K.  - 1.5  percent nickel  The  latter  and  to  considerable  i s released  upon heat-  temperature of dehydroxy1ation -  percent  limonites  chromium and and  analyze t y p i c a l l y  n i c k e l , 0.1 45  - 0.2  percent  - 50 percent  be considered  iron.  iron.  nickeliferous  range -  3.0  In a d d i t i o n to important as a  A l l four metals should  as p o t e n t i a l market  Table 1.1  in the  c o b a l t , 1.5  c o b a l t , these ores are obviously  source of chromium and  1.3  diaspore,  presence of up  6  Nickeliferous 0.8  the  shown the  therefore  products.  shows the d i s t r i b u t i o n of major elements in limonites.  Economics, Market Survey -and-Mine'Production of • Ni ckel 1.3.1  State  of the Nickel  Salient i s to the played  i r o n and  statistics steel  Industry have revealed  i n d u s t r y and  in the development of the  Nickel's  greatest  value  where i t adds strength range of  temperatures.  the  current  key  how  corrosion  nickel  r o l e i t has  aerospace  i s i n a l l o y s with other and  vital  industry.  elements,  r e s i s t a n c e over a wide  7  Tab 1e 1.1  Distribution  of Major Elements  in Nickeliferous  Limonites  Di s t r i buti on Percent  Content Percent NICKEL Goethi te  a-FeOOH  Manganese Oxi des  0. 5 4  Y-Fe 0  2  75 - 95  - 20  5 - 15  0. 2 -  1  2 - 15  2  -  5  1 - 5  Manganese Oxi des  4  - 20  Maghemi te  0  -  Maghemi te Silicates  2  3  COBALT  0.3  80 - 100 0-20  CHROMIUM Goethite Spinel  10  1  50-70  - 30  30 - 50  IRON Goethi te  50  90+  8  Until posits  1870,  nickel  in China, Germany, Greece,  the United S t a t e s . New  A nickel  7  Caledonia in 1864  g a r n i e r i t e was  named.  of n i c k e l  1875  from  producer. pal  production was  The  silicate  ore was  New  until  Caledonia was 1905,  in the  the p r i n c i p a l  and  refineries  when Canada became the l e a d i n g  industries  Huntington,  remained the  princi-  in market economy of Caledonia  and  15 mines i n Canada, with several  f i r m a l s o operated  ore c o n c e n t r a t o r s , smelters  i n Canada, as well as a n i c k e l  in Clydach, Wales, and  source  I n t e r n a t i o n a l Nickel Company of  Canada, Ltd. (INCO) operated The  d i s c o v e r e d in  world.  the main n i c k e l  (see Table 1.2).  on standby.  de-  by G a m i e r , a f t e r whom the mineral  the f r e e world, were l o c a t e d in Canada, New Australia  to small  I t a l y , Norway, Sweden, and  Sudbury area of Canada has  source of n i c k e l  In 1977,  limited  carbonyl  a large integrated r o l l i n g  mill  refinery at  West V i r g i n i a .  Falconbridge Nickel Mines Ltd. operated mines, concentrators and  smelters in Ontario and Manitoba.  Smelted  matte  shipped to the f i r m ' s r e f i n e r y at K r i s t i a n s a n d , Norway. t h i s f a c i l i t y , cathode nickel  n i c k e l , nickel  sulphate were produced  was At  p l a t i n g anodes and  along with other a s s o c i a t e d  metals.  S h e r r i t t Gordon Mines Ltd. p r e s e n t l y operates a r e f i n e r y  Table 1.2  Principal World Nickel Producers  Country  Nickel Products  Company  Nickel metal and matte. Nickel oxide and mixed nickel-cobalt sulfides. Nickel-copper-cobalt matte. Nickel oxide sinter, soluble nickel oxide, nickel metal (cathode and p e l l e t s ) , u t i l i t y shot and pig. Nickel-copper matte. Nickel metal. Nickel oxide and sulphide. Ferronickel.  Dominican Republic.  Nickel  metal, oxide, salts.  tARCO-Socie'te' Miniere el Metallurgique de tarymna S.A. . .  Ferronickel.  Exploraciones y Explotaciones Hineras Izabel (Inco Ltd.).  Nickel matte. Nickel matte. Ferronickel. Nickel metal. Nickel metal. Ferronickel. Ferronickel. Ferronickel. Ferronickel. Ferronickel. Ferronickel. Nickel oxide. Nickel oxide. Nickel oxide. Ferronickel shot, matte. Nickel metal. Nickel briquets, powder, nickel-cobalt sulfides.. Nickel metal. Nickel matte. Nickel metal and nickel-cobalt salts. Ferronickel. Nickel briquets and powder.  U.S.S.R  Nickel metal and matte.  10  at Fort Saskatchewan, A l b e r t a , using imported and  high grade concentrates  nickel materials  from INCO's Mine in Thompson Mani-  toba, a f t e r the former company shut down i t s Lynn Lake mine in  1977.  In c o u n t r i e s with c e n t r a l l y c o n t r o l l e d U.S.S.R. produced 80 percent of a l l n i c k e l  economies, the output.  The  l a t e r i t e mines i n Cuba r e p o r t e d l y produced most of the  The was  principal  nickel  S o c i e t e Metal 1urgique  operated  mines and  past, SLN exported  producer  Le N i c k e l ,  a ferronickel  together with  of n i c k e l  the f i r m operated  In the  t i o n of a new  Independant Des  Mines have  ore to Japan.  during 1977.  several mines and  a smelter at K a l g o o r l i e and  the l a r g e s t  In Western  producer  Australia  a c o n c e n t r a t o r at Kambalda,  a refinery  at Kwinana.  Installa-  high c a p a c i t y s h a f t smelting furnace was  pleted  in l a t e 1978.  nickel  matte and  Since then, the company has  concentrate  1977  smelter at Doniambo.  Corporation Ltd. was  in A u s t r a l i a  (SLN).  in  company  Le Syndicat  S.A.  Caledonia  rest.  The  l a r g e tonnages of n i c k e l  Western Mining  i n New  nickel  com-  exported  to Japan.  g Table capacities  1.3  lists  by country.  production was  the 1977 As  nickel  production and p r o j e c t e d  i s shown, 25 percent of a l l n i c k e l  d e r i v e d from n i c k e l  l a t e r i t e s w h i l s t 80  percent  Table 1.3  World Nickel Mine Production, 1977, and Capacity 1977, 1973, and 1980 (Thousands  Production in 19/7 North America: United States Canada Total Central America and Caribbean Islands: Cuba Dominican Republic Guatemala Total Europe: Poland U.S.S.R. Other! Total Oceania: Australia New Caledonia Total Asia: Indonesia Philippines Total Africa: Botswana Rhodesia, Southern South A f r i c a , Republic of Total Other World Total  Tons)  Capacity 1977  1978  1980  13.7 259.4  18 275  18 275  16 275  273.1  293  293  291  40.6 26.7  42 37  --  --  42 37 10  52 37 14  67.3  79  89  103  3.1 158.0 21.4  3 170 50  3 170 50  4 210 70  182.5  223  223  284  94.5 120.2  95 150  95 150  115 170  214.7  ' 245  245  285  15.4 16.5  29 35  29 35  70 55  31.9  64  64  125  13.3 17.6 25.4  20 17 25  20 17 25  20 22 28  56.3 25.2  62 25  62 25  70 752  851.0  991  Western Europe, principally Greece and Yugoslavia. Host expansion will occur in Central and South America.  1.001  1,233  12  of world in  r e s o u r c e s , e x c l u s i v e of seabed nodules,  are  contained  laterites.  1.3.2  Marketed Ni ckel Primary  cathodes,  Products  nickel  i s marketed i n the form of n i c k e l  powder, b r i q u e t s , r o n d e l l e s , p e l l e t s , i n g o t s , metal  shot, n i c k e l  oxide s i n t e r and  p o s i t i o n s of commercially  ferronickel.  The  produced primary  chemical  nickel  com-  forms are  Q  given i n Table 1.4. normally more than and  nickel The  oxide  Commercial 99.5  percent  nickel  i n these  pure except  forms i s  for ferronickel  sinter.  ferronickel  produced i n the United States contains  40 to 50 percent n i c k e l  and  i s sold  in 50-pound p i g s , whereas  that produced i n other c o u n t r i e s contains 20 to 38 nickel. new  Nickel oxide s i n t e r contains 76 percent n i c k e l .  product,  incomet, introduced in 1974,  percent n i c k e l sinter  and  has  The  nickel  oxide  produced only by Queens-  p r o p r i e t a r y in A u s t r a l i a .  availability  of carbonyl  p e l l e t s was  greatly in-  creased with the s t a r t up of INCO's Canadian Copper Refinery i n 1974.  increased due handling and  A  contains 94 to 96  replaced the 90 percent  introduced in Canada, but now  land n i c k e l  Nickel  percent  Demand f o r t h i s form of n i c k e l  to i t s high p u r i t y storage.  Cliff  (99. 97 p e r c e n t ) , ease of  has  Table 1 .4  Commercial Forms of Primary Nickel Composition, percent Ni  C  Cu  Fe  S  0.002  0.001  0  Co  Si  Cr  ...  ~ •• -  Pure unwrought nickel: Cathode  39:9  Pellets  99,97  0.01  0.005  .01  .0001  .0015  ...  .01  .001  .001  .002  .0035  Powder  99.74  .1  Briquets  99.9  . .01  .0003  99,25  ..022  20-50  1.5-1.8  —  Balance  76,0  —  .75  .3  .006  Nickel chloride  24,70  ...  —  —  —  Nickel nitrate  20,19  —  ...  ...  ...  Nickel  20.90  Rondelles 2  Ferronickel^ Nickel oxide Nickel s a l t s :  .046  .087  .004  0.00005  —  0.15  —  .03 .37 (2)  .3 1.0  —  ...  . — —  .042  ...  ...  1.8-4  Balance  ...  —  —  ...  ...  3  sulfate  Ranges used to denote variable grades produced. Cobalt (1 to 2 percent) included with nickel. 'Theoretical nickel content.  ...  "--  1.2-1.8  ...  14  1.3.3  State of the Nickel Market Sharp swings i n . n i c k e l  duction  have occurred  since 1967.  producer i n v e n t o r i e s during d e c l i n e in 1978-1979.  deliveries  and  A significant  1975-1977 was  However, during  r e f i n e d probuildup  followed  1981  of  by a steep  a modest  increase  in producer i n v e n t o r i e s i s a n t i c i p a t e d .  The  short and  illustrated g and  drastic  in the f o l l o w i n g c h a r t s .  1.4.  See  Figures  Recent market s t u d i e s suggest that the  growth in n i c k e l  consumption of 6 percent  weaken in 1975-1976. year  i s a reasonable  1985  and  It i s now  capital  utilization  a s s o c i a t e d with  estimated  per year  1.2,  The  4 percent  spending w i l l of n i c k e l  will  coal p r o c e s s i n g , o i l and  1.3  began to  that 4 percent  per  through  trend assumes that  be s t i m u l a t e d , and occur  are  historical  y a r d s t i c k f o r growth expectations  p o s s i b l y in 1990.  the rate of creased  swings in consumption patterns  that i n -  in energy programs gas  drilling  and  the development of the n i c k e l - z i n c b a t t e r y . 1.3.4  Prices In 1980,  across-the-board tive  reasons.  following  INCO introduced  discount  a temporary 6  from published  percent  p r i c e s f o r competi-  Further p r i c e e r o s i o n i s not expected f o r the  reasons:  15  Figure 1.2  Nickel producer inventories, 1967-1980 (Noncommunist World).  16  Refined nickel production and producer deliveries, 1967-80 (Noncommunist World) 1.400  1,200  1.000  1966  1968  1970  1972  1974  1976  1978  1980  Year end —-—  Figure 1.3  Refined nickel production 1967-79 Refined nickel producer deliveries 1S67-79 Estimate Estimate  Refined nickel production and producer deliveries, 1967-80 (Noncommunist World).  17  F i g u r e 1.4 t  Noncommunist World n i c k e l  consumption.  18  1)  Producer  inventories will  able l e v e l s and  be maintained  at more reason-  consumer i n v e n t o r i e s now  stand at a low  1evel . 2)  Production cutbacks producers  have been i n i t i a t e d  by the major  in order to keep i n v e n t o r i e s in l i n e  with  demand. 3)  Production costs have continued to e s c a l a t e s h a r p l y . Nickel account  products  d e r i v e d from  l a t e r i t e ores  f o r about 45 percent of non-communist  production) are under s p e c i a l tain  laterite  based  cost pressure.  facilities,  60 percent of the t o t a l 4)  (which  energy  world At c e r -  costs are  production c o s t .  Under present economic circumstances, the published price, of $3.45 (U.S.) per pound does not y i e l d adequate return on  Over the longer term  portation  sectors.  anticipated i d l e standby  through  however, n i c k e l  markets face an  Normal l e v e l s of n i c k e l 1982,  c a p a c i t y may  be r e q u i r e d .  consumption  are  currently  In other words, the  not yet run i t s course, but  confidence are growing, now  ahead.  and t r a n s -  by which time, some of the  c u r r e n t market weakness has mism and  an  investment.  impressive b u i l d i n g of l a t e n t demand in the energy  lies  50-  opti-  that stronger demand  19  1.3.5  Resources - Reserves of Nickel Total  estimated  at 230  were 60 m i l l i o n  i d e n t i f i e d resources of n i c k e l m i l l i o n tonnes, w h i l s t world tonnes.  the combined sulphide and  figure  nickel  reserves  g  A r e p o r t from the U.S.  mately 7 b i l l i o n  have been  Geological S u r v e y ^ indicated  l a t e r i t e world  tonnes averaging  resource was  about 1 percent  that  approxi-  nickel.  This  appears to be very modest, because counting only d e p o s i t s  in c o u n t r i e s bordering on the Caribbean  and  Islands of the  Western P a c i f i c , the tonnage of ni ckel i ferous l a t e r i t e s ana-: l y s i n g more than 0.8  percent n i c k e l  cent c o b a l t , amounts to at l e a s t  1.3.6  and  averaging  10 b i l l i o n  about 0.1  per-  tonnes.  Uses In 1979,  pure unwrought n i c k e l  cent of the t o t a l primary  nickel  c o n s t i t u t e d 68  market; f e r r o n i c k e l , 20  perper-  8 cent; and  nickel  oxide  were u t i l i z e d mainly  s i n t e r , 11 percent.  i n the production of n i c k e l  products, h i g h - n i c k e l heat copper-base a l l o y s and  the oxide  stainless  and  and  and  in e l e c t r o p l a t i n g ,  steels.  pure forms wrought  corrosion-resistant alloys,  s i n t e r were used l a r g e l y alloy  The  whereas  ferronickel  i n the production  of  20  Table 1.5  Identified World Nickel Resources (Thousand Tons)  Reserves North America: United States Canada  Other , Resources  Total Resources  200 8,700  14,900 12,500  15,100 21,200  8,900 2,300  27,400 6,700  36,300 9,000  3,400 1,100 300  14,200 100 900 900  17,600 1,200 1,200 900  Total Europe: U.S.S.R.  4,800 8,100  16,100 13,200  20,900 21,300  Oceania: Australia Indonesia New Caledonia Philippines  5,600 7,800 15,000 5,700  3,200 55,000 31,000 10,600  8,800 62,800 46,000 16,300  Total  34,100  99,800  133,900  460 900  3,640 600 700  4,100 1,500 700  1,360  4,940  6,300  60,000  168,000  228,000  760,000  760,000  Total Africa Central America and Caribbean: Islands: Cuba Dominican Republic Guatemala Puerto Rico  South America: Brazil Colombia Venezuela Total 2 World total (rounded) World total,seabed nodules  3  —  Derived in consultation with U.S. Geological Survey and revised March 1978. 2 Excludes nickel associated with seabed manganese nodules. 3 Based on Holser, 1975 paramarginal resource estimate of 76 billion dry short tons of sea nodules and the NMAB-323, 1976 estimate of average nodule composition of 1 percent copper, 1 percent nickel, 24 percent manganese, and 0.35 percent cobalt.  21  The approximate  c u r r e n t use pattern of n i c k e l  i s shown  below: Percentage of A l l Nickel  Uses Stainless Nickel  steels  41  plate  High n i c k e l Nimonic  16 alloys  alloys  (monels, coinage)  12  (60% N i ) , Cr, Fe  10  Iron and s t e e l c a s t i n g s  9  Copper  3  and brass products  Others ( b a t t e r i e s , magnets, c a t a l y s t s )  9 100  1.4  Economics, Market 1.4.1  State of the Cobalt Market and Industry World  1980 remained nes.  c o b a l t production from primary sources i n  unchanged from the previous year at 26,000 ton-  Secondary  percent.  Survey and Mine Production of Cobalt  production increased to 1,000 tonnes, up 20  However, real  consumption  cent bel ow the 1 979 l e v e l . ing, It  sumption, ing  Moreover,  the apparent consumption i s generally f e l t increased  fell  fell  as a r e s u l t of destock4  by as much as 35 percent.  that the combined substitution  as much as 15 per-  e f f e c t s of lower con-  and unprecedented destock-  reversed the world c o b a l t demand equation f o r 1980.  22  Cobalt's use i n high performance guarantees i t s continued growth prices. tively  services  practically  i n demand, r e g a r d l e s s of high  There are two areas i n which c o b a l t seems to be immune to s u b s t i t u t i o n  twenty y e a r s .  rela-  i n the time horizon of ten to  These are super a l l o y s and c a t a l y s t s .  Super  a l l o y s are p r i m a r i l y used i n three major growth areas: 1)  Turbines and j e t engines.  2)  Surgical  3)  Oil f i e l d  implants. goods.  In a p p l i c a t i o n s where the high temperature performance i s c r u c i a l , p r o p e r t i e s imparted by c o b a l t are so v a l u a b l e the p r i c e  that  i s l e s s important than long-term a v a i l a b i l i t y .  The second most important m e t a l l u r g i c a l in magnets.  use of c o b a l t i s  Permanent magnets of the a l n i c o v a r i e t y , which  e x h i b i t e x c e l l e n t magnetic p r o p e r t i e s , have t r a d i t i o n a l l y a large consumer of c o b a l t .  Recently, however, t h i s demand '  f o r the metal has been d e c l i n i n g ferrites  as a s u b s t i t u t e .  been  due to the advent of hard  The approximate c u r r e n t use pat-  tern of cobalt, i s shown in Table 1 . 6 .  1.4.2  Resources - Reserves of Cobalt Most c o b a l t resources are only a v a i l a b l e as by-  products of mining f o r more abundant  elements.  Only the  23  Table 1.6  Western  World  Cobalt Market  Consumption  Shares  9 (Percentage)  1970  1980  1990  20  16  17  5  7  8  Superalloys and Other Alloys  45  47  40  Ceramics and Enamel -  12  10  8  Chemicals  18  20  27  Magnetic Alloys  Cemented Carbides  Estimated  1  24  Moroccon Bouazzer deposit sitate  i s of a high enough grade to neces-  production of c o b a l t as the p r i n c i p a l  Much of the world's i d e n t i f i e d of  lateritic  Philippines,  nickel  resources are i n the form  ores i n t r o p i c a l  Indonesia  duction from l a t e r i t e s  metal.  r e g i o n s , such as the  and New C a l e d o n i a .  A u s t r a l i a n pro-  has become an i n c r e a s i n g l y  source as has the Cuban.  N e v e r t h e l e s s , most c o b a l t  significant currently  comes from sulphide and oxide deposits i n Z a i r e , Zambia, Finland and Canada. Reserves It has been estimated that the world's c o n t i n e n t a l r e sources amount to some 9 m i l l i o n mation by country i s o u t l i n e d  3,090,000 tonnes  Zambia  1,704,000 tonnes  Cuba  1 ,049,000 tonnes  USA  764,000 tonnes  Canada  249,000 tonnes  Zaire  An e s t i -  as f o l l o w s :  Zaire  Of these r e s o u r c e s ,  from a t o t a l  tonnes of c o b a l t .  the estimated reserves a r e : 1,520,000 tonnes  42%  Zambia  699,000 tonnes  19%  Canada  20,000 tonnes  reserve of 3 ,618,000 tonnes.  0.5%  To t h i s can be added  a f u r t h e r 1 2 mi 11ion tonnes resource h o i s t a b l e from the sea bed.  25  Thus, i t can be seen that Z a i r e and Zambia possess 53 percent of.the  known, land resource  1.4.3  Production The  lated  and 51 percent  of the proven  of Cobalt  s i g n i f i c a n c e of these reserves  i n t o production  reserves.  has been t r a n s -  and the c o n t r i b u t i o n of Central  Africa  i s as f o l l o w s : During the period  1925-1975 Z a i r e produced 947,500 tonnes 1933-1975 Zambia produced 51,993 tonnes  and  more r e c e n t l y : Zaire (tonnes)  Zambia (tonnes)  Canada (tonnes)  World (tonnes )  1 976  10,700  1 ,700  1 ,900  17,400  1977  10,200  1 ,700  1 ,400  17,435  1 978  12,300  1 ,800  1 ,450  20,090  1979  12,000  3,000  1 ,600  21,800  1980  13,400  3,000  -  23,214  Hence,  the Central A.fri can  producer of some 70 percent  source i s e s t a b l i s h e d as the of the world's  cobalt.  26  1.5  Iron Ore 1.5.1  - Market Relevance to Iron Residue  The  State of Steel  World s t e e l annually and  since 1977,  Steel  717.7  million  recession Europe. there  p r o j e c t e d by the  ( I I S I ) , to f a l l  tonnes.  in the  p r o d u c t i o n , which had  was  Institute  Production  This was  i r o n and  by 4 percent  in 1980  to  to a s t a t e of  i n d u s t r y in North America  and  However, d e c l i n e i s not the whole p i c t u r e , because  i s an a n t i c i p a t e d increase in s t e e l  percent  advancing  I n t e r n a t i o n a l Iron  p r i m a r i l y due  steel  been  in eastern bloc c o u n t r i e s , and  output  3.6  of about  percent  in  2.2  develop-  ing c o u n t r i e s .  It was ficant  expected  production  that three c o u n t r i e s would record  i n c r e a s e s in 1980.  percent, B r a z i l  up by about 10.7  by 13.1  over  the 1979  Role  of the  percent  1.5.2  The  in the  scaled  by the end  had  and  9.8  South Korea up  figures.  Iron Residue from N i c k e l - L a t e r i t e s of Iron  o p e r a t i o n s , 12 d i r e c t  been a p p l i e d commercially  of 1979  up by about  (DRI)  a r a t h e r u n c e r t a i n s t a r t with  up commercial  processes  percent  D i r e c t Reduction  Despite  Italy  signi-  (see Table  1.8).  Industry regards  reduction  to  iron  throughout the  world  27  Table 1.7  World Raw Steel Production by Region (Million Tonnes)  1977  7088  World  Projected 1980  Percentage Change 1979-1980  1978  1979  712.5  747.4  717  - 4.0  U.S.  132.2  123.8  123.3  100.8  -18.2  Japan  117.1  102.1  111.7  111 .8  0  E.E.C.  155.6  132.4  140.0  128.4  - 8.2  31.1  46.6  55.6  57.6  + 3.6  185.1  211.9  209.4  214.4  + 2.2  Developing Countries  Eastern Europe  Source:  International Iron & Steel Institute.  Table 1.8  Direct-reduced Iron Processes Applied Commercially at Year-end 1979  Process  Product  Reductant  Type and Equipment Gas  Sponge iron, lump, or pellets.  Vertical Shaft  Gas  Sponge iron or lump.  Saggers in tunnel kiln  Coal or coke  Sponge iron or metal powder.  Shaft  Gas  Lump or pellets.  Shaft  Gas  Lump or pellets.  Fluid bed  Gas  Iron briquets.  SL/RN  Rotary kiln  Coal or coke  Lump, pellets, fines, or briquets.  Kinglor-Metor  Rotary kiln  Coal or coke  Lump or pellets.  Esso (FIOR)  Fluid bed  Gas  Briquets  Purofer  Shaft  Gas  Lump or pellets.  Krupp  Rotary kiln  Coal  Sponge iron.  Rotary kiln  Coal/oil/gas  Sponge iron.  Rotary kiln  Coal or coke  Pellets.  Sumitomo  Rotary kiln  Coal or coke  Pellets.  Kawasaki  Rotary kiln  Coke breeze  Pellets.  Batch  Hyl  Retort Hoganas  High-iron  briquets(HIB)  -Chalmers (ACCAR) Nippon Steel 1  1  1  designed to produce sponge iron from waste materials accumulated at integrated steel plants. oo  29  The steel  importance  of d i r e c t - r e d u c e d i r o n  i n d u s t r y i s reaching new  has  During  i n the past 10 years  percent to 20.46 m i l l i o n  It i s a n t i c i p a t e d that new  struction  world's  (see  the 11-year period 1970-1980, DRI c a p a c i t y  i n c r e a s e d over 970  year.  i n the  h e i g h t s , as demonstrated by the  r a p i d growth of p l a n t c a p a c i t i e s Table 1.9).  (DRI)  tonnes per  plants c u r r e n t l y  should take c a p a c i t y to over 31.0  under  con-  m i l l i o n tonnes by  1 982.  The  U.S.S.R. remains the worl d s .leader :in s t e e l 1  with an estimated output of 152 was  up 1.9  million  percent above the 1979  tonnes i n 1980,  figure.  output of 111.8  million  tonnes i n 1980,  cal  level.  However, the f i n a l  to the 1979  the world's  third  approximately  The  18.2  largest steel  which  Japan showed an  which was  producer,  percent i n 1980  production  almost  identi-  f i g u r e s f o r the  U.S.,  revealed a d e c l i n e of  output.  g r e a t e s t c o n c e n t r a t i o n of DRI  production i s l o c a t e d  in developing c o u n t r i e s , where e l e c t r i c - a r c s t e e l making, with its  low  investment  c o s t , i s very popular.  DRI  is attractive  in such nations because they do not have good sources of scrap f o r supplying i r o n u n i t s to t h e i r e l e c t r i c a l s o a growing i n t e r e s t means of d i l u t i n g taminate steel  i n DRI  producers  among developed  the u n d e s i r a b l e r e s i d u a l  t h e i r scrap s u p p l i e s .  furnaces.  There i s  c o u n t r i e s as a  elements which  F i n a l l y , a concern  i n c o u n t r i e s , such as the U.S.,  con-  of many  i s that the  Table 1 .9  Growth of World DRI c a p a c i t y  (Tonnes)  Year  Capacity  1970  1 ,906,000  1971  2,754,000  1972  3,324,000  1973  4,650,000  1974  5,775,000  1975  6,650,000  1976  7,810,000  1977  10,775,000  1978  14,325,000  1979  17,625,000  1980  20,460,000  31  r a p i d l y growing number of e l e c t r i c - a r c demand and these  furnaces w i l l  p r i c e of scrap beyond economical  f a c t o r s contribute: to the high l e v e l  The  DRI  high-grade  process  can be c l a s s i f i e d  i m p u r i t i e s , or those a high-grade  that can  concentrated  in.the.former  1.5.3  in a DRI  Outlook The  DRI.  limitations  on  It i s a n t i c i p a t e d  that  iron, residue could meet acceptable alumina  process.  f o r the Future  future u t i l i z a t i o n  residue from n i c k e l  in  that r e q u i r e  s p e c i f i c a t i o n s with regard to n i c k e l , chromium, and for u t i l i z a t i o n  A l l of  of i n t e r e s t  strict  the  r e j e c t the i m p u r i t i e s to produce  product.  case.treated  limits.  i n t o those  iron ore or agglomerates with  raise  laterites  Use  of the Iron Residue  of chemi cal 1 y t r e a t e d i ron  in DRI  processes  appearspromising  f o r the f o l l o w i n g reasons: 1)  The  DRI  processes  throughout  should continue  the world  to r i s e  as i n c r e a s e d use  in p o p u l a r i t y  i s made of  electric-  arc furnaces. 2)  The  g r e a t e s t c o n c e n t r a t i o n of DRI  located steel  i n developing  making, with  production w i l l  c o u n t r i e s , where  i t s low  investment  be  electric-arc c o s t , i s very  popular. 3)  The  U.S.  and  other developed  p o l i c y of h e l p i n g developing  nations have embarked on a c o u n t r i e s help  themselves.  32  4)  The l a r g e s t known t e r r e s t i a l  reserves  of n i c k i 1 i f e r o u s  l a t e r i t e s occur in developing c o u n t r i e s instances 5)  c l o s e to e x i s t i n g Bauxite  and i n some  Industries.  By-product c a u s t i c from the Bayer process can be employed f o r chromium e x t r a c t i o n  1.6  from the leached o r e .  Review of E x i s t i n g Methods of Nickel  Extraction  From  L a t e r i tes 1.6.1  L a t e r i t e Processing There are several  exist The on  Methods - General  commercial  alternatives  f o r the e x t r a c t i o n of n i c k e l from n i c k e l l a t e r i t e  choice several  of the e x t r a c t i o n  ores.  process employed, however depends  f a c t o r s such as:  1)  The p h y s i c a l  2)  The geographical  and chemical  nature of the ore body.  l o c a t i o n , which i s d i r e c t l y  supply arid cost of necessary raw m a t e r i a l s 3)  that  The m a r k e t a b i l i t y geographical  Several  r e l a t e d to  and energy.  of the end products, may depend on  location.  processes f o r the recovery of n i c k e l and c o b a l t  have been d e s c r i b e d ,  a l l of which, however, show some d i s -  advantages.  examples of these processes a r e : s'el.ec-  Typical  13 14 t i v e e x t r a c t i o n with d i l u t e acids, ' selective  33  conversion of n i c k e l o u s and hydrogen c h l o r i d e  1 5  '  1 6  '  cobaltous oxides with  and  1 7  selective  gaseous  r e d u c t i o n of the  above-mentioned oxides with carbon monoxide/carbon d i o x i d e mixtures, f o l 1 owed by e x t r a c t i o n with ammonia-ammonium  carbon-  1 ft  ate  solutions. 19  Van  Nes  and Heertjes  l a t e r d e s c r i b e d a method of i n -  c r e a s i n g the r a t i o of the amounts of n i c k e l respect to i r o n . oxide and  This was  c o b a l t oxide, almost  i n t o the corresponding used  realized  in which a gaseous mixture  c h l o r i d e was  passed  through  and  A step-wise  of steam and  a fluidized  bed  ore, under proper c o n d i t i o n s of temperature The  c o b a l t with  by c o n v e r t i n g n i c k e l  selectively  chlorides.  and  c h l o r i d e s were recovered by e x t r a c t i n g  completely, process  was  hydrogen of the granulated and c o n c e n t r a t i o n .  the  chloridized  ore with hot water. Roorda and Queneau, based ous  11  more r e c e n t l y proposed  a process,  on p y r o m e t a l 1 u r g i c a l s e l e c t i v e r e d u c t i o n of n i c k e l i f e r -  l i m o n i t e s , f o l l o w e d by aqueous c h l o r i n a t i o n  Though conducted  in seawater.  only on a l a b o r a t o r y s c a l e , process  were kept w i t h i n s p e c i f i c c o n s t r a i n t s , which could be industrially.  variables imposed  The methods employed were simple, f l e x i b l e  and  amenable to economic, l a r g e s c a l e , automated u n i t o p e r a t i o n s .  34  S i g n i f i c a n t advantages of t h i s process i n c l u d e : a high ery of n i c k e l and c o b a l t of over 90 percent,  recov-  the p o t e n t i a l  important source of chromium and i r o n due to c h l o r i n e of the o r e , r a p i d d i s s o l u t i o n rates which minimize circuit  c o s t s , the use of s a l t  f i n a l l y , the i n t r i n s i c  leaching  leaching  r a t h e r than f r e s h water and  s u p e r i o r i t y of c h l o r i d e systems i n  s o l v e n t e x t r a c t i o n with i t s a t t r a c t i v e process economics.  The pressure nickel  processes c u r r e n t l y i n commercial a c i d l e a c h i n g , matte s m e l t i n g ,  by e l e c t r i c or b l a s t furnace  roast/ammoniacal  1.6.2  Pressure A c i d  of f e r r o -  and s e l e c t i v e r e d u c t i o n  Leaching  ground ore i s s l u r r i e d  a c i d at high  production  include:  leach.  In the pressure and  operation  a c i d leach and leached  temperature and pressure,  522°K and 4.1 x 10  6  -2 Newtom metre" .  process,  finely  crushed  with d i l u t e s u l p h u r i c u s u a l l y i n excess of  At these temperatures  i r o n and aluminium form b a s i c sulphates  of low r e s i d u a l s o l u -  bility.  s o l u t i o n i s then  The r e s u l t i n g metal  containing  separated  from the s o l i d  thickners  and the metal values  tion  residues  p r e c i p i t a t e d by sulphide  ( u s u a l l y hydrogen s u l p h i d e ) .  product recovery l i q u o r followed  by means of dewatering  An a l t e r n a t i v e route to  i s solvent e x t r a c t i o n of the pregnant by  electrowinning.  addi-  leach  35  Recoveries ing  of d e s i r e d metal  are u s u a l l y very high.  very s e l e c t i v e . of  values by a c i d  leach  process-  Furthermore, a c i d l e a c h i n g i s not  Magnesia and alumina  consume excessive amounts  s u l p h u r i c a c i d , meaning that the feed ore must be low i n  these compounds or operating costs may become T h e r e f o r e , the a p p l i c a t i o n of a c i d narrow range of ore types.  prohibitive.  leaching i s limited  It should a l s o be noted  basic sulphate residue i s a source of environmental because of d i s s o l u t i o n  of sulphate and metal  to a  t h a t the pollution,  ions i n t o r u n - o f f  waters.  1.6.3  Matte  Smelting  In t h i s process, ground ore i s charged furnace  i n the presence  coke i s present  of coke, gypsum', and limestone.  as a reducing agent to convert n i c k e l  oxides to the metals. ide,  The gypsum i s reduced  which r e a c t s with the n i c k e l  sulphide matte. temperatures  and i r o n  and i r o n to produce a metal  In a d d i t i o n to the molten matte, the high  of the process  result  i n the formation of a molten  bility  of the slag and matte f a c i l i t a t e s  tion.  The molten n i c k e l - i r o n matte i s then  v e r t e r s to o x i d i z e the i r o n . iron-rich  what i s now the n i c k e l roasting  The  to calcium sulph-  slag by the remainder of the ore and limestone.  a secondary  to a b l a s t  their physical  A d d i t i o n of s i l i c a  flux  in nickel  produces  separated  Further refinement  followed by r e d u c t i o n r e s u l t  separa-  a i r blown i n con-  s l a g , which can be e a s i l y matte.  The i m i s c i -  from  by o x i d a t i o n  metal.  36  Matte smelting i s used the inherent s e l e c t i v i t y is  very energy  geographical  on a wide v a r i e t y of ores due  of the process.  intensive,  locations.  and may Sulphur  nickel  d i o x i d e gas emission  crude  Production  Ferronickel  production i s very s i m i l a r to that of  agent  i s added.  ferronickel  phosphorus i n a secondary  reduction  ferronickel  slag.  silica  ore  f u s i o n and  silicate  as carbon,  s i l i c o n , chromium, and  slag.  be t r e a t e d , but  those  are d e s i r a b l e because of the a b i l i t y  a good primary  sive, particularly  and  u s u a l l y o x i d i z e d i n a converter  Here, a wide range of ores may high in s i l i c a t e s  slag.  This process  i f electric  (high-silica  no  As a r e s u l t , the i n i t i a l  i s then  remove i m p u r i t i e s such  from  process.  Ferronickel  step produces a molten crude  to  of t h i s  i s an  matte p r o d u c t i o n , the major d i f f e r e n c e being.that  sulfidizing  The  process  be r u l e d out in c e r t a i n  unwanted, but unavoidable, by-product  1.6.4  However, the  to  to  i s very energy  smelting i s used  to melt a high-  ores have higher temperatures  r e q u i r e the accurate temperature  inten-  control  of  that can  be provided by e l e c t r i c f u r n a c e s ) .  1.6.5  S e l e c t i v e Reduction  Roast/Ammoniacal  Leach  The main o b j e c t i v e i n the s e l e c t i v e r o a s t / l e a c h route i s to reduce  the d e s i r e d metal  oxides  in l a t e r i t e  ores  37  to the r e s p e c t i v e metals, using moderately high  temperature.  a gaseous reductant  The metals are then  and a oxidized  in an ammoniacal-ammoniurn carbonate s o l u t i o n .  The  most important precaution  oxides in l a t e r i t e in the l e a c h .  i s ensuring  are not reduced to a form that  This a f f e c t s the o x i d a t i o n  s o l u b i l i z a t i o n of the n i c k e l and c o b a l t . duction costly  reductants.  The d e s i r e d  covered from s o l u t i o n by several  one  followed  i s soluble  and subsequent Furthermore, r e -  to m e t a l l i c i r o n r e s u l t s i n excessive  extraction  that the i r o n  consumption of  s o l u b i l i z e d metals are r e e s t a b l i s h e d methods.  by e l e c t r o w i n n i n g  Solvent  or hydrogen reduction i s  such example.  Other r e d u c t i v e  roast/ammonia leach  processes c u r r e n t l y  in advanced stages of development, but not i n commercial operation,  includes  the U.S. Bureau of Mines (USBM) process 3  and  the UOP a d d i t i v e process.  ammonium sulphate  The USBM uses ammoniacal-  solution f o r leaching.  20  38  Chapter 2 A REVIEW OF PREVIOUS INVESTIGATIONS ON DIRECT ACID LEACHING  2.1  D i r e c t Acid Leaching of N i c k e l i f e r o u s L a t e r i t e s 13 14 21 Many l e a c h i n g  obtaining Although  methods  '  '  22 '  have been proposed f o r  n i c k e l and c o b a l t from n i c k e l i f e r o u s  laterites.  processes considered cover a wide v a r i e t y of  procedures, they a l l have c e r t a i n aspects in common.  leaching These  are: 1)  A pretreatment stage, u s u a l l y reduction  2)  high temperature-pressure  roasting  and/or  leaching.  In view of e s c a l a t i n g energy  c o s t s , many workers have  concentrated t h e i r e f f o r t s on bypassing the expensive pretreatment reduction vestigations  and  stage.  However, most of these i n -  have been on a l a b o r a t o r y  up to the p i l o t  Proposed  roast  plant  s c a l e , and  in some cases  level.  processes f o r d i r e c t e x t r a c t i o n of the n i c k e l  c o b a l t values without r o a s t i n g  include  sulphuric,  2 c h l o r i c , and n i t r i c  acid leaching.  Due  to a lack of  hydro-  39  s e l e c t i v i t y , and severe c o r r o s i v e c o n d i t i o n s , the use of mineral cal  cac'id.s. has so f a r been u n s a t i s f a c t o r y .  behaviour of the oxides  S i m i l a r chemi-  r e s u l t s i n mechanically  complex  u n i t o p e r a t i o n s , which may be p r o h i b i t i v e .  23 At the present  w r i t i n g , laboratory  cate that a promising acid  process  l e a c h i n g of serpentine  investigations  may be devised  type ores  indi-  for hydrochloric  (high magnesium  silicates).  This was based on the f a c t that the r e l a t i v e q u a n t i t i e s of i m p u r i t i e s , which d i s s o l v e and consume a c i d , are much lower i n such ores.  However, there was l e s s optimism f o r d i r e c t  ing of n i c k e l i f e r o u s l a t e r i t e 2.1.1  (low magnesium).  D i r e c t Leaching of Goethite M i n e r a l o g i c a l l y , the predominant mineral  present  in N i c k e l i f e r o u s l a t e r i t e s  HFe02 or ^e^O^.H^O), as quartz  varying  i s goethite  One of the more s t r i k i n g  or more of the p a r t i c l e s  Due to the h i g h l y disseminated  physical  b e n e f i c i a t i o n of three  from g o e t h i t e  attempt to. describe laterites goethi t e .  is virtually direct  (Si0  2  f e a t u r e s of  s i z e of g o e t h i t e . i s smaller  nature of such  quarters  species  (a-FeO(OH),  amounts of impurity  i s the extremely f i n e p a r t i c l e  U s u a l l y , 50 percent  value  with  or s i l i c a t e ) .  such l a t e r i t e s  10 ym.  leach-  than  deposits,  of the ore's n i c k e l  impossible.  As a r e s u l t , any  a c i d l e a c h i n g of ni ckel i f erous  i s incomplete without c o n s i d e r i n g  the l e a c h i n g of  40  Goethite has tropic  an orthorhombic  in nature.  Figure 2.1  structure' '*and  shows i t s c r y s t a l s t r u c t u r e ,  which i s isomorphous with diaspore atoms are arranged  (a-Al0(OH),).  in a hexagonally  the i r o n atoms in octahedral  is aniso-  1  The  close-packed  oxygen  l a y e r , with  interstices.  26 A d r a s t i c change i n surface area due  to p i t t i n g ,  is  known to occur with h y d r o c h l o r i c a c i d attack of g o e t h i t e . 27 28 Various workers crease  '  29 '  have shown rates of a t t a c k , which i n -  in the order - P e r c h l o r i c a c i d <sulphuric  acid  c h l o r i c a c i d , when c o n s i d e r i n g s o l u t i o n s of equal 30 g r e a t e r than these  IN... Azuma and :  Kametani  normality  subsequently  correlated  i n c r e a s i n g absolute rates of l e a c h i n g in d i f f e r e n t  with the anions  i n c r e a s i n g complexity  for f e r r i c  Goethite has  constants  energies obtained 26 27 '  ion. an a c t i v a t i o n energy f o r d i r e c t  dissolution  Activation  f o r d i f f e r e n t acids are l i s t e d  in Table  28 '  No s i g n i f i c a n t  change in a c t i v a t i o n  values with acid c o n c e n t r a t i o n was solution  rates in h y d r o c h l o r i c a c i d  observed,  energy  although  dis-  increased sharply up to  28 6N.  acids  of the r e s p e c t i v e  in various acids s i m i l a r to that of hematite.  2.1.  hydro-  Surana  p o s t u l a t e d that both  react by s i m i l a r chemical  g o e t h i t e and  mechanisms.  hematite  V-c=z-aoA—;  Figure 2.1  The s t r u c t u r e o f d i a s p o r e  and g o e t h i t e ( a f t e r Bragg).  42  Table 2.1  A c t i v a t i o n Energies f o r D i r e c t  Dissolution  (Kcal/mol)  ACID Material  HC1  Massive red  a  Fe  2°3  Botryoidal  a  Fe  2°3  Brazilian  a  Fe  2°3  Synthetic  a  Fe  2°3  Goethite  2  4  HC10  4  23.4.  1.8.7 + 2.5  23.2  20.2 + 1.8  21.1 + 5.2  18.4 + 2.0  22.1 + 4.5  22.7 22.6 21.1  Synthetic  a  Fe  2°3  Single crystal  a  Fe  2°3  Goethite Synthetic  H S0  a  Fe  2°3  19.5 - 21.6 20 - . 2 4 22.5  19.8  21.9  18.2  19.2 - 21.4  43  2.1.2  Mechanisms of Leaching of Goethite Bath  proposed  of g o e t h i t e i s f i r s t  a mechanism by which  the surface  assumed to undergo h y d r a t i o n .  This i s  b e l i e v e d to be r a p i d .  In order to d e s c r i b e the mechanisms, a hydrated s u r f a c e will  be represented by:  -0-Fe-OH  The  surface may -  be protonated , 0-Fe-OH  + H!O  ,  3  The anion CI"may be adsorbed •O-Fe  and t h i s  •O-Fe  L  r  onthe  + 2H 0 2  surfacesite •O-Fe-Cl  + C1  complex may then desorb, (rate determing  ^  •O-Fe-Cl  The o v e r a l l  FeOCl  step)  aq  reaction is 0-Fe-OH + H.O 3  + C l " — — > FeOCl  . + 2H 0 aq 2 n  and the rate equation i s : d  aa * = K K,k 2 l 2 dt  { F e )  a q  0  K  k  [  •0-Fe-OHl a ..a H Cl J  9  44  Ahmed and Maksimoir  32  i n t h e i r study of zero  charge of hematite in various face may undergo protonation attacked  directly  acids, postulated  point of that the sur-  to form an aquo complex or be  by the anion.  A dual  mechanism may thus be  operative.  The  surface may f i r s t  undergo a protonation  as p r e v i o u s l y  d e s c r i bed. '1  -0-Fe-OH + H 0  •0-Fe(H 0)  3  2  This aquo complex may e i t h e r  + H0 2  desorb k  •0-Fe(H 0)  U -Fe(H 0);  2  0  2  q  or adsorb an anion X •0-Fe-(H 0)X  •0-Fe(H 0) + X'  2  2  The  resulting  complex then desorbs  •0-Fe(H 0)X  -  2  Assuming once again the o v e r a l l  0-Fe(H 0)X 2  that desorption  aq  i s the rate l i m i t i n g  r e a c t i o n may be w r i t t e n • O.Fe-OH + 2H 0 ;  3  0-Fe(H 0) 2  a q  +  +  :x"  0-Fe(H 0)X 2  >  aq  +  2H 0 2  step  45  and the rate w i l l  be given by: d.[0-Fe(H 0) ]  +  +  d [Fe]  2  d.[0-Fe(H 0)X] 2  dt  dt  dt = k K ]  M  ]  -0-Fe-OH] a  + k ^ ! ^  +  (k,+k K a  K, f I - O - F e - O H T a , Is H 1  [| -O^Fe-OH] a  0  1  1  L  a  • X  )  0  L  + H  X~  In t h i s case, the anion C l " i s a good complexer with i r o n , and K  2  will  on the surface tion  be l a r g e .  As the anion w i l l  -0-Fe-H 0  will  2  be low, and the rate equa-  is simplified to, d [Fe]  k„K K 0  n  J  •0-Fe-OH  a  dt K a  where  +  H  a  Cl  a ,a H 61 +  k.j  K It  cal  r a p i d l y adsorb  K2 ((surface sites remaining: constant)  i s i n t e r e s t i n g to note that t h i s expression  to that obtained  experimental  p r e v i o u s l y , which i s known to f i t the  results for hydrochloric  At higher  HC1 c o n c e n t r a t i o n ,  acid.  c h l o r i d e ions may adsorb  on the s u r f a c e , and the e q u i l i b r i u m may be w r i t t e n : •O-Fe  i s identi  + Cl" -  O-Fe-Cl  46  At high  enough h y d r o c h l o r i c  s i t e s become saturated  acid concentration,  with anions.  proceed by a f u r t h e r protonation •0-Fe-Cl + H 0  This would be followed of the f e r r i c  OH-Fe-Cl  3  +  then  surface H0  by the rate-determining  2  desorption  ion complex k,  OH-Fe-Cl  where  D i s s o l u t i o n may  of the a c t i v a t e d  K ^  3  the surface  ^*  FeOHCl aq  i s the r e a c t i o n rate  constant.  The rate equation  i n strong  d [ F e J ^  =  +  a c i d s o l u t i o n i s then  k K 2  3  •0-Fe-Cl  J  a  u+  dt  The rate of l e a c h i n g the  now  depends on K , which may 3  " a c t i v a t i o n " of the surface  turn could ferric  by each anion,  be r e l a t e d to the complexing  depend on  and t h i s i n  power of anions f o r  ions.  2.1.3  Direct leaching  of Low Magnesium  Limonites  23 Laboratory experiments of n i c k e l l a t e r i t e  i n v o l v i n g the leaching  ores in h y d r o c h l o r i c  a c i d have shown that  the e x t r a c t i o n of n i c k e l and i r o n i s c l o s e l y r e l a t e d to the  47  weight of g o e t h i t e d i s s o l v e d . at  ambient  Very l i t t l e  temperatures, u s u a l l y  e x t r a c t i o n occurs  l e s s than 10 percent.  s o l u t i o n of the g o e t h i t e i n c r e a s e s d r a s t i c a l l y 348°K, and complete  d i s s o l u t i o n may  from  Dis-  about  be expected at 423°K f o r  a l e a c h i n g time of one hour, at h y d r o c h l o r i c acid concentrat i o n g r e a t e r than  2M.  The general c o n c l u s i o n s are t h a t , at low  temperatures,  a c i d c o n c e n t r a t i o n i s the dominating f a c t o r i n the percentage metal  extraction.  However, l e a c h i n g at higher temperatures,  353°K and over, r e s u l t s tion  i r r e s p e c t i v e of a c i d c o n c e n t r a t i o n .  nickel of  2.2  in almost the same percentage  extraction  extrac-  However, maximum  i s only achieved with complete  dissolution  the ore.  Hydrothermal Mainly F e r r i c 2.2.1  Precipitation  in S o l u t i o n s Containing  Ions  H y d r o l y s i s of Metal Species at Elevated Temperatures Very l i t t l e  r e a c t i o n s of i n o r g a n i c due in  i s known regarding the h y d r o l y s i s ions at higher temperatures.  This i s  to a dearth of thermodynamic data f o r aqueous s o l u t i o n s the temperature  on the temperature  range 373 - 573°K. coefficients  obtained before i t was  Many of the o l d e r data  of simple c a t i o n s have been  recognized that d i m e r i z a t i o n  and  48  p o l y m e r i z a t i o n had to be c o n s i d e r e d .  33 34 The correspondence p r i n c i p l e of C r i s s and Cobble t h e r e f o r e been used to more a c c u r a t e l y p r e d i c t equilibria  at elevated temperatures.  and heat c a p a c i t i e s of i o n i c reaction changes  are u t i l i z e d  at temperatures other than  has  thermodynamic  In e f f e c t ,  entropies  species p a r t i c i p a t i n g  i n computing  '  i n a given  the standard free  energy  298°K.  A useful method of p r e s e n t i n g thermodynamic data r e l a t e d to the h y d r o l y s i s of metal  species at elevated  temperatures,  i s the use of temperature/pH diagrams, such as the Fe 35 system shown i n Figure 2.2.  The p r e c i p i t a t i o n  3+ " —H^O  temperature  and the composition of the p r e c i p i t a t e formed were shown to be dependent though tion  on the pH of the i n i t i a l  precipitation  nitrate solution. Al-  of hematite from f e r r i c  i s not expected to show i d e n t i c a l  chloride  behaviour, the  soluequili-  brium datagram;may serve as a guide. 2.2.2  P r e c i p i t a t i o n of Iron as F e r r i c  Oxide  An examination of the temperature versus pH suggests that i r o n can be removed from leach s o l u t i o n s h y d r o l y s i s at high temperatures of about 473°K.  plot by  In p r a c t i c e  however, i t has been found that i n the absence of j a r o s i t e p r e c i p i t a n t s , the extent of h y d r o l y s i s  and p r e c i p i t a t i o n of  49  50  ferric  oxide  content  at 473°K i s not always s u f f i c i e n t  of the f i n a l  i s of p r a c t i c a l  and  lowered to a l e v e l , which  methods of i n c r e a s i n g the extent  precipitation  of f e r r i c  oxide.  One  heat the leach s o l u t i o n to well over 473°K. results  in an  corrosion  i n c r e a s e in operating  problems.  of p r e c i p i t a t i o n acid' level  iron  importance.  There are two lysis  s o l u t i o n to be  f o r the  of hydro-  method i s to This however  pressure,  and  increased  A l t e r n a t i v e l y , an i n c r e a s e in the  i s accomplished  of the hydrolyzed  In c o n s i d e r i n g s t a b i l i t y  by a decrease in the  extent 'free  liquor.  r e l a t i o n s of the compounds 3+  a  ~ F 2 ^ 3 ' and e  a-FeO(QH) in aqueous s o l u t i o n s of Fe  temperatures, the general can  at  various  form of the p r e c i p i t a t i o n r e a c t i o n  be w r i t t e n : 2M  X+  Considering  + yH .0 2  the  to the p o s s i b i l i t y  =  HO-  (y-x)H 0 + 2xH  systems in the form M  of r e p r e s e n t i n g  x+  —M„0 L.  r e a c t i o n s on  pH p l o t s of the type  shown in Figure 2.2.  therm may  as:  be w r i t t e n  +  2  The  X  —H„0 (—  leads  temperaturestandard  iso-  51  AG  o  -RT  6  T  In  a  a + H  M C y (y-x)H 0 2  2  2x  y  and  s impli f i ed to : 2xpH  =  AG  b T  - 2 .Log m M  4.575T The  x+  2 Log  Y  M  x+  pH at which various compounds are in e q u i l i b r i u m  aqueous s o l u t i o n s of the metal a f u n c t i o n of temperature.  with  ions can thus be c a l c u l a t e d  However, at temperatures  373°K, very few values of a c t i v i t y c o e f f i c i e n t in order to c a l c u l a t e the a c t i v i t y of the metal  as  above  (y±) are known ion.  37 L i e t z k e and that a c t i v i t y  Stoughton  have shown r a t h e r c o n c l u s i v e l y  c o e f f i c i e n t s can be c o r r e l a t e d  by various  Debye-Huckel expressions up to 523°K as e a s i l y at room temperature.  This method was  as they  f u r t h e r developed  are by  38 Cobble  to p r e d i c t s o l u b i l i t i e s  of s a l t s  in water up to 523°K.  These Debye-Huckel expressions show a decrease c o e f f i c i e n t with temperature,  in a c t i v i t y  which can become very  signifi-  cant at higher c o n c e n t r a t i o n s . 39 Meissner,  Kusik and  Tester  have d e s c r i b e d a method,  which u t i l i z e s vapour pressure measurement and  the  Gibbs-  Duhem equation. However, t h i s d i d not serve the purpose of  52  calculating  the value of the a c t i v i t y  c o e f f i c i e n t of f e r r i c  c h l o r i d e , due to the u n a v a i l a b i l i t y of data on i t s vapour pressure.  An ship  attempt was t h e r e f o r e  between the a c t i v i t y  hematite, and g o e t h i t e . various  elevated  made to e s t a b l i s h a r e l a t i o n -  of f e r r i c  ion i n e q u i l i b r i u m  The s o l u b i i i t i e s  with  of i r o n compounds at  temperatures were estimated from a knowledge  of the e q u i l i b r i a  c o n s t a n t s , which in turn were c a l c u l a t e d  from the standard free energy changes f o r each  reaction  according to equations: AG.  RT  AG.  =  AG  I n K,  298  AS  +  2 9 8  A C  pj  298  (T-298)  (T-298) - T A>Cp  298  In  T 298  where AG g--= 2g  o  =  AG^  AS gg= 2  standard f r e e energy of r e a c t i o n  at 298°K  standard f r e e energy of r e a c t i o n  at T°K  standard entropy change of r e a c t i o n  at 298°K.  CMT  AC. 298::  the  average  reaction  heat  between  capacity  change f o r the  298° and T°K.  53  2.2.3  Hydrothermal  P r e c i p i t a t i o n of Iron  The degree to which from f e r r i c  ion i s dependent  leach  III Compounds  s o l u t i o n s can be freed  on the s o l u b i l i t y  of the pre-  40 cipitate. the  Feitknecht  solubility  at 298°K, the  and S c h i n d l e r  have c r i t i c a l l y  reviewed  r e l a t i o n s h i p s of i r o n III oxides and hydroxides  and t h e i r f i n d i n g s are summarized on the basis of  following  aging scheme: > FeQ(OH)  AMORPH.. Fe(0H) . (ACTIVE)-^-  -> AMORPH. Fe(0H) (INACTIVE)  3  3  *  Fe  2°3  They proposed that f r e s h l y ! p r e c i pi tated hydroxide slowly  converts to g o e t h i t e .  a c t i v e amorphous  In a d d i t i o n , a s o l i d  transformation hydroxide. complete  occurs r e s u l t i n g i n a more s t a b l e amorphous 41 Biedermann and S c h i n d l e r have shown that the  transformation  requires  about 6-8  days, but l e s s  42 than one day at 373°K. ture  Goethite i s s t a b l e at room termpera43  but dehydrates to hematite above about 403°K.  a n t i c i p a t e d , that  in leaching  hematite i s nucleated Fe  Ferric  3 +  experiments at about  It i s 423°K,  homogeneously by the h y d r o l y s i s  + 3 H0 2  =  1 Fe 0  hydroxide i s . u n s t a b l e  a c i d i t y and temperature, and w i l l  2  3  + 3 H  reaction  +  under such c o n d i t i o n s not be f u r t h e r  of  considered.  54  2.2.4  Hematit.e-GoethT.te R e l a t i o n s i n Acid  Solutions  44 Tunell g o e t h i t e i n 0.1 MCI  and Posnjak  cited  an experiment i n which  s o l u t i o n was converted to hematite at 373°K. 45  This decomposition r e q u i r e d a few weeks. Gruner, in d i s t i l l e d  usingigoethite  water, took about ninety days to e f f e c t  t h i s decom-  p o s i t i o n to hematite at temperatures of over 473°K.  The q u a l i 46  t a t i v e e f f e c t o f pH on the decomposition o f g o e t h i t e , the decomposition temperature i s near 373°K i n a c i d and above 423°K  in a l k a l i n e  i s that  solutions  solutions.  In l i g h t of the f a c t that the decomposition of g o e t h i t e to hematite i s k i n e t i c a l l y a slow p r o c e s s , i t i s imperative that complete d i s s o l u t i o n occurs to produce the f e r r i c intermediate f o r subsequent h y d r o l y s i s to hematite.  chloride  Hydrolysis  47 of f e r r i c  chloride  2.2.5  i s known to occur at as low as 393°K.  The E f f e c t of pH on the S o l u b i l i t y Compounds Without  of Iron III  Complexing  With knowledge of the working pH range during l e a c h i n g experiments, and c a r e f u l diagrams,  51  relatively  3+ only the F q e  a  s c r u t i n y of the i r o n E - pH  species was c o n s i d e r e d .  For a  complete treatment of the iron-water r e l a t i o n s ,  over 50 e q u i l i b r i a r e a c t i o n s are u s u a l l y r e q u i r e d to d e s c r i b e the s o l u b i l i t y of a s i n g l e compound. be pointed out that not only d i s s o l v e d  Furthermore, i t should species f o r which  free  55  energy  values are a v a i l a b l e should be considered but, f o r  example, Fe(0H)2  or u n d i s s o c i a t e d d i s s o l v e d  hydroxide, because i t may be an important solubility  ( J . Winchester,  l e s s , an attempt Fe  3+ aq  ferric  c o n t r i b u t o r to i r o n  personal communication).  Neverthe-  was made to show the r e l a t i o n s of f e r r i c  , to the oxides and hydroxides  ions,  of i r o n ,  J  Table 2.2 shows values of the e q u i l i b r i u m  constant  obtained using equation 2:1, together with the a s s o c i a t e d pH, which were c a l c u l a t e d the a c t i v i t y  using equation 2.4 and assuming that  of f e r r i c  ions i n s o l u t i o n was u n i t y .  It should be noted  that lower  pH values would be  obtained f o r the h y d r o l y s i s r e a c t i o n at higher c o n c e n t r a t i o n s , because Debye-Huckel expressions i n d i c a t e a decrease i n 35 activity  c o e f f i c i e n t with  2.2.6  Considering the F e r r i c Ion--Hematite E q u i l i b r i u m Fe  3+ aq  The hematite to  temperature.  +  3 H0 2  aq  9  L  standard free energies f o r the h y d r o l y s i s of  at various temperatures  (see Appendix A.3) -.were.- used  c a l c u l a t e the e q u i l i b r i u m constant v i a the r e l a t i o n s h i p : Log K  -AG  o  T  2.3 RT  . . . 2 .1  56  Eliminating  Fe^O  and H 0 from  the constant  9  because  t h e i r a c t i v i t y was assumed to be c l o s e to u n i t y . 3 a  K =  +  — a  Fe  r  ...2.2  3+  and Log  K  =  3 Log a - Log a ^ H+ Fe  Log  K  =  -3 pH - Log a  .2'.':-3  therefore 3  ...2.4  +  Fe The log of the a c t i v i t y Fe^Og  i s seen  of F e r r i c  ion i n equi1ibriurn with  to be a l i n e a r f u n c t i o n of pH, with a slope of  c minus 3. activity  As a r e s u l t , i f a  temperature  and f e r r i c ion  are s t i p u l a t e d , then the pH i s f i x e d .  At a l e a c h i n g temperature Log  [Fe ] 3 +  =  of 423°K  -4.8 - 3 pH  . . .2.5  The pH a s s o c i a t e d with various a c t i v i t i e s  of f e r r i c  e q u i l i b r i u m with hematite  using equation 2.;5,.  Activity tion  were c a l c u l a t e d  values higher than  10  _ 1  fall  i n such a high  ion i n  concentra-  range that a marked departure from m o l a l i t i e s can be  expected.  57  Table 2.2  Equilibrium  Data , f o r the Fe  ?  ?  System  PH  Log K  Temperature °K  — F e 0 —H 0  Calories '  -0.62  298  -2550  1 .87  333  -4774  3.13  -1.04  373  -6621  3.88  -1.29  423  -9295  4.80  -1.60  473  -11880  5.49  -1.83  58  2.2.7  Considering the F e r r i c Ion >T-Goethi te E q u i l i b r i u m Fe  ;i  +  3 +  2H 0 2  =  FeOOH  +  3H  +  The f r e e energy and pH values shown i n Tables 2.4  and 2.5 were obtained i n the s i m i l a r manner described i n section  2.2.6, and making the same assumption.  At a l e a c h i n g  temperature of 423°K. Log  2.2.8  [Fe  3 +  ]  =  4.44 - 3pH  Considering the F e r r i c Ion r-Ferri  c Hydroxide  Equi1i b r i urn 3+ Fe'  At  3H 0 2  a leaching  Log In  +  [Fe  3 +  constructing  ]  =  Fe(0H)  3  +  3H  temperature of 423°K =  -0.13 - 3pH  a pseudo phase  diagram  f o r the  3+ Fe  —^ 2^3—^2^  zed  to c a l c u l a t e the e q u i l i b r i u m  and  activities:  e  pH  The librium Fe  3+  s  =  y  s t e m  1 3  '  t  n  e  log  following  expression i s u t i l i -  pH at various  temperatures  K - l o g a .. Fe" 5  same e x p r e s s i o n was u t i l i z e d  to c a l c u l a t e  pH at various temperatures and a c t i v i t i e s  —FeOOH — H 0 metastable 2  system.  the equi f o r the  59  Table 2.3  The  pH Corresponding  Ferric  to Various A c t i v i t i e s  Ion in E q u i l i b r i u m  Log  [Fe ] 3 +  0  with Hematite  PH  -1 .60  -1  -1.27  -2  -0.93  -3  -0.60  -4  -0.27  -5  -0.07  of  60  Table 2.4  Equilibrium Metastable  1  Temperature °K  Data f o r the Fe  — FeOOH — H 0 2  System.  AG°  T  Log  K  PH  Calories  298  -2500  1 .83  -0.61  333  -4250  2.79  -0.93  373  -6185  3.62  -1.21  423  -8598  4.44  -1.48  473  -10859  5.02  -1.67  61  Table 2.5  The  pH Corresponding  Ferric  to Various A c t i v i t i e s  Ion in E q u i l i b r i u m with  Goethite  Log  PH  [Fe ] 3 +  0  -1 .48  -1  -1.15  -2  -0.81  -3  -0.48  -4  -0.15  -5  -0.19  of  62  f a b l e 2.6  Equilibrium  Data f o r the Fe  Metastable  System.  Temperature  AG j  °K  C a l o r i es  298  — Fe(OH), — FLO  Log K  pH  4700  -3.45  1.15  333  3176  -2.08  0.69  373  1585  -0.93  0.31  423  -250  0.13  -0.04  473  -1826  0.84  -0.28  0  63  Table 2.7  The  pH Corresponding  Ferric  to Various A c t i v i t i e s of  Ions in E q u i l i b r i u m  Log  [Fe  3 +  ]  with F e r r i c  pH  0  -0.04  -1  0.29  -2  0.62  -3  0.96  -4  1 .29  -5  1 .62  Hydroxide  64  Table 2.8  Theoretical  Equilibrium  pH at Various  Temperatures  3+ and A c t i v i t i e s  —Fe 0„—H 0 9  9  System  Activity of Ferric Ions  Temperature °K  f o r the Fe  Log K  1M  0.5M  0.2M  0.1M  PH  PH  PH  PH  298  1.87  -0.62  0.52  -0.39  -0.26  333  3.13  -1.04  -0.94  -0.81  -0.71  373  3.88  -1.29  -1.19  -1.06  -0.96  423  4.80  -1.60  -1.49  -1.37  -1.27  473  5.49  -1.83  -1.73  -1.59  -1.49  65  Table 2.9  Theoretical  Equilibrium  pH at Various  Temperatures  3+ and A c t i v i t i e s  f o r the Fe  —FeOOH—H 0 2  Metastable  System  Activity of Ferric Ions Temperature °K  Log K  1M  0.5M  0.2M  0.1M  PH  PH  PH  PH  298  1.83  -0.61  -0.51  -0.38  -0.28  333  2.79  -0.93  -0.83  -0.70  -0.60  373  3.62  -1.21  -1.11  -0.97  -0.87  423  4.44  -1.48  -1.38  -1.25  -1.15  473  5.02  -1.67  -1.57  -1.44  -1.34  323  373 Temperature  423  473  (K) cn  Figure  2.3  Free energy versus temperature f o r i r o n  (III)  hydro!isis reactions  0 1  Figure 2.4  Influcence of pH on the s o l u b i l i t y of iron (III) and oxide at 423°K.  hydroxides  69  2.3  Thermodynamic Considerations Treatment.ofiNickel  Underlying  the  L a t e r i t e With F e r r i c  Hydrothermal  Chloride  43 It has to  been shown  t h a t the d i r e c t conversion  hematite i s a r e l a t i v e l y  dynamically  explained  slow r e a c t i o n .  of g o e t h i t e  This can  by c o n s i d e r i n g the f r e e energy  temperature r e l a t i o n s h i p f o r h y d r o l y s i s r e a c t i o n s  be thermoversus  (see  Figure  2.3). Fe 0 .  H0  (+2500 c a l o r i e s ) +  HC1  2  3  -50  2  calories » si ow  Fe 0 2  •HC1 FeCl  +  3  H0 2  (-2550 c a l o r i e s )  3  fast At 298°K, the conversion with  of g o e t h i t e to hematite proceeds  a r e d u c t i o n of f r e e energy of only approximately  -50  calories.  Figure 2.3 tite  and  a l s o i l l u s t r a t e s that the h y d r o l y s i s of hema-  g o e t h i t e have s i m i l a r thermodynamic d r i v i n g f o r c e s ,  which increase with hydroxide standard  temperature.  The  h y d r o l y s i s of  appears to be the.rmodynamical l y favored conditions.  under experimental  Its presence however, i s not  c o n d i t i o n s because of slow  ferric  under expected  kinetics.  36  G e n e r a l l y , the extent crease  of h y d r o l y s i s  in temperature and  of the hydrolyzed  liquor.  i s enhanced by an i n -  a decrease in the f r e e a c i d l e v e l  70  The  overall  of hematite has t h i s provides  c o n c l u s i o n t h e r e f o r e , i s that the h y d r o l y s i s the l a r g e s t thermodynamic d r i v i n g  a possibility  f o r c e , and  f o r a f a s t conversion  of g o e t h i t e  to hematite under c o n d i t i o n s where g o e t h i t e can d i s s o l v e rapidly.  2.3.1  ferric  The  E f f e c t of C h l o r i d e  Due  to the complexing power of c h l o r i d e ion f o r  i o n s , the e f f e c t on f e r r i c  be considered.  can  Figure 2.4 bility  ferric  be estimated  illustrates  ion a c t i v i t y , and  should  i t s effect  the  ferric  out that these  ion a c t i v i t y ; the f e r r i c  as by departures  2.3.2  data  hydroxide.  It should  are in terms of the  ion a c t i v i t y  The serve  from i d e a l i t y  Temperature/pH  i s dependent  Consideration  to i n d i c a t e the temperature of t r a n s f o r m a t i o n  identification  as  in strong s o l u t i o n s .  pseudo-JDhase diagram of Figure 2.5  g o e t h i t e to hematite.  on  i n f l u e n c e of pH on the s o l u -  on the degree to which i t i s complexed by c h l o r i d e ions well  also  from e q u i l i b r i u m c o n s i d e r a t i o n s .  of hematite, g o e t h i t e and  however be pointed ferric  ion s o l u b i l i t y  Each complex predomn^nste's under d i f f e r e n t  c o n d i t i o n s of pH and solubility  Complexing  cannot of  This must be done e x p e r i m e n t a l l y ,  of the compounds p r e c i p i t a t e d a t  various  by  71  temperatures  and pH.  Furthermore, the curves were obtained by assuming stant values of f e r r i c ture.  ion a c t i v i t y with increased  con-  tempera-  In f a c t , one can only assume the c o n c e n t r a t i o n remains  constant, because., the a c t i v i t y c o e f f i c i e n t temperature.  decreases with  As a r e s u l t , lower values of pH were c a l c u l a t e d  using the e q u a t i o n : 2xpH  =  AG  o  - 2 Log  [M ]* x +  4:575T instead of: 2xpH  =  AG  o  - 2 Log m , -- 2c Log Luy Y  +  T  4.575T While the pseudo-phase diagram may serve as a guide i n describing due  the temperature-pH  to the u n a v a i l a b i l i t y  of data on the a c t i v i t y  as a f u n c t i o n of temperature.  * Concentration (M)  relationship, i t i s inaccurate, coefficient  72  Chapter  3  EXPERIMENTAL  3.1  Mineralogical 3.1.1  Investigation  ENERGY DISPERSIVE X-ray ANALYSIS VIA The  scanning e l e c t r o n microscope  was  SEM u t i l i z e d in  determining the nature of a wide v a r i e t y of p a r t i c l e s in the mineral  sample s u p p l i e d by S h e r r i t t  Limited/Sherritt  Research  1)  Quartz  Gordon Mines  Centre, Fort Saskatchewan.  d i s c r e t e types of p a r t i c l e s were  Three  identified.  or Si 1 i c a t e  ( P a l e - y e l l o w p a r t i c l e s , which were r e l a t i v e l y 1argest 2)  found  the  observed.)  Chromite (Black or dark-brown p a r t i c l e s , which were m a g n e t i c a l l y separated and s m a l l e r i n s i z e than those of quartz.)  3)  Goethite (Redish-brown p a r t i c l e s of very f i n e s i z e , which possessed  the highest n i c k e l  content.)  73  3.1.2  X-ray D i f f r a c t i o n A n a l y s i s X-ray d i f f r a c t i o n patterns of the ore sample,  precipitated  hematite and magnetic  p a r t i c l e s were obtained.  The 2Q and r e l a t i v e i n t e n s i t y values were compared with those :  of the r e s p e c t i v e m i n e r a l s , as given i n the ASTM c a r d .  These  values are reported i n Ta'bl.es B . 1 , B.2 and B.3 of Appendix  B.  The ore sample was found to be composed mainly of g o e t h i t e , which was .poorly c r y s t a l l i n e . . There was no i n d i c a t i o n of a d i s c r e e t  nickel  mineral such as g a r n i e r i t e .  The  presence of an a p p r e c i a b l e amount of hematite was d e t e c t e d .  In each case, the r e l a t i v e i n t e n s i t i e s showed some variation. the  3.2  There was e x c e l l e n t  agreement on the 2;e values of  peaks f o r hematite and chromite but not f o r g o e t h i t e .  Q u a n t i t a t i v e Chemical Several  samples  Analysis  of n i c k e l  l a t e r i t e were d i g e s t e d  zing  two standard methods of d i s s o l u t i o n :  1)  Hydrochloric/Nitric  2)  Perchloric  acid  acid  solution  dissolution  matter with n i t r i c  utili-  i n the r a t i o 3:1  a f t e r removal  of organic  acid.  Determinations were conducted  by atomic a b s o r p t i o n  74  spectrometry.  The r e s u l t s obtained by the above methods were  compared with those obtained from general t e s t i n g  Total  3.3  A n a l y s i s of the ore i s shown i n Table  Apparatus  It was  which was  3.1.  Design  An a l l t i t a n i u m autoclave of 100 mis zed.  laboratories.  placed i n a h o r i z o n t a l l y  c a p a c i t y was  shaken heating j a c k e t ,  connected to a t h e r m i s t o r temperature c o n t r o l l e r  voltage r e g u l a t o r . also employed  A potentiometer with a thermocouple  to o c c a s i o n a l l y monitor the temperature.  main f e a t u r e s of the apparatus are shown i n Figure  3.4  utili-  and  was The  3.2.  Pressure Leaching Experiments 3.4.1  Experimental Procedure The experimental procedure c o n s i s t e d of the f o l l o w -  ing 1)  steps: The powdered sample ( u s u a l l y of  16 gms)  added  A pressure of 4.1  x 10  2  Newton metre"  nitrogen was  ployed to minimize vapour t r a n s p o r t i n t o tubing nect ions and 3)  to 40 mis  solution. 6  2)  was  con-  valves.  The t h e r m i s t o r was  set at the r e q u i r e d  temperature.  em-  75  e 3.1  Chemical  Element  Analysis  of the N i c k e l i f e r o u s L a t e r i t e  Percentage wt. Obtained  44.5  Fe  Percentage wt. Obtained (General T e s t i n g Lab)  44.60  2  Ni  1 .25  Co  0.15  0.14  Cr  2.24  2.28  Mn  1 .08  1 .08  Al  4.70  4.66  Mg  2.30  2.32  3  1 .24  Ca  -  0.12  Si  -  2.72  9.68  LOI  Source :  Marinduque N i c k l e Mines, P h i l i p p i n e s  S u p p l i e r suggested  43.9  suggested  1.27  Supplier  9.68  76  MET  10  Figure 3.1  POT  The  leaching apparatus,  showing from  (L to R):  the potentiometer,  autoclave  mounted on a shaking  voltage  r e g u l a t o r and  c o n t r o l 1er.  the  the  titanium  device,  thermister  Figure  3.2  The  pressure  filter  device.  78  4)  Shaking  was s t a r t e d with a constant heating rate cor-  responding 5)  to the maximum v a r i a c  Ten degrees  setting.  below the r e q u i r e d temperature,  s e t t i n g was adjusted to that corresponding quired 6)  calibrated  to the r e -  temperature.  The autoclave was quenched i n a p a i l one  the v a r i a c  hour a f t e r having  reached  of water e x a c t l y  the d e s i r e d l e a c h i n g  temperature.  3.4.2  Liquid/Solid  Separation  Figure 3.1 shows the pressure f i l t r a t i o n which was employed to speed  up f i l t r a t i o n ,  and at the same  time prevent any evaporation of the f i l t r a t e . filtration  Although  was much f a s t e r with a buchner funnel and f i l t e r  pulp, there were two disadvantages.  Firstly,  recovery of the  i r o n residue was d i f f i c u l t when mixed with the pulp. the hot f i l t r a t e low  evaporated  order to reduce  residue and the a c i d i c  Secondly,  to a c e r t a i n extent due to the  pressure on the vacuum side of the f i l t e r i n g  In  device,  medium.  the contact time between the i r o n f i l t r a t e , a l a b o r a t o r y c e n t r i f u g e was v  employed.  A f t e r about 5 minutes of c e n t r i f u g i n g , the s o l u -  t i o n was decanted water.  and the s o l i d s  immediately  swamped with  79  3.5  Analytical 3.5.1  Methods  Atomic Absorption A n a l y s i s Samples of f i l t r a t e were p i p e t t e d and d i l u t e d to  the a p p r o p r i a t e c o n c e n t r a t i o n f o r accurate measurement of t h e i r contents by atomic  a b s o r p t i o n spectrometry.  Samples of the  corresponding residues were d i g e s t e d and analyzed thorough  washing.  A mass-balance technique was  after  adopted  as a  means of checking the accuracy of the d e t e r m i n a t i o n s .  N i c k e l , c o b a l t , i r o n , manganese, magnesium, aluminium chromium were determined tion  instrument.  It was  compositions  in sample d i l u t i o n was  made p o s s i b l e  the atomic. a b s o r p t i o n burner head, thereby path length through  which the beam was  versus c o n c e n t r a t i o n curve was  mately  solu-  solutions.  20 times.  the lamp beam l i n e  by  changing  passed. ;Using  t h i s procedure, the l i n e a r p o r t i o n of each element's tion  absorp-  hoped that t h i s procedure would compensate f o r  Flexibility  the flame  atomic  of the unknown f i l t r a t e  the flame matrix e f f e c t s of the f i l t r a t e  rotating  306  For a l l a n a l y s e s , standards were f i r s t made  up to approximate tions.  on a Perkin-Elmer  and  absorp-  increased by a p p r o x i -  (That i s , by having the burner normal to r a t h e r than c o - l i n e a r with i t . )  sample d i l u t i o n s were r e q u i r e d by employing  this  Fewer  technique.  80  3.5.2  Determination The  of "Free A c i d "  pH .at which the p r e c i p i t a t i o n  ch! o r i d e s o l u t i o n s . o c c u r were f i r s t metal  of c a t i o n s i n -  determined,  by adding  c h l o r i d e s o l u t i o n s to the same a l i q u o t p o r t i o n of  standard h y d r o c h l o r i c a c i d , and t i t r a t i n g with sodium  An a u t o t i t r a t o r  hydroxide.  i n the i n f l e c t i o n  mode of o p e r a t i o n pro-  duced the curves shown i n Figure 3.3.  These curves served to  i n d i c a t e the r e l a t i o n s h i p lysis  between the pH value at which  occurs and volume of t i t r a n t .  A symmetric t i t r a t i o n tor  hydro-  curve i s produced  when the i n d i c a -  e l e c t r o d e i s r e v e r s i b l e , and when there are an equal  number of t i t r a n t  reagent and r e a c t a n t species i n the equiva-  lence equation. titration  In a simple acid-base pH t i t r a t i o n , the pH  curve f o r equation H  +  f  Fe  3 +  A titration  OH"  + 30H"  (3.1 ) i s symmetri c.  = H0  ...(3.1)  2  = Fe(0H)  ...(3.2)  3  e r r o r can however, be generated  i f the s o l u -  t i o n contains a s p e c i e s , which c h e m i c a l l y i n t e r f e r e s with the titrant of  or r e a c t a n t and i n so doing, d i s t o r t s  the t i t r a t i o n  curve  (equation ( 3 . 2 ) ) .  g r e a t e s t when the e q u i l i b r i u m  the symmetry  This e r r o r i s  constant f o r the r e a c t i o n between  the r e a c t a n t (or the t i t r a n t ) and an i n t e r f e r i n g  species i s  81  Table 3.2  pH Values of Hydroxides Metal  Ions  PH Hydroxides  i n E q u i l i b r i u m with T h e i r  Published  0.5M[M ] n+  lM[M ] n+  Data .001  M[M ] n+  Fe(0H)  3  2.1  1 .61  2.61  Al(0H)  3  3.5  3.22  4.22  Cr(0H)  3  4.5  3.93  4.93  7.2  6.09  7.49  Ni(OH)  2  Mn(0H)  2  8.4  7.65  9.15  Mg(0H)  3  9.5  8.48  9.98  2  6.5  6.65  8.15  Fe(0H)  82  co  CM  X  CL  Na OH Figure  3.3  pH  titration  chloric  acid  solution, cm  curves  of  metal  versus  sodium  chlorides hydroxide.  in  hydro-  83  c l o s e to that of the r e a c t i o n between the t i t r a n t reactant.  I f the i n t e r f e r e n c e r e a c t i o n i s with the t i t r a n t  a second end point may be seen. an a c i d strength (ApK  (Basset  f o r the clean  et a l . , 1978).  type of t i t r a t i o n  In acid-base ph t i t r a t i o n s ,  d i f f e r e n c e of s i x orders  = 6) i s r e q u i r e d  points  and the  of magnitude  separation  of two end  However, the magnitude of t h i s  e r r o r depends h e a v i l y on the r e l a t i v e  q u a n t i t i e s of the species  involved.  Table 3.2 shows the pH at which the h y d r o l y s i s of several c h l o r i d e s occur.  I t also shows the v a r i a t i o n in pH values  with the r e l a t i v e q u a n t i t i e s of species M —M:(:0H)  equilibrium.  n+  the  n  pH value  Acid"  Figure  involved  3.3 i l l u s t r a t e s  i n the how c l o s e  corresponding to n e u t r a l i z a t i o n of the "Free  i s to that f o r the h y d r o l y s i s of f e r r i c  For t h i s reason, d i r e c t t i t r a t i o n  ions  of the f i l t r a t e  in solution. with 2N NaOH  s o l u t i o n , with the a u t o - t i t r a t o r i n the d e r i v a t i v e mode, r e sulted  i n very  inflection  An ing  broad peaks.  on pH t i t r a t i o n  In most cases,  the points of  curves were a l s o u n s a t i s f a c t o r y .  a l t e r n a t i v e method was t h e r e f o r e  the "Free A c i d " c o n c e n t r a t i o n  devised  i n determin-  of the f i l t r a t e .  In t h i s  procedure, an a c c u r a t e l y measured volume of standard c h l o r i c a c i d was added to an a l i q u o t of the f i l t r a t e .  2N hydroAny  extra volume of 2N sodium hydroxide, beyond that which was required  to n e u t r a l i z e the a c i d , was obtained  di f f e r e n c e .  by f i n d i n g the  84  Chapter  4  RESULTS  4.1  The l e a c h i n g Ferric All  + 2°K.  Chloride  leaching  titanium  of Nickel i f e r o u s L a t e r i t e i n Aqueous  t e s t s were performed  autoclave,  i n the 100 ml  capacity  the temperature of which was c o n t r o l l e d to  The e x t r a c t i o n s  of n i c k e l , c o b a l t , manganese and  chromium were determined as a f u n c t i o n o f : 1)  Temperature ranging from 373°K to 473°K.  2)  Concentration of f e r r i c to  3)  c h l o r i d e ranging from 0 . 5 M "  4.'0M. ,  Pulp density  4.1.1  ranging from 100 g/1 to 400 g/1 .  E f f e c t of Temperature Using 1 and 2 molar f e r r i c  c h l o r i d e s o l u t i o n s with  a constant 1 hour r e a c t i o n time, the e f f e c t of r e a c t i o n temperature i s shown i n Figure increased  with i n c r e a s i n g  of Table 4.1). provided  4.1.  In g e n e r a l ,  temperature  metal  (see leaching  extraction results  At 423°K, n i c k e l e x t r a c t i o n was over 90 percent,  the c o n c e n t r a t i o n  of f e r r i c  c h l o r i d e was greater  than  Tab!e  4.1  Metal  S o l u t i o n Type FeCl (M) 3  Extraction  Temp. °K  From N i c k e l i f e r o u s  Pulp  Density 9/1  Ni  Laterite  Metal  w i t h Aqueous F e r r i c  Cone. Co  1r  Fi 1 t r a t e gpi Mn Cr  Chloride  % Ni Extraction  0.5  448  100  1.2  0.15  0.16  1 .0  96 ;  0.5  448  200  2.1  0.30  0.19  1 .9  84  1.0  373  200  0.6  1.10  0.14  0.7  24  1.0  398  200  1.2  0.20  0.21  1 .3  48  1.0  423  200  2.4  0.38  2.0  96  1.0  448  200  2.5  0.30  0.21  2.2  98  1.0  448  300  3.4  0.45  0. 20  3.0  91  2.0  373  200  0.7  0.10  0.19  0.8  28  2.0  398  200  1.2  0.23  0.28  1 .5  50  2.0  423  200  2.4  0.30  0.50  2.1  96  2.0  448  200  2.5  0.30  0.40  2.2  98  2.0  448  300  3.6  0.45  0,. 28  3.1  96  1.0  373  100  0.31  25  1.0  423  100  1 .24  99  1.0  473  100  1 .24  99  1.0  523  100  1.24  99  1.0  423  400  4.3  88  2.0  423  4C0  4.9  .  0.30  0.60  0.45  4.0  96  87  1M.  The  c o n c e n t r a t i o n of chromium in the f i l t r a t e  increased  with  i n c r e a s i n g temperature up to around 423°K but  decreased  at higher temperatures.  This behaviour  due  of a ferric-chromium  to the p r e c i p i t a t i o n  4.1.2  and  4.2  t u r e s , 348°K, the percentage on f e r r i c  extraction  metal  resulted  E f f e c t of Pulp The  more depen-  in almost  the same  percentage  pulp d e n s i t y of the leach did not appear to  enough r e a c t i o n time was were a v a i l a b l e . nickel  s o l u t i o n was  on metal  allowed  and  e x t r a c t i o n , provided sufficient  With pulp d e n s i t i t e s of 100 e x t r a c t i o n at 423°K, with  98 percent, 96 percent and  illustrates  this effect  which i s n e a r l y h o r i z o n t a l . percentage  e x t r a c t i o n was  tempera-  Density  significant effect  Figure 4.3  At low  i r r e s p e c t i v e of c o n c e n t r a t i o n .  4.1.3  g/1,  extraction.  ferric  c h l o r i d e c o n c e n t r a t i o n whereas l e a c h i n g at  higher temperatures  400  to be  complex.  show the e f f e c t of  c h l o r i d e c o n c e n t r a t i o n on n i c k e l  have any  suspected  E f f e c t of Concentration Figures 4.1  dent  was  nickel  d e n s i t i e s of 300  c h l o r i d e ions  g/1,  and  400  and  90 percent  respectively.  in the form of a curve,  Figure 4.2  g/1.  g/1  1M f e r r i c c h l o r i d e  shows low values of  e x t r a c t i o n , which were obtained g/1  200  Such low  at pulp  percentages  were  FeCI ,(M) 3  Figure 4.2  Effect of FeCL-, concentration on nickel extraction at 448°K.  100  200  300 Pulp  Figure 4.3  density,  400  g/1  Effect of pulp density on" nickel extraction with IMMFeClg at 423°K.  90  to be expected because of the low c o n c e n t r a t i o n chloride  s o l u t i o n employed and the subsequent u n a v a i l a b i l i t y  of s u f f i c i e n t tained  4.2  of f e r r i c  chloride  ions  to react with metal values con-  i n the ore.  The Leaching of N i c k e l i f e r o u s Chloride/Hydrochloric It was postulated  that  "free a c i d " would not only  Acid  Laterite in Ferric  Solutions  the presence of higher amounts of increase  metal  recovery at lower  temperatures, but also reduce the consumption of f e r r i c - a more expensive reagent. solutions  Various a c i d i f i e d  ferric  chloride  chloride  were prepared from a stock s o l u t i o n of h y d r o c h l o r i c  a c i d , and used as the l i i x i v i a n t .  As  shown i n Figure  4.4. n i c k e l e x t r a c t i o n  t i v e to f e r r i c  chloride  chloric acid.  In f a c t , i t was apparent that  a c i d s l i g h t l y decreased the  concentration  was more s e n s i -  than to that of hydro-  nickel extraction  amount of i r o n leached i n t o s o l u t i o n .  the presence of  and g r e a t l y  increased  The l a t t e r , however,  occurred only when there was an excess of' "free a c i d " over which was required of the l a t e r i t e . tion  to react with a l l the metal  consitituents  It should be noted that maximum n i c k e l  i n the presence of "free a c i d " occurred only  chloride  concentration  greater  than 1.5 M.  that  extrac-  with a f e r r i c  100  Cone of O • O A  FeCI  M  3  0.5 1.0 M |.5 2.0  M M  25  0  0  i  2  HCI  (M ) CO  Figure 4.4  Effect of "Free Acid" concentration at several FeCl, concentrations on nickel extraction at 423°K and a pulp density of 400 g/1  Tab!e  4.2  Leaching Results  S o l u t i o n T /pe HCI(M) FeCl (MJ 3  In  the  Presence  of  "Free  Pulp Dens 1ty .9/1  N1 Cone. 1n, F11 t r a t e gpl  % Nickel Extraction  Acid"  In  at  423°K  Fe Cone. Lixlvlant gpl  Fe Cone. 1n F i l t r a t e gpl  "Free  Acid" In FI 1 t r a t e  "Free A c i d " Consumed HCl(M)  0.24  2 .00  200  2 1  82  13  23  0. 17  1.83  0.45  1 .93  200  2 2  88  25  33  0. 17  1.76  0.86  1 . 79  200  2 3  90  48  53  0. 1 1.  1.68  1 .57  1 . 50  200  2 4  96  88  88  0. 05:  1.45  0. 24  2 .00  400  3 0  60  1 3  fi.3  0. 09  1.91  0.45  0 .55  400  2 7  54  26  0.2  0. 08-  0.47  0.45  0 .98  400  2 9  58  25  1.2  0. 09  0.89  0.45  1 .93  400  3 8  76  25  14  0. 09  1 .84  0. 58  3 .28  400  4 3  86  33  44  0. 09  3.19  1.57  1 . 50  400  4 7  94  88  62  0. 05  1.45  3 .39  400  4 4  88  26  38  0. 09  3.30  3 .16  400  2 5  50  48  75  0. 04  3.12  0.47 0.86  1  0.86  3 .16  400  4 5  90  48  55  0. 02  3.14  1 .52  2 .84  400  4 6  92  85  85  0. 02  2.82  1.92  3 .00  400  4 2  84  107  110  0. 09  2.91  Leaching  time  Leaching  In  15  minutes.  a l a r g e autoclave  (2  litres  capacity)  with very  little  agitation.  to ro  93  Table 4.2 ferric  of i r o n in the  lixiviant  were due  to d i s s o l u t i o n  ore  in S e c t i o n 4.4).  with the  l e s s than t h i s t h e o r e t i c a l  of f e r r i c  chloride.  The  used and  of i r o n c o n c e n t r a t i o n  in the  the  4.3  of a c i d  value r e s u l t e d  reflected  filtrate  Leaching of N i c k e l i f e r o u s  of  the  concentra-  in the  hydrolysis  depended on in the  the  decrease  as compared to that  in  retard  the  the  rate  chloride,  in the  utilized  Presence  in an  of p r e c i p i t a t i o n of hematite.  thereby speeding up  p r e c i p i t a t e would  of  the  of n i c k e l . on  It was  to  envisaged  increase,  presence of  to a greater extent than h y d r o c h l o r i c  chloride  effort  filtration.  observed however, that  extraction  ferrous  reagent was  p a r t i c l e s i z e of the  It was  Laterite  Chloride  Ferrous c h l o r i d e  the  use  amount,  1i xi vi ant.  Ferrous  that  the  metal c o n s t i t u e n t s The  was  hematite.  theoretical  extent of h y d r o l y s i s  c o n c e n t r a t i o n of a c i d  corresponding  same, whenever  equal to the  to react  using  Higher concentra-  of p r e c i p i t a t e d  i r o n remained the  which i s required  tions  solutions.  as compared to the  c o n c e n t r a t i o n employed was  (as d e s c r i b e d  r e s u l t s obtained  acid  filtrate  c o n c e n t r a t i o n of  acid  leaching  chloride/hydrochloric  tions  The  shows the  nickel  Table 4.3  shows the  extraction.  ferrous  acid, effect  inhibited of  94  Table 4.3  Leaching Results Chloride  in the  at a Pulp Density  %  Solution Type  Presence of Ferrous  Nickel Extraction  of 400  g/1.  Fe Cone. Fe Cone, in Lixiviant" in Filtrate gpl gpl  Acid Consumed HCl(M),  2  36  51  43  -  IM FeCl , 3M HCl  71  55  59  2.80  88  55  55  2.76  IM FeCl , 3M HCl 3  94  55  55  2.82  IM FeCl  3  90  55  12  -  IM. FeCl  2  0.5M FeCl , 0.5M 3M HCl  FeCl,,  9  L  4.4  6  Acid  Consumption During a Batch . Leach  Table 4.4. with each metal exception  shows the amount of a c i d consumed in r e a c t i n g species  of i r o n .  concentration represented  (423°K)  present  These values  of each metal  the q u a n t i t y  leaching  c y c l e , providing  reaction  to supply  acid.  in the  l a t e r i t e , with  the  were c a l c u l a t e d by using  i n the  filtrate.  of a c i d to be there was  no  The  replenished additional  total  the  value  a f t e r each hydrolysis  95  Table 4.4  Acid Consumption During  a Batch  Leach  at 423°K  with a Pulp Density of 400 g/1.  Metal  1  Metal Cone, in Filtrate gpl  Acid Consumption by Individual Metal qpl  Equivalent Acid Concentration HC1(M)  Co  0.6  0.74  0.02  Cr  0.5  1.05  0.03  Mn  4.1  5.58  0.15  Ni  5.0  6.21  0.17  Mg  8.0  24.00  0.66  59.19  1.62  96.77  2.65  Al  14.6  Total  The  calculated  value of 2.65M  h y d r o c h l o r i c a c i d com-  pare f a v o r a b l y with 2.82M, which was obtained using the autot i t r a t i o n method. was to be expected, solution  of f i n e l y  of time taken  The s l i g h t l y  t a k i n g into c o n s i d e r a t i o n f u r t h e r precipitated  to dismantle  An attempt  higher value of a c i d consumed dis-  hematite, during the period  the apparatus  and f i l t e r  was t h e r e f o r e made to determine  the s o l i d s .  i f in fact a  p o r t i o n of the " f r e e a c i d " d i d become consumed i n the d i s solution  of f i n e l y  precipitated  hematite  after leaching.  96  A laboratory  centrifuge  was employed to reduce the period of  time during which the s o l u t i o n was i n contact with the i r o n residue.  By reducing t h i s period  there was an increase  i n " f r e e a c i d " c o n c e n t r a t i o n from about  0.05M to approximately 0.2M. than the t h e o r e t i c a l  This  from 1 hour to 15 minutes,  This  was however, s t i l l  lower  value of about 0.5M.  was confirmed by determining the c o n c e n t r a t i o n of  "free a c i d " produced by heating f e r r i c  chloride  alone, at temperatures of 423°K and 453°K.  solutions  The acid  results  obtained due to h y d r o l y s i s  were compared with those obtained  a f t e r leaching  chloride  mixtures.  with f e r r i c  and a c i d / f e r r i c  chloride  In one experiment, the s l u r r y obtained a f t e r  ing was allowed to stand f o r 13 hours, and t h e . " f r e e centration  i n the f i l t r a t e f e l l  t i o n of i r o n increased  slightly.  leach-  a c i d " con-  to a lower value,, The concentraThe r e s u l t s obtained are shown  in Table 4.5.  ".  . 4.4.1  The E f f e c t of H y d r o l y s i s  on Acid  Consumption  47 Hydrolysis  of f e r r i c  chloride  i s known to begin  at around 393°K, producing hematite and h y d r o c h l o r i c Table 4.5 shows that concentration hydrolysis resulted  at room temperature, the "free  in f e r r i c  chloride  of t h i s s o l u t i o n  s o l u t i o n was 0.06M.  acid. acid" However,  at temperatures, 423°K and 453°K  i n " f r e e a c i d " c o n c e n t r a t i o n of 0.38M and 0.50M  Table 4 . 5  Comparison of " F r e e A d d " C o n c e n t r a t i o n Coneentratlon  S o l u t i o n Type HCT FeCl  Due to the H y d r o l y s i s of F e r r i c  Temperature  Pul p Dens 1ty 9/1  3  In F i l t r a t e s  in  Fe Cone, Lixlvlant  1n  with Acid  Chloride Fe Cone. Filtrate gpl  "Free Add" 1 n Lixlvlant HCl(M)  "Free A d d " 1n F i l t r a t e HCl(M)  2M  -  42 3  -  112  109  0.06  0.38  2M  -  453  -  112  106  0.06  0.50  2M  -  423  400  112  60  0.06  0.07  2M  -  453  40 0  112  58  0.06  0.03  HCl  423  400  110  in-  3.00  0.02  3M HCl  453  400  no  ns  3.00  0.003  2M, 3H 2M,  1  ^ S l u r r y from t h i s run was allowed to stand f o r  13 h o u r s .  98  respectively. with  This i n c r e a s e i n a c i d c o n c e n t r a t i o n  a decrease i n i r o n c o n c e n t r a t i o n  Leaching  of the f i l t r a t e .  experiments were conducted at the same tempera-  t u r e s , employing the same c o n c e n t r a t i o n Lower values  of i r o n c o n c e n t r a t i o n  that f u r t h e r h y d r o l y s i s occurred, necessary  coincided  i n the f i l t r a t e i n d i c a t e d i n order to supply  to r e a c t with metal values  "free a c i d " l e v e l  of f e r r i c c h l o r i d e .  present  more a c i d  i n the ore. The  i n the f i l t r a t e approximated to that i n the  1 i x i v i a n t.  In a n o t h e r l e a c h i n g acid  experiment, an excess of h y d r o c h l o r i c  (over that which was r e q u i r e d f o r complete metal  t i o n ) , was added to a l i x i v i a n t amount of f e r r i c concentration tion  s o l u t i o n c o n t a i n i n g the same  c h l o r i d e used before.  of i r o n  extrac-  A slightly  higher  i n the f i l t r a t e i n d i c a t e d some d i s s o l u -  of the i r o n r e s i d u e .  Further d i s s o l u t i o n was observed on  l e a v i n g the leach s l u r r y to stand  f o r 13 hours.  It f o l l o w s t h e r e f o r e , that d i s s o l u t i o n of the ore gradually  occurred,  producing  was promptly hydrolysed present tained  a ferric  to hematite.  i n the l i x i v i a n t , i n the l a t t e r  chloride intermediate,  Once enough a c i d was  h y d r o l y s i s of f e r r i c  was probably  c h l o r i d e con-  insignificant.  It i s not  known at t h i s stage, what p r o p o r t i o n of the hematite tated from f e r r i c 1ateri te.  which  c h l o r i d e of the l i x i v i a n t  precipi-  or from d i s s o l v e d  99  4.4.2  "Free A c i d " Concentrations  in F e r r i c  Chloride  S o l u t i ons Several  concentrations  of f e r r i c  were heated under the same c o n d i t i o n s  chloride solution  used f o r l e a c h i n g  experi-  ments. The hematite c o l l e c t e d was weighed and the f i l t r a t e analysed  f o r i r o n and " f r e e a c i d " c o n c e n t r a t i o n .  Table 4.6  shows the percentage of i r o n p r e c i p i t a t e d from these along  with t h e i r a c i d c o n c e n t r a t i o n s .  hematite i s p r e c i p i t a t e d from f e r r i c  The extent  i n Figure  released  are i l l u s t r a -  4.5.  At f e r r i c ' c h l oride concentrations quantity  to which  c h l o r i d e s o l u t i o n s , and  the amount of " f r e e a c i d " thereby being ted  solutions  greater  than IM, the  of a c i d l i b e r a t e d due to h y d r o l y s i s was more dependent  on temperature than on c o n c e n t r a t i o n experiment, using concentration  a 1 molar f e r r i c  of h y d r o c h l o r i c  of the former.  In one  c h l o r i d e s o l u t i o n , the  a c i d determined was 0.39M at  423°K, as compared to 0.53M at 453°K.  4.5  The Determination of Leaching Calculated  amounts of n i c k e l c h l o r i d e hexahydrate were  added to each batch of leach and  Equilibrium  s o l u t i o n to give 20 g p l , 40 gpl  60 gpl n i c k e l r e s p e c t i v e l y .  Leaching experiments were  conducted at 423°K and 448°K, and the i r o n residue was c a r e f u l l y washed and  analysed.  obtained  Table 4.6  Iron P r e c i p i t a t i o n  Fe.Cone. in S o l u t i o n gpl  Fe Cone, in F i 1 t r a t e gpl  From F e r r i c Chloride S o l u t i o n s at 423°K.  wtiJ of  Fe  Preci pi tated gms  Percentage Preci pi t a t i on of Fe  "Free A c i d " Cone, in F i 1 t r a t e HCT(M)  27.2  19.8  7.4  27  0. 51  54.4  47.5  7  13  0. 50  109  105  4  3.7  0.39  110  104  6  5.4  0.53  1  21 7  215  2  0.01  0.41  2  Determined at 453°K. Determined at 433°K. o o  0.5  20  —o—H  0.4 h  £  4)  0.3  o  Precipitation  \  12  Free  acid  °. o  3  \  \  0.2  ° "0 CO  \ A \  16  H  \  8  «04  +.  \  U-  \ 0.  0 0  40  \  A  80  120  L  +  60  200  240  ](gpi)  Figure 4.5 "Free Acid" concentration and percentage iron precipitation versus iron (III) concentration at 423°K.  102  Results 90  shown in Table 4.7  percent n i c k e l can  reagent, in the Table 4.7  be e x t r a c t e d  L a t e r i t e in the  Solution  with 1M  ferric  chloride  presence of up to 60 gpl n i c k e l .  Percentage Nickel  of  i n d i c a t e that at 423°K over  Extraction  from  Nickeliferous  Presence of High Concentrations  Nickel  Pulp Dens i ty , .g-.p-.l-.  Type  Nickel Cone, in F i l t r a t e gpl  Percentage Nickel E x t r a c t i on  20 gpl  Ni,  2M  FeCl  3  200  22.5  98.4  40  gpl  Ni , 2M  FeCl  3  200  42.2  97.6  60 gpl  Ni , 2M  FeCl  3  200  62.5  95.2  60 gpl  Ni , 1M  FeCl  3  200  62.0  91 .2  4.6  Simulation  of a Continuous Leaching  A constant c h l o r i d e ion a c t i v i t y  Circuit  was  maintained by  adding  calculated  amounts of 6N magnesium c h l o r i d e , aluminium c h l o r i d e ,  and  c h l o r i d e to a constant volume of 9.6N  ferric  acid.  These c h l o r i d e s wen.e known to be  of the  filtrate.  leaching  c y c l e was  The the  tofral  the main  volume of the  same, and  the  final  hydrochloric constituents  lixiviant acid  in each  concentration  103  Was  2.4N  hydrochloric acid.  c h l o r i d e s o l u t i o n was shown f o r comparison  •Figure 4.5  A S i m i l a r run with  conducted and (see Table  illustrates  how  the r e s u l t s obtained  acid concentration, resulted extracted.  manganese showed s i m i l a r e x t r a c t i o n behaviours, little  nium and crease  chromium was  extracted.  magnesium decreased  in f e r r i c  are  a decrease in f e r r i c c h l o r i d e  in a decrease in the percentage of n i c k e l  very  ferric  4.8).  c o n c e n t r a t i o n , d e s p i t e a constant  and  only 6N  The  Cobalt whilst  e x t r a c t i o n of  alumi-  g r a d u a l l y as a r e s u l t of the  de-  c h l o r i d e c o n c e n t r a t i o n , and/or because of the  common ion e f f e c t .  4.7  Morphology of the 4.7.1  described  (see Table  Scanning E l e c t r o n Microscope was  p a r t i c l e s obtained in Section 4.4.2.  in the nature, different  Residue  Hematite from the H y d r o l y s i s of F e r r i c The  scrutinize  Iron  shape and  from each of the There was  Chloride  employed to  experiments  no d e t e c t a b l e d i f f e r e n c e ,  s i z e of the p a r t i c l e s obtained  temperatures - only  at  in the q u a n t i t y of p r e c i p i t a t e  4.6).  There was  however, an  increase in p a r t i c l e s i z e of the  hematite p r e c i p i t a t e d from f e r r i c  c h l o r i d e s o l u t i o n s ranging  Table  4.8  Percentage  1 i Yi vi ant S o l u t i o n Type  Metal  ComDOsition Volume  (mis)  Extraction  in a S i m u l a t e d  Metal Cone, in Li xi vi ant gpl  Continuous L e a c h i n g  Fe Cone. in F i l t r a t e gpi  Circuit  Percen tage  Met al  E x t r a : t i on  Ni  Co  . .Mn  Cr  Al  Mg  98  91  91  20  78  76  91  90  91  20  76  75  85  89  90  20  74  74  65  85  88  20  59  49  56  75  77  20  48  25  50  48  62  20  16  15  Staqe 1 6N  FeCl  3  40  110  60 Stage 2  HCl  10  6M F e C l  3  30  6N A l C I  3  6N M g C l  2  9.6N  82.5  75  Stage 3 9.6N 6N  1 0  HCl  FeCl  3  6N A l C I  3  22.5  6N MgCU  52  5  6  2.5  5  58  Stage 4 9.6M HCl  10  6N  15  41  10  12  5  10  FeCl  3  6N A l C I  3  6N M g C l  2  i  60  Stage 5 9.6N 6N  10  HCl  FeCl  3  6N A l C I  3  6N M g C l  7.5 1 5 '  2  7.5  21  42  18 15 Stage 6  9.6N 6N  HCl  10 26  FeCl  3  6N A l C I  3  20  24  6N M g C l  2  10  19  1  Lixiviant  composition (gpl)  Figure 4.6 Metal extraction versus lixiviant composition at 423°K and a pulp density of 400  Table 4.9  Chemical A n a l y s i s of the Iron Residue From Each Stage Stages  Element  1  3  ... -2  4  5  6  Weight Percentage  • Laterite . Sample  44.55  Fe  57.5  57.5  56.2  48.2  45.4  44; 7  Ni  0.02  0.17  0.38  0.54 .  0.64  0.7  1 .25  Co  0.014  0.01.5  0.017  0.022  0.038  0.078  0.15  Cr  1.81  1 .81  -  -  -  -  2.26  Mn  0.10  0.10  0.11  0.13  0.25  0.41  1 .08  Mg  0.34  0.44  0.49  0.95  1 .72  2.07  2.31  Al  9.90  0.88  1 .08  2.72  3.09  3.58  4.68  Si  2.46  -  -  -  -  2.65  1  -  Estimated. o  cn  107  in c o n c e n t r a t i o n from 0.5M  to 2M.  Figures 4.7 ( a ) , ((b), (c) and  (d) show SEM photomicrographs of hematite p a r t i c l e s at 5000 times m a g n i f i c a t i o n , with p a r t i c l e s i z e to 2v -  The p a r t i c l e s were s p h e r i c a l  m  increasing  from 0.8ym  and uniformly  shaped,  with a tendency to agglomerate.  u :, 4.7.2  Iron Residue from the Hydrothermal of N i c k e l i f e r o u s  Treatment  L a t e r i t e with F e r r i c  Chloride  Solutions Hematite p a r t i c l e s p r e c i p i t a t e d experiments, i n which the l i x i v i a n t chloride, larger  employed was  possessed h i g h l y etched s u r f a c e s .  leaching  ferric  P a r t i c l e s were  than those obtained from the h y d r o l y s i s of f e r r i c  chloride solution  alone, and were i r r e g u l a r  The surfaces of p a r t i c l e s may be somewhat d i f f e r e n t graphs  during  (Figure 4.8).  solution  in p a r t i c u l a r  immediately a f t e r  precipitation  from those shown i n the photomicro-  There were i n d i c a t i o n s directions  t i o n of flow of the f i l t r a t e solution  in shape.  of surface  corresponding to the d i r e c -  during f i l t r a t i o n .  was p a r t i c u l a r l y v i s i b l e  This  solution"  dis-  i n photomicrographs of  p a r t i c l e s obtained through pressure f i l t r a t i o n , which an average of 30 minutes  dis-  f o r completion.  required  Such "laminar d i s -  was not apparent on p a r t i c l e s recovered using the  centrifugal  technique.  Figure  4.7  (a)  (b)  (c)  (d)  Hematite p a r t i c l e s p r e c i p i t a t e d from s o l u t i o n s at 423°K. a)  from 0.5M  FeCl  b)  from 1M F e C l  3  (5000 x)  c)  from 2M  FeCl  3  (5000 x)  d)  from 4M  FeCl,  3  (4000 x)  (5000 x)  ferric  Figure 4.8  Iron r e s i d u e o b t a i n e d from the hydrothermal of  nickeliferous  laterite  with f e r r i c  a)  from 2M  F e C l g , 433°K  ( 380 x)  b)  from 1M  FeCl  (2000 x ).  3 >  423°K  treatment  chloride  solutions.  o  no  The cause of such r e d i s s o l u t i o n was  the r e v e r s a l of the  h y d r o l y s i s r e a c t i o n on c o o l i n g .  This behaviour was  by the thermodynamic  developed in Section 2.2.6,  information  and evidenced by the l o s s of " f r e e a c i d " during tact  between residues  Temperature  morphology  4.7.3  of the f e r r i c c h l o r i d e  of the p a r t i c l e s .  Iron Residue from the Hydrothermal  Treatment of  Nickeliferous  Chloride/  L a t e r i t e with F e r r i c Solutions  The photomicrographs of Figure 4.9 faces of p a r t i c l e s obtained  f i n e r than those obtained This r e d u c t i o n was  show the sur-  from the above l e a c h i n g e x p e r i -  ments to be porous and h i g h l y etched.  4.8  4.4.  did not have any s i g n i f i c a n t e f f e c t on the  H y d r o c h l o r i c Acid  solution  extended con-  and s o l u t i o n , as shown in Section  and c o n c e n t r a t i o n  s o l u t i o n employed  predicted  The p a r t i c l e s were  from the preceding  experiment.  a t t r i b u t e d to a greater extent  of r e d i s -  of the p r e c i p i t a t e on c o o l i n g .  Comparison  of N i c k e l i f e r o u s L a t e r i t e and the Iron  Residue by E l e c t r o n M i c r o a n a l y s i s Figure 4.11 nickel-bearing residues  shows SEM  laterite  X-ray analyser  particles  spectra taken f o r  (see Figure 4.10),and  p r e c i p i t a t e d under d i f f e r e n t  iron  leaching conditions.  Figure 4.9  Iron r e s i d u e o b t a i n e d from the hydrothermal of n i c k e l i f e r o u s l a t e r i t e hydrochloric  with f e r r i c  treatment  chloride /  acid solutions.  a)  from IM F e C l g , 3M HCl, at 423°K  b)  from IM F e C l , , 2.5M  (2000 x )  H C l , at 423°K  (800 x ) .  (b)  (a) Figure 4.10  a)  Main n i c k e l - b e a r i n g p a r t i c l e s c o l o u r , 2000 x) white areas g o e t h i t e ; or quartz darker magnetic regions high  b)  Predominantly  (of r e d i s h brown  d e p i c t the mineral areas  represent  i n chromium,  g o e t h i t e (4000 x ) .  (a)  to +J  c  3 o c_>  N  i  \*V  —  CD  o  (b)  Mg Al  CI  Ca  Cr  Cr Fe  -> X-ray Energy Figure 4.11  Fe  T t  Ni Ni  "  (keV)  SEM x-ray analyser spectra for nicke iferous laterite and iron residue (a) ...Iron residue from leach with 2M FeCl at 453°K (b) Nickeliferous laterite (c) Iron residue from leach with 2M FeCl , 3M HCl, at 453°K 3  3  114  The s p e c t r a , c o n t a i n i n g  500,000 counts each, are shown together  in order to accentuate t h e i r d i f f e r e n c e s . feature i l l u s t r a t e d ium and n i c k e l  4.9  The most s t r i k i n g  i s the disappearance of aluminium, magnes-  from the l a t e r i t e .  Comparison  of P a r t i c l e s  Found i n N i c k e l i f e r o u s  and the Iron Residue by E l e c t r o n  Laterite  Microanalysis.  The photomicrographs shown i n Figures 4.12 and 4*13 i l l u s t r a t e the various shapes and r e l a t i v e in the l a t e r i t e  and i r o n r e s i d u e .  s i z e s of p a r t i c l e s found  Figure 4.14 shows the cor-  responding SEM X-ray analyser spectra f o r some of those p a r t i c l e s before l e a c h i n g . sence and r e l a t i v e  Each spectra served to iindicate the pre-  abundance of elements without being t r u l y -  quanti t a t i ve.  Quartz and chromite p a r t i c l e s were i n s o l u b l e under ing c o n d i t i o n s .  However, there were i n d i c a t i o n s of the removal  of magnesium, aluminium and minor amounts of n i c k e l particles.  Some p a r t i c l e s  a significant which  referred  from these  to as magnetic, contained  amount of magnesium, as d i s t i n c t  from chromite,  showed stronger peaks of chromium with l e s s magnesium.  The spectra shown i n Figure 4.15 i l l u s t r a t e s appearance of magnesium, aluminium and n i c k e l after  leach-  leaching.  from  the d i s particles  (a)  Figure  4.12  (b)  a)  Silicate  particles  b)  Pale-yellow  after  silicate  (400  leaching x).  in  HC1/HN0  3  (200  x)  116  Figure 4.13  (a)  (b)  (c)  (d)  Magnetic particles found in nickeliferous laterite and the iron residue a)  magnetic particle before leaching (2000 x)  b)  from 2M FeCl , at 453°K (340 x)  c)  from IM FeCl , 3.6HC1, at 423°K (1500 x)  d)  from 2M FeCl_  3  3  v  at 423°K (4200 x)  (a)  CO  o o  (b)  O  (c)  Mg Al Si Cl  Cr  Cr Fe  X-ray Energy Figure 4.14  Fe e .7"Ni Ni* :  !  "  '•  (keV)  SEM x-ray analyser spectra f o r s i l i c a t e (a) Insoluble s i l i c a t e (b) . Magnetic ' p a r t i c l e before l e a c h i n g (c) Chromite p a r t i c l e before l e a c h i n g  and magnetic  particles  Cr • SEM  Cr  Fe  > X-ray Energy  x-ray analyser  in the iron  Fe (keV)  spectra f o r magnetic  particles  residue.  (a) Magnetic p a r t i c l e from leach with TM FeC13, 3.6M HCl, at 423°K. (b) Chromite  particle  119  Chapter  5  DISCUSSION  5.1  Review of Leaching  Results  It was  in the  established  i r o n e x t r a c t i o n and from g o e t h i t e and  therefore  the  were p r o p o r t i o n a l  c h l o r i d e ion a c t i v i t i e s .  done by the  l i t e r a t u r e that the rate of rate of n i c k e l e x t r a c t i o n  to the  However, leaching  author i n d i c a t e that e x t r a c t i o n was  dependent on c h l o r i d e ion a c t i v i t y  This was constant one  confirmed by  hydrochloric  more h e a v i l y activity.  experiments in which a  c h l o r i d e ion c o n c e n t r a t i o n 91  hydrogen  experiments  than hydrogen ion  leaching  case, n i c k e l e x t r a c t i o n was  a ferric  product of the  of 5.5N percent  was using  employed. In a  5.5N  a c i d s o l u t i o n , as compared to 94 percent  using  c h l o r i d e / h y d r o c h l o r i c a c i d mixture of a t o t a l  chloride concentration  of 5.5N.  The  use  of f e r r i c  alone r e s u l t e d in a n i c k e l e x t r a c t i o n of 96 concentration  of c h l o r i d e ion was  mated the  total  chlorides  (see Section  chloride  percent.  This  employed, as i t approxi-  amount of a c i d consumed in producing metal 4.4)  at a pulp d e n s i t y  of 400  g/1.  120  Magnesium and  aluminium showed s i m i l a r e x t r a c t i o n  haviour, with approximately 75 under most c o n d i t i o n s  percent of the metal  of a c i d and  ferric  chloride  be-  extracted  concentra-  tions.  Maximum e x t r a c t i o n under c o n d i t i o n s be  previously  expected, because of the  metal  5.2  manganese was  described.  The  function  shown in. Chapter 2, that the  two  g/1  of pH with a slope  Fe)  of minus 3.  log of the  in s o l u t i o n , the  pH  Potential/pH  diagram  51  f o r the  ions were observed to be  at about the  same  due  H0 2  of  (approx.  to  of  ferric  the  system at 423°K,  in e q u i l i b r i u m with  hematite  pH.  However, these s l u r r i e s were cooled filtration  a linear  to h y d r o l y s i s  With reference Fe —  activity  At a temperature  ion a c t i v i t y of about 1M  c h l o r i d e would be around -1.6.  ferric  Hydrolysis  ion in e q u i l i b r i u m with hematite was  423°K with a f e r r i c  -1.6  however, to  close a s s o c i a t i o n of the  S i g n i f i c a n c e of A c i d i t y During  of f e r r i c  and  This was  achieved  oxides.  It was  56  of c o b a l t and  or c e n t r i f u g e  separation  below 353°K before  of s o l i d s was  at t h i s lower temperature the e q u i l i b r i u m at 423°K to -1.04  attempted,  pH  r i s e s from  at 333°K (see Table 2.2),  a decrease  121 [  in  f r e e a c i d of a f a c t o r of 3.6.  i s t h e r e f o r e a n t i c i p a t e d , but  R e d i s s o l u t i o n of hematite  because i t i s slow, i t i s more  s e r i o u s under c o n d i t i o n s of long conditions  5.3  of short c e n t r i f u g a l s e p a r a t i o n  Nature of the Table  5.1  r e s i d u e , with  Iron  Steel  compared f a v o r a b l y , the  diffraction  f o r the  i n t e n s i t y of the  c h l o r i d e s o l u t i o n s only may  residue by  the  obtained  from leaches  However, the  Therefore,  nickel,  considera-  peaks obtained  from leaches  with  in x-ray ferric  have been more c r y s t a l l i n e  particle  i t i s not  than  in the presence of hydro-  in the presence of a c i d was  s i z e of residues  smaller  ob-  than that in the  known at t h i s p o i n t , whether  the decrease in peak i n t e n s i t y was  The  ore.  steelmaker.  p a t t e r n s , i r o n residues  chloric acid.  iron  Other d e l e t e r i o u s i m p u r i t i e s such as  Judging from the  particle  iron  aluminium would a l s o r e q u i r e separate  t i o n , reserved  former.  a n a l y s i s of the  too much chromium f o r large-tonnage use  magnesium and  tained  times.  that of c u r r e n t l y marketed r e g u l a r i r o n  Industry.  residues  times than under  Residue  compares the chemical  Although the analyses contained  filtration  due  to a decrease in  s i z e or reduced c r y s t a l 1 i n i t y .  SEM  X-ray analyser  spectra of magnetic  particles  122  Tab!e 5.1  Comparison of Raw  Materials  Iron and Steelmaking  Analysi s • Dry %  Fe  Leached Nickeliferous Laterite  57.5  Used i n the  Industry  Iron Ore Pel 1ets  64  Normal Iron Ore  59  Si  2.46  2.8  4.2  Al  0.90  0.27  0.8  Ca  -  -  0.2  Mg  0.34  0.3  0.1 2  Mn  0.10  0.2  0.5  Cr  1 .81  0.01  0.01  Co  0.01  0.01  00.01  Ni  0.1  0.01  0.01  123  before and a f t e r l e a c h i n g experiments showed very extraction  of chromium.  more e a s i l y  It was apparent that n i c k e l  r e l e a s e d from i t s l a t t i c e  and that the r e s i d u a l  nickel  positions  and chromite p a r t i c l e s .  5.4  P r e c i p i t a t i o n of Hematite i n  Supersaturated 5.4.1  Ferric  Homogeneous  was  in goethite,  occurred mainly as replacement  atoms i n s i l i c a t e  Hydrothermal  little  Chloride  Solutions  Nucleation  Thermodynamical1y, a homogeneous  supersaturated  solution  i s i n a metastable s t a t e and may remain so i n d e f i -  nitely.  Before n u c l e i  critical  equilibrium  (volume  can grow, the system must overshoot a  point and pass i n t o the region where  free energy) i s negative.  ponds to a f i n i t e  critical  formed can grow.  Such n u c l e i  This e q u i l i b r i u m  AG  corres-  s i z e , at which a nucleus i f so can be formed spontaneously  w i t h i n the system due to s t a t i s t i c a l  fluctuations  energy, or may be provided a r t i f i c i a l l y  The Gibbs f r e e energy of n u c l e a t i o n  i n the free  by seeding.  i s given by the  52 expresslon: AG = d AG  +  3  11  y  ad  2 Y  •  ...5.1  124  where d  = The a p p r o x i m a t e  diameter  of  the  nucleus  3  d  = volume  ad  of  = surface  2  a  the  nucleus.  area,  = A factor  related  (approximately AG  = Volume f r e e  y  required in Y  square  of  depends  on  absolute  for  to  free  interface  per  shows  surface  unit  of  d  energy  to  AG v a r i e s  the  solid/  the  bulk  free  according  the  energy  to  the  nucleus.  temperature  ferric  ions  values  of  d,  surface  volume  solutions).  be d e p e n d e n t on  Therefore,  d the  be  and-a.  cube.  the  of  to  positive).  whereas  the  volume  assumed  area  dimensions  of  nucleation).  phase  nuclear  volume  nucleus  supersaturated  (always  be i n d e p e n d e n t  to  large  energy  the  energy/unit  negative  lative  at  (free  1 piece;  v  its  When the  energy  of  homogeneous  solid  5.1  the  5 for  shape  form the  liquid  Equation  the  to  = Surface  Assume y . ' a n d A G  to  in  is  such  solution,  that AG  hematite is  y  term d o m i n a t e s  free  energy  is  stable  negative.  and AG i s  term d o m i n a t e s  At  re-  small  positive; because  this  3  is  proportional  passes  through  depend on A G hematite  y  to  d .  At  a maximum and thus  particles  a critical  particle  d e n o t e d by W.  upon  smaller  the than  The v a l u e  temperature. d  leads  size  to  of  Growth an  d^, AG W and d^ of  increase  in  125  the  free energy  particles r  c  to d i s s o l v e  are s t a b l e  free energy. equal  and thus,there i s a g r e a t e r tendency  because  rather  than grow; p a r t i c l e s l a r g e r  growth i s accompanied  P a r t i c l e s of diameter d  chance  of d i s s o l v i n g  illustrates  there i s a g r e a t e r tendency  to thermal  5.4.2  due  of the diameter  fluctuations  (  5 3  from s u p e r s a t u r a t e d phase,  of atoms across an i n t e r f a c e with a r e species.  ducted, i t was expected that  In leaching  experiments  factors:  1)  The d e t a i l e d mechanism by which  2)  The rate  3)  Size  the i n t e r f a c e  of d i f f u s i o n of the atoms i n both Small  con-  the growth rate may have depended  upon some or a l l of the f o l l o w i n g  solubility  b a r r i e r W due  the formation of the p r e c i p i t a t e  d i s t r i b u t i o n of s o l u t e  effects:  although  and grow.  Growth of N u c l e i  involves  T<Tr;,  f o r p a r t i c l e s of diameters d , and  some may overcome the f r e e energy  to the t r a n s f e r  radii  the free energy of  At temperatures  The growth of p r e c i p i t a t e s solutions  by a decrease i n  are unstable having an  embryos as a f u n c t i o n  f o r a s e r i e s of temperatures.  &2 t° s h r i n k ,  c  than  or growing.  Figure 5.1 g r a p h i c a l l y formation of s p h e r i c a l  f o r such  propagated.  phases.  p a r t i c l e s of a phase have a higher  than l a r g e r ones, due to d i f f e r e n c e s  of curvature of the i n t e r f a c e s .  i n the  Figure  5.1  The free energy of formation of spherical embryos as a function of the diameter for a series of temperatures.  127  The sults (see the  heating of f e r r i c  i n a system c o n t a i n i n g Figure 5.1).  system could  total  chloride  interfaces.  The chloride due  in equilibrium  5.5  p a r t i c l e s to  with a p r e c i p i t a t e  from the s o l u t i o n  i s larger  near to small  coarsening of p r e c i p i t a t e s with i n c r e a s i n g  ferric  c o n c e n t r a t i o n as shown i n Figure 4.7, may have been nature of the increase  of varying  sizes within  i n the quantity  each system.  to provide the s o l u t e  Goethite Saturated  of  Furthermore,  p r e c i p i t a t e p a r t i c l e s are more s o l u b l e ,  they  f o r growth of the l a r g e r  The Degree of S u p e r s a t u r a t i o n  The  to small  requires  causes the l a t t e r to d i s s o l v e .  because small dissolved  process  i n the  p a r t i c l e of p r e c i p i t a t e than f o r a large one).  to the gradual  particles  f r e e energy of  ones (because the c o n c e n t r a t i o n of s o l u t e  T h e r e f o r e , removal of s o l u t e particles  This  from regions c l o s e  regions around large  f o r a small  i n the o v e r a l l  nuclei  only be accomplished by a reduction  of s o l u t e  in the s o l u t i o n  above 393°K r e -  mixed s i z e s of hematite  A reduction  area of i n t e r n a l  diffusion  solution  ones.  f o r Hematite i n a  Solution.  f r e e energy per u n i t volume f o r n u c l e a t i o n  can be  54 expressed by: AG  =  RT In  a a  o  .5.2  128  where a c t i v i t y of the d i s s o l v e d matter  a  solubility using  S =  AG  at the actual  a.• ( s u p e r s a t u r a t i o n  temperature.  ratio)  RT In S  v  Equation 5.3 shows that an increase tion  ratio  solution.  r e s u l t s i n an increase  i n the  supersatura-  of the f r e e energy of the  This added f r e e energy i s then a v a i l a b l e to over-  come the n u c l e a t i o n  f r e e energy b a r r i e r .  If the f r e e energy  a v a i l a b l e from t h i s source exceeds the c r i t i c a l energy f o r the most unstable  n u c l e i i n Figure  maximum f r e e  5.1, a l l s i z e s  of n u c l e i become s t a b l e and the b a r r i e r f o r n u c l e a t i o n ishes.  Under these c o n d i t i o n s  nucleation  growth rates are almost i r r e l e v a n t ; t h i s a large number of very  In l e a c h i n g goethite  particles.  experiments conducted, -* i t appeared that the  s o l u t i o n s with the inherent  A large amount of very  the  large i n t e r f a c i a l  super-  f a s t rate of n u c l e a t i o n .  f i n e hematite p a r t i c l e s p r e c i p i t a t e d  under c o n d i t i o n s  particles  that  s o l u t i o n produces  d i s s o l v e d r a p i d l y to produce s u f f i c i e n t l y  saturated  rapidly  small  i s so f a s t  van-  where growth was l i m i t e d because of  area  generated by n u c l e a t i o n .  Such  r e c e i v e a l i m i t e d amount of p r e c i p i t a t i n g s o l u t e  which r e s u l t e d i n f i n e p r e c i p i t a t e s and poor  fi1terabi1ity.  129  However, equation 5.3 i n d i c a t e s  that  i f a lower degree of  supersaturation  can be e s t a b l i s h e d  (and  a decrease i n the f r e e energy of formation AG),  therefore,  hematite p a r t i c l e s w i l l  during  goethite  not nucleate spontaneously.  do surmount the f r e e energy b a r r i e r and grow w i l l l a r g e r than under spontaneous n u c l e a t i o n fi1terabi1ity  can t h e r e f o r e  By c o n s i d e r i n g activities  Those  that  become much  conditions.  Improved  be expected.  the t h e o r e t i c a l e q u i l i b r i u m  of f e r r i c  dissolution  ion as described  pH at several  in sections  2.2.5 to  2.2.7, the free energy f o r the p r e c i p i t a t i o n of hematite from a goethite ferric lated  saturated  s o l u t i o n can be c a l c u l a t e d .  ion a c t i v i t y  in equilibrium  at room temperature using pH  =  1 3  Assuming t o t a l pH, were f i r s t  •log K  Values of  with hematite were c a l c u -  the r e l a t i o n s h i p : log  Fe  3  +  d i s s o l u t i o n of g o e t h i t e ,  the  associated  c a l c u l a t e d , employing the e q u i l i b r i u m  constant  3+ f o r the Fe  - FeOOH e q u i l i b r i u m  at 423°K.  were then used to c a l c u l a t e the a c t i v i t y equilibrium  These pH values  of f e r r i c  ion i n  with hematite, t h i s time, employing the e q u i l i 3+  brium constant f o r the Fe  - F^O^  equilibrium  at the same  temperature. The r e s u l t s obtained are shown below: Log [ F e ] pH Log [ F e ] [ F e ] (Hematite) 3+  3+  3+  3+  (from dissolved FeOOH)  (in'equilibrium with Fe^Og) , [Fe ] (Goethite)  0  -1.48  0.36  2.29 x  -1  -1.15  -1.35  2.24 x  -2  -0.81  -2.37  2.34 x  130  Using equation 5.3,  (Max.)  RT In 2.3 700  c a l o r i e s MOL  Fe  These data make i t c l e a r that 700 c a l o r i e s are a v a i l a b l e  from  a saturated solution  the n u c l e a t i o n free energy probably  3+  at 423°K.  per mole Fe  3+  of g o e t h i t e to overcome  b a r r i e r of hematite.  This value i s  high enough to cause spontaneous n u c l e a t i o n of hema-  tite yielding  very f i n e , poorly f i l t e r a b l e  precipitates.  131  Chapter  6  CONCLUSION  T!he  r e s u l t s of the  leaching  promising process might be  experiments i n d i c a t e that a  devised f o r the  treatment of n i c k e l i f e r o u s l a t e r i t e solutions.  D i r e c t ore  pyro-metal1urgical  attack  reduction,  with f e r r i c  obviates the but  hydrothermal  at the  chloride  need f o r p r i o r  expense of  unit  operations to recover magnesium, aluminium, manganese, and chromium.  Of the and  chlorides  magnesium hydrolyze r e a d i l y at moderate temperatures.  Hydrochloric  a c i d can  l i q u o r by h y d r o l y s i s 1958), and  recycled  therefore  be  system.  Close s c r u t i n y of the  leaching  of a continuous leaching  stages of l e a c h i n g  to obtain  recovered from the mother  in an Aman-type r e a c t o r in the  simulation two  present in s o l u t i o n , i r o n , aluminium  at l e a s t 90  r e s u l t s obtained circuit,  would have to be percent n i c k e l  (AMAN, J .  indicate  utilized,  extraction.  1956,  in  the  that  in order  132  Owing to the amorphous and cipitated order  residue, f i l t r a t i o n  to thoroughly  wash the  repulp at l e a s t twice. chlorides.  friable  was  r e s i d u e , i t was  acceptable probably  p r a c t i c e , an economic  more, recovery  without  regard  The  balance  evaporating  further beneficiation.  o f , at most, h a l f of the ore's  Further-  chromium con-  but of doubtful  merit.  marked d i f f e r e n c e in the morphology of hematite  precipitated  from f e r r i c due  c h l o r i d e reagent,  and  iron  residue was  1)  D i s s o l u t i o n of the p r e c i p i t a t e on c o o l i n g .  2)  Rapid p r e c i p i t a t i o n  that of  pitation  under super-saturated  conditions. filter-  It appears however, that once c o n d i t i o n s of can  the  to the f o l l o w i n g :  These c o n d i t i o n s r e s u l t e d in a p r e c i p i t a t e of poor ability.  residue.  to chromium, and  tent by p h y s i c a l means i s a p o s s i b i l i t y industrial  to  i r o n ore residue would not meet  s p e c i f i c a t i o n s with  nickel  In  necessary  the l o s s of c h l o r i d e s in the  It appears that the  pre-  removed a l l of the  would have to be struck between the cost of excess wash water and  of the  extremely d i f f i c u l t .  This v i r t u a l l y  In i n d u s t r i a l  nature  preci-  be c o n t r o l l e d , some improvement in p a r t i c l e  s i z e and/or shape may  be expected.  b e t t e r f i 1 t e r a b i 1 i t y of the i r o n  This should  residue.  r e s u l t in  133  Chapter  7  SUGGESTIONS FOR  7.1  FUTURE WORK  Improvement i n Experimental In  this  Procedure  i n v e s t i g a t i o n , l e a c h i n g was  runs using a small titaniurn a u t o c l a v e . ,  restricted  to batch  Such runs had the  drawback that a s i g n i f i c a n t amount of h y d r o l y s i s occurred i n the  heating up p e r i o d , which  therefore d i f f i c u l t  took about 20 minutes.  to assess the e f f e c t of v a r i a b l e s such as  r e t e n t i o n time and temperature  from such  experiments.  A continuous experimental arrangement be d e v i s e d , i n which  should t h e r e f o r e  the leach s o l u t i o n to be hydrolysed i s  pumped c o n t i n u o u s l y i n t o a heated a u t o c l a v e . slurry  The  reacted  i s allowed to overflow c o n t i n u o u s l y into a r e c e i v i n g  v e s s e l , the contents of which may  be p e r i o d i c a l l y adjusted  and r e c y c l e d .  With  be in a regime  s u i t a b l e f o r continued growth,  such back mixing, hematite n u c l e i because  t i o n s of severe s u p e r s a t u r a t i o n can be avoided. of  It was  supersaturation will  precipitates.  would condi-  Lower l e v e l s  lead to slow n u c l e a t i o n and coarse  134  REFERENCES 1  Queneau, P.E. and Roorda, H.J. Cobalt and the N i c k e l i ferous Limonites. De Ingeneur, V o l . 83, No. 28, (1971), pp. 1-9.  2  B o l t , J.R., Queneau, P.E. The Winning of N i c k e l . 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The S t a b i l i t y R e l a t i o n s of Goethite and Hematite ( D i s c u s s i o n ) - Econ. Geol ., V o l . 26 , (1 931 ), pp. 442-445.  46  Smith, F.G. and Kidd, D.J. (1949), p. 403.  47  Katsurai , T. and Watanabe, T. The S t r u c t u r e of Iron Oxide Prepared by the Autoclave Treatment. S c i . Pap. Inst. Phys. Chem. Res., Tokyo, V o l . 13, pp. 89-92.  48  Queneau, P.E. Cobalt and the N i c k e l i f e r o u s Limonites Doctoral T h e s i s , U n i v e r s i t y of D e l f t , 1971, p. 254.  Am. M i n e r a l o g i s t , V o l . 34,  137  49  K e l l e y , K.K. U.S. Bureau of Mines B u l l e t i n 476 U.S. Government P r i n t i n g O f f i c e , Washington, D.C., 1949.  50  Barner, H.E. and Scheurman, R.V. Handbook of Thermochemical Data f o r Compounds and Aqueous Species 1978.  51  B i e r n a t , R.J. and Robins, R.G. High Temperature Potential/pH Diagrams f o r the Iron-Water System E l e c t r o c h i m i c a Acta, V o l . 17, (1972), pp. 1261-1283.  52  C o t t r e l l , A. An I n t r o d u c t i o n E d i t i o n , SI U n i t s .  53  Burke, J . Metals.  54  N i e l s e n , A.E.  to M e t a l l u r g y ,  Second  The K i n e t i c s of Phase Transformations in K i n e t i c s of P r e c i p i t a t i o n  Pergamon.  Appendix A  CRISS AND COBBLE CALCULATIONS  139  , Appendix A  The E f f e c t 1)  of Temperature on Thermodynamic Parameters  Consider the E f f e c t a S i n g l e Species  of Temperature on Enthalpy of  Involved in a Reaction  S and AH  C  p  =  /  C  2  p  (T -T,) 2  average being used due to the f a c t that C  normally constant between the  2)  The E f f e c t  of Temperature on  AS„ P  =  C  P  In  T _2 0  temperatures.  Entropy  p  i s not  140  3)  The  E f f e c t of Temperature temperature, T ^  At  on Free  =  At temperature, T ^  ^2  -,T-jS^  ^2 ~  =  Energy  ^2^2  therefore. =  AG  - ( 2" J T  AH  T  S  l "  T  2  A S  where A H and AS have a l r e a d y been d e f i n e d .  Considering now reaction  the change in f r e e energy of a  in going from 298°K to temperature  AGj - A G °  g 8  = AH° - A H ° . -. g 8  g  ...(a)  AC° d (In T)  ...(b)  (TAS°  - 298AS° g)  T.  however, AS° - A S °  =f  9 8  AC° d (In T) 298  therefore, TAS° = T A S °  + T f  g 8  '2 98 now A H  T  *  AH  298 f =  A C  p  ••'  d T  298  J  by s u b s t i t u t i n g AG° = A G °  9 8  t  (c) and  f  (b) i n t o  AC° dT - T A S °  » o  (a) we  g 8  r\ t  298  f '298  AC° d ( l n T) + 298  AS°  g 8  - T  get:  ( c )  141  by r e a r r a n g i n g AG  T  = AG  /"  2 9 8  - ATAS  AC° dT - T f  T  ^298  +  2 9 8  AC° d ( l n T)  J  (d)  ^298  o  The  d e t a i l e d v a r i a t i o n of C  p  with temperature  u s u a l l y w e l l known, but s a t i s f a c t o r y obtained from average range.  estimates may be  values of Cp over the  T h e r e f o r e , using average  i s not  temperature  values of Cp, equation  (d) becomes: o  AG  T  o  = AG  o 2 g 8  - ATAS  J + AC. 1 298 p J  2 g 8  ,T AT - TAC°] 298 0  In T/298  ...(e)  p  where AT  =  T - 298  o  AG  o  and AS  values are well e s t a b l i s h e d by  at 298° K. T h e r e f o r e , i n order to solve equation necessary to estimate AC '298 P  experiment (e), i t is  142  A.2  C r i s s and Cobble  Entropy Correspondence  Principle  33 34 C r i s s and Cobble established  '  using data at d i f f e r e n t  a correspondence  temperatures  p r i n c i p l e , whereby the entropy at  o  a given temperature, S perature,  i  such  that:  o  S  can be expanded about a r e f e r e n c e tem-  T 2  o  T  2  = a  o  + b S, *2 l  T  Z  X  + C '2 T  i  o  o  p  ( S - r+ d 'l '2 T  (S 'l  T  T  )  It was shown that a standard s t a t e can be chosen temperature, such that the p a r t i a l  at every  molal e n t r o p i e s of one c l a s s  of ions i n s o l u t i o n at that temperature  are l i n e a r l y  related  to the corresponding e n t r o p i e s at some r e f e r e n c e temperature. o  S  o  =  T  a  T  + b  T  S  2 Q 8  o  S gg i n the above e x p r e s s i o n i s expressed i n absolute 2  u n i t s , which  i s defined as:  o S  298  where  o =  Abs flh  Z  S  298  =  . " '°( > Conventional 5  r  Z  C a l s  M o 1 _ 1  D e  +  g  _ 1  Ionic Charge  In a subsequent  p u b l i c a t i o n , the f o l l o w i n g  procedure was  adopted: When the entropy of an ion i s known  (or can be a c c u r a t e l y pre-  d i c t e d at two temperatures, then the average  value of the heat  143  - 12 T  capacity  C  can be c a l c u l a t e d 0 S  0  _  T " 298 S  a  T  therefore,  =  C  p  In T/298  298  + (b -l) S T  2 9 8  = C  In T/298  p  298  T a  T ' 298 - T In T/298  a  T  298 and  S  ( 1  b  }  o  P J298  +  6  T 298 S  where a  I In T/298  and - D - b  T  ]  In T/298  The  heat c a p a c i t y  anions, and oxyanions  constants a-p, gy of simple  cations,  e t c . at various temperatures  are shown  o,T  in Table A . l .  T h e r e f o r e , from c a l c u l a t i o n s of C | , i t is o 298 p o s s i b l e to determi ne ^C^ , which can be i n s e r t e d i n 298 equation (e;.  Table A.I  Best Values of a ,b ,a ,B t  Temperature s  t  < H+ >  CB]^98  (H ) +  Cations:  a^  and S  298 °K  333°K  373°K  423°K  473°K  -5  -2.5  + 2.0  + 6.5  (11.1)  0  23  31  33  (35)  0  3.9  10.3  16.2  1 .000  0.955 35  t  a  (H ) at Several Temperatures +  t  .. -0.41 Anions  a^ b  t  a  t  0 1 .000  -0.28  Oxy anions  a^.  0  i . e . CO^  b^  1 .000  4.  c o 2  a  a^  0  i . e . HCQ~  b  1 .000  2 4 HP0= P 0  HSO"  a  1 .217 1 .96  t  Acid Oxyanions  H  -14.0 -127  t  e  4  0.969 -46  h  S 0  -5.1  t  t et  -13.5 1 . 380 -1 22 3.44  0.876  0. 792  (23.3) (0.711 )  46  46  (50)  -0.55  -0.59  (-0.63)  -13.0 1 .000 -58 0.000 -31 .0 1.476 -1 38 2.24  -30.3 1 .894 -135 3.97  -21.3 0.989 -61 -0.03 -46.4 1 .687 -133 2.27  (-50) (2.381 ) (-143) (3.95)  (-30.2) (0.981 ) (-65) (-0.04) (-)67.0) (2.020) (-145) (2.53)  (-70) (2.960) (41-52) (4.24)  Table A.2  Standard  Free Energies, Entropies and P a r t i a l  Adopted f o r Species P a r t i c i p a t i n g 3+ Fe —H^O System 333°K ,o T  Molal  in Reactions  Ionic Heat C a p a c i t i e s  Considered  i n the  373°K o T C 298  423°K o TC 298  473°K o T  23  31  33  35  -5  0  Fe  69.9  92.8  96.2  103.6  -85.1  -1.1  H0  18.04  18.04  18.15  18.15  16.7  -56.7  26.5  27.9  29.4  30. 7  21.5  -177.4  19.0  20  21 .5  22  22  -117  20  20  20  20  25.5  -166.5  Speci es  p  H  +  2  F e  2°3  FeOOH Fe(0H)  3  298  p  P  c  S  n p  o  298  o  298  298 K.Cals G  on  146  A.3  Sample C a l c u l a t i o n Data at Elevated  f o r the Estimation of Thermodynamic  Temperatures  H y d r o l y s i s of Hematite ..3+  +  Fe  3 2  At 2 9 8 ° K , reaction  =  H„0  +  3H  +  using the G^gg value f o r each  l[(-177.4)  •2550  o  the standard f r e e energy change f o r the  is calculated  '298  1 Fe 0_ 2  + 3(0)]  -  [-1.1  + 3  species  (-56.7J  cals  S i m i l a r l y , the standard entropy change f o r the r e a c t i o n o  is calculated  AS  298  from the S^gg value f o r each  = j~l_v(21.5) + 3 ( - 5 ) J  •85.1 + 3 (16.7)] 2  species.  55.8 e.  .333 =  AC  l  r  69.9 + 3 (18.04)1 = 15 Cal Mol "°K  (26.5) + 3.(23)]  298  2  373 4C P  ]  = [l  (27.9) + 3(31)]  92 .8 +.3  298  9  423 Ac] = | l 298 2 p J  L  (29.4) +  3(33)1 J  - 96.2  J  (18.04)] = -13  + 3 (18.15)] = -10 2 J  473 = [l 298 2 L  (30.7) + 3(35)  -  103.6+ 3 (18.15)] = 2  •10  147  The 423° and  free energy  473°K are then c a l c u l a t e d  T  AG  =  G  333  298  +  C  (T-298) - S (T-298) - T C 298 ™  p  333°,  373°,  using equation ( e ) .  T  o A G  changes at temperatures  o  T  ?pR  P  298  In  T 298  = -2550 + [-15x35] - [55.8x35] - [222x-15x.Hl] = -4774 Cals  AG°  73  = -2550 + [-13x75] - [55.8x75] - [373x73x.2245] = -6621 Cals  AG°  23  = -2550 + [-10x125] - [55.85x125] - [423x-10x.35] = -9295 Cals  AG°  73  = -2550 + [-10x175] - [55.85x1.75] - [473x-10x.462] = -11880 Cals  The  summary of a v a i l a b l e measured data on free  and entropy actions ionic  of species p a r t i c i p a t i n g in the h y d r o l y s i s  c o n s i d e r e d , i s shown in Table A.2.  heat c a p a c i t i e s were c a l c u l a t e d  pJ  and  energy  T  2 9 8  u t i l i z i n g values of a  T  and  T  e , T  Partial  re-.,  molal  using;  298  which are given in Table  A.l .  Table A.3 temperature  shows the average  ranges  heat c a p a c i t i e s  over  c o n s i d e r e d , f o r each h y d r o l y s i s  These values were u t i l i z e d in equation  the  reaction.  ( e ) , f o r the computa-  o  tion  of the free energy,  fied  temperature.  The  AG^. of each r e a c t i o n  at the  summary of the computed free  specienergies  of each r e a c t i o n  i s shown i n Table A.4  Thermodynamic data were considered f o r the f o l l o w i n g equilibria Fe  reactions.  + + +  + 3 H0 2  ;==* 1 f e 0 2  3  + 3H  4- 4-4-  Fe  Fe  (1)  4-  + 2H 0 2  + + +  +  + 3H Q 2  i = t FeOOH + 3H  Fe(0H)  3  + 3H  (2)  +  (3)  Table A.3  Summary of Average Heat C a p a c i t i e s Over the Ranges to Upper L i m i t s of 333°, 373°, 423° and 473°K  of 298°K  (Estimated by  the Correspondence P r i n c i p l e ) AC o.  Reaction  A S  298 e. u.  333  AC pJ  298  . p Ave  373 AC . •PJ298 0 1  Cal M o l o  - 1  Deg"  .423  AG P J  298  1 o,473  AC  n P J  298  (1)  55.8  -15  -13  -10  -10  (2)  51  -18  -16  -12  -13  (3)  45.5  -35  -34  -32  -33  Table A.4  Summary of Computations of the Free Energy of H y d r o l y s i s Considered  i n the Fe  3+  - H „ 0 System  AG°(T), Cal  Reacti on  Reactions  at  Indicated Temperatures  -  298° K  333°K  373° K  423° K  473°K  (1)  -2550  -4774  -6621  -9295  -11880  (2)  -2500  -4250  -6185  -8598  -10859  (3)  4700  3176  1585  -250  -1826  O  Appendix B  X-RAY DIFFRACTION  RESULTS  Appendix B  Table B.I  X-ray  Diffraction  Patterns of Goethite Using  Reported  the Fe  Radi a t i on  Sample  d° A  I/l!  d° A  5.0  20  4.92  30  4.21  100  4.29  100  3.37  20  -  -  2 .69  80  2.87  2.57  20  -  -  2.48  20  2.71  100  2 .44  70  2.65  65  2.25  20  -  -  2.18  40  2.44  40  1.719  50  -  -  I  /  !  l  75  en ro  Table  B.2  X-ray D i f f r a c t i o n  Patterns of Hematite Using  Reported  Sample (Fei C l +  the  Leach)  3  *  Fe k  Radi a t i on  Sample  (FeCl /HCl  d°A  3  *  d°A  I/I-  d°A  3.66  25  3.92  50  3.81  50  2.69  100  2.89  1 00  2.88  90  2.51  50  2.72  100  2.72  100  2.201  30  2.45  35  2.45  40  1 .838  40  2.16  40  2.16  40  1 .690  60  2.06  60  2.06  60  1.596  16  2.01  16  2.01  16  1 .484  35  1 .96  35  1 .96  35  1 .452  35  1 .95  35  1 .95  35  +  Relative visual  ,  I  /  r  i  i n t e n s i t i e s , powder camera, CoK  radiation  R e l a t i v e d i f f r a c t o m e t e r peak heights  cn Co  Table B.3  X-ray D i f f r a c t i o n  Patterns  Magnetic  Reported d°A  of Chromite Using Fe K  Particles *  d°A  i / i /  I/I,  4.82  50  4.92  10  2.95  60  3.12  40  100  2.73  100  2.40  10  -  2.07  70  2.34  70  40  2.06  40  90  2.0  90  2 .52  1 .69 1 .60  •  +  Relative visual  *  Relative diffractometer  Radi a t i on  -  i n t e n s i t i e s , powder camera, MoK^ peak  heights.  radiation  

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