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Controlled redox potential microbiological leaching of chalcopyrite Blancarte-Zurita, Martha Alicia 1988

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C O N T R O L L E D REDOX POTENTIAL MICROBIOLOGICAL  LEACHING OF  CHALCOPYRITE by  MARTHA ALICIA  BLANCARTE-ZURITA  IBQ Institute Politecnico Nacional  1981  MASc Chemical Engineering UBC 1984 A THESIS SUBMITTED  IN PARTIAL FULFILMENT OF  THE REQUIREMENTS  FOR T H E DEGREE OF  DOCTOR OF PHILOSOPHY  in THE F A C U L T Y OF GRADUATE STUDIES Chemical Engineering We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA June  1988  ® Martha Alicia Blancarte-Zurita, 1988  In  presenting  degree freely  at  this  the  thesis  in  partial  University  of  British  available for  copying  of  department publication  this or of  reference  thesis by  this  for  his  scholarly her  for  of  Chesntc&L  purposes  Date  DE-6  (2/88)  ^hne  29  /  gain  &n<zjif)eeZirin  98&  may  representatives.  financial  The University of British C o l u m b i a Vancouver, Canada  the  requirements  I further agree that  permission.  Department  of  Columbia, I agree that the  and study.  or  thesis  fulfilment  It  shall not  be  be  an  advanced  Library shall make  permission for  granted  is  for  by  the  understood  that  allowed  without  it  extensive  head  of  my  copying  or  my  written  Chercher c'est tout d'abord se rendre libre, a. l'image de la realite qui est elle—raerae une question  —M. Random  11  ABSTRACT  Leaching of chalcopyrite by Thiobacillus ferrooxidans under standard microbiological leaching sulfur.  conditions The  resulted  sulfide  portion  in  simultaneous  was  oxidized  solubilization preferentially  of copper, over  iron  iron and in  solution  suggesting a direct attack mechanism by the bacteria on the mineral particles.  Copper extractions  were low,  29-44%, with maximum specific  copper extraction  rates of the order of 0.001-0.006 h"*- and cell yields per unit of copper released 4-43mg TOC/mg Cu.  Leaching under redox-controlled conditions required a minimum pulp density, ca. 200 g/1, to result in elemental sulfur production. Some unknown factor, resulting from biological leaching activity under standard conditions the  liquid phase  redox-controlled  of the  inoculum, was  conditions.  Copper  needed  extractions  for the of  and transferred with leach  44-100%  to occur under were  achieved.  Maximum specific copper extraction rates were of the order of 0.002-0.007 h"\ with cell yield per unit of copper released of the order of 0.12-3.32mg TOC/g Cu for batch cultures. Ferrous iron in solution appeared to be the energy source for  cell  growth  under  redox-controlled  conditions.  The  cells'  sulfide  oxidizing  capacity seemed to be inhibited at the metabolic regulation level and not at the enzyme synthesis level. Cells growing under the standard conditions underwent a lag low  phase, upon transfer to the redox-controlled medium. During this lag phase metal  solubilization  growth started,  the  rates  and low  S° production occurred, but when  leaching rates increased and the  m  cell  mineral dissolved rapidly.  Electron diffraction X-ray silver  in the  analyses were carried out to investigate the role of  controlled-redox  leaching.  No silver  was  observed  to  be on  the  surface of the chalcopyrite particles before or after the initial activation stage of the controlled-redox process.  Silver deposits were observed after many hours of  leaching.  A  mathematical  model  to describe  the  kinetics  of microbial leaching,  using a  shrinking particle concept as its basis, was developed. When tested against data from the literature for leaching of Zinc from ZnS concentrate  it was  predict  gave  particle  size  as  a  function  of  leach  time.  It  also  able to  reasonable  predictions of particle size as a function of leach time for standard leaching of chalcopyrite but failed to predict accurate values for particle size as a function of leach time for the controlled-redox process.  iv  TABLE  OF CONTENTS  Abstract  iii  Table of Contents  v  List of Figures  ix  List of Tables  xiii  Nomeclature  xvii  Chapter  1. I N T R O D U C T I O N  1  Chapter 2. L I T E R A T U R E R E V I E W 2.1. PRELIMINARIES 2.2. G E N E R A L O V E R V T E W 2.3. T H I O B A C I L L U S F E R R O O X I D A N S : 2.3.1. M O R P H O L O G Y 2.3.1.1. E N E R G Y S O U R C E S 2.3.1.2. C A R B O N A N D N I T R O G E N SOURCES 2.3.1.3. I S O L A T I O N A N D C U L T U R E 2.3.1.4. C H E M I C A L COMPOSITION 2.3.2. M I N E R A L M I C R O B E I N T E R A C T I O N S 2.3.2.1. A T T A C H M E N T 2.3.3. E N U M E R A T I O N 2.4. M E T A B O L I S M A N D G R O W T H 2.4.1. IRON O X I D A T I O N 2.4.1.1. IRON O X I D A T I O N M E C H A N I S M 2.4.2. S U L F I D E O X I D A T I O N ., 2.4.2.1. S U L F I D E O X I D A T I O N M E C H A N I S M 22 2.5. M I N E R A L C O N C E N T R A T E S . S T A N D A R D B I O L O G I C A L LEACHING A N D BIOLOGICAL LEACHING UNDER CONTROLLED REDOX POTENTIAL 2.5.1. C H A L C O P Y R I T E 2.5.2. S T A N D A R D B I O L O G I C A L LEACHING 2.5.3. C O N T R O L L E D R E D O X P O T E N T I A L L E A C H I N G 30 2.5.4. C H E M I C A L A C T I V A T I O N 2.6. F A C T O R S A F F E C T I N G M I C R O B I A L L E A C H I N G 2.6.1. M E T A L T O L E R A N C E 2.6.2. N U T R I E N T S  v  6 6 6 7 7 8 8 8 11 12 12 14 16 16 18 20  25 27 29 .... 31 34 34 35  2.6.3. P A R T I C L E SIZE A N D SURFACE AREA 2.7. M O D E L L I N G B A C T E R I A L L E A C H I N G 2.7.1. M O D E L L I N G A N D K I N E T I C S 2.7.2. M O D E L S IN B I O L O G I C A L L E A C H I N G 2.7.2.1. SHRINKING CORE, SHRINKING P A R T I C L E M O D E L S Chapter  3. T H E O R Y 3.1. S H R I N K I N G P A R T I C L E M O D E L F O R C O N C E N T R A T E LEACHING 3.1.1. D E V E L O P M E N T O F T H E M O D E L  36 37 38 39 . 41 43 43 43  Chapter 4. M A T E R I A L S A N D M E T H O D S 54 4.1. C O P P E R C O N C E N T R A T E S 54 4.1.1. S A M P L E P R E P A R A T I O N 54 4.1.2. S C R E E N A N A L Y S E S 54 4.1.3. A S S A Y S 55 4.1.4. P A R T I C L E SIZE 55 4.1.4.1. C O N C E N T R A T E F R A C T I O N A T I O N ... 55 4.1.4.2. P A R T I C L E SIZE A N A L Y S E S 56 4.1.4.3. R E D O X P O T E N T I A L 58 4.1.4.4. D E N S I T Y 59 4.1.4.5. SPECIFIC S U R F A C E A R E A 59 4.2. B I O L E A C H E Q U I P M E N T A N D M E T H O D S 61 4.2.1. S H A K E F L A S K S : 61 4.2.2. B E A K E R S ... 62 4.2.3. 1L T A N K S 62 4.2.4. 3 L T A N K S 63 4.2.5. C O N T R O L L E D R E D O X L E A C H T E S T S 63 4.2.6. L E A C H I N G T E S T S 65 4.3. B A C T E R I A L C U L T U R E S 66 4.3.1. S O U R C E O F C U L T U R E S 66 4.3.2. M A I N T E N A N C E O F B A C T E R I A L C U L T U R E S ... 66 4.3.3. B A C T E R I A L G R O W T H .' 66 4.4. A N A L Y S E S 68 4.4.1. C O P P E R 68 4.4.2. IRON 68 4.4.3. E L E M E N T A L S U L F U R 68 4.4.4. S C A N N I N G E L E C T R O N M I C R O S C O P E TECHNIQUES 69 4.4.5. X - R A Y A N A L Y S E S 69 r  Chapter  5. R E S U L T S A N D D I S C U S S I O N 5.1. S T A N D A R D B I O L E A C H I N G 5.1.1. W I T H O U T B A C T E R I A L I N O C U L U M 5.1.2. A S R E C E I V E D C O N C E N T R A T E 5.1.3. - 4 0 0 M E S H C O N C E N T R A T E 5.1.3.1. B A C T E R I A L G R O W T H  VI  71 71 71 71 74 75  5.1.3.2. FERROUS/FERRIC IRON PROFILES 77 5.1.3.3. MINERAL SURFACE CHANGES 85 5.1.4. "MONOSIZE" LEACHES 90 5.1.4.1. PARTICLE SIZE MEASUREMENT 92 5.1.4.2. PARTICLE COMPOSITION 96 5.1.4.3. LEACHING EXPERIMENTS 97 5.1.4.4. SHEAR AND PARTICLE ATTRITION 108 5.1.4.5. AUTOGENOUS MILLING I N MONOSIZE LEACHES I l l 5.2. MODELLING THE CONVENTIONAL LEACH 114 5.2.1. INITIAL CONSIDERATIONS 114 5.2.1.1. SOFTWARE 114 5.2.1.2. SHRINKING RATES FOR CONVENTIONAL LEACHING 117 5.2.2. APPLICATION OF THE MODEL TO MONOSIZE LEACHES 118 5.2.2.1. PARTICLE SHRINKAGE AND COPPER SOLUBILIZATION 118 5.3. CONTROLLED REDOX POTENTIAL LEACHING 119 5.3.1. PULP DENSITY 119 5.3.2. INITIAL CONDITIONS 121 5.3.3. BACTERIAL INOCULUM 121 5.3.3.1. REDOX-CONTROLLED LEACHING WITH AND WITHOUT INOCULUM ... 121 5.3.3.2. PARTICLE FREE INOCULUM 126 5.3.4. -400 MESH CONCENTRATE 138 5.3.4.1. BACTERIAL GROWTH 139 5.3.4.2. FERROUS/FERRIC PROFILES UNDER REDOX CONTROL 142 5.3.4.3. CELL GROWTH AND ELEMENTAL SULFUR PRODUCTION 146 5.4. AERATION 153 5.4.1. SUSPENSIONS 153 5.5. MINERAL SURFACE CHANGES 164 5.5.1. BEFORE LEACHING 164 5.5.2. AFTER LEACHING 165 5.5.3. SPATIAL DISTRIBUTION 174 5.6. MONOSIZE LEACHES 178 5.6.1. ADDITIVE CONCENTRATION 178 5.6.2. CELL GROWTH IN MONOSIZE LEACHES 182 5.6.3. SOFTWARE 193 5.6.4. APPLICATION OF THE MODEL TO CONTROLLED REDOX LEACHING 194 5.7. CONTROLLED REDOX LEACHING 196 vii  5.8. C O M P A R I S O N S U M M A R Y O F S T A N D A R D VS C O N T R O L L E D R E D O X L E A C H I N G  LEACHING 203  Chapter 6. C O N C L U S I O N S 6.1. Leaching Under Standard Conditions  206 206  6.2. Leaching Under Controlled Redox Conditions Chapter 7. R E C O M E N D A T I O N S  FOR  FUTURE  STUDIES  210  BIBLIOGRAPHY  211  APPENDIX I C H E M I C A L A P P E N D I X II M I X E D APPENDLX  ANALYSES  232  POPULATION AND  III P A R T I C L E S H R I N K A G E STANDARD  APPENDIX 5 FORTRAN  PROGRAM  APPENDIX 6 G E N E R A L  LEACHING DATA  7 LOW  CULTURE  CONDITIONS  DATA  APPENDIX 4 PROGRAM  APPENDIX  207  240  LEACHING CONTROLLED  293 REDOX LEACHING  PULP DENSITY REDOX CONTROLLED  APPENDIX 8 PUBLICATIONS  234  .... 298 302  LEACHING  ... 355 359  VIU  LIST  OF  FIGURES  Fig. 1. Space Lattice of Chalcopyrite  28  Fig. 2 Logic diagram of the computer simulation  48  Fig. 3 Zn  extraction as function of pulp density  51  Fig. 4 Zn  extraction reactor #1  of a series of 2  52  Fig. 5 Zn  extraction reactor #2  of a series of 2  53  Fig. 6 Leaching system diagram  64  Fig. 7 Standard leaching as received concentrate. (11 day Fig. 8 Standard leaching as received concentrate. (6 day Fig. 9 Newmont and  old inoculum) old inoculum)  Gibraltar leaching profile comparison  72 73 76  Fig. 10 Ballmiiled concentrate. Standard leaching profile  78  Fig. 11 Ballmiiled concentrate. Standard leaching profile  79  Fig. 12 Cell growth and  80  copper leaching in ballmiiled concentrate  Fig. 13 Iron leaching in ballmiiled concentrate  81  Fig. 14 Redox potential induced transition states in cell growth  83  Fig. 15  Iron leaching, under increased redox potential  84  Fig. 16  EDXA  analyses of concentrate before leaching  86  photograph of concentrate before leaching  87  Fig. 17 S E M Fig. 18 X — r a y  line scan of freeze-dried, leached concentrate  88  Fig. 19 S E M  photograph of freeze-dried leached, concentrate (6000 X)  89  Fig. 20  SEM  photograph of freeze—dried leached concentrate (800 X)  91  Fig. 21  Size distribution of -400  Fig. 22  Size distribution of concentrate fractions  Fig. 23  Cell growth and  Fig. 24  Eh  and  mesh concentrate  94  copper leaching of 52.1  iron leaching profiles for 52.1  ix  93  ixm  material  j/ra material  98 99  nm  Fig.  25 Cell growth and copper leaching of 33.8  Fig.  26 E h  Fig.  27  Fig.  28 E h  Fig.  29 Cell growth and copper leaching of 9.3  Fig.  30 E h  Fig.  31 Cell growth and copper leaching of 2.8  Fig.  32 E h  and  Fig.  33  Cu  leaching in monosize fractions (nominal size)  109  Fig.  34  Cu  leaching in monosize fractions (true size)  110  Fig.  35 Particle fracture in ^32  Fig.  36 Size distribution after mechanical fracture 32  Fig.  37 Cu  Fig.  38 Model predictions of particle shrinkage for standard leaching  120  Fig.  39  123  Fig.  40 Cell growth when leaching under controlled redox conditions  124  Fig.  41 Iron leaching profile under controlled redox conditions  125  Fig.  42 Cell packet inoculum effects on the iron profile  128  Fig.  43  129  Fig.  44 Inoculum  cell carbon effect on iron leaching  131  Fig.  45 Inoculum  cell carbon effect on growth and copper extraction  132  Fig.  46 Iron leaching for inoculum drained of the soluble components  133  Fig.  47 Copper leaching for inoculum drained of the soluble components  134  Fig.  48 Iron leaching. Solid—free inoculum soluble fraction included  136  Fig.  49  137  and  iron leaching profiles for 33.8  (im material  Cell growth and copper leaching of 15.9 and  and  iron leaching profiles for 15.9  iron leaching profiles for 9.3  iron leaching profiles for 2.8  material  Mm  um  um  um  material material  102 103 104  material  105  jim material  106  material  107  jini material (6 //m  median size)  112  /xm  113  material  extraction rate as function of size  Cell packet inoculum effects on growth and  115  Cu extraction  leaching. Solid—free inoculum soluble fraction included  x  101  ixm material  Redox-controlled leaching without bacterial inoculum  Cu  100  Fig.  50 Cell growth and Cu leaching with Eh control  140  Fig.  51 Iron leaching under E h control  143  Fig.  52 Soluble  144  Fig.  53 Sulfur and cell growth under E h control  145  Fig.  54 Iron oxidation  147  Fig.  55 Sulfur profiles for E h controlled leaching  Fig.  56 Gel electrophoresis of outer membrane proteins  Fig.  57 Effect of 0.8 vvm on growth and Cu leached under E h control  156  Fig.  58 Effect of 0.8 vvm on iron leaching under E h control  157  Fig.  59 Effect of 1.5 vvm on growth and Cu extraction under E h control ....158  Fig.  60 Effect of 1.5 vvm on iron leaching under E h control  Fig.  61 Effect of 2.99 vvm on growth and Cu extraction under E h control  Fig.  62 Effect of 2.99 vvm on iron leaching under E h control  Fig.  63 Effect of 5.98 vvm on growth and Cu extraction under E h control  Fig.  64 Effect of 5.98 vvm on iron leaching under E h control  163  Fig.  65 E D X A  of concentrate before activation  166  Fig.  66 E D X A  of concentrate during  167  Fig.  67 Leaching profiles E D X A  Fig.  68 E D X A  of solids after 93 h of E h controlled leaching  169  Fig.  69 E D X A  of solids after 136 hours of E h controlled leaching  171  Fig.  70 E D X A  of concentrate residue  172  Fig.  71 E D X A  of concentrate 187 h leaching  Fig.  72 E D X A  of concentrate 234 h leaching  Fig.  73 Concentrate element distribution by X — r a y mapping  176  Fig.  74 Concentrate element distribution. 234 h of leaching. X—ray map  177  iron oxidized under E h control  and cell growth under E h control  148 152  159  161  activation. Stage 1 and 2  specimen  .. 162  168  after solvent extraction  xi  .. 160  .  173 175  Fig. 75 Sulfur production and maximum extraction rate as function of ssa Fig. 76 Growth and copper extraction from Fig. 77 Iron profiles for fraction 52.1  52.1  um  material  um  15.9  Mm material  Iron profiles for fraction of 2.8  Fig. 86 Copper  187 188  Mm material  Mm  Fig. 84 Growth and copper extraction from 2.8 Mm material Fig. 85  185 186  Mm  Fig. 82 Growth and copper extraction from 9.3 Fig. 83 Iron profiles for fraction of 9.3  Mm material  Mm  Fig. 80 Growth and copper extraction from Fig. 81 Iron profiles for fraction of 15.9  183 184  Fig. 78 Growth and copper extraction from 33.8 Fig. 79 Iron profiles for fraction of 33.8  ... 179  Mm  extraction rate data for E h controlled leaching  189 190 191 192 195  Fig. 87 Curve fit monosize  fraction 1 leach  197  Fig. 88  Curve fit monosize  fraction 2 leach  198  Fig. 89 Curve fit monosize  fraction 3 leach  199  Fig. 90 Curve fit monosize  fraction 4 leach  200  Fig. 91  Curve fit monosize  fraction 5 leach  201  Fig. 92  Curve fit for monosize leaching  202  Fig. 93 Metal leaching in stock culture  235  Fig. 94 Effect of serial transfer on metal solubilization  236  Fig. 95 Mixed  238  culture effects  Fig. 96 Program logical diagram  for shrinking diameters  xii  293  LIST OF TABLES Table  1 Experimental and calculated percentage of zinc extraction  50  Table 2 Sieve Analysis of Gibraltar Concentrate  55  Table 3 Concentrate  56  Elemental Analyses  Table 4a Size Fractionation for as received Gibraltar Concentrate  59  Table 4b Size Fractionation for -400 mesh Newmont Concentrate  60  Table 5 Specific Surface Area  61  for Monosize Fractions  Table 6 Cell Yields in Conventional (Conv) and Controlled-Redox  (C-R) Leaching 142  Table 7 Aeration  Effects  155  Table 8 Effects of Catalyst / Specific Surface Area  Ratio  181  Table 9 Controlled Redox Monosize Leaches  194  Table 10 Copper Extraction Rates for C-R and Standard Table  Leaching  205  11. Monosize leach 2.58 Mm  240  Table 12. Monosize leach 2.58 um  240  Table  13. Monosize leach 2.58 Mm  241  Table 38. Monosize leach 2.58 Mm  241  Table  242  14. Monosize leach 2.58 Mm  Table 39. Monosize leach 2.58 (im  .242  Table 15. Monosize leach 2.58 Mm  :.  243  Table 67. Monosize leach 46.8 Mm  243  Table  16. Monosize leach 8.63 Mm  244  Table  17. Monosize leach 8.63 Mm  245  Table  18. Monosize leach 8.63 Mm  246  '.  Table 19. Monosize leach 8.63 Mm Table 2 0 . Monosize leach 8.63 Mm  247 248  xiii  Table 21. Monosize leach 14.3 Mm  249  Table 22. Monosize leach 14.3 Mm  250  Table 23. Monosize leach 14.3 Mm  251  Table 24. Monosize leach 14.3 Mm  252  Table 25. Monosize leach 14.3 Mm  253  Table 26. Monosize leach 14.3 Mm  254  Table 27. Monosize leach 30.4 Mm  255  Table 28. Monosize leach 30.4 Mm  256  Table 29. Monosize leach 30.4 Mm  257  Table 30. Monosize leach 30.4 Mm  258  Table 31. Monosize leach 30.4 Mm  r  259  Table 32. Monosize leach 30.4 Mm  260  Table 33. Monosize leach 46.8 Mm  261  Table 34. Monosize leach 46.8 Mm  262  Table 35. Monosize leach 46.8 Mm  263  Table 36. Monosize leach 46.8 Mm  264  Table 37. Monosize leach 46.8 Mm  ...  265  Table 40. Monosize leach 2.58 Mm  266  Table 41. Monosize leach 2.58 Mm  267  Table 42. Monosize leach 2.58 Mm  268  Mm  269  Table 44. Monosize leach 8.63 Mm  270  Table 45. Monosize leach 8.63  Mm  271  Table 46. Monosize leach 8.63  Mm  272  Table 47. Monosize leach 8.63  (im  273  Table 43. Monosize leach 8.63  xiv  Table 48.  Monosize leach 8.63  Mm  274  Table 49.  Monosize leach  14.3  Mm  275  Table 50.  Monosize leach  14.3  Mm  276  Table 51.  Monosize leach  14.3  Mm  277  Table 52.  Monosize leach  14.3  Mm  278  Table 53.  Monosize leach 14.3  Mm  279  Table 54.  Monosize leach 14.3  Mm  280  Table 55.  Monosize leach 14.3  Mm  281  Table 56.  Monosize leach 30.4  Mm  282  Table 57. Monosize leach 30.4 Mm  283  Table 58.  Monosize leach 30.4  Mm  284  Table 59. Monosize leach 30.4  Mm  285  Table 60. Monosize leach 30.4  Mm  286  Table 61.  Monosize leach 46.8  Mm  287  Table 62.  Monosize leach 46.8  Mm  288  Table 63.  Monosize leach 46.8  Mm  289  Table 64.  Monosize leach 46.8  Mm  290  Table 65.  Monosize leach 46.8  Mm  291  Table 66.  Monosize leach 46.8  Mm  292  Table 68  Experiment 1 as received, st, 6 day inoculum  302  Table 69  Experiment 2 as received, st, 11  302  Table 70  Experiment 3 ballmilled, st  303  Table 71  Experiment 4 ballmilled, c-r  303  Table 72  Experiment 5 ballmilled, c-r  304  Table 73  Experiment 6 38Mm, c-r, low pulp  305  xv  day inoculum  Table 74  Experiment 7 28nm,  Table 75  Experiment 8 ballmiiled, c-r, low  pulp  307  Table 76  Experiment 9 ballmiiled, c-r, low  pulp  308  Table 77  Experiment  10 ballmiiled, c-r, low pulp  309  Table 78  Experiment  11 ballmiiled, c-r, low pulp  310  Table 79  Experiment  12 ballmiiled, c-r, low pulp  311  Table 80  Experiment  13 ballmiiled, c-r, low pulp  312  Table 81 Experiment  14 ballmiiled, c-r, low pulp  313  Table 82  Experiment  15 ballmiiled, c-r, low pulp  314  Table 83  Experiment  16 ballmiiled, c-r, low pulp  315  Table 84 Experiment  17 ballmiiled, st  316  Table 85  Experiment  18 as received, c-r,low pulp  317  Table 86  Experiment  19 ballmiiled, c-r, low pulp  318  Table 87  Experiment 20 ballmiiled, c-r, low pulp  319  Table 88 Experiment 21 ballmiiled, c-r, low pulp  320  Table 89  Experiment 22 ballmiiled, st, freeze dried  321  Table 90  Experiment 23 ballmiiled, c-r  322  Table 91  Experiment 24 ballmiiled, st, inoculum age  323  Table 92  Experiment 25 ballmiiled, c-r, aeration  324  Table 93  Experiment 26  ballmiiled, st, inoculum age  325  Table 94  Experiment 27  ballmiiled, c-r, aeration  326  Table 95  Experiment 28  ballmiiled, c-r, aeration  327  Table 96  Experiment 29  9K  328  Table 97  Experiment 30 ballmiiled, c-r, aeration  329  Table 98  Experiment 31 c-r, solid free inculum  330  st  306  iron, st  xvi  Table 99 Experiment 32 c-r, solid free inoculum  331  Table  332  100 Experiment 33 9K  iron, cell composition  Table 101 Experiment 34 c-r, high aeration  333  Table 102 Experiment 35 c-r, w.o. inoculum  334  Table  103 Experiment 36 c-r, solids inoculum  335  Table  104 Experiment 37 c-r, liquid supernatant inoculum  336  Table 105 Experiment 38 2.58 /zm, c-r  337  Table 106 Experiment 39 2.58 M m , st  338  Table 107 Experiment 40 46.8 Mm, c-r  339  Table 108 Experiment 41 46.8 M m , st  340  Table  341  109 Experiment 42 ballmilled, c-r  Table 110 Experiment 43 46.8 M m , st  342  Table 111 Experiment 44 30.4 Mm, c-r  343  Table 112 Experiment 45 30.4Mm, st  344  Table 113 Experiment 46 14.3 M m , c-r  345  Table 114 Experiment 47 14.3 M m , st  ....346  Table 115 Experiment 48 8.63 Mm, c-r  347  Table 116 Experiment 49 8.63 Mm, st  348  117 Experiment 49 8.63 Mm, st  349  Table  Table 118 Experiment T2 2L tank, c-r  350  Table 119 Experiment T3 2L tank, c-  351  Table  120 Experiment RT  352  Table  121 Experiment b3 c-r, aeration  353  Table  122 Experiment b5 c-r, A g concentration  354  Table  123. Controlled —Redox monosized  358  2L tank, c-r  leaches  xvii  NOMENCLATURE  C  Q  dp dp  =  particle concentration at start of leach  =  particle diameter  =  0  particle diameter at start of leach  CSTR E  =  =  completely  stirred tank reactor  age distribution of particles in reactor outlet  f =  mass fraction of metal in concentrate  r  rate of change of metal ion concentration  =  t = T  m  a  X X  time - arbitrary  x  =  time  fractional extraction of metal =  m  r  maximum  =  mean fractional extraction of metal mean residence  time in reactor  TOC  =  total organic carbon  SHE  =  standard  hydrogen electrode  SEM  =  scanning  electron microscope  SSA  =  specific surface  EDXA K  =  =  area  electron difraction x-ray analysis  one thousand daltons  Eh  =  c-r  = controlled redox leach  st =  oxidation-reduction potential  standard  leach  XVUl  in solution  ACKNOWLEDGMENTS  Financial  support  for this work was provided by E l Consejo  Nacional de Ciencia  y Tecnologia (Mexico), The University of British Columbia and B.C. Research. Assistance UBC)  with  analyses  was provided  by Dr. Barry  C. McBride (Microbiology,  and Dr. Alastair J. Sinclair (Geology, UBC).  Helpful  discussions  with  all the members  of my  Review  Branion, Dr. R. Lawrence, Dr. D. Duncan, Dr. L. Gormely and  with B.C. Research  Committee  Dr. R.  and Dr.R McElroy  Staff Ms. G. Chua, Mr. R.J. Vos and Mr. A. Vizsolyi  are acknowledged.  Special thanks  to Dr. R. Branion for his guidance  xix  in preparing this  manuscript.  CHAPTER 1. INTRODUCTION  Metal transformations, was  first  carried out by microorganisms, have been studied since it  discovered  that  natural and man-made  bacteria  contributed  processing likely  extracted,  For the most  of low grade ores  increase  with  of minerals in  environments. The contribution of bacterial leaching to the  world wide production of metals represents of metal  to the leaching  time  part  such  in dumps  as high  an important part of the total amount leaching  has been  and heaps. This  grade  ores  sources  limited  to  contribution will become  the  most  depleted and  industry starts looking for economical ways of processing low grade ores.  Potential  uses  of such  recovery  of precious  streams. Some microbial  (Torma been  metals  of these  metal  developed  areas  to the pilot  plant  et al, 1979; Lawrence  proposed  important  are only  starting  the leaching stage,  costs  than  and the margin  grade  of  available ores.  pyrometallurgical  in ore  Commercial  waste  of minerals  from  these  concentrates has  application seems feasible  pyrometallurgical  processes  processes  have  for  are air pollution free and they  are that they  of profits  from  the  the  of metal values. The advantages cited for  factors in decision making as  strict  in  to be developed. Among  et al, 1981). Hydrometallurgical  for the recovery  processes  are in ore processing,  and commercial  as alternatives to traditional  hydrometallurgical capital  transformations  and in the removal of toxic materials  transformations  treatment of minerals  lower  microbial  processes.  These  environmental processing  applications  of  characteristics are  regulations  decrease  have  due  become to  more  the lower  hydrometallurgical processes  include the ferric chloride plant for the processing of sulfide copper concentrates 1  INTRODUCTION of  the Duval  Sherritt  Corporation  Gordon  Mines  i n the United  process  States  for ammonia  (Lawrence  / 2  et al, 1985), the  leaching of nickel  concentrates and  the Sherritt-Cominco process for pressure leaching of zinc concentrates in Canada. Other  processes  ammonia  include ammonia—ammonium  leaching of nickel  Hydrometallurgical  concentrates  processes  are also  carbonate  reduction for nickel, and  and of smelted  extensively  used  nickel—copper for leaching  mattes.  of oxides  (Gormely, 1988). The bacterial  leaching of sulfide concentrates as an alternative  to  for the  pyrometallurgical processes  contemplated  as  more  and  (McElroy and Bruynesteyn,  As  base  have the  metal  prices  concentrated  more  recovery  of metals  hydrometallurgical processes  of pilot  have  Resources,  Ltd.,  plant  been  unstable  for the past  studies  NWT  and  some  Equity  pressure oxidation of the sulfide  process  is being  used  Silver  used.  several years, studies  progress  Mines,  being  Ltd.  the pretreatment  made to  (Giant Bay B.C.).  Most  of gold ores  portion to expose gold for cyanidation. This  i n the United  States  (California,  Brazil and South Africa. With respect to base metals understanding  are being  of biohydrometallurgical processes  hydrometallurgical applications in this area concern by  actively  1978).  on gold-bearing minerals, with  level  is being  Utah  and Nevada), i n  significant progress in the  of the biological leaching of sulfides has been made. Most studies  have  concentrated  on the leaching of copper  since  it is the most  abundant source  sulfides, chalcopyrite in particular,  of copper.  Extraction  systems have  been  designed  for abiotic leaching and biological leaching of chalcopyrite ores. In these  systems  the metals  been,  in some  end up  cases,  high  as sulfates. enough  Metal  for direct  concentrations electrowinning  in solution of the  have  Ieacheate  INTRODUCTION / 3 solutions  to  be  (Lawrence and  considered.  Typical  copper  extractions  are  between  Hackl, 1982).  Improvements to the levels of extraction have been obtained by in  both  (Miller  biological and  sulfur  as  end  (McElroy  1979).  conducted an  by-product  leaching  Portillo,  chalcopyrite  The  product.  for the sulfur  process.  (McElroy  Such  and  Duncan,  addition  of  at high temperature S°  has  is  1974)  silver  in  also  always  et al, 1974). For  case  both  for  abiotic  and  the  been  abiotic leaching  abiotic  considered  silver  and  to  opposed  a neutralization step has  the  addition of silver  and/or pressure, results  component of the sulfide, as  When sulfuric acid is produced, the  40-60%  leaching of in elemental  be  the  ideal  to sulfuric  acid.  to be incorporated into  addition  biological  to  biological  leaches  leaching of chalcopyrite,  silver addition can result in higher metal extractions.  The first  conversion of sulfide-sulfur to elemental sulfur in the presence of silver observed  controlled al,  at  redox  1986).  A  near  ambient  temperature  and  bioleaching process developed variety  redox—controlled  of  process  studies  eg.  have  by  atmospheric  pressure  B.C.  Research  investigated  various  its applicability  to  different  in  (Bruynesteyn aspects  ores,  the  of  was the et this  secondary  processing of the leachate to recover silver, etc. However to fully comprehend the mechanisms  of these  silver  mediated  reactions further  studies are  needed.  The  objectives of this study were to increase the understanding of the controlled redox bioleaching  process, through  process, and be  useful  to develop  comparative  study  with  the  standard bioleaching  a kinetic model for the bioleaching process which would  in determining  concentrate. More  a  the  specifically  size they  of were  reactor necessary to clarify  to  leach  a  particular  the inter—relationships  among  INTRODUCTION / 4 the following components of the  Cell  Study  process:  population  the role  of Thiobacillus ferrooxidans in the leaching  of sulfides in  the  controlled redox process and the changes in the cell—substrate interactions due to the controlled redox conditions. Obtain data regarding bacterial yield and bacterial growth rate and compare them with  those obtained  in a standard  or conventional  understanding of the controlled redox  leaching  process to gain an  process.  Substrate  Investigate  changes  in bacterial  conditions by measuring substrate Investigate copper  changes  extraction  conditions  metabolism  and secondary them  from  controlled  redox  utilization.  in the concentrate  and compare  resulting  during  product  to those  Measure the change in concentrate  chemical formation  activation and measure under  of the standard  controlled  bioleaching  redox process.  particle diameter as a function of leach time.  Mechanism  Study the leaching mechanism through the development of a model. Simulate the effects of particle using  a  shrinking  simulating leach  with  size on the leaching particle  leaching  of copper  mechanism  from  which  zinc sulfide leaching. Compare the simulation the redox controlled biological leach  chalcopyrite  concentrate,  has proven  effective in  of the standard  biological  as means of detecting differences  INTRODUCTION / 5 in the mechanics of the two processes. Verify the reproducibility of the process  under various conditions, through  limited  testing of some of the experimental variables such as cell age and pulp density.  CHAPTER 2. LITERATURE REVIEW  2.1.  A  PRELIMINARIES  variety of chemoautotrophs,  acidophilic  and thermophilic  microorganisms are  relevant to microbial leaching and there are many substrates that serve energy  sources.  excellent  These  papers  —  microbial transformations  Tuovinen and  and Kelly  Karavaiko  (1985)  Olson  and  concentrate  on T. ferrooxidans  have  been  (1974), Torma  Kelly  (1986).  The  reviewed  as their  in several  (1977), Brierley following  (1978),  review  will  and their involvement in leaching of sulfide  ores,  with the emphasis on copper sulfides.  2.2. GENERAL  Use  OVERVIEW  of microorganisms in hydrometallurgical processing provides  the traditional metal smelting of the copper processing The  of low grade  by Taylor time  Hinkle of  in the United ores  T.  and Whelan  it was not known  isolated  T. ferrooxidans  ferrooxidans  in metal  have arisen because of the  and  which  It has been estimated  that  States  hydrometallurgical  originates from  maintenance  of  the  of the Rio Tinto operation that from  bacteria were  microbial 6  although at  involved. In 1947 Colmer and  has been  lack of appropiate  1975).  was made in  in Spain,  acid coal mine drainage;  solubilization  different  11.5 percent  is microbially assisted (Wadsworth,  first report of copper extraction by hydrometallugical processes  1943 the  produced  processes.  an alternative to  slowly  techniques  strains  after this the role clarified.  Difficulties  for enumeration, culture  isolated  and  because  the  LITERATURE variety  of  substrates  and  processes  employed  makes  REVIEW / 7  it difficult  to  compare  results.  The  standard  leaching of sulfides has  ores. Trends can tend  to  depend  used. Our kinetic  be on  compared the  ore  among different mineralogy  work in conventional  data,  for  the  been extensively studied for a  and  leaching was  particular  concentrates  systems, but the  quantitative results  history of  focused and  on  the  microorganisms  the controlled-redox process. At  we  X-ray  techniques  such  as  microorganism  obtaining some reliable  which to base a comparison with used  analysis  to  variety of  we  used,  on  the same time  investigate cell-substrate  interactions. With respect _ to controlled-redox leaching, until very recently all work done on the  this subject was  foundation  Ballester  for  the  (1985) have  carried out present  done  (Ballester,  study.  Research. Their work is considered  Recently  Copper  some experiments trying  work. Most of their work was successful  at B.C.  carried out  1987). This  can  be  at low  (1985)  to duplicate B.C.  pulp  explained  Cooper  by  density and the  and  Research  it was  portion of this  not work  that examines pulp density effects (appendix 8).  2.3. THIOBACILLUS FERROOXIDANS  2.3.1. MORPHOLOGY  T. ferrooxidans  are  rod shaped bacteria about 0.5  length. It is a gram negative, non-spore forming, also  acidophilic,  growing  optimally  at  pH  2-3  Mm  in diameter x  1.0  aerobic, motile bacterium. and  at  mesophilic  Mm  in  It is growth  LITERATURE temperatures (20-35°C) (Temple  2.3.1.1. ENERGY  and Colmer,  REVIEW / 8  1951).  SOURCES  T. ferrooxidans derives  of reduced  or partially  reduced sulfur compounds. It can oxidize ferrous iron to ferric iron  and a wide  variety  of metal  energy  from  reported  iron  its energy  from  sulfides to the corresponding soluble oxidation  of the iron  to use copper as an energy  and Kelly, 1972;  T. ferrooxidans obtains  nitrogen  component  sulfates. It also  of disulfides  derives  and has been  source (Nielsen and Beck, 1972;  Tuovinen  Ehrlich, 1978; Tuovinen et al, 1978).  2.3.1.2. CARBON AND NITROGEN  usually  the oxidation  its carbon  as an ammonium (Mackintosh,  SOURCES  by fixing  carbon  dioxide. A  nitrogen  salt is required, although it has been reported  1976; Stevens  source, to  fix  et al, 1986). The nutritional, requirements  were established by Silverman and Lundgren  (1959) whose 9K medium  is often  used for culturing T. ferrooxidans.  2.3.1.3. ISOLATION AND CULTURE  A  variety  of strains  environments  have  and maintained  been  isolated  in laboratory  strain used in this study. These  Thiobacilli  from  natural  cultures. This  sulfide  ore weathering  is the case  for  the  can be associated with populations of  LITERATURE acidophilic cultures  and/or  heterotrophic  bacteria  are maintained under non-sterile  question.  Heterotrophic  bacteria  carbon  sources  growth  conditions  bacteria.  This  than  co-culture  can be changed  of the culture  exert  and the use of different  sources, an isolate  a selection  culture  from  iron (Kelly,  is open to  from  co-culture  to oxidize  bacteria  T. ferrooxidans  one medium  1987), so culturing  at the optimum over  iron, sulfur and  with  respect  and acidophilic  to another  other  can encourage the  to their bacteria in  and be purified.  example T. albertis, an acidophilic microorganism can oxidize to oxidize  Because the  pressure  mediums  on its ability  of the acidophilic  containing  / 9  in mineral concentrates in the absence of  of T. ferrooxidans will  and the limitations  milieu.  to be eliminated  CC^. Maintenance  of T. ferrooxidans. Based  purification sulfides,  other  natural  conditions then, their purity  are supposed  with T. ferrooxidans by serial culturing  energy  in their  REVIEW  For  sulfur but is unable  the isolate that contains T. albertis in  co-culture with T. ferrooxidans in a F e S C ^ sulfur free  medium will eliminate T.  albertis.  A  large  body  laboratories,  of literature  supposedly  has resulted  using  the same  from  studies  carried  microorganism,  out in different  which  report  different  values for kinetic parameters, metal tolerances, etc. Some of the variation such  lab results  these display  iron  lately  oxidizing  differences  has been  attributed  Thiobacilli. In addition  in physiology  to uncertainty different  about  strains  among  the purity of  of T.  ferrooxidans  and morphology. (Silver, 1978; DiSpirito  et  al,  1981).  Techniques  such  as D N A  homology  have  been  used  to verify  the purity of  LITERATURE of T. ferrooxidans. Of 23 strains  strains quarter  were  contaminants  found have  to be  examined  contaminated  with  REVIEW  by Harrison  heterotrophs.  (1982), one  Two  common  isolated, Acidophilium cryptum (Harrison, 1981)  been  and T.  acidophilus (Arkesteyn and DeBont, 1980). Other heterotrophs and mixotrophs exist in co-culture with  / 10  that  T. ferrooxidans are T. albertis, Leptospirillum ferrooxidans  T. rubellus (Kelly, 1987); these are for the most part resistant to traditional  and  purification techniques.  Not  all variations  in physiology  can be attributed  to co-cultures, Yates  (1987) studying the genetic character of T. ferrooxidans of spontaneous variation in the ability of the bacterium  found  a high  et  al  frequency  to utilize ferrous iron as  source using clones of T. ferrooxidans. These variations may be attributed  energy  to unstable genes. Guay et al (1976) reported on differences in D N A composition within  strains  proposed  as T.  classified  with  ferrooxidans. Later  G/C (Guanine/Cytosine)  mol ratios  7  homology  between  groups  were  52 and 62 percent  (Harrison, 1982). Part of this difference in the G/C mol ratio values can be the result  of repetitive  gene  sequences  and mobile  sequences  in the D N A  of T.  ferrooxidans .  DNA the  homology studies are based same  strain.  Fragments  on identity of D N A sequences among  of D N A  These enzymes will produce single of  nucleotides. These  chain pairing  fragments when  single  obtained  put into  strand  strand  from  contact  are split  using  fragments  fragments  will  with  endonucleases.  specific base sequence  be complementary  a different  culture  with  fragments  DNA  restriction  and will from  cells of  to other  hybridize by base other  cultures. The  LITERATURE REVIEW percentage hybridization is then a measure of the relatedness  / 11  of the two strains  of bacteria (Yates and Holmes, 1986).  The  discovery  doubts  into  genes will  of repetitive genes by Yates  DNA  homology  hybridize,  even  studies  that  in non-related  et al (1987) has introduced  use single  copy  strains, producing  probes  certain  because  these  false results in  the  measurement of percentage hybridization, and hence in the identity of different T. ferrooxidans  strains. It has also been reported  by Yates et al (1987), that the  position on the genome of these repeated sequences changes when T. ferrooxidans cells are cultured  under different conditions,  giving rise to unstable genes  which  produce a shuffling of the genome resulting in "mutation like" results. Even in clones, changes in family I were detected at a rate one million times faster than spontaneous mutation. Repeated elements have been grouped in families and can be  tested  by hybridization  with  fragments  of D N A obtained  by digestion  with  restriction endonuclease of D N A from cells cultured under different conditions. Just  how these  changes  in the genome  known, but back reversions  result in phenotypic  variations  is  not  are also of very high frequency (Yates et al, 1987).  2.3.1.4. CHEMICAL COMPOSITION  The  cell  percent  composition protein,  of Thiobacillus ferrooxidans has been  26 percent  lipid,  15 percent  carbohydrate  reported  to be 44  and 10 percent ash  (Lundgren et al, 1964).  The  cell  cytoplasmic  envelope  consists  of three  zones  according  to  Lundgren  (1978): a  membrane which constitutes the inner layer of the envelope bordering  LITERATURE the  cytoplasm, a central zone  the  periplasmic  that  space, and an outer  includes  a rigid  layer which  R E V I E W / 12  layer of peptidoglycan and  contains  lipopolysaccharide and  lipoprotein.  Elemental analysis of the dried microorganism grown in batch, was 47.6 percent carbon, 10.1 percent  nitrogen and 7.3 percent hydrogen (Jones and Kelly, 1983).  2.3.2. MINERAL MICROBE INTERACTIONS  2.3.2.1. ATTACHMENT  Bacterial and  of sulfides requires  and indirect  bacterium  a close  association between  the bacteria  surface. T. ferrooxidans is known to attack sulfides through both  the mineral  direct the  oxidation  mechanisms. The direct mechanism  and the mineral;  oxidation-reduction  the indirect  potentials (Eh) through  ferrous iron present  involves  mechanism  contact  between  place  at high  takes  the microbial cell's re-oxidation of any  in solution which then abiotically attacks the sulfide  causing  the metal component to go into solution.  For  the direct mechanism  the  solid  attached  mineral cells  Drummond presence regions  there  particles.  represent  This  is evidence of attachment attachment  the largest  (1973) demonstrated  of T. ferrooxidans.  that  seems  proportion pitting  Evidence  to occur  of cells  of pyrite  of attachment  of bacterial cells to rapidly  present.  Duncan and  was associated of bacterial cells  of chalcopyrite ore by T. ferrooxidans has been presented  and the  with the to sulfide  in the form of  LITERATURE electron  microscope  identified from  the presence  bacterial  use  photographs  of pits, chains  and Tributsch  by Duncan  (1978).  et al (1964)  has been studied  who found  that  production  has been shown to produce surfactants  can not be induced  have  solely  (Groudev  by the presence  by  leaching  the  rates  agents. Although T.  in the presence of added surface tension modifying  ferrooxidans  They  and clusters on pyrite surfaces resulting  activity. The nature of this attachment  of surfactants  increased  by Bennett  R E V I E W / 13  et al, 1978), their  of a solid  substrate  (Tuovinen et al, 1978).  Attempts  to clarify  been made. Using  how the bacterium washed  interacts with  of the cells were attached  the  absence of surfactants  more  than  that  initial  one mechanism attachment  van der Waals  Longer  term  substrate Studies groups  sorption  have  5 minutes 25  by the cells, indicating that there  for cell place  attractive  involves  sorption was rapid; within  to the mineral. Such sorption could occur  produced  takes  London  surface  cell suspensions Tuovinen et al (1983) found sorption  of T. ferrooxidans cells to pyrite. This %  a mineral  other  may be  attachment  to solid  particles. They  through  electrostatic  interactions  forces  and/or  factors  electrical  such  even in  suggest such as  double-layer  as the wettability  forces. of  the  and cell integrity which suggest that the cell surface may be involved. carried out using  from  sulfur. This  T. thiooxidans growing  on sulfur indicate  the cell envelope are essential for the adhesion could  mean  that  there  is a biochemical  that  thiol  of the bacteria to  reaction occurring  between  the cell and the sulfur surface because sorption of T. thiooxidans to sulfur is an energy dependent process  (Takakuwa et al, 1979). It it not known whether thiol  groups are involved in the adhesion to sulfides by T. ferrooxidans, but studies of  LITERATURE  REVIEW  / 14  cell attachment to pyrite indicate that the bacteria must adhere to or be in the vicinity  of the surface  subsequently  The  to thrive,  with  cells  doubling  at the surface and  attaching to it (Yeh et al, 1987).  extent of cell adhesion  to the mineral surface is very high, Grudov  et al,  (1978) have reported that over 80 % of the cells were atttached to the mineral by  the end of the log phase  estimated  that  95.6 %  in batch  cultures.  Gormely  of a T. ferrooxidans population  and Duncan  would  (1974)  be attached to  chalcopyrite and 65 % of the cells were estimated to be attached to sphalerite in separate can  experiments.  Cell  attachment  to solid  products  present  in the medium  also occur as is the case when jarosites are formed as a result of ferrous  iron oxidation. McGoran et al (1969) estimated  that 9 0 % of the cells where so  associated when grown in 9K medium. This attachment was quite tenacious,  and  the cells could not be removed either by sonication or by the use of surfactants. Cells attached to pyrite could not be removed by repeated washings (Tuovinen et al,  1983). Tenacious  cell attachment to solid particles has also been reported by  Pinches (1972) and Myerson and Kline  (1983).  2.3.3. ENUMERATION  A  variety of methods have been employed to estimate T. ferrooxidans populations;  these  can be classified  attempt Probable  as direct  methods  or indirect  to measure the bacterial numbers directly such Number  (MPN) methods,  plate  count  methods. Direct  methods  is the case for the Most  methods  and microscope  count  methods. Indirect methods correlate some cell component to the bacterial m a s s or  LITERATURE numbers. Among total  organic  these  carbon,  methods  we  radioactive  find  protein content,  C O 2 fixation,  total  adenosine  REVIEW / 15  organic nitrogen,  triphosphate (ATP)  content, oxygen uptake rate, and iron oxidation rate.  DIRECT M E T H O D S  Most probable for  estimation  FOR C E L L  ESTIMATION  number, plate count methods and microscopic counts of cells  growing  on mineral  concentrates.  are inaccurate  In the slurry,  cells  associate to the mineral resulting in an uneven distribution of cells between the solid  and the liquid  the case of M P N  phase which  and plate count  produces errors in the dilution  procedures (in  methods). This uneven distribution also results  in errors in the microscope cell counts due to masking of cells by particles.  INDIRECT  METHODS  Indirect methods estimate T. ferrooxidans populations by correlating their numbers to the  biomass or metabolite particular  application  concentrations. The method and the availability  to be selected depends on  of the necessary  equipment and  materials. Indirect techniques  do not distinguish between live and dead cells and  are  they  not specific, nevertheless  can be used  directly in slurries avoiding the  problems associated with the direct methods.  Of  the indirect methods, protein measurement (LeRoux et al, 1973) and adenosine  triphosphate  (ATP) content  (Tuovinen  and Sormunen,  1978) are difficult  to use  with mineral concentrates due to inerferance from inorganic ions from the culture medium. Oxygen  uptake rate (LeRoux,  1973; Brierley,  1978) and carbon  dioxide  LITERATURE fixation  R E V I E W / 16  (Smith et al, 1972; Brierley, 1977) have been used for estimation of cell  numbers. Both methods organic  carbon  and  require special equipment which was  total  organic  Gormely  (1974) have shown  be  to estimate  used  analyses  nitrogen  that these  bacterial  were  two  numbers  then  methods  when  solid  not available. Total  considered. were  Duncan  and  equivalent and could  substrates  were made directly on the slurries and included both  were  used.  attached  The  and non  attached cells.  Cell nitrogen is the difference between the total nitrogen determined by Kjeldahl digestion and inorganic nitrogen as determined Gormely  and  by  steam distillation at high  Duncan, (1974) correlated the non-distillable  nitrogen with  pH.  organic  carbon and cell numbers estimated using a Petroff-Hausser counting chamber, and reported a value of 0.157 x 0.767 x Kelly  l O " ^ mg 1  (1973). Given  C  l O " ^ mg 1  N  per cell agrees with the tediousness  per cell. Their cellular carbon value of the value  obtained  involved in obtaining total  by  Tuovinen and  organic  nitrogen  measurements and the availability of an automated T O C  analyzer, in this  total organic carbon measurements were used to estimate  bacterial growth.  2.4. METABOLISM  2.4.1.  IRON  AND  study,  GROWTH  OXIDATION  Oxidation of iron by T. ferrooxidans can be described by the following equation:  LITERATURE 2FeS0  The  rate  depends  of iron  4  +  1/2 0  oxidation  on the conditions  28-35°C  is 3.6-10.0  oxidation  T.  by  concentrations)  h  + H S0 = 2  (McGoran  through  fixed  et al, 1969; free  Fe^ /Fe^ +  + H 0 ..(1)  3  2  growth  rate,  time  et al,  change  1971).  Iron  A F (physiological  bacteria for C 0  electron  fixation via the  2  18 A T P and 12 N A D H  of one hexose  transport  since  Calvin cycle (Kelly  NAD  sugar. +  The N A D H  per  6C0  2  is generated  can not be reduced  couple. Large amounts of ferrous iron are oxidized by the  +  in turn  for the bacteria at  Tuovinen  energy  which  kcal/mol at p H 2.0 (Lees et al, 1969). Up to 8 0 % of this  to the level  reverse  4  of cell  Jones, 1978). The Calvin cycle requires  molecules  2  The doubling  ferrooxidans has a  = -7.1  Fe (S0 )  4  is a function of culture.  energy is employed by the and  2  R E V I E W / 17  by  the  bacterium  when the culture is rapidly growing. Kelly and Jones (1978) have shown that T. ferrooxidans cells can  oxidize up to 30 times their mass in an hour.  Iron oxidation in batch cultures has been shown to be product inhibited (Wong et al, 1973; at  30 °C,  Kelly and Jones, 1978). Wong et al (1973) found that inhibition occurs pH  concentrations  2.0 and a  greater  than  cell  concentration  0.14 g/L. Later  of 2.5 mg/L studies  by Steiner  (1974) and Kelly and Jones (1978) put this limit at 11-12 indicated  that  concentrations  oxygen  uptake  iron  and Lazaroff  Liu et al (1988) when  ferric  iron  reached 24 g/L for cells grown in agitated tanks. Kelly and Jones sites for ferrous iron exist  within the cell and that ferric iron acts as a competitive  exact  g/L.  by T. ferrooxidans was affected  (1978) suggest that two or more transport or binding  The  for ferric  mechanism  of iron oxidation  is uncertain  inhibitor.  but there  is evidence  that  LITERATURE two  sets of electron carriers exist in the cell; one for the  and  one for the sulfur oxidation  are  independent.  selectively  Duncan  inhibited  system. It is believed  et al (1967)  by cytochrome  showed  inhibitors  that  such  R E V I E W / 18  iron oxidizing system that  iron  these two systems oxidation  as sodium  can be  azide,  without  affecting T. ferrooxidans ability to oxidize sulfur.  Norris et al (1987) found  that different proteins  for the oxidation of sulphur  are present  and iron. Oliver and V a n Slyke  in T.  ferrooxidans  (1987) have shown  that exposure to amorphous sulfur of iron grown cells, in the presence of iron, will  turn  protein  off  iron  synthesis,  indicates that the  oxidation  thus  but without sulphur  inhibiting  affecting D N A  RNA  synthesis  synthesis  and consequently  or CO2 fixation.  and iron oxidation systems are  This  somehow connected at  the level of metabolic regulation.  2.4.1.1. IRON OXIDATION MECHANISM  The  iron oxidation mechanism  has been proposed to be as follows. Ferrous iron  is oxidized at the external cell wall surface because of a polynuclear coat that helps  electron transfer across  the  outer  ferric iron  wall. Iron donates electrons to  rusticyanin, a copper containing protein, which acts as an initial electron receptor. This  exchange  protein  with  takes  place  molecular  outside  weight  requirement for iron oxidation this electron acceptor periplasmic  of the cell  of 92,000 (Kulpa  site. Rusticyanin  space level. Rusticyanin  membrane.  Da (92K)  A n outer  has been  identified  and Mjoli, 1987), and could and cytochrome c are  membrane as a  be related to  both located at the  comprises about 5 % of the  total cell protein  LITERATURE and  it is directly reducible by  shown  that  nature  of  the  the  levels of this  levels  growth  gene in T.  compared  This  studies on  cytochromes, two  first step  has  regulated  bacterium  expression  on  the  Schnaitman membrane  70,000 Da  transport  in an  by  suggesting  electron aceptor cytochrome a^  et al, 1969). The  sites, and  ferrous  could  iron  to  also serve  as  oxidation of iron mediated by  T.  the  synthesis  that  contains  (Ingledew, 1980). The  biological  reaction rate  rate that could be obtained Low  pH  is needed  for the  increases  come ligand  into  may  contact  for the  be  3.6  location  to depolarize binding  or  of complexes  Schnaitman et al, 1969).  (Schaitman et al, 1969). At  500,000 times over  establishment  three  Lees et al,  with  formation  the  under the same conditions (Lacey  membrane, this gradient allows  of  the cell membrane (Ingledew, 1982).  ferrooxidans takes place at pHs  iron oxidation declines rapidly above pH the  elemental  that the rusticyanin  chain,  role of sulfate ions  that could then be oxidized. (Lazaroff, 1977;  The  higher  et al, 1986).  been suggested to be  allowing  the  of the rusticyanin  There is a requirement of sulfate for iron oxidation, (Lazaroff, 1963; 1969;  by  resulting in much  this induction is accompanied  cytochromes c and  of cytochrome a^  the  are  gene is inducible when the cells are grown in the  gene is part of an operon (Kulpa  is the  of iron  to growth of the  additional proteins of 32,000 and  Rusticyanin  ferrooxidans  presence  been confirmed by  ferrooxidans.  / 19  (Ingledew, 1982). Jedlicki et al (1986) have  2  medium, the  presence of ferrous iron, and two  +  rusticyanin in T.  of  protein when  sulfur. This has  Fe  REVIEW  of a  proton  chemical and  gradient  the coupling of phosphorylation  and  below pH  3.5, 2.2  oxidation  Lawson, 1970). across  the  cell  iron oxidation  LITERATURE  REVIEW  / 20  (Ingledew, 1982). High levels of sulfate (12g/L) can inhibit iron oxidation, perhaps uncoupling uptake  the phosporylation  first.  This  reaction  indicates  that  since this  iron  sulfate  oxidation  can  inhibition  occur  affects  in the  oxygen  absence  of  oxygen reduction (Steiner and Lazaroff, 1974).  2.4.2. SULFIDE OXIDATION  Growth The  T. ferrooxidans  of  cell  yield  T.  for  can  occur at the expense  ferrooxidans  growing  on  of reduced  solid  sulfur  sulfides  species.  is, for  zinc  concentrate, 43mg C/g zinc released (Gormely, 1973). Generation times for growth on  zinc  sulfide  concentrates  have  been  reported  to range  from  6.7h  (Gormely,  1973) to 52.2h (Sanmugasunderam, 1981).  Consider and  the  present the  the  oxidation  principal and  commercial  standard  formation  of chalcopyrite source  leaching  of copper  and  (CuFeS2), a  complex  of copper. In  this  in aqueous ferric  media,  sulfates  and  at low  copper-iron  sulfide, pH  sulfuric  iron  sulfide, is also  values, results in  acid, according  to the  following reactions:  10CuFeS  +  2  42.50  3Fe (S0 ) 2  4  CuFeS  2  3  2  +  +  +  5H S0 2  14H 0 2  =  2Fe (S0 ) 2  4  4  =  10CuSO  +  4  5Fe (S0 )  2H OFe (S0 ) (OH) 3  3  =  3  CuS0  4  4  +  2  2  +  6  5FeS0  4  4  3  +  5 H 0 ..(2) 2  5H S0 ..(3) 2  +  4  2S°..(4)  LITERATURE 2S°  Reactions  HCuFeS  (2) and  30  +  2  2H 0  45.50  +  2  HH 0 2  3  equal  studies  amounts, that  sulfide  oxidation  bacterium has  The  with  4  shown  between  that  been subcultured  2  attached  Pinches,  6  =  HCuS0  +  2H S0 ..(6) 2  of  being  the  the  has  result  5FeS0  +  4  4  oxygen  result  +  4  iron  uptake  of  iron  are  solubilized in  is the  result  oxidation  when  of the  on the mineral (Duncan et al, 1967).  to  the  mineral  surface  cultures  iron  will  preferentially  surface  during  reaction with  oxidation  (McGoran  the bacteria et  al,  1969;  1975).  some  This  4  copper, sulfur and  68-74%  23-30%  2H S0 ..(5)  bacterial dissolution of chalcopyrite is a  being  In  have  / 21  T. ferrooxidans, the overall reaction is:  2(H 0)Fe3(S0 )2(OH)  Manometric  =  2  (5) are mediated by  +  2  +  REVIEW  of  oxidation.  been the Other  be  attributed to the  deposition  partial  of  oxidation  cultures  will  attacked of S°  on  over the  sulfur (Beck, mineral  sulfide  which  then  blocks  preferentially  leach  copper,  crystal further  with  1960).  leach  as  a  sulfide residues  enriched in iron sulphide (Beck, 1969). Complete breakdown of the mineral particles is not achieved of insoluble secondary  products that obstruct the  the  1972;  surface  (Pinches,  Roman  Changes in the  surface of the  residual  layers, deposition  and  leached  deposition  of jarosite  and  mineral of  compounds.  to the deposition  accessability of the  Benner,  during  due  1973  leaching  and  Lawrence,  include  the  precipitates resulting from (Lawrence,  1974;  bacteria to  Gormely  1974).  formation  iron and  of  hydrolysis Duncan,  LITERATURE  REVIEW  / 22  1974).  2.4.2.1. SULFIDE OXIDATION MECHANISM  It  has been  attacks  proposed  the solid  that  matrix  the actual  mechanism,  of the mineral,  involves  by which a reaction  T.  ferrooxidans  similar  to  the  cathodic depolarization that takes place in microbial corrosion of metals, with the bacterium oxidizing the sulfur in the mineral  lattice (Tuovinen and Kelly, 1974).  Tributsch and Bennett (1981) suggested that protons may be involved in breaking chemical bonds at the an  mineral  surface creating "SH groups. The creation of such  altered surface controls the rate of dissolution of the metal sulfide. When the  "SH  groups  are removed  recycled. Sulfide system. Tano cytoplasmic Sulfide  then  from  enters  the cell  and Lundgren  membrane  oxidation  the surface  and is oxidized  (1978) have  for sulfide  has been  shown  oxidation  studied  by the bacterium  the proton is  by the sulfur oxidizing  the need  for an intact inner  by T. ferrooxidans in acid  in T. concretivorus,  T.  medium.  thiooxidans and T.  thioparus. These Thiobacilli are closely related to T. ferrooxidans  as indicated by  high R N A homologies (Lane et al, 1985). It is then likely that their mechanisms of sulfur oxidation are very  similar to those of T. ferrooxidans .  Sulfide oxidation proceeds in two stages, in the first stage the sulfide loses two electrons. This  reaction is catalyzed  resulting S atoms occurs (Moriarty 1973;  by sulfide oxidase and polymerization and Nicholas,  Lundgren and Tano, 1978) according  SH"  = S + H  1969; Aminuddin  and Nicholas,  to the following reactions:  +  + 2e .-(7) _  of the  LITERATURE 2S  S-S +  Thus oxidation of short chain These  polysulphides  =  / 23  S-S ..(8)  SH* =  S-S-SH- .. (9)  polysulphide  are thought  REVIEW  to polymeric  to be membrane  sulfur compounds results.  bound  (Lundgren  and Tano,  1978). Hazeu et al (1987) have shown the presence of S° granules  in the periplasmic  space and in the outer membrane of T. ferrooxidans when it was grown in high concentrations  of sulfides. The oxidation of polysulphide can be represented as:  "S-S-SH +  where  X  is a  linkage  group  X  =  between  X-S-S-SH ..(10)  the polysulfide  and the membrane  This  linkage group could be a copper protein (Moriarty and Nicholas, 1969). In  the next step  polysulphide  oxidase  catalyzes  the oxidation  of polysulphide to  S° according to:  2(X-S-S-SH) =  The a  last step sulfhydryl  is the conversion containing  X-S -X .. (11) 6  of S° to sulfite. Elemental sulfur is attacked by  agent  resulting  S  GSH  in an  organic  polysulfide  containing  glutathione (G):  The  6  +  =  G S S H ..(12) 6  sulfur oxidizing enzyme catalyzes the oxidation of the terminal  is then removed hydrolytically as sulfite:  atom  which  L I T E R A T U R E R E V I E W / 24 GS SH  + 0  6  GS S0 H 6  The  organic  2  2  = G S S 0 H ..(13) 6  2  + H 0 = GS SH 2  5  + H S0 2  3  ..(14)  polysulfide minus one molecule of sulfur is then attacked  again by  the sulfur oxidizing enzyme (Silver, 1978).  The an  exact location of this enzyme has not been determined, nevertheless outer  cultured  membrane protein (50K) in the presence  that is present  only  in cells  of sulfur, but which is not found  there is  that have been  when  the  cells are  cultured in ferrous iron -which could be this glutathione-dependent sulfur oxidizing enzyme (Kulpa T. ferrooxidans  and Mjoli, 1987). The fact that this enzyme is not present is cultured in ferrous  is not  constitutive and could  ability  to oxidize  Tuovinen  sulfur  et al, 1976)  sulfur substrates  (Unz  when  sulfate would indicate that sulfur oxidation  explain why some cultures seem to have lost their  (Duncan  et al, 1967; Silver  or displayed  diauxic  growth  and Lundgren, 1961). It has  and Torma,  in a mixture  1974  and  of iron and  also been suggested by Yates  et al (1987) that loss of the ability to oxidize sulfur by T. ferrooxidans could be explained  as a result of the  enzymes involved  in S° oxidation  forming  part of  mobile sequences in the genome.  The  final  step  of sulfide  oxidation  oxidation. The electrons resulting from transport chain produce  is the generation the oxidation  of A T P from  of sulfite enter  the  sulfite electron  at the level of cytochrome c, and upon transfer to cytochrome a  A T P at what  constitutes  the phosphorylation  site  in T. ferrooxidans.  L I T E R A T U R E R E V I E W / 25 From cytochrome c an for  NAD" "  reduction  1  energy dependent reverse through  cytochrome  b,  electron transport chain  ubiquinone  and  flavin  functions  (Bell  et al,  1987).  Given  the  oxidation,  number there  than from sulfide  transferred  more energy  with  free energy  examined  results of the present  2.5. MINERAL  to  the  the  bacterium  available from in turn, mean  iron  for sulfide oxidation  relative  the  energy  in detail for the  during  oxidation  higher  growth. This  sulfide  of sulfides  bacterial yields  is also  apparent  on  when  to sulfate (-140.6 kcal/mol)  of ferrous iron oxidation  significance of  will be  ferrous  (AG)  free energy (AG)  1984). The  AND  be  compared  comparing the  yield  should  electrons  iron oxidation. This should,  when  with the  of  (-10  kcal/mole) (Brock et al,  availability  controlled-redox  with  respect  to  cell  process in light of  the  study.  CONCENTRATES.  BIOLOGICAL  STANDARD  LEACHING  BIOLOGICAL  UNDER  LEACHING  CONTROLLED  REDOX  POTENTIAL  Leaching of sulfide containing for  a  number  of years  using  provides  suitable conditions  bacterial  activity  atoms are  is the  a  standard  for the  inoculated  or  breakdown of the  mineral  sulfates and  put into contact with an  with  the  bacterium  conventional  development of T.  oxidized, producing soluble  usually milled and been  ores, in particular chalcopyrite, has  and  been practiced  leaching  ferrooxidans. The  structure as sulfuric  acid. The  some  mineral  that  result of  sulfur and  iron  mineral  is  pH  that  has  salts  that  are  aqueous solution at low  contains  process  L I T E R A T U R E R E V I E W / 26 essential  for its development,  sulfate. The liquid  is also  including  contacted  a  with  nitrogen  source  air enriched  provide oxygen for the oxidation reactions and carbon process  has been carried  with  usually  ammonium  carbon  dioxide, to  for bacterial growth. This  out in reactors of various shapes  and configurations,  packed beds, stirred tanks, pachuca tanks, etc.  Improvements  to the rate of leaching achieved  in the standard biological leach  have been obtained by the development of a controlled redox potential biological leaching process  (Bruynesteyn  at low E h potentials  et al, 1986). In this process leaching takes place  (0.54-0.66 Standard  Hydrogen  Electrode (SHE) volts) with  participation of the cuprous/cupric couple as oxidant in the presence amount  of silver. Copper  extractions are improved  leaching  process. This process will also  over  advantageously  of a small  the standard  biological  convert sulfide sulfur to  elemental sulfur avoiding the need of neutralization before disposal of the residual broth after copper some importance  has been recovered  in the case  is oxidized to sulfuric controlled acid  of standard  solution. Neutralization costs are of  biological leaching where sulfide sulfur  acid. The oxidation of sulfide to elemental  sulfur in the  redox potential leach converts the bioleaching of chalcopyrite from  producing  sulfide-sulfur oxidation  from  process to  is 3.4  to an  elemental times  less  acid . consuming  sulfur, than  the  process.  oxygen  With  requirement  the requirement  an  the oxidation of for chalcopyrite  in standard  leaching. This  provides an economic advantage for the controlled-redox leach over  the standard  leach (Lawrence et al, 1984).  The  use of silver  in catalytic  amounts  has  been  previously  investigated in  LITERATURE REVIEW systems that employ (1979) described chalcopyrite A  a  the ferrous/ferric couple  non-biological, hydrometallurgical  that produced  similar process,  as an oxidant.  high  Miller  process  and Portillo  for the leaching of  levels of copper extraction and elemental  T. ferrooxidans to provide  but employing  / 27  ferric  sulfur.  iron  using  ferrous iron as a substrate, has been developed by Palencia et al (1987). In this process clear  ferric iron is used as an oxidant  from  elemental  their  results whether  they  in the presence of silver, but it is not achieved  conversion  of sulfide  sulfur to  sulfur or if sulfide was oxidized to sulfuric acid.  2.5.1. CHALCOPYRITE  The  amenability  mineralogy. resistance  to leaching  Chalcopyrite  of a  mineral  is considered  to oxidation. Chalcopyrite  a  other  minerals  sometimes  recalcitrant  iron  and copper  perpendicular contain with  atoms  containing  gold  a  face  and  of its  because  of its  series of complex  silver  (Mellor,  1947). The  the axial ratios a:b:c =  centred  to the tetragonal axis contain  the planes  iron atoms. The sulfur atoms are located also on a face centred  lattice  of the sulfur atoms  Ellis, 1917).  lying  of the iron  copper  lattice,  planes  the planes  only  tetragonal  1:1:0.985.  atoms; alternate  directions between the planes and  form  of a  function  iron pyrites, pyrrhotite, siderite, bornite  space lattice of chalcopyrite is tetragonal with The  is a mineral  (CuFeS2) is part  copper iron sulfides found associated with and  concentrate  midway  in all three  of the axial  and copper atoms. See Fig. 1  (Burdick  L I T E R A T U R E R E V I E W / 28  •  o  Fe atoms  Cu atoms  e> S atoms  Fig. 1. Space Lattice of Chalcopyrite  LITERATURE 2.5.2. S T A N D A R D  REVIEW /  29  BIOLOGICAL  LEACHING  Leaching of chalcopyrite can  2CuFeS  +  2  Chalcopyrite soluble  8.50  is  copper  according  represented by  H S0 2  •» 2 C u S 0  4  attacked  by  sulfate.  Ferric  the following set of reactions:  the  bacteria, sulfate  +  4  Fe (S0 ) 2  producing  undergoes  4  +  3  H 0  ..(15)  2  soluble  ferric  hydrolysis  in  sulfate the  and  medium  to:  3Fe (S0 ) 2  As  +  2  be  4  +  3  14H 0  =  2  the ferric iron concentration  2(H 0)Fe (S0 ) (0H) 3  3  in the  4  2  +  6  medium increases  5H S0 2  and  .. (16)  4  the  redox potential  increases, ferric iron can directly attack the sulfide.  CuFeS  Elemental  2  +  2Fe (S0 ) 2  4  sulfur produced  by  3  =  CuS0  reaction  17  +  4  5FeS0  undergoes  +  4  2S° ..(17)  oxidation  in  a bacterially  mediated reaction.  2S°  Reaction consuming associated  18  +  converts process  30  the  2  +  process  (consider  with chalcopyrite  2H 0 2  to  reaction such as  bacteria • 2H S0 ..(18) 2  4  an  acid  producing  15  and  acid  CaC0  3  and  process, from  consumption  the  due  2  4  3  +  2H 0 2  =  2Fe(OH)S0  4  +  to  precipitation of basic  sulfates (Krauskopf, 1967)).  Fe (S0 )  an  H S0 ..(19) 2  4  acid  gangue ferric  LITERATURE A  secondary  reaction is the formation  of jarosite, a basic  REVIEW  ferric  / 30  sulfate formed  below p H 3 resulting from precipitation reactions of ferric sulfate (McGoran et al, 1969;  Duncan and Walden, 1972  3Fe (S0 )3 2  The  4  leaching  +  14H 0  and Sakaguchi, 1976).  = 2(H 0)Fe (S0 ) (OH)  2  3  of chalcopyrite  3  usually  (Bruynesteyn  and Duncan,  1970). This  that  the mineral  surface  modify  of the  mineral  Mehta and Murr, 1982;  2.5.3.  to render  1973;  6  + 5H SO ..(20) 2  in 50-60%  4  copper  extraction  it impervious  of basic are  ferric  by T.  to attack  sulfates  and jarosites.  necessary to further increase the  Torma and Legault,  1973;  Torma,  1977;  Keller and Murr, 1982)  CONTROLLED REDOX POTENTIAL LEACHING  Leaching of copper concentrates by  results  and re-leaching  copper extraction yields (Ivarson,  2  low extraction is the result of changes  ferrooxidans and to the precipitation Regrinding  4  under controlled redox conditions has been studied  Bruynesteyn et al, (1983, 1986)  differences with the standard  leach are  medium  are controlled by the  that  "catalytic"  a  amount  and Lawrence, et al (1984, 1985). The main that the  of silver  is present the  from  acid  elemental  producing  leaching  addition of sodium thiosulfate and cupric ions, and  medium. These changes result in changing an acid  redox conditions of the  process  sulfur and producing  to an  high  copper  in the aqueous biological leaching consuming  recoveries  acid  of chalcopyrite  process,  at high  leaching  generating  biological  leach  rates. Another effect of leaching under controlled redox conditions is the selective leaching of chalcopyrite over pyrite and other sulphide  minerals.  LITERATURE The  thiosulfate  and  promotes leaching. (Bruynesteyn  been proposed  CuFeS  added  FeS0  0  +  2  +  4  l/2Fe (S0 ) 2  serves  to complex  silver  and dissolved  / 31 copper  et al, 1986). The following stoichiometry has  (Lawrence et al, 1984):  +  2  apparently  REVIEW  4  3  2H S0 2  l/40  +  2  +  7/3H 0 2  Ferrous iron produced  4  =  CuS0  1/2H S0 2  =  4  =  4  +  FeS0  +  4  l/2Fe (S0 ) 2  4  l/3(H 0)Fe (OH) (S0 ) 3  3  6  4  2S° +  3  2  +  +  2 H 0 ..(21) 2  1/2H 0..(22) 2  5/6H S0 2  4  ..(23)  by reaction 22 is oxidized by the bacteria to ferric iron in  reaction 20 and then hydrolyzed to form jarosite.  The  reactions that take  grouped under the term of  thiosulfate  place  to produce  the low redox  conditions have  been  of chemical activation of the concentrate, because addition  and cupric  ions gives more consistent results when  added  at the  beginning of the leach, thus "activating" the concentrate.  2.5.4. C H E M I C A L  This  stage  ACTIVATION  consists  of mixing  copper  sulfate  solution  (SHE),  under  which  excess  of silver  and the concentrate. A t E h  conditions leaching takes  effective  oxidant.  In  oxidation  process.  Cupric  according to:  an  such  conditions  ions  the  are reduced  complexed values lower  place, the ferric  cupric-cuprous and  with  cuprous  thiosulfate,  than iron  couple  600  is not "an  acts  thiosulfate  mV  in the  is formed  LITERATURE Cu  +  2 +  S 0 2  2Cu  As  cuprous  thiosulfate  thiosulfate  2 3  +  +  -  =  S 0 2  is formed,  is consumed, and  Cu  2 3  -  +  +  =  the  R E V I E W / 32  1 / 2 S 0 " ..(24) 2  4  Cu S 0 2  2  excess  6  ..(25)  3  thiosulfate  precipitation of silver  protecting  the  sulfide, cuprous  and  silver cupric  sulfide occurs.  Cu S 0  3  +  H 0 2  =  Cu S  +  H S0  4  ..(26)  Ag S 0  3  +  H 0  =  Ag S  +  H S0  4  ..(27)  2  2  It  is thought  that  2  2  these  2  sulfides  2  2  are  oxidized  2  2  at  the  mineral  surface  with  corresponding acid consumption and elemental sulfur production. Then  chalcopyrite  dissolves  equilibrium.  to  replace  Thermodynamically,  the  it can  copper be  sulfide  shown  that  sulfur, resulting in the formation of CuS  Cu S 2  re-establish  the  cannot coexist  with  elemental  (Hiskey and Wadsworth, 1981);  Cu S  +  S° =  +  2H -  =  Cu  by  the  2  and  2CuS ..(28)  which is then oxidized:  CuS  The  equilibrium  +  is  l/20  2  +  re-established  2 +  +  H 0 2  following  +  S .. (29) 0  silver  (Lawrence et al, 1984):  CuFeS  2  +  Cu  2 +  =  2CuS  +  Fe  2 +  ..(30)  mediated  reaction  LITERATURE At  this stage, an  a result of reaction 30  Following  leaching  unattacked  ferrous iron which forms at the  the  leach are  biological  solid-liquid interface as  (Bruynesteyn et al, 1983).  solid  residue  typically  pyrite, basic iron sulphates  1986). The  leaching  T. ferrooxidans is introduced. It is postulated  active culture of  that bacteria oxidize the  elemental sulfur (Bruynesteyn  this process in terms of  encountered  by  of  Cooper  (1985) and  oxidation of the concentrate,  to the particular culture of  During the epoxy  were  and  to a  then  polished  leaching  observed  concentration  after  Ag S04./L) but 10  1 2  Mm . 2  (1985)  problems have been attributed to  the  surface.  environment. The leaching  1.2  subject of the  2  the  surface  T. ferrooxidans used.  x  only in  polished  continuous  were  of A g S  that  2  used a  10^  Mm . 2  area  that  deposits  surfaces  leaching. In his chalcopyrite study he exposed surface  cavities  grain  present  present  exposed  occurred  These  were  of 0.65g/L; the  the epoxy probe was the  and  Ballester  course of his studies Ballester (1985) embedded chalcopyrite particles  chalcopyrite samples before  is  et al,  not well undestood. Difficulties in reproducing been  aspects  Their  exposed  chalcopyrite,  controlled redox potential  have  biochemical  unleached  the  rates  and  and  contains  leaching chalcopyrite concentrate.  in  R E V I E W / 33  of the  chalcopyrite  silver concentration surface  area  was  the  Ag S0 2  4  chlcopyrite particles in  In the sort of concentrate  thesis, the  in  was  of the  leaching, which similar (0.58g order  of 9  x  LITERATURE  REVIEW  / 34  2.6. FACTORS AFFECTING MICROBIAL LEACHING  2.6.1.  METAL TOLERANCE  T. ferrooxidans tolerance for metals has been widely recognized but specific limits are  difficult  Metal  to establish due to variations  toxicity  depends  of tolerance  on the physiological state  among  different  of the microorganism,  strains. on  the  chemical form of the metals and on the degree of interaction of the metals with the environment  Tuovinen  (Norris and Kelly, 1978).  and Kelly  (1972) reviewed  the limits  of tolerance  for a variety of  metals, with the limit for copper being set at lOg/L, this seems very low since T. ferrooxidans has frequently  been  concentrations  et al, 1986. With  see Bruynesteyn  reported  to grow  at much  respect  higher  to silver  reported by Tuovinen and Kelly (1972) was 50-100mg/L. Ehrlich  copper  the limit  (1986) reported  that some strains tolerated silver concentrations of up to 170mg/L.  In the presence of metals T. ferrooxidans exhibits a lag which  is presumably an  adaptation  (Tuovinen et  or selection  period, before iron  oxidation  1971). T. ferrooxidans is more tolerant to heavy ferrous  iron  as opposed  to thiosulfate  metals when  solutions.  enzymes may be more succeptible to heavy  can occur  This  it is growing in  suggests  metals. Silver forms  al,  that  certain  complexes  with  cysteine, consequently it will affect enzymes that depend on thiol groups for their activity  (Gruen,  1975).  Silver  also  accumulates  accumulation results in Mg and K losses.  in T.  ferrooxidans cells,  this  LITERATURE REVIEW Interactions  of  silver  with  the  medium,  will  decrease  the  effective  concentration, thus explaining some of the differences in the toxic  cation  concentrations  reported. This is the case of the increase in resistance to silver reported ferrooxidans to  Ag2S, reducing  of the cation. A  the effective  similar pattern  copper toxicity. Copper in concentrations CO2  fixation  when  for T.  when cultured on sulfides. Silver has affinity for sulfur and will bind  it forming  toxicity  / 35  concentration  has been  of 0.1-1.0 M  hence  observed  reducing  for the case of  inhibits iron oxidation and  (Tuovinen and Kelly, 1974). In this study cell growth occurred  copper  concentrations,  controlled-redox  leaching  increasing throughout  initial  C u  +  the leach, reached  concentrations  +  the  of 0.45M  even  1.5M. For  (copper  added  during conditioning of the concentrate) had no effect on iron oxidation.  2.6.2. NUTRIENTS  T. ferrooxidans, This  is generally  carbon CO2  being  dioxide  an autotroph,  supplied  consumption  can be supplied  in the form  of carbon  by active  cultures could  to the media  solubility. In addition to a carbon ion is needed, other supplied  and  nutrients such  by the medium  Magnesium  utilizes carbon dioxide  (Tuovinen,  source,  dioxide  as a carbon enriched  exceed  source.  air, because  the rate  at which  1972) due to its relatively low  a nitrogen  source,  as potassium, calcium  which is usually the 9K  usually  ammonium  and magnesium are  medium of Silverman  (1959).  is necessary for carbon dioxide fixation and also for energy fixation,  is a factor in a variety of metabolic  energy metabolism. (Tuovinen et al, 1971).  reactions. Phophorus also participates in  LITERATURE  REVIEW  / 36  2.6.3. PARTICLE SIZE AND SURFACE AREA  Leaching of mineral concentrates involves the surface of the concentrate particles. There  are two  amount  ways  of surface  in which  area  we  per unit  can study volume  on  the effects the leaching  of changes process.  in the  Increased  surface area can be the result of decreasing the size of the solid particles for a fixed amount of mass of solids (eg. by grinding the concentrate), or by increasing the mass of solids per unit volume maintaining the same particle size (increasing the  pulp  density).  In the leaching  of sulfide  minerals  the rate  oxidation increases when the particle size of the mineral decreases 1966;  Bruynesteyn  and Duncan,  1970; Torma  of bacterial  (Duncan et al,  et a l / 1972; Sakaguchi  et  al,  1976). Copper  leach rates increase linearly  with  increasing  60g/L, above this value other factors such  solids concentrations up to  as particle  sedimentation  and limited  mixing come into effect. This is a pulp density effect (Pinches et al, 1976). Gormely et al (1975) found  that for zinc sulfide, the leach rates were first order  with respect to surface area per unit volume. Pinches et al (1976), working with Zambian concentrate of chalcopyrite, found the  external surface  area  for particles  leaching rates increased linearly this  size  dependence  the copper  extraction  of the copper  that copper larger  than  yield 7  extraction  was  rate  with  For particles of 5.4 Mm the copper extraction rate was  found  that  size up to 10 M m ,  102mg/L particle  proportional to  /un. They  with decreasing particle rate  was  h. Below size  10  for  Mm the  became non linear.  121mg/L h. Below 4 Mm  the leach rate was less dependent on particle size and for 2.1 Mm particles the rate  was  134mg/L  h. They  suggested  that this complex  behaviour  may  be the  LITERATURE result in changes in the active  leaching  volume  which  REVIEW  would be a constant for  particles larger  than 7 um, but decrease for smaller particles. Alternatively,  suggested  this behaviour  that  / 37  they  might be the result of changes in the interaction  of the particles with the bacterial cells and flocculation of the smaller particles.  Available  area  for the reaction  is a function of particle  size, and for a fixed  amount of solid material, increases with the fineness of the material. In theory the  optimum  Leaches  of  particle Newmont  for leaching  would  concentrate  of  be a single chalcopyrite  crystal under  (Tuovinen,  standard  1972).  conditions  conducted with monosize particles of less than 7 ^tm, showed that the maximum copper extraction obtained when  rate (28mg/L. h), and maximum  the particles  (Blancarte—Zurita,  1983).  had a size comparable to the bacterial  This  effect  could  leaching. Jones and Peters (1974) found copper  extraction  mechanism  did not improve  of attack  extent of leaching (98%) were  of ferric  only  characteristic  (1 nm)  of biological  that for abiotic Caching of chalcopyrite,  for particles  iron  be  size  lixiviant.  below  150 fim  Leaching  takes  because  place  along  of the grain  boundaries and fissures, so particle reduction stops being beneficial when no more grain  boundaries  leaching  was  can be exposed  also  studied  by  by grinding. The effect of grinding  Beckstead  et al (1976)  improved with particle size reductions down to 0.5 ixm.  2.7. MODELLING  BACTERIAL  LEACHING  who  found  in abiotic extractions  2.7.1.  The  LITERATURE  REVIEW  / 38  and product  formation  that  MODELLING AND KINETICS  search  for a  adequately  pattern  describes  of substrate  bacterial leaching  utilization has  been  seriously  limited  because of  difficulties in characterization and quantification of the bacterial populations, and their involvement in the leaching of metal values. of bacterial attack  on a sulfide concentrate  models ..for the design  effect  on  particle  metal  size,  concentrations  would be useful in producing better  and control of leaching  for the most part, constrained leaching.  stirring  Knowledge of the mechanism  systems. Initially  to investigations of operating  Roman  speed,  and  oxygen  Brenner  attempts  parameters and their  (1973) discuss  concentration,  were,  the effects of  temperature  and  reagent  on the rate of dissolution of different copper concentrates  for both  biological leaching and abiotic leaching.  The of  complexity of the kinetic descriptions that are necessary to describe minerals  can  electrochemical proposed  be  estimated  processes  parabolic  and  kinetics  non-biological  there  was  for abiotic leaching  equation  leaching.  literature Dutrizac  of models for et  al  of chalcopyrite. They  of the chalcopyrite. Dutrizac  no  general  agreement  of chalcopyrite, since  linear kinetics (Lowe, 1970). Sepulveda balance  the  (1971),  found the  to be diffusion of ferric sulfate through a thickening sulfur  layer formed on the surface that  reviewing  kinetics for abiotic leaching  rate controlling step  reported  by  leaching  with  kinetics based  with  and MacDonald  respect  to the type of  some investigations had shown  and Herbst (1978) proposed  on topochemical  rate expression) for leaching of chalcopyrite. They  (1974)  leaching  a  population  (a shrinking  found the leaching  core  reaction to  LITERATURE REVIEW / be  electrochemical  in nature  with  the  conduction of electrons through  layer as the rate controlling step. The  kinetics followed  39  the sulfur  a shrinking core model.  2.7.2. MODELS IN BIOLOGICAL LEACHING  Difficulties in modelling cells  abiotic leaching  are only  in biological leaching. Incorporation  the  components of the  all  the  interactions  unattainable.  This  of all the  leaching medium  between difficulty  the can  cells be  compounded by  the  presence of  different relationships among  in a theoretical description that  includes  and  moment  the  explained  substrate  if we  is for  consider  a  the  typical  leach  medium where several processes are occurring concurrently, these involve reactions in  solution, . acid-base  rheology  of  Also, from  the the  equilibria,  precipitation  medium, dissolution of cell  the  point of view, in batch  reactions,  mineral, growth  changes  in  pH  and  gas-liquid exchanges, etc. the  following processes  are  taking place -induction, repression, growth, death, lysis, etc. Sanmugasunderam et al (1985) applied a  model proposed by  of predicting the rate of growth of T. was  Gormely et al (1975) which was ferrooxidans on  ZnS  concentrate  capable but  which  made  by  not successful in predicting the rate of metal release.  Attempts  to simplify the  description of a  leaching  system  have  been  grouping all the variables derived from the interactions of the cell with the substrate the  in an  process from  variables and  experimentally the  substrate  the general  measured  leach rate. It is possible then  point of view, gaining  mechanisms.  solid  to study  insight into the controlling  LITERATURE REVIEW Models  developed  from  described  for various  approach  considers  considers  the  the  solid  experimental,  microbiological  substrates. Two  the  solid  solid to be  surface. Both  main  subject  attacked  to  leaching  approaches have  uniform  approaches  are  valid  been  conversion,  at loci which can  be  data  the  / 40  have  been  followed. other  One  approach  randomly distributed on  depending  on  the  substrate  being  proposed.  Locus  considered.  For  locus  conversion be  conversion,  models  of  pore  leaching  meet  and  leaching  takes place  coalesce,  through  removing  moving  pyrite from  of refractory gold—bearing  regions  of the concentrate  of the  leaching residues. For  boundaries the  30%  rates depended on  size (Hansford  and  hybrid  based  model of  auriferous  pyrite, caused  the  planes  crystal  in the  using  the  surface  oxidation, gold area  on  pyrite.  propagating They  found  lattice. These an  increase  shrinking core  model  containing chalcopyrite, sphalerite and  nucleii, that  Another  example is  pores  develop  subsequent liberation  concentrations and  pores that  Southwood and  biological  surface  area  exclusively. For  but  and  that the  90%  on  or  particle  (1986) proposed cores  leaching  with  cyanidation  was  not  shrinking  dislocations were caused in the  this  Selective leaching in the gold rich  development of pores that coincided  pores represented  for by  sulfide  these  penetrating  gold liberation by  Drossou, 1987). Southwood both  around  coal matrix.  pyrite where  lead to high  higher. Leach  The  been  form of pyrite inclusions in coal. For  leaching takes place through pore propagation.  leaching  have  is clearly applicable for coal desulphurization where coal particles could  seen as containing nucleii, in the  case  propagation  of  for  a the  auriferous  preferred dislocation by  gold inclusions.  was case  pyrite (average metal contents  not  accounted  of waste  ores  of 0.82%  Cu  LITERATURE REVIEW and  0.82  factor  %  Zn),  Bruynesteyn  in biological  particle surface  leaching  area  and  proportion  of the  was  the  liquor into the particle. The  and  Duncan the  active  leaching  depth of penetration  increase  in leach rates obtained  ores could  also  considered  locus being  the  minerological  a  as  special case  phases on  exposed, thus explaining the increased  uniform conversion. leaching by  the  Until now  no  and  Southwood  Pores observed in pyrite by  of leached 1983). For  concentrate  of the  host  locus  rock. The to the  leaching  the  conversion  (1986), had  the  the  number of loci  per  increase  and  diameters of the Drummond  much larger than the  in surface  has  area  been found for pores  order  pits observed on of 2 Mm  CORE, SHRINKING  the  70 surface  been proposed.  PARTICLE MODELS  of a shrinking core  model for leaching of  mineral  be  the  jim.  (Blancarte-Zurita,  They estimated from experimental data, that the by  observed  of 5-25  (1973) were around  a shrinking particle mechanism has  covered  leach  with  zinc sulfide concentrate. would  the  increasingly large  (Blancarte-Zurita, 1983). The  Gormely et al (1975) proposed the use  surface  of  is believed to occur through  particles which are of the order  uniform conversion,  2.7.2.1. SHRINKING  of the bacteria and  evidence of pore formation  Duncan  in diameter. These pores are  up  leaching rates for small particle sizes.  sphalerite concentrates  of chalcopyrite concentrates  Southwood  made  the particle size decreased. Waste  unit mass, increases for small particle sizes due  chalcopyrite and  volume,  the controlling  the particle size decreased, thus explaining  exponential  For  that  active leaching volume became an  total volume as  be  (1970) proposed  / 41  bacteria  during  leaching  and  complete that  a  LITERATURE  R E V I E W / 42  model based on  Levenspiel's  model (1972) for a shrinking core, spherical particle  when  chemical  reaction  the  Using  a  similar zinc  at  sulfide  stage reactors  amount of leaching could be  controls  concentrate  application of a shrinking core state in two  surface  the  Sanmugasunderam  run  in straight through  approximated by  sulfide mineral  concentrates.  standard  leaching  ores. Trends can tend  to  used. Our  depend  same  on  compared the  ore  used  and  the  leaching was  techniques  such  all work done on  Ballester  this subject was  foundation  (1985) have  done  for  the  history  focused  as  x  some  work. Most of their work was  carried out present  ray  on  experiments  for a  successful (Ballester, 1987). This  can  be  explained  that examines pulp density effects (appendix 8).  previous  shrinking  variety of  quantitative results  of  the  microorganism  obtaining  some reliable process.  leaching, until very Research. Their  Recently  Cooper  trying to duplicate  at low  the  At  analysis to investigate cell-  at B.C.  study.  carried out  that  have proposed  which to base a comparison with the controlled-redox  time we  the  studied  among different systems, but mineralogy  found  steady  a shrinking reactive core.  been extensively  substrate interactions. With respect to controlled-redox  considered  and  the whole particle  diameter particle which has  work in conventional  kinetic data on the  be  mode  achieved  the  the microbiological leaching of  model is based on  of sulfides has  applied.  (1981) pursued  Appendix 8) we  the shrinking core model to describe This  be  a shrinking core model. In  a variation on  The  could  model. Using CSTRs in series he  papers (Blancarte-Zurita et al, 1986a, 1986b, see  rather than on a constant  process  pulp density by  the  portion  work is  (1985)  B.C.  and  recently  and  Research  it was of this  not work  CHAPTER 3. THEORY  3.1.  SHRINKING PARTICLE MODEL FOR  3.1.1.  DEVELOPMENT OF THE  CONCENTRATE  LEACHING  MODEL  During leaching, material is being  solubilized  from the  concentrate  particles. It is  assumed that the particle gets smaller. This would not be the case if there were enough  inert  maintain  the  material  associated  physical integrity  with  of the  the  material  being  leached  particle. It also ignores  any  solids on  the  particle size. It also assumes that the particle composition  the particle surface such as jarosite, which would tend  as the particle shrinks and  The  its components are  t time. Assuming that the particle has dn  We  can  to  deposition of to increase  remains unchaged  — dn/dt where n is the a constant density  particle  (p)  dV  dt Where V  as  solubilized.  rate of decrease in particle size is given by  mass and  the  so  P  ...(31)  dt  is the particle volume. represent  shape factor. Now  V  by  V  =  adp^  where dp  =  particle  the change in particle size is d[ad ] 3  p  p  which, if we  assume a constant  dt  shape factor, becomes  3ad  2 n  43  diameter, and  a  =  T H E O R Y / 44 Experimentally call  the rate of appearance of the metal in solution can  this rate r which is expressed in unit of mass/(volume x  the rate of metal dissolution to a rate of particle dissolution we by  the weight fraction of metal in the concentrate.  So  the rate of particle dissolution is r/f.  -  3 a,d 9 p  — P^ dt d [ d  2  n  y  represents  the  made in a  dissolution rate  system  containing  of  a  many  single  is the  3  0  and  dp  0  time). To  convert  have to divide r  ]  particles per  is equal to Co/(ap d p ) where Co  measured;  Let this weight fraction be f.  particle;  particles disappear during leaching, then the  be  the  measurement  of  unit volume. Assume  r is  that  number of particles is constant initial mass concentration  no and  of particles  is the initial particle diameter.  So: 3pad Co d[d ] ?—7— ) — ? apd dt  r  2  n  -(  n  =  ...(32)  f  3  p o  or d [dp] dt  Integration of equation 33 particle  size and  r =  d (  f  3  )  P n  3C d 0  -(33)  2 p  requires a knowledge of how  time. This  requires  experimental  r varies with respect to  measurements. These  done in shake flask studies or other lab scale reactors by several, more or less monosize metal ion concentrations metal concentration  fractions of concentrate  for r.  be  leaching suspensions of  particles, and  in solution as a function of time. The  vs time gives a value  can  measuring  slope of a plot of  T H E O R Y / 45 Solution of equation 33 gives concentrate particle diameter Experimental  support  for the validity  of equation  Blancarte-Zurita et al (1986a,b). See Appendix in  Appendix  They  8 should  are appended  be considered rather  than  33  as a function of time. has been  provided  by  8 and section 5.2. These  papers  to be a part of the work of this  thesis.  included  in the main  text  only  to avoid  reproducing material already printed.  The  fractional  throughout  extraction  (X) of metal,  assuming  it is uniformly  distributed  the concentrate particle, is given by p £- ... (34) dpo d  X  =  1  3  6  u  Levenspiel  (1972) has shown  that the mean  fraction  ( X ) not extracted in a m  continuous, stirred tank reactor is  1 -  where  E  X  m  =  is the age distribution  Jo (1 - X) Edt ... (35)  of the particles  in the reactor outlet.  For a  perfectly mixed reactor  E  Where  T  =  mean  leaching in a finite 34  and 36, as  =  1 -  t exp [- -  T  T  residence time. Since time  equation  ] ... (36)  particles  can disappear  35 should be rewritten, after  as a result of combining  with  THEORY 1 -  X, m  exp [ —  / 46  t ] dt ... (37)  7  where T is the time it takes for particle diameter to go to 0.  A  digital computer program has been written to solve equation 37.  The  required input data for this program are  1.  concentrate particle size distribution  2.  an empirical  equation or equations, derived  dp  other relationship  or some  such  from  as tables  experiment,  relating r to  of values of r at various  values of time and particle size. 3.  feed pulp density  4.  mean residence time in the reactor  5.  fraction of metal in the concentrate  6.  an arbitrary  maximum  time  (T  m a x  )  to leave the program  when  retention  times exceed practical levels for the conversion specified 7.  the number of tanks in series if multiple stage simulation is contemplated.  For  concentrate having a particle size distribution, the procedure is discussed on  Blancarte-Zurita, into  various size  represented one  fraction  range 33 a  1986a  (appendix  categories.  by the mid-range  8). The particle size  A l l particle particle  Then  in each  of d . Then p  program  it repeats them  the lab scale experiments  the calculated  particle  diameter  puts particles  size  category are  then  starts  for the next  a time interval At the particle size is calculated  and the information obtained from function  diameter. The  and does its calculations.  etc. After  diameters  distribution  with size  using equation  which  is compared  give r as with the  T H E O R Y / 47 diameter if  range of applicability of the particular r(dp) relation being used  the same  one should  be used  in the next  required. If the same one is to be used elapsed than  compared  T  m  a  step  different  one is  the calculation is repeated and the time  to an arbitrary, maximum  time  (T  the calculations are repeated. When t =  x  or if a  to see  m a x  T  ).  If the time  is less  a  the average  particle  m  x  size is printed. The range of validity of each equation is included as part of the program (see appendix 4).  If  at any  time  the particle  shrinks to such  an  extent  that  it moves  different size class so that a different r(dp) equation is needed, the time be  set =  0 again  to get the proper  This is corrected for when T  Next  conversion  calculated the  %  m  a  is calculated  using equation  retention  continued  time  of dp  using  equation  a preassigned  is too long  for any  of multistage leaches if the specified  the  stage  repeated. When has  34.  value, T  simulation first  calculations.  is reached.  or the run is abandoned  required  in subsequent  has to  The  mean  conversion is  37. In the simulation of a single stage of leaching if  extraction is less than  calculations  x  values  to a  another a second  to be calculated. If %  tank  in added  to  or subsequent tank  with  m  a  x  the conclusion  practical %  is increased and the  consideration. In the  extraction  the system  that the  is not achieved in  and  is added a new  the calculations feed pulp density  extraction is to equal or greater than the preassigned  value the program prints the %  extraction.  All of the above is explained in the computer program logic diagram of F i g 2.  T H E O R Y / 48  START \DATA ^FRACTIONS SIZE DISTRIBUTION MEAN RESIDENCE TIME NUMBER OF TANKS  READ FOR FRACTION N Zn PERCENTAGE IN CONCENTRATE INITIAL PARTICLE SIZE dpo  CALL LEACH SEARCH FOR SIZE CLASS  [ C A L C U L A T E C O N V E R S I O N ]  CALCULATE RATE FOR O p o INCREASE NUUBCR or TANKS  CALCULATE SHRINKING NEW Op  | 'f LESS THAN NT f  j i r EQUAL TO NT \  tVERSION  I RACTIONS |  ELSE CALCULATE NEW SIZE DISTRIBUTION  TEST OPE IS NEW Op LESS T H A N L O W E R LIMIT OF CLASS  INCREASE  DISPLAY VALUE OF TIME AND Dp  [If CQNVEI 1 EQUAL * I S T O R E  CALCULATE INITIAL U A S S CONCENTRATION  TI'MT  TEST TIME LARGER THAN TMAX  T I M E r  CALCULATE AVERAGE PARTICLE SIZE  I'.NF'JT REACTOR N*\|  CALCULATE ELAPSEO TIME SINCE LEACH BEGAN  Fig. In  I N I T I A L I Z E  ,L r  -j  END  |  2 Logic diagram of the computer simulation  order to test the relevance of this computer program some comparisons were  made  between  %  extractions  of  experimentally by Sanmugasunderam  Zn  from  ZnS  concentrate,  as  measured  et al (1985), and % extractions predicted by  THEORY the  / 49  program for the conditions of those experiments. The calculated and measured  results are presented in Table  1 and Fig. 3. Agreement is within  The  1 are for runs  results presented in Table  1-13 made by  about  +20%.  Sanmugasunderam  (1985) for one stage leaching of ZnS concentrate. The availability of the program described above allows one to predict the effects of the  changes in the operating parameters %  of the leach reactor on such  metal extraction. For example Fig. 4 plots %  things as  Zn extraction as a function  of mean residence time for a single stage reactor with a pulp density of lOOg/L. Fig. 5 shows the effect of adding a second stage with the same residence time. Percentage zinc values are the overall extraction of the concentrate after passing through the two reactors as a function of residence time in each tank.  Reactor #2 feed pulp density depends on the levels of extraction  of reactor #1,  and varies between 59g/L for 10 h residence time in the first reactor, to 24g/L for  300  reactors  h. Reactor combined)  #2  as a  conversions go function  from  of residence  40—60%. time  Total  conversion  (Fig. 5) shows  froth  that the  advantage of using Reactor #1 and Reactor #2 in series is a + 4 0 % increase in conversion over a single tank.  THEORY /  Run  1 2 3 4 5 6 7 8 9 10 11 12 13  r  ZINC % EXP  ZINC % CALC  (hours)  F E E D PULP DENSITY (g/L)  83.7 102.0 102.0 102.0 117.6 76.9 76.9 76.9 76.9 76.9 66.6 66.6 66.6  57 123 159 206 311 213 143 177 205 280 73 145 76  54.4 48.7 51.8 51.8 41.0 52.1 43.3 37.1 42.0 33.7 57.6 55.1 57.1  66.5 51.8 45.6 39.7 36.4 38.5 46.9 42.3 39.2 25.6 60.5 44.8 40.7  Table 1 Experimental and calculated percentage of zinc extraction  T H E O R Y / 51  • O  EXPERIMENTAL CALCULATED  O a  O  o  o o O  '  i  50  100  Fig. 3 Zn  1  150  1  200  1  250  Feed pulp density ( g / l )  ,  300  extraction as function of pulp density  r—  350  T H E O R Y / 52  Reactor  one  100 - r —  OH  20H  1 100  I ISO  1 200  i 250  M e a n r e s i d e n c e time ( h o u r s )  Fig. 4 Zn extraction reactor #1  of a series of 2  f— 300  T H E O R Y / 53  Reactor 1 0 0 -1  two  —  20-i  1  1 40  1 60  M e a n r e s i d e n c e time ( h o u r s )  Fig. 5 Zn extraction reactor #2  of a series of 2  80  C H A P T E R 4. MATERIALS AND METHODS  4.1. COPPER  Leach  CONCENTRATES  experiments were carried out on  concentrates,  obtained  from  two  the B.C.  different commercial flotation copper  mines  of Gibraltar  Mines  Limited and  Newmont Mines Limited.  4.1.1. S A M P L E  The at  PREPARATION  Newmont concentrate had previously been wet ballmiiled, as a lot of 200Kg, 5 5 % solids for 1 h to 91.8 %  Gibraltar concentrate for  70  minutes  -400 Tyler mesh, filtered, and dried at 60°C.  was a lot of 50Kg and was wet ballmiiled  to  attain  a  similar  size  reduction  to  that  at 3 0 % solids of  Newmont  concentrate. It was wet sieved to 100% -400 mesh, filtered and dried at 50°C.  4.1.2. A 200  SCREEN  sieve  ANALYSES  analysis of the as-received  g sample  obtained  lot of 60 kg. It showed  Gibraltar  concentrate  was  performed  using a chute splitter, from the contents  on a  of an original  45.8% -400 Tyler mesh; the results of a sieve analysis  of this concentrate are shown in Table 2.  54  MATERIALS AND  Tyler  M E T H O D S / 55  Mesh  + 150 -150 +200 -200 +270 -270 +325 -325 +400 -400  11.90 13.71 13.66 5.39 9.50 45.82  Table 2 Sieve Analysis of Gibraltar  Concentrate  4.1.3. ASSAYS  Both concentrates  were  assayed  for copper,  iron  and sulfur  (for the procedures  see appendix 1). Results of these analyses are tabulated in Table 3.  4.1.4. P A R T I C L E SIZE  4.1.4.1. CONCENTRATE  A  simple  sedimentation  FRACTIONATION  method  "monosized" fractions. The beaker differences at such can  was  used  to  decantation method  in the terminal velocities of spherical  rates that the Reynolds' number  be calculated  separate  (Pryor, 1965) is based  particles falling  is less than  using Stokes' law for any given  velocity a sedimentation time can be estimated.  the concentrate  through  into on  a fluid  0.2. This terminal velocity particle size, and from the  MATERIALS AND  ELEMENT  (%  by weight)  M E T H O D S / 56  NEWMONT  GIBRALTAR  27.8 28.0 31.1 5.5  25.7 26.2 31.3 16.8  COPPER IRON SULFUR INSOLUBLE  Table 3 Concentrate Elemental Analyses For  the  chalcopyrite  concentrates  fractions obtained  by  because  non-spherical  of  the  the  actual  this method, differs character  particle  from of  size  of the  those calculated the  mineral  by  "monosized" Stokes' law,  particles  and  the  entrapment of small particles during the settling of the larger ones. To minimize this  last  problem  hexametaphosphate removed cake  from  in water  found  and  obtain  homogeneous  was  added  to  the settled two  were measured  particle  a  dispersant,  suspension  "monosized" fractions by filtering and  or three  in Blancarte-Zurita  the  dispersions  times. A  (1983). The  complete  description  and  sodium  subsequently  resuspending the  of the procedure is  particle sizes of the "monosized"  fractions  by image analysis as described below.  4.1.4.2. PARTICLE SIZE ANALYSES  Particle size distributions were measured  by image analysis, using a  Leitz  Image  leach  tests,  Analyzer.  In  order  to  analyze  the  concentrate  particles  obtained  from  the  MATERIALS AND METHODS / 57 samples of the suspensions were filtered through millipore membranes (0.2 Mm) and  the  solids  were washed  with distilled water,  to remove soluble  salts. For  samples of elemental sulfur producing leaches, the solids were also washed with ethanol  and carbon disulfide, to remove sulfur particles. The cake was  resuspended  in ethanol.  Solid particles  from the  dry concentrate  finally  were directly  suspended in ethanol.  Using  an ultrasonic bath  suspension  was  withdrawn  the  samples  using  a  were dispersed  Pasteur  pipette  transferred to a microscope slide; the slide was mounted on a microscope  stand. A television  and with  a  portion of  a  the  broken tip and  then allowed to dry and was  camera captured the  image and  transferred it to a T V imaging device. The TV screen was calibrated according to  the  magnification  used  in  the  microscope.  After  editing  the  image  and  adjusting contrast and focus, the image was processed by means of a program called  TASSEP.ENG  (software,  Leitz-image  analyzer).  In  this  program,  size  measurement is based on continuous erosion of the two-dimensional image of each individual particle within a field. The number of step erosions are counted and the equivalent diameter of the particle calculated. A meander is pre-programmed into the  computer which allows  microscope  stand,  field  parameters specifying  by  field  the  examination of the slide  automatically.  The  meander  width and length of field of examination  fields to examine to the right or left,  mounted on the consists  of four  and number of  up or down from the initial position of  the microscope ocular in the sample. For size analyses a double blind procedure was coded  used; ihe samples, and  analyzed  drawn sequentially randomly,  so  as  from the experiments, not  to  influence  the  were number selection  of  MATERIALS AND magnification.  In  every  examined. Duplicates ensure  that  the  measured using  group  of  from the  apparatus  samples  same sample  was  at  on  least one  were analyzed on  performing optimally.  the image analyzer  sedimentation times are  analyzed  M E T H O D S / 58  The  duplicate  was  alternate days, to  average  particle sizes  the monosize fractions together with their  shown for as received  Gibraltar concentrate in Table  and  for -400  The  median particle size is often employed as a characteristic size for particulate  systems. equals  mesh Newmont concentrate in Table  4a,  It is defined  50%  of the  as  the  total. For  median size. (Stockman and  4.1.4.3. REDOX A  reaction  charged  metal)  an  the The the with  ions  and  electric  reaction.  neutral  molecules  charges  (i.e. electrons  For  any  potential at which the equilibrium  potential (Eh)  reference  given  of particles  is the  coupling electrode  the  value  of the  electrode  (hydrogen  on  number  state of the  which  the  calomel  is in electrochemical used was  equilibrium  (Pourbaix,  platinum/calomel.  1974). In  positively or  arising from  a  reaction  exists a fixed value of  equilibrium  electrode,  and/or  electrochemical  reaction is obtained.  potential difference  reaction electrode,  electrode) i.e. the value of the potential difference when the  of electrodes  amount  1978)  substances, free  electrochemical  cell formed by a  the  under fixed physico-chemical conditions, there  electrode redox  which  distributions it is also called the  Fochtman,  involving chemical  taking place  number  for  POTENTIAL  negatively is  particle size  4b.  is taking silver  whole of the  this study  the  of  place  chloride system  combination  MATERIALS AND METHODS  Settling time  Mean  (sec)  (Mm)  (Mm)  7.56 11.8 21.0 47 189 832  46.8 43.7 38.2 30.4 14.3 8.6 2.5  47.6 43.8 41.2 30.9 14.4 8.6 2.1  50%  size  oo  / 59  value  Table 4a Size Fractionation for as received Gibraltar  Concentrate  4.1.4.4. DENSITY  Density of the concentrates was determined  in a liquid pyknometer by measuring  the mass and volume of a sample of particles suspended in distilled water plus sodium hexametaphosphate as dispersing agent. The be  procedure  is described in Allen, (1981).  3.83 ± 0.07 g/cra  3  at 23°C.  4.1.4.5. SPECIFIC SURFACE Specific  surface  concentrate, Portland  area  (ssa),  was determined  Cement  AREA expressed using  Blaine  by A i r Permeability  Air Permeablity  as square  the Standard  following the plateau principle suggested The  The average density was found to  Apparatus  Apparatus  centimeters  Test  Method  (ASTM,  per gram of for Fineness of  Designation  C204-81)  by Price, (1976). allows  a definite  quantity of air to  be  M A T E R I A L S AND  M E T H O D S / 60  Mean  Settling time  50%  size  (sec)  (Mm)  21.2 37.8 84.9 340.9 1500  6.4 5.9 3.5 2.8 2.7 0.2  4.00 4.10 2.20 2.10 1.80 0.18  Table Size Fractionation for -400 passed The  through  a fixed bed  4b  mesh Newmont  of compressed  of the pores in the bed and  consequently  Concentrate  powder with porosity of 0.5  size of the particles present in the bed  will determine  of material in 1 g  intervals  the rate of airflow through  small variations of ssa around one weight  produced  a  bed  and  the  ssa was  this weight, beds were prepared  with the exact weight and  ssa  for a  given  sample  was  size  using different In general  particular value occurred, indicating that this  required compactness. For  the rates of airflow through  0.005.  the bed.  determined.  of the  and  +  the number and  For each measurement, several beds of concentrate were prepared amounts  value  better accuracy that weight  using  ±0.05 g  the three beds were measured in triplicate, the  the  average  value  calculated  from  the  measured  rates. Table  5  presents  the  Gibraltar concentrate.  average  values  of  ssa  for  the  "monosize"  fractions  of  MATERIALS AND METHODS / 61 Table 5 Specific Surface Area for Monosize Fractions Mean Diameter  SSA  (Mm)  (cm /g)  46.8 43.7 30.4 14.3 8.6  453 637 808 1398 1816 4132  z  2.5  4.2. BIOLEACH  EQUIPMENT  4.2.1.  FLASKS  Shake  SHAKE  flasks  bacterial  were  inocula.  bottom—baffled, solution  (Silverman  suspension plastic  250  used In  for  all  culture  maintenance of  ml Erlenmeyer flasks;  70  and  cases,  METHODS  g  adjusted to 2.0  foam  AND  Lundgren,  7.5  1959)  were  and  for  concentrate  (to  preparation of  were  mL of iron—free added  with IN H2SO4. The flasks  plug and incubated overnight  the  allow  and  Canadian Liquid Air Ltd.).  from the shaker, the pH was  the  pH  of  the  were stoppered with a  for  After incubation, the  adjusted back to 2.0  in  9K medium  acid consumption  gangue) in a dark room with a carbon dioxide enriched atmosphere dioxide,  placed  flasks  by  (dry carbon  were removed  and the flask  was  sealed  using parafilm and stored under refrigeration at 4°C until used. The  temperature of the incubation room was controlled at 35°C by means of a  temperature controller (Honeywell type RP 908).  MATERIALS  AND  M E T H O D S / 62  4.2.2. B E A K E R S  Preliminary beakers  bioleach tests on "monosized" fractions were carried out in 100  which  were  agitated by a  controlled by using a p H delivered losses  12N  due  H2SO4.  magnetic  meter—controller,  The  to evaporation.  beakers These  were  stirrer. The pH  to activate a peristaltic covered  plates  of the pulps  were  with  acrylic  perforated  to  pump  mL was  which  plates  to avoid  insert  the  pH  electrode, which was immersed into the agitated pulp, and to insert the acid feed line for p H control.  4.2.3. 1L  A for  TANKS  Virtis  Omni—Culture  small  scale,  Benchtop  tank  leach  laboratory  tests.  The  fermenter  (No.6700-0060) was  fermenter  consisted  of  a  1  used liter  borosilicate, baffled, glass culture vessel, a stainless steel perforated headplate and two  six bladed  impellers  were  (4.9 cm  in diameter),  bottom-driven  by  a  shaft  mounted  magnetically  turbine  coupled  impellers.  drive.  The  The  working  volume of the fermentor was 350mL. Temperature was controlled by cooling coils. A  mixture  situated  of air—carbon  between  controlled maintained  from  dioxide  the impellers.  a panel  located  in the dark using  ( 1 % v/v) was Temperature,  under  introduced  agitation  through  and  a  sparger  air supply  were  the fermentor. The vessel contents  were  a removable exterior cloth cover.  been shown to be inhibitory to some species of Thiobacilli  Visible light has  (LeRoux and Marshall,  1977). For  controlled-redox  leaches  the p H  of the pulps  was  maintained  at 2 . 2 as  MATERIALS  AND  M E T H O D S / 63  described for the beaker experiments. A  diagram  of the system  is shown in Fig. 6.  4.2.4. 3L TANKS  Baffled, plexiglass tanks equipped large  scale  motor  was  tests.  The  located  plexiglass was  working  on  top  with 4 blade, turbine impellers volume  of  the  for these  reactor,  a  tanks  was  perforated  were  used for  The  impeller  2L.  headplate  used to cover the reactor, the perforation was  made  in the form  of  of a  radial cut so the headplate could be removed, while the impeller  was operating,  to  electrode  scrape  material dioxide  walls  of  the  tank,  and  clean  the  top  out  of  the  liquid  with  the  foam.  A  carried (1%  impeller. room  the  v/v) was  The  tanks  at 35°C.  For  described above. The  metered were  in with  maintained  catalyzed  a  rotameter  in the dark  leaches, the  operation diagram  pH  of  mixture  and in a  of the  the  of  from  air—carbon  introduced under controlled  pulps was  the  temperature controlled  as  is the same as for the I L fermentor.  4.2.5. CONTROLLED REDOX LEACH TESTS  The  procedure for preparing 2L of medium for standard catalyzed leaches was  follows.  A  solution  mixed with  containing  of a  Ag S0 2  lOOmL of a solution containing  concentrate were added and IL  1.16g  solution  containing  suspension. After a further  4  in 400mL  12.4g  of distilled  15  minutes  was  2  of C u S 0 4 . 5 H 0 2  2  Na S203.5H20. Then 400g of  the resulting suspension mixed for 20 142.8g  H 0  as  2  was  added  minutes. Next to the  mixed  of mixing, 20mL of each of the nutrient  MATERIALS  3  AND  M E T H O D S / 64  —KD 4  10  0 1 SULPHURIC ACID RESERVOIR 2 pH M E T E R CONTROLLER 3 CO, HUMIDIFIER < AIR HUMIDIFIER 5 SAMPLING  PORT  6 CONDENSATION  FLASKS  7 pH E L E C T R O D E 8 STIRRER 9-10 CONSTANT T E M P E R A T U R E RECIRCULATION S Y S T E M II LEACH TANK  Fig. 6 Leaching system  diagram  MATERIALS salt solutions required to produce iron free, 9K  AND  M E T H O D S / 65  medium, were added.  4.2.6. LEACHING TESTS  In  all cases  leaching  tests  were  above. After inoculation the and  standard  made up the  up  with distilled  formed  as  a  according  sampling schedule was  leaching tests. Every day water, and  electrodes, baffles, etc  foam  set  result  of  be  dissolved  samples,  depending  according  to  the  sample was sample  and  on  Eh  the  freed  intense  analyses  stored used and  dissolved  metal  at  would  total to  transferred to a  was  sample was  For  oxygen  from  4°C  until  after no  the  sulfur  residue analyses.  were  the  For  be  total  be  surfaces  of  accumulated  mixing.  Every  would  At  other  point  leach only),  and  2—8mL processed a  1ml  H2SO4 were added, and  the  size  organic  this  day  drawn  when  analyses  carbon  a  lmL  slurry  processed as described under size analyses.  analysis  the  sample  more  acid  was  taken  and  allowed  diluted with 0.01  consumption  when copper extraction stopped for standard of  For  of 5N  analyzed.  portion of the clear supernatant was terminated  2mL  controlled-redox  (for controlled redox  volume, would  described  to evaporation  and  carried out.  carried out.  vial and  same for  froth. Froth  aeration  be  leach  be  the  procedures  walls of the reactors and  measurements of temperature, acid consumption pH,  the  water losses due  the  would  to  occurred leaches. At  dried. These  samples  to  sediment  N  H2SO4.  for  catalyzed  and  a  lmL  Leaches  were  leaches  and  that time 20mL samples were  used  for  elemental  MATERIALS  AND METHODS  / 66  4.3. BACTERIAL  CULTURES  4.3.1. SOURCE OF  CULTURES  The  was a strain of T. ferrooxidans originally isolated from the  bacterial culture  Britannia  Mine  maintained  near  on copper  Vancouver  (Razzell  concentrate  at B.C. Research.  concentrates in non sterile conditions See  and Trussell,  could  1963),  and routinely  Subculturing  in time give  on different  rise to mixed  cultures.  Appendix 2.  4.3.2. MAINTENANCE OF BACTERIAL CULTURES  Cultures  of T. ferrooxidans were  routinely  solution (Silverman and Lundgren, 1959)  maintained  on medium  in which the ferrous  9K  nutrient  iron energy source  was  replaced  by the mineral concentrate. The schedule of transfer of cells to a  new  medium  was found to be a parameter of paramount importance in assuring  that the culture would perform optimally. day  period  A frequency of transfer within  was set as a limit. A complete discussion  of culture  a 4—6  maintenance is  found in Appendix 2.  4.3.3. BACTERIAL GROWTH  Bacterial  growth  was  estimated  using  organic  carbon  measurements.  Since all  carbon present in the sample is of bacterial origin, the measurements were made directly  on the  slurry  samples.  The apparatus used to  make  the determination  MATERIALS was  a laboratory  total organic carbon  of analysis is based present  in  the  transported by  on  ultra—violet  sample  by  AND  analyzer (Astro model  M E T H O D S / 67 1850). The  promoted, chemical oxidation  sodium  persulfate  to  an oxygen carrier gas stream to an  carbon  method  of the carbon  dioxide  which  infrared detector. The  is  system  is microprocessor controlled.  Standard  solutions  of ethylene glycol of  10,  50  or  used for calibration of the apparatus depending on analysis  of samples  concentration, was until it was  of slurry  a  1  to  5mL  1000  ppm  of carbon  the scale range used. For the  portion,  depending  on  diluted with I N H 2 S O 4 to a lOmL volume and  analyzed. The  portion was  were  the  carbon  stored at 4°C  then transferred to a syringe and diluted  to 20mL.  A  series  of  measurements Agency  (water  within the 9 5 % ppm,  and  carried  tests  was  using a pollution  carried  quality  verify  control  the  check  the U.S.  accuracy  of  the  Environmental  samples).  The  TOC  TOC  Protection  results  were  confidence interval reported; for the low range (0—50 ppm),  for the high range  out to check  (0—100 ppm),  for interference by  concentrations studied  0.50g/L Ag).  to  standard provided by  present in the slurry samples. No the  out  (up  to  ±  17 ppm.  the high  metal and  effect on the TOC 61.8g/L  Cu,  up  Another  test was  4  also  salt concentrations  measured was to  ±  5.3g/L  Na  detected for and  up  to  MATERIALS  AND  METHODS  / 68  4.4. ANALYSES  4.4.1.  COPPER  Copper  in solution was determined by atomic absorption spectrophotometry (Atomic  Absorption necessary  Spectrophotometer, dilutions  with  Perkin  0.0 I N  Elmer  sulfuric  306). Portions  acid,  were  of lmL, after the  analysed  following  standard  practices.  4.4.2. IRON  Ferric  iron  in solution  was  determined  by  the sulfosalicylic  method. Total iron was measured by the same method following ferrous The  iron  with  sodium  persulfate;  method is described in Appendix  ferrous  iron  was  acid  colorimetric  oxidation  determined  of the  by difference.  1.  4.4.3. ELEMENTAL SULFUR  Elemental  sulfur  was  determined  gravimetrically.  suspension was dried at 95°C  and ground  solids  Buchner  were  dissolved  transferred  using  sulfur was dried  carbon  to a  disulfide. After  A  20mL  sample  in a mortar. Approximately  funnel  where  of  2g of the  the elemental sulfur  evaporation of the carbon  leach  was  disulfide the  and weighed. The amount of sulfur present in the sample was  expressed as percentage on a dry basis.  MATERIALS  AND  M E T H O D S / 69  4.4.4. SCANNING ELECTRON MICROSCOPE TECHNIQUES  A  scanning  electron  microscope  (S.E.M. autoscan  number  26,  operated at 20kV in the secondary  electron emission mode was  the  dry  specimens  directly  on  of concentrate.  aluminum  stubs  For  (14mm  x  concentrate 14mm)  over  the a  Etec used  samples  thin  Corporation) to examine  were  layer  mounted  of graphite in  ethanol (20% graphite) and coated with gold, using a Hummer gold spotter coater for  4  minutes  samples, a 65°C,  at  170  millitorr  vacuum  portion of the culture  and  maintained  in  a  and  suspension  9 was  dessicator until  milliamperes  D.C.  filtered, washed  analyzed.  Samples  For  slurry  and  dried  at  for  bacterial,  analyses were freeze—dried and stored frozen in a dessicator until analyzed.  The  electron beam  raster pattern and presented  an  was  the  to scan  the  surface of  the  the image signal displayed on a cathode  image of the  to examine the type and and  used  presence  sample  surface topography.  extent of attack on  of bacteria  and  secondary  sample  in a  square  ray tube. The  These images  signal  were  used  the mineral surface during leaching reaction  products  at  the  mineral  surface.  4.4.5.  X-RAY ANALYSES  The  primary  and  energy  beam which  of the S.E.M. generates can  be  detected  by  a  solid—state gathered  detector.  X—ray  spectra  for samples  were  elements  present  in the  solid  and  sample  X—rays  give  an  of characteristic energy and  dispersive  used  indication  wavelength  to of  X—ray  identify their  the  relative  M A T E R I A L S AND amounts  and  distribution.  To  determine  elements within a sample, X — r a y peak plotted over a dots  corresponding  can  then  be  obtained by  scanned  to the  correlated SEM,  and  area  relative  with are  the  the  spatial  distribution  peaks were selected and as  a  M E T H O D S / 70 (map)  of  the count rate of the  series of dots, with the density of the  amount  of the  corresponding  element  images  of  present. These the  mineral  maps  surface  useful to indicate the existence of preferential  of attack on the mineral surface.  the  areas  CHAPTER 5. RESULTS AND DISCUSSION  5.1. STANDARD BIOLEACHING  5.1.1. WITHOUT BACTERIAL INOCULUM  In order  to investigate if copper leaching takes place  under  the initial  mesh  Newmont  without  conditions  of the leaching  concentrate  was  set up  were zero  h) and iron extraction was  6.9%. This  low  following  the addition of inoculum. Under  bacterial carbon concentration  E h potential (under 605 mV  medium,  these  in the absence of bacteria, an experiment  the standard  conditions  for the duration indicates that  using  —400  procedure, but  copper  extraction and  of the experiment (282  under initial  conditions of  SHE), chemical leaching was negligible.  5.1.2. AS RECEIVED CONCENTRATE  Experiments  were carried out using  densities  of 107g/L in 1L tanks  brackets  following  numbers from old  as  described  number  appendix 6. Two  Gibraltar concentrate  in Chapter  indicates  3. The  the source  separate experiments, using  at pulp  number in  of data  as  table  11 day and 6 day  inocula, resulted in copper extractions of 4 and 7% respectively. Figures 7(69)  and  8(68) present  pH  and total  copper day  the figure  "as received"  the profiles of copper extraction and cell growth, together  iron concentration  dissolution, during  the  during  first  100  these  leaches.  hours  following  old culture, was related to a modest increase 71  Figure  7  inoculation  indicates with  in cell concentration;  an  with that 11  but after  R E S U L T S AND  DISCUSSION / 72  10n  r  300  N h-200 b o S  u o  .a. •-G-  100  -ET  150 T I M E  Fig. 7 Standard  -0^  200  250  300  --G'"  350  h 100  400  (hours)  leaching as received concentrate. (11 day old inoculum)  RESULTS AND  DISCUSSION / 73  HH  Fig. 8 Standard leaching as received concentrate.  ( 6 day old inoculum)  RESULTS  AND  D I S C U S S I O N / 74  this period copper dissolution and cell growth declined. The iron profde  of Figure  7, indicates that iron dissolution continued  in the absence of copper solubilization.  This  that  may  medium  be  might  explained be a  by  mixed  considering  inoculum  culture, the population  coming  balance  from  of which  a  spent  shifted in  favor of the iron oxidizing, but non-sulfide oxidizing bacteria. Discussion of such mixed cultures is presented be  the result of chemical  in Appendix  2. Alternatively, iron release could also  leaching. If we  Figure 7 with the 6.9% iron leached  compare the amount of iron leached in  in the absence of cell inoculum  5.1.1.) the two amounts are of the same  order  present in the culture as shown by microscopic been  utilizing  soluble iron  for energy. The  (see Section  of magnitude. Viable cells were examination and they  results  presented  could have  in Figure  8  that the use of a 6 day old inoculum resulted in a lag phase lasting over hours. This  period was  slow, but simultaneous, day  by an increase in cell numbers associated  copper and iron solubilization. In both cases,  and 6 day old inoculum experiments, very  the in  followed  lag  phase was  shortened  Extraction levels improved  when the concentrate  100 with  for the 11  low copper extraction levels and  long lag phases obtained, can be attributed to the large particle the "as-received" concentrate.  show  sizes found  considerably  and the  was ballmilled to 9 0 % -400 mesh  as will be shown in the following section.  5.1.3. -400 MESH CONCENTRATE  Figure  9(89,93) presents  leached TOC  under  the same  leaching profiles for Newmont and Gibraltar concentrates conditions. The  and Fe. Newmont concentrate  profiles  are very  similar  in terms of  seems to have a greater amount of initially  R E S U L T S AND soluble  Cu  than  Gibraltar  concentrate  similar too. Both concentrates  5.1.3.1. BACTERIAL  Leach IL  experiments  reactors  measured profiles were  at  in  48  and  using  pulp  mesh  TOC/g  density.  under  20h;  cell  Cu  leached  conventional  after this phase  11  presents  a further 300  metal release  follow  stop  iron curves can  be  explained  medium;  a  high  passivating stopped  any  from the  for these  and  and  residual  by  redox  0.0125g Cu/L  mineral  were  11(84) show  h. Figure  of copper and  10  the  shows a  iron took  a net increase in the cell  in Figure  was place,  population.  10,  extended  carried out to investigate the  behavior  for the  was  jarosites eventually  dissolution. After  11  indicates that cell  duration  of the  difference between the  taking into account the  chalcopyrite;  34%  lag phase for microbial growth  hours. The  forming  and  corresponding overall  growth phase. Figure  potential  29  in  experiments. Cell yields  respectively. The  similar patterns  after 650  solution,  further  are  were carried out  10(70) and  simultaneous release  decline of the  leaching phase, and  precipitated  growth  hours; this experiment was  when  profiles  mineralogy.  of  a duplicate of the experiment reported  of the culture at the growth and  extractions  Figures  leach: the  associated with a decrease in the pH,  Figure  Copper  and  copper extraction rates were of 0.013 typical profile for a  leaching  Gibraltar concentrate  experiments.  extraction  47mg  Cu  are similar in composition and  —400  separate  of copper  the  GROWTH  107g/L  two  otherwise  D I S C U S S I O N / 75  at  on  particle  the  (at 620h  around of  copper  redox conditions  reached,  around  in  400h,  surfaces  600h) this  leaching,  active  there  and the iron thus  process was  a  RESULTS AND  DISCUSSION /  9 Newmont and Gibraltar leaching profile comparison  R E S U L T S A N D DISCUSSION / 77 short period of about 24h where an increase in cell concentration in  the medium  indicates  that  possibility entered  and was not accompanied by a metal concentration the cells  examined  were  probably  oxidizing the F e  in the following section. After  ions  + +  this  increase. This in solution, a  24h period,  the stationary phase and no further growth or metal release  5.1.3.2. FERROUS/FERRIC  To  was measured  and cell  growth,  occurred.  IRON PROFILES  investigate the relationship between the oxidation  solution  the culture  two experiments  were  state  carried  of the iron ions in  out.  Iron,  in its two  oxidation states, copper, cell carbon and redox potential were measured during leach.  Fig.  12-13(93)  show  the results  of an  experiment  lasting  150 h.  Comparing the total iron curve of Fig 13 with the copper curve of Figure is  evident  that  chalcopyrite released  copper  (molar  and iron  ratio  were  being  leached  1:1.01). T O C concentration  simultaneously rose  the  12, it  from the  as the metals  were  into solution. The cell yield for this experiment was 35.6mg TOC/g Cu  leached. Of  the total iron in solution, 7 5 % was found as ferrous iron. This indicates that  T. ferrooxidans was obtaining  energy  from  the breakdown  crystal, by oxidizing the sulfide component of the this source to ferrous iron ions in solution. This potentials redox  below  420mV.  Since  potential, and since  compared  to the ferric  (16.6-55.8g F e  + +  +  /L)  mineral,  mechanism  of the chalcopyrite and that  it preferred  predominated  ferric  iron  is not an effective oxidant  the ferric  iron  concentration  iron  concentrations  (Miller and Portillo,  normally  1979), then  is low, used  at this  1.8g F e  in abiotic  one could  at E h  + +  +  leaching  speculate  that  RESULTS  Fig. 10 Ballmiiled concentrate. Standard  AND  DISCUSSION / 78  leaching profile  RESULTS AND  Fig. 11 Ballmiiled concentrate. Standard  DISCUSSION / 79  leaching profile  RESULTS AND  10  DISCUSSION / 80  n  r  TIME  300  (hours)  Fig. 12 Cell growth and copper leaching in ballmiiled concentrate  R E S U L T S AND  Fig. 13 Iron leaching in ballmilled  concentrate  DISCUSSION / 81  RESULTS in  standard  leaching  there  could  be  a  direct  attack  AND by  D I S C U S S I O N / 82  the bacteria  on the  chalcopyrite lattice.  To  find  out what happened  at higher  redox  potentials an experiment  was  set up and extended to 300h. The results of this experiment are shown in Figures  14-15(91). Fig. 14 shows that 5 0 % of the copper was  extracted at  a rate of 0.048g Cu/L h from the chalcopyrite in 283h (a longer lag phase in this experiment was slowed  down from  due to the use of an older inoculum). Cell  0.76mg TOC/L  h  to 0.15mg TOC/L  48 hours of the copper extraction period. Examination that  during  this  same  535mV. Hydrolysis iron  hydroxides.  48  hours,  the redox  h during  examination  of  potential rose  the  the last  of Fig. 15 indicates  of ferric iron resulted in the formation Upon  growth  particles  from  420 to  of jarosites and using  reflectance  microcopy (Sinclair, 1987) some of the particles appeared to be coated with unidentifiable  matter  that  also occurred  rendering  could  be jarosite. Passivation  of the chalcopyrite  it impervious to further attack, as was the case for  the experiment presented in F i g 13. It appears that the cells turned use  of  the  passivated, longer  available  and  iron  the energy  enough to sustain  growth  rate  present  in the medium  rate at 0.76mg TOC/L 0.15mg TOC/L  solution  obtained  the large  (0.76mg TOC/L  iron oxidation provided  in  cell  from  the  chalcopyrite  chalcopyrite  population  0.007  oxidation  and maintain  of the soluble  became was  no  its high  ferrous iron  to 0.063g F e + ^ / L  h. This  energy but not enough to sustain the growth  h which  h. The ferric  from  h). The oxidation  increased some  when  to the  slowed  down considerably  iron concentration  at this point to  in solution did not exceed  RESULTS AND DISCUSSION / 83 4.4g/L.  Redox potential induced transition states in cell growth  RESULTS AND  DISCUSSION / 84  Fig. 15 Iron leaching under increased redox potential  R E S U L T S AND  5.1.3.3. MINERAL  To  identify  leaching,  the  SURFACE  changes  electron  concentrate leach. To  CHANGES  taking place at the  micrographs  D I S C U S S I O N / 85  were  mineral surface during conventional  taken  of  samples  from  a  Newmont  determine the element distribution of the concentrate,  x—ray  line scans were also done. Figure  16  is a photograph of an  sample  of — 4 0 0  peaks from Cu  and  Fe  mesh  are  situated  composition  corresponds  concentrate  to  to  the  right  to the left  Cu,  ka  of the  found contain  by  of the  chemical  copper,  leaching. The Fe  and  three  sulfur peak. These  sulfur  Table  and  an  highest  sulfur; peaks for kj3  corresponding  analysis (see  iron,  ka  peaks. Another silicon  results correspond 2),  which  insoluble  shows  fraction,  and to the  which  in the x ray analysis to silicon.  Several samples of the concentrate same composition (SEM)  to k a  before  analysis (EDXA) of a  present in the sample in significant amounts was  its peak is situated  concentrate  Newmont  right to left correspond  element which was  the  energy dispersive x — r a y  photograph  was of  found. the  were analyzed by  Figure  same  17  presents  sample.  a  EDXA scanning  Examination  reveals that the surface for the most part was  and  of  in all cases  electron the  featureless and  the  microscopy  particle  surface  smooth, except at  the edges of the particles which were roughened by milling.  After  144  hours  of leaching an  x—ray  relative proportions of copper, iron and undergoing  leaching;  simultaneously.  consequently  line  scan  (Figure  18)  sulfur were maintained  all  three  elements  showed in the  were  that the  concentrate  being  leached  RESULTS AND  Fig. 16 E D X A  D I S C U S S I O N / 86  analyses of concentrate before leaching  RESULTS AND  Fig. 17 S E M  D I S C U S S I O N / 87  photograph of concentrate before leaching  R E S U L T S A N D D I S C U S S I O N / 88  :Fe:  :Cm:  !SbSb isbSb bbbb 0 . 80 0  R a. n g e =  20. 4 6 0 k e V  20.140 I n t e q r a. 1 0  Fig. 18 X — r a y Figure  18022  line scan of freeze-dried, leached concentrate  19 is a S E M photograph  of a chalcopyrite  particle  after  144 hours of  leaching. The slurry sample was freeze—dried, a procedure  which  observe bacteria attached to the surfaces. This  is difficult to observe,  attachment  permits one  to  RESULTS AND  DISCUSSION / 89  RESULTS  AND  DISCUSSION / 90  when the particles are oven dried, because of heat damage. Figure  20  is the  magnification.  same  This  sample  sample  (144  shows  the  hours  of  pitted  leaching),  surface  each  should  other.  cause  jarosite  The  net result  the particle  to shrink  precipitate; at this  Extensive  was  time  deposition of jarosites  an  erosion  with  with  time. In Figure  has been  shallow  of the particle  the deposition  was  20  limited  previously  at  a  resulting from  leaching seems to have taken place all over the surface to  but  shown  lower  leaching; pits joined  surface,  we  which  can identify  to a  small  to take  area.  place. For  example, after 200 hours of leaching, chalcopyrite particle surfaces from Newmont concentrate  were  almost  completely  covered  (Blancarte—Zurita, 1983). These observations mechanism  for conventional  leaching  elsewhere. The x ray analyzes  tend  of  by  support  precipitates.  the view of a direct attack  chalcopyrite  to confirm  jarosite  as  has  been  that in conventional  described leaching of  chalcopyrite simultaneous release of copper, iron and sulfur is taking place.  5.1.4. " M O N O S I Z E "  In  order  to test  LEACHES  the validity  mechanism  for the leaching  mechanism  was  measured  for  experiments leaching during  tested 5  of the concept of copper  using  "monosize"  carried out in 1L  time  for the duration  the leach  experiments  ferrous, ferric and total iron.  from  experimental fractions  of  of a  shrinking  sulfides a  data.  Copper  Gibraltar  reactors. Particle  "monosize"  model  based  extraction  concentrate  shrinkage  of the experiments. Other with  particle  fractions  was  on  rates in  pH,  this were  separate  monitored  parameters were  as the  with  measured Eh,  T O C ,  Fig. 20  SEM  photograph of freeze-dried leached concentrate (800  X)  RESULTS AND 5.1.4.1. PARTICLE  "Monosize"  SIZE  fractions,  DISCUSSION / 92  MEASUREMENT  obtained  by  sedimentation  comprised  not just  one  particle  size, but a narrow size distribution; consequently particle size measured by analyses generated  a number  image  size distribution, which for modelling purposes  was  represented by the median size of the number distribution.  This  choice  experimental Most  fine  particle  of  procedure particle  size  adequately  and  a  the  formed  that  by  two  by  obey  distribution  fractions  and  comminution  the  values,  mean  based  size  vs  paper.  If  to sieving certain  a  bulk  material  distribution  and  the  cumulative the  particles  this procedure  particle  size,  percentage  will  belonging remove  producing  a  oversize to  such  all particles  distribution  shows  size how  vs  cumulative  the  distribution  approached. When using  a  largest time given  percentage deviates  can  be  a  line  plotted  on  distribution  are  greater or smaller  that becomes  mesh  from  the  as  have  asymptotic  is a plot of  concentrate larger  sizes  and are  — 4 0 0 mesh concentrate is separated into "monosize" fractions,  sedimentation  method, the  distribution  size end, into fractions whose lower  (i.e. those  and  are  oversize for — 4 0 0 linearity  the  standard deviation  towards the sizes that have been removed. (Allen, 1981). Figure 21 particle  on  is explained as follows.  of  log—normal  the  was  Fochtman, 1978). Log—normal distributions produce a straight  log—probability  than  for  to obtain the  systems  distributions  particle  subjected  tendency  used  represented  (Stockham when  central  is subdivided, starting  limit is given by  their  from  the  sedimentation  particles that because of their small size did not sediment in a  time, remained  in suspension  and  were  not  included in that particle  size  RESULTS  Fig. 21 Size distribution of -400 mesh  AND  DISCUSSION / 93  concentrate  R E S U L T S AND  Fig. 2 2 Size distribution of concentrate  fractions  DISCUSSION / 94  R E S U L T S AND fraction). The  particle size distribution  DISCUSSION / 95  of these "monosize" fractions  from linearity but towards the smaller sizes as shown in Figure  The  presence  of  small  particles  fraction being separated is due size distribution will extend  with  sedimentation  to entrapment, and  to the right and  times  for such  also deviates  22.  below  that  of  the  a fraction, a particle  will result in extreme values on  the  small side of the distribution. If the mean size of a number distribution is used to represent it, its value will be  greatly  influenced by  the extreme values of the  distribution because the main characteristic of the mean is that it is affected all values actually A  by  observed.  better choice for representing the  central  tendency  of the  distribution  would  then be the median size, because in monosize leaches, small particles, even when present  in large  concentrate distribution  numbers,  being into  two  therefore provides Stockam  and  distributions,  leached  a  equal  represent while areas  the and,  better estimate  Fochman the central  (1978)  only  small  median, is less  of the  also  a  have  mass  which  divides  affected  central found  tendency is more adequately  fraction  by  the  tendency that  for  of the  skewed by  total  frequency  extreme  of the  represented  the  values,  distribution. frequency the  median  than the mean.  The for  size distribution, mean, and the  monosize fractions  each particle fraction.  and  median size values are presented in Appendix for the  slurry  samples  taken  3,  during leaching of  R E S U L T S AND 5.1.4.2.  When  PARTICLE  / 96  COMPOSITION  the concentrate  was  fractionated,  according to their size. The spread on  DISCUSSION  the  particles  reported  of particle sizes found  to  a  fraction  in a powder depends  the milling procedure. In our case the concentrate was wet ballmiiled. During  milling, mineral particles were broken of the crystal structure determined force  applied. It follows that  up mechanically  and the relative strength  the extent of the size reduction for a given  differences  in composition  different crystal strengths, would produce particles with  of the mineral, hence  a preferred size. Particle  fracture is caused  by crack growth, and cracks can be stopped by inclusions and  grain  so that heterogeneous  boundaries,  components  (Perry,  1973).  If this  materials can be  were  the case,  stronger  the result  than  would  their  be the  abundance of one particular phase in certain fractions. For example if the silicon fraction  were  leaching  rates  to report to the largest among  the fractions  size  would  fraction,  become  a  then  the comparison of  function of the chemical  composition of the fraction as well as the size of the particles.  To  investigate if the composition  particle  size,  sections  of concentrate  examined  samples  of different samples  sizes  showed  angular  particles  present and some gangue—like was  estimated  particles were observed.  around  material changed  were examined  embedded  using a reflectance microscope.  concentrate  content  of the fractionated  in epoxy Examination  with the  mineralogically. Polished  resin  were  prepared  and  of unfractionated Gibraltar  of chalcopyrite with  some  chalcocite  being  material in very low proportion (= 1%). The pyrite 5%,  mostly  as  individual  particles;  no  locked  RESULTS AND  D I S C U S S I O N / 97  When the fractionated concentrate was analyzed using the same technique, it was observed — 1%,  that the low proportion of non—-metallic  was  enriched  maintained,  but that fraction  in pyrite. From  the original  2 with  estimate  material (quartz or feldspar) particle  of 5 %  size  pyrite  of 9.3  jim was  the content  was  estimated to be 1 5 — 2 0 % pyrite.  5.1.4.3. LEACHING  Leach  EXPERIMENTS  profiles are presented  in Figures 23-32 for fractions of decreasing initial,  nominal, median particle sizes from  52.1 ^nti to 2.8 /um. See Section 5.1.4.4 for  further discussion on the true particle sizes of these fractions. Figures with  23-24(110) are the leaching profiles for the fraction  initial  size  simultaneous  of 52.1 fim. Copper  (for  and cell  growth  seemed  to be  processes; ferrous iron in solution was oxidized after 200 hours of  leaching, at the same time surpassed  extraction  containing particles  500 mV.  33.8 nm),  some iron precipitation occured when the E h potential  The same  tendency  was observed  when  Figures  25—26(112)  27-28(114) (for 15.9 /nm), 29(116)-30(117) (for 9.3  31—32(106) (for 2.8 fira) were analysed. As was  (im) and  shown in Section 4.1.3, this  was the same sort of behavior exhibited by — 4 0 0 mesh concentrate.  The  difference  copper  among  the different  extraction, which unexpectedly  This decrease growth,  found  in copper  and by  decrease in copper  an  size  decreased  fractions when  was  the particle size  extraction was accompanied by lower  also  unexpected  decrease  in the extent of  in copper  decreased.  levels of microbial  extraction  rate.  This  extraction rate, as particle size decreases, can be observed by  RESULTS AND DISCUSSION / 98  Fig. 23 Cell growth and copper leaching of 52.1 m M  material  RESULTS AND  DISCUSSION / 99  15n  TIME  (hours)  Fig. 24 E h and iron leaching profiles for 52.1 m M  material  RESULTS AND  20  DISCUSSION / 100  n  Fraction 4  TIME  Fig.  (hours)  25 Cell growth and copper leaching of 33.8 y m material  RESULTS  AND  DISCUSSION / 101  15-i  TIME  (hours)  Fig. 26 E h and iron leaching profiles for 33.8 um  material  RESULTS AND  DISCUSSION / 102  I6-1  Fraction 3  TIME  (hours)  Fig. 27 Cell growth and copper leaching of 15.9 n m material  RESULTS AND  DISCUSSION / 103  15-i  TIME  (hours)  Fig. 28 E h and iron leaching profiles for 15.9 um material  RESULTS AND  D I S C U S S I O N / 104  16n  Fraction 2  TIME  (hours)  Fig. 29 Cell growth and copper leaching of 9.3 /nm material  RESULTS AND DISCUSSION / 105  700 600  o  a L  •  F« ~  A  F« ~  o  To t a 1 F o  •  3  Eh  Fraction 2  150  200 T I M E  250  1  D T  300  350  400  450  500  (hours)  Fig. 30 Eh and iron leaching profiles for 9.3 um  material  ^  400  W  300  2  100  500  RESULTS AND  DISCUSSION / 106  I6-1  Fraction 1  TIME  (hours)  Fig. 31 Cell growth and copper leaching of 2.8 M m material  RESULTS AND  Fig. 32 E h and iron leaching profiles for 2.8  Mm  D I S C U S S I O N / 107  material  R E S U L T S AND comparing  the  fractions  slopes  of  the  of Figure 33. The  copper  reproducibility  performing a leach in duplicate. The Figures The  29  and  30. The  extraction  curves  of the  DISCUSSION  for  the  experiments  / 108  different  was  size  checked  by  results for both runs are plotted together in  data spread is reasonable for this type of experiment.  decrease in copper extraction rate as the particle size decreased could not be  explained on  the basis of previous knowledge which would suggest that extraction  rate increased as particle size decreased (Blancarte-Zurita, 1983).  Examination  of particle  leaching  time  (>5jtmi)  the  copper had on  the  in  size, as  these  median  size  diameters  correlation  as  between  by  image  leaches  decreased  rapidly  showed before  did  not  that any  represent  the particle sizes initially observed  particle  analysis, as for  a  function of  large  significant  particles  amount  of  the initial measurement of the particle size made  concentrate, apparently  leaching started. When particle  "monosized"  been extracted. So  dry  measured  immediately  diameter  and  the  particle  size  when  measured were replaced by  before  copper  extraction  rate  extraction  began,  changed. See  the the  Fig. 34  and discussion below.  5.1.4.4. SHEAR AND  In  PARTICLE  ATTRITION  order to achieve reasonable mixing  criteria  of  indicated rpm. higher  The  complete  that  off—bottom  this condition  speed  the speed,  of  the  was  impeller  of the solid  suspension achieved could  be  suspension in the tanks, the  was  at an an  followed. impeller  important  the greater the proportion of the  power  Visual  speed  observation  of around  parameter,  since  introduced that  300 the goes  RESULTS AND  DISCUSSION / 109  20 -i  TIME  Fig. 33 C u leaching  (hours)  in monosize fractions (nominal size)  RESULTS AND  DISCUSSION / 110  20-1  TIME  Fig. 34 Cu leaching  (hours)  in monosize fractions (true size)  R E S U L T S AND into  developing fluid velocity, and  levels of fluid shear and  turbulence may  collisions between particles and etc. For the purposes shrinkage due  particle sizes concentrate 300  rpm  (Oldshue, 1983).  forces (attrition) from  to leaching. Figure 35  suspension of  the size  shows  9K  107g/L in iron-free  to differentiate  the  23  changes found  hour  indicated  to study a  that  the  larger  monosize fraction  sizes  without  a  were  monosize fraction and  264  hours  reduction larger  was  used. Particle  of agitation  at 300  than  /xm  rpm.  The  in the number of particles larger 20  (im  this  breakdown  disappearance of all particles larger 20  size was  over a  100  at  results of  the  most  this  possibility. Figure  affected,  more  than 40  10  after  indicate nm  50,  that  a  and  we 36  32  Mm  77,  167  significant  occurred. For  severe  /ira and  22,  so  time for  pulp density. A  measured  than  was  10%  results  a  that particles decreased in  to investigate  non—inoculated monosize leach  in the  inoculum, at  presents the particle size distribution changes as a function of agitation samples from  by  period of stirring  medium  indicates  particle  reduction caused  causing the distribution to shift towards the left. The  experiment  High  of the particles with the impeller, baffles,  in the Virtis fermentor. Figure 35  proceeded  shear  111  give rise to autogenous milling, due to  for "as received" concentrate over a  size with time this  due  impact  fluid  of this work it became important  to mechanical  particle dissolution  consequently  DISCUSSION /  resulted  particles in  most of those larger  the than  hour period.  5.1.4.5. AUTOGENOUS MILLING IN MONOSIZE LEACHES  Because different  of  such  monosize  size  reduction  leaches  in  due  to  autogenous  terms  of  copper  milling,  extraction  when  rate,  the  comparing starting  R E S U L T S A N D DISCUSSION /  PARTICLE SIZE  (micrometers)  Fig. 35 Particle fracture in <32 um material  (6 um median size)  112  R E S U L T S AND  DISCUSSION / 113  100-1  80-  60-  40-  Legend LZ3 20-  0 h 50 h  CD 77 h W 167 h C S 264 h 10  ~r~  20  i  30  I  40  50  Size (micrometers)  Fig. 36 Size distribution after mechanical fracture 32 um  material  R E S U L T S AND diameter was the  dry  copper  taken not  powder, but  as  solubilization  function  of  that  as the  the  diameter  original size measured for a particular  size of the  (generally  around  are  2.8  to  somewhat being 2.23  a  true  resistant much  nm;  Mm,  2.36 to  4  100  fraction  mineral from  than  33.8  to  sample at the  hours). Copper  in  Figure  rates  a  1 decreased from a  nominal  2  5.94  due  to  to  /xm,  its high  chalcopyrite; fraction 2.67  Mm  and;  changes  as  follows: fraction 9.3  The  rapid  median  from  37.  fraction in  onset of the  extraction  114  in  autogenous milling  harder  fraction  slurry  shown  particle diameters observed were as size  DISCUSSION /  fraction  this  pyrite 3  fraction  content,  went from 5  from  was pyrite  15.9  52.1  to  size  due  to 4.85  Mm.  For  the  largest  particle  sizes  significant  reductions  in  particle  to  autogenous milling occurred.  5.2. MODELLING  THE  CONVENTIONAL  LEACH  5.2.1. INITIAL CONSIDERATIONS  5.2.1.1. SOFTWARE  A  Fortran  computer  leaching. The 4.  The  was  program  copper content in the  calculation  of the  written  to  predict  particle  shrinking  version for conventional leaching is presented  input data for the  density and The  program  program  was:  during  in Appendix  initial particle size, leaching time, pulp  concentrate.  shrinking diameter that is the  focus of the  program,  was  R E S U L T S A N D DISCUSSION / 115  ~! 1  I 2  1  ,  3  MEDIAN DIAMETER  '  1  4  5  (micrometers)  Fig. 37 Cu extraction rate as function of size  RESULTS based  AND  on the experimental copper extraction rates, which  of the particle rate was  diameter. A n  equation relating  included in the program  particle  D I S C U S S I O N / 116  were in turn  size to copper  functions extraction  and was used to calculate the rate of copper  extraction at the start of the leach and every time the particle shrank in size. For  practical  purposes  the rate calculation was  hours of leaching, this interval was such  an interval  were small  shrinking process. A  There from  are several monosize  carried out at intervals of 50  selected on the basis that rate changes for  enough  so as not to affect the continuity of the  logic diagram for the program  possible  batch  ways  of using  is presented in Appendix  experimental copper  leaches to produce  a  rate  function  extraction  that  relates  data copper  extraction rate to particle size for use in the program. As in any batch experiment, the rate of reaction changes extraction  rate  increased  hours and during rate  phase  extracted  from  leach  with time during bioleaching. The copper  the induction  phase,  which  lasted for about  20  which' time the copper extraction was very low, to a constant  lasting  (depending  for about on  280  the initial  leach, and the concentrate).  hours  where  the bulk  of the copper  size,  the type  of process  particle  was  used to  After the bulk of the copper extraction took place, it  was followed by a phase of decreasing  Any  4.  extraction rate.  batch leach experiment can be characterized by the several copper extraction  rates  mentioned  leach  time. To select the rate  diameter,  above,  it became  plus  an overall extraction rate calculated over the total  necessary  calculate the particle diameter.  to be used  in the calculation of the shrinking  to consider  how  the model  used  this  data to  R E S U L T S AND Ideally three shrinking rates could be three  phases the  culture goes through during  induction, rapid growth model were  incorporated  to be  and  used  stationary  to  in a  a  model accounting  leaching  would  of particles in leaches  rapid copper extraction phase would be  depending addition,  on  the  copper  conditions  of  solubilization  particle  size reduction  changes  in  particle  due  size  cultivation  in  to  the  induction  copper  would  be  and  different, with the harvesting phase  solubilization,  below  the  for the  is  other  detection  of  the  be  the  length time  inoculum.  of  In  consequently  very  limits  a  than  induction  minimal;  would  are  arise if such  monosize leaches, because for each particle size the induction time and of the  117  experiment. These  phase. Difficulties  predict shrinking  DISCUSSION /  small, the  and  available  methods for measuring particle size. Alternatively,  use  of  the  rate  obtained  from  extraction vs time curve, would better represent due  to copper  solubilization  solubilization, they could be  Since  the  leaching rate was  and  the the  linear  portion  if changes in particle  obtained  from  the  size occur due  portion of the  should  to copper  leach  5.2.1.2. SHRINKING RATES FOR  where rapid the model to  be made starting from the onset  of the rapid growth phase, after the induction phase has  copper vs  copper  easily measured.  the particle size measured experimentally,  of the  the  process of particle shrinking  growth occurred, then the comparison of the shrinking predicted by  Straight lines were fitted by  of  CONVENTIONAL  ended.  LEACHING  least squares to the portion indicated by  times curves of Figures  23,  25,  27,  29  and  31  the  arrows  (Cu = g/L  and  RESULTS AND DISCUSSION / 118 time(t) = hours). Fraction 1  Cu = 0.0325t + 1.8786 ..(38)  Fraction 2  Cu = 0.0295t -  2.7180 ..(39)  Fraction 3  Cu = 0.0372t -  4.8223 ..(40)  Fraction 4  Cu = 0.0584t -  4.6231 ..(41)  Fraction 5  Cu = 0.0803t -  6.4880 ..(42)  A plot of copper extraction rate, for the different monosize leaches, as a function of median particle diameter measured after  100 h is shown in Fig. 37. The  copper extraction rate data was fitted with equation 43, an exponential equation, where copper extraction rate is given in g/L h and the size dp is in p.m. The dashed line in Fig. 37 is the curve fit of the experimental data with equation 43. It has a correlation coefficient of 0.963. Cu extraction rate = 11.94 e  - 0  -  3 2  ( P) ... (43) d  This equation shows that the copper extraction rate (r) (g/L h x 10 ) increases 2  with decreasing particle size (p.).  5.2.2. APPLICATION OF T H E M O D E L TO MONOSIZE L E A C H E S  5.2.2.1. PARTICLE SHRINKAGE  A  AND COPPER  SOLUBILIZATION  comparison of particle size measured during active copper leaching  and the  particle shrinkage predicted by the model is depicted in Fig. 38. The scattered  R E S U L T S AND points are the experimental model using equation 44  measurements, and  =  P  reasonable  fit was  [ 1 - -- ] ^ ^o 0  obtained  integrity  fractions  under  was the  preserved  same  5.3.1.  ... (44)  except  it was  out  the  at  experiments  greater  due  extent  fraction  was  5.94  fim  fraction,  compared also  to  the  the  other  fraction  more  to its high pyrite content was  also the  solubilization and lowest copper extraction rate.  REDOX  POTENTIAL  LEACHING  that  planned  same  pulp  that the  catalyzed leach experiments  density  as  the  conventional  using monosize concentrate, using this low lower  amounts  of  fractionated  concentrate  would have been advantageous because the procedure concentrate was at  the  PULP DENSITY  Initially  meant  a  conditions. This  with the lowest copper  5.3. CONTROLLED  predictions of the  faster than experimental sizes indicating that  to  resistant to autogenous milling, and one  3 3  for all fractions  where the predicted sizes decreased particle  lines the  119  to calculate particle shrinkage.  - dpo  A  the  DISCUSSION /  would  leaches:  107  be  carried  g/L.  pulp density would would  used  be  For have  needed;  this  to obtain fractionated  very lengthy. But even more significantly, controlled-redox leaches  107g/L, did not  produce  elemental  consumption with variable copper the begining of the leach and  sulfur  and  in all cases  extraction. Although  was  had  erratic  redox potential was  maintained, through  low  acid at  the addition of thiosulfate  in the chemical conditioning stage, these leaches did not produce elemental sulfur.  RESULTS AND  DISCUSSION / 120  Fig. 38 Model predictions of particle shrinkage for standard leaching  RESULTS So  an extensive  catalyzed of  study  leaching at such  the experiments  Appendix below  catalyzed  precisely determined,  5.3.2. I N I T I A L  key  carried  undertaken  low pulp  leaching  to search  DISCUSSION  for conditions  densities was feasible. A  out at a  7. The results indicated  which  Chemical  was  AND  pulp  density  did not take  under  which  detailed discussion  of 107g/L  that there was a lower  / 121  is presented in  limit to pulp density  place. This  limit  has not been  but it was somewhere in the range 107— 180g/L.  CONDITIONS  conditioning of the concentrate  as described in section 2.5.0.4, was the  step in setting up a catalyzed leach. Such pre-treatment  of the concentrate  established the conditions of low E h potential and excess cupric ions which seem to  be necessary  oxidation  for acid consumption and elemental  of chalcopyrite concentrates.  completed, inoculum for  6—8  Chapter  After  sulfur production during the  the initial  conditioning step  was introduced. This was a culture of  days in the conventional mode on the concentrate  was  T. ferrooxidans grown of interest. Refer to  3 for culture maintenance.  5.3.3. B A C T E R I A L I N O C U L U M  5.3.3.1. REDOX-CONTROLLED LEACHING WITH AND WITHOUT INOCULUM  The  importance  of  the  bacterial  studied in a series of experiments  culture  in  the  catalyzed  leaching  process  was  in which different inocula were tested. First, it  RESULTS was  AND  DISCUSSION  / 122  necessary to test if the presence of bacteria was a requisite for chemically  conditioned controlled-redox leaching. Fig. 39(102) shows the results of an attempt to  leach  the concentrate  concentration  without  inoculum.  was zero for the duration  For this  experiment  of the experiment, copper  the carbon concentration  was also zero and only 4% of the iron present in the concentrate was extracted. The  Eh  rose  slowly  from  310mV  to 360mV  over  280h, and 4.7mL  of 12N  H 2 S O 4 were consumed to maintain the p H at 2.0.  Typical leaching curves for a leach of -400 mesh Newmont concentrate inoculated with  a  Newmont  Elemental sulfur  grown  bacterial  culture  are presented  was produced, the maximum  in Figs.  cell concentration  40—41(120).  was  101 mg/L,  copper extraction was 100% and 410 ml of 12N acid were consumed to give a molar  acid:copper  ratio  of 1:1.1  (the theoretical  ratio  being  1:1.6 based  on  CuFeS ). 2  The  results  inoculation potential  of these with  a  conditions  two  experiments  bacterial and  culture  silver  (Figures  39,40,41)  is necessary,  complexed  with  demonstrate  in addition  to low  an  of  excess  that redox  thiosulfate  (Bruynesteyn et al, 1983), for controlled-redox copper leaching to occur.  To a  inoculate an experiment cell  an actively growing bacterial culture in the form of  suspension obtained from  a 6—8  day old culture  grown  in —400  mesh  concentrate was used. Such a cell suspension contained part of the leached solids from  the culture medium  particles the  had a variety  from  which  the inoculum  of sizes. When  studying  had been taken. These  leaching  of monosize  solid  fractions,  introduction of such solids with the inoculum was not desirable since it would  RESULTS AND  DISCUSSION / 123  Fig. 39 Redox-controlled leaching without bacterial inoculum  RESULTS AND  DISCUSSION / 124  75-,  T I M E  (hours)  Fig. 40 Cell growth when leaching under controlled redox conditions  RESULTS AND  DISCUSSION / 125  Fig. 41 Iron leaching profile under controlled redox conditions  RESULTS AND DISCUSSION / 126 modify the particle size distribution of the monosize  fraction being studied. For  this reason the possibility of obtaining a particle free inoculum was contemplated.  5.3.3.2. PARTICLE FREE  INOCULUM  Microscopic observations of the medium had indicated that during the first days of leaching following inoculation, most  cells were to be found at  the mineral  surface with freely suspended cells appearing only after 4 or 5 days. The 6—8 day old culture, normally used as inoculum, would then contain freely suspended cells,  so it was decided to investigate the possibility of recovering these freely  suspended cells, for use as inoculum, by centrifugation. Cell yields obtained from an inoculation medium by centrifugation were estimated by measuring TOC.  The first attempt was made with 65mL of slurry from a 12 day old culture. After  12 days  of cell growth,  the  culture medium when observed  under  the  microscope, typically contains large amounts of cells non-associated to the mineral particles.  The suspension  fractions,  sediment  supernatant,  was  allowed  and supernatant,  was centrifuged  to  sediment  were  treated  for  30  minutes.  separately:  The  fraction  1,  two the  to recover free cells at 600 x g for 10 minutes  (Dauve, 1983; Parry and Pedersen, 1983; Bailey and Ollis, 1986). The cells were washed  by  resuspending  the  precipitate  in  0.0 IN  H2SO4  and  recovered  by  centrifugation. The washed cell pellet was finally suspended in 10 mL of 0.01N H2SO4 and was found to contain 2.8 mg of carbon. Fraction 2, the sediment from the initial settling of the medium was resuspended in  0.01N  R E S U L T S AND H2SO4  and  agitated  cells that may and  minutes  to remove any  originally, freely  127  suspended  have been entrapped during sedimentation of the mineral particles,  if possible  After the 30  for 30  DISCUSSION /  recover some cells  minutes  those  attached to the mineral surface.  of agitation the suspension was  remove the mineral solids, and g to recover the cells. No freely suspended  from  the supernatant was  centrifuged  at 50  again centrifuged  x  g to  at 600  x  cell packet appeared. This indicated that most of those  cells, observed under the microscope in the original culture, were  collected in fraction  1 and  that cells  attached to the mineral surface could not  be removed by the method used.  Figures 42—43(98) present the results of a leaching experiment particle—free  cell suspension obtained by  culture, by centrifugation for 5 minutes obtain a cell packet by was  at 50  centrifugation at 600  2 ml of a cell suspension containing 0.8  copper no  removing  extraction  was  elemental sulfur  medium,  following  only 5% was  over  produced.  inoculation,  287  below  analysis method (the concentration was was  Figs. 1.4mg  x g for 10  6 day old  minutes. The  of carbon. For this  initial  the  a  using the supernatant to  hours, acid consumption  Since the  was  the solids from  x g, and  mg  inoculated with a  carbon  detection  calculated to be  inoculum experiment  was  zero  and  concentration in the  limits  for  0.8mg/L), the  the  carbon  experiment  repeated using a larger inoculum.  44—45(101) C.  Copper  consumed and measured  no  in the  present  data  extraction  for  was  5.4%  elemental sulfur was medium  was  an  experiment over  300  using hours,  produced. The  3mg/L, which  was  inoculum 0.4mL  initial  the same  of  containing acid  were  carbon concentration initial concentration  RESULTS AND  DISCUSSION / 128  Fig. 42 Cell packet inoculum effects on the iron profile  R E S U L T S AND  Fig. 43 Cell packet inoculum effects on growth and Cu  D I S C U S S I O N / 129  extraction  R E S U L T S AND used in the experiment shown in Figures 100%.  This  inoculum  indicated that  to remove  the  Alternatively, it could to cells attached  although  mineral  DISCUSSION /  130  40—41 for which copper extraction  was  inoculum  solids had  size was  adequate, processing  somehow changed  its characteristics.  also mean that freely suspended cells were not  to the mineral  surface, and  that attached  the  equivalent  cells were  responsible  for starting catalyzed leaching.  This  second  alternative  46—47(103)  for  which  was  tested  the  in  inoculum  centrifuging a cell suspension for 10 this centrifugation was  no  Upon  review  recalled  of  that  contained 9K and  600  cell  used  belonging  to  x  g,  had  any  48—49(109) show the suspension 12  x  obtained  g. In soluble  over 140  to  the  obtain  1.27  in  solids  Figures  obtained  by  pellet resulting from  used as  hours, no  inoculum.  acid was  the  on  particle  free  supernatant, every  For  consumed  when the  soluble extracellular material  cells  it  obtained  occasion.  was after  This fraction  leach was  products of leaching: metal  set up ie.  ions, acid, etc.  produced  by  the  cells.  results of an experiment inoculated with a particle by  centrifuging when the  by—products,  the  original  cell  suspension  supernatant, containing  was  leach resulted: elemental sulfur was  consumed; and  the  and  turbid, blue  been discarded  this case cell  reported  produced.  salts. It also contained  acid, and  catalyzed  9%  procedure  would also contain  minutes at ions,  at  of  H2SO4  soluble materials: those first introduced  medium  Figures free  the  material  centrifugation  consisted  resuspended in 0.0 IN  elemental sulfur was  experiment  minutes at 600g. The  this experiment copper extraction was and  the  used produced;  as  inoculum  1.74  Moles of copper were extracted, to give  for  5  cells, metal a  successful  Moles of acid were a  molar acid:copper  RESULTS AND  Fig. 44 Inoculum  D I S C U S S I O N / 13  cell carbon effect on iron leaching  RESULTS AND  DISCUSSION / 132  10n  Inoculum cell carbon effect on growth and copper extraction  RESULTS AND  DISCUSSION / 133  Fig. 46 Iron leaching for inoculum drained of the soluble components  RESULTS AND  Fig. 47 Copper leaching for inoculum drained  DISCUSSION / 134  of the soluble  components  RESULTS ratio of and  1:1.37. Of  metal ions  that  the  those materials  were also present  fraction  containing  centrifugation), also contained needed for controlled-redox  present in the  the an  in this new  soluble  cells  are  washed  have been made on  as an  culture medium. It follows  then,  (supernatant,  renders  them  to be  characterized.  strongly associated  Agate for by  cells and  depending on  et  reported  the  and  may  by  Schnaitman and  complex  some  of  being  be  playing  since the  substrate  of the  iron grown  and  iron grown cells they proposed  the  medium, 20%  the an  The  +  +  where none was  higher  phospholipid  of which  carbon  were  a  cells  the  extracellular complex  different role depending complex  was  sulfur changed  portion  on  of  the  substrate.  involved in the  F e  +  +  cell's  medium  oxidized. Additionally they 3%  the  They suggest  quantities of complex found in the  became completely  present  lipid  for sulfur grown cells 70%.  that the  not  compounds  extracellular complex  that for iron grown cells the extracellular complex contained +  studies  Lundgren  ferric iron precipitates, but  Lundgren, as  used. For  phospholipid  electron transfer processes,  Fe  1988). Some  when  lipopolysaccharide. They examined both iron and  substrate  that  off as  with  found that the composition  40%  leveled  was  not been determined.  inactive (Duncan,  al (1968) characterized  Schnaitman and  complex contained the  This factor  g  T. ferrooxidans concerned with the type of  culture filtrates of  containing phospholipid grown  x  the cells, which is eliminated  energy source, released carbon compounds into the  unaccounted  600  F. ferrooxidans growing on a mineral salts medium with ferrous iron  were found  For  salts  leaching to occur. Its nature has  and  135  medium  extracellular material, factor X.  compounds found after cell growth. It was (1965) that  DISCUSSION /  inoculum, 9K  materials  This factor could be a surfactant produced by the  AND  and  found 0.5%  in the sulfur grown cells.  content of the  complex  for sulfur grown  cells  and  the  R E S U L T S AND  DISCUSSION / 136  Fig. 48 Iron leaching. Solid-free inoculum soluble fraction included  RESULTS  AND  DISCUSSION / 137  35-1  T I M E  Cu  (hours)  leaching. Solid-free inoculum soluble fraction included  R E S U L T S AND absence  of iron  compared  to  associated  with  it, as  complex  from  iron  the  well  as  grown  its lower  cells  DISCUSSION / 138 protein content  (16.3%),  led Agate  et  suggest that the extracellular complex played a role as a wetting agent sulfur  grown  cells.  phospholipids in T.  There for  A  similar  been  suggested  washed  cell  on  mineral  suspensions  concentrates, but  normally  on  may  be  the spent  for its presence  medium  upon  (Duncan,  transfer  synthesis of such a complex was a^ culture growing the  inoculum  demonstrated  Duncan  et al (1964)  use  of washed cells in  1988)  If factor  to  X  corresponded  to  would  new  medium  affected by  exposure  introduce  factor  controlled-redox leaching  can  would  indicate  to the new  that  the  medium. For  X  to be  the  leach,  maintained  it  under  culture (Lawrence et al, 1984), then the cells must be able to produce once a certain concentration is present in the medium.  5.3.4. -400 MESH CONCENTRATE  a  for sulfur grown cells, then the  actively, as in continuous leaching, the critical stage would  which that  active  related to the elimination of biological surfactants present  surfactant like the extracellular complex proposed need  surface  T. ferrooxidans showed the need of  of  surfactants for the leaching of chalcopyrite to occur. The our experiment  for  for the  similar studies made on spent growth medium contents  T. ferrooxidans growing with  has  al to  thiooxidans by Schaeffer and Umbreit (1963).  have not been any  working  role  (6.4%)  has  be  been  continuous factor  X  R E S U L T S AND 5.3.4.1. BACTERIAL  Fig.  mesh, redox-controlled  copper extraction was  73%.  leach  The  metal extraction pattern was these results with et  at  0.27-0.45g/L h. Our  1985)  thus being  variations in between  Lawrence  et  al, (1984) have present  obtained  for  leaching, we Table a  do  6. Now  total  of  in fact find  molecule. For  electrons  maximum  a  concentrate  lots  that  oxidation  of  mediated. For  those  available from  where  Compare  leach due  levels  obtained  for  1-5  only  iron  oxidation  the  at  electrons are iron  of S"  oxidation  2  one  be  redox  reflected  See  leaching  chalcopyrite  available for each  oxidation  is biologically  to S° is also biologically  is biologically  mediated,  would expect for controlled redox leaching of chalcopyrite that a reduction of or 0.058 in energy should  the  cell yields  controlled  of  of  reduction in  it stopped  compare  be  procedures.  lower to a  of  concentrate  difference may  we  the  4 electrons more if the conversion case  mesh  be  when  and  leaching. Lawrence  about the reasons for this. For conventional  are  leach  lower cell yield in controlled redox leaching.  controlled redox leaching only  the  process.  ballmilling  would  sulfide  to sulfate. When with  and  there  molecule of chalcopyrite oxidized. 1 electron - if only mediated, and  this  copper extraction rates  lower. This  controlled-redox  leaching  lets speculate 17  the  opposed  conventional  200g/L. For  for conventional  somewhat  suggested  in the  from  sulfur state as  of  copper extraction rates for -400  to  elemental  11  have reported  maximum  obtainable  density  relationship between bacterial growth pattern  attributed  energy  pulp  different than for the conventional  were of 0.27-0.35mg/L h,  the  cell growth as a function of time for a  those shown in Figure  al (1982,1984 and  bacterial populations  139  GROWTH  50(118) shows copper extraction and  — 400  DISCUSSION /  in a similar reduction  we 1/17  in bacterial yields.  RESULTS AND DISCUSSION / 140  50-i  T I M E  (hours)  Cell growth and Cu leaching with Eh control  RESULTS  AND  DISCUSSION  If the oxidation of sulfide is also cell mediated the reduction 5/17 or 0.29, and we supports  the  view  and  that  that  the  reduction  to the sole  the sulfide  mediated. In all three  in bacterial  use of ferrous  conversion  cases  ratio of cell yield reduction similarly that A F  the ratio  yield  in  controlled-redox  iron as energy  to elemental  sulfur  of cell yield  source  is not  and  of 0.058. In terms of free energy decrease we  mol.  The  ratios  for oxidation  conditions to oxidation under redox-controlled  sulfide  bacterially  find  for oxidation of sulfide to sulfate is -215.14Kcal/g mol, A F for  is -17.8Kcal/g  standard  in this  is closer to the calculated  oxidation of SH" to elemental sulfur is -57.8Kcal/g mol, and that A F oxidation  would be  would expect a similar reduction in the cell yield. Table 6  leaching, corresponds leach,  in energy  / 141  oxidation  are  biologically  mediated,  for F e  of chalcopyrite  +  +  under  conditions are, if both iron  0.25  and  if only  iron is  biologically oxidized 0.04.  Fig.  50 indicates that growth of T.  stopped  in  necessary  the  controlled-redox  to investigate  what  ferrooxidans continued  bioleach  happened  process.  A  to the cells  after copper extraction  longer after  experiment  the  controlled-redox  leaching of copper stopped. A t this point in the leach, the conditions potential  around  500  mV,  jarosite  precipitates. The  energy  source  bacterial  copper remaining  for continuing  energy  requirements  in solution, presumably sulfide  (if any) could  bacterial growth. were  Other  the oxidation  sulfur. These two alternatives are considered  were redox  as C U S O 4 , be  of ferrous  iron and  available  possibilities iron  was  as  an  for supplying or elemental  in the following two sections.  RESULTS  AND  DISCUSSION  / 142  Fraction  Leach  Cell Yield mg TOC/g Cu extracted  5  C-R Conv  2.27 18.35  0.12  C-R Conv  0.87 12.30  0.07  C-R Conv  3.12 35.20  0.08  4  2  Ratio  Table 6 Cell Yields in Conventional (Conv) and Controlled-Redox (C-R) Leaching  5.3.4.2. FERROUS/FERRIC According  PROFILES  to the stoichiometry  UNDER REDOX  for controlled-redox  CONTROL  leaching  discussed  in Chapter  2, the net sulfuric acid consumed in the leaching of copper is a function of the levels of oxidation of ferrous sulfate and hydrolysis of ferric sulfate. The net acid consumption due to these  reactions  can be estimated  if the amounts of ferrous  and  ferric iron in solution are known. Fig. 51(118) presents  the  leach  concentrate  presented was  being  oxidized  occur  mostly  found  in Fig. 50.  soluble  throughout  the leach,  in the ferric  represents  iron,  vs  19%  of the  in solution, compared to 7 3 %  form, only  ferrous state. Cell concentration the  Only  time  and by  iron  contained  in the  of the copper. Iron  the end of the leach  was  seemed to  0.3g/L of a total of 4.2g/L were in the  and ferric iron concentration,  are presented  the chemical oxidation  the iron profiles for  in Fig. 52(118).  expressed The  as %  shaded  of area  of iron that occurs in the absence of bacteria.  Bacterial growth seems to be related to ferrous iron oxidation because for ferric  RESULTS AND DISCUSSION / it has to come from oxidation of ferrous iron.  r  700  r  T I M E  (hours)  Fig. 51 Iron leaching under Eh control  6  0  0  9  143  RESULTS AND DISCUSSION / 144  Fig. 52 Soluble iron oxidized under Eh control  RESULTS AND  DISCUSSION / 145  Fig. 53 Sulfur and cell growth under E h control  RESULTS 5.3.4.3. CELL  Fig.  GROWTH  AND  ELEMENTAL  AND  SULFUR  DISCUSSION / 146  PRODUCTION  53(118) shows the relationship between copper extraction, Eh, consumption of  H2SO4,  S^ and cell growth. To maintain a constant  from the start of the leach. This demand  continued  pH  required  H2SO4  addition  after the leaching of copper  stopped. This later acid was used for oxidation of ferrous iron via equation 1.  After  an  initial,  unproductive  extraction  started  increasing  ceased. After population decrease  period  with  elemental  time.  After  about  240 h, the amount of S ° tended  was  still  of S®.  increasing  Either  S^  Two  was  possibilities oxidized  by  sulfur  production  280  h  and  copper  to decrease while come  to mind  dissolved  oxygen  copper  extraction  the bacterial  to explain the (Dutrizac  and  Macdonald, 1974) or bacterial oxidation thereof was occurring.  Another was  experiment  taking  was  carried out to investigate  place. The results are presented  of Fig. 54 between 0—310 the concentration  if bacterial oxidation  in figures 54—55(119). The portion  hours shows that cell concentration  of ferric iron implying  of S^  that ferrous  increases  as does  iron is decreasing. Bacterial  growth declines as all the available iron has been oxidized. Thus it seems that even when there  is S° present,  T. ferrooxidans  preferentially oxidizes ferrous iron  Inhibition of cell mediated S° oxidation, could  be caused by the presence of ree  over elemental sulfur.  thiosulfate in the culture medium conditioning  step  r  since an excess of thiosulfate was  (for the formation  of the  silver  thiosulfate  used in the  complex  during  RESULTS AND  DISCUSSION / 147  _,- • "~°-' ----A^—O--: A^>Q- - Q — Q - - O - Q — Q Q  r  100  80  60  40  O  r—<  X (fi  (fi  o a, o, o O •a a «  ^  cr A—A-  o © A S  •  H  2  S O  4  -200  sTOC  160  -1 \ 120 5? a -80  -40  0  100  200  300  400  500  600  700  800  Time (hours)  Fig. 54 Iron oxidation and cell growth under Eh control  RESULTS AND  D I S C U S S I O N / 148  0.12  -Q-B-  0.10  - • — B — B -  600  0.08  500  W  400  8  300 0.06  .0.04H chalcopyrite '  0.02  s o l i d s  0.00 « — O — © 0 100  i 200  1  300 300 Time  r 400 40'  IS  d e n s i t y  D  Eh 500  g/l  x  10"  m v  600  700  (hours)  Fig. 55 Sulfur profiles for E h controlled leaching  800  RESULTS AND DISCUSSION / 149 pre—treatment of the concentrate).  Free thiosulfate  has been reported to inhibit  so oxidation (Landesman et al, 1966). Given the acid conditions of the medium it does not seem likely that any free Alternatively  if thiosulfate  decomposed  thiosulfate  is  in existence in solution.  it would liberate silver, which has  been reported to inhibit sulfur oxidation by interfering with glutathione  also  dependent  enzymes or with enzymes containing cysteine near their active sites (Kulpa and Mjoli, 1987).  Fig. 55 is the time profile of S° expressed as g S°/g initially added chalcopyrite and  g  S°/g solids.  The difference  between these  two  curves  is  due  to  the  increase in the pulp density caused by the formation of basic ferric sulfates and jarosites. Since S° concentration was expressed on a mass basis based on solids present in the culture medium, taking this increase in mass of solids  in the  medium into account makes the decrease of S ° less significant, indicating that S ° was  in fact  stable in this  system.  This  also means  that S° was  not being  oxidized by oxygen. Refer to the S° profile of Fig. 55. After 600h of leaching the cell growth and oxidation of chalcopyrite has ceased. Even though air was continually injected to the medium, the S ° concentration remained constant.  The by  dependence of cell growth on ferrous iron oxidation can be further analyzed calculating an overall yield of bacteria based on ferrous iron oxidation. A  very high yield relative to expected  values for growth on F e  + +  could indicate  that an energy»source other than ferrous iron was available for bacterial growth. The 54  yield based on iron oxidation for the period between 0—310 hours of Fig. was  calculated  to be  12  mg of cell—carbon/g F e  + +  oxidized.  Kelly and  R E S U L T S AND Jones F e  +  (1978,1983) reported oxidized. Liu  +  This  indicates  produced  that  amounts  g  F e  +  oxidized  +  2.23  mg  TOC  and / g  of  cells  present  in  energy  from  ferrous  iron  controlled-redox  leach  process cell growth  obtaining  for the  CI  mg  al (1988) reported  the  solely by  suggest that  et  166  DISCUSSION /  our  632 F e  +  150  mg  C/g  oxidized.  +  experiment  could  be  oxidation. These results depends  on  iron  oxidation.  Now  let's consider  some mechanisms through which this can  bring about copper  release. It could be that iron oxidation shifts the equilibrium of the reaction: CuFeS towards the driving could  force be  the  right. By  2  +  Cu  —->  2 +  +  Fe  2 +  ..(30)  consuming ferrous iron, the bacterial cells would create  which causes  the  dissolution of chalcopyrite. This  major role played  by  the  formation  of elemental sulfur could be  oxidation  and  bacterial  sulfide oxidation  for  mechanism  this  2CuS  not necessarily  a  and  cells in the  the  sulfur oxidation in  controlled-redox  shift  leach.  The  result of the controlled redox, chemical  direct result of any  is discussed  equlibrium  a  section  biochemical  process.  Possibly  were inhibited. Additional  5.6.2. for cell  growth  in  support monosize  leaches.  The  presence  before  of a  lag  phase  in  the  leaches  may  be  due  to an  cell growth occurs,  cells to gear up  under  redox  controlled conditions,  induction period  necessary  their metabolic reactions for iron oxidation. This could be  to the pattern of diauxic growth wherein cells, in the presence of two rapidly  metabolize  phase before  the  one  which  yields more  reassuming growth using the  energy  and  then  second substrate. In our  for  the  likened  substrates,  undergo  a  case the  lag first  RESULTS substrate  is the sulfide  growing under  standard  being  oxidized  AND  in the inoculum  DISCUSSION  from  conditions, and the second substrate  product of chalcopyrite oxidation. Following  this  reasoning  into the medium  of the lag  in the medium,  with  systems in the bacteria starting  only after a certain, amount of ferrous iron was present iron is released  culture  is the soluble iron  the length  phase would be controlled by the ferrous iron concentration induction of the necessary iron oxidizing enzyme  the stock  / 151  in the medium.  Ferrous  as a result of the chemical reactions between  the C u / C u " " couple and the sulfide see equations 24 et seq for dissolution of +  +  1  chalcopyrite.  Support for the proposed mechanism was outer  membrane  — 400 mesh gel  preparation  Newmont concentrate  electrophoresis  protein  of cells  (McBride,  bands show  grown under  from an analysis of the  redox-controlled  conditions in  by sodium dodecyl sulfate (SDS)  polyacrylamide  1988).  the presence  et al, 1986;  also obtained  The  results  of a protein Kulpa  unique  The  to sulfur grown cells at  (Kulpa  inhibition  of sulfur oxidation  synthesis  of the protein is not inhibited. Additionally an outermembrane protein  be  92K, needed for iron oxidation (Kulpa under redox—controlled standard  at the metabolic  needs to be induced before  patterns  This  indicates  regulation  level,  that since  and Mjoli, 1987) was found in cells grown  conditions on sulfides, which points  proteins  1987).  conditions. This protein is not found in cells grown under  mechanism is not normally  The  Mjoli,  in Fig. 56.  45-50K  may  and  are shown  functioning when  to the fact that  the iron oxidation  the cells are oxidizing sulfides and  synthesis of the enzymes can proceed.  of the cells  of the microorganism  involved  in this  study,  RESULTS  1  2  120 K 92 K  B  45 K  DISCUSSION / 152  3 4 5  FT 66 K  AND  ft  s 27 K 18 K -+ * 14 K — ^  line 1 molecular weight size markers line 2 T. ferrooxidans ATCC strain membrane fraction line 3 T. ferrooxidans controlled redox -  purified membrane fraction line 4 T. ferrooxidans controlled redox -  membrane fraction line 5 molecular weight size markers Fig. 56 Gel electrophoresis of outer membrane proteins  R E S U L T S A N D D I S C U S S I O N / 153 cells grown under redox-controlled conditions, shown in lines 3 and 4 of Figure 56  are very  similar  to those  of T. ferrooxidans (line 2)  strain  involved is in fact T. ferrooxidans.  implying that the organism  5.4.  of the A T C C  AERATION  5.4.1. SUSPENSIONS  The  leaching medium  was typically  an aerated  mineral  concentrate  suspension  containing 1 0 — 2 0 % solids; it contained particles in the micrometer range and for this reason could be expected The  to behave in a non—Newtonian mode.  mechanics of mass transfer in non—Newtonian fluids are complicated by the  presence  of solid  interfacial oxygen  particles  that  interfere  area of the system, thus  transfer  from  air to liquid  concentration compared to a medium  with  the generation  reducing the value by as much  of gas—liquid  of kj^a associated with  as 2 8 % for a  2 0 % solids  with no solids (Liu, 1973). Changes in the  "viscosity" of the medium with time may also take place during leaching because of  the dissolution of the mineral particles and the formation of precipitates; such  time dependent responses coefficients in such  are factors to consider when determining  a system. Other  mass—transfer  factors include: agitator and tank  geometry,  air bubble and cell dimensions, fluid characteristics and power input.  An  in depth  beyond  study  of the mechanics of mass  transfer in leaching systems was  the scope of this work, but it was necessary  nevertheless to insure an  adequate oxygen supply to the medium, in order to avoid a limiting oxygen level  R E S U L T S AND which  would  affect metal  extraction  rates  metal extraction rates were determined and  a  level  was  established  as  the  and  cell  growth.  at several aeration minimum  aeration  oxygen dependent metal extraction rates were obtained. behaved differently, 2L gas in the  rates (vvm). For 1L  tanks have higher  For  above  Larger  reactors,  which  increased  surface  gas  reincorporation  in the  non  scale experiments  velocities for the  at lower aeration rates in 2L  154  purpose  levels in 1L rate  superficial gas  this  this reason similar metal extraction rates to those  tanks were achieved  result of  DISCUSSION /  achieved  tanks. This larger  same  could  be  tanks due  to  changes in the tank geometry.  To  study the  effects of aeration levels and  establish a minimum  series of leaches  using  catalyzed  in terms of copper extraction rates (overall and  various  leaches  — 4 0 0 mesh concentrate  aeration levels expressed as  presented in Table 0.8vvm, Fig.  7. The  was  aeration level, a results of  maximum) for  volumes of air/volume of medium  leaching profiles are  59-60(121) for  carried out. The  (wm)  are  presented in Fig. 57—58(94) for  1.5vvm, Fig. 61-62(109) for  2.99vvm  and  Fig.  63-64(97) for 5.98vvm.  Based  on  the  results presented  in Table  7  an  aeration  level of 2.99vvm  was  selected as the minimum aeration rate for obtaining leaching rates that would independent  of  the  air  flow  through  extraction rates were dependent on the  figures corresponding to aeration  (Figs. 59—60) it is evident oxidation  reactions.  This  that the was  the  the  reactors.  air flow  Below  through the  2.99vvm  copper  reactor. Examining  rates of 0.8vvm  (Figs. 57—58) and  air supplied  not enough to support  confirmed  by  was  the  low  be  elemental  sulfur  1.5vvm the  levels  RESULTS  AND  DISCUSSION / 155  Table 7 Aeration Effects  REACTOR SIZE  AERATION  COPPER EXTRACTION RATE overall-max  (L)  (vvm)  (g/L h)  1 1 1 1  0.80 1.50 2.99 5.98  0.06-0.12 0.08-0.13 0.09-0.32 0.09-0.31  0.12 0.00 2.98 2.06  2 2  0.68 0.68  0.12-0.35 0.19-0.33  1.22 3.24  measured  in the medium  sulfide-sulfur The  molar  to elemental  rate  of 2.99vvm  supplied  in this case was  %  dry residue  at the end of the leach, indicating low conversion sulfur (see Table  acid:copper ratio  aeration  ELEMENTAL SULFUR  was  7), and the low acid  0 for 0.8wm  and  the profiles of Figs. 6 1 — 6 2  0.75  of  consumption.  for 1.5vvm. For an  indicate that  enough to carry out the oxidation  the oxygen  reactions, and acid  was consumed, to give a molar acid:copper ratio of 1.8. Figs. 63—64 present the case of excess air supply, rates obtained the a  the copper extraction rates did not increase above the  for 2.99wm aeration and ferrous iron was completely oxidized by  end of the leach. Elemental sulfur was  molar acid:copper ratio of 1.53.  produced and acid consumed to give  RESULTS AND  DISCUSSION / 156  12-1  T I M E  Fig.  Effect of 0.8  vvm  (hours)  on growth and Cu leached under Eh control  RESULTS AND  Fig. 58 Effect of 0.8 vvm  D I S C U S S I O N / 157  on iron leaching under E h  control  RESULTS AND  Fig. 59 Effect of 1.5 vvm  DISCUSSION / 158  on growth and Cu extraction under E h control  R E S U L T S AND  Fig. 60 Effect of 1.5 vvm  DISCUSSION / 159  on iron leaching under E h  control  R E S U L T S AND  DISCUSSION / 160  35 - i  T I M E  Fig. 61 Effect of 2.99 vvm  (hours)  on growth and Cu extraction under Eh control  RESULTS AND  Fig. 62 Effect of 2.99 vvm  DISCUSSION / 161  on iron leaching under E h  control  R E S U L T S AND  D I S C U S S I O N / 162  45-i  0  50  100  150  200  T I M E  Fig. 63 Effect of 5.98 vvm  250  300  350  400  450  (hours)  on growth and Cu extraction under Eh control  RESULTS AND DISCUSSION / 163  T I M E  Fig. 64 Effect of 5.98 vvm  (hours)  on iron leaching under E h  control  R E S U L T S AND  5.5. MINERAL  SURFACE  DISCUSSION /  164  CHANGES  5.5.1. BEFORE LEACHING  During  the  complexed between  chemical form  as  Ag2S04  activation Ag2S203  with  stage  (Lawrence  Na S 032  of the  With  2  concentrate,  et al, 1984) an  initial  silver  resulting  is found from  concentration of  a  in a  reaction  400mg/L  of  silver (Lawrence, personal communication) less than O.lmg/L remained in solution. Therefore it was  believed that the initial concentration of 0.58mg/L used  tests would be in a complexed form soluble  silver  has  been  reported  concentrations higher than It  was  not  known  any  to  thus not in a free, soluble form. Free,  inhibit  the  lmg/L. (Hoffman and  whether  solution or if it would  and  this  the  T.  of  ferrooxidans at  Hendrix, 1976). complex  mineral. To  would  investigate  remain  samples  stages  during  diffraction  of concentrate  were  the  activation  X—ray  chemical analysis  taken  (EDXA).  from  procedure  Fig. " 65  chalcopyrite particles before treatment, Fig. 66 sodium  thiosulfate  (first  9K  copper  iron and  silver—thiosulfate  silver  would  activation.  An  be  of  the  at  different  and  by  electron  presents  analyzed  the  results  of E D X A  after addition of silver sulfate  activation)  and  after  addition and  of  of and  cupric  /3 peaks for  the sulfur peak are present, as well as the silicon peak. If complex  present arrow  activation  catalyzed leach  medium salts (second stage). In all cases the a  sulfate and and  stage  a  in  if there were  changes taking place at the mineral surface during the chemical  stage,  the  growth  silver—thiosulfate  associate with  in our  precipitated  in the  in Figure  EDXA 66  on  the  mineral  (Fig. 6 6 ) after  indicates  the  surface, a the  expected  first position  signal for  stage of a  of  the  silver  RESULTS peak. Since  no silver could be detected  remained in  solution.  The E D X A  the  A N D DISCUSSION /  silver—thiosulfate  a n a l y s i s of stage 2 (concentrate  complex  165  must  at the end of the chemical  have  activation  stage) also indicated that no silver was associated w i t h the m i n e r a l surface.  5.5.2. A F T E R Fig.  67(5)  LEACHING  presents  the  leaching  profiles  for  concentration, cell growth and acid consumption potential  (67b)  measured  100% a n d i r o n extraction end of the  68  presents  leach (68a)  was  leach showed it  acid:copper ratio of  Fig.  during  leaching.  (67a)  Copper  concentrate:  and iron extraction  extraction  for  2 2 % ; c h e m i c a l analysis of the  contained  16% sulfur.  this  copper and  leach  Eh was  solid residue at  A c i d w a s consumed to give  the an  1.25.  the  a n d after  X—ray  analyses  of  the  concentrate  at  the  start  9 3 h of leaching (68b). F i g u r e 68b was obtained b y  the S E M into a pit.  T h e analyses indicate  composition  and  pits,  composition  compared  release  the  of  Gibraltar  that  to  elements  where the of  active  rest the  of  that the solid m a t r i x  leaching is the  matrix,  taking This  is  and  contrasts  the  focusing  has changed its  place, have  mineral.  of  due  to  different sequential  sharply  with  the  concentrate  after  136  simultaneous element release i n conventional leaching.  Fig.  69  hours Copper  presents  of  the  leaching,  mapping  the detection  with  was  limits.  results the  attempted  of  X—ray  analyses  corresponding but  the  of  element  the maps  concentration  The peaks corresponding to copper  in  for  this  a and  iron sample are  and was  sulfur. below  considerably  RESULTS AND  DISCUSSION / 166  ,S  Fig. 65 E D X A  of concentrate before activation.  RESULTS  1  AND  DISCUSSION / 167  A9  Kot.Ca  K^Ga  K Ca.  Fig. 66 E D X A  of concentrate during activation. Stage 1 and 2.  Fig. 67 Leaching profiles E D X A  specimen  RESULTS AND DISCUSSION / 169 Vert«  290 c o u n t s  lM p= S  1  E 1 a p s e d ••  18  secsi  •lllliillliiiliiiiliiiii-.^  \Cu:  ;:;;;;:Fe:;::::;::: VVy  4-  Vert=  <-  0.008  Range"  .:::::::::•  10.230 keV  ::::::::::  10.110 -f 12669  350 cou  0.000  Range-  10.238 keV  9.958  -f  24194  Fig. 68 E D X A  of solids after 93 h of E h controlled  leaching  RESULTS reduced compared  to the  initial  sample. This  of this element from the mineral. The by  the  same  considering  a  Iron at the  proportion small  peak  mineral  as  the  (see  a  reduction  and  copper  AND  DISCUSSION / the  leaching  /3 peaks for iron are not  reduced  peaks.  results from  170  This  can  arrow) that indicates the  be  explained  presence  by  of potassium.  surface, in excess of the stoichiometric equivalent of copper,  could then be in the form of potassium jarosites, resulting from the hydrolysis of ferric iron. The  peak corresponding  the  mineral  the  intensity of the signal in the  map.  surface  to sulfur indicates that a  After  obtained  at the end  extraction with  indicating that  Silver  was  detected  EDXA  for concentrate  of the  most  during  of  disulfide the  active  after 187  h  copper extraction at this point was indicates  that  leach. This  sulfur map,  carbon  lot of sulfur was  S°  was  confirmed by  relative to the the  was  EDXA easily  controlled-redox  present  comparing  signal of the  iron  in Fig. 70  was  shown removed  leaching.  at  by  the  Fig. 71  solvent.  shows  an  of leaching under redox controlled conditions; 24%.  it participates actively  The  during  presence of silver at the leaching,  even  though  surface,  none  was  detected during the activation stage.  After EDXA surface  234  h  of the  of leaching, copper extraction was leached  indicating that  surface silver  also showed remained  reports to the tailings at the end  silver  associated  of the leach.  84%.  As  to be with  shown in Fig.72, present  the  at the  solids  and  an  mineral that it  RESULTS AND  DISCUSSION /  RESULTS AND  ,". Fe  Fig. 70 E D X A  of concentrate  DISCUSSION / 172  / Ca  residue after solvent extraction  RESULTS A N D DISCUSSION /  173  ::H;; ;::;; S :  :  c  :  i ;  :::::::::::::::::::::::-  9i;; ;;;;; ;;; ;;;;  :A  0.000  : ::  ::  :::  Range=  :Fe:::ii::::Cu:::::::::::::::::::::::::::::::::::::::::::::::::::"""::::::::::::":::::::::::j 20.460  keV  20.140 Integral  Fig. 71 E D X A  of concentrate  0  187 h leaching  =  10633  RESULTS  A N D DISCUSSION /  174  5.5.3. SPATIAL DISTRIBUTION  In  order  to  verify  distribution  of the  of  within  regions  the  homogeneity  elements, X — r a y a  concentrate  of  the  concentrate  m a p s were used to  that  were  particularly  in  terms  search for rich  in  of  the  spatial existence  silicon or  pyrite.  F o r the two concentrates used i n this study, m a p s of element distribution show  any  measurable  differences  in  the  proportions  of  copper,  iron  did  and  not  sulfur  present i n the concentrate, (a lower proportion of copper w i t h respect to iron sulfur  could indicate  the  presence of  i r o n , copper and s u l f u r for  X—ray during  maps  were  leaching, as  remains  also it  unattacked  pyrite  regions). F i g . 73  used  had  during  to  search  for  been reported catalyzed  regions  that  (Bruynesteyn  leaching.  al,  1986)  Attempts  to  find  of  of  micrograph 74 234 the  together h  covering  the  of a jarosite—covered, N e w m o n t with  the  corresponding  of leaching. T h e  iron  copper  jarosites  distribution  copper,  and  subtracting  t h a t of the iron m a p . S u l f u r  the  concentrate  of jarosites  map. I r o n , i n the f o r m of jarosite,  map  surfaces  iron  density  of  remained  et  were  presence. of  map  of  G i b r a l t a r concentrate before leaching.  leached concentrate, t h a t contained regions of p y r i t e , the  is such a  and  and  that  pyrite  particles  of  not successful because  the  residual  particle sulfur  mineral.  X—ray  maps  after  is homogeneous, as indicated  s i g n a l of  the  A  is s h o w n i n F i g .  can be estimated b y the  unattacked  considering  copper  map  also seems to be homogeneously distributed.  by the  from  RESULTS AND  D I S C U S S I O N / 175  i  Fe ::::::..:::::.::::::::::.:::::  p:::::::::  ::::::::::r>. ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::  e C u iT::'  :;Fei::^;;::cu:::i;:::;:;;:::;i!::;::;::::i;::::i:i::;;:  e  0.000  Range=  20.460 k e V Integral  Fig.  :::::::::::::::::::::::::::::::::::::::  72 E D X A  8  of concentrate 234 h leaching  =  20.220 81522lj  RESULTS AND  DISCUSSION / 176  Fig. 73 Concentrate element distribution by x—ray mapping  RESULTS AND  DISCUSSION  RESULTS  5.6. MONOSIZE  5.6.1. A D D I T I V E  Since  DISCUSSION / 178  LEACHES  CONCENTRATION  the controlled-redox  produce  AND  process  S ° and consume  didn't  acid, it was  dependent on an activation  always  work,  postulated  of the concentrate  that  particle  i.e., did not  the leach surface  was  always  somehow  and that perhaps  the ratio of Ag, and/or thiosulfate, and/or Cu"*" ions to particle surface area had to be within a narrow range.  Miller the  and Portillo  (1979) found, for non—biological leaching of chalcopyrite, that  copper extraction rate  from  17—36g/kg  enhance density  the rate of  increased, as initial  of concentrate. of reaction  Beyond  but reduced  3g/L. For controlled-redox  this  silver  concentration  level,  it slightly  bioleaching,  proposed a range of 0.1 — 4.0gAg/kg of concentrate  was  increased  additional silver  did not  in leaches  Bruynesteyn  in order  with  a  pulp  et al, (1983)  to generate  elemental  sulfur from the leaching of chalcopyrite in leaches with pulp densities of 200g/L.  To  try to elucidate the relationship between silver concentration, copper extraction  rate and mineral  surface  area, a series of catalyzed bioleaches  at pulp densities  of 180g/L was carried out using monosized fractions of Gibraltar concentrate specific surface  areas  (s.s.a.) ranging 75  plots  from  maximum  with  454—4132 cm /g as measured on dry 2  concentrate.  Figure  copper  extraction  concentration  at the end of the leach as function of s.s.a.  rates  and  S°  RESULTS  S.S.A.  maximum  DISCUSSION / 179  (cmVg concentrate)  Fig. 75 Sulfur production and maximum The  AND  extraction rate as function of ssa  rate of copper extraction and the production of S° increased with  increments  of s.s.a. up to 1390cm /g. Subsequent  decreasing  extraction rates  2  and decreasing  increases of s.s.a. resulted in  amounts  of S°  all for a  constant  RESULTS AND  DISCUSSION / 180  amount of catalyst (3.1 x 1 0 g Ag2S04/g concentrate). —3  As  shown in Fig. 75, leaching of the finest concentrate  did  not  produce  insufficient  any  silver  elemental  addition, a  sulfur.  series  To  fraction (ssa = 4132cm /g) 2  determine  of leaches  was  if this  carried  was  due  to  out in which the  amount of silver added gave varying silver to mineral surface area ratios (Table 8).  In this series the amount of copper sulfate and sodium thiosulfate was varied  in  a similar manner. The ratios of silvensurface area to be tested were selected  based  on knowledge  nominal  that  a  leach of a monosize  median  particle  diameter  acid.  For that  leach  consumed concentrate  was  particle  surface  surface  area  2.9mg  which  of 30.4jxm the amount  was  were  3.8xl0" mg 2  elemental  of Ag2S04  added  to  3xl0~~ m g  and  2  2  having  sulfur  and copper 4.4xl0~ g  2  of of  in terms of  Cu /cm .  4  a  and  per gram  Ag2S04/cm  3  of thiosulfate  Na2S 03/cm  fraction  produced  equivalent  area. The concentrations  concentrate  +  2  The  results are shown in Table 8.  In  run 2 the ratio  3 x l 0 mg/cm . ]\T —3  of Ag2S04  2  0  addition  s u  if  u r  W  to surface area  as  was  to particle  produced. maintained  surface area  In run 5  was  kept  the same  ratio  but the amount of copper  constant at of silver added  was  increased; there was still no elemental sulfur generated. Runs 1 and 4 had lower silver  to surface  produced. Run no  so  decrease  area  ratios  than  the base  case  (run 2) but no  3 had a higher silver to surface area ratio than  appeared. The results show that the increase in s.s.a. corresponding of particle  size  from  30  fim (base  case) to 2.5  maintain  a constant  ratio of reagent  nm  to surface area. Since  preconditioning additives ( A g , thiosulfate, C u +  +  +  )  was  run 3 but still  could  compensated for by increasing the concentration of silver sulfate or other to  S^  to a  not be reagents  the ratio of the  to particle surface area seemed  R E S U L T S AND Table  DISCUSSION /  181  8  Effects of Catalyst / Specific Surface Area Ratio  Run number  mg Ag S0 2  1 2 3 4 5  to  have  prior  to  mg Ag S0  4  2  /g cone.  /cm  8.7 14.8 22.2 8.7 14.8  2xirr 3xl0" 5xl0" 2xl(r 3xl0"  no  effect  and  leaching, on  S° 4  2  2  3 3 3  Ag  surface  was  by  mg Na S 0  4  2  2  CUSO4  mg 3  /moles Cu  /g cone.  /g cone.  12.96 17.76 13.93 9.79 2.50  93.0 158.5 237.5 93.0 158.5  357 357 357 911 1822  0 0 0 0 0  3 3  since no the  moles H S0  ever  EDXA  observed one  after  concludes  conditioning, but  that the  ratio  of  additive to surface, within the range studied, is not significant.  It is strange that a process but an smaller  um  particle cannot  be  leached by  the controlled-redox  initially larger particle continues to be leached even when it gets this  time.  resulted  in a  change in the leaching characteristics of the concentrate, with some copper  being  Grinding  than  2.5  the  2.5  um.  concentrate  No  explanation for this  to sizes below  2.5  leached but no elemental sulfur produced. density  of the  experiment,  there is a  the copper  from  (im  be  provided  seems to have  at  These results indicate that, at the pulp  limiting  reaction is not initiated. Once the reaction was of  can  s.s.a. above which the catalyzed initiated extractions of  —400 mesh concentrate were not uncommon, and  70—95 + % indicated  that all particles would eventually dissolve. This finding contrasts with the effects of  increased s.s.a. for non—biological  leaching (Miller  and  Portillo,  1972)  where  R E S U L T S AND increased  rates  concentrate 50%  of  was  reaction  ground, and  minus 0.5  Mm.  are  role  establishing  supports  different  the  production, produced  as  when  the  s.s.a.  the particle size went from  and the  postulate  because  found  increased,  50%  182  when  minus  20  the  um  to  This difference suggests that the mechanisms for these  processes in  were  DISCUSSION /  that ssa  or  particle diameter  controlled-redox  of  section  if sulfur  a result of a  reaction.  5.3.4.3. regarding  were  a  chemical  its production should not be  bioleach  bacterial  plays  the  This  product  as  opposed  particle  the particle size of the  important  finding  mechanism  reaction involving the  affected by  some  two  also  of  sulfur  to  being  surface  then,  concentrate.  5.6.2. CELL GROWTH IN MONOSIZE LEACHES  Leach  profiles are presented  in Figures  nominal, median particle size from 52.1 Figures  76  and  77(107) are  the  particles with initial size of 52.1 extracted, and Copper was  acid was  extraction and  cell growth  iron in solution in the  followed  by  the  other  80-81(113) (for 15.9  were  was  the  2.8  84—85(105)).  Mm This  fraction monosize  a  initial  Mm.  profiles  not  for  the  hours 36.7%  molar  fraction  of the copper  acid:copper  simultaneous  containing  ratio  processes;  was  of 1:1.97. cell  growth  only reached significant levels after the  taken place at around 425  ferrous form  Mm),  to 2.8  to give  particle sizes as  Mm),  for fractions of decreasing  After 526  related to ferrous iron oxidation and  bulk of the copper extraction had the  Mm  leaching  Mm.  consumed  76—85  was  hours. Only  oxidized. This general  observed  15%  of  pattern  was  in Figs. 78—79(111) (for  33.8  82-83(115) (for 9.3  which  did  not  fraction  was  discussed  Mm).  produce in  The  only  elemental section  exception  sulfur  (Fig.  5.6.1. Table  9  RESULTS AND DISCUSSION / 183  T I M E (hours)  Growth and copper extraction from 52.1 /xm material  R E S U L T S AND  Fig. 77 Iron profiles for fraction 52.1  D I S C U S S I O N / 184  RESULTS AND DISCUSSION /  36-)  T I M E (hours)  Fig. 78 Growth and copper extraction from 33.8  urn material  185  RESULTS AND  Fig. 79 Iron profiles for fraction of 33.8 /im  D I S C U S S I O N / 186  RESULTS AND DISCUSSION /  TIME  (hours)  Fig. 80 Growth and copper extraction from 15.9  nm material  187  RESULTS  AND  Fig. 81 Iron profiles for fraction of 15.9  urn  DISCUSSION / 188  R E S U L T S A N D D I S C U S S I O N / 189  48-j 44-  ' 0  I" i" i" i 50  1  1  r"—i =i—=i—=h  1  1  1 ^0  100 150 200 250 T300 400 450 500 550 600 650 700 750 I M350 E (hours)  Fig. 82 Growth and copper extraction from 9.3 (im material  RESULTS AND  Fig. 83 Iron profiles for fraction of 9.3  um  DISCUSSION / 190  RESULTS AND  DISCUSSION / 191  T I M E (hours)  Fig. 84 Growth and copper extraction from 2.8 um  material  RESULTS AND  Fig. 85 Iron profiles for fraction of 2.8  Mm  DISCUSSION / 192  R E S U L T S A N D DISCUSSION /  193  summarizes the results from these runs which produced elemental sulfur in terms of copper extraction, moles of iron oxidized and moles of cell—carbon produced.  As  was shown in section 5.3.4. for — 4 0 0  controlled-redox cells.  There  is a  concentration iron  leaches  is dependent  on ferrous  iron is released  pathway  starts.  into  The length  copper leaching in  iron oxidation  of T.  lag in the growth  of ferrous  oxidation  mesh concentrate,  by the  ferrooxidans until  the medium  a  bacterial certain  and induction  of the lag phase  of the  increased  with  increasing particle size, for 2.23 um it lasted 260 h, for 2.67 um 338 h, for 4.85  fim 425 h and for 5.94 um  450 h. This  effect is probably  due to  dependence of iron solubilization rates on particle size, since the substrate for  the  needed  induction is soluble ferrous iron. The time required for the iron concentration  to reach a threshold that starts induction and growth of the cells will depend on the particle size.  5.6.3. SOFTWARE  The  Fortran  presented  in Appendix  size, leaching case  program version used to predict particle shrinking during leaching is 5. The input  time, pulp  the initial  particle  density  data  for the program  was: initial  particle  and copper content in the concentrate.  In this  size was the particle  diameter  after  and  the leach time started at lOOh.  The  calculation of the shrinking diameter was done in the  conventional  leaching  case, and was based  rates. For the controlled-redox  leach  lOOh  of leaching,  same way as for the  on the experimental copper extraction  the rates were calculated from  the portion  RESULTS AND  DISCUSSION / 194  Table 9 Controlled Redox Monosize Leaches  FRACTION  5 4 2 3  of the copper  IRON OXIDIZED  MOLES  %  MOLES  0.001 0.002 0.010 0.012  36.4 44.2 62.0 91.6  0.006 0.015 0.023 0.031  indicated by the arrows.  0.061, for 5.94 um  in Fig. 86. The copper  of the curves  extraction  of Fig. 86  APPLICATION  OF  rates  are only  THE  2.6 2.9 5.3 5.6  The rates in g Cu/L h  an  copper  MODEL  extraction  estimated  from  approximation  behaviour. The copper extraction rate exhibits a complex  5.6.4.  s°  0.071, for 2.23 urn 0.155, for 2.67 (im  and for 4.85 i i m 0.060. The experimental  presented portion  COPPER EXTRACTION  vs times curves  were for 2.36 um 0.054  CELLTOC  TO  data are  the "linear" of the curve  pattern.  CONTROLLED  REDOX  LEACHING  Comparisons  of particle  sizes  measured  during  active  particle shrinkage predicted by the model are depicted fractions of concentrate having These nominal  sizes correspond  nominal  The scattered  points  leaching  and the  in Figs. 8 7 — 9 1 for the 5  sizes 52.1, 33.8, 15.9, 9.3 and 2.8  to the following sizes measured  2.34, 2.90, 3.15, 2.61 and 2.33 um. 92.  copper  A l l fractions are plotted  are the experimental  um.  after 100 hours: together  in  Fig:  measurements, and the lines the  RESULTS AND DISCUSSION / 195  • /  /  /  // / / /  Size ia m i c r o m e t e r s  /  / S / H - X t  X /  A X  X  -  /  '  •'  F R A C T I O N  1  2.36  F R A C T I O N  2  5.94  o F R A C T I O N  3  2.23  H  F R A C T I O N  A  2.67  2  F R A C T I O N  5  4.85  O A X-  300  400  500  600  700  T I M E (hours)  Fig.  86 Copper extraction rate data for E h controlled leaching  predictions  of the model.  significant  particle  size  As  in the case  reduction  occurred  RESULTS AND  DISCUSSION / 196  of conventional  monosize  during  the first  100  leaches  hours  a  due to  autogenous milling, for this reason the comparison in particle shrinking was made after 100 hours.  The  model  where  underpredicts  the particle  shrinking  the shrinking  sizes  were  at an accelerated  below  taking  2.0  rate. This  place  at the end of the leach  p.m and the particles seemed  particle  shrinkage  size is a critical parameter to start the controlled-redox  indicates that  to be particle  leach reaction, but once  the reaction is underway, it will proceed even for particles below 2.0 (im.  The  model fails because  we  assumed  simultaneous leaching  of copper  However the results show that significant amounts of iron are leached copper is leached  thus our assumption  and iron. before any  is not correct. Nevertheless the particles  get smaller as the particle size measurements show so there is some justification for  using  a  shrinking  particle  model.  The  electron  micrographs  indicate  that  shallow pits form on the surface of particles during leaching so, in addition to to the pore  shrinking particle concept, one should model  of Hansford  and  Drossou  also consider  adapting  (1987) to produce  the propagating  a combined  shrinking  particle, propagating pore model for bioleaching.  5.7. CONTROLLED  REDOX  From the studies reported the  controlled-redox  leach.  LEACHING  in sections 5.3 to 5.5 we obtained It requires  a  minimum  pulp  a clearer picture of  density,  produce elemental sulfur. Some factor produced by the inoculum  ca. 200g/l, to cells when  they  RESULTS AND  D I S C U S S I O N / 197  2.8 micrometers u  4) O  5  s  o u  a w  A  3H  W 2H  A  i 100  i 200  1  |  300 400 T I M E (hours)  Fig. 87 Curve fit monosize fraction  1 leach  1  500  |  600  RESULTS AND  100  200  300 T I M E  400  D I S C U S S I O N / 198  500  (hours)  Fig. 88 Curve fit monosize fraction 2 leach  600  RESULTS AND  Fig. 89 Curve fit monosize fraction 3 leach  DISCUSSION / 199  RESULTS  AND  DISCUSSION / 200  33.8 micrometers  1°0  200  300 TIME  400  500  (hours)  Fig. 90 Curve fit monosize fraction 4 leach  600  RESULTS  AND  DISCUSSION / 201  52.] micrometers *"  5  4  A A  2-i  A  1  0  0  200  300 TIME  400  500  (hours)  Fig. 91 Curve fit monosize fraction 5 leach  600  RESULTS  AND  DISCUSSION  true size •micrometers  u <u  4H  a  ^fraction 1  2.36  •  fraction 2  5.94  O fraction 3  2.23  •  fraction A  2.67  •  fraction 5  4.85  B o u o  a  w  H  04100  200  300  TIME  Fig. 92 Curve  400  500  (hours)  fit for monosize leaching  600  / 202"  R E S U L T S AND are  growing in conventional mode is needed to start controlled-redox  controlled-redox  leaching  metal release from copper  this  mineral  are  Lawrence  80-98.4% with obtained  an  cells  results  concentrates  subject.  the  the  release. The  -400mesh  we  DISCUSSION /  use  only  matrix  from  al  this  work with  (1985)  average of 89.7%  iron  as  is sequential with  comparable  et  ferrous  in the those  reported  for 9  controlled-redox  of the copper  with  source.  an  literature  leaching of available on  extractions  of In  between  this  average of 76.1%  (Lawrence et al, 1985)  vs  271-353mg/L h  work  for  concentrates. Copper extraction rates are also comparable 150-650mg/L h 350mg/L h)  The  participating in  different concentrates.  comparable extractions 6 0 - i 0 0 %  leaching. In  energy  silver  203  two  (average  (average 303mg/l h) of  this work.  5.8.  COMPARISON  CONTROLLED Table of  10  mesh  processes.  concentrate  want  it can  faster  than  be  seen  the  as  from  column  we  and  LEACHING  VS  controlled-redox leaching  monosize  leaches  extraction in these  it, because have  used  the  controlled-redox  leaching  process;  effects of the  be long  have been eliminated. For  using batch  both  leaches  it changes throughout several measures  10. Comparing overall rates as  same conclusion can  in which the process  that  all the  of copper  to measure  standard  mesh leaching. The  controlled-redox  rate  in Table  -400  3  well  experiment. Therefore  reported them 2  as  of the  where you  of the  rate and  copper  STANDARD  LEACHING  Measurement  depends on  column  REDOX  OF  includes selected resuts from both standard  -400  duration  SUMMARY  leaching  much  faster  the  of this  represented  by  process  releases  in the  case  drawn for a -400  of  mesh leach  lag times associated  with  the  the  when  we  monosize leaches  R E S U L T S AND compare order  the two  processes  also in column  2 the rates seem to be of the  of magnitude for comparable particle  in column  4  with  the exception of the  controlled-redox leach leaching  however  rates are  the  size. For  fraction  significantly  standard  leaches  DISCUSSION /  maximum nm  of 4.85  higher  were  the  than  conducted  were divided by  the  same  rates shown  in diameter all the  those  of the  at  pulp  a  107g/L whereas the controlled-redox were done at 200g/L. To this pulp density difference the maximum  204  standard  density  of  try to correct for  rates of copper extraction in column  initial copper concentration as  4  supplied in the chalcopyrite.  These specific copper release rates are shown in column 5 in h"-*-. For the  -400  mesh concentrate the controlled-redox process copper release rates are significantly greater  than  those  of the  there does not appear to be  standard any  leaching process.  For  the  monosize  leaches  significant difference between the standard  and  the controlled-redox process in terms of specific copper release rate.  From  Table  10  can  be  seen  in column  copper using the controlled-redox process material than two  out  when using the standard  of five  extraction  in the  of  the  particle  controlled-redox  6  are  that  the  percentage  extraction of  always greater for the -400  mesh  leaching process. In the monosize leaches  sizes  tested showed  process  for the  greater  other  three  percentage the  values  copper were  more or less the same.  More cell mass measured by in  the  standard  column 7 of Table  leach 10.  TOC,  compared  was to  generated  the  per gram of copper solubilized  controlled-redox  leaches  as  shown  in  RESULTS AND  DISCUSSION / 205  Table 10 Copper Extraction Rates for C-R and Standard Leaching  1  2 g Cu/L h  3  4  5  g Cu/L h  g Cu/L h  h"  CONVENTIONAL LEACHING  3.24 9.74 2.78 2.47 2.50 -400m 400m :  0.034 0.011 0.022 0.033 0.056 0.013 0.012  0.035 0.011 0.038 0.039 0.072 0.013 0.012  6  7  % C u ext  mg TOC/g Cu  0.00275 0.00105 0.00206 0.00228 0.00575 0.00079 0.00130  33.0 36.0 30.6 47.2 37.0 29.0 34.0  4.1 35.1 6.3 12.3 18.4 39.6 43.5  0.00258 0.00274 0.00429 0.00303 0.00227 0.00527 0.00599 0.00686 0.00548  33.5 62.0 91.6 44.2 36.4 60.0 72.0 72.7 100.0  3.6 0.9 3.2 0.9 0.6 0.5 0.1 1.9 3.3  1  1 .  1  0.076 0.029 0.057 0.063 0.159 0.022 0.036  REDOX--CONTROLLED LEACHING \ 2.36 5.94 2.23 2.67 4.85 -400m -400m -400m -400m  0.043 0.044 0.082 0.053 0.036 0.093 0.100 0.140 0.188  0.064 0.077 0.150 0.043 0.079 0.216 0.140 0.197 0.251  0.133 0.141 0.221 0.156 0.117 0.271 0.308 0.353 0.282  1. 2.  true particle size am. overall copper extraction rate from time zero to the end of the leach.  3.  after lag phase copper extraction rate from the start of copper solubilization  4. 5. 6. 7.  to the end of the leach. maximum copper extraction rate extraction has maximum change.  from  the time  specific copper extraction rate from the maximum copper content of chalcopyrite used in the leach. percentage copper extraction. 7 cell yield.  interval rate  where divided  copper by the  CHAPTER 6. CONCLUSIONS  6.1. LEACHING UNDER STANDARD CONDITIONS  For  the  conditions  concentrate  in  this  is negligible. Inoculation  medium with  Copper and  and  work  of the  chemical  leaching  of  chalcopyrite  suspension of chalcopyrite in nutrient  T. ferrooxidans resulted in significant leaching of copper and iron.  iron were leached  concentration copper  employed  as  measured by  iron  simultaneously TOC  concentration.  and  analysis, was  This  is not  an  in T.  ferrooxidans  with an  increase in  increase  associated  in conflict  with  the  idea  that  T.  ferrooxidans directly acts on the chalcopyrite lattice.  T. ferrooxidans preferentially oxidizes the sulfide-sulfur portion of chalcopyrite over ferrous sulfate in solution.  Electron  microscope  particle surface, leaching, copper  the  jarosite  were  photos  low  show  presence  deposits (ca.  on  30%)  T. ferrooxidans attached  of pits the  in the  particle  probably  surface,  and  surfaces.  because  of  to  the  after  some  Percentage  passivation  concentrate hours  extractions  of  the  of of  particles'  surfaces by jarosite deposits.  Maximum  specific  0.006h"l. Copper 4-43mg of TOC/g  copper  extraction  extractions  ranged  rates  were . of  from  29  Cu.  206  to  the  47%.  order Cell  of  yield  0.00lh"^ ranged  to  from  CONCLUSIONS / Particle size as  a  function of leach time followed  particle kinetic model provided  the  start of active bioleaching. This standard  leaching of ZnS  6.2.  LEACHING  UNDER  The  pretreatment  phase  and  also  tested  shrinking  measured  using  at  the  literature data for  performed well in this test.  CONTROLLED  REDOX  CONDITIONS  of controlled redox bioleaching  directions outlined in Section may  predictions of a  initial particle diameter was  model was  concentrate  the  207  2.5.4. must be  is a  sensitive one.  followed precisely. If not  not work, ie. not generate elemental sulfur or produce an  The  the process  elevated  level of  copper extraction.  Inoculation  of the  pretreated  suspension of chalcopyrite in nutrient medium  with  T. ferrooxidans is necessary for the controlled redox bioleach. Absence of bacteria resulted in an insignificant amount of copper solubilization.  There  is  some  extracellular leaching  factor  organic  in  the  material,  liquid  phase  maintained  environment, which has  to be  of  on  present  the  inoculum,  chalcopyrite in order  in  probably a  some  conventional  for the controlled redox  bioleach to work.  The  controlled  redox  above 180g/L but was  The  controlled redox  process  was  successfully  demonstrated  at  pulp  densities  not successful at a. pulp density of 107g/L.  process  was  successfully demonstrated  using  unfractionated,  CONCLUSIONS / -400  mesh concentrate,  median  particle  diameters  fraction having an overcome by  or using "monosize" fractions of concentrate larger  than  4  um.  It failed  initial, median diameter of 2.6  changing  the  ratio of Ag,  Cu  um.  , or  +  to  leach  208  having initial, a  "monosize"  This failure could not  thiosulfate to  particle  be  surface  area.  No  silver  after  was  observed  on  pretreatment. Silver  the was  particle  surface; using  observed  on  the  EDXA,  surface  either before  after several  or  hours  of  leaching.  Copper  extractions  (44-100%) were  leaching (29-47%). Maximum  higher  than  those  obtained  controlled redox process requires a  reactions between significant  cell  growth  mineral  and  following  oxidation contrasts markedly with standard  Elemental sulfur is generated as process. controlled  The  cells'  redox  sulfide  an  the  sulfur  end  oxidation  oxidizing  enzymes.  in this lag phase. The inoculation  product of the  probably  as  a  postulated absence  result of  of  sulfide  seems due  to  controlled redox bioleach  to the  mechanism of wetting  This  of the  leaching.  system  potential conditions,  with proteins involved either in the  participates in any  reactants  immediately  of  long lag time (300-400 h) for bacterial  clear if T. ferrooxidans the  order  solubilized.  1  growth. It is not  standard  specific copper extraction rates were in the  0.002 to 0.007b- . Yields of cells were 0.12-3.32mg TOC/g Cu  The  under  inhibition  results  be  inactive  silver of the in  the  under  the  ions interacting sulfur or appearance  with of  CONCLUSIONS elemental sulfur in the medium Additional obtained  support  for this  that  view  in the form  conditions. In the former the T O C  20mg/L while in the latter it was  in  comes  unattacked  of low bacterial yields  loss of sulfide oxidation capabilities by T. the microorganism  undergoing  a  leaching  high rate. Oxidation  rate  was  around  ferrooxidans in the medium results  lag phase.  induction of the iron oxidizing system grow, the metal  concentration  160mg/L.  During  solubilization takes place at a low rate with very  by  by the bacterial cells.  in the controlled redox potential leaching compared to the yields obtained  under the standard  The  remains  / 209  the lag phase  little S° being  metal  formed. When  of the cells occurs and the cells start to  increases  several  fold  and S ° is produced  at a  of ferrous iron would tend to shift the equilibrium expressed  equation 30 so that more copper goes into solution as CuSO^.  Prediction  of particle  size as a function  kinetic model was erratic and not very of that  model, that  the remainder  of leach  accurate  time by a shrinking  particle  probably because an assumption  of the concentrate  particle  retains the same  composition as the particle gets smaller, was violated by the release of iron but no  copper early in the leach.  CHAPTER 7. RECOMENDATIONS FOR  1.  Investigate  inocula maintained  on  FUTURE STUDIES  chalcopyrite, ferrous  iron, or  ferrous  sulfide in terms of their ability to reduce the lag time. Check protein patterns sulfide  and  investigate sulfur metabolism in more detail. Inhibition of  oxidation  band  could  disappeared  ferrous 5 OK  be  at  when  the  cells  were  sulfide to chalcopyrite  proteins  conditions  synthesis  level  transferred  if the from  50K  protein  chalcopyrite  or  under controlled redox conditions. If the  were still present after culturing under controlled redox  then inhibition could be postulated  to occur at the  substrate  utilization level. 2.  Since lag time would not be during the  transitions from one  effectiveness  of  important other than at the operating  the  controlled  start up  or  condition to another, demonstrate redox  bioleaching  process  using  continuous culture. 3.  Isolate  and  characterise  component of the  the  inoculum  factor  transferred  that is necessary  with  for the  the  liquid  operation  of the  controlled redox bioleach process. 4.  Test  for  the  process by 5.  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July  (1987)  Mobile  their  possible  Biohydrometallurgy 12-16.  significance for International  APPENDIX I CHEMICAL ANALYSES C O P P E R AND  A  l g sample  of concentrate  was  placed  IRON  in a  200mL  beaker and  bromine water were added, after 5 minutes, the beaker was plate and The  9mL  of aqua  beaker was  Upon  addition  boiled for a made  up  regia  covered with a watch  of 50mL further  to  parts of HNO3,  ( 3  lOOmL  30  of distilled  6 parts  20mL  with  distilled  HC1), were added.  water. Copper  boiled to dryness.  of HC1  minutes; then the mixture was  the sample  filtered  and  of  transferred to a hot  glass and the sample  water and  2—3mL  iron  and  were  was  the filtrate  measured  by  atomic absorption spectrophotometry.  SULFUR  The  above  digestion  step  was  carried  ANALYSIS  out as  described  concentrate up to the point where the sample was of distilled water the sample the  concentrate. The  At  this  HC1  point  until  chloride  a  brown  was  sample  of  dried. After addition of 50  ml  filtered. The residue was brought to pH  precipitate  formed, then  were  added, then  which  sample was  was  minutes. Total  then  sulfur  warm boiled  5%  BaCl2  for one  ashed at 820°C  was  the insoluble part of  the sample  added  hour, then for 30  0.5g  1.8 with concentrated  that precipitate dissapeared. At that point 2mL  completed. The paper  filtrate  was  for a  of  was  minutes and  precipitation on ash free at 420°C  is the weight of the dry barium sulfate  0.1373.  232  acidified  with  hydroxylammonium  until  filtered  NH4OH.  in grams  was filter  for 20 times  F E R R O U S / F E R R I C IRON  Ferric leaching  iron  was  determined  medium. The  at pH  and  using a  formed with the  10/il sample  lmL  measured by  3.5  (0.05M N H A c 4  vortex mixer. The  sulfosalicylic acid was  +  0.5M  233  from  the  ANALYSES  of  clear  supernatant  micropipette and  of sulfosalicylic acid was  glacial acetic acid:water) and  acid buffer mixed  a  sample was  plastic vial to which acetic acid (1:10  in  /  added, followed by  3.0mL of ammonium CH3COOH). The  optical density read at 530  transfered  nm,  of the  to  1 mL  a of  acetate—acetic vial was  closed  ferric iron complex  after 3 minutes.  APPENDIX II MIXED POPULATION AND CULTURE CONDITIONS INOCULUM  In  all batch  inoculum drawn  experiments,  seeding of the culture  of living cells growing  from  suspension medium  a  used  6—8  AGE  day  was  made  in the exponential phase. Inoculum  old stock  as inoculum  medium  culture  growing  in a  with  was  shake  flask.  medium  salts, products  and metabolic products  from  have shown that the age of the inoculum of the lag phase. Older cells its metabolic  concentration  rates  cell growth. Bailey  and  products  and OUis  (1976)  has a strong influence on the length  result in longer lag phases  upward  or deinhibition  The  of leaching  such as copper, iron and sulfuric acid in solution, as well as secondary  gears  typically  contained all the ingredients present in the culture  ie. the mineral concentrate and 9K  like jarosites  an  while the population  in response  to induction  derepression  as  toxic  by  and  higher  nutrient  growth—inhibiting  substances diffuse out of the older cells into the fresh medium.  For  microbial  phases  leaching  were found  of the chalcopyrite  when  Fig. 8 with an inoculum days,  for this  inoculum  second  inoculum  age exceeded  age of 6 days  case  concentrate in this  study  8 days. For example, compare  and Fig. 6 with inoculum  the lag phase  longer lag  age of 24  is considerably longer. The effect of  age was neglibible when it was maintained between 6—8days.  Fig. 93 presents the metal leaching profdes in a stock culture typically  used as  inoculum. The The  profiles indicate that copper and iron were being leached out of the mineral. measured  copper  concentration  was  234  always  almost  twice  the  iron  Fig. 93  Metal leaching in stock culture  / 236  lO-i  • • •  \  •  to  O «  6  X  H  Q Z, <  X  X X  w O H  O O  2H  0  1 SERIAL  2  3  TRANSFER  Fig. 94 Effect of serial transfer  4  NUMBER  on metal solubilization  / concentration  in  solution  indicating  that  some  of  the  solubilized  237  iron  was  precipitating. This  indicates  that  a  typical inoculum  will  contain  besides the  active  cells  and  soluble metals, some iron precipitates. The  metal  indicated  extraction  by  Fig. 94  levels in the  stock culture  that  the  presents  transfers. Each pair of data represents that the culture was  longer  periods  (subculturing),  of  the  and  Cu  time  culture  would  less constant  as  for serial  1 flask after 8 days of growth, showing  released  were  more or  metal concentrations measured  stable when a strict subculturing  relative amounts of Fe  If  are  schedule was  followed.  The  are more or less constant.  allowed  between  changes  preferentially leach  of  iron from  culture  medium  chalcopyrite  over  copper, this resulted in higher concentrations of iron measured in solution at all times. Fig. 95 with  a  mixture  measured leach, the  presents copper  the  first  of  in solution cell-carbon 100  sample  16  and  surpassed curve  iron 8  the  indicates  measured  day copper that  of this culture  rapid growth. This revealed  was  observed  sample  of  The  concentration a  very  from  an  iron the  inoculated  concentration onset  of  rapid growth occurred  under the  the  during  results of Fig. 8  microscope to search  ie. a  active  culture  with  the  this culture  was  sent  to  for  the  ferrooxidans that could account for this  examination of slurry samples and  that is Gram—negative, motile cells of the A  cultures.  experiment  expected.  presence of microorganisms other than T.  only  old  in an  hours, which is unexpected in view of the  long lag phase was A  24,  and  normal  Gram—stained  morphology  normal size and Dr.  P.  Norris  of  preparations,  T. ferrooxidans,  shape.  (University  of  Warwick,  / 238  •  C  O  F» F» E  R  TIME  (hours)  Fig. 95 Mixed culture effects  / 239 England) to investigate the possibility patterns  using  ferrooxidans. indicated  of a mixed  gel electrophoresis, and comparing  Preliminary  results obtained  examining  it to standard  by Dr. Norris  a pure culture of T.  that this was  culture by  (personal  ferrooxidans  protein  patterns  of T.  communication)  But after  subsequent  cultivation by Dr. Norris it was revealed that in fact the culture was a mixture of T. ferrooxidans Leptosporillium ferrooxidans,  and another bacteria.  ferrooxidans (Kelly,  has  been  shown  1987) If this was  could explain the results obtained  to grow  the bacterium  in association present  with  T.  in our culture it  since this organism leaches pyrite but is unable  to oxidize sulfur. If L. ferrooxidans this  bacterium  producing  predominates in older cultures then, if a high concentration of were  introduced  into  a  new  medium  it would T.  the fast release of iron shown in fig. 95, while  still be undergoing a lag phase. Furthermore pyrite and could remain undetected even though its spiral form is very  L.  ferrooxidans  in the microscopic  attack  ferrooxidans attaches  pyrite would  firmly  to  examination of the culture  different from the rod shaped T.  ferrooxidans  . This population change was reflected in the characteristics of the medium, the color  of the leachate  resulting due  from  changed  simultaneous  from  copper  the normally  and iron  observed  solubilization  bright  blue—green  to a dull  green color  to a higher iron concentration and a thin layer of foam normally  the stable culture was absent.  present in  APPENDIX Standard  Table Time= 0.0 h Number of particles = 1029 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65 11.13  III  PARTICLE  SHRINKAGE  Leaching: Gibraltar  Concentrate  11. Monosize leach 2.58 nm  number 280 333 207 99 49 30 12 7  percent 27 32 20 10 5 3 1 1  MEAN: 2.98 MEDIAN: 3.24 S T A N D A R D D E V I A T I O N : 2.2544  Table Time= 65.83 h Number of particles = 1026 Mean diameter 0.27 0.82 1.37 1.91 2.46 3.01 3.55 4.10 4.65 5.20 5.74  12. Monosize leach 2.58 Jim  number  percent  326 262 163 110 55 36 24 11 13 8 6  32 26 16 11 5 4 2 1 1 1 1  MEAN: 1.29 MEDIAN: 1.2 S T A N D A R D DEVIATION: 1.2658  240  DATA  Table  13. Monosize leach 2.58 um  Time= 162.57 h Number of particles = 1335 Mean  diameter  0.27 0.82 1.37 1.91 2.46 3.01 3.55 4.10 4.65 5.20 5.74 6.29 6.84 7.38  number 364 299 201 156 100 61 43 31 19 16 8 11 7 7  percent 27 22 15 12 7 5 3 2  M E A N : 1.63 MEDIAN: 1.37 S T A N D A R D D E V I A T I O N : 1.6432  Controlled—Redox  Potential Leaching  Table 38. Monosize leach 2.58 um  Time=  0.0 h  Number of particles = 1096 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65  number 508 330 155 53 16 9 11  MEAN: 2.22 MEDIAN: 2.33 S T A N D A R D D E V I A T I O N : 2.1159  percent 46 30 14 5 1 1 1  / 242 Table 14. Monosize leach 2.58 Mm  Time= 261.31 h Number of particles = 1326 Mean diameter 0.27  0.82 1.37 1.91 2.46  number 649 445 153 47 18  percent 49 34 12 4 1  MEAN: 0.69 MEDIAN: 0.83 S T A N D A R D DEVIATION: 0.5237  <SETMARGINS,-  Table 39. Monosize leach 2.58 Mm  Time= 65.83 h Number of particles = 1868 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16  number 986 601 192 59 21 14  MEAN: 1.80 MEDIAN: 2.14 S T A N D A R D DEVIATION: 1.4169  percent 53 32 10 3 1 1  / Table  T i m e = 357.31 h N u m b e r of particles = M e a n diameter  15. Monosize leach 2.58 u-tn  1150  number  0.27 0.82 1.37 1.91 2.46 3.01 3.55  560 312 142 76 26 12 12  percent 49 27 12 7 2 1 1  M E A N : 0.80 M E D I A N : 0.82 S T A N D A R D D E V I A T I O N : 0.7142 Table 6 7 . Monosize leach 46.8  T i m e = 575.06 h N u m b e r of p a r t i c l e s = M e a n diameter 0.27 0.82 1.37 1.91 2.46 3.01 3.55  1007  number 655 216 66 . 24 11 11 6  M E A N : 0.60 M E D I A N : 0.67 S T A N D A R D D E V I A T I O N : 0.6536  percent 65 21 7 2 1 1 1  um  243  / 244  Table 16. Monosize leach 8.63 jun  Time= 0.0 h Number of particles = Mean diameter 1.45 4.34 7.23 10.12 13.01 15.90 18.79  1077  number 169 75 252 304 162 76 30  MEAN: 8.85 MEDIAN: 10.42 STANDARD DEVIATION: 4.6467  percent 16 7 23 28 15 7 3  / 245 Table 17. Monosize leach 8.63 um  Time= 95 h Number of particles = 1285 Mean diameter 1.45 4.34 7.23 10.12 13.01 15.90 18.79 21.68  number 109 180 399 336 148 65 22 17  MEAN: 8.70 MEDIAN: 9.747 STANDARD DEVIATION: 4.3836  percent 8 14 31 26 12 5 2 1  / 246 Table 18. Monosize leach 8.63 um Time= 191.75 h Number of particles = 1605 Mean diameter 1.45 4.34 7.23 10.12 13.01 15.90 18.79 21.68  number 434 194 314 354 187 81 24 10  MEAN: 7.39 MEDIAN: 8.675 STANDARD DEVIATION: 4.9781  percent 27 12 20 22 12 5 1 1  / 247 Table  19. Monosize leach 8.63 Mm  Time= 459.56 h Number of particles = 1355 Mean diameter 1.45 4.34 7.23 10.12 13.01 15.90 18.79 21.68  number 230 211 418 276 126 53 21 10  M E A N : 7.63 MEDIAN: 8.81 S T A N D A R D DEVIATION: 4.4765  . percent 17 16 31 20 9 4 2 1  / 248 Table 20. Monosize leach 8.63 um  Time= 555.22 h Number of particles = 1180 Mean diameter 1.45 4.34 7.23 10.12 13.01 15.90 18.79  number 202 157 320 265 142 70 11  M E A N : 7.87 MEDIAN: 9.15 S T A N D A R D DEVIATION: 4.4026  percent 17 13 27 22 12 6 1  / 249 Table 21. Monosize leach 14.3 um  Time= 48.08 Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65 11.13  1370  number 645 475 127 41 38 18 9 8  M E A N : 2.15 MEDIAN: 2.35 S T A N D A R D DEVIATION: 2.1022  percent 47 35 9 3 3 1 1 1  / 250 Table 22. Monosize leach 14.3  Time = 140.41 h Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16  1109  number 366 496 159 51 20 7  MEAN: 2.28 MEDIAN: 2.78 S T A N D A R D DEVIATION: 1.6646  percent 33 45 14 5 2 1  um  / 251 Table 23. Monosize leach 14.3 f i m  Time= 230.9 Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 11.13  1365  number 525 451 210 92 35 31 7  M E A N : 2.41 MEDIAN: 2.72 S T A N D A R D D E V I A T I O N : 1.9645  percent 38 33 15 7 3 2 1  / 252 Table 24. Monosize leach 14.3  Time= 325.23 h Number of particles = Mean diameter 0.74 2.23 3.71 5.20  1497  number 783 560 125 20  M E A N : 1.62 MEDIAN: 2.11 S T A N D A R D D E V I A T I O N : 1.0757  percent 52 37 8 1  um  / 253 Table 25. Monosize leach 14.3 nm  Time= 424.23 h Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65  1457  number 1003 263 92 43 23 11 8  MEAN: 1.61 M E D I A N : 1.81 S T A N D A R D D E V I A T I O N : 1.7896  percent 69 18 6 3 2 1 1  / 254 Table 26. Monosize leach  Time = 574.39 h Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65  2292  number 1327 630 182 75 35 15 14  M E A N : 1.76 MEDIAN: 2.02 S T A N D A R D D E V I A T I O N : 1.6517  percent  -  58 27 8 3 2 1 1  14.3 /xm  / 255 Table 27. Monosize leach 30.4  Time= 97.16 h Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16  1421  number 640 521 168 64 12 9  M E A N : 1.95 MEDIAN: 2.47 S T A N D A R D DEVIATION: 1.4298  percent 45 37 12 5 1 1  Mm  / 256 Table 28. Monosize leach 30.4 (im  Time= 196.15 Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16  2045  number 815 773 301 102 25 19  M E A N : 2.12 MEDIAN: 4.48 S T A N D A R D DEVIATION: 1.5196  percent 40 38 15 5 1 1  / 257 Table 29. Monosize leach 30.4  Time= 292.48 h Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16  1181  number 530 342 185 84 24 6  M E A N : 2.12 MEDIAN: 2.48 S T A N D A R D DEVIATION: 1.6136  percent 45 29 16 7 2 1  Mm  / 258 Table 30. Monosize leach 30.4  Time= 339.23 Number of particles = Mean diameter 0.74 2.23 3.71 5.20  1188  number 672 367 119 22  M E A N : 1.62 MEDIAN: 2.04 S T A N D A R D DEVIATION: 1.2307  percent 57 31 10 2  um  / 259 Table 31. Monosize leach 30.4 /zm  Time= 384.56 h Number of particles = 1254 Mean diameter 0.74 2.23 3.71 5.20  number 832 330 79 15  MEAN: 1.41 MEDIAN: 1.84 S T A N D A R D DEVIATION: 1.0831  percent 66 26 6 1  / 260 Table 32. Monosize leach 30.4  Time= 432.09 h Number of particles = Mean diameter 0.27 0.82 1.37 1.91 2.46  308  number 161 89 37 13 8  MEAN: 0.70 MEDIAN: 0.798 S T A N D A R D DEVIATION: 0.5684  percent 52 29 12 4 3  um  / 261 Table 33. Monosize leach 46.8 /nm  Time= 0 h Number of particles = Mean diameter 1.45 4.34 7.23 10.12 13.01 15.90 18.79  1605  number 740 435 234 94 57 25 9  MEAN: 4.41 MEDIAN: 4.87 S T A N D A R D D E V I A T I O N : 3.8522  percent 46 27 15 6 4 2 1  / 262 Table 34. Monosize leach 46.8  Time= 93.25 h Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65  1530  number 670 487 206 87 46 21 11  MEAN: 2.26 MEDIAN: 2.5 S T A N D A R D D E V I A T I O N : 1.9002  percent 44 32 13 6 3 1 1  um  / 263 Table  35. Monosize leach 46.8 AUTI  Time= 189.66 h Number of particles = 1082 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16  number 516 311 124 68 22 11  M E A N : 2.21 MEDIAN: 2.28 S T A N D A R D D E V I A T I O N " 2.0018  percent 48 29 11 6 2 1  / 264 Table 36. Monosize leach 46.8 (in>  Time = 285.23 h Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16  1369  number 654 447 162 60 26 10  M E A N : 1.98 M E D I A N 2.31 S T A N D A R D D E V I A T I O N : 1.5868  percent 48 33 12 4 2 1  Table 37. Monosize leach 46.8  Time= 382.73 h Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68  1433  number . 715 468 173 46 18  M E A N : 1.85 MEDIAN: 2.20 S T A N D A R D D E V I A T I O N : 1.4307  percent 50 33 12 3 1  v.  Table 40. Monosize leach 2.58 jim  Time= 162.57 h Number of particles = 1240 Mean diameter 0.74 2.23 3.71 5.20  number 689 412 106 17  M E A N : 1.59 MEDIAN: 2.04 S T A N D A R D D E V I A T I O N : 1.1371  percent 56 33 9 1  1  2  6  6  / 267 Table 41. Monosize leach 2.58 um  Time= 261.31 h Number of particles = 1281 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65  number 495 391 199 109 38 23 12  MEAN: 2.48 MEDIAN: 2.8 S T A N D A R D DEVIATION: 2.0223  percent 39 31 16 9 3 2 1  / 268 Table 42. Monosize leach 2.58 Mm  Time= 357.31 h Number of particles = Mean diameter 1.45 4.34 7.23 10.12  1623  number 1008 504 98 15  M E A N : 2.70 MEDIAN: 3.78 S T A N D A R D DEVIATION: 1.8846  percent 62 31 6 1  4  / 269 Table 43. Monosize leach 8.63  Time= 22.5 H Number of particles= 1216 Mean diameter 1.45 4.34 7.23 10.12 13.01 15.90  number 435 272 236 157 72 30  M E A N : 5.50 MEDIAN: 5.91 S T A N D A R D DEVIATION: 4.1294  percent 36 22 19 13 6 2  um  / 270 Table 44. Monosize leach 8.63 um  Time= 120.16 h Number of particles = 1181 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65 11.13 12.62  number 496 322 151 71 47 39 27 15 11  M E A N : 2.76 MEDIAN: 2.61 S T A N D A R D DEVIATION: 2.6549  percent 42 27 13 6 4 3 2 1 1  / 271 Table 45. Monosize leach 8.63 um  Time= 223.07 h Number of particles = 1120 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65 11.13  number 416 299 154 94 61 53 20 13  M E A N : 2.94 MEDIAN: 2.89 S T A N D A R D DEVIATION: 2.5878  percent 37 27 14 8 5 5 2 1  / 272 Table 46. Monosize leach 8.63  Time= 459.56 h Number of particles = 1164 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65 11.13 12.62  number 552 265 126 73 61 37 26 9 11  MEAN: 2.67 MEDIAN: 2.36 S T A N D A R D DEVIATION: 2.6755  percent 47 23 11 6 5 3 2 1 1  / 273 Table 47. Monosize leach 8.63 jum  Time= 444.82 h Number of particles = 1253 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16  number 556 371 182 80 35 16  MEAN: 2.20 MEDIAN: 2.476 S T A N D A R D DEVIATION: 1.7921  percent 44 30 15 6 3 1  / 274 Table 48. Monosize leach 8.63  Time= 535.98 h Number of particles = Mean diameter 0.27 0.82 1.37 1.91  1353  number 854 399 64 14  MEAN: 0.50 MEDIAN: 0.689 S T A N D A R D DEVIATION: 0.35531  percent 63 29 5 1  um  / 275 Table 49. Monosize leach 14.3 um  Time= 0 h Number of particles = Mean diameter 1.45 4.34 7.23 10.12 13.01 15.90 18.79 21.68  1074  number 603 211 82 72 53 23 16 10  MEAN: 4.50 MEDIAN: 4.03 S T A N D A R D D E V I A T I O N : 4.7390  percent 56 20 8 7 5 2 1 1  / 276 Table 50. Monosize leach 14.3 um  Time= 165.73 h Number of particles = 1337 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65 11.13 12.62 14.10  number 402 392 208 142 70 43 31 17 13 11  M E A N : 3.31 MEDIAN: 3.15 S T A N D A R D DEVIATION: 2.9836  percent 30 29 16 11 5 3 2 1 1 1  / 277 Table 51. Monosize leach 14.3 p.m  Time= 262.48 h Number of particles = 1198 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65 11.13 12.62 14.10  number 382 323 196 103 73 42 35 14 14 9  M E A N : 3.30 MEDIAN: 3.21 S T A N D A R D D E V I A T I O N : 2.9366  percent 32 27 16 9 6 4 3 1 1 1  / 278 Table 52. Monosize leach 14.3  Time= 333.73 Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65 11.13  1268  number 562 361 169 74 37 18 22 13  M E A N : 2.46 MEDIAN: 2.44 S T A N D A R D DEVIATION: 2.3702  percent 44 28 13 6 3 1 2 1  um  / 279 Table 53. Monosize leach 14.3 fim  Time= 435.48 h Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65 11.13  1256  number 670 403 82 34 29 10 11 7  M E A N : 1.91 MEDIAN: 2.14 S T A N D A R D DEVIATION: 1.9016  percent 53 32 7 3 2 1 1 1  / 280 Table 54. Monosize leach 14.3 ^im  Time= 479.31 h Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16  2850  number 1655 906 185 75 24 15  M E A N : 1.66 MEDIAN: 2.05 S T A N D A R D DEVIATION: 1.4152  percent 58 32 6 3 1 1  / 281 Table 55. Monosize leach 14.3 |im  Time= 575.30 Number of particles = 1951 Mean diameter 0.74 2.23 3.71 5.20  number 1202 626 101 19  M E A N : 1.45 MEDIAN: 1.94 S T A N D A R D D E V I A T I O N : 1.0360  percent 62 32 5 1  / 282 Table 56. Monosize leach 30.4 / i m  Time= 96.92 h Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65 11.13 12.62 14.10 15.59 17.07  452  number 187 98 66 40 14 10 9 8 7 3 4 5  MEAN: 3.18 MEDIAN: 2.90 S T A N D A R D DEVIATION: 3.4104  percent 41 22 15 9 3 2 2 2 2 1 1 1  / 283 Table 57. Monosize leach 30.4 um  Time= 195.91 h Number of particles = 1398 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65 11.13 12.62  number 541 424 187 98 59 34 14 19 8  M E A N : 2.34 MEDIAN: 2.38 S T A N D A R D D E V I A T I O N : 2.3159  percent 39 30 13 7 4 2 1 1 1  / 284 Table 58. Monosize leach 30.4 um  Time= 292.32 h Number of particles = 1174 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65 11.13  number 417 321 180 113 61 29 20 14  MEAN: 2.93 MEDIAN: 2.88 S T A N D A R D DEVIATION: 2.6003  percent 36 27 15 10 5 2 2 1  / 285 Table 59. Monosize leach 30.4 um  Time= 384.57 h Number of particles = 1071 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65 11.13 12.62  number 448 298 153 69 53 30 7 14 6  M E A N : 2.67 MEDIAN: 2.7 S T A N D A R D D E V I A T I O N : 2.4488  percent 42 28 14 6 5 3 1 1 1  / 286 Table 60. Monosize leach 30.4 nm  Time= 431.93 h Number of particles = 1311 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16  number 535 456 212 62 33 14  MEAN: 2.27 MEDIAN: 2.65 S T A N D A R D DEVIATION: 1.7919  percent 41 35 16 5 3 1  / 287 Table 61. Monosize leach 46.8 Mm  Time= 0 h Number of particles= 1036 Mean diameter 2.93 8.79 14.65 20.51 26.37 32.23 38.09 43.95 49.80 55.66 61.52  -  number 270 239 143 103 79 60 69 16 36 13 12  MEAN: 17.49 MEDIAN: 15.48 S T A N D A R D DEVIATION: 15.0303  percent 26 23 14 10 8 6 7 2 3 1 1  / 288 Table 62. Monosize leach 46.8 urn  Time = 98.58 h Number of particles= 1178 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65 11.13 12.62  number 536 320 121 68 46 25 17 9 6  M E A N : 2.73 MEDIAN: 2.34 S T A N D A R D D E V I A T I O N : 3.2553  percent 46 27 10 6 4 2 1 1 1  / 289 Table 63. Monosize leach 46.8 urn  Time= 190.24 h Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 11.13 14.10  931  number 502 231 104 39 15 15 9 5  MEAN: 2.11 MEDIAN: 2.12 S T A N D A R D DEVIATION: 2.3064  percent 54 25 11 4 2 2 1 1  / 290 Table 64. Monosize leach 46.8 /um  Time= 287.90 h Number of particles = 1077 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65  number 510 293 127 65 37 15 15  M E A N : 2.32 MEDIAN: 2.23 S T A N D A R D DEVIATION: 2.2480  percent 47 27 12 6 3 1 1  / 291 Table 65. Monosize leach 46.8 um  Time= 382.31 h Number of particles = 1144 Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65 11.13  number 557 295 134 59 36 20 14 15  MEAN: 2.37 MEDIAN: 2.23 S T A N D A R D DEVIATION: 2.4280  percent 49 26 12 5 3 2 1 1  / 292 Table 66. Monosize leach 46.8 um  Time= 478.81 Number of particles = Mean diameter 0.74 2.23 3.71 5.20 6.68 8.16 9.65  1188  number 821 203 78 34 25 9 9  MEAN: 1.64 MEDIAN: 1.82 S T A N D A R D D E V I A T I O N : 1.8227  percent 69 17 7 3 2 1 1  APPENDIX  4  PROGRAM  STANDARD  LEACHING  START ENTER DATA dp SEARCH FOR SIZE CLASS CALCULATE RATE FOR dp CALCULATE SHRINKING NEW dp  -NO INCREASE TIME  TEST dp IS NEW dp LESS THAN LOWER LIMIT OF CLASS  YES OISPLAY VALUE OF TIME ANO OP  STORE TIME  •NO  TEST TIME LARGER THAN TMAX  INITIALIZE TIME YES  CALCULATE AVERAGE PARTICLE SIZE CALCULATE ELAPSED TIME SINCE LEACH BEGAN STOP  Fig. 96  Program logical diagram for shrinking diameters  293  / 294 C C C C  T H I S P R O G R A M C A L C U L A T E S SHRINKING DIAMETERS F O R C O N V E N T I O N A L L E A C H I N G O F MONOSIZE PARTICLES AS A FUNCTION OF L E A C H I N G TIME  33 20 10 11 C C C C C  IMPLICIT REAL*4(A-H,0-Z) REAL*4EXP,PA,PB,PC,PD,PE READ(5,20) DPE,TMAX,DELT,F,C0,DP0, *DP1,DP2, DP3,DP4 FORMAT(9(D13.5,/),D13.5) WRITE(6,10) F0RMAT(1H1, 'PARTICLE C H A N G E S SIZE CLASS',/) WRITE(6,11) FORMAT(2X,'TIME',6X,'DIAMETER',3X,//) S E A R C H I N G F O R T H E SIZE C L A S S C O R R E S P O N D I N G T O T H E INITIAL D I A M E T E R A N D INITIALIZING T H E COUNTERS FOR TIME AND PARTICLE DIAMETER T T E 0 = 0.0 T T E 1 = 0.0 T T E 2 = 0.0 T T E 3 = 0.0 T T E 4 = 0.0 PA=0.0 PB = 0.0 PC = 0.0 PD = 0.0 P E = 0.0 T = 0.D0 T=T+DELT PA=DPE IF(DPE.GE.DPO.OR.DPE.GT.DP1)GO TO 50 PB = D P E IF(DPE.LE.DPl.AND.DPE.GT.DP2)GO TO 150 PC = D P E IF(DPE.LE.DP2.AND.DPE.GT.DP3)GO TO 250 PD = D P E IF(DPE.LE.DP3.AND.DPE.GT.DP4)GO TO 275 PE=DPE IF(DPE.LE.DP4)GO T O 300  C C C  CALCULATION  OF  P A R T I C L E SHRINKING  RATE  50 R = 0.01*(11.944*EXP(-0.32123*DPE)) DP = ((DPE**3.D0)-(T*R*(DPE**3.D0))/(F*C0))**0.3333D0 C C C C  THE  SHRINKING  PA = DP  R A T E IS E V A L U A T E D AS A F U N C T I O N THE PARTICLE DIAMETER  OF  77  51 100  150  78  151 101  250  79  251 102  IF(DP.LE.DPl)GO T O 51 T=T+DELT TTE0=T WRITE(7,77)TTE0,PA FORMAT(2X,F7.2,2X,F7.2) IF(TTE0.GT.TMAX-DELT)GO T O 1000 GO T O 50 WRITE(6,100)T,DP FORMAT(2X,F7.2,2X,F7.2) T = 0.0 T=T+DELT PB=PA R=0.01*(11.944*EXP(-0.32123*PA)) DP=((PA**3.D0)-(T*R*(PA**3.D0))/(F*C0))**0.3333D0 PB=DP IF(DP.LE.0.01)GO T O 500 IF(DP.LE.DP2) GO T O 151 T=T+DELT TTE1=T TT=TTE0+TTE1 WRITE(7,78)TT,PB FORMAT(2X,F7.2,2X,F7.2) I F ( T T E 0 + T T E l.GT.TMAX-DELT)GO T O 1000 IF(T.GT.TMAX-DELT)GO T O 1000 GO T O 150 WRITE(6,101)T,DP FORMAT(2X,F7.2,2X,F7.2) T=0.0 T=T+DELT PC=PB R=0.01*(11.944*EXP(-0.32123*PB)) DP=((PB**3.D0)-(T*R*(PB**3.DO))/(F*CO))**O.3333D0 PC=DP IF(DP.LE.0.01)GO T O 500 IF(DP.LE.DP3)GO T O 251 T=T+DELT TTE2=T T T = T T E 0 + T T E 1+TTE2 WRITE(7,79)TT,PC FORMAT(2X,F7.2,2X,F7.2) IF(TTE0+TTE1+TTE2.GT.TMAX-DELT)GO T O 1000 IF(T.GT.TMAX-DELT)GO T O 1000 GO T O 250 WRITE(6,102)T,DP FORMAT(2X,F7.2,2X,F7.2) T=0.0 T=T+DELT PD = PC  / 296  275 R = 0.01*(11.944*EXP(-0.32123*PQ) DP = ((PC**3.D0)-(T*R*(PC**3.D0))/(F*C0))**0.3333D0 PD = DP IF(DP.LE.0.01)GO T O 500 IF(DP.LE.DP4)GO T O 276 T = T + DELT TTE3=T TT = TTEO+TTE1 + TTE2+TTE3 WRITE(7,80)TT,PD 80 FORMAT(2X,F7.2,2X,F7.2) IF(TTE0 + T T E 1+TTE2+TTE3.GT.TMAX-DELT)GO T O 1000 IF(T.GT.TMAX-DELT)GO T O 1000 GO T O 275 276 WRITE(6,103)T,DP 103 FORMAT(2X,F7.2,2X,F7.2) T=0.0 T=T+DELT P E = PD 300 R=0.01*(11.944*(EXP(-0.32123*PD))) DP = ((PD**3.D0)-(T*R*(PD**3.D0))/(F*C0))**0.3333D0 P E = DP IF(DP.LE.0.01)GO T O 500 T=T+DELT TTE4=T TT=TTEO + TTE1 + T T E 2+TTE3+TTE 4 WRITE(7,81)TT,PE 81 FORMAT(2X,F7.2,2X,F7.2) I F ( T T E 0 + T T E 1 + T T E 2 + T T E 3 + TTE4.GT.TMAX-DELT)GO T O IF(T.GT.TMAX-DELT)GO T O 1000 GO T O 300 1000 C O N T I N U E C C C C  RECORDING T H E  P A R T I C L E SIZE A T T H E E N D D E L T A TIME INTERVAL  OF  1000  THE  500 WRITE(6,108) 108 F0RMAT(1H2,2X,' TIME', *2X,' DIAMETER',//) WRITE(6,109) T,DP 109 F0RMAT(2X,F7.2,6X,F13.5) C C C C  CALCULATION  OF  E L A P S E D TIME SINCE L E A C H  T T E = TTEO + T T E 1 + T T E 2 + T T E 3 + T T E 4 WRITE(6,110) 110 F0RMAT(1H2,2X,'LEACHING TIME',//) WRITE(6,111)TTE  BEGAN  Ill  FORMAT(3X,F7.2) IF (DP4.LE.0.01) GO GO T O 33 34 S T O P END  TO  34  APPENDIX 5 FORTRAN PROGRAM CONTROLLED REDOX  C C C C  THIS P R O G R A M C A L C U L A T E S S H R I N K I N G D I A M E T E R S FOR C O N T R O L L E D R E D O X L E A C H I N G O F M O N O S I Z E P A R T I C L E S AS A F U N C T I O N O F L E A C H I N G T I M E IMPLICIT REAL*4(A-H,0-Z) REAL*4EXP,PA PB,PC,PD,PE READ(5,20) DPE,TMAX,DELT,F,CO,DP0, *DPl,DP2, DP3.DP4 FORMAT(9(D13.5,/),D13.5) WRITE(6,10) F O R M A T Q H l , 'PARTICLE C H A N G E S SIZE CLASS',/) WRITE(6,11) FORMAT(2X,'TIME',6X 'DIAMETER',3X,//) )  33 20 10 11 C C C C C  )  T H E SHRINKING R A T E IS E V A L U A T E D A S A FUNCTION OF T H E PARTICLE DIAMETER TTEO = 0.0 T T E 1 = 0.0 T T E 2 = 0.0 T T E 3 = 0.0 T T E 4 = 0.0 PA=0.0 PB = 0.0 PC = 0.0 PD = 0.0 P E = 0.0 T=0.D0 T=T+DELT PA = DPE IF(DPE.GE.DP0.OR.DPE.GT.DPl)GO TO 50 PB=DPE IF(DPE.LE.DPl.AND.DPE.GT.DP2)GO T O 150 PC=DPE IF(DPE.LE.DP2.AND.DPE.GT.DP3)GO TO 250 PD = D P E IF(DPE.LE.DP3.AND.DPE.GT.DP4)GO T O 275 PE = DPE IF(DPE.LE.DP4)GO TO 300  C C  LEACHING  CALCULATION  OF  PARTICLE SHRINKAGE  C 50 R=0.022 DP = ((DPE**3.D0)-(T*R*(DPE**3.D0))/(F*C0))**0.3333D0  298  77  51 100  150  78  151 101  250  79  251 102  PA = DP IF(DP.LE.DP1)G0 T O 51 T=T+DELT TTE0=T WRITE(7J7)TTE0,PA FORMAT(2X,F7.2,2X,F7.2) IF(TTE0.GT.TMAX-DELT)GO T O 1000 G O T O 50 WRITE(6,100)T,DP FORMAT(2X,F7.2,2X,F7.2) T=0.0 T=T+DELT PB = P A R=0.0519 D P = ((PA**3.D0)-(T*R*(PA**3.D0))/(F*C0))**O.3333DO PB=DP IF(DP.LE.0.01)GO T O 500 IF(DP.LE.DP2) GO T O 151 T=T+DELT TTEl=T TT=TTEO+TTE 1 WRITE(7,78)TT,PB FORMAT(2X,F7.2,2X,F7.2) IF(TTE0+TTEl.GT.TMAX-DELT)GO T O 1000 IF(T.GT.TMAX-DELT)GO T O 1000 G O T O 150 WRITE(6,101)T,DP FORMAT(2X,F7.2,2X,F7.2) T=0.0 T=T+DELT PC = PB R=0.06955 DP = ((PB**3.D0)-(T*R*(PB**3.DO))/(F*C0))**O.3333D0 PC=DP IF(DP.LE.0.01)GO T O 500 IF(DP.LE.DP3)GO T O 251 T=T+DELT TTE2=T TT=TTEO+TTE1+TTE2 WRITE(7,79)TT,PC FORMAT(2X,F7.2,2X,F7.2) IF(TTE0 + T T E 1+TTE2.GT.TMAX-DELT)GO T O 1000 IF(T.GT.TMAX-DELT)GO T O 1000 G O T O 250 WRITE(6,102)T,DP FORMAT(2X,F7.2,2X,F7.2) T = 0.0 T=T+DELT  / 300  PD = PC 275 R=0.0326 DP = ((PC**3.D0)-(T*R*(PC**3.D0))/(F*CO))**0.3333DO PD = DP IF(DP.LE.0.01)GO TO 500 IF(DP.LE.DP4)GO T O 276 T=T+DELT TTE3=T T T = T T E O + T T E 1 + TTE2 + TTE3 WRITE(7,80)TT,PD 80 FORMAT(2X,F7.2,2X,F7.2) IF(TTEO+TTE1+TTE2+TTE3.GT.TMAX-DELT)GO T O 1000 IF(T.GT.TMAX-DELT)GO T O 1000 GO T O 275 276 WRITE(6,103)T,DP 103 FORMAT(2X,F7.2,2X,F7.2) T=0.0 T=T+DELT P E = PD 300 R=0.0439 D P = ((PD**3.D0)-(T*R*(PD**3.D0))/(F*C0))**0.3333D0 P E = DP IF(DP.LE.0.01)GO T O 500 T=T+DELT TTE4=T T T = T T E O + T T E 1+TTE2 + T T E 3 + T T E 4 WRITE(7,81)TT,PE 81 FORMAT(2X,F7.2,2X,F7.2) I F ( T T E O + T T E 1 + T T E 2 + T T E 3 + TTE4.GT.TMAX-DELT)GO T O IF(T.GT.TMAX-DELT)GO T O 1000 GO T O 300 1000 C O N T I N U E 500 WRITE(6,108) 108 F0RMAT(1H2,2X,' TIME', *2X,' DIAMETER',//) WRITE(6,109) T,DP 109 FORMAT(2X,F7.2,6X,F13.5) C C C C  CALCULATION  OF  ELAPSED  TIME SINCE L E A C H  TTE=TTEO + T T E 1 + TTE 2 + TTE3 + TTE 4 WRITE(6,110) 110 F0RMAT(1H2,2X,'LEACHING TIME',//) WRITE(6,111)TTE 111 F0RMAT(3X,F7.2) IF (DP4.LE.0.01) GO TO 34 GO T O 33  1000  BEGAN  34 S T O P END  APPENDIX 6 GENERAL LEACHING DATA Table 68  TIME Hours 0.00 24.75 72.08 115.91 167.57 217.57 260.98  pH 2.00 1.98 2.20 2.40 2.12 2.35 2.14  Experiment  1 as received, st, 6 day inoculum  COPPER g/L 0.0 1.4 1.7 1.7 1.8 1.8 1.9  T-IRON g/L 0.0 1.2 1.4 1.4 1.6 1.6 1.6  TOC ppm 0 0 0 0 31 26 57  TEMP °C 34 34 38 35 34 32 35  SIZE Um  3.14 2.97 3.06 3.35 2.52 2.47 2.59  Table 69  Experiment 2 as received, st, 11 day inoculum  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  TEMP o  SIZE Um  0.00 49.16 96.16 145.16 192.82 243.32 288.15 338.48 385.56  1.82 2.42 2.21 2.37 2.20 2.80 2.30 2.20 2.56  0.3 0.5 0.8 0.9 0.8 0.9 1.0 1.0 1.0  0.4 0.7 0.9 1.0 1.3 1.5 2.0 2.6 2.5  39 38 47 23 5 13 27 19 20  35 29 28 28 45 36 38 40 36  2.46 2.62 3.03 2.58 3.23 2.54 1.72 3.06 4.03  302  c  / 303 Table 70 Experiment 3 ballmiiled, st  TIME Hours  PH  COPPER g/L  T-IRON g/L  TOC ppm  TEMP °C  SIZE Mm  21.50 69.66 118.16 168.99 215.10 261.46 312.04 360.12 407.20 452.20 524.61 572.81  2.12 2.05 1.67 1.42 1.30 1.30 1.10 1.10 1.30 1.90 1.15 1.00  0.6 1.2 1.5 2.0 2.2 2.5 3.0 3.5 4.3 5.1 6.8 7.7  0.7 0.7 1.0 2.3 3.0 3.8 4.6 5.1 5.9 6.6 8.4 9.8  19 20 38 47 123 80 80 155 130 250 307 230  31 26 26 28 30 28 34 33 39 35 35 32  2.69 3.73 3.07 3.50 4.69 3.34 7.76 4.20  Table 71  Experiment 4 ballmiiled, c-r  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  TEMP °C  23.00 68.00 117.41 162.91 212.41 261.32 310.98 361.98 408.59 456.22  2.04 1.84 2.09 2.08 2.02 1.90 1.87 1.94 1.93 1.72  1.5 2.4 2.8 2.4 3.5 4.8 4.8 5.8 5.8 6.0  0.7 1.0 1.8 1.8 2.2 2.6 2.6 3.0 3.0 3.6  23 15 14 23 24 22  0.8 2.4 3.7 4.4 4.4 4.4 4.4 4.4 4.4 4.4  35 35 32 33 39 32 34 30 34 34  Table 72 Experiment 5 ballmiiled, c-r  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  SIZE Mm  0 48.16 87.49 135.99 184.49 226.49  1.92 2.15 2.16 2.16 1.96 1.87  0 10.6 23.1 48.4 55.2 64.3  0 3.0 6.2 3.3 5.4 4.5  9 12 22 51 57 81  0 3.3 16.8 28.5 30.0 31.6  6.50 6.86 2.98 2.34 2.77  TIME Hours  TEMP °C  OXYGEN ppm  0 48.16 87.49 135.99 184.49 226.49  35 33 28 28 28 28  2.3 2.0 1.6 2.8 3.4  / 305 Table 73 Experiment 6 38um, c-r, low pulp  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  SIZE (xm  0 39.16 90.66 135.57 186.98 233.31 278.81 326.14 374.89 426.39 493.14 542.30 595.80 642.80  1.86 2.06 2.09 2.10 2.15 2.07 2.13 2.12 2.07 2.10 2.15 1.51 1.89 2.16  0 2.2 4.8 5.0 4.7 4.6 4.4 5.8 7.3 8.3 9.3 9.1 11.9 10.8  0 1.0 2.4 2.4 2.5 2.4 2.7 3.3 3.5 4.5 5.0 5.6 6.8 7.0  20 30 93 42 52 22 78 30 37 49 53 82 81 66  0 1.6 4.3 4.3 4.3 4.9 5.5 6.3 7.1 8.0 9.2 11.5 11.6 12.0  3.20 2.66 2.37 2.89 3.02 2.00 2.81 2.58 6.25 2.36 4.82 3.90 2.05 1.98  TIME Hours  Eh mV  TEMP °c  OXYGEN ppm  0 39.16 90.66 135.57 186.98 233.31 278.81 326.14 374.89 426.39 493.14 542.30 595.80 642.80  355 340 400 380 340 380 395 365 370 395 390 375 360 350  35 32 27 27 28 28 25 29 32 30 32 30 28 26  5.0 5.8 5.4 3.2 3.6 3.6 5.7 5.3 4.4 2.7 4.2 6.0 4.6 6.4  Table 74 Experiment 7 28um, st  TIME Hours  PH  COPPER g/L  T-IRON g/L  TOC ppm  SIZE um  0 44.50 99.50 165.00 214.25 265.50 310.91 357.91 404.75  1.98 2.06 1.78 1.64 2.09 1.64 1.64 1.61 1.62  0 3.4 11.5 12.5 13.6 14.0 14.0 14.0 14.2  0 4.0 8.9 7.8 9.8 9.8 11.3 10.8 10.3  50 53 438 596 155 97 137 122 153  2.73 2.52 2.08 2.83 1.18 1.07 0.95 1.09 1.28  TIME Hours  Eh mV  TEMP °C  OXYGEN ppm  0 44.5 99.5 165.00 214.25 265.50 310.91 357.91 404.75  315 355 530 485 520 665 680 660 675  38 38 40 36 39 36 36 37 36  6.0 5.4  6.2 4.6 6.4  / 307 Table 75 Experiment 8 ballmilled, c-r, low pulp  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  44.5 93.34 140.34 187.92  1.75 1.68 1.70 1.79  0.3 3.0 10.2  0.5 0.6 3.3 3.2  0 0 20 309  0.5 0.5 0.5 0.5  TIME Hours  Eh mV  TEMP °C  OXYGEN ppm  44.5 93.34 140.34 187.92  355 350 405 465  30 30 32 31  7.2 7.0 3.4 3.0  Table 76 Experiment 9 ballmiiled, c--r, low pulp  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  SIZE /xm  0 45.75 91.0 138.33 189.99 237.24 288.49 330.15  2.0 2.1 2.0 1.9 1.8 1.4 1.4 1.4  0 4.6 14.4 21.4 35.9 8.9 11.1 11.4  0 3.0 0.1 T 1.7 0.5 1.0 1.3  66 240 309  3.4 3.94  TIME Hours  Eh mV  TEMP °C  OXYGEN ppm  0 45.5 91.0 138.33 189.99 237.24 288.49  360 420 565 575 570 445 420  38 32 31 31 31 36 33  6.2 4.0 4.7 5.8 4.6 7.2 6.6  5>296 509 256 175 192  / 309 Table 77 Experiment 10 ballmilled, c-r, low pulp  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 20 65.6 109.6 153.6 179.4 252.4 297.6  2.0 2.2 1.6 1.4 1.4 1.4 1.4 1.4  0 0.6 7.2 6.7 11.5 11.8 14.5 15.7  0 0.6 4.7 6.6 7.7 7.6 7.5 6.8  41 64 123 262 402 444 530 487  0 1.2 2.3 2.3 2.3 2.5 2.5 2.5  TIME Hours  Eh mV  TEMP °C  OXYGEN ppm  35 34 35 35 34 33 34 33  3.4 4.0 3.8 3.8 3.5 3.8 3.0  0 20.0 65.6 109.6 153.6 179.4 252.4 297.6  395 405 435 445 460 615  / 310 Table 78 Experiment  11 ballmiiled, c-r, low pulp  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 43.0 96.75 138.5 193.0 235.0 289.25 336.25 382.75 431.25  2.0 1.4 1.4 1.3 1.3 1.3 1.2 1.2 1.2 1.2  0 2.2 7.1 8.4 10.5 11.7 17.6 24.4 25.1 21.9  0 1.6 4.9 5.7 8.5 7.6 7.7 9.7 9.6 8.0  15 113 268 281 293 284 339 557 595 512  0 0 0 0 0 0 0 0 0 0  TIME Hours  Eh mV  TEMP °C  OXYGEN ppm  0 43.0 96.75 138.5 193.0 235.0 289.25 336.25 382.75 431.25  355 395 400 410 420 430 445 460 505 545  24 37 36 35 35 34 34 35 35 35  7.8 6.3 6.0 6.6 5.6 3.6  / 311 Table 79 Experiment  ballmilled, c-r, low pulp  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  Eh mV  TEMP °C  0 55.16 100.41 146.91 195.41 242.82  2.0 2.2 2.1 2.0 2.0 2.0  0 0 0.7 1.1 1.7 2.9  0 1.3 1.5 2.1 2.6 3.0  30 34 57 33 41 76  0 3.35 3.75 3.75 3.75 3.75  325 335 365 360 365 360  25 32 35 36 38 36  Table 80 Experiment 13 ballmiiled, c-r, low pulp  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 45.91 93.24 141.57 209.20 285.48 334.56 382.39 429.98  1.8 1.5 2.0 1.4 1.8 1.0 1.0 1.0 1.0  0 1.4 2.4 3.9 5.7 7.6 6.8 8.7 8.7  0 1.5 4.6 6.0 7.3 8.7 8.8 8.7 9.0  18 62 156 114 198 120 176 153 164  0 7.0 7.0 17.6 17.6 17.6 17.6 17.6 17.6  TIME Hours  Eh mV  TEMP °C  0 45.91 93.24 141.57 209.20 285.48 334.56 382.39 429.98  325 375 375 405 400 400 410 410 415  32 38 38 34 25 26 26 26 26  Table 81 Experiment 14 ballmiiled, c-r, low pulp  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 46.3 96.38 193.79 264.95  2.0 1.7 1.8 1.6 1.6  0 0 1.6 9.0 13.2  0 1.7 3.8 7.9 9.5  23 16 131 339 357  0 0 0 0 0  TIME Hours  Eh mV  TEMP °C  0 46.3 96.38 193.79 264.95  320 360 380 390 400  31 34 34 34 34  Table 82 Experiment 15 ballmilled, c-r, low pulp  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 45.5 93.5 143.75 185.75  2.0 2.4 2.0 1.6 1.4  0 3.7 14.2 13.5 12.1  0 2.7 3.4 7.0 7.9  20 24 98 251 389  0 5.1 9.9 9.9 9.9  TIME Hours  Eh mV  TEMP  0 45.5 93.5 143.75 185.75  325 390 390 395 385  33 34 33 33 33  °  C  Table 83 Experiment 16 ballmilled, c-r, low pulp  TIME Hours  PH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 46.5 92.83 116.83 139.49  2.0 1.7 1.8 1.8 1.8  0 1.6 5.3 7.4 6.9  0 1.8 4.6 6.2 6.9  34 178 172 223 225  0 0 0 0 0  TIME Hours  Eh mV  TEMP °C  0 46.5 92,83 116.83 139.49  330 375 380 385 390  31 36 35 35 35  / 316 Table 84 Experiment 17 ballmiiled, st  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  EH mv  TEMP °C  0 44.5 117.25 163.83 211.99 256.49 308.49 356.15 404.15 452.23 500.48 548.48 620.14 644.72 693.63 739.46 789.46 839.46 891.96  1.99 2.56 2.64 2.56 2.17 2.00 1.96 1.93 1.80 1.99 1.86 1.81 1.86 1.90 2.02 1.91 1.94 1.97 1.94  0 0.5 1.4 2.2 2.6 2.5 2.8 3.2 3.8 4.8 6.6 7.8 8.8 7.7 8.5 9.2 8.6 7.4 8.6  0 0.2 0 0.2 0 0.3 0.4 1.0 1.7 2.7 3.0 3.8 4.8 4.7 4.6 4.7 5.2 4.3 4.3  24 36 60 100 72 91 121 110 140 141 169 220 344 403 300 313  470 500 500 515 550 580 590 590 600 550 500 480 520 510 510 505 495 480 500  35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35  313 306  / 317 Table 85 Experiment 18 as received, c-r,low pulp  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  TEMP °C  EH mV  0 48.0 94.58 142.74 187.24 239.24 286.90 334.90 382.98 431.23 479.23 550.89 575.47 624.38 670.21  1.93 1.82 2.14 1.85 1.93 1.98 1.82 1.69 1.58 1.55 1.56 1.57 1.58 1.55 1.45  0 2.0 1.2 1.4 4.2 8.2 17.4 23.0 22.2 23.2 23.7 27.1 28.4 32.0 34.0  0 0.4 0.9 2.0 3.6 8.6 9.6 11.4 13.7 16.0 16.0 17.6 16.0 17.0 18.0  16 11 12 67 20 292 727 738 686 714 666 723 754 745 715  35 35 34 36 35 32 32 31 30 31 31 30 30 32 31  385 365 375 370 380 410 455 590 610 630 650 660 660 650 630  / 318 Table 86 Experiment 19 ballmilled, c-r, low pulp  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 43.75 93.5 142.25  2.05 1.64 1.67 1.70  0 0.6 0.8 0.8  0.5 1.1 2.3 2.9  0 7 7 0  0 0 0 0  TIME Hours  Eh mV  TEMP °C  OXYGEN ppm  0 43.75 93.5 142.25  360 385 370 385  29 35 35 35  2.2 2.4  Table 87 Experiment 20 ballmiiled, c-r, low pulp  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 46.5 89.25 136.92 187.75 234.08 285.99 334.82 380.98 427.48  2.0 2.12 2.09 2.15 2.29 2.09 2.15 2.24 2.14 2.06  0 0.3 2.2 3.2 6.7 23.2 11.3 19.0 14.8 16.5  4.4 1.2 2.3 4.2 5.3 6.9 9.2 9.9 8.3 8.7  2 0 0 0 0 0 7 0 0 8  0 1.1 3.7 7.9 12.5 17.8 22.5 25.8 29.4 32.2  TIME Hours  Eh mV  TEMP °C  0 46.5 89.25 136.92 187.75 234.08 285.99 334.82 380.98 427.48  345 385 410 395 415 415 395 415 420 420  35 35 35 35 35 35 35 35 35 35  / Table 88 E x p e r i m e n t 21 ballmilled, c-r,  low  pulp  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 45.75 96.75 192.74 241.32 287.48 335.64 387.30 431.38  2.32 2.30 2.07 2.13 2.19 2.04 2.09 1.79 2.08 2.10  0 0.7 1.1 3.1 1.7 2.0 2.1 1.4 1.2 0  0.3 0.9 1.8 2.9 3.1 3.4 3.9 4.0 4.5 4.9  0 0 0 0 0 0 0 0 0 0  0 0.8 3.0 3.5 4.1 5.2 5.2 5.7 5.7 6.6  TIME Hours  Eh mV  TEMP °C  OXYGEN ppm  0 45.75 96.75 144.66 192.74 241.32 287.48 335.64 387.30 431.38  315 400 370 365 370 370 370 370 380 375  31 35 35 35 35 35 35 35 35 35  0.2 1.4 3.2 3.3  144.66  320  Table 89 Experiment 22 ballmiiled, st, freeze dried  TIME Hours  P  H  COPPER g/L  T-IRON g/L  TOC ppm 3 74 64 216  0 47.5 96.16 142.24  2.50 2.04 2.06 2.03  1.5 5.8 8.5 9.4  0.7 4.2 6.1 7.0  TIME Hours  Eh mV  TEMP °C  OXYGEN ppm  0 47.5 96.16 142.24  335 360 375 385  36 35 35 35  4.7  / 322 Table 90 Experiment 23 ballmiiled, c-r  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 43.33 96.16 142.57 188.98 236.56 286.47 335.05 381.05 430.30 483.21 535.87 583.37 620.20 677.86 725.86  2.08 2.22 2.14 2.13 2.22 2.11 2.25 2.32 2.51 2.41 2.09 2.08 2.13 2.10 2.17 2.14  0 0.7 2.2 2.8 1.7 4.0 10.4 10.8 13.6 13.0 12.6 15.7 6.3 10.1 20.2 20.0  0.9 2.2 3.7 5.0 5.6 6.8 8.1 7.6 5.7 5.4 6.4 8.2 7.6 9.0 8.8 9.6  0 0 0 0 0 0 0 0 0 0 0 0 4 1 0 9  0 1.3 5.7 11.1 15.0 22.7 28.1 32.9 35.4 38.8 43.9 48.2 51.5 54.2 56.8 59.8  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  TEMP °C  0 43.3 96.16 142.57 188.98 236.56 286.47 335.05 381.05 430.30 483.21 535.8.7 583.37 630.20 677.86 • 725.86  300 355 360 370 370 380 380 385 385 395 400 400 400 405 405 410  1.2 2.3 3.5 5.8 6.6 8.1 7.8 7.9 5.9 6.2 7.8 10.3 8.2 9.5 10.0 9.5  0 0.2 0.3 0.7 0.9 1.0 1.2 1.9 1.2 1.2 1.3 3.4 2.1 2.2 2.6 3.8  35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35  Table 91 Experiment  TIME Hours  P  H  24 ballmilled, st, inoculum age  COPPER g/L  T-IRON g/L  TOC p  p  m  0 46.6 94.32 142.32 192.57 235.57 283.15  2.08 2.50 2.39 2.25 2.28 2.16 1.81  0 0.1 0.8 4.4 6.2 7.3 13.8  1.2 1.3 2.2 32 4.2 4.9 4.4  0 0 0 3 18 108 115  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  TEMP °C  0 46.6 94.32 142.32 192.57 235.57 283.15  380 350 365 390 405 420 535  0.7 1.2 2.1 2.7 3.4 3.5 0  0.5 0.1 0.2 0.4 0.8 1.4 4.4  35 35 35 35 35 35 34  / 324 Table 92 Experiment 25 ballmiiled, c-r, aeration  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 25.25 68.25 115.83 167.25 214.0 262.25 308.3 359.7 405.4  2.10 2.13 2.23 2.23 2.28 2.24 2.26 2.16 2.15 2.26  0 1.4 0 15.4 15.0 21.2 25.4 26.7 28.5 26.3  1.5 2.1 2.8 5.6 9.0 10.5 11.4 11.0 11.6 9.4  0 0 0 0 0 5 18 70 12 2  0 0.2 1.9 11.2 19.4 28.7 32.9 38.9 42.1 43.8  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  TEMP °C  0 25.25 68.25 115.83 167.25 214.0 262.25 308.3 359.7 405.4  355 360 380 390 390 395 400 395 395  1.1 1.9 2.6 4.9 7.8 9.2 9.8 9.0 9.4 7.8  0.4 0.1 0.2 0.7 1.1 1.3 1.6 2.0 1.6 1.6  35 35 34 35 35 35 35 35 34 35  Table 93 Experiment  26 ballmilled, st, inoculum age  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  0 45.25 92.0 140.25  2.01 1.84 1-90 1.95  0 3.0 6.2 8.1  0.8 3.9 5.6  73  0 24 86 285  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  TEMP °C  0 45.25 92.0 140-25  410 380 400 420  0.8 3.5 4.8 5.5  0.1 0.4 0.8 1.8  35 34 35 35  / 326  Table 94 Experiment 27 ballmiiled, c-r, aeration  TIME Hours  PH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 22.33 68.99 117.19 163.19  2.02 2.09 1.97 2.08 2.02  0 0 1.8 7.5 10.3  1.1 1.0 2.9 5.5 6.4  7 0 12 175 63  0 0 0 0 0  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  TEMP °C  0 22.33 68.99 117.19 163.19  315 370 385 395 415  1.0 0.9 2.5 4.6 5.1  0.1 0.1 0.4 0.9 1.3  35 35 35 35 35  Table 95 Experiment 28 ballmilled, c-r, aeration  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 45.75 89.75 139.66  2.05 1.84 1.95 1.96  0 10.3 12.0 15.0  1.0 1.1 2.7 4.8  0 0 0 24  0 0 0 0  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  0 45.75 89.75 139.66  320 370 380 385  0.8 1.1 2.4 4.2  0.2 0 0.3 0.6  Table 96 Experiment 29 9 K iron, st  TIME Hours  pH  T-IRON g/L  TOC ppm  2.66 18.83 65.33 115.74 163.57 210.98  1-98 2.03 2.12 2.22 2.26 2.18  7.9 7.9 7.3 6.3 5.0 4.5  0 12 0 0 0 0  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  TEMP °C  2.66 18.83 65.33 115.74 163.57 210.98  335 355 390 420 590 570  7.2 7.5 6.2 4.0 0.1 0  0.6 0.4 1.0 2.2 4.8 4.5  35 35 35 35 35 35  Table 97 Experiment 30 ballmilled, c-r, aeration  TIME Hours 2.66 18.33 65.33 115.74 163.57 210.98 . 260.31 306.31 355.56 400.31  pH  2.17 2.10 2.30 2.12 2.07 2.06 2.12 2.14 • 2.22 2.10  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 0 0 0 3.1 17.8 23.5 29.7 37.4 40.0  1.9 2.1 2.8 4.0 6.8 13.0 10.0 12.2 15.2 15.2  0 0 0 0 0 0 0 2 5 0  0 0 0.6 3.8 11.7 27.4 38.8 49.1 56.6 56.6  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  TEMP °C  2.66 18.33 65.33 115.74 163.57 210.98 260.31 306.31 355.56 400.31  315 340 365 370 385 400 410 425 450 525  1.7 1.9 2.4 3.6 5.8 11.0 7.7 7.2 4.2 0  0.1 0.2 0.4 0.4 1.0 1.9 2.3 4.9 11.0 15.2  27 32 35 35 35 35 35 35 35 35  / 330 Table 98 Experiment  31 c-r, solid free inculum  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 48.33 94.66 143.66 188.33 235.99 287.15  2.12 1.90 2.09 2.07 2.10 2.07 1.98  0 0.5 0 0.2 2.0 2.5 1.4  1.6 1.6 1.8 3.3 5.1 5.5 5.6  0 0 0 78 94 0 0  0 0 0 0 0 0 0  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  0 48.3 94.66 143.66 188.33 235.99 287.15  320 365 365 385 380 380 390  1.4 1.5 1.7 2.9 4.5 4.9 5.0  0.2 0.1 0.1 0.4 0.6 0.6 0.6  Table 99 Experiment 32 c-r, solid free inoculum  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 48.33 94.66 143.66 188.33 235.99 287.15  2.25 2.01 2.10 2.10 2.18 2.09 2.01  0 0 0 0.5 3.9 5.0 9.5  1.3 1.6 1.8 1.7 5.6 7.0 7.8  0 0 0 87 190 213 0  0 0 0 1.9 1.9 1.9 1.9  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  0 48.33 94.66 143.66 188.33 235.99 287.15  315 360 360 380 395 400 400  1.2 1.5 1.7 1.6 4.7 5.9 6.5  0.1 0.1 0.1 0.1 0.9 1.1 1.3  / 332 Table 100 Experiment 33 9K iron, cell composition  TIME Hours  pH  T-IRON g/L  TOC ppm  0 22.3 71.3 116.3 167.3  2.04 1.99 2.10 2.13 2.13  7.6 7.9 7.6 9.1 7.4  7 12 21  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  TEMP °C  0 22.3 71.3 116.3 167.3  340 370 390 410 440  7.2 7.4 6.6 6.9 3.5  0.3 0.5 1.0 2.2 3.9  35 35 35 35  Table 101 Experiment 34 c-r, high aeration  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 43.16 94.49 142.24 192.32 261.98 307.81  2.32 1.99 2.06 2.15 2.11 2.12 2.06  0 0 0 0 0.7 2.8 3.0  1.1 1.9 2.6 2.7 4.2 4.6 6.4  3 21 0 0 0 0 0  0 0.1 0.1 0.2 0.3 0.3 0.4  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  TEMP °C  0 43.16 94.49 142.24 192.32 261.98 307.81  305 350 360 375 375 380 380  1.1 1.8 2.3 2.5 3.8 4.3 5.7  0 0.1 0.3 0.2 0.4 0.4 0.6  35 35 35 35 35 35 35  Table 102 Experiment  35 c-r, w.o. inoculum  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 17.66 68.99 116.74 166.82 236.48 282.31  2.20 2.07 2.24 2.37 2.16 2.28 2.29  0 0 0 0 0 0 0  1.4 2.0 2.0 2.6 3.3 3.9 3.0  0 0 0 0 0 0 0  0 1.9 2.3 2.7 4.3 4.6 4.6  TIME Hours  Eh mV  TEMP °C  FERROUS g/L  FERRIC g/L  0 17.66 68.99 116.74 166.82 236.42 282.31  310 350 355 355 355 360 360  35 35 35 35 35 35 35  1.4 1.8 1.8 2.5 3.0 3.5 2.9  0 0.1 0.2 0.1 0.3 0.4 0.1  / 335 Table 103 Experiment 36 c-r, solids inoculum  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0.25 47.25 94.66 140.49  2.09 1.83 1.93 1.99  0 1.8 4.7 4.3  1.5 1.7 3.5 4.3  0 0 0 0  0 0 0 0  TIME Hours  Eh mV  TEMP °C  FERROUS g/L  FERRIC g/L  0.25 47.25 94.66 140-49  320 370 380 380  35 35 35 35  1.4 1.5 3.1 3.8  0.1 0.2 0.4 0.5  / 336 Table 104 Experiment  37 c-r, liquid supernatant inoculum  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0.25 47.25 94.66 140.49  2.25 2.02 2.12 2.05  0 1.8 0 0  1.8 1.7 1.3 1.8  0 0 0 0  0 0 0 0  TIME Hours  Eh mV  TEMP °C  FERROUS g/L  FERRIC g/L  0.25 47.25 94.66 140.49  310 360 370 370  35 35 35 35  1.7 1.5 1.2 1.6  0.1 0.2 0.1 0.2  / 337 Table 105 Experiment 38 2.58 um, c-r  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 20.83 65.83 119.49 162.57 210.48 261.31 310.31 357.31  2.25 1.83 2.22 2.10 2.13 2.16 2.27 1.99 1.81  0 0.8 1.3 1.1 3.2 9.6 9.1 13.6 15.7  1.7 1.9 1.6 1.6 3.4 6.8 9.1 7.8 10.0  0 0 0 0 0 2 16 11 56  0 0 0.2 0.6 0.6 0.6 1.5 1.5 1.5  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  MEAN um  0 20.83 65.83 119.49 162.57 210.48 261.31 310.31 357.31  315 360 355 365 360 375 385 390 390  1.6 1.6 1.6 1.4 3.1 5.9 7.6 6.2 8.0  0.1 0.2 0.0 0.3 0.3 0.9 1.5 1.5 2.0  1.98 1.84 1.61 2.01 2.33  SIZE  / 338 Table  106 Experiment 39 2.58 Mm, st  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC PPm  TEMP °C  0 20.83 65.83 119.49 162.57 210.48 261.31 310.31 357.31  2.00 1.85 1.88 2.07 2.26 2.02 2.01 1.80 1.56  0 0.6 4.0 5.7 7.2 7.5 9.1 8.6 6.7  2.0 2.6 4.6 7.3 8.2 10.6 8.8 8.7 8.5  0 0 0 15 0 14 38 0 8  35 35 35 36 33 35 35 35 35  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  5 0 % SIZE Mm  0 20.83 65.83 119.49 162.57 210.48 261.31 310.31 357.31  340 350 360 380 385 400 415 530 540  1.9 2.4 4.3 6.2 7.2 8.3 6.3 3.1 1.5  0.0 0.2 0.3 1.1 1.1 2.3 2.5 5.6 7.0  2.50 0.94 1.12 0.56 0.57  / 339 Table  107 Experiment 40 46.8 um, c-r  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 50.58 98.58 145.83 190.24 236.74 287.90 335.15 382.31 430.31 478.81 526.06 575.06  2.31 1.97 2.26 2.30 2.22 2.12 2.19 2.05 2.21 2.20 2.07 2.28 2.17  0 0 0 0 0 0 0 4.7 8.4 10.4 16.1 18.9 15.0  0.6 0.5 0.6 1.3 1.6 2.4 3.8 6.3 7.8 13.0 10.0 9.1 6.9  0 01 0 0 0 0 0 0 0 0 6 12  0 0 0.2 1.1 1.9 3.3 5.6 12.3 21.7 27.7 31.5 32.2 33.9  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  TEMP °C  50% um  0 50.58 98.58 145.83 190.24 236.74 287.90 335.15 382.31 430.31 478.81 526.06 575.06  295 350 350 350 350 350 350 360 370 385 390 390 390  0.3 0.3 0.6 1.2 1.6 2.2 3.5 5.6 6.6 11.1 8.8 8.0 6.0  0.3 0.2 0.0 0.1 0.0 0.2 0.3 0.7 1.0 1.9 1.3 1.2 1.0  35 35 35 35 35 35 35 24 35 35 35 35 35  SIZE  12.5 4.93 4.56 3.34 2.53 1.55 1.83  / 340 Table  108 Experiment 41 46.8 Mm, st  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  50% Mm  0 50.58 98.58 145.83 190.24 236.74 287.90 335.15 382.31 430.31 478.81  2.14 2.04 2.00 2.16 2.26 2.12 1.75 1.54 1.46 1.60 1.55  0 0.7 1.1 4.2 6.4 8.1 9.5 10.4 10.1 17.0 14.0  1.5 2.0 3.5 5.4 7.1 7.1 6.7 9.3 11.0 10.0 9.4  0 0 0 0 0 0 41 211 377 338 310  1.68  TIME Hours  Eh mV  TEMP °C  FERROUS g/L  FERRIC g/L  0 50.58 98.58 145.83 190.24 236.74 287.90 335.15 382.31 430.31 478.81  335 330 355 375 390 400 535 560 580 555 550  35 35 34 35 35 34 35 35 35 32 35  1.3 2.0 3.2 4.9 6.0 5.6 0.6 0.8 0.4 0.2 0.6  0.2 0.2 0.3 0.5 1.2 1.5 6.1 8.5 10.6 10.0 8.8  1.53 1.44 1.24 1.38 1.23  / 341 Table  109 Experiment 42 ballmiiled, c-r  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 44.33 92.74 139.07 189.57 237.98 285.23 332.23 382.73 426.73  2.35 2.17 2.21 2.07 1.94 2.18 2.17 2.30 2.04 2.16  0 0 0 0 0 7.5 18.2 31.0 31.0 28.3  0.5 1.3 1.7 1.9 3.0 4.8 10.6 12.2 12.2 14.1  0  0 0 1.1 2.4 6.8 15.4 27.35 38.65  TIME Hours  Eh mV  TEMP °C  FERROUS g/L  FERRIC g/L  50% Mm  0 44.33 92.74 139.07 189.57 237.98 285.23 332.23 382.73 426.73  300 355 355 360 375 385 395 400 410 410  35 35 35 35 35 35 35 35 35 35  0.4 0.8 1.3 1.6 2.7 4.0 8.8 9.8 8.8 10.3  0.1 0.4 0.4 0.3 0.4 0.7 1.9 2.4 3.3 3.8  7.01  0 0 0 49.5 51.6  3.39 1.95 2.21 1.31 1.77  / 342 Table  110 Experiment 43 46.8 um, t s  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  50% um  0 44.50 93.25 139.25 189.66 237.99 285.23 332.23 382.73  2.18 1.96 2.35 1.79 2.01 1.88 1.66 1.69 1.64  0 0.7 1.0 4.7 8.7 16.4 16.7 18.8 17.0  1.5 1.6 2.2 5.0 9.9 8.7 10.5 12.6 11.4  0 0 0 2 32 209 255 345 313  3.28  TIME Hours  Eh mV  TEMP °C  FERROUS g/L  FERRIC g/L  0 44.56 93.25 139.25 189.66 237.99 285.23 332.23 382.73  365 350 335 380 415 550 585 635 630  35 35 35 35 35 35 35 35 35  1.4 1.4 2.1 4.4 6.9 0.2 0.4 0.3 0.0  0.1 0.2 0.1 0.6 2.9 8.5 10.0 12.3 11.4  1.79 1.59 1.57 1.48  / 343 Table 111 Experiment 44 30.4 um, c-r  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  1.0 50.92 96.92 145.08 195.91 244.57 292.32 339.07 384.57 431.93  2.46 2.16 2.19 2.18 2.15 2.02 2.25 2.21 2.19 2.11  0 0 0 0 0.8 7.7 15.2 18.7 21.3 22.8  0.8 1.2 1.5 2.6 3.7 7.4 11.8 10.0 10.5 10.6  0 0 0 0 0 0 0 0 5 20  0 0.4 1.1 2.2 5.1 15.9 28.6 35.4 38.0 40.0  TIME Hours  Eh mV  TEMP °C  FERROUS G/L  FERRIC G/L  50% Um  1.0 50.92 96.92 145.08 195.91 244.57 292.32 339.07 384.57 431.93  305 355 355 360 365 385 395 400 390 395  35 35 35 34 35 35 35 35 35, 35  0.7 1.0 1.4 2.1 3.4 6.5 9.8 8.4 8.4 8.2  0.3 0.2 0.1 0.4 0.4 1.0 2.0 1.6 2.1 2.4  32.29 2.03 2.03 2.24 1.97 1.92  i  / 344 Table 112 Experiment 45 30.4Mm, st  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  SIZE Mm  0 51.80 97.16 145.24 196.15 244.73 292.48 339.23 384.56 432.09  2.03 3.31 2.81 1.74 1.84 2.17 1.63 1.82 1.80 1.86  0 1.0 1.7 3.8 7.0 9.6 10.1 11.9 13.1 12.8  2.3 2.5 3.4 7.0 6.5 8.4 8.8 10.2 11.0 9.4  0 0 0 6 30 102 134 122 141 161  32.29  TIME Hours  Eh mV  TEMP °C  FERROUS g/L  FERRIC g/L  0 51.80 97.16 145.24 196.15 244.73 292.48 339.23 384.56 432.09  350 350 340 360 390 530 590 600 610 600  35 32 34 34 34 33 34 35 34 34  2.0 2.4 3.1 6.2 5.3 0.4 0.2 0.2 0.0 0.2  0.3 0.0 0.3 0.7 1.3 7.9 8.7 10. 11. 9.3  1.67 1.87 1.71 1.31 1.13 1.0  / 345 Table 113 Experiment 46 14.3  um, c-r  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  SIZE um  0 21.66 71.82 119.73 165.73 210.98 262.48 333.73 380.98 425.48 479.31 524.97 575.30  2.20 1.83 2.37 2.20 2.38 1.85 2.32 2.13 2.16 2.19 2.14 2.34  0 0 0 0 0 0 0 9.3 19.7 24.8 33.3 42.0 47.1  1.0 0.8 1.4 1.4 1.5 2.7 3.6 9.1 4.4 3.3 4.1 7.3  0 0 0 0 0 0 0 6 32 23 62 110 149  0 0 0.6 1.2 1.8 4.0 5.5 18.2 23.7 32.6 42.0 46.1 46.1  2.58  TIME Hours  Eh mV  TEMP °C  FERROUS g/L  FERRIC g/L  0 21.66 71.82 119.73 165.73 210.98 262.48 333.73 380.98 425.48 479.31 524.97 575.30  310 350 380 355 350 355 365 390 395 410 425 430 435  35 35 35 35 35 35 35 35 35 35 35 35 35  0.8 0.5 1.2 1.1 1.2 2.5 2.5 6.3 3.8 2.8 2.8 2.3  0.1 0.3 0.2 0.3 0.3 0.2 1.0 2.9 0.6 0.6 1.3 5.0 3.9  1.99 1.42 1.21 1.37 1.68 1.21  / 346 Table 114 Experiment 47 14.3 izm, st  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  SIZE Mm  48.08 93.75 140.41 185.49 230.90 281.23 325.23 376.23 424.23 472.98 574.39 616.23  2.48 3.05 2.56 1.85 1.56 1.65 1.35 1.55 1.85 1.65 1.51 1.52  0 0.3 0.0 1.1 3.8 5.7 7.3 8.4 7.7 7.2 7.9 8.4  1.0 1.6 7.4 2.2 4.6 6.2 8.2 9.1 11.4 13.3 13.7 13.7  10 10 11 5 18 17 15 42 37 52 53 37  1.61  TIME Hours  Eh mV  TEMP °C  FERROUS g/L  FERRIC g/L  48.08 93.75 140.41 185.49 230.90 281.23 325.23 376.23 424.23 472.98 574.39 616.23  355 340 335 350 370 385 415 485 600 660 670 680  33 35 35 35 35 35 35 35 35 35 35 35  0.7 1.1 7.4 2.0 4.2 5.3 6.1 1.1 0.0 0.4 0.0 0.0  0.3 0,4 0.0 0.3 0.4 1.0 2.1 8.1 11.4 12.9 13.7 13.7  2.05 1.98 1.41 1.07 1.28  / 347 Table 115 Experiment 48 8.63 /nm, c-r  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC PPm  ACID mL  50% /nm  22.5 72.16 120.16 171.07 223.07 269.32 316.82 364.82 444.82 486.65 535.98 605.31 652.31 700.81 748.81 796.31 844.47  2.56 1.85 2.40 1.95 2.11 2.20 2.11 1.96 2.10 2.02 1.81 2.13 2.20 2.17 2.07 2.16 2.15  0 0 0 0.8 2.2 5.2 4.3 5.0 6.4 12.3 17.5 19.8 23.8 30.3 31.9 30.5 37.1  0.8 1.8 1.6 2.2 3.5 5.0 6.4 7.6 10.6 11.4 10.5 4.6 4.2 2.4 2.1 1.7 1.9  0 0 0 0 2 8 10 2 3 19 31 73 116 71 75 180 180  0.6 0.9 1.3 1.7 2.0 3.2 3.3 3.3 3.35 3.35 3.35 4.65 9.75 14.15 16.55 16.75 17.0  4.68  TIME Hours  Eh mV  TEMP °C  FERROUS g/L  FERRIC g/L  22.5 72.16 120.16 171.07 223.07 269.32 316.82 364.82 444.82 486.85 535.98 605.31 652.31 700.81 748.81 796.31 844.47  345 365 355 360 380 375 375 390 400 415 425 425 440 475 475 470 435  35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35  0.7 1.3 1.3 2.0 3.0 4.2 5.6 6.5 7.8 8.5 6.8 3.1 1.9 0.5 0.5 0.4 1.1  0 0.5 0.3 0.2 0.5 0.8 0.8 1.1 2.9 2.9 3.7 1.5 2.2 2.0 1.6 1.3 0.7  7.03 2.96 2.19 4.45 2.89 2.21  1.24  Table 116 Experiment 49 8.63 Mm, st  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  0 44 48 92.97 240.43 288.76 336.16 432.32  1.90 1.66 2.01 2.00 1.94 1.45 1.66 1.37  0.4 0.8 0 1.5 3.0 4.0 3.9 4.2  1.9 2.0 1.9 1.2 4.1 6.8 6.5 9.0  3 8 2 0 0 0 19 8  TIME Hours  Eh mV  TEMP °C  FERROUS g/L  FERRIC g/L  0 44 48 92.97 240.73 288.76 336.16 432.32  345 370 415 385 420 685 655 685  35 35 35 35 35 35 35 35  0.8 1.8 1.4 2.7 3.1 0.2 0 0  1.0 0.2 0.5 0.4 0.9 6.7 6.5 9.0  SIZE Mm  8.33 9.07 7.37 7.40  Table  117 Experiment 49 8.63 um, st  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  0.0 44.80 48.14 92.30 240.31 280.81 336.14  2.00 1.96 1.98 2.05 2.11 2.18 1.37  0 1.1 0.6 2.7 4.5 6.5 4.0  1.0 2.2 1.1 2.7 4.1 5.7 8.7  0 22 0 0 0 31 38  TIME Hours  Eh mV  TEMP °C  0 44.80 48.14 92.30 240.31 280.81 336.14  340 370 350 405 400 405 680  35 35 35 35 35 35 35  SIZE Mm  8.15 6.03 8.29 8.27  / 350 Table 118 Experiment T2 2L tank, c-r  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 48.16 94.74 142.90 191.56 238.64 287.64 337.00  2.21 2.17 1.99 2.16 2.20 2.47 2.43 2.26  0 2.0 2.3 5.7 22.9 31.1 40.4 40.4  1.6 2.5 5.3 10.3 10.5 7.8 4.4 4.2  0 3 7 10 33 20 . 54 78  0 15 53 133 193 245 275 292.5  TIME Hours  Eh mV  TEMP °C  SULPHUR %  FERROUS g/L  FERRIC g/L  0 48.16 94.74 142.90 191.56 238.64 287.64 337.00  315 390 390 410 430 450 465 515  35 35 35 35 35 35 35 35  0 0 0 0.29 1.33 1.75 1.20 1.23  1.5 1.9 3.7 6.9 5.2 2.4 0.8 0.3  0.1 0.6 1.6 3.5 5.3 5.3 3.6 3.9  / 351 Table  TIME  pH  Hours  119 Experiment T3 2L tank, c-  COPPER  T-IRON  TOC  ACID  so  g/L  g/L  ppm  mL  g/L  12 9 31 183 80 70 130 196 161 150 166 143 151 132 117 143 64 76  0 18 65 178 252.5 375 435 440 445 445 450 452.5 452.5 457.5 457.5 460 460 460  0 0 0 6.44 7.34 19.45 21.03 13.72 14.16 13.42  FERROUS  FERRIC  0.58 47.58 92.91 138.41 166.41 216.41 264.41 312.41 357.66 411.16 482.16 528.58 573.32 627.32 672.98 718.64 763.64 814.97  1.98 2.05 2.10 2.18 2.23 2.14 2.04 2.23 1.89 1.95 1.94 1.83 1.87 1.81 1.93 2.01 2.08 2.05  0 0 3.6 16.5 25.8 38.4 51.3 58.9 47.0 57.7 43.4 46.0 47.5 43.1 45.8 42.2 44.3 40.6  2.7 4.7 5.6 7.6 7.4 10.0 15.2 15.8 14.9 17.5 15.2 17.4 13.7 15.8 16.9 16.9 17.4 14.5  TIME  Eh  Hours  mV  TEMP °C  g/L  0.58 47.58 92.91 138.41 166.41 216.41 264.41 312.41 357.66 411.16 482.16 528.58 573.32 627.32 672.98 718.64 763.64 814.97  330 385 390 440 450 500 580 350 590 590 610 610 610 610 610 600 600  35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35  .  DENSITY  278.7 268.4 271.3 307.9 325.0 372.5 415.2 422.7 413.5 425.9 381.3 394.7 396.8 393.0 392.4 371.6 381.4  g/L 1.9 4.1 4.4 3.5 2.5 1.4 0.8 0 0 0.4 0 0.5 0 0 0 0 0 0  g/L 0.8 0.6 1.2 4.1 5.0 8.7 14.5 15.8 14.8 17.1 15.2 16.8 13.7 15.8 16.8 16.8 17.4 14.5  17.89 15.89 17.18 16.90 16.38  Table 120 Experiment RT 2L tank, c-r  TIME Hours  pH  COPPER g/L  T-IRON g/L  0 46.5 97.75 143.41 194.82 243.71 289.90 340.40  2.14 2.42 1.94 2.33 2.21 2.11 2.12 2.18  0 21.9 29.9 70.2 51.7 59.7 60.4 67.1  0 1.0 9.9 18.5 4.9 3.1 1.4 1.2  TIME Hours 0 46.5 97.75 143.41 194.82 243.71 289.90 340.40  TOC ppm  ACID mL 0 0 115 220 280 353 380 410  Eh mV  4 0 5 61 84 79 101  405 420 495 435 475 490 500  Table  121 Experiment b3 c-r, aeration  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  1 73.83 119.33 169.74 214.24 265.99 312.32  2.13 2.05 1.98 1.68 1.54 1.51 1.54  0 6.1 2.0 2.8 2.4 0.6 4.0  1.0 4.9 5.0 6.2 7.4 8.5 8.8  0  0 0.1 1.3 2.4 2.4 2.4 2.4  TIME Hours  Eh mV  TEMP °C  FERROUS g/L  1 73.83 119.33 169.74 214.24 265.99 312.32  325 370 390 375 385 390 400  1.0 4.3 4.2 5.6 7.3 7.1 7.0  0 0.6 0.8 0.6 1.0 1.4 1.8  37 72 150 144  FERRIC g/L  Table 122 Experiment b5 c-r, A g concentration  TIME Hours  pH  COPPER g/L  T-IRON g/L  TOC ppm  ACID mL  0 44.83 92.33 142.24 190.74 236.74 287.90 341.23 393.81  2.06 2.18 1.66 1.53 1.69 1.66 1.99 1.96 2.08  0 0 0 4.5 9.1 8.3 7.6 13.6 15.4  1.3 1.5 4.5 8.2 12.9 14.5 14.5 16.3 16.3  0 22 95 151 347 250 569 797  0 0.35 2.4 2.5 2.5 2.6 2.6 2.7 2.8  TIME Hours  Eh mV  FERROUS g/L  FERRIC g/L  0 44.83 92.33 142.24 190.74 236.74 287.90 341.23 393.81  325 370 380 380 400 410 445 475 570  1.3 1.4 4.1 6.0 9.8 9.8 5.1 3.0 1.1  0.0 0.1 0.4 1.2 3.1 4.7 9.4 13.3 15.2  APPENDIX 7 LOW In  catalyzed leach  production and can  be  PULP DENSITY REDOX CONTROLLED LEACHING  experiments  there  acid consumption, one  consumed  without  any  correlation  depends on  elemental  attributed to acid consumption due the pH  is a  sulfur  being  measured, this  acid  may  be  to gangue in the concentrate, which increases  above the control level of 2.2.  density  of  107  copper  (0—0.4  g/L  did not  produce  extractions between  %  of  the  residue  concentrate  was  done  in  was  the  methods section. After repeated controlled-redox standard  leach  conditions  controlled-redox  were  in table  description 123  and  %  S°)  and  attempts  altered  consume little acid  way,  described  in  acid.  pulp  Leaches  elemental well  in table 1). Chemical  sulfur  below  the  activation of the the  material  and  which were unsuccessful in obtaining a sulfur  search  of  in aeration level  of these  concentrates at a  very  consumed  elemental in  did not  produced  1,2,3  produced  Gibraltar  and/or  standard  leaching. Changes  made, the  presented  that  S°  48-91  stoichiometric ratio, (see experiments  were  elemental  the other. In some cases  sulfur  Controlled-redox leaching of both Newmont and  with  between  experiments  for comparison  purposes  and  consumed  appropiate and  acid,  the  conditions  for  inoculum  age  follows. A l l the  and  results  the results of an  size are  elemental  sulfur producing leach at 200g/L pulp density are also presented.  Inoculum  age.  Experiments elemental and  4,5,6  test different inoculum  sulfur was  acid was  not produced, copper  ages between 4—17 extraction was  well below the stoichiometric ratio.  355  low  days,  for all cases  between  11—44  %  / 356 Inoculum  size.  Inoculum  size was varied from  of  142.8  ml  Experiments was  inoculum/L  a low of 10.7 ml inoculum/L  medium,  7,8,9,10,11 and  with  12 indicate  medium  the standard  inoculum  that between  11—55  leached without elemental sulfur being produced, acid  being %  was  to a high 20 ml/L.  of the copper also  well below  the stoichiometric ratio.  Aeration.  Various cases  aeration  experiments  levels  were studied  13,14  and  15  between  (Table  0.13  vvm  123) indicate  and that  3.14 wm, not only  in was  all no  elemental sulfur produced but copper leaching was limited by low aeration levels (only 3 %  copper was extracted for an aeration level of 0.13 vvm).  / 357  Table 123. Controlled—Redox monosized leaches  Run No.  1 2 3 4 5 6 7 8 9 10 11 12 13 14  ~  AIR FLOW  INOC AGE-SIZE  Cu  S°  ACID  TYPE  vvm  days-**  %  %  ***  *  2.85 2.85 2.85 2.85 2.85 2.85 0.80 0.80 0.80 0.80 2.85 3.14 3.14 0.13 0.75  6-71.4 7-71.4 6-71.4 4-71.4 14-71.4 5-71.4 7-20.0 6-10.7 6-20.0 6-20.0 17-142.8 7-71.4 6-71.4 6-71.4 6-37.5  91 76 48 11 23 44 35 50 43 55 38 58 27 3 73  0.1 0.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.22  0 0 2.8 4.7 12.6 0 0 0 1.0 0 0 0.6 0 0 1.38  G G N G G N N N N N G G G G N  * N = Newmont G = Gibraltar ** Inoculum size = ml/1 medium *** moles acid / moles copper ~ Pulp density = 200g/L  APPENDIX 8 PUBLICATIONS  Particle Size Effects in the Microbiological Leaching of Sulfide Concentrates by Thiobacillus Ferrooxidans  M . A . Blancarte-Zurita a n d R. M . R. Branion Department of Chemical Engineering, University of British Columbia, Vancouver, British Columbia, Canada V6T 1W5 R. W . L a w r e n c e B.C. Research, 3650 Wesbrook Mall, Vancouver, British Columbia, Canada V6S 2L2 Accepted (or publication July 9, 1985  INTRODUCTION  The microbiological leaching of metals from sulfide minerals has attracted much attention from researchers and metal producers. An excellent critical review of this topic has been published by Brierley.' One of the foci of such research is the leaching of sulfide mineral concentrates, which is the concern of the present work. Specifically, this communication deals with the effects of leaching on particle size when Cu and Fe are leached from a chalcopyrite concentrate and Zn is leached from a ZnS concentrate by Thiobacillus ferrooxidans.  for I h to give 91.8% smaller than 400 Tyler mesh. It was then recovered byfiltrationand dried at 60°C. The elemental analysis of the concentrate was 27.8% copper, 28.0% iron, 31.1% sulfur, and 5.5% insoluble.  C u l t u r e Technique  All experiments were carried out in 250-mL bottombaffled Erlenmeyer flasks containing 7.5 g of concentrate and 70 mL of the iron-free 9 K medium of Silverman and Lundgren. The pH was adjusted to 2.0 with IN H S0<. Theflaskswere loosely stoppered with a cotton plug and mounted on a gyratory shaker. The shaker was located in a dark room, maintained at 35°C with a C0 -enriched atmosphere. Before inoculation, but after the adjustment of pH to 2, theflaskswere held for 24 h to allow for acid consumption by alkaline gangue present in the concentrate. After this the pH was readjusted to 2.0 and the flasks inoculated with 5 mL of T. ferrooxidans suspension. • Evaporative water losses were made up periodically by adding distilled water. In the sterile control flasks 1 mL of 1:70 v/v phenol solution was added instead of inoculum. 3  2  MATERIALS A N D METHODS  2  Microorganism  The microorganism used in this study was originally isolated by Razzell and Trussell from a copper mine located at Britannia, B.C. It has been routinely maintained on copper concentrate suspended in the 9 K medium, but without the iron described by Silverman and Lundgren. Il was determined'' that to minimize the time taken to reach maximum copper concentration and to maximize the rate of copper extraction an inoculum age of 8 days was optimal. Thus transfers to new media were made every 8 days. 2  3  Analyses Substrate  The chalcopyrite concentrate used in this study was a commercial flotation concentrate supplied by Newmont Mines Ltd., Similkameen Div., Princeton, B.C. This concentrate was wet ball milled at 55% solids  The copper and iron contents of the medium were determined at various times by stopping the shaker, allowing the solids to settle for 10-15 min, then withdrawing a I-mL sample of the supernatant. The metal analyses were done using an atomic absorption spectrophotometer.  B i o l e c h n o l o g y a n d Bioengineering. Vol. XXVIII. P p . 751-755 (19861 © 1986 J o h n Wiley & S o n s . Inc.  C C C 0006-3592/86/05075)-OSS04.00  Concentrate S i z e Fractionation In some of our studies we wanted lo follow the effects of leaching on particle size and vice versa; thus we needed to get fractions of chalcopyrite having different particle sizes. The beaker decantation method is a simple way of doing this. Concentrate is added lo water in a large beaker or any other suitable container. The slurry is stirred to mix it well then allowed to settle for a predetermined time. The larger particles settle while the smaller ones remain in suspension. The supernatant suspension is carefully poured off into another beaker and the process repeated using a longer settling time, etc. This fractionation procedure requires the use of a defloculating agent to obtain uniform dispersions. Tween 40 (polyoxyethylene sorbitan monopalmitate) was used. It was subsequently removed from the fractionated particles by solvent extraction with isopropanol in the presence of K 2 C O 3 . Tween 40 inhibited leaching but after removal by the solvent extraction technique no such inhibition was observed. 99% removal of the dispersant could be achieved.  assuming that the particle shape factor is constant gives for the change in particle mass dN - —  = -Ipadp  2  ddp —  (3)  5  6  The rate of appearance of Cu in solution can be measured; call this rate r which is expressed in terms of mass x volume x time" . To convert the rate of Cu dissolution to a rate of particle dissolution we must divide r by the weight fraction f of Cu in the concentrate. Thus the rate of particle dissolution is rlf. The term — 3a dp (d dpldt) represents the dissolution rate of a single particle. The measurement of r is made in a suspension containing many particles per unit volume. Let n be the number of particles per unit volume. Assume that no particles disappear during leaching; then n is a constant and is equal to CJpa dp , where C is the initial mass of concentrate per unit volume in the leach system and dp is the initial particle diameter. Then -1  1  1  3  0  0  0  pa  4  (4)  dp,  which reduces to Particle Size A n a l y s i s  - 3C  0  Dilute suspensions of the various fractions were made in 10 mL of ethanol using 0.1% aerosol GPG (sodium dioctyl sulfosuccinale in ethanol and water) as a dispersant in an ultrasonic bath. Microscope slides were prepared from these suspensions and size distributions were measured using an eyepiece micrometer in a microscope to measure the Martin's diameters of 100 particles. After the leaching phase of this study was completed use of a Leitz image analyzer became possible so the unleached fractions were reanalyzed using this instrument counting at least 1000 particles.  The following shrinking particle model is proposed to describe the leaching behavior. Since material is being solubilized fromthe particles the particle mass decreases and it is assumed that as leaching occurs the particles get smaller. The rate of particle size decrease is given by — dNIdt, where N is the particle mass and t is time. Assuming that the particles have a constant density p, we have dN  dV  ' dt  dt  a dp*  (2)  where dp is the particle diameter and a the particle shape factor. Now substituting eq. (2) into eq. (1) and  2  d dp dt  r  (5)  f  a  0  2  DISCUSSION  Table 1 provides.data about the initial sizes of the various fractions used in the leaching experiments as well as the mean size of the unfxactionated concentrate. Table I.  Properties of particle size fraction's. Mean particle diameter (/mi) Fraction number  (I)  where V is particle volume, which can be represented by  dp  r, f, and dp can be measured, and C can be set by the experimenter; thus eq. (5) can be integrated to give particle diameter as a function of time. If necessary the assumption of no total disappearance of particles during leaching can be relaxed but then the integration must be done, numerically; r is a function of the amount of mineral surface per unit volume available to the organism and thus a function of dp since surface area is proportional to dp . For batch leaches r is also a function of time. RESULTS A N D  THEORETICAL  752  dpj  I  2 3 4 5 6 Unfractionated concentrate  BIOTECHNOLOGY ANO BIOENGINEERING. VOL. 28. MAY 19SC  Microscope  Image analyzer  0.38 1.81 1.67 3.10 5.64 6.74 1.86  0.20 2.68 2.76 3.53 5.98 6.45 2.86  s  e  t  • «  U.  COMMUNICATION TO THE EDITOR  753  13 11  leg*  1« z o <  (z Ul o z o u  « U  a. a. o o  ^fraction |  t-  Ofroction 2  0  S froction i  * (f o<li«n 3  7  X fraction 5 fi froction 6  «  a <£  S • 4  <  J -  a  •"  0  A f0ACTION 2 ! KfCACTION 3\ Q f g A C T I O N 3*  o-'-o-  n  SO  100  ISO  300  ISO  JOO  ISO  400  4S0  0  SO  100  TIME (h)  Figure 1 shows a typical size distribution as a function of leach time (for fraction 2), indicating that particle size does decrease with time but not, for this particular concentrate, by very much. Figure 2 plots copper concentration as a function of leach time for the various concentrate fractions. Figure 2 shows that the rate of Cu dissolution r is a function of dp and of time. However, since this concentrate did not leach very well, i.e., the Cu extraction was typically of the order of 26%, we assumed the r would not change much as a result of particle size changes during leaching; however, r was treated as a function of leach time f. Curves of the form [Cu) = ai"  (6)  where a and b are constants and (Cu] is copper concentration were fitted to the data of Figure 2 tor each particle size fraction. From (6) abt"  dt  300  330  300  130  400  430  T I M E (hours)  Figure 2. Copper concentration solution as a function of leach time for various particle sizes.  </[Cu]  ISO  figure 3, Particle size vs leach time for fractions 2. 3. and 5. The lines are calculated using eq. (9). The points are experimental measurements using a microscope.  Figure 3 and 4 show that the predictions of the model are not in disagreement with the measured data and thus the model has some credibility. On the other hand, there is a great deal of scatter in the measured data. Moreover, the concentrate used did not leach very well and thus did not provide an ideal test of the model for particle shrinkage. Torma et al. measured particle size distributions initially and at various intervals during the leaching of a ZnS concentrate. They and Sanmugasunderam also published data from which the rate of Zn dissolution can be calculated. In these ZnS leaching studies much higher levels of Zn extraction were observed (80 + % ) ; thus the particles would become much smaller or, in the case of the smaller ones, disappear. 7  8  (7)  Introducing (7) into (5) leads to 3Co 3C„ dpo  f fdp dp J dp  t""  dt  (8)  a  which integrates to  d'  or* dp  0  ('  (9)  Plots of dp vs. t for fractions 2, 3, and 5 of Table I as calculated by eq. (9) are shown in Figure 3. Also shown are the measured values taken from Figure 1 and others like it (not shown). These values are those measured using the microscope. Later a test was run using the unfractionated concentrate and analyzing particle size distribution with the image analyzer. These results are presented in Figure 4. 754  100  130  100  330  T I M E (hours) Figure 4. Particle size vs. leach time for the unfractionated concentrate. The line is calculated using eq. (9). The points arc experimental measurements using an image analyzer.  B I O T E C H N O L O G Y A N O BIOENGINEERING. V O L . 28. M A Y 1986  and Engineering Research Council of Canada, and El Consejo National de Ciencia y Tecnologia (Mexico!.  NOMENCLATURE a, b C d d f N n / r v a p p  w  0  5  10  13  34  33  10  13  PARTICLE DIAMETER (urn) Figure 5. Cumulative panicle size (mass basis) distribution of a ZnS concentrate after 212 h of leaching. The line is calculated using a program based on eq. (5). The points represent the experimental data of Torma et al.'  A computer program based on the model presented in this work was written to predict the size distributions measured by Torma et al.' A more detailed description is given in ref. 9. This program integrated eq. (5) using equations fitted to Torma's and Sanmugasunderam's data to give r as a function of dp. It also allowed for the disappearance of particles before completion of the leach. Figure 5 plots the cumulative mass-based particle size distributions as calculated by the program and as measured by Torma et al. Agreement is good, 7  thus lending further credibility to this model. Financial assistance for this project has been provided by B.C. Research, The University of British Columbia, The Natural Sciences  Constants Initial mass of concentrate per unit volume (g/L) Particle diameter (cm) Initial particle diameter (cm) Weight fraction of copper in concentrate Particle mass (g) Number of particles per unit volume (L"') Time (h) Leaching rate (g/L h) Particle volume (cm') Particle shape factor Density of concentrate (g/cm').  References 1. C . L. Briefly. "Bacterial leaching," CRC Crit. Rev. Microbiol., 207 (1978). 2. W. E. Razzel and P. C . Trusscl, J. Bacteriol., 85, 595 (1963). 3. M. P. Silverman and D. G. Lundgren, J. Bacteriol.. 77,642 (1959). 4. M. A. Blancartc-Zurita. "Effect of particle size on the kinetics of microbiological leaching of chalcopyrite," M.A.Sc. Thesis, University of British Columbia, (1983). 5. E. J. Pryor. Mineral Processing (Elsevier, Amsterdam. 1965). 6. Organization for Economic Co-operation and Development (OECD). Proposed method for the determination of the biodegradability of surfactants used in synthetic detergents, Paris, 1974. 7. A. E. Torma, C. C . WaJden, and R. M. R. Branion. Biotechnol. Bioeng.. 12, 500(1970). 8. V. Sanmugasunderam. "Kinetic studies on the biological leaching of ZnS concentrate in 2 stage, continuous, stirred tank reactors," Ph.D. Thesis, University of British Columbia (1981). 9. M. A. Blancarte-Zurita. R. M. R. Branion. and R. W. Lawrence, Preprints. International Symposium on Biohydrometallurgy. Vancouver, 1985.  COMMUNICATION TO THE EDITOR  755  Fundamental  and Applied  Biohydrometallurgy,  243  edited by R.W. Lawrence, R.M.Il. Branion and H.G. Ebner Elsevier Science Publishers B.V., Amsterdam, 1986 — Printed in The Netherlands  APPLICATION O F A SHRINKING PARTICLE M O D E L TO T H E KINETICS O F MICROBIOLOGICAL L E A C H I N G  M.A. BLANCARTE-ZURITA 1 , R.M.R. BRANION 1 and R.W. LAWRENCE2 iDept. of Chemical Eng., University of B.C., Vancouver, B.C., Canada, V6T 1W5 2B.C. Research, 3650 Wesbrook Mall, Vancouver, B.C., Canada, V6S 2L2  ABSTRACT A shrinking particle model is presented to describe the effects of leaching on particle size. This model was tested using closely sized fractions of concentrates whose mean particle diameters were measured as functions of time for chalcopyrite and zinc sulphide concentrates. The use of the model for sizing continuous leaching reactors is also described.  INTRODUCTION In the design of a microbiological leaching plant tht; designer has to select an appropriately sized reactor for the mineral being leached. In. order to be able to do this it is necessary to have some knowledge of the kinetics of the leaching process. Ideally the designer could obtain this information from the literature and without further recourse to experiment, proceed to size the reactor. However since the Iikelyhood of finding the right data in the literature is small, and since kinetic data varies widely with the type and source of concentrate, some experimental data should be generated before doing the full scale reactor design. In this paper a method is proposed for using batch shake flask leaching data for the scale up of continuous microbiological leaching reactors via a shrinking particle model. L E A C H I N G TESTS Chalcopyrite Concentrate The concentrate used was a commercial flotation concentrate supplied by Newmont Mines Ltd. Similkameen Div., Princeton, B.C. This concentrate was wet ballmiiled at 55% solids for 1 h to give 91.8% smaller than 400 Tyler mesh. It was then recovered by filtration and dried at 60°C. The elemental analysis of the concentrate was 27.8% copper, 28.0% iron, 31.1% sulphur and 5.5% insoluble. The concentrate was separated into 6  244  fractions by beaker decantation (ref 1). The properties of the fractions are presented in Table 1.  TABLE 1 Average particle size in fractionated copper concentrate  Fraction  Particle size  (jtm) 0.20 2.68 2.76 3.53 5.98 6.45  1 2 3 4 5 6  Culture Technique All experiments were carried out in 250 ml shake flasks containing 7.5 g of concentrate and 70 ml of Silverman and Lundgren's (ref 2) 9K medium without iron, inoculated with 5 ml of an eight day old culture of  Thiobacillus ferrooxidans  routinely  maintained on the same medium, and originally isolated by Razzell and Trussell (ref 3) from the copper mine located at Britannia, B.C. The pH was adjusted to 2.0 with IN H2SO4 and the flasks incubated on a gyratory shaker at 35 °C in a dark room with a C O 2 enriched atmosphere.  Metal  concentration  was  determined by  atomic absorption  spectrophotometry and particle size distribution by image analysis or by microscopic measurement (ref 4). Zinc Sulphide Leaching The data used for this portion of the work was abstracted from Torma (ref 5) and Sanmugasunderam (ref 6). The concentrate they used was a high grade zinc sulphide concentrate supplied by Cominco Ltd. Trail, B.C., after special flotation to remove pyrite. The concentrate was wet ballmiiled to minus 400 mesh and dried at 45"C. The analysis of the concentrate was 60.78% zinc, 33.23% sulphur, 2.5% iron, 1.79% lead, 1.29% calcium oxide and some impurities (Cd,Cu,Mg) Two fractionation techniques were used to separate the concentrate into monosize fractions. Five fractions were obtained using a Warman cyclosizer and eight fractions using a Bahco No. 6000 microparticle classifier  (see Table 2).  245 TABLE 2 Average particle size in fractionated zinc concentrate  Sample  'CS CS 2  Particle Diameter (pun) 3.5 8.8 12.6 19.1 25.6 2.2 3.6 5.4 9.0 13.6 21.7 27.8 39.9  1  CS 3 CS 4 CS 5 **BS 1 BS 2 BS 3 BS 4 BS 5 BS 6 BS 7 BS 8 * Warman Cyclosizer ** Bahco Classifier  Culture Technique Zinc sulphide suspensions of 16% pulp density in 9K medium (without iron), inoculated with 5 ml of a cell suspension of  Thiobacillus  ferrooxidans  routinely maintained  in zinc sulphide medium were incubated in shake flasks at pH = 2.3, 3 5 ° C and supplied with 1% CO2 enriched air. Metal concentration was determined by atomic absorption spectrophotometry and particle size was measured using a graticule mounted on a microscope, as the average of the two largest dimensions exhibited by the particle.  THE MODEL During leaching, material is being solubilized from the concentrate particle. It is assumed then that the particle gets smaller. This would not be a valid assumption if the concentrate contains enough inert material to maintain the particle structure and size as metal is leached out. If such were the case a shrinking core, as opposed to a shrinking particle model could be developed. The rate of decrease in particle size is given by -dn/dt where n is the particle mass and t time. Assuming the particle has a constant density (p) -dn/dt = -p dV/dt Where V is the particle volume.  (1)  246  We can represent V by V = adp3 where dp = panicle diameter, a = shape factor. Now the change in panicle size is - pd/dt (adp3) which if we assume a constant shape factor.becomes -3ordp2 pd/dt(dp). Experimentally the rate of appearance of the metal in solution can be measured, call this rate r which is expressed in units of mass/(vo!ume x time). To convert the rate of metal dissolution to a rate of particle dissolution we have to divide r by the weight fraction of metal in the concentrate. Let this weight fraction be f. So the rate of particle dissolution is r/f. -3adp2 pd/dt(dp) represents the dissolution rate of a single particle; the measurement of r is made in a system containing many particles per unit volume. Assume that no particles disappear during leaching, then the number of particles is constant and is equal to Co/(a dp 3) where Co is the c  initial mass  concentration of particles and dp is the initial particle diameter. So: (-3padp2 Co/adpo.3) d/dt(dp) = r/f  (2)  (-3Co dp2/dp 3) d/dt(dp) = r/f  (3)  Q  Integration of equation 3 requires knowledge of the variation of r with respect to particle size (dp) and time (t). For steady state, continuous leaching r is not a function of t, but for batch or unsteady state, continuous leaching it is. To get the functional dependence of r on dp and t a series of experiments can be done in which metal concentration in solution is determined as a function of leach time. The concentrate is first separated into fractions having different ranges of particle diameter, then the leaches are carried out on the various size fractions. The slope of the plot of metal concentration vs time gives a value for r. The fractional extraction of metal (X) can be expressed as: X = (adp 3 - adp3)/o:dp 3 = l - dp3/dp 3 0  0  Q  (4)  It can be shown (ref 7) that the mean fraction of concentrate not extracted in a continuous reactor is 1 - X where: 1 -X =  (1-X) E dt  (5)  E is the age distribution (ref 7) of particles in the reactor outlet. For a perfectly mixed reactor (ref 7): E = exp (-t/t )/t  (6)  where t is the mean residence time in the reactor which is given by: t = Vol/Q  (7)  where Vol = reactor volume, Q = flow rate of feed to the reactor. Let T be the time required for complete extraction of metal from a concentrate particle, then if t = T, dp = 0  247  and X = 1. Thus the upper limit for the integral in equation 5 should be T rather than oo. So equation 5 combined with 4 and 6 becomes: (8) dp can be determined as a function of time by integrating equation 3. Then T can be determined from the result by setting dp = 0. Then equation 8 can be integrated. This should give X as a function of t for a particular size fraction of concentrate. Then the total conversion of the concentrate over all particle sizes can be calculated by a weighted average summation of all the individual fractional extractions. Finally then we would have a means of determining the fractional extraction for various values of mean residence time. Thus if we set a desired fractional extraction we could determine the required values of mean residence time and from equation 7 calculate the required reactor volume for any chosen value of throughput Q. If Q, X and pulp density are known metal concentrations in solution can be easily calculated.  TESTS .OF T H E KINETIC M O D E L The results of leaching various size fractions of a chalcopyrite concentrate are presented in Fig.l. These were fitted with equations of the form: (see Table 3) [Cu] = a tb  (9)  Where [Cu] = copper concentration, a and b are constants.  Differentiating 9  d[Cu]/dt = r = abtb-1  (10)  Substitution of 10 into 3 and integrating gives: dp/dp = (1 - at b n Co)(l/3)  (ID  Q  TABLE 3 Curve fitting coefficients for copper extraction from fractionated concentrate  Fraction  2 3 4 5 6  Constants a  b  0.201 0.186 0.556 0.298 0.399 0.232  0.430 0.380 0.290 0.450 0.440 0.680  248  In doing this integration it was assumed that for a particular size fraction that dp would not change significantly thus r would only be a function of t for a particular size fraction. This was acceptable because the chalcopyrite concentrate used did not leach to high levels of fractional copper extraction (typically 26%) thus particle diameter did not change much. Fig. 2 plots dp vs t for 3 of the fractions of Table 1 as calculated from  legend A fraction 1 • fraction 2 x fraction 3 2 fraction 4 X fraction 5 £ fraction 6  o •<  OS  friz;  Ul cj z o o OJ w c  0. o o SO  100  150  200  ISO  300  350  400  450  T I M E (h)  Fig.l.  Effect of particle size on copper extraction  | RC ACI TION 2 jjQKA FFfRiACF TA IOT NON33  ia  S. <  200  250  300  350  T I M E (hours)  Fig.2. Change in average particle size for monosize leaches of copper concentrate  249  equation  11. Also shown are experimental measurements  of mean particle size  determined at various leach times. Agreement of the predictions of the model with the data is tolerable but the data is quite scattered. Thus further testing of the model was done, this time using a concentrate which leached to a greater extent. Torma et al. (ref 8) have published some data on particle size distribution as a function  of leach  time  for ZnS  Sanmungasunderam (ref 6), who  concentrate  leaching. In addition  they  and  used a similar concentrate, have measured zinc  concentration as a function of leach time for various particle sizes. See Figs. 3 and 4. From these figures leach rate r (the slope of the linear portion of Figs. 3 and 4) was determined and plotted as shown in Fig. 5. Two straight line portions on this semilog plot were discernable. These were fitted with the following equations: In r = - 0.136 dp + 7.452  dp < 12 nm  (12)  In r = - 0.030 dp + 5.880  dp > 12 um  (13)  100 T I M E (h)  Figure 3: Effect of particle size on zinc extraction A Fortran program was written to integrate equation 3 incorporating equations 12 and 13 and recalculating Co if any particles disappeared during the leach period. The logic algorithm for the program is presented in Fig. 6. Comparison of the cumulative weight percent particle size distribution as measured by Torma et al. (ref 8) and as calculated using the shrinking particle model is shown in Fig. 7 using Torma et al's. data after 212 h of leaching. Fig. 8, again based on Torma et al's. data (ref 8) compares calculated and measured distributions after 338 h of leaching. Agreement between the calculated and measured results is quite good thus providing support for the use of  250  equation 3 as a basis for a kinetic model. Work on application of this model to continuous leaching system, the data for which are provided in (ref 9), is in progress.  z o  ES «.-<»<=>  < oi H  z w o z o o o z  T I M E (h)  Figure 4: Effect of particle size on zinc extraction  10  20 DIAMETER  30 (micrometers)  Figure 5: Effect of particle size on zinc extraction, the logarithm of extraction rate plotted against average particle diameter  25L  IS K w • » U S S Of Ct-'SS  I SIDtC T«*C)  TGSI T « E L A R G C R TMAN TMAX  CALCOLAIC CLA^SCO L C A C H BCCAM  Figure 6. Computer logic diagram ACKNOWLEDGEMENTS Financial support for this work was provided by El Consejo Nacional de Ciencia y Technologia de Mexico, B.C. Research and the Natural Sciences and Engineering Research Council of Canada.  NOMENCLATURE a b Co [Cu] dp dp E f n Q r t  constant constant initial number of particles in suspension per unit volume copper concentration in solution particle diameter initial particle diameter age distribution of particles in reactor outlet stream mass fraction of metal component in concentrate panicle mass flow rate of suspension into (and out of) reactor rate of change of metal ion concentration in solution time  t V Vol X  mean residence time in reactor particle volume volume occupied by suspension in reactor fractional extraction (solubilization) of metal  X a p  mean fractional extraction panicle shape factor panicle density  Q  /  252  PARTICLE DIAMETER  (am)  Figure 7: Particle size distribution of zinc concentrate after 212 h of leaching. Given as cumulative weight percent.  PARTICLE DIAMETER  (um)  Figure 8: Panicle size distribution of zinc concentrate after 338 h of leaching. Given as cumulative weight percent.  372  253 REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9.  EJ.Pryor, Mineral Processing, Elsevier Publishing Co. Ltd., Appendix B, (1965). H.P.Silverman, D.G. Lundgren, J. Bacteriol 77, 642 (1959). W.E.Razzell, P.C.Trussell, J. Bacteriol 85, 595 (1963). M.A.Blancarte-Zurita, Effect of Particle Size on the Kinetics of Microbiological Leaching of Chalcopyrite, MASc Thesis, UBC, Vancouver, (1983). A.E.Torma, Microbiological Leaching of a Zinc Sulphide Concentrate, Ph.D. Thesis. UBC, Vancouver, (1970). V.Sanmugasunderam, Kinetic Studies on the Biological Leaching of a Zinc Sulphide Concentrate in Two Stage Continuous Stirred Tank Reactors, Ph.D. Thesis, UBC, Vancouver, (1981). O.Levenspiel, Chemical Reaction Engineering, John Wiley & Sons (1972). A.E.Torma, CC.Walden, D.W.Duncan, and R.M.R.Branion, Biotechnology and Bioengineering 14 (1972) 777. V.Sanmugasunderam, R.M.R.Branion, and D.W.Duncan, 77iZs volume.  MICROBIOLOGICAL FERROOXIDANS. A  LEACHING OF CHALCOPYRITE CONCENTRATES COMPARATIVE STUDY OF A CONVENTIONAL CATALYZED PROCESS.  BY THIOBACILLUS PROCESS AND A  M.A BLANCARTE-ZURITA Chemical Engineering, University of British Columbia and BC Research, Vancouver BC Canada R.M.R. BRANION Chemical Engineering, University of British Columbia, Vancouver BC Canada R.W. LAWRENCE. Coastech Research Inc., N. Vancouver BC Canada  SUMMARY Limits on pulp density and specific surface area for chalcopyrite concentrate leaching are established and data regarding bacterial growth in batch reactors are discussed for an elemental sulfur producing, acid consuming, catalyzed bioleach. The role of T. ferrooxidans in the catalyzed process is discussed on the basis of a changing growth medium during batch leaches. The effects of aeration, inoculum size and inoculum age are also considered. INTRODUCTION In the biological leaching of chalcopyrite concentrate, copper recovery has been improved through the use of silver as catalyst The catalyzed process and its advantages over the conventional sulfate producing bioleach have been described elsewhere (Bruynesteyn et al, 1983) (Lawrence et al, 1985) (Bruynesteyn et al, 1986). The advantages are quantitative conversion of sulfide sulfur to the elemental form in a low temperature, ambient pressure process and the increase of one-pass copper extraction from chalcopyrite. There is still need to adequately describe limits for the conditions of the process and the role of Thiobacillus ferrooxidans. This work compares the main features of both processes and studies the relationships between iron oxidation, cell growth, elemental sulfur production and copper release for the silver catalyzed leaching of chalcopyrite. MATERIALS AND  METHODS  The microorganism used for inoculum preparation and the culture techniques are described in Blancarte-Zurita et al, (1986). The two substrates used in these studies; were -400 mesh flotation concentrates supplied by Newmont Mines Ltd. and Gibraltar Mines Ltd., B.C The compositions are, for Newmont concentrate, 27.8% Cu, 28% Fe and 31.1% S, and for Cibraltar concentrate 25.76% Cu, 26.23% Fe and 31.3% S. Specific surface area was measured by air permeability and particle size by image analysis. EQUIPMENT Leach tests were conducted in 100 ml, magnetically agitated beakers, Il baffled glass reactors and 31 baffled, plexiglass tanks equipped with 6 blade turbine impellers. For the 1 & 31 tanks, air enriched in C O 2 (1%) was introduced under the impeller. For catalyzed leaches, the pH of the pulps was controlled at 2.2 by using a pH meter-controller, to activate a peristaltic pump which delivered 12N sulfuric add. The temperature of the reactors was maintained at 35 °C.  LEACH TESTS The procedure for preparing 21 of medium for standard catalyzed leaches was as follows. A solution containing 1.16 g A g 2 S 0 in 400 ml of distilled was mixed with 100 ml of a solution containing 12.4 g Na S20 5H20. Then 400g of concentrate was added and the resulting suspension mixed for 20 minutes. Next 11 of a solution containing 142.8 g of C u S 0 S H 0 was added to the mixed suspension. After a further 15 minutes of mixing 20 ml of each of the nutrient salt solutions to produce iron free, 9K media (Silverman and Lundgren, 1959) were added. 4  2  2  4  3  2  Conventional leaches were carried out in II glass reactors at pulp densities of 107 g concentrate/l; the concentrate was added to 350 ml of iron free 9K media and agitated overnight to allow for gangue acid consumption, the pH was adjusted to 2.0 with 12 N H2SO4 and 25 ml of a 6 day old inoculum were added, air containing 1 % C 0 was sparged under the turbine agitator at a rate of 2.85 wm (ml air/ml media per minute). 2  ANALYSES Cell growth was estimated b y measuring total organic carbon in samples of pulp with a TOC analyzer. Cu and Fe concentrations were measured using atomic absorption spectrophotometry. Elemental sulfur was measured gravimetrically after extraction with carbon disulfide, and its expressed as grams of elemental sulfur per gram of solids in suspension or per gram of chalcopyrite (g of substrate). Ferric iron was determined by the sulfosalicylic acid colorimetric method. Total iron was measured by the same method following oxidation of the ferrous iron with sodium persulfate; ferrous iron was determined b y difference. THEORY Conventional reaction: 4CuFeS  2  bioleaching  +  170  +  2  of  4H  +  chalcopyrite  =  4Cu  +  2 +  can  4Fe  be  represented  +  3 +  8S0 "  +  2  4  by  the  following  2H 0... (1) 2  Sulfide sulfur is oxidized completely to sulfate and ferrous iron to feme At pH's favoured b y T. ferrooxidans, feme iron tends to hydrolyze and precipitate as jarosite, releasing acid according to equation 2. 3Fe  +  3 +  2S0 -  +  2  4  7H 0  =  2  H OFe (SO ) (0H) 3  3  4  2  6  +  SH + ... (2)  Thus, the overall reaction is a net acid producer  4CuFeS + 1702 + 7 / H 2 0 = ' / 3 ( H 3 0 F e ( S 0 ) ( O H ) ] + 2 / ,  1  2  2  3  3  Catalyzed bioleaching of chalcopyrite (Lawrence et al, 1984):  4  2  6  has been described  3  H  +  + S*/  S0 "+4Cu ...(3) 2  3  by the following set of reactions  OiFeS+0 + 2HS0 = CuS0 + FeS0 + 2S° + 2H0...(4) 2  2  2  4  4  4  FeS0 + '/,0 + '/ H S0 = '/Fe(S0)3 4  2  2  2  4  2  2  4  2  +  '/jh^O.-.'S)  V Fe (S0) + 2H 0=/H Fe (0H) (S0 ) + /HS0...(6) 2  2  43  2  ,  t  2  6  12  2+  4  44  5  6  2  4  The  overall reaction can be given by: CuFeS + 1'/,0 2  RESULTS AND CATALYST  +1 / 2  2  3  H S O = C u S O + 2S 2  4  +'/ H 0+  0  4  2  2  V H 3  Fe (OH) (S0 )4..<7)  2  6  l2  4  DISCUSSION  CONCENTRATION  Miller and Portillo (1979) found that for non-biological leaching of chalcopyrite the copper extraction rate increased with an increase in initial silver concentration from 17-36 g/kg concentrate. Beyond this level, additional silver did not enhance the rate of reaction or, even reduced it slightly, in leaches with a pulp density of 3 g/1. For catalyzed bioleaching, Bruynesteyn et al, (1983) proposed a range of 0.1-4.0 g Ag/kg concentrate in order to obtain elemental sulfur from the leaching . of chalcopyrite in leaches with pulp densities of 200 g/I. In the culture medium silver was initially found in a complexed form as A g f S j O j ^ (Lawrence et al, 1984), resulting from a reaction between A g S 0 with Na S C>3 in the first step of the procedure used to set up leach tests. For an initial concentration of 400 ppm (unpublished data), less than 0.1 ppm of silver remained in solution. Therefore the initial concentration of 0.58 ppm used in our tests will most likely be in complexed form and not in soluble form. Soluble silver was reported to cause inhibition in the growth of T. ferrooxidans at concentrations higher than 1.0 ppm. (Hoffman and Hendrix, 1976). 2  4  2  2  In order to elucidate the relationship between silver concentration, copper extraction rate and mineral surface area, a series of catalyzed bioleaches at pulp densities of 180 g cbncentrate/1 was carried out using monosized fractions of Gibraltar concentrate with specific surface areas (s.s.a.) between 454 - 4132 cm^/g. Figure 1 shows maximum copper extraction rates and S° concentration as function of s.s.a. The maximum attainable rate of copper extraction and the production of S° increased with increments of s.s.a. up to 1390 cm^/g. Subsequent increases of s.s.a. resulted in decreasing extraction rates and decreasing amounts of S° ' for constant amount of catalyst (3.1 x 10'^g Ag S0 /g concentrate). Figure 2 show's moles H SC>4 consumed/ moles of Cu extracted as a function of s.s.a. A stoichiometric ratio of 1.5-2.0 moles H S0 /mol Cu leached (dashed line), depending on the level of ferrous iron oxidation, was obtained for a s.s.a. of 12S0 cm /g or less. 2  2  4  2  4  2  Table 1 shows data for leaches of the concentrate fraction having a s.s.a.=4132 crn^/g. In these leaches the amount of A g S 0 added was proportional to the amount of surface area per unit volume. This amount was based on a ratio of 2.9 mg A g S 0 / g of concentrate (standard addition), equivalent to 3 x 10"^ mg A g S 0 / c m for a monosized concentrate fraction of 30.4 um, which produced an elemental sulfur and acid consuming leach. 2  4  2  2  2  4  4  r-  .355-1  100  H  1  1  1  1  ,  1  1  0  500  1000  1500  2000  2500  3000  3500  r-« 4000  1-0 4500  S.S.A. (cm'/g concentrate)  Fig. 1 S and Cu extraction vs s.s.a.  TABLE 1  -  EFFECTS OF CATALYST/SPECIFIC SURFACE AREA RATIO g g2 °4 /cm  S°  /g conc 3.19 8.7 14.8 22.2 8.7 14.8  7.7x1 cr 2x103x105x102x103x10-3  0 0 0 0 0 0  mg  Ag S0 2  4  m  A  S  2  4  3  3  3  3  moles  H2SO4  mg  Na S 03 2  2  mg  CuS0  /moles Cu  /g cone.  /g cone.  0.108 12.96 17.76 13.93 9.79 2.5  34.1 93 158.5 237.5 93 1S8.5  393 357 357 357 911 1822  4  As shown in Fig. 1, leaching of the finest concentrate fraction (ssa=4132 cm /g) did not produce any elemental sulfur. To determine if this was due to insufficient silver addition, a series of leaches was carried out in which silver was added in amounts to give varying silver to mineral surface ratios. In this series, the amounts of thiosulfate and copper sulfate were similarly varied. The results are given in Table 1. The results presented in Table 1 show that the increase in s.s.a. corresponding to a decrease of particle size from 30/im to 2.5 fim could not be compensated for by increasing the concentration of silver sulfate or other reagents to maintain a constant ratio of reagent to surface area. This resulted in a change in the leaching characteristics of the concentrate, with some copper being leached but no elemental sulfur produced. Tlie Tesults indicate that, at the pulp 2  /  3  1000  1500  2000  2500  3000  3500  4000  4500  S.S.A. (cm'/g c o n c e n t r a t e )  Fig. 2 Acid consumption vs s.s.a.  density of the experiment, there is a limiting S-S.a. above which the catalyzed reaction is not initiated. Once the reaction is initiated extractions of 70-95+% of copper from -400m concentrate were not uncommon, and indicated that all particles would eventually dissolve. This finding contrasts with the effects of increased s.s.a. for non-biological leaching (Miller and Portillo, 1972) where increased rates of reaction were found when the s.s.a. increased, when the concentrate was ground, and the partide size went from 50% minus 20tim to 50% minus 0.S;zm. This difference suggests that the mechanisms for these two processes are different and points to the critical nature of s.s.a. to establish the catalyzed bioleach reaction. This finding also allows some postulation regarding the mechanism of sulfur production. Sulfur is more likely being formed in the catalyzed leach at the mineral surface than within the bacterial cell since the later should not be affected by partide size. COPPER EXTRACTION AND  CELL GROWTH.  figure 3 is a plot of copper concentration and cell growth (as organic carbon) for conventional leaching of -400 mesh Gibraltar concentrate. Copper extraction was 34%. Cell growth and copper release are simultaneous processes and cell growth stops after copper leaching stops. Similar results were obtained for Newmont concentrate (Blancarte-Zurita, 1983). figure 4 shows copper extraction and cell growth as a function of time for a -400 mesh Newmont catalyzed leach; copper extraction was 73%. As expected, the relationship between bacterial growth and metal extraction is different between the catalyzed process and the conventional process. Lawrence et al, (1984) have suggested that the lower bacterial populations present in the catalyzed leach are due to a reduction in the energy obtainable from the oxidation of sulfide when it stops at the elemental sulfur state. Figure 4 indicates that growth of T. ferrooxidans continues after copper extraction stops for the catalyzed bioleach.  378  / 379  \  be  a o  o O  100  200  300  400  Time  500  600  700  800  (hours)  Fig- 3 Cell growth in conventional leaching  bo  a o o h  30  O. O, o O  200  Time  (hours)  Fig. 4 Cell growth in catalyzed leaching  900'  • Conrentional E Catalyzed o Control  12  bo  /  / «\  !  v -  S00  600  o  -r  100  —I— 200  300  400  Time (hours) Fig.  roo  5 Ferric iron profiles  A longer experiment was necessary to investigate what happens to the cells after the catalyzed leaching of copper stops. At this point in the leach, the conditions were: a redox potential around 500 mV, some ferrous iron in solution, the appearance of elemental sulfur and copper sulfate resulting from the oxidation of the sulfide, as well as some secondary products like jarosites and ferric sulfate. The remaining sulfide (if any) could be available as an energy source for continuing bacterial growth. Other possibilities for obtaining energy are the oxidation of ferrous iron or elemental sulfur. These two alternatives are considered in the following two sections.  FERROUS I FERRIC PROFILES FOR CATALYZED LEACHES. According to the stoichiometry of reactions 3-6, the net sulfuric acid consumed by the leaching of copper is a function of the level of oxidation of ferrous sulfate and hydrolysis of ferric sulfate. The net acid consumption due to these reactions can be estimated if the amounts of ferrous and ferric iron in solution are known. Rg 5 shows the percentage of iron in solution as feme vs time for a catalyzed, a non-inoculated catalyzed, and a conventional leach. The profiles of the conventional and catalyzed leaches show that the different redox conditions in solution result in different profiles of iron oxidation and hydrolysis. In the catalyzed leach, low redox values prevail throught most of the leach. In the conventional leach redox values are higher. Thus, jarosites resulting from hydrolysis of ferric iron are being produced in larger amounts and at an earlier stage lor the conventional leach causing the leaching of copper to stop due to the accumulation of precipitate on the chalcopyrite surface. SEM (scanning electron microscope) studies support this theory (Blancarte-Zurita, 1983). Fig 6 presents % iron and copper leached as functions of time for conventional and catalyzed leaches. Cell concentrations for catalyzed and conventional leaches are plotted in figs 7 and 8, together with ferric iron concentrations expressed as a % of the soluble iron vs time.  / 381 too  °Co coarcatioail «Fe coounlioo'l • Co C l t l l j K l f T3  a, a, o  60 •  HFc c«t«ljK(i  40 -  U  •a  0 100  200  400  Time (hours)  Fig. 6 Metal extractions 100  a o,  90  A ^  d  <S>  80  Fc""  H T.O.C  6  /  70  a  60 S0-\  K  o a o  3  40 30  H  8  /  20 10  K  0 0  40  80  120  160  200  240  280  320  Time (hours) Fig. 7 Cell growth and ferric iron concentration (catalyzed)  no S o, O  .  110-  6  »0-  •a ai  80-  **  «o-  •o -o "K  o a o i~.  ***  o  3  *o <o K  1  100-  WT.O..  ro-  5040302010-  \ cH«««.eol OKi.dati.oo  0-1 120  160  200  240  2S0  Time (hoars) Fig. 8 Cell growth and  feme iron concentration  (conventional)  Bacterial growth in both cases seems tied to ferrous iron oxidation, but copper extraction for the catalyzed leach is independent of ferrous iron oxidation. In both cases, iron concentration during and at the end of the leaches is related to the formation and precipitation of jarosites. The profile of the non-inoculated catalyzed leach shows that T.fenooxidans needs to be present for the catalyzed bioleaching to occur. Without it, iron extraction was only 6.9% and TOC and Cu concentrations were zero for the duration of the experiment. ELEMENTAL SULFUR PRODUCTION  AND  CELL GROWTH.  fig 9 shows the relationship between copper extraction, consumption of H2SO4, S and cell growth. To maintain a constant pH requires H2SO4 addition from the start of the leach. This demand continues after the leaching of copper stops. As pointed out earlier, this later acid is used for oxidation of ferrous iron. Elemental sulfur and copper extraction increase with time. After 240 h, the amount of S° decreases while the bacterial population is still increasing. There are two possibilities to explain the decrease of S°. Either S° is oxidized by ferric iron (the redox potential increases to higher values at this point), or bacterial oxidation is occurring. Another experiment was conducted to test these possibilities; the results are shown in Figs 10 and 11. fig 10 is the time profile of S° expressed as g S°/g substrate and g S° /g solids. The distance between these two curves is due to the increase in the pulp density caused by jarosite formation and precipitation, when this increase is taken into account, the decrease of S° becomes less significant The portion of fig 11 between 0-310 h shows that cell growth is tied to the availability of ferrous iron for oxidation and stops when all the available iron has been oxidized. This cell increase appears to be responsible for the oxidation of S°. If this oxidation was due to ferric iron, the reaction favoured by the increase of the redox potential to 500 mV, would proceed to completion. c  In the conventional leach, oxidation of sulfide through to sulfate proceeds in enzyme-mediated stages in the cell membrane. The energy as electrons from the oxidation  / 383  400  o co  300  X -a a  a  300  X CO  ."2  100  CO  bo O  100  00  200 Time  300  (hours)  Fig. 9 S and cell growth 0.12  -B-  - O — B — S  -a I  •600 •a 500  O.OS-^p^cf  W  400 6  /  bo CO  /  0.04-^  0.02  0.00  h300  /  O 0.06  J B  \  B-B .  / 100  EX t r S * / « r  substrate  ©  solids  cS*/ff  Odonsity •  200  300  400  1 0 Sulfur  x  10"'  E h  500  T i m e (hours)  Fig.  gr/j  profiles  600  1— 700  800  Fig.  11  Sulfur profiles  reactions is transferred via the cell to the ultimate acceptor oxygen. Consequently, copper released by the mineral oxidation is growth-associated. Lawrence et al, (1984) have provided detailed account of the chemistry involved in the catalyzed leach and postulated two possible biological mechanisms to explain how elemental sulfur is formed. Our results indicate that copper leaching is not directly related to cell growth and is more dependent on ferrous iron oxidation. This supports the view that the formation of elemental sulfur is due to catalyzed chemical oxidation and that the sulfide oxidation pathway in the cell membrane is inhibited. The major role of the cells may be to shift the equilibrium of the catalyzed mineral dissolution reaction by the oxidation of ferrous iron.  PULP DENSITY In our studies we conducted a series of leaches at pulp density around 10% solids. None of these leaches produced elemental suKur. This led to an extensive study of the phenomenon to determine why the catalyzed reaction did not occur. This include investigation of silver concentration, aeration rate, inoculum size and inoculum age. In all cases, the catalyzed reaction could not be induced. We conclude that there is a minimum pulp density below which the catalyzed reaction will not occur. The limiting value has not been determined. INOCULUM Tlie effect of inoculum age was negligible when it was maintained between 6-8 days. On the other hand, limits for inoculum size were established to be around 20-71.4 ml/1 of inoculum grown in sulfate producing mode at pulp density of 107 g concentrate/1. The higher limit of inoculum size is likely related to the amount of ferric iron introduced with the inoculum, which will increase the redox potential of the medium and interfere with the proper establishment of the catalysis reactions. Fig. 12 a plot of cell growth and iron concentration in the inoculum medium, shows that cell growth and iron release are simultaneous processes. For the 6 day old cells, used typically as inoculum, a considerable amount of iron (7.3 g/1) is present in solution. Inoculum size was also tested using washed cells. Leaches inoculated with the supernatant culture medium that had been centrifuged 10 minutes at 1000 rpm to remove solids, were not affected and leaching proceeded at nomial rates. When this supernatant was again cen.trifuged and the cell packet used as inoculum, in otherwise standard conditions, bioleaching did not take place. This points to the existence of a component not present in fresh medium, but produced by the cells at some stage during leaching, which needs to be present when these cells are transfered to a new medium. AERATION In order to study the effects of increased levels of aeration above the standard conditions of 0.75 wm, a series of leaches using -400 mesh Newmont concentrate was carried ouL No significant effects on copper extraction rates or acid consumption rate were observed in the interval studied (0.75-6.0 wm). ACKNOWLEDGMENT Financial Assistance for this project has been provided by B.C. Research, The University of British Columbia, The Natural Sciences and Engineering Council of Canada and El Consejo Nacional de Ciencia y Tecnologia (Mexico).  / 300  TIME  Fig. 12  (hours)  Inoculum Effects  REFERENCES Blancarte-Zurita, M.A. (1983) "Effect of particle size on the kinetics of microbiological leaching of chalcopyrite". MaSc-Thesis. University of British Columbia, Vancouver, B.C. Blancarte-Zurita, MA, R.M.R. Branion, and R.W. Lawrence. (1986) "Particle size effects in the microbiological leaching of sulfide concentrates by Thiobacillus ferrooxidans". Biotechnology and Bioengineering 28,751. Bruynesteyn, A., R. Hadd, R.W. Lawrence and A. Vizsolyi (1986) "Biological-add leach process". U.S. Patent 4,571,387 Bruynesteyn, A., R.W. Lawrence, A. Vizolyi and R. Hadd (1983) "An elemental sulfur produdng biohydrometallurgical process for treating sulfide concentrates". In: "Recent Progress in Biohydrometallurgy". E Rossi and A.E. Torma Eds., Assoc Mineraria Sarda, Italy. Hoffman,LF_, J.L. Hendrix. (1976) "Inhibition of Thiobacillus ferrooxidans". Biotechnology and Bioengineering 8:1161 Lawrence, R.W., A. Vizsolyi and R.J. Vos (1984) "Continuous bioleaching of copper concentrates". AI.Ch.F_ National Meeting, March 11-15, Atlanta, Georgia. Lawrence.RAV., A.Vizsolyi. and R.J. Vos (1985) T h e silver catalyzed bioleach process for copper concentrates". In: "Microbiological effects on Metallurgical Processes". J.A Clum and LA. Hass Eds., Met Soc A.I.M.E., New York., 65-8Z MillerJ.D., H.Q. Portillo. (1979) "Silver catalysis in ferric sulfate leaching of chalcopyrite". Thirteenth International Mineral Processing Congress, Warsaw. Silverman,M.P., D.C.Lundgren. (1959) "Studies on a chemoautotrophic iron bacterium Ferrobacillus ferrooxidans I". Journal of Bacteriology. 77,642  386  

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