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Biooxidation of a zinc sulphide ore Lehmann, Matthew Karl Wilhelm 2003

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B I O O X I D A T I O N O F A Z I N C S U L P H I D E O R E by M A T T H E W K A R L W I L H E L M L E H M A N N B . A . S c , The University of British Columbia, Canada, 2000 A THESIS S U B M I T T E D IN P A R T I A L F U L F I L L M E N T OF T H E R E Q U I R E M E N T S F O R T H E D E G R E E OF M A S T E R OF A P P L I E D S C I E N C E in T H E F A C U L T Y OF G R A D U A T E STUDIES Department o f Metals and Materials Engineering We accept this thesis as conforming to the required standard T H E U N I V E R S I T Y OF BRIT ISH C O L U M B I A October, 2003 ® Matthew Kar l Wi lhelm Lehmann, 2003 In presenting this thesis in partial fulfillment of the requirement for an advanced degree at the University of Brit ish Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of the Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. idaTfkew-J^W. Lehmann Department of Metals and Materials Engineering The University of Brit ish Columbia Vancouver, B .C . October 01. 2003 date A B S T R A C T A n experimental program was conducted on a zinc-sulphide ore containing 15% zinc in support of the development of the Teck Cominco HydroZinc™ process. The two primary types of experiments that were conducted were bacterially assisted short column experiments, and controlled potential, isothermal, chemical leaching experiments. This program was carried out in order to determine the kinetics of heap biooxidation of this zinc ore at controlled temperatures, and to determine the rates of heat generation under those conditions. In addition, the ores' topology, activation energy, and dependence on ferric and ferrous ions were determined. Once the primary objective of generating consistent, meaningful data was achieved, a concerted effort was made to fit the results with an existing mathematical model. This exercise was met with mixed results and it was concluded that the mathematical model, in its current stage of development, is insufficient to accurately describe the leaching of this ore. It was concluded from both the experimental data and the mathematical fits that the rate of bacterial leaching of this zinc ore is limited by transport of oxygen into solution. Results of the potentiostatic experiments indicate that the ore follows a variable order model, has an activation energy of 58.23 kJ m o l - 1 , a reaction order of 2.30, and a dependency on ferric ions ofO.342. i i T A B L E OF C O N T E N T S A B S T R A C T •. " F I G U R E S v T A B L E S x A C K N O W L E D G M E N T S x i i i 1. I N T R O D U C T I O N 1 2. L I T E R A T U R E R E V I E W 3 2.1 Early Hydrometallurgical Operations 5 2.2 Modern Hydrometallurgical Operations 5 2.3 Processing Technology for Zinc 6 2.3.1 Roast-Leach-Electro winning 7 2.3.2 Ac id Pressure Leaching 14 2.3.3 Heap Leaching 21 2.3.4 Goethite Process 24 2.3.5 Haematite Process 25 2.3.6 Jarosite Process 26 2.3.7 Sherritt Zinc Pressure Leach Process 27 2.3.8 Mount Isa Mines Process 29 2.3.9 Additional Processing Technology 32 2.4 Bacterial Leaching 33 2.4.1 Biology of Bacteria .36 2.4.2 Bacterial Growth Kinetics 38 2.4.3 Bacterial Dependence on Temperature 42 2.4.4 Bacterial Dependence on Nutrients 44 2.4.5 Bacterial Leaching Mechanisms 47 2.4.6 Electrochemical Aspects of Bioleaching of Sulphides 51 2.5 Kinetics of Leaching Zinc Sulphide 57 3. E X P E R I M E N T A L P R O C E D U R E S 60 3.1 Bacterially Assisted Short Column Leaching 60 3.1.1 Bacterial Culturing 63 3.1.2 Sample Preparation 66 3.1.3 Experimental Program 70 3.2 Controlled Potential, Isothermal, Chemical Leaching 73 3.2.1 Sample Preparation 75 3.2.2 Experimental Program 76 4. E X P E R I M E N T A L R E S U L T S 79 4.1 Results of Bacterially Assisted Short Column Leaching Experiments 79 4.1.1 Results of Experiment Number 1 - Four Replicates at 30°C 79 4.1.2 Results of Experiment Number 2 - Four Replicates at 50°C 93 4.1.3 Results of Experiment Number 3 - Four Replicates at 70°C 101 4.1.4 Results of Experiment Number 4 - Four Columns in Tandem at 30°C 110 i i i 4.1.5 Results of Experiment Number 5 - Four Columns in Tandem at 50°C 119 4.1.6 Results of Experiment Number Six - Two Replicates at 70°C with 100% Oxygen 128 4.2 Results of Controlled Potential, Isothermal, Chemical Leaching Experiments... 136 4.2.1 Model ing Potentiostatic Data 139 4.2.2 Determination of Activation Energy 144 4.2.3 Determination of Ferric and Ferrous Dependency 145 5. M O D E L I N G OF S H O R T C O L U M N D A T A A N D D I S C U S S I O N 147 5.1 Results of Modeling Experiment Number 1, Replicate 4 149 5.2 Results o f Model ing Experiment Number 2, Replicate 4 156 5.3 Results of Modeling Experiment Number 3, Replicate 4 162 6. C O N C L U S I O N S 169 7. R E C O M M E N D A T I O N S 171 8. R E F E R E N C E S 172 A P P E N D I X A : Bacterially Assisted, Short-Column Leaching Experimental Data 185 A P P E N D I X B: Controlled Potential Chemical Leaching Experimental Data 203 A P P E N D I X C: Analytical Procedures 209 iv F I G U R E S Figure 2-1. The basic roast-leach-electro winning flowsheet for the electrolytic recovery of zinc 8 Figure 2-2. Eh-pH diagram for the Z n - H 2 0 system at 25°C and 1 bar pressure, total dissolved zinc = 1.0 molal (1.0 mol k g - 1 H 2 0 ) 11 Figure 2-3. The Sherritt-Gordon autoclave for zinc pressure leaching 14 Figure 2-4. The basic acid pressure leach flowsheet for the recovery of zinc 15 Figure 2-5. Eh-pH diagram for the S - H 2 0 system at 25°C and 1 bar pressure, total dissolved zinc = 1.0 molal (1.0 mol k g - 1 H 2 0 ) 16 Figure 2-6. Eh-pH diagram for the Z n - S - H 2 0 system at 25°C and (STP) 17 Figure 2-7. A typical heap leach flowsheet 23 Figure 2-8. Region where bacterially assisted oxidation predominates 35 Figure 2-9. Gram stain of rod-shaped Acidithiobacillus ferrooxidans 37 Figure 2-10. Schematic diagram of Acidithiobacillus ferrooxidans 37 Figure 2-11. Typical bacteria growth curve 39 Figure 2-12. Change in biological activity with temperature 42 Figure 2-13. Optimum temperature ranges for bacteria 43 Figure 2-14. Direct leaching of a sulphide substrate 48 Figure 2-15. Indirect leaching mechanism 49 Figure 2-16. Galvanic effect during the leaching of ZnS with FeS 2 52 Figure 2-17. Effect of pyrite on the bacterial leaching of sphalerite 54 Figure 2-18. Zinc extraction with galvanic couple (FeS 2 / ZnS) 54 Figure 2-19. Effect of iron content on (Zn, Fe)S on the rate of dissolution 58 Figure 3-1. Bacterially assisted short column leaching apparatus 60 Figure 3-2. Short column configuration 62 Figure 3-3. Four columns operating in tandem 63 Figure 3-4. Particle size distribution of blended zinc-sulphide ore 67 Figure 3-5. Typical composition of a) the blended zinc ore and b) agglomerated zinc ore 69 Figure 3-6. Appl ikon reactor: controlled potential leaching apparatus 74 Figure 3-7. Particle size distribution for -400 mesh material used in potentiostatic experiments 76 Figure 4-1. Zinc concentration in solution for four replicate columns operating at 30°C 79 v Figure 4-2. Iron concentration in solution for four replicate columns operating at 30°C 80 Figure 4-3. Zinc extraction in solution for four replicate columns operating at 30°C (based on solution assays) 81 Figure 4-4. p H for four replicate columns operating at 30°C 82 Figure 4-5. O R P of four replicate columns operating at 30°C 82 Figure 4-6. Zinc extraction of four replicate columns operating at 30°C (based on solids assays) 83 Figure 4-7. Bacterial cell counts for four replicate columns operating at 30°C 84 Figure 4-8. Heat generated by four replicate columns operating at 30°C 91 Figure 4-9. Zinc concentration in solution for four replicate columns operating at 50°C 93 Figure 4-10. Iron concentration in solution for four replicate columns operating at 50°C 94 Figure 4-11. Zinc extraction in solution for four replicate columns operating at 50°C (based on solution assays) 95 Figure 4-12. p H for four replicate columns operating at 50°C 95 Figure 4-13. O R P of four replicate columns operating at 50°C 96 Figure 4-14. Zinc extraction of four replicate columns operating at 50°C (based on solids assays) 96 Figure 4-15. Bacterial cell counts for four replicate columns operating at 50°C 97 Figure 4-16. Heat generated by four replicate columns operating at 50°C 99 Figure 4-17. Zinc concentration in solution for four replicate columns operating at 70°C... 101 Figure 4-18. Iron concentration in solution for four replicate columns operating at 70°C... 102 Figure 4-19. Zinc extraction in solution for four replicate columns operating at 70°C (based on solution assays) 103 Figure 4-20. pH for four replicate columns operating at 70°C 103 Figure 4-21. O R P of four replicate columns operating at 70°C 104 Figure 4-22. Zinc extraction o f four replicate columns operating at 70°C (based on solids assays) 104 Figure 4-23. Bacterial cell counts for four replicate columns operating at 70°C 105 Figure 4-24. Heat generated by four replicate columns operating at 70°C 107 Figure 4-25. Summary of zinc extraction, based on both solution and solid assays, for experiments one, two, and three 109 Figure 4-26. Zinc concentration in solution for four columns operating in tandem at 30°C. 110 Figure 4-27. Iron concentration in solution for four columns operating in tandem at 30°C .111 Figure 4-28. Overall zinc extraction in solution for four columns operating in tandem at 30°C (based on solution assays) 112 vi Figure 4-29. p H for four columns operating in tandem at 30°C 112 Figure 4-30. O R P of four columns operating in tandem at 30°C 113 Figure 4-31. Zinc extraction of four columns operating in tandem at 30°C (based on solids assays) 113 Figure 4-32. Bacterial cell counts for four columns operating in tandem at 30°C 114 Figure 4-33. Heat generated by four columns operating in tandem at 30°C 116 Figure 4-34. Zinc concentration in solution for four columns operating in tandem at 50°C. 119 Figure 4-35. Iron concentration in solution for four columns operating in tandem at 50°C . 120 Figure 4-36. Overall zinc extraction in solution for four columns operating in tandem at 50°C (based on solution assays) 121 Figure 4-37. p H for four columns operating in tandem at 50°C 121 Figure 4-38. O R P of four columns operating in tandem at 50°C 122 Figure 4-39. Zinc extraction of four columns operating in tandem at 50°C (based on solids assays) 122 Figure 4-40. Bacteria cell counts for four columns operating in tandem at 50°C 123 Figure 4-41. Heat generated by four replicate columns operating in tandem at 50°C 125 Figure 4-42. Summary of zinc extraction, based on both solution and solid assays, for experiments four and five 127 Figure 4-43. Zinc concentration in solution for two replicate columns operating at 70°C with 100% oxygen 128 Figure 4-44. Iron concentration in solution for two replicate columns operating at 70°C with 100% oxygen 129 Figure 4-45. Zinc extraction in solution for two replicate columns operating at 70°C with 100% oxygen (based on solution assays) 130 Figure 4-46. p H for two replicate columns operating at 70°C with 100% oxygen 130 Figure 4-47. O R P of two replicate columns operating at 70°C with 100% oxygen 131 Figure 4-48. Zinc extraction of two replicate columns operating at 70°C with 100%) oxygen (based on solids assays) 131 Figure 4-49. Bacteria cell counts for two replicate columns operating at 70°C with 100% oxygen 132 Figure 4-50. Heat generated by two replicate columns operating at 70°C with 100% oxygen 134 Figure 4-51. Comparison of zinc extraction under low oxygen (air + 1%C02) and high oxygen (100%) 02) conditions 135 Figure 4-52. Zinc extraction by solution assay for constant potential experiments (temperature, F e 3 + : F e 2 + ratio) 136 vi i Figure 4-53. Zinc extraction by solution assay for constant temperature experiments at (temperature, F e 3 + : F e 2 + ratio) 137 Figure 4-54. Variable order fit for experiment number T l 141 Figure 4-55. Variable order fit for experiment number T2 141 Figure 4-56. Variable order fit for experiment number T3 142 Figure 4-57. Variable order fit for experiment number PI 142 Figure 4-58. Variable order fit for experiment number P2 143 Figure 4-59. Variable order fit for experiment number P3 143 Figure 4-60. Arrhenius plot 145 Figure 4-61. Dependency on F e 3 + ions 146 Figure 5-1. Model ing the zinc concentration in column effluent for experiment number 1, replicate 4 150 Figure 5-2. Model ing the iron concentration in column effluent for experiment number 1, replicate 4 151 Figure 5-3. Model ing the overall zinc extraction for experiment number 1, replicate 4 151 Figure 5-4. Model ing the p H in column effluent for experiment number 1, replicate 4 152 Figure 5-5. Model ing the O R P in column effluent for experiment number 1, replicate 4 152 Figure 5-6. Model ing the bacterial populations in column effluent for experiment number 1, replicate 4 153 Figure 5-7. Model predictions of marmatite and pyrite for experiment number 1, replicate 4 154 Figure 5-8. Model ing the dissolved oxygen concentration in column depth with time for experiment number 1, replicate 4 156 Figure 5-9. Model ing the zinc concentration in column effluent for experiment number 2, replicate 4 157 Figure 5-10. Model ing the iron concentration in column effluent for experiment number 2, replicate 4 158 Figure 5-11. Model ing the overall zinc extraction for experiment number 2, replicate 4 158 Figure 5-12. Model ing the p H in column effluent for experiment number 2, replicate 4 159 Figure 5-13. Model ing the O R P in column effluent for experiment number 2, replicate 4... 159 Figure 5-14. Model ing the bacterial populations in column effluent for experiment number 2, replicate 4 160 Figure 5-15. Mode l predictions of marmatite and pyrite for experiment number 2, replicate 4 161 Figure 5-16. Model ing the dissolved oxygen concentration in column depth with time for experiment number 2, replicate 4 161 vi i i Figure 5-17. Model ing the zinc concentration in column effluent for experiment number 3, replicate 4 .' 164 Figure 5-18. Model ing the iron concentration in column effluent for experiment number 3, replicate 4 164 Figure 5-19. Model ing the overall zinc extraction for experiment number 3, replicate 4 165 Figure 5-20. Model ing the pH in column effluent for experiment number 3, replicate 4 165 Figure 5-21. Model ing the O R P in column effluent for experiment number 3, replicate 4... 166 Figure 5-22. Model ing the bacterial populations in column effluent for experiment number 3, replicate 4 166 Figure 5-23. Model predictions of marmatite and pyrite for experiment number 3, replicate 4 168 Figure 5-24. Model ing the dissolved oxygen concentration in column depth with time for experiment number 3, replicate 4 168 ix T A B L E S Table 2-1. Potential advantages and disadvantages of hydrometallurgical technology over traditional smelting technologies 4 Table 2-2. Major uses and trends of zinc in the Western World 7 Table 2-3. Addit ional processing technology for zinc from a primary source 32 Table 2-4. Bacteria of importance in hydrometallurgy 34 Table 2-5. Min imum doubling times of Acidithiobacillus ferrooxidans grown on various substrates 40 Table 2-6. Composition of Silverman and Lundgren's 9 K nutrient medium 45 Table 2-7. Galvanic series of some base metal sulphides in a bioleaching medium 52 Table 2-8. Average oxidation rates constants of sulphide minerals under varying conditions 55 Table 2-9. Activation energies for the dissolution of zinc sulphide 59 Table 3-1. Characterization of bacteria adapted to zinc sulphide ore 63 Table 3-2. Nutrient medium composition 65 Table 3-3. Composition of the trace elements solution 65 Table 3-4. Mineralogical analysis of the as-received ore 66 Table 3-5. Chemical analysis of as-received zinc sulphide ore 68 Table 3-6. Overview of bacterially assisted, short column leaching experiments 70 Table 3-7. Chemical analysis of-400 Mesh zinc sulphide ore 75 Table 3-8. Overview of controlled potential, isothermal, chemical leaching experiments 77 Table 4-1. Extraction values obtained by solution and solids analysis for four replicate columns operating at 30°C 83 Table 4-2. Zinc mass balance for four replicate columns operating at 30°C 85 Table 4-3. Overall mass balance for four replicate columns operating at 30°C 85 Table 4-4. Chemical analysis of tailings from four replicate columns operating at 30°C 85 Table 4-5. Reaction enthalpies of several important oxidation reactions 86 Table 4-6. Redox reactions and their associated heat generation values 87 Table 4-7. Assay data for replicate number 1 of experiment number 1 88 Table 4-8. Mass balance incorporating assay data for replicate 1 of experiment number 1.... 88 Table 4-9. Heat analysis of replicate 1 of experiment number 1 89 Table 4-10. Extraction values obtained by solution and solids analysis for four replicate columns operating at 50°C 97 Table 4-11. Zinc mass balance for four replicate columns operating at 50°C 98 Table 4-12. Overall mass balance for four replicate columns operating at 30°C 98 Table 4-13. Chemical analysis of tailings from four replicate columns operating at 50°C 98 Table 4-14. Extraction values obtained by solution and solids analysis for four replicate columns operating at 70°C 105 Table 4-15. Zinc mass balance for four replicate columns operating at 70°C........ 106 Table 4-16. Overall mass balance for four replicate columns operating at 70°C 106 Table 4-17. Chemical analysis of tailings from four replicate columns operating at 70°C... 107 Table 4-18. Extraction values obtained by solution and solids analysis for four columns operating in tandem at 30°C 114 Table 4-19. Zinc mass balance for four columns operating in tandem at 30°C 115 Table 4-20. Overall mass balance for four columns operating in tandem at 30°C 115 Table 4-21. Chemical analysis of tailings from four columns operating in tandem at 30°C. 115 Table 4-22. Heat analysis of experiment number 4 118 Table 4-23. Extraction values obtained by solution and solids analysis for four columns operating in tandem at 50°C 123 Table 4-24. Zinc mass balance for four columns operating in tandem at 50°C 124 Table 4-25. Overall mass balance for four columns operating in tandem at 50°C 124 Table 4-26. Chemical analysis of tailings from four columns operating in tandem at 50°C. 124 Table 4-27. Extraction values obtained by solution and solids analysis for two replicate columns operating at 70°C with 100% oxygen 132 Table 4-28. Zinc mass balance for two replicate columns operating at 70°C with 100% oxygen 133 Table 4-29. Overall mass balance for two replicate columns operating at 70°C with 100% oxygen 133 Table 4-30. Chemical analysis of tailings from two replicate columns operating at 70°C with 100% oxygen 133 Table 4-31. Chemical analysis of tailings from the controlled potential, isothermal, chemical leaching experiments 137 Table 4-32. Summary of results for the controlled potential, isothermal, chemical leaching experiments 138 Table 4-33. Zinc mass balance for controlled potential, isothermal, chemical leaching experiments 138 Table 4-34. Variable order fit parameters for potentiostatic experiments 140 Table 5-1. Column parameters 148 x i Table 5-2. Column operational parameters 148 Table 5-3. Agglomeration parameters 148 Table 5-4. Mineral leach parameters 149 Table 5-5. Bacterial rate parameters for mesophilic bacteria 150 Table 5-6. Bacterial rate parameters for moderate thermophilic bacteria 157 Table 5-7. Bacterial rate parameters for extreme thermophilic bacteria 163 x i i A C K N O W L E D G M E N T S I would like to express my sincere gratitude to my thesis supervisor Dr. David G. Dixon for his advice, guidance, and patience during the course of my study. Sincere appreciation is also extended to Elizabeth whose continued support and insight during the trying times is treasured. I would like to extend my appreciation to my fellow graduate students and the research engineers in the Hydrometallurgy Group, in particular Mr . Hamid Hatami and Mr . Jacky Cheng. The financial assistance from Teck-Cominco, the Cy and Emerald Keyes Foundation, the Nadeau Award Committee, C I M ' s Hydrometallurgy Award, and T M S / A S M ' s Extractive Metallurgy Divis ion is gratefully acknowledged. x i i i Chapter 1: Introduction 1. I N T R O D U C T I O N Equation Section (Next)The direct oxidation of sphalerite ore under atmospheric pressure with bacterial assistance is emerging as a viable alternative technology to existing hydrometallurgical processes, including roast-leach-electrowinning and zinc pressure leaching. The ability to leach complex zinc sulphide ore in a heap leaching operation offers a mine the opportunity to economically process their ore without beneficiation. Furthermore, by util izing a sulphate media an operation can avoid the environmental and equipment complications associated with using a corrosive media such as chlorine. In response to the economic reality of high production costs for zinc (34 USjzi lb - 1 ) in a market where the price o f zinc is low (45 USe" l b - 1 ) , a corporate challenge was issued to Teck Cominco Research in 1999, "to find innovative ways for making zinc, source to market, for 25 US0 lb~ ' " . [ 1 ] Teck Cominco Research developed a comprehensive program to identify alternative routes to the conventional roast-leach-electrowin and zinc pressure leaching technologies. The mine-to-metal HydroZinc™ process is the culmination of this work and involves heap leaching, neutralization, solvent extraction, and electrowinning. The economics show that, depending on location and using a zinc price of 45 USc" l b - 1 , internal rates of return of up to 14% are achievable; this represents an operating cost of 28.2 USj£ l b - 1 which is more competitive than the operating costs of all conventional mine-to-metal processes} l^ 1 Chapter 1: Introduction This research was conducted in support of the laboratory scale research on heap leaching that was performed during the development of the HydroZinc™ process. A s with any new process, the need arises to characterize the leaching behavior of the ore and to identify fundamental parameters which are required to model the leaching process. A n experimental program was conducted in order to identify these parameters. The approach taken was twofold. First, the leaching profile of the ore with mixed particle size was established through experimentation in short columns with bacterial assistance. The kinetics were experimentally quantified by performing each test at the optimal cardinal temperature regime corresponding with the three primary bacterial groups that were employed, namely mesophiles (30°C), moderate thermophiles (50°C), and extreme thermophiles (70°C). This also allowed for the tracking of solution potential, acidity, and bacteria counts in the effluent, and for the determination of the amount of heat generated during the experiment. Second, the activation energy and reaction order were established by performing leaching experiments on ground samples of the sphalerite ore. The mineral was leached in a batch-wise mode while the temperature, solution potential, and p H were held constant. This concept is termed "controlled potential, isothermal, chemical leaching". Finally, this data was integrated into a mathematical model which was used to describe the results. This model became a tool which was used to establish the oxygen dissolved in solution within the respective systems. 2 Chapter 2: Literature Review 2 . L I T E R A T U R E R E V I E W Equation Section (Next)Historically, the dominant processing route for both base and rare metals has been through the implementation of high-temperature, pyrometallurgical techniques. [ 2 ' 3 ] In these smelting operations, sulphide minerals are particularly desirable as the sulphur supplies a significant component of the energy required in the process. [ 4 ' 5 ] Weak sulphur dioxide (SO2) is created within the smelters, roasters, reverberatory furnaces, and multiple-hearth roasters used to process ores. This SO2 escapes at furnace openings and from launders, casting moulds, and ladles carrying molten materials. As a result, the SO2 from these sources never makes it to the scrubbing systems which are intended to catch the toxic off-gas and convert it into a manageable gypsum sludge, elemental sulphur (S°), or rich liquid S02. [ 5" 7 ] These fugitive SO2 gases ultimately lead to the formation of acid rain and result in serious environmental problems J 8 " 1 ^ These environmental issues coupled with the decreasing availability of commercial ore grades that can be processed economically via existing pyrometallurgical operations are driving the f3' 12' 131 research into alternative methods for metal extraction and recovery.1 ' ' J Many secondary pyrometallurgical operations are adopting hydrometallurgical processing circuits as part of their downstream flow sheet, which results in notable environmental benefi ts. [ l 4 ] In addition to a decrease in pollution, hydrometallurgical operations also have the distinct advantage of having a lower capital and operating costs based on aqueous metallurgy. [ 2 ] Hydrometallurgical technology also provides comparatively small mines the ability to operate independently of a smelter (with its associated smelter charges) in locations that would 3 Chapter 2: Literature Review normally be cost prohibitive due to large transportation costs. Dutrizac summarizes the potential advantages and drawbacks of hydrometallurgical leaching technologies over traditional smelting processes in Table 2-1. Table 2-1. Potential advantages and disadvantages of hydrometallurgical technology over traditional smelting technologies Advantages Disadvantages • formation of elemental sulphur or soluble sulphate such that SO2 emissions are entirely avoided • ability to treat low grade or highly complex feeds • pyrite is often "inert" • viable at either a small or large scale • potential for lower capital costs and incremental plant additions • potentially easier to instrument and control • greater flexibility in product purity and form source: Dutrizac, J. E. (1991). "The leaching of sulphide minerals in chloride media." Hydrometallurgy™ • the need to demonstrate a significant advantage over existing technologies • they are often energy intensive because of the high specific heat of water and the use of electrochemical technologies • water pollution problems • recovery of A u and A g by-products is difficult and requires additional processing steps 4 Chapter 2: Literature Review 2.1 Early Hydrometallurgical Operations Hydrometallurgy is a field of chemical technology concerned with the production of metals from their ores and secondary sources. The science of hydrometallurgy has been employed as an effective means for the extraction of minerals from the earths' crust since the days of antiquity. The Romans first discovered how to process sulphidic ores around 400 B C ; their technique consisted of collecting and drying acidified rain water that had percolated through their underground mines. [ 1 5 ] Similar discoveries were being made at the copper smelters on the island of Kypros (Cyprus in the Eastern Mediterranean basin). Here, they used the acidic run-off from their ore stockpiles to enrich their ore with cryptocrystalline opaline silica. The silica that was leached via hydrometallurgical techniques was then used to lower the melting point and regulate the viscosity of the melt . [ 1 6 ] These methods were later refined (as early as 1737) for large scale copper recovery from the vast sulphide deposits of Rio T in to . t 3 ' 1 5 1 A technique was developed whereby copper ore was broken into manageable pieces and stacked into heaps. The solution that emerged from the bottom of the heap, which was pregnant with copper sulphate, could then be cemented onto i r on . [ 3 ' 1 5 1 2.2 Modern Hydrometallurgical Operations The advent of modern hydrometallurgy began in the early 1880's with the development of a process which involves producing pure alumina from cryol i te. [ 1 7 ] In the 1940s to the mid 50s, the need to extract uranium from pitchblende ores was a significant driving force for research into new areas such as solvent extraction and pressure hydrometal lurgy. [ 1 8 ' 1 9 ] The present stage of hydrometallurgy has seen this technology come into an age of maturity; in 1994 over 200 hydrometallurgical processes and sub-processes were being applied industrially, with a 5 Chapter 2: Literature Review significant number of refinements under development. The technology of hydrometallurgy now accounts for a substantial percentage of the world's production of metals, over 90% in the case of gold and around 80% for z i n c . [ 2 0 ' 2 1 ] Worldwide zinc production has increased 19%> over the past decade: 8.2 mil l ion tonnes of zinc in 1999 vs. 6.9 mil l ion tonnes of zinc in 1 9 9 1 . [ 2 2 ; 2 3 ] 2.3 Processing Technology for Zinc The following discussion provides an overview of current hydrometallurgical technology for the processing of zinc. The discussion is limited to those technologies that treat zinc as a primary source and does not include secondary processing routes. The primary mineral source of zinc is the sulphide mineral, sphalerite (ZnS). Sphalerite is often found in association with iron, lead, copper, and cadmium sulphides. Marmatite, a ferruginous variety of sphalerite, contains iron in solid solution within the ZnS matrix. Zinc is the fourth most widely employed industrial metal, surpassed only by iron, aluminum, and copper. In the United States alone, zinc is consumed at a rate of one mil l ion metric tons annually. According to the U.S. Bureau of Mines, the average person wi l l use approximately 730 pounds of zinc in his or her l i fet ime. [ 2 4 ] Due to zinc's low melting point, it can be cast in fine detail into complicated shapes, making it ideal for die casting. It is often employed as a galvanizing agent since it is anodic to steel and has a low and uniform rate of corrosion. Furthermore, zinc can be easily transformed into various grades of zinc oxide, which have useful chemical, electrical, optical, and thermal properties. Zinc is typically found in rubber, paints, ceramics, chemicals, and photocopy paper, as well as more traditional materials such 6 Chapter 2: Literature Review as brass and bronze. J Table 2-2 outlines the most common applications of zinc and their current trends in the Western World. Table 2-2. Major uses and trends of zinc in the Western World Application % of Use Trend Hot Dip Galvanizing 48 Increasing Brass and Bronzes 19 Decreasing Zinc-Base Al loys 13 Decreasing Chemicals 10 Steady Other 10 Steady source: Diaz, G. and Martin, D. (1994). "Modified Zincex Process - The clean, safe, and profitable solution to the zinc secondaries treatment." Resources Conservation and Recycling}26^ Approximately 80% of all zinc is produced by roast-leach-electrowinning, with the Imperial Smelting Process (ISP) accounting for most of the remainder. [ 2 1 ' 2 7 1 Pressure leaching is another significant processing technology for zinc. A n emerging technology for the treatment of zinc sulphides is heap leaching, with recent attention being given to bacterially-assisted heap leach technology. These technologies are reviewed in the following discussion. 2.3.1 Roast-Leach-Electrowinning A generalized flowsheet for the Roast-Leach-Electrowinning (RLE) process is shown in Figure 2-1. Within the roasting circuit, sphalerite is oxidized in air to form a mixed zinc oxide-ferrite calcine according to the following react ions: [ 1 1 , 2 0 J 7 Chapter 2: Literature Review Z n S + 1.5 0 2 = Z n O + S 0 2 2.1 ZnS + 2 FeS + 5 0 2 = Z n O F e 2 0 3 + 3 S 0 2 2.2 Within roast-leach-electrowinning operations the sulphur dioxide is sent to an acid plant where it is converted into sulphuric acid. H 2 S 0 4 A Zinc Sulphide Concentrate Acid Plant S O , Roasting Plant Leach Residue Acid Leach Neutral Leach Spent Electrolyte Calcine Crude Leach Liquor Zn Dust 1 Purification Electro winning Cd, Cu, N i , Co Pure Z n S 0 4 Electrolyte Zn Cathodes Figure 2-1. The basic roast-leach-electrowinning flowsheet for the electrolytic recovery of zinc source: Monhemius, A. J. (1980). "The electrolytic production of zinc." Critical Reports on Applied Chemistry, Volume /.'28] 8 Chapter 2: Literature Review The calcine (ZnO), which results from reactions 2.1 and 2.2 is then passed through a two-stage countercurrent leach in which the calcine readily dissolves in the presence of sulphuric a c i d , v i z : [ 1 , ; 2 9 ] ZnO + 2 H + = Z n 2 + + H 2 0 2.3 Reaction 2.3 is best understood by examining the corresponding Pourbaix diagram (Eh-pH diagram), which was first developed by Marcel Pourbaix in 1938 at the Technical University of Delft. A Pourbaix diagram is an attempt to overlay the redox and acid-base chemistry of an element onto the water stability diagram. These diagrams require both redox potentials and solubility products for their construction. They have been repeatedly proven to be an elegant way to represent the thermodynamic stability of chemical species in given aqueous environments.^ However, it should be noted that there are some points of interest which are not typically included in an Eh-pH diagram; these drawbacks can often lead to misinterpretations of a hydrometallurgical systems and care must be taken in extracting meaningful relationships from the diagram. The major drawbacks associated with using an Eh-pH diagram in practical mineral systems are summarized by House : [ 3 1 ] reaction kinetics are not generally considered^ intermediate reactions are not addressed (but which may be rate controll ing)' 3 3 1 • the chemical composition of solid or solution products may be uncertain • porous product layers, e.g. sulphur or hydroxides, may prevent further reaction • local solution conditions (pH, [M], etc.) may differ from those in bulk solution * Interested readers are encouraged to review Peters 1973 paper titled The Physical Chemistry of Hydrometallurgy for a complete discussion on the construction of Eh-pH diagrams and reaction kinetics.1 9 Chapter 2: Literature Review • gaseous reactant and / or product concentrations may be unknown chemical environment may be i l l defined, e.g. organics, anions and Fe° (grinding media) may be present • multimetallic particles may be present, producing catalytic effects or local galvanic couples • non-stoichiometric phases may be formed for which thermodynamic data are not considered or are unava i lab le^ Furthermore, House also suggests areas in which the general accuracy of the diagrams is diminished: [ 3 1 ] • accuracy is highly dependent on the extent and quality of the thermodynamic data used to construct the diagrams • accuracy decreases with decreasing relative concentration of the active species • accuracy decreases at the extremes of Eh and pH accuracy may be impacted for systems that operate at elevated temperatures (implementation of free-energy estimations are then required) • accuracy is impacted when the system is not at equilibrium • accuracy is impacted i f the nature of the solid species is i l l defined The Eh-ph diagram of the Zn-H jO system is shown in Figure 2-2. As illustrated, the dissolution of the zinc calcines wi l l occur at pH values of less than 5.5, hence the success of the neutral leach in the R L E process. 10 Chapter 2: Literature Review pH Figure 2-2. Eh-pH diagram for the Zn-HaO system at 25°C and 1 bar pressure, total dissolved zinc = 1.0 molal (1.0 mol kg" 1 H 2 0 ) source: adapted from Pourbaix, M. (1974). "Zinc. "Atlas of Electrochemical Equilibriums in Aqueous SolutionsP5^ In most operations, manganese di-oxide (MnCh) is added to oxidize ferrous iron to ferric iron, which then precipitates as ferric hydroxide, Fe(OH)3. Ferric hydroxide is a gelatinous slurry that is virtually impossible to filter and separate from the valuable zinc electrolyte. Removal of other impurities such as arsenic, antimony, and germanium from the system is achieved by adsorption on, or co-precipitation with, the ferric hydroxide. During roasting, iron in the feed combines with zinc to form ferrites, which are weak-acid insoluble. A s a result, ferritic zinc reports to the solid leach residues, which significantly 11 Chapter 2: Literature Review impacts overall zinc recoveries. This problem is especially pronounced in systems that have high iron concentrations in their f e e d / 1 2 8 ] The viability of the R L E process for the economic recovery of zinc from sulphide deposits that have inherently high iron content received a dramatic boost approximately 25 years ago with the advent of the Jarosite process. [ 2 8 ] With this process, iron is precipitated as a crystalline iron sulphate which can be readily filtered and removed from the system. Since the initial development of this technology a number of other effective methods for iron removal have been introduced, including: the Goethite process and the Haematite process. Greater detail is provided on each of these processing technologies in subsequent sections. As a result of the introduction of the Jarosite process into electrolytic plants, typical zinc recoveries have increased from approximately 89% to 9 8 % . [ 1 1 ' 2 8 ] Following the neutral leach, the pregnant solution is purified with zinc dust whereby impurities such as cadmium, copper, cobalt, nickel, arsenic, and antimony are precipitated by cementation, v iz: C d 2 + + Zn° = Z n 2 + + Cd° 2.4 6 C u 2 + + 2 A s 3 + + 9 Zn° = 9 Z n 2 + + 2 C u 3 A s 2.5 Fol lowing the purification stage, the pregnant electrolyte is sent to an electrowinning tankhouse where zinc metal is deposited on aluminum starter sheets, as shown in reaction 2.6. 12 Chapter 2: Literature Review cathodic reaction (E° = -0.763 volts) 2.6 Z n 2 + + 2 e " = Zn' The anodic reaction proceeds as follows: anodic reaction: (E° =+1.228 volts) 2.7 2 H 2 0 = 0 2 + 4 H + + 4 e According to thermodynamics, hydrogen gas wi l l be evolved before zinc ions can be reduced to zinc metal (i.e., E ° + / H = 0 V > ^Zni*/Zn« = -0.76 V ) . However, hydrogen gas requires a large overvoltage before it can evolve at an appreciable rate. This fortuitous circumstance renders the electrowinning of zinc from acidic electrolytes possible. Any impurities such as cadmium, cobalt, and arsenic, wi l l reduce this overvoltage and are therefore highly deleterious to zinc electrowinning. Although the conventional roast-leach-electrowinning process is, in essence, a hydrometallurgical process, it does not solve the inherent problem of SO2 emissions. Furthermore, as Verbaan advises, the cost of the equipment required to produce, store, and transport sulphuric acid often adds significantly to the process. [ 3 6 ] New processes that aim to avoid the production of SO2 are showing promising results. These processes produce elemental sulphur (acid pressure leaching) or sulphate in solution (heap leaching). 13 Chapter 2: Literature Review 2.3.2 Acid Pressure Leaching The acid pressure leaching of zinc sulphide concentrates is a complex process involving simultaneous dissolution of the sulphide minerals and precipitation of iron from solution within a pressurized and heated vessel, known as an autoclave. [ 3 7 ] The process of autoclaving sulphides was first proposed by Dr. Frank A . Forward of The University of Brit ish Columbia in 1948 and was eventually developed into a successful nickel refinery for Sherritt Gordon Mines, L t d . [ 3 0 ] A typical autoclave is illustrated in Figure 2-3 and a generalized flowsheet for the recovery of zinc via acid pressure leaching is illustrated in Figure 2-4. Feed, 70°C Figure 2-3. The Sherritt-Gordon autoclave for zinc pressure leaching A n adaptation o f this process was later developed for the processing of zinc sulphides; Sherritt's Zinc Pressure Leach process and the Sherritt-Cominco Process are discussed in greater detail in section 2.3.7. 14 Chapter 2: Literature Review Since its initial development the technology has been modified for a wide variety of existing operations and a number of spin-off processes have been proposed; the Vieil le-Montagne research department in Belgium has been particularly successful in addressing some of the iron control issues. [ 3 g ] The principal advantage of direct leaching under oxidizing conditions is that elemental sulphur, rather than sulphur dioxide, is formed. Furthermore, by eliminating the roasting stage in the R L E process the formation of ferrites can be avoided, and thus the processing of mixed sulphides or low-grade concentrates becomes viable. 07 Zinc Sulphide Concentrate i ZnS Pressure Leaching Spent Electrolyte L/S Separation Solids • Air, CaCQ 3 Liquor I Flotation JLAL Iron Removal Sulphur PbSC-4 Separation Separation is" \ Ta i l s \ PbS0 4 Electrowinning LA Zn Dust Purification Iron Residue T Cd, Cu t Zn Figure 2-4. The basic acid pressure leach flowsheet for the recovery of zinc source: Monhemius, A. J. (1980). "The electrolytic production of zinc." Critical Reports on Applied Chemistry, Volume /.[281 15 Chapter 2: Literature Review The behavior of sphalerite dissolution in an aqueous environment can vary dramatically, depending on the potential of the system and the level of acidity. Once again we rely on the Eh-pH diagram to help determine the various dissolution reactions that are possible. Unl ike the relatively simple diagram presented in Figure 2-2, we need to account for the presence of sulphur in the sphalerite. Our task is then to construct a S-H2O diagram and overlay it onto the Zn -F^O system; the results of this undertaking are illustrated in Figure 2-5 and Figure 2-6, respectively. 1.0 0.8 0.6 0.4 0.2 1 0.0 w -0.2 •0.4 -0.6 -0.8 •1.0 S03(a) HS04(-a) n 1 1 r "i r ~i 1 r H2S(a) S04(-2a) HS2(-a) HS(-a) 6 8 p H 10 S(-2a) 12 14 16 Figure 2-5. Eh-pH diagram for the S - H 2 0 system at 25°C and 1 bar pressure, total dissolved zinc = 1.0 molal (1.0 mol kg" 1 H 2 0 ) source: adapted from Peters, E. (1986). "Leaching of sulfides." Society of Mining Engineers, IncP0] 16 Chapter 2: Literature Review 1.0 0.8 0.6 T r -H S 0 4 1 soi H , 0 Figure 2-6. Eh-pH diagram for the Z n - S - H 2 0 system at 25°C and (STP) source: Peters, E. (J976). "Direct leaching of sulfides: chemistry and applications." Metallurgical Transactions B.m As can be observed in Figure 2-6, a very low pH would be required to achieve acid dissolution of sphalerite. This reaction, which occurs at pH < -2 .0 , proceeds as follows: ZnS + 2 H + = Z n 2 + + H 2 S 2.8 A t low pH and intermediate electrode potentials, zinc sulphide wi l l anodically dissolve to yield elemental sulphur, according to the following reaction: 1 3 9 1 ZnS = Z n 2 + + S° + 2 e" 2.9 17 Chapter 2: Literature Review The coupled cathodic reaction involves the reduction of oxygen to yield water: 0.5 0 2 +2 H + + 2 e " = H 2 0 2.10 The sulphur species that is thermodynamically stable at elevated electrode potentials is sulphate, which can be formed via the following reactions: The anodic reactions shown in reactions 2.9, 2.11, and 2.12 must be coupled with a cathodic reaction. It should be noted that the formation of elemental sulphur is preferable to that of sulphate as significantly less oxidizing agent is required {i.e., 2 e~ vs. 8 e~). The two predominant cathodic processes in zinc hydrometallurgy are the reduction of oxygen gas or the reduction of ferric ions. Oxygen gas is typically supplied either in air, or as a cryogenic gas. The reduction of oxygen to water is as follows: ZnS + 4 H 2 0 = Z n 2 + + S 0 4 2 " + 8 H + + 8 e 2.11 ZnS + 4 H 2 0 = Z n 2 + + HSO^ + 7 H + + 8 e 2.12 0 2 + 4 H + + 4 e = 2 H 2 0 2.13 18 Chapter 2: Literature Review The primary problems associated with the use of oxygen as an oxidant is that it has small solubility in aqueous solutions (although this can be offset with an increase in partial pressure), and it has a high cathodic activation over-potential on most mineral surfaces (i.e., activation polarized). A s a result, ferric ions are often used as a "surrogate oxidant" at the mineral surface in place of oxygen. The reduction of ferric ions by sphalerite is as follows : [ 3 0 ] The ferrous iron produced in reaction 2.14 is then re-oxidized to ferric by oxygen viz: Thus, combining reactions 2.9, 2.11, or 2.12 with either 2.13 or 2.14, plus reaction 2.15, yields the overall leaching reactions for sphalerite at electrode potentials > +0.3 volts (SHE), given as either reaction 2.16 or 2 .17 . [ 3 7 ' 4 0 ] ZnS + F e 2 ( S 0 4 ) 3 = Z n S 0 4 + 2 F e S 0 4 + S' 2.14 2 F e S 0 4 + H 2 S 0 4 + 0.5 0 2 = F e 2 ( S 0 4 ) 3 + H 2 0 2.15 ZnS + H 2 S 0 4 + 0.5 0 2 = Z n S 0 4 + S° + H 2 0 2.16 ZnS + 2 0 2 = Z n 2 + + S 0 4 ,2- 2.17 19 Chapter 2: Literature Review Concentrate pulp is leached at elevated temperature (150°C) under 1000 kPa oxygen pressure in a horizontal autoclave which is divided into four reaction chambers, as shown in Figure 2 -3 . [ 2 5 ; 4 1 ] Due to the relatively low melting temperature of sulphur (119°C), any elemental sulphur which is formed tends to produce insoluble product layers which coat un-reacted sphalerite particles. This effectively terminates leaching of the metal values since transport of an oxidant through the liquid sulphur layer is effectively impossible beyond a certain zinc convers ion .^ This tremendously detrimental effect is prevented by the addition of a surfactant known as lignin sulphonic acid to the leach solution, which disperses the sulphur and reveals the valuable zinc sulphide surface to the aggressive environment in the autoclave chamber. [ 4 2 ] Regeneration of the acid is achieved within the electrowinning tankhouse. Water is reduced to yield oxygen and two protons, as shown in equation 2.18. It should be noted that, as shown in reaction 2.16, two protons are consumed in the autoclave. Hence, the net acid consumption of the circuit is zero. H 2 O = 0.5 0 2 + 2 H + + 2 e " 2.18 The acid generated is then recycled back to the initial leaching stage where it drives the base metal sulphide dissolution reaction. Any need for makeup acid is generally satisfied by the partial oxidation of elemental sulphur in the autoclave, v iz: S + 1.5 0 2 + H 2 0 = H 2 S 0 4 2.19 20 Chapter 2: Literature Review Iron in the concentrate is rejected from the system as un-reacted pyrite mixed with elemental sulphur, or as jarosites in the leach residue; sulphur is separated by flotation or screening. Dissolved iron in the pregnant leach solution is removed by the addition of calcium carbonate; the iron then precipitates as a ferric hydroxide. Electrolyte purification and electrowinning are otherwise identical to that of the R L E process. [ 2 5 ] This process is highlighted in section 2.3.7, where the Sherritt-Cominco process is discussed in detail. 2.3.3 Heap Leaching The heap leaching of low-grade minerals is one of the oldest metallurgical operations known, yet its physics, chemistry, and hydrology have been poorly understood. [ 4 3 ] Heap leaching is useful for recovering metal values from low-grade ores. Mined ore is first crushed to liberate and expose the sulphide minerals; the crushed ore is then stacked on an impermeable pad and iron sulphate-sulphuric acid solution is sprayed or flooded on the upper surface of the heap. [ 2 ' 4 4 ] The acidic ferric sulphate solution is then allowed to trickle, under gravity, through the heap; metal sulphides react with the ferric iron according to reaction 2 .20 : [ 2 ' 4 5 ] M S + 2 F e 3 + = M 2 + + 2 F e 2 + + S° 2.20 In addition, the direct leaching of the metal sulphides by oxygen can be expressed as: . [46] 2 M S + 2 H 2 S 0 4 + 0 2 = 2 M S 0 4 + 2 S° + 2 H 2 0 2.21 21 Chapter 2: Literature Review Although direct oxidation of metal sulphides by oxygen does occur within sulphate media, its rate is hindered by the low solubility of oxygen in water coupled with the high temperature dependency of the reaction. Hence, the reaction expressed in equation 2.20 wi l l typically predominate within a heap leach environment. The resulting solution, which is pregnant with divalent metal ions, M , is collected at the base through perforated drain pipes and is then sent to purification and solvent extraction (SX) and eventual electrowinning (EW) for metals recovery. A typical heap flowsheet is shown in Figure 2-7. Although the process flowsheet for a typical heap leach operation is quite simple in contrast to the other processes discussed in this review, the complex chemistry that is involved in accurately describing its operation has made it far from being a simple technology to implement. Dutrizac and MacDonald postulated that the reactions that occur during heap leaching are complex and likely change with geometric position within the heap and with elapsed leaching time at any particular locat ion.^ This change in the leaching reaction is dependent on the leaching mechanism that is dominant at the individual leaching sites and can vary between: a) direct oxygen attack of the sulphide minerals, b) the dissolution by acidified ferric sulphate solutions, or c) the bacterial attack of sulphide minerals. 22 Chapter 2: Literature Review • t t t *_ —Ore From Mine-Stacked Ore Heap -To S X / E W -Pregnant Leach Pond -Barren Raffinate • Figure 2-7. A typical heap leach flowsheet One of the significant advantages of employing an acidified ferric ion leach is that the iron sulphate-sulphuric acid leaching medium can be prepared by the bacterial oxidation of pyrite (which is typically found with most sphalerite ores), either in situ (i.e. within a heap) or in separate aerated batch reactors. [ 2 J In addition, the acid is regenerated within the electrowinning circuit and is recycled back to the heap. It should be noted that the reagent concentration within a heap is typically low and at any particular time there is a deficiency of reagent in contact with the ore; as a consequence, continuous or repeated application of barren raffinate is essential to successful operation. [ 4 7 ] These reagents include sulphuric acid, ferric sulphate, and oxygen from air. 23 Chapter 2: Literature Review In addition to the complex chemical conditions that exist within a heap, the shear bulk of material that is processed can contribute to the difficulty in operating a heap; the mass of ore can be as much as 10, 000, 000 tonnes. [ 4 7 ] Furthermore, the operational time scale for a heap may extend to many years. Prosser observes that due to these complexities, there exists a great potential for serious errors to occur between the design and the operation of a heap. [ 4 7 ] 2.3.4 Goethite Process The Goethite process, as introduced in section 2.3.1, is a method for the reduction and elimination of iron from zinc sulphide ores that contain high iron content. The feed stream to the Goethite process is typically a zinc calcine, which is a value-added zinc oxide product from a roaster. The primary objective in the Goethite process is that of iron elimination in the roast-leach-electrowin process. [ 2 3 ] Zinc roaster calcine is leached with dilute acid in two stages. In the first stage ferrous iron is oxidized to ferric iron by injected air. The resulting ferric iron then precipitates as a hydrated ferric hydroxide, according to the reac t i on : [ l l ' 2 8 ] 4 F e 2 + + 0 2 + 6 H 2 0 = 4 F e O O H + 8 H + 2.22 This effectively prevents any iron from entering the zinc electrolyte purification and electrolysis stage. The ferric hydroxide is then re-dissolved (as is any iron in the zinc ferrite) in a subsequent hot acid leach. In the partial neutralization step that follows, calcine is first added to reduce the ferric iron in solution. This is done with the intent of preventing any uncontrolled precipitation of ferric hydroxide in the neutralization step; solid-liquid separation 24 Chapter 2: Literature Review is then carried out. A second stage of neutralization with ferrite-free calcine is then performed to adjust the pH of the solution to 3. This stage is also accompanied by further oxidation of F e 2 + to F e 3 + with injected air. Once the solution is neutralized gcethite precipitation takes place at 90°C viz: 2 F e 3 + + 4 H 2 0 = F e 2 0 3 • H 2 0 + 6 H + 2.23 A n adaptation of this process, known as the Paragcethite process, differs in that the ferric iron reduction stage is absent from the flowsheet. 2.3.5 Haematite Process The Haematite process employs a complex iron neutralization approach that is similar in nature to that of the Gcethite process. [ 1 1 ] In this process zinc ferrite is dissolved in the presence of sulphur dioxide and sulphuric acid to form ferrous sulphate according to the reaction: ZnO • F e 2 0 3 + S 0 2 + 2 H 2 S 0 4 = Z n S 0 4 + 2 F e S 0 4 + 2 H 2 0 2.24 Following the acid leach step, the leach liquor is reduced with either concentrate or SO2. The reduced liquor is then treated with calcine or calcium carbonate (CaCOs) in a pre-neutralization step. The pH is then adjusted with further additions of calcine or calcium carbonate and haematite. The solution is then fed to an autoclave operating at 180 - 200°C under 20 bar pressure (2MPa) in the presence of oxygen. The ferrous iron is oxidized to ferric iron and then precipitated as haematite according to the reaction: 25 Chapter 2: Literature Review 2 F e S 0 4 + 2 H 2 0 + 0.5 0 2 = F e 2 0 3 + 2 H 2 S 0 4 2.25 2.3.6 Jarosite Process The Jarosite process is the most widely employed iron precipitation process in zinc hydrometal lurgy. [ 1 1 ' 2 8 1 Iron precipitation is carried out on the leach liquor following p H adjustment to 1.5 with calcine as it exits a hot acid leach at 95°C. The iron is precipitated as sodium or ammonium salt as follows: 3 F e 3 + + M + + 2 S O 2 " + 6 H 2 0 = M F e 3 ( S 0 4 ) 2 ( O H ) 6 + 6 H + 2.26 where M + is N a (yielding natrojarosite) or N H 4 (yielding ammoniojarosite) Once formed, the jarosites wi l l not re-dissolve, even in strong acid. Hence, the residues may be subjected to a further hot acid leach step, called jarosite acid washing, which selectively dissolves any zinc ferrites, leaving only the jarosite residue, along with any insoluble lead or silver. A significant improvement on this technology was developed by Outokumpu and is called the Conversion process. The primary difference between this process and its predecessor is that the jarosite precipitation and acid-washing are combined in one step, according to the following reaction: 3 ZnO«Fe 2 0 3 + 6 H 2 S 0 4 + ( N H 4 ) 2 S 0 4 = 2 N H 4 F e 3 ( S 0 4 ) 2 (OH) 6 + 3 Z n S 0 4 2.27 26 Chapter 2: Literature Review By controlling the pH (to 1.7), conditions are created whereby zinc ferrites dissolve while jarosites simultaneously form and precipitate. The reaction is easily controlled by the feed rate of acid and virtually 100% leach recoveries have been achieved consistently.' 1 1 1 2.3.7 Sherritt Zinc Pressure Leach Process The Sherritt Zinc Pressure Leach process was first developed to treat zinc or lead-zinc concentrates to produce zinc sulphate directly in so lu t ion . [ 4 8 ' 4 9 ] The process was initially designed for direct integration into existing roast-leach-electrowin zinc operations in an attempt to reduce air pollution, brought about by the formation of sulphur dioxide; and solids pollution, in the form of non-leachable zinc ferrites. [ 5 0 J Fol lowing a successful demonstration of this technology in 1977, the world's first zinc pressure leaching plant at Cominco's Trail operations started production in 1981. [ 5 1 " 5 3 ] In the Sherritt-Cominco process, zinc is pressure leached in spent electrolyte by the oxidation of zinc sulphide with oxygen at 160°C and under 1000 kPa oxygen pressure in a horizontal autoclave (Figure 2-3). Elemental sulphur is produced instead of sulphur dioxide, and high leaching efficiencies, above 97%, are achieved in a single leaching step. [ 5 4 ] At elevated temperatures and pressures, sphalerite (ZnS), pyrrhotite (Fei_ xS, where x = 0 to 0.2) or iron within the sphalerite lattice (Zn[Fe]S - known as marmatite), galena (PbS), and chalcopyrite (CuFeS2) react with oxygen and sulphuric acid to form sulphates, elemental sulphur and water via the following react ions: [ 5 2 ' 5 3 ' 5 5 " 6 0 ] ZnS + H 2 S 0 4 + 0.5 0 2 Z n S 0 4 + H 2 0 + S1 i0 2.28 FeS + H 2 S 0 4 + 0.5 O F e S 0 4 + H 2 0 + S1 i0 2.29 PbS + H 2 S 0 4 + 0.5 0 2 P b S 0 4 + H 2 0 + S' 2.30 27 Chapter 2: Literature Review CuFeS 2 + 2 H 2 S 0 4 + 0 2 - C u S 0 4 + F e S 0 4 + 2 H 2 0 + 2 S1 iO 2.31 However, decomposition of the zinc sulphide by oxidative pressure leaching was found to be very slow; dissolved iron was shown to facilitate oxygen transfer and thereby significantly increased the dissolution rates of the sphalerite. The ferrous iron produced is further oxidized to ferric iron, a key to both zinc dissolution and the patenting of this technology, by the following reaction sequence^ 6 0" 6 2 1 Following zinc dissolution, the ferrous iron is subsequently reacted with oxygen and sulphuric acid to regenerate the ferric iron. As the leaching approaches completion (at elevated temperatures (160°C) and with diminishing acid concentrations) the lead and most of the ferric iron precipitates as complex plumbojarosite and hydronium jarosite, respect ive ly : [ 5 9 , 6 3 ] 2 F e S 0 4 + H 2 S 0 4 + 0.5 0 2 = F e 2 ( S 0 4 ) 3 + H 2 0 2.32 F e 2 ( S 0 4 ) 3 + ZnS = 2 F e S 0 4 + Z n S 0 4 + S' iO 2.33 3 F e 2 ( S 0 4 ) 3 + P b S 0 4 + 12 H 2 0 = P b F e 6 ( S 0 4 ) 4 ( O H ) 1 2 + 6 H 2 S 0 4 (plumbojarosite) 2.34 3 F e 2 ( S 0 4 ) 3 + 14 H 2 0 = ( H 3 0 ) 2 F e 6 ( S 0 4 ) 4 ( O H ) l 2 + 5 H 2 S 0 4 (hydronium jarosite) 2.35 28 Chapter 2: Literature Review According to the initial pilot plant trials, plumbojarosite retains approximately 2% zinc in its crystal structure (1% zinc remained as unreacted sulphide and the remaining 97% reported to the leach solut ion). [ 5 2 ] If sodium, potassium, or ammonium ions are present in the leach solution, the corresponding jarosite species wi l l be precipitated in the low acid leach. The resulting jarosites can be treated by any of the conventional iron precipitation processes, i.e., jarosite, haematite, gcethite, or paragoethite, for the removal of iron prior to zinc recovery. The acid that is generated as a result of the jarosite precipitation reactions is then recycled back to the initial leach stage of the process. [ 4 8 ] Elemental sulphur is separated from the plumbojarosite leach residue in a series of flotation cells. After remelting and hot filtration, the elemental sulphur is shipped to market in rail tank cars. Un-reacted zinc sulphide is separated from the molten sulphur and recycled to the zinc roasters for further recovery of the zinc values. [ 5 1 ] The slurry of zinc sulphate solution and leach residues is pumped to the Sulphide Leaching Plant for further processing. [ 6 4 ] Purification of the zinc sulphate solution and electrowinning of zinc metal is accomplished by conventional techniques. 2.3.8 Mount Isa Mines Process In 1994 Winborne and Wong, of Mount Isa Mines Ltd., patented an innovative process for the low temperature (30°C) extraction of zinc from a zinc transition ore by biological means. [ 6 5 ] A transition ore is the oxidized upper layer of an ore body, and in the case of sphalerite, contains the oxidation products: ZnSC^, Z n C 0 3 , ZnO, and ZnC>2. In addition, a large 29 Chapter 2: Literature Review component of the zinc remains in the sulphide form, ZnS. In this process, the ore can be stacked and treated in a heap or leached in-situ. The chemical dissolution of the oxide zinc species is believed to proceed as follows: In the column experiments that helped to form the backbone of the Mount Isa patent, chemical dissolution of the oxide products (plus the ZnSC>4 already present) accounted for approximately 20% of the total dissolved zinc. The remaining sphalerite is then oxidized by ferric sulphate in solution, viz: The ferric sulphate is continually regenerated by the oxidation of the reduced iron species, ferrous sulphate, via a biological oxidation mechanism. Microbial colonies that contain Thiobacillus ferrooxidans and Leptospirillum ferrooxidans exist within the heap and are responsible for the conversion of ferrous iron to ferric iron. In addition, the elemental sulphur that is formed in equation 2.38 can be further oxidized by the bacterial cultures to form sulphuric acid, v iz: Z n C 0 3 + H 2 S 0 4 = Z n S 0 4 + H 2 0 + C O 2.36 ZnO + H 2 S 0 4 = Z n S 0 4 + H 2 0 2.37 ZnS + F e 2 ( S 0 4 ) 3 = Z n S 0 4 + 2 F e S 0 4 + S1 2.38 30 Chapter 2: Literature Review 2 S° + 3 0 2 + 2 H 2 0 = 2 H 2 S 0 4 2.39 Thus, combining equations 2.38 and 2.39, the overall oxidation reaction of sphalerite can be written: 2 ZnS + 2 F e 2 ( S 0 4 ) 3 + 3 0 2 + 2 H 2 0 = 2 Z n S 0 4 + 4 F e S 0 4 + 2 H 2 S 0 4 2.40 Fol lowing dissolution of the zinc species, the pH of the solution is adjusted from 1.6 to 3.0 with limestone. This results in the precipitation of ferric hydroxide (Fe(OH)3). This step is vital to the process in that it purifies the solution prior to solvent extraction and electrowinning, and it also prevents a build up of iron in solution. A build up of iron may eventually lead to iron precipitating within the heap, which would ultimately lead to hydrology issues in the form of percolation problems. The resulting calcium sulphate and ferric hydroxide are then removed by filtration. The pregnant leach solution is then contacted with di-2-ethyl hexyl phosphoric acid (D2EHPA) and is subsequently stripped with sulphuric acid. The electrolyte can then be processed via conventional electrowinning. With this process, a total of 81% zinc was recovered from a transition ore that contained 3.79% zinc in a period of 290 days. 31 Chapter 2: Literature Review 2.3.9 Additional Processing Technology The following table provides information on additional processes for the recovery of zinc. Table 2-3. Additional processing technology for zinc from a primary source Process Name Leach Environment References of Interest C A N M E T F e C l 3 - N a C l [3; 66] C E N I M - L N E T I N H 4 C l - 0 2 (105°C and 150 kPa of 0 2 pressure) [3; 66] Comprex Ac id leach (200 to 220°C) [54] Elkem F e C l 3 / C u C l 3 (110°C) [12] Intec Zinc B r C L f (Halex™) (85°C) [67] Minemet Recherche C u C l 2 (50 to 100°C) [3; 68] Modif ied Zincex Dilute H 2 S 0 4 [26; 29; 54; 69] 32 Chapter 2: Literature Review 2.4 Bacterial Leaching From as early as 1947, bacteria have been widely recognized as playing an important role in the dissolution of sulphides, although the exact function of the bacteria still remains uncertain. [ 7 0 " 7 2 ] Microbial leaching was widely practiced in dump and underground uranium operations, as outlined by McCready and Gould for the Ell iot Lake area in Ontario, Canada. 1 7 3 1 The ore was treated by a modified in-situ technique in which the ore was leached with microbial assistance in previously mined underground stopes. It has also gained acceptance in the recovery of copper and gold in various operations around the wor ld . [ 7 4 " 7 6 ] Heap bio-leaching of secondary copper sulphide ores has been employed commercially since 1980 at numerous operations. [ 7 7 ] In 1989, it was estimated that over 25% of all copper produced in the United States came from biological processes. [ 7 8 ] The advent of biologically assisted leaching has allowed for the development of previously known ore deposits which, due to their complex chemistry, have remained unexplo i ted. [ 7 9 ' 8 0 1 The development and optimization of these processes requires a fundamental understanding of the mechanisms and behavior of the bacteria involved in the oxidation of sulphide minerals. Within an acid environment there are a host of bacteria that have been identified as being able to facilitate the oxidation of sulphide minerals: Acidithiobacillus spp., Ferrobacillus spp. and the genera Sulfolobus, Leptospirillum, and Metallogenium are implicated.^ 4 5 1 Habashi offers a brief list of bacteria that he believes is of primary interest in the leaching of ores, Table 2-4. It should be noted that within Table 2-4, Habashi incorporates Byrner's assertion that the 33 Chapter 2: Literature Review bacteria derive their energy for growth from either the oxidation of sulphide ions to sulphate, or from the oxidation of ferrous iron to ferric i ron . [ 8 1 ] Table 2-4. Bacteria of importance in hydrometallurgy Bacterium Source of Energy Discoverer Acidithiobacillus thiooxidans Oxidation of S°, S 0 2 , S 2 0 2 " Waksman and Joffe (1922) Acidithiobacillus ferrooxidans Oxidation of F e 2 + , S 2 0 2 " Colmer, Temple, and Hinkle (1949) Ferrobacillus ferrooxidans Oxidation o f F e 2 + Leathen and Braley (1954) Bryner and Jameson (1958) Ferrobacillus sulphooxidans Oxidation o fS° , F e 2 + Kinsel (1960) source: Habashi, F. (1970). "Leaching of sulfides." Hydrometallurgy: Principles of extractive metallurgy. Oxidation potentials within these systems can reach, and maintain, values in the 600 - 800 m V S H E range. This corresponds to the high ferric to ferrous ratios that can be obtained in solut ion. [ 8 2 ] If we invoke the Eh-pH diagram that was previously introduced (Figure 2-6), we can superimpose the region where bacterially assisted oxidation predominates. This is shown in Figure 2-8. 34 Chapter 2: Literature Review There is significant controversy over identifying the number of bacterial species that are involved in the leaching process. Torma concluded that only two species were active during leaching, viz. Acidithiobacillus ferrooxidans, and Acidithiobacillus thiooxidans^ Studies by Silver indicated that the organism known as Acidithiobacillus ferrooxidans may not be one distinct bacterium, but rather a group of metabolically similar microbesJ 8 4- 1 His evidence was based on the fact that these bacteria, when grown on different sulphide substrates, were found 35 Chapter 2: Literature Review to contain deoxyribonucleic acid ( D N A ) of different base compositions.* A n explanation of this phenomenon was to come in 1988 with Norr is 's research which revealed the existence of another important bacterial strain, Leptospirillum ferrooxidans^ This host of bacterial agents assists in the dissolution of metal sulphides by catalyzing the oxidation reactions that would otherwise not proceed at a commercially useful rate at ambient temperature and pressure. The notable difference between these species of bacteria resides in the elements from which they obtain their energy for growth. These characteristics are discussed below. 2.4.1 Biology of Bacteria The iron-oxidizing, Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans, and sulphur-oxidizing bacteria, Acidithiobacillus thiooxidans (and to some extent Acidithiobacillus ferrooxidans), are widely distributed in nature and can often be found in soils, sediments, and the effluent of mine tailings and waste dumps. They are morphologically similar to each other and physically resemble the bacteria shown in Figure 2 -9 . f 8 7 ] A schematic representation of the cell structure of A. ferrooxidans is provided by Rossi in Figure 2-10. Leptospirillum ferrooxidans are not related to the Acidithiobacilli, but the two are commonly associated during the leaching of sulphide minerals. [ 8 8 ] L. ferrooxidans can be distinguished * Interested readers are directed to Rawlings recent paper (2001) titled The molecular genetics ofThiobacillus ferrooxidans and other mesophilic, acidophilic, chemolithotrophic, iron- or sulfur- oxidizing bacteria for a thorough review of the molecular genetics of these bacteria.'851 36 Chapter 2: Literature Review from A. ferrooxidans by visual examination, as its form ranges from a helix to a curved rod to a vibrio (comma shaped), whereas A. ferrooxidans are simply rod-shaped (with varying widths). L. ferrooxidans are efficient at oxidizing Fe(II), but are not capable of oxidizing S°. Figure 2-9. Gram stain of rod-shaped Acidithiobacillus ferrooxidans The flagellum (tail) of the Acidithiobacillus ferrooxidans gives the organism mobility source: photograph taken by Amy Chan, Earth and Ocean Sciences, The University of British Columbia, 2001. OM ML N CM > 4 NF Figure 2-10. Schematic diagram of Acidithiobacillus ferrooxidans OM = outer membrane; ML = electron-transparent layer; I = electron-dense middle layer; N = electron-transparent layer separating cell wall from plasma membrane; CM = cytoplasmic membrane; M = mesosome-type structure; NF = DNA filaments; R = ribosomes; MS = membrane structure; G = bean-like small granules with large inclusions C; P = cytoplasm; NR = nuclear region; J, = inclusions displaying internal structure; J 2 = inclusions with a "foot". source: Rossi, G. (1990). "Fundamentals."Biohydrometallurgy, pg. 51 [S-l] 37 Chapter 2: Literature Review Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans are the most commercially useful of the bacterial species that have been isolated. Bryner and Jameson were successful in isolating bacterial organisms on both ferrous ions and a sulphur substrate and described the Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans to be motile, gram negative rods that varied in width from 0.5 - 0.8 microns and in length from 1.0 - 1.3 microns. [ 8 1 ] Since that time, researchers have been striving to identify the characteristics that define each bacterial strain. [ 9 0 ] These microorganisms are acidophilic, aerobic, and autotrophic, i.e., they function best in acidic mediums of pH 0.5 - 3, require oxygen, and derive energy for cell structure and metabolic growth from an inorganic carbon source, such as carbon d iox ide . [ 8 7 ' 9 1 1 It is felt that, in comparison with Acidithiobacillus thiooxidans, Acidithiobacillus ferrooxidans are more efficient at oxidizing sphalerite. [ 9 2 ] 2.4.2 Bacterial Growth Kinetics There are four distinct phases of growth for all bacterium species in batch reactors, namely, the lag phase, the growth phase, the stationary phase, and the death phase. These phases are shown graphically in Figure 2-11. 38 Chapter 2: Literature Review stationary phase time Figure 2-11. Typical bacteria growth curve source: adapted from Rossi, G. (1990). "Fundamentals." Biohydrometallurgy, pg. J / . ' 8 9 ' The lag phase typically occurs following inoculation of a system with a fresh bacterial culture. The length of the lag phase is a function of the age of the inoculum, the viable cell concentration of the inoculum, the extent to which the bacteria have been adapted to the substrate, and the presence of any inhibitory or deleterious substances. The growth phase, also known as the exponential phase, occurs when the cells have adapted to their new environment and are dividing at a constant rate (z. e., the maximum rate for the species under the given conditions of temperature, pH , nutrients, oxygen, etc.) and are beginning to contribute to the oxidation of the target sulphide. The onset of bacterial leaching, taking sphalerite as an example, is indicated by: a) a rapid increase in the dissolved concentration of Z n 2 + , b) a rapid increase in solution potential (Eh) due to the oxidation of Fe(II) to Fe(III), and c) an increase in acidity (if acid generating conditions are favored (i.e., pyrite oxidation)). [ 9 3 1 39 Chapter 2: Literature Review Within the growth phase the time required for a population of microorganisms to increase by a factor of two (doubling time) is a measure of both the growth rate of the bacterial population and the suitability of the substrate to promote and support microbial growth. [ 8 9 ] Rossi summarizes the minimum doubling times of Acidithiobacillus ferrooxidans grown on a variety of substrates in Table 2-5. O f note is that the doubling time for A. ferrooxidans can range from 6 hours when grown on ferrous iron to 8 days when grown on sulphur. Table 2-5. Min imum doubling times of Acidithiobacillus ferrooxidans grown on various substrates Organism Substrate Doubling Time (h) A cidithio bacil lus ferrooxidans Iron medium 10 Acidithiobacillus ferrooxidans 9K medium 8 Acidithiobacillus ferrooxidans Ferrous iron 6 . 5 - 1 0 . 0 Acidithiobacillus ferrooxidans Ferrous iron 5 - 6 Acidithiobacillus ferrooxidans Sulphur 192 Acidithiobacillus ferrooxidans Sulphur 168 Acidithiobacillus ferrooxidans Chalcopyrite cone. 1 4 - 1 7 Acidithiobacillus ferrooxidans Chalcopyrite cone. 38.4 ±2 .9 Acidithiobacillus ferrooxidans Galena bulk cone. 39.6 ±2 .7 source: adapted from Rossi, G. (1990). "Fundamentals." Biohydrometallurgy, pg. 50. 40 Chapter 2: Literature Review The stationary phase represents a point in the life-cycle of the bacteria where there is no longer a net increase in the cell population. This can be the result of a number of detrimental factors, including energy source depletion (or the source is no longer bioavailable), nutrient depletion, intolerable concentration of waste products in the medium, low solution pH (due to the acid generating nature of the dominant reactions), impaired gas-liquid mass transfer, or an unacceptable increase in the temperature of the environment (due to localized internal heat generation as a result of sulphide conversion or due to external environmental sources). As a result, the rate of cell division wi l l equal the rate of cell death, and the net growth becomes zero. Within a hydrometallurgical operation this phase is usually denoted by a decrease in the leaching rates and a leveling of the solution potential. The death phase represents the point where the bacteria's environment can no longer sustain life and is usually a result of an unbearable level of toxicity from waste products. If fresh nutrients or substrate are not introduced the bacteria wi l l die. Within a hydrometallurgical operation this phase is typically characterized by a sharp decline in solution potential and a reduction in the rate of new metal dissolving into solution. It is desirable, from an operations standpoint, to make the appropriate changes to the biological system such that the system, as a whole, remains in the growth phase (Figure 2-11). With this taken into consideration, it is possible to operate in a continuous fashion. 41 Chapter 2: Literature Review 2.4.3 Bacterial Dependence on Temperature Bacterial growth rates and biological activity are profoundly affected by the ambient temperature and each microbial species has three temperature values, known as cardinal temperatures', a minimum temperature, below which growth does not occur (due to death or dormancy); an optimum temperature, at which the growth rate is maximal, and a maximum temperature, which is typically only a few degrees Celsius higher than the optimal temperature. Beyond the maximum temperature threshold of the respective bacteria death is usually imminent. Figure 2-12 illustrates this change in biological activity with temperature. 1/T Figure 2-12. Change in biological activity with temperature Current literature on the application o f biological processes continues to be dominated by studies of low-temperature bacteria such as A. ferrooxidans and L. ferrooxidans. However, it has long been known that certain species are capable of withstanding elevated temperatures. Sulfolobus acidocaldarius, Sulfolobus BC, and Acidianus brierleyi have been shown to be 42 Chapter 2: Literature Review able to perform their metabolic processes at elevated temperatures.' 9 4 ' 9 5 J Recently, another high-temperature bacterium, Sulfolobus rivotincti, has been shown to have a capacity for recovering high percentages of copper and z inc. ' 9 6 1 When discussing the role of these various bacteria in a commercial application it is often convenient to group them into three broad categories on the basis of the temperature range in which they are the most active. Figure 2-13 illustrates the optimum temperature ranges for these three categories: mesophiles, moderate thermophiles, and extreme thermophiles. These three categories encompass the entire spectrum of biological species that contribute to the leaching o f ores in hydrometallurgical systems. o ;' / ' \ Mesophiles ' Thermophiles -*—s ' / Extreme ^ 1 f Thermophiles ( / ' \ / \ / i : : ' * A / 7 x i < 20 30 40 50 60 70 80 90 Temperature, ° C Figure 2-13. Optimum temperature ranges for bacteria source: adapted from Todar, Kenneth (2003). "Physical Requirements of Microorganisms: the effect of temperature on growth" University of Wisconins-Madison} 43 Chapter 2: Literature Review By taking advantage of both the catalytic effect and the optimal operating temperature of the bacteria a hydrometallurgical operation can be tailored to achieve maximum recoveries J 9 8 ' For instance, a batch leach operation may only employ high temperature extreme thermophiles, whereas a heap leach operation may employ all three types of bacteria during the various stages of the heap's "warm-up" cycle. This assumes that heat is generated within the heap as the bacteria oxidize sulphide minerals to form acid and heat. t 1 0 0 1 The presence of temperature-tolerant bacteria presents new possibilities for leaching, since an increase in temperature may result in an increase in the rate of metal extraction. A rule of thumb is that the chemical reaction rate doubles for each 10°C rise in temperature. This relationship has been confirmed for Acidithiobacillus ferrooxidans that have been cultured on sphalerite. [ 1 0 1 ] 2.4.4 Bacterial Dependence on Nutrients In addition to requiring an energy source that can be oxidized, there are several inorganic salts which are essential for bacterial growth. The nutrient requirements for Acidithiobacillus ferrooxidans are said to be typical for a chemosynthetic autotroph and include: carbon dioxide (for cell growth), ammonium sulphate and di-potassium hydrogen phosphate (as nitrogen and phosphate sources), ferrous iron and sulphur compounds (as energy sources), and magnesium sulphate, potassium chloride and calcium nitrate (as growth factors) . [ 8 3 ' 1 0 2 1 Although a wide variation in nutrient media can be utilized to maintain bacterial cultures, the most commonly used is called the 9 K medium, which was originally developed by Silverman and Lundgren, Table 2 -6 . [ 1 0 3 ] 44 Chapter 2: Literature Review Table 2-6. Composition of Silverman and Lundgren's 9 K nutrient medium Compound Concentration ( g L ') F e S 0 4 - 7 H 2 0 44 .2 T ( N H 4 ) 2 S 0 4 3.0 K 2 H P 0 4 0.5 M g S 0 4 - 7 H 2 0 0.5 KC1 0.1 C a ( N 0 3 ) 2 4 H 2 0 0.01 H 2 S 0 4 0.49 source: Silverman, M. P. and Lundgren, D. G. (1959). "Studies on the chemoautotrophic iron bacterium Ferrobacillus ferrooxidans: I. An improved medium and a harvesting procedure for securing high cell yields. "Journal of Bacteriology.'l03] 9 K nutrient solution is only employed for laboratory culturing of bacteria since in an industrial operation the reagent consumption would be cost prohibitive. Tuovinen et al. have shown that for a suspension of 10 8 cells m L - 1 the lowest concentrations of magnesium and sulphate, that would not limit bacterial growth, were 2 mg L _ 1 and 2 g L _ 1 , respectively. From an industrial scale, nitrogen and phosphorous can be added in the form of relatively inexpensive fertilizers, or can exist as a result of blasting with ammonium nitrate and fuel oi l (ANFO) . Because oxygen is the primary electron acceptor for bacterial respiration and for oxidation reactions, it is required in large quantities (every pound of sulphur as sulphide requires about this corresponds to ~ 9 g L 1 Fe2 +, hence the name 9K 45 Chapter 2: Literature Review two pounds o f oxygen for complete conversion to sulphate).' 8 3 1 Independent studies by Bai ley and Hansford (1994) and Boon and Heijnen (1998) confirmed that one of the major factors affecting the rate of biooxidation was the magnitude of the oxygen demand and that designers must maximize the oxygen transfer potential of the sys tem. ' 1 0 4 ' 1 0 5 1 The low solubility of oxygen in typical bioleach solutions (6 to 8 mg L - 1 at STP) necessitates rates of gas-liquid mass transfer. L i u et al. determined that i f the oxygen concentration in solution falls below 0.2 mg L _ 1 then biooxidation of ferrous iron ceases. ' 1 0 6 1 Savic et al. determined that the critical oxygen transfer rate for the oxidation of F e 2 + by Acidithiobacillus ferrooxidans was approximately 0.03 mmol 0 2 L _ 1 m i n - 1 . ' 1 0 7 1 The need to design a leaching system with high agitation and/or high rates of aeration also lends itself to the bacteria's need for carbon dioxide. The microorganisms require carbon dioxide for carbon synthesis (which builds biomass) and since air only contains 0.03% CO2, high rates of aeration are required to achieve and maintain high biomass. Norris observed that although thermophilic bacteria were affected by a lack of carbon dioxide their effective activity on the oxidation of pyrite was unchanged at values as low as 0.1% (v v _ 1 ) CO2. ' 1 0 8 1 Torma et al also observed that the overall zinc extraction rate was highly dependent upon the carbon dioxide content of the air that is used in aerating a leach. ' 1 0 9 1 Norris and Owen caution that although these nutrients are required by all bacterial species, their utilization and metabolism are unique to phylogenetically distinct groups. ' 1 1 0 1 Hackl recommends that the actual amounts of nutrients required for a particular application need to be determined on a case-by-case basis. ' 9 1 1 46 Chapter 2: Literature Review 2.4.5 Bacterial Leaching Mechanisms Sutton and Corrick, whose initial work on the bacterial oxidation of pyrite laid the foundations for our current understanding of the leaching mechanisms, believed that the pyrite was initially oxidized by air, as shown in equation 2 . 4 1 . ^ The resulting ferrous iron is then oxidized by the bacteria to a trivalent state via equation 2.42. The ferric sulphate subsequently attacks the pyrite to form sulphuric acid and more ferrous sulphate, as shown in equation 2.43, which is then oxidized via equation 2.42. This so-called propagation cycle now forms our current understanding of acid rock drainage ( A R D ) . f 4 5 ' 7 1 ' m ' " 2 ] Sutton and Corrick also proposed that the resulting ferric sulphate medium produced by bacterial action on pyrite could leach other base metal sulphides such as chalcocite, covellite, and bornite. 2 FeS 2 + 7 0 2 + 2 H 2 0 = 2 F e S 0 4 + 2 H 2 S 0 4 2.41 bacteria * A^ 4 F e S 0 4 + 2 H 2 S 0 4 + 0 2 = 2 F e 2 ( S 0 4 ) 3 + 2 H 2 0 2 - 4 2 7 F e 2 ( S 0 4 ) 3 + FeS 2 + 8 H 2 0 = 15 F e S 0 4 + 8 H 2 S 0 4 2.43 Two bacterial leaching mechanisms have been proposed for the oxidation of sulphide minerals: a) the direct bacterial attack of the mineral in the presence of dissolved oxygen, and b) the indirect leaching action of ferric ion brought about by bacterial oxidation of dissolved iron in the presence of oxygen.^ Equation 2.44 and Figure 2-14 illustrates the oxidation of sphalerite under direct attack by bacteria, and equations 2.45 and 2.46 and 47 Chapter 2: Literature Review Figure 2-15 illustrate the indirect leaching route. The role of the bacteria in the latter leaching mechanism is to continually re-oxidize ferrous ions to ferr ic. [ 3 3 ] bacteria o A A ZnS + 0.5 0 , + H , S 0 4 = Z n S 0 4 + S° + H 2 0 z - 4 4 4 F e 2 + + 0 2 + 4 H + = 4 F e 3 + + 2 H 2 0 2.45 ZnS + 2 F e 3 + = Z n 2 + + S ° + 2 F e 2 + 2.46 Cell Wall Fe2* Cell Membrane FT 0 , +4H • 4e >2H20 Cytoplasm Periplasm JEfl > v — ^ r r e / / / / / / / Sulfide Mineral/ / Figure 2-14. Direct leaching of a sulphide substrate T E M picture shows Leptospirillum ferrooxidans with elemental sulphur colloids source: adapted from Boon, M. and Heijnen, J. J. (2001). "Solid-liquid mass transfer limitation of ferrous iron in the chemical oxidation ofFeS2 at high redox potential." Hydrometallurgy. 48 Chapter 2: Literature Review Figure 2-15. Indirect leaching mechanism source: adapted from Boon, M. and Heijnan, J. J. (1993). "Mechanisms and rate limiting steps in bioleaching of sphalerite, chalcopyrite and pyrite with Acidithiobacillus ferrooxidans." Biohydrometallurgical Technologies: Bioleaching Processes. The Minerals, Metals and Materials Society (TMS)}U^ Controversy remains as to whether direct bacterial attack occurs at the sulphide surface or not. Different groups of workers have reached different conclusions on this point with respect to chalcopyrite, bornite, sphalerite, galena, molybdenite, and pyr i te. [ 4 5 ] In addition, the possibility for "microenvironments" to be established in the form of a biof i lm at the surface of pyrite minerals may further muddy the waters as to what is classified as "direct" or " indirect" . 1 1 1 5 1 In 1990, Wil l iams offered a possible phenomenon which he believed occurred in conjunction with both direct and indirect mechanisms, and in the case of sulphide oxidation, might underlie much of the discrepancies that exist between various f indings. [ 4 5 ] Wi l l iams suggested that Acidithiobacilli may be capable of effectively removing a protective elemental sulphur film from the surface of sulphide particles, thereby exposing fresh sulphide surfaces for further oxidation by ferric sulphate. This phenomenon has been supported by both 49 Chapter 2: Literature Review experimental studies as well as mathematical models. ' 1 1 6 1 Long-term biological leaching experiments by Byerley and Scharer on the bacterially assisted leaching o f sphalerite concluded that the rate-controlling step is the direct oxidation of the sulphide sulphur moiety with oxygen as the terminal electron receptor.' 1 1 7 1 Studies by Cheng-Hsien and Harrison (1995), and Fowler and Crundwell (1998) have concluded that they could find no evidence that supports a direct leaching mechanism for the bacterial leaching of sphalerite, although the solution potential of a system with bacteria is elevated relative to those systems wi thout . ' 9 5 ' 1 1 8 1 Fowler and Crundwell refined their statement in 1999 to include the possibility that Acidithiobacillus ferrooxidans may also enhance the leaching rate of sphalerite by removing a thin elemental sulphur layer from the mineral . ' 1 1 9 1 A similar conclusion was reached by Boon and Heijnen who proposed a model that described the indirect leaching mechanism of sphalerite and the formation of jarosite layers that inhibit leaching. ' 1 1 4 1 A separate study by Boon et al. also led to the conclusion that indirect leaching was the primary mechanism by which sphalerite is ox id ized. ' 1 2 0 1 It is probable that both mechanisms occur simultaneously and cooperatively during actual leaching operations involving commercial o r e s . ' 2 ' 7 0 ' 1 1 4 ' 1 2 1 - 1 2 4 1 There remains, however, a profound lack of knowledge on the extent to which a system wi l l experience oxidation via bacteria attack vs. chemical attack. Taylor et al. has attempted to quantify these oxidation mechanisms using stable isotopic fractionation techniques and has concluded that Acidithiobacillus ferrooxidans contributes significantly to the oxidation of 50 Chapter 2: Literature Review sulphide minerals in well-aerated, unsaturated environments (as much as 77% contribution to pyrite conversion by direct attack).' 1 2 5 1 Sharma et al. quantified this effect on zinc contained in low-grade flotation tailings and found that approximately 50% o f total zinc extracted was a result of the presence of bacteria (25% Zn extraction by purely chemical means and 75% by a T126' 1271 combination of both chemical and bacterial). ' ' As in most cases in hydrometallurgy, the true answer may lie in the kinetics of the system. Singer and Stumm determined that oxidation of ferrous ion by Acidithiobacillus ferrooxidans proceeded at a rate 10 6 times faster that the chemical oxidation of ferrous ions by dissolved oxygen (2x10 - 1 3 g m i n - 1 ce l l " 1 ) . ' 7 6 ' 1 1 2 1 This dramatic increase in the activity of the system with the presence of bacteria may provide the definitive answer to addressing the issue of direct vs. indirect bacterial oxidation of sulphide minerals. 2.4.6 Electrochemical Aspects of Bioleaching of Sulphides Sulphide minerals, which behave as anodic electrodes within an acid medium, can be arranged in the form of a galvanic series, as shown in Table 2-7. In an electrochemical cell formed by two sulphide minerals of different potential values, the sulphide having the lower potential wi l l dissolve first. As soon as this sulphide is consumed (or passivated) the material with the next lowest potential wi l l begin to dissolve. ' 1 2 8 1 The selective dissolution of a sulphide mineral, such as sphalerite, can be achieved from a complex, multisulphide system which contains nobler sulphides, such as pyrite or chalcopyrite. Furthermore, the rate of galvanic dissolution can be accelerated by the presence of bac ter ia . ' 1 2 9 ' 1 3 0 ] This galvanic leaching mechanism is illustrated in Figure 2-16. 51 Chapter 2: Literature Review Table 2-7. Galvanic series of some base metal sulphides in a bioleaching medium Sulphide Mineral Chemical Formula Pyrite FeS 2 N O B L E Chalcopyrite CuFeS2 Pentlandite (Fe, N i ) 9 S 8 Galena PbS Pyrrhotite Fe i . x S Sphalerite ZnS B A S E source: Natarajan, K. A. (1990). "Electrochemical aspects of bioleaching of base-metal sulfides." Microbial Mineral Recovery.[m] Figure 2-16. Galvanic effect during the leaching of ZnS with FeS 2 source: adapted from Venkatachalam, S. (1998). "Electrochemistry in leaching of sulphides." Transactions of the Indian Institute of Metals.^ Malouf and Prater first demonstrated the galvanic effect of pyrite addition on the oxidation of sphalerite in the presence of bacteria, as shown in Figure 2-17. ' 1 3 ' 1 Sphalerite leaching was dramatically augmented with the addition of pyrite. They believed that the bacterially generated ferric ions significantly increased the oxidation of sphalerite and that the bacteria 52 Chapter 2: Literature Review were operating as catalysts in the system. Work by Konishi et al. supported this claim and found that the leaching rates of zinc from sphalerite were enhanced by the presence of i ron . [ 1 2 4 ] Early studies by Romankiw and Bruyn (1963) on the leaching of natural sphalerite containing iron in the lattice (marmatite) showed an increase in the rate of dissolution over that of crystalline zinc sulphide. [ 1 3 2 ] Similar work by Frenay (1985) indicated that the presence o f iron in the lattice o f a sphalerite mineral dramatically increases the conductivity of sphalerite, and thus, its rate of dissolution. ' 1 3^ Murr and Mehta confirmed that galvanic conversion and bacterial catalysis (with Acidithiobacillus ferrooxidans) of sphalerite each have a significant, yet independent, effect on the rate of leaching, as shown in Figure 2 - 1 8 . [ 1 3 4 ' 1 3 5 1 It is readily apparent in Figure 2-18 that coupling the pyrite with sphalerite significantly accelerates the conversion of zinc. It is also evident that the presence of bacteria contributes appreciably to the overall extraction of zinc, both in the galvanically coupled systems and in the monosulphide experiments. This galvanic preference has been observed by Torres et al. who also suggested that the presence of Cu(II) promotes the dissolution of sphalerite. 1 1 3 6 1 53 Chapter 2: Literature Review Sphalerite plus Pyrite, Inoculated Sampl Sphalerite. Inoculated Sample , Sphalerite plus I'vrite, Sterile Sample w ^ — — — I S O l00 0 a y s 3 5 0 Figure 2-17. Effect of pyrite on the bacterial leaching of sphalerite source: Malouf, E. E. and Prater, J. D. (1961). "Role of bacteria in the alteration of sulfide minerals." Journal ofMetals.[n]] teocnms time (days) Figure 2-18. Zinc extraction with galvanic couple (FeS2 / ZnS) Leaching in acid-sterile lixiviants is denoted C, while leaching in acid-bacterial lixiviants is denoted A.f. (A. ferrooxidans) and TH (thermophiles), respectively. Conditions: pH 2.3; 100 rpm agitation rate. Symbols represent (0) TH, 55°C; (•) A.f., 30°C; (•)TH, 55°C; (Q) C, 55°C; (•) A.f., 30°C; (•) C, 30°C; (o) C, 55°C; (o) C, 30°C. source: Murr, L. E. and Mehta, A. P. (1983). "The role of iron in metal sulfide leaching by galvanic interaction." Biotechnology and Bioengineering}]M^ 54 Chapter 2: Literature Review Typical oxidation rate constants for pyrite, chalcopyrite, and sphalerite are summarized in Table 2-8. From Table 2-8 it can be seen that the presence of bacteria can increase the rate constant for sphalerite by. up to four orders of magnitude. Also seen in this Table is the effect of lowering the temperature and raising the acidity of the system beyond the bacteria's optimal values. Table 2-8. Average oxidation rates constants of sulphide minerals under varying conditions Oxidation Rate Constant (mol m 2 h ') Components T = 30°C;pH = 3.0 T = 4°C; pH = 7.0 With Bacteria Chemical With Bacteria Chemical Pyrite 2.39x10 - 5 1.53xl0" 6 2.32x10"7 2.30x10" 7 Chalcopyrite 2.40x10 - 6 4.83xl0~ 1 0 1.5xl0"1 0 1.5x10"'° Chalcopyrite with Pyrite 5.16xl0" 6 6.75x10" 7 2.13xl0"7 2.10xl0" 7 Sphalerite 2.79x10" 6 6.87x10"" 2.3x10"" 2.3x10"" Sphalerite with Pyrite 5.07xl0" 6 2.49x10 - 7 8.47x10"8 8.4x10 - 8 source: Byerley, J. J. and Scharer, J. M. (1992). "Natural release of copper and zinc into the aquatic environment." Hydrometallurgy.1"71 Natarajan examined the effects of various electro- and bio-chemical mechanisms involved in the bioleaching of mixed sulphide sys tems. ' 1 3 0 ' I 3 7 ; 1 3 8 ] He has shown that both the activity and growth of Acidithiobacillus ferrooxidans and the dissolution of pyrite, chalcopyrite, and sphalerite were enhanced at a positive applied potential in the range o f 400 to 650 m V (vs. 55 Chapter 2: Literature Review S C E , saturated calomel electrode). Natarajan also demonstrated that sphalerite dissolution is solely promoted under a negative applied potential of -500 m V (SCE). Natarajan concluded that electrobioleaching enables faster and more selective dissolution of sulphide minerals from complex sulphides over that of simple bioleaching. ' 1 3 7 1 Furthermore, it has also been demonstrated that under negative applied potentials the reduction of ferric iron to ferrous dramatically promotes bacterial activity and growth. ' 1 3 9 1 This effect was also illustrated in Yunker and Radovich's 1986 study whereby Acidithiobacillus ferrooxidans, maintained at 29°C and a pH of 1.6, experienced an increase in the rate of F e 2 + oxidation in the order of 1.5 times, and cell production rate in the order of 6.5 times, when a constant current of 1000 raA was appl ied. ' 1 4 0 1 Selvi et al. continued Natarajan's original work and found that electrobioleaching of a sphalerite concentrate (monosulphide) under a positive potential of +400mV (SCE) was more efficient than at -500 m V (SCE) due to the fact that under the positive potentials the formation of elemental sulphur was favored and the direct attack mechanism became predominant.' 1 4 1 1 Jyothi et al. have reported the influence of galvanic interactions in the bioleaching of mixed sulphides containing pyrite, chalcopyrite, galena, and sphalerite with respect to different binary, ternary, and quaternary mixtures. ' 1 4 2 1 They have correlated the galvanic currents and combination potentials, measured in different combinations with the observed leaching behavior o f chalcopyrite and sphalerite. 56 Chapter 2: Literature Review Balaz et al. have determined that bacterial leaching of mixed sphalerite-pyrite systems can be dramatically augmented by mechanically activating the respective minerals by intensive grinding. The changes to the surface-structure of sphalerite led to an increase in the bacterial leaching kinetics of 3 to 4 t imes. ' 1 2 8 1 Additional augmentation of a bioleach system containing A. ferrooxidans was studied by Harahuc et al. who determined that addition of phosphates and chlorides could result in the preferential oxidation of the zinc over i ron. ' 1 4 3 1 By selectively adding specific anions and inhibitors they were able to manipulate the metals extracted from an ore sample, and thus, eliminate or reduce the amount of contaminating metals in the pregnant leach solution. 2.5 Kinetics of Leaching Zinc Sulphide Determination of the activation energy of zinc sulphide varies from system to system, and from ore to ore. In 1988 Crundwell described a fundamental model for the dissolution of sphalerite. The model incorporates the entire structure of sphalerite (which includes iron in the lattice) with semiconductor electrochemistry. The model predicts a first-order dependence of the dissolution rate on the concentration of iron in the sphalerite and a half-order dependence on the concentration of oxidant in solut ion. ' 1 4 4 1 Figure 2-19 shows the effect of iron content of (Zn, Fe)S on the rate of dissolut ion. ' 1 1 7 1 57 Chapter 2: Literature Review iron content of (Zn, FtjS, *fc Figure 2-19. Effect of iron content on (Zn, Fe)S on the rate of dissolution source: adapted from Crundwell, F. K. (1988). "Effect of iron impurity in zinc sulfide concentrates on the rate of dissolution." American Institute of Chemical Engineers, 34(7), 1128-1134.1"71 Perez and Dutrizac also observed that the rate of sphalerite leaching increased in a linear manner with increasing iron content. They also concluded that the activation energy for sphalerite in a sulphate system operating between 20 and 90°C ranged from 41 to 72 kJ m o l - 1 and that activation energy decreased with increasing iron content in the sphalerite matr ix. [ 2 7 ] Dutrizac observed that the leaching reaction is electrochemical in nature and is controlled by charge transfer at the sphalerite surface.^ The dissolution of sphalerite in aqueous sulphuric acid, as measured by Romankiw and Bruyn, was determined to be 46.05 kJ m o l - 1 . Choi et al. found the dissolution o f zinc sulphide flotation concentrate to be controlled, at high leaching rates, by solid-state diffusion of Zn through the ZnS lattice with an activation energy of 21.3 kJ mol - 1. 1- 3 3- 1 Ballester et al. observed a similar value of 21.86 kJ mol" 1 during bioleaching of sphalerite concentrates.' 1 4 5 1 The activation energy for the pressure oxidation of zinc sulphide in dilute sulphuric acid in the presence of cobalt was found by Niederkorn to be 21.27 kJ mol ' . [ 5 0 1 Harvey et al. observed a wide range of activation energies in pressure oxidation 58 Chapter 2: Literature Review experiments of sphalerite from a complex ore; activation energy values ranged from 16.4 to 40.0 kJ m o l - 1 , depending on the oxygen concentration employed. [ 4 0 ] Pressure oxidation experiments conducted by Misra on a multimetallic zinc sulphide had an activation energy of S S k J m o r 1 . 1 1 4 6 1 A further summary o f activation energy values for the dissolution o f zinc sulphide is provided by Kaskiala and reproduced in Table 2-9. [ 1 4 7 1 Table 2-9. Activation energies for the dissolution of zinc sulphide Researcher Temperature, °C [Fe3 + ] , M [ H 2 S 0 4 ] , M E a , kJ mol 1 Halavaara 50-80 0.3 0.25 ' 29.5 Halavaara 80-100 0.3 0.25 74.4 Palencia 50-90 0.3 0.3 41-72 Crundwell 78 0.5 0.1 46 Verbaan [ 1 4 8 ] 25-85 0.4 0.1 56.64 •: adapted from Kaskiala, T. (2001). "Atmospheric direct leaching of sphalerite: Part 11 - Reaction kinetics. " Rep. TKK-MK-125, Helsinki University of Technology, Helsinki University of Technology. 59 Chapter 3: Experimental Procedures 3. E X P E R I M E N T A L P R O C E D U R E S Equation Section (Next)The experimental program developed for this study was divided into two phases: • Bacterially assisted, short column leaching of sphalerite; • Controlled potential, isothermal, chemical leaching of sphalerite. 3.1 Bacterially Assisted Short Column Leaching This phase of the study was conducted in an attempt to characterize the leaching behavior of the sphalerite ore with a mixed particle size at a specific temperature. The tests were conducted in short (1-foot in length) leaching columns submerged in thermostatic water baths, as shown in Figure 3-1. The configuration of an individual column is illustrated in Figure 3-2. Chapter 3: Experimental Procedures These baths each contain four leaching columns, a baffle to ensure adequate circulation of the heated water, an immersion heater, a recirculation pump, a fitted hood which helps maintain the temperature of the bath, and caps for each column to help minimize evaporative losses. The polyethylene construction of the apparatus allows for tests to be performed at temperatures up to 80°C, at either a constant temperature or along any desired temperature-time trajectory. This makes them ideal for testing various thermal phenomena that occur during heap leaching such as heap warm-up and diurnal cycling. Leach Solution Column Cap 1 Schedule 80 P V C Pipe Perforated Insert Bottom of Water Tank Double Bolted |_ Flange Pregnant Leach Solution A i r Feed 61 Chapter 3: Experimental Procedures Figure 3-2. Short column configuration Furthermore, since the columns are independent of each other, each may be started up and broken down without affecting the other columns sharing the same water bath. This allows for identical columns to be run in parallel for different lengths of time. Since the columns are small, the kinetics are comparatively uniform across the length of the column, thus facilitating the rapid and accurate determination of leaching kinetics. If desired, the columns may be run in tandem by pumping solution and/or air from column to column, both within a single bath at a single temperature, or across baths at different temperatures to simulate f low through a heap with a significant thermal gradient. With this configuration, simulation of depth within a heap can be achieved (in 1 -foot increments). A schematic of four columns operating in tandem is shown in Figure 3-3. Raffinate Feed A i r + 1 % C 0 2 P L S Col lect ion; 62 Chapter 3: Experimental Procedures Figure 3-3. Four columns operating in tandem To enhance the leaching kinetics, and to simulate conditions in a'full-scale, industrial heap leaching operation, bacteria were introduced into the system. 3.1.1 Bacterial Culturing Bacterial cultures from each of the three broad categories that were discussed in section 2.4 (mesophiles, moderate thermophiles, and extreme thermophiles) were obtained from Little Bear Labs in Golden Colorado (5906 Mclntyre St Bldg #2 Golden, C O 80403, Phone: 303-273-5697, Fax: 303-273-0494). These cultures were developed from a host of sources and had been adapted and grown on pulverized sphalerite ore from an industrial source. The characterization of the respective bacterial groups, as identified by Little Bear Lab, is presented in Table 3-1. Table 3-1. Characterization of bacteria adapted to zinc sulphide ore Bacterial Group Identified Strains / Notes Mesophiles developed from mixed environmental isolates included some mixed heterotrophs A cidithiobacillus ferrooxidans Acidithiobacillus thiooxidans Acidiphilium acidophilum mixed sulfur and iron oxidizers Leptospirillum ferrooxidans Moderate Thermophiles developed from mixed environmental isolates Sulfobacillus spp. Acidithiobacillus caldus 63 Chapter 3: Experimental Procedures Extreme Thermophiles developed from mixed environmental isolates and strains purchased from the Deutsche Sammlung von Mikroorganismen und Zellkulturen G m b H (DSMZ) Catalogue of Strains mixed Archaea Acidianus brierleyi Metallosphaera sedula mixed Sulfolobus spp. undefined strains: not fully characterized The mesophiles, moderate thermophiles, and extreme thermophiles were cultured in shaking incubators (150 rpm) at temperatures of 30, 50, and 70°C, respectively. To reduce the concentration o f total dissolved solids in solution and to replenish the supply o f nutrients available for metabolic growth, the cultures were transferred on a weekly basis into fresh medium. Transferring the cultures on a frequent schedule ensures that bacterial populations never achieve the stationary phase, but remain perpetually in the growth phase of the logistic growth curve (Figure 2-11). This results in hearty and robust cultures. The complete transferring procedures are provided in Appendix C. The nutrient medium into which the respective cultures were transferred was adapted from the 9 K solution and the strain-specific media recommended by the Deutsche Sammlung von Mikroorganismen und Zellkulturen G m b H (DSMZ) Medium archive, and are shown in Table 3-2. The notable decrease in ferrous iron concentration, as compared to the 9 K solution, can be attributed to the fact that the bacteria are cultured on sphalerite ore, which contributes the majority of the iron that is required by the bacteria. 64 Chapter 3: Experimental Procedures Table 3-2. Nutrient medium composition . . . Moderate and Mesophiles „ „ , , ., Extreme Thermophiles Component Concentration, g L" 1 Concentration, g LT1 ( N H 4 ) 2 S 0 4 0.8 1.5 K H 2 P 0 4 0.3 0.25 MgS0 4 «7H 2 0 2.0 0.7 F e S 0 4 ' 7 H 2 0 1.0 0.5 trace elements solution 1.0 1.0 pH adjusted to 1.8 with 6MH2SO4 Individual S° requirements are added during the transferring The composition of the trace elements in solution is shown in Table 3-3, and was adapted from D S M Z Media #88. Table 3-3. Composition of the trace elements solution Component Concentration, mg L 1 M n C l 2 * 4 H 2 0 1.8 N a 2 B 4 O 7 * 1 0 H 2 O 4.5 ZnS0 4 »7H 2 0 0.22 C u C l 2 ' 2 H 2 0 0.05 VOS0 4 »2H 2 0 0.03 C o S 0 4 0.01 65 Chapter 3: Experimental Procedures 3.1.2 Sample Preparation A homogenous blend of ore was achieved through repeated coning and quartering of the as-received zinc sulphide ore. Representative sub-samples were obtained by passing the blended ore thrice through a Jone's riffle splitter. Table 3-4 summarized the mineralogical analysis of the ore, as provided by Tech-Cominco. Table 3-4. Mineralogical analysis of the as-received ore Composition Zn(Fe)S FeS 2 PbS B a S 0 4 S i 0 2 CdS S C Grade, % 19.94 9.05 5.335 3.398 58. 0.128 0.12 0.25 The particle size distribution of the blended ore was established by passing the material through a standard Tyler sieve series on a RoTap Sieve Shaker for 15 minutes. The mass of material that was retained on each sieve was then used to determine the cumulative weight percent of material that passed a respective sieve size; the particle distribution is shown in Figure 3-4. Approximately 80% of the blended material passed through a 3/8" screen (Pgo = 9.2 mm). Random samples were extracted from the blended ore and pulverized. The head grade for the bacterially assisted short column leaching experiments was determined by taking an average of three random scoops of the pulverized sample, followed by analysis via Induction Coupled Plasma. The sulphur species assays were determined by gravimetric analysis. The procedures for ICP and gravimetric analysis are given in Appendix C . 66 Chapter 3: Experimental Procedures 100 90 ^ 80 ri> .S 70 in in ro Q. 60 c a> " 50 0) Q. re | 30 5 20 1.5 2.0 2.5 3.0 3.5 L o g Part icle S ize , Log(um) 4.0 X X X X X X X X X X X X V , — i i ' 1 4.5 Figure 3-4. Particle size distribution of blended zinc-sulphide ore A more accurate head analysis was achieved by taking the average of repetitive scoops from individual size fractions of the blended ore; the collected samples were then ground and pulverized and analyzed by ICP. The head grade for each element was then determined by summing the weighted grades from each sieve size; this calculation is shown in equation 3.1. 4.13 %Zn=Yj(%wtmainedtl)-(%Zn) 3.1 1=1.72 The results of these chemical analyses are shown in Table 3-5. As can be seen, the results are very similar. For the purposes of establishing the percent extraction in subsequent experiments, the head analysis which was determined via sieve analysis was utilized. 67 Chapter 3: Experimental Procedures Table 3-5. Chemical analysis of as-received zinc sulphide ore Sample Zn (%) Pb (%) Fe (%) S T (%) S° (%) S2 _ (%) S S 0 4 ( % ) As-Received Pulp: 3 Random Scoops of Pulverized Head Sample Replicate 1 14.87 5.01 6.37 14.97 0.12 14.16 0.52 Replicate 2 15.20 4.38 5.61 13.38 0.12 12.84 0.53 Replicate 3 15.51 4.78 6.48 14.81 0.19 13.78 0.64 Average 15.19 4.72 6.15 14.49 0.14 13.59 0.56 As-Received Pulp: Random Scoops of Pulverized Size Fractions 0 weighted values) +3 Mesh 4.74 1.27 2.54 5.08 0.02 4.85 0.16 +6 Mesh 3.14 0.92 1.21 2.88 0.02 2.74 0.10 +8 Mesh 1.09 0.31 0.43 1.00 0.01 0.95 0.04 +10 Mesh 0.76 0.22 0.30 0.71 0.01 0.67 0.03 +20 Mesh 1.14 0.33 0.45 1.09 0.01 1.03 0.04 +28 Mesh 0.50 0.14 0.19 0.46 0.01 0.43 0.02 +35 Mesh 0.42 0.13 0.16 0.40 0.01 0.37 0.02 +50 Mesh 0.39 0.12 0.15 0.37 0.01 0.34 0.02 +65 Mesh 0.37 0.11 0.14 0.35 0.01 0.32 0.02 +100 Mesh 0.84 0.25 0.29 0.74 0.02 0.66 0.06 +150 Mesh 0.40 0.13 0.13 0.35 0.01 0.32 0.03 +200 Mesh 0.45 0.14 0.15 0.38 0.01 0.34 0.03 -200 Mesh 0.81 0.26 0.26 0.69 0.03 0.61 0.06 Sum 15.03 4.31 6.39 14.49 0.17 13.62 0.60 68 Chapter 3: Experimental Procedures The homogenous sub-samples, which were obtained after the series of coning and quartering and riffle splitting procedures, were then agglomerated with 3 M sulphuric acid on a bottle-roll apparatus for approximately 15 minutes. The resulting moisture content was 5%. The blended ore and the resulting agglomerates are shown in Figure 3-5. Figure 3-5. Typical composition of a) the blended zinc ore and b) agglomerated zinc ore The agglomerated ore was then stacked into 1 -foot leaching columns as illustrated in Figure 3-2. Leach solution with a pH of 1.10 (10 g L _ 1 acid) and a redox potential (ORP s ) of 475 m V vs. A g / A g C l (697 SHE) was then fed at a rate of 1 litre per day with a specific f low rate of 5.3 L m~ hr - 1 . The potential of the leach solution was obtained by thoroughly mixing 25.14 g of ferrous sulphate (FeS0 4 »7H 2 0), 22.61 g of ferric sulphate (Fe 2 (S0 4 ) 3 »5H 2 0) , and 100 g of pure H 2 S 0 4 in 10 litres of deionized water, thus yielding a ferric ion to ferrous ion ratio (Fe 3 + :Fe 2 + ) of 1:1. § ORP determined by Nernst Equation ( EAg/Agci = E° - R17NF • ln(Fe2+/Fe3+) - 222.30 mV) 69 Chapter 3: Experimental Procedures 3.1.3 Experimental Program A total o f six bacterially assisted, short column leaching experiments were performed. 3-6 provides an overview of the conditions of the respective experiments. Table 3-6. Overview of bacterially assisted, short column leaching experiments Experiment Temperature A i r Depth Experiment Leach Chemistry Number °C Feed ft [ F e U g L""1 F e 3 + : F e 2 + [Acid] t ot , g L - 1 1 30 A i r + 1 % C 0 2 1 1 1:1 10 2 50 A i r + 1 % C 0 2 1 1 1:1 10 3 •70 A i r + 1 % C 0 2 1 1 1:1 10 4 30 A i r + 1 % C 0 2 4 1 1:1 10 5 50 A i r + 1 % C 0 2 4 1 1:1 10 6 70 100% 0 2 1 1 1:1 10 Experiments 1 to 3 consisted of four identical columns per experiment (replicates), and simulated the top one foot of a heap. Each experiment operated at a temperature regime corresponding with the three primary bacterial groups that were employed, namely mesophiles, moderate thermophiles, and extreme thermophiles, and operated at their respective optimum cardinal temperatures: 30, 50, and 70°C. A i r , enriched with 1% carbon dioxide, was introduced at the base of each column. This provided both a source of oxygen for bacterial respiration and sphalerite oxidation, and a source o f carbon for bacterial growth. 70 Chapter 3: Experimental Procedures Experiments 4 and 5 were run with each of the four columns (per leaching apparatus) arranged in tandem (Figure 3-3). Solution from the bottom of each column was pumped to the top of the next column in the series. In this manner, the top four feet of a heap were simulated. Experiments 4 and 5 were also run at 30 and 50°C, respectively. A i r , enriched with 1 % carbon dioxide, was introduced at the base of each column. Experiment number 6 was identical to number 3 except that 100% 0 2 was introduced to two replicate columns to help promote sphalerite oxidation. This experiment was initiated as a scoping study to determine i f the rates of oxidation in the other experiments were oxygen limited. It was felt that sufficient carbon dioxide for metabolic growth of the bacteria would diffuse into the column from the environment. Approximately one week after each column was loaded with agglomerated ore, 150 mL containing a consortia of equal parts of mesophiles, moderates, and extreme thermophiles was introduced as an inoculum. The one-week waiting period was imposed for two reasons. First, it allowed for the determination of readily leachable zinc (ZnO and ZnS04). The solution collected during the initial two days of the experiments was rich in dissolved zinc. This mass of zinc seen during the initial stages of leaching was taken as the amount of acid soluble zinc in the ore. Second, it allowed the initial acid used during ore agglomeration to be flushed from the columns, thereby raising the p H of the system to correspond with that of the entering leach solution. This ensured that the bacteria would not be entering a hazardous environment. 71 Chapter 3: Experimental Procedures The pregnant leach solution exiting the columns was collected after a single pass and analyzed for dissolved zinc and iron via atomic adsorption spectroscopy ( A A S procedures are provided in Appendix C). Sampling of each column was conducted twice a week; p H , O R P , solution-borne bacterial populations, and dissolved zinc and iron were monitored and recorded. pH was measured using a V W R standard calomel combination p H electrode (33221-048) with a V W R meter (model 2100 with temperature correction). O R P was measured using an Orion combination platinum electrode (9678BN) and V W R meter (model 2100). Bacteria samples containing 5 mL of P L S were first fixed with 0.5 m L formaldehyde before being sent for bacterial enumeration (bacterial enumeration procedures are provided in Appendix C). Based on the extent of oxidation with time established by the solution assays, one column from experiments 1, 2, 3, and 6, was broken down and the solids were analyzed for attached bacterial populations, zinc, iron, lead, elemental sulphur, sulphide sulphur, and sulphate sulphur. This allowed for the accurate tracking of the extent of oxidation with time within each of the replicate sets of columns. To determine the number of bacteria attached to mineral surfaces, approximately 15 g of solids were fixed with 1 m L of formaldehyde and 10 mL of the mesophile medium described in Table 3-2. The fixed sample was then sent for bacterial enumeration (Appendix C). 72 Chapter 3: Experimental Procedures Since the columns within experiments 4 and 5 were operating in tandem, the extent of oxidation within each foot of the 4-foot simulation could not be determined until the end of the experimental program. 3.2 Controlled Potential, Isothermal, Chemical Leaching This phase of the study was conducted to identify three fundamental aspects of sphalerite leaching: 1) the topology of the ore, 2) the activation energy of the oxidation reaction, and 3) the dependency of the ore on ferric and ferrous ions. The controlled chemical leaching experiments were performed in a jacketed stirred tank Appl ikon reactor, as shown in Figure 3-6. The versatility of the solid-state circuitry in the Appl ikon controller allows for the precise control of redox potential, p H , and temperature. A peristaltic pump delivers 4% hydrogen peroxide (H2O2) as required to maintain a constant redox potential through the subsequent regeneration of ferric ions. Similarly, p H is controlled through the addition of 6 M sulfuric acid (H2SO4). Temperature is maintained with a hot water bath, a dedicated pump, and the water jacket that surrounds the reactor. Oxygen migration into the reactor vessel is countered by introducing nitrogen into the system via a nitrogen sparger. Agitation of the suspended solids is provided by a variable-speed stirrer operating at 800 rpm with a stainless steel pitched-blade impeller. A set of four stainless steel baffles are inserted into the vessel to prevent vortexing of the solution. The amount of reagent added is determined by placing the vessels which contained the respective reagents onto a 73 Chapter 3: Experimental Procedures BP3100 S Sartoris laboratory scale, and recording the difference in mass over time. The Pyrex container which is used to hold the reservoir of H2O2 is covered and sealed to minimize decomposition of the hydrogen peroxide by ultraviolet light. N 2 Sparger L H2SO4 Port Water Jacket e Agitator m pH and Eh Probes Condenser —I H 2 0 2 Port Controller Agitation H 2 0 2 H 2 S 0 4 Control Pump Pump Ijgg Figure 3-6. Appl ikon reactor: controlled potential leaching apparatus 74 Chapter 3: Experimental Procedures 3.2.1 Sample Preparation The material used in this study was a ground and pulverized sample of the blended as-received ore discussed in section 3.1.2. The pulverized material was then screened to ensure that a minus 38 um particle size was obtained. Replicate samples of this -400 mesh material were sent to International Plasma Laboratory (IPL) for analysis via Inductively Coupled Plasma Emission Spectrophotometry (ICP). The result of the analysis of two replicates of the sub 400 mesh material is shown in Table 3-7. Table 3-7. Chemical analysis of -400 Mesh zinc sulphide ore Sample Zn (%) Pb (%) Fe (%) S T (%) S° (%) S2 _ (%) S S 0 4 ( % ) Replicate 1 23.03 7.96 6.54 18.74 0.40 16.76 1.41 Replicate 2 22.34 7.81 6.45 18.18 0.37 16.32 1.44 Average 22.69 7.88 6.49 18.46 0.39 16.54 1.43 A particle size distribution was obtained for the -400 mesh particles by util izing a Malvern Mastersizer 2000. Fitting the particle size distribution data from an average of two samples with known numerical methods revealed that the ore closely follows a Rosin-Rammler distribution with a parameter value of m = 1.18, D* = 15.51, and a P 8 0 of 24 um, as shown in Figure 3-7. 75 Chapter 3: Experimental Procedures -0.50 0.00 0.50 1.00 , 1.50 2.00 L o g D (um) Figure 3-7. Particle size distribution for -400 mesh material used in potentiostatic experiments 3.2.2 Experimental Program In each experiment, 20 g of -400 mesh ore was added to 1.6 L of deionized water containing 10 g LT 1 H 2 S 0 4 (pH 1.1) resulting in a 1.25% pulp density. Iron was added to the solution in the form of ferrous sulphide (FeS0 4 »7H 2 0) and ferric sulphide (Fe2(S0 4)3»5H 20) (to a total of 1.0 g Fe) according to the target ferric to ferrous ratio. Table 3-8 provides an overview of the conditions of the respective experiments. 76 Chapter 3: Experimental Procedures Table 3-8. Overview of controlled potential, isothermal, chemical leaching experiments Experiment Temperature O R P , m V F e 3 + : F e 2 + Total Iron Pulp Density Number °C vs. A g / A g C l Ratio g % T l 70 525 . . 1.05 0.994 1.24 T2 55 495 1.05 1.021 1.28 T3 40 490 1.05 1.062 1.33 PI 70 661 98.60 0.998 1.25 P2 70 580 9.97 0.983 1.23 P3 70 451 0.10 0.988 1.23 Although a constant ferric to ferrous ratio was utilized in experiments T1-T3 a decrease in the redox potential was noted. This is a function of the decrease in the operating temperature. To start an experiment, the reactor containing 1.6 L of deionized water containing 1.0 g total iron (composed of a mixture of the respective ferrous and ferric salts) and 10 g L" 1 acid was first heated to the target operating temperature. Once the desired temperature was achieved, the Appl ikon controller was programmed to maintain the at-temperature O R P and pH of the system. Fol lowing this, the reactor was charged with 20 g of -400 mesh sphalerite ore to a pulp density of 1.25%. p H and solution O R P were measured using the same probes discussed in section 3.1.3. The solution potential was maintained through the addition of 4% H2O2. The oxidation of ferrous ions to ferric ions occurs according to equation 3.2:^ 1 4 9 1 H 2 0 2 + 2 F e 2 + + 2 H + = 2 F e 3 + + 2 H 2 0 3.2 77 Chapter 3: Experimental Procedures Solution samples were taken at appropriate sampling intervals with a syringe. The samples were centrifuged at 800 g and 5 mL of supernatant were extracted into a sealed via l ; the remaining solution and solids were returned to the reactor. Upon completion of each experimental run, the reactor contents were filtered and dried at 40°C to minimize the tendency for further oxidation. The dried solids were sent for 30-element ICP analysis and the solution samples were analyzed in-house via atomic adsorption spectroscopy for aqueous zinc and iron. 78 Chapter 4: Experimental Results 4. E X P E R I M E N T A L R E S U L T S Equation Section (Next)The following chapter provides a summary of the results that were obtained from both the bacterially assisted short column leaching experiments and the controlled potential, isothermal chemical leaching experiments. 4.1 Results of Bacterially Assisted Short Column Leaching Experiments The complete results for the bacterially assisted short column leaching experiments can be found in Appendix A . 4.1.1 Results of Experiment Number 1 - Four Replicates at 30°C The dissolved zinc and iron concentrations with time, as determined by A A S , for four replicate columns operating at 30°C (experiment number 1 as summarized in Table 3-6) are shown in Figure 4-1 and Figure 4-2, respectively. 5500 5000 4500 4000 3500 L 0)3000 E ^ 2 5 0 0 2000 1500 1000 500 0 0 &£a a o <^ CECl n A 0 A ° A 2 " O O rfgHHn A A q>c§ A £n • A A A • ^ O ^ . - A AA O ay a A ^ g -o * A A A A 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n S t ream, d o Replicate 1 o Replicate 2 o Replicate 3 A Replicate 4 Figure 4-1. Zinc concentration in solution for four replicate columns operating at 30°C 79 Chapter 4: Experimental Results 2500 2000 7 1500 _l E o" £. 1000 500 • A A a A A B P o A A A 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 Time on Stream, d © Replicate 1 • Replicate 2 o Replicate 3 A Replicate 4 Figure 4-2. Iron concentration in solution for four replicate columns operating at 30°C note: the entering leach solution contained 1 g L'1 dissolved iron A s outlined in the experimental procedures (Table 3-6), there is a concentration of 1.0 g LT1 iron in the entering leach solution entering the solution. Thus, it can be noted from Figure 4-2 that there is an increase in the concentration of dissolved iron in this system. The amount of zinc extracted with time can be determined via equation 4.1. The zinc extraction profile is shown in Figure 4-3. % Zn Extracted = 1=1 ([Zn\,gL-iy (Volume, L) [Zn Grade, %)• [Packed Mass, g) 4.1 Based on the extent of oxidation established by the solution assays, one column from experiments 1-3 was broken down and the solids analyzed. The respective columns were 80 Chapter 4: Experimental Results taken offline after being leached for 54, 117, 234, and 305 days. When the last column was taken offline, the maximum extraction achieved was 74.3%. 100 90 80 o 20 10 >0 . A A A A A A 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 3: T i m e on St ream, d o Replicate 1 • Replicate 2 o Replicate 3 A Replicate 4 Figure 4-3. Zinc extraction in solution for four replicate columns operating at 30°C (based on solution assays) The pH and potential (ORP) of the four replicates are shown in Figure 4-4 and Figure 4-5, respectively. 81 Chapter 4: Experimental Results 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 °d33&n to • A j , 6 AQ A A A • - A A A A £ A A -20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n S t ream, d o Replicate 1 • Replicate 2 o Replicate 3 A Replicate 4 Figure 4-4. p H for four replicate columns operating at 30°C 800 750 700 O 650 < O) 600 < > E 500 O 450 400 350 300 0 O A A o QAA 'Jo 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n S t ream, d o Replicate 1 • Replicate 2 o Replicate 3 A Replicate 4 Figure 4-5. O R P of four replicate columns operating at 30°C It should be noted that the percentage of zinc extracted calculated in equation 4.1 is based on the cumulative amount of zinc that has been assayed in solution. Therefore, any errors in 82 Chapter 4: Experimental Results assaying wi l l accrue over time. Analysis of the solids recovered from each column provides a more accurate determination of the amount of zinc extracted with time. Figure 4-6 illustrates the zinc extraction based on solids analysis (ICP) and Table 4-1 summarizes these extraction values. 100 80 70 c 60 o I 50 4-1 X 111 c N 40 30 20 10 0 -| , , , , , r—_, , , , , , , , r — 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n S t ream, d Figure 4-6. Zinc extraction of four replicate columns operating at 30°C (based on solids assays) Table 4-1. Extraction values obtained by solution and solids analysis for four replicate columns operating at 30°C Replicate Time on Stream . Zinc Extraction, % Number days Solution (AAS) Solids (ICP) 1 2 3 4 54 117 234 305 20.49 51.03 65.15 74.33 21.50 44.85 64.93 74.62 83 Chapter 4: Experimental Results Solution samples sent for bacterial analyses indicate that there is a large difference between the bacterial populations attached to particle surfaces and in solution. Figure 4-7 illustrates this difference for the last replicate that was taken off stream from experiment number 1 (30°C). The results of bacterial enumeration have been normalized to cell count per m L of solution. The numbers of bacteria attached to mineral surfaces were measured upon taking down the respective columns. X o o o o o o 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 Time on Stream (since inoculation), d o Bacteria in Solution x Bacteria on Solids I Figure 4-7. Bacterial cell counts for four replicate columns operating at 30°C Table 4-2 summarizes the mass balance for zinc and Table 4-3 summarizes the overall mass balance for experiment number 1. 84 1E+11 1E+10 1E+09 1E+08 c % 1E+07 W1E+06 •jjj 1E+05 in =1E+04 O 1E+03 1E+02 1E+01 1E+00 Chapter 4: Experimental Results Table 4-2. Zinc mass balance for four replicate columns operating at 30°C Replicate Head Tails Solution Total Out Close Number g g g g % 1 630.68 495.06 129.21 624.27 1.02 2 631.20 348.10 322.10 670.20 -6.18 3 636.30 223.18 414.55 637.73 -0.22 4 635.59 161.34 472.46 633.80 0.28 Table 4-3. Overall mass balance for four replicate columns operating at 30°C Replicate Mass In Mass Out Difference Close Number g g g % 1 4196.15 4065.79 130.36 3.10 2 4199.58 3977.24 222.34 5.29 3 4233.56 3865.77 367.79 8.69 4 4228.80 3909.73 319.07 7.55 Table 4-4 summarizes the chemical analysis of the tailings from each of the replicates. Table 4-4. Chemical analysis of tailings from four replicate columns operating at 30°C Replicate Zn Pb Fe St S° s-2 Ss04 Number % % % % % % % 1 12.60 4.68 5.87 14.22 0.76 12.76 0.55 2 9.62 5.39 5.38 13.31 2.73 9.89 0.67 3 6.61 4.27 5.02 10.82 2.47 7.60 0.57 4 4.82 5.93 3.39 12.23 5.42 5.78 0.83 85 Chapter 4: Experimental Results Rates of heat generation can be estimated from the metallurgical balances for zinc, lead, iron, and sulphur based on the following four assumptions: 1. No heat is generated or consumed during the dissolution of oxides 2. No heat is generated or consumed during the precipitation of basic sulphates 3. Each mole of electrons transferred generates approximately 100 kJ of heat 4. A l l sulphidic iron is oxidized to ferric The third assumption is validated by comparing the standard enthalpy values of various sulphide oxidation reactions, as shown in Table 4-5. Table 4-5. Reaction enthalpies of several important oxidation reactions Overall Oxidation Reaction AH°, k J 1 Oxidation of sphalerite to elemental sulphur (2 electrons): ZnS + 0.5 0 2 + H 2 S 0 4 -> Z n S 0 4 + S° + H 2 0 -238 (-119 per e" ") Oxidation of galena to elemental sulphur (2 electrons): PbS + 0.5 0 2 + H2SO4 -> PbS0 4 (s) + S° + H 2 0 -201 (-100 pere" ') Oxidation of pyrite to elemental sulphur (3 electrons): FeS 2 + 0.75 0 2 + 1.5 H 2 S 0 4 -> 0 .5Fe 2 (SO 4 ) 3 + 2 S° + 1.5 H 2 0 -306 (-102 per e" ') Oxidation of pyrite to sulphate (15 electrons): FeS 2 + 3.75 0 2 + 0.5 H 2 0 -> 0.5 Fe 2 (S0 4 ) 3 + 0.5 H 2 S 0 4 -1505 (-100 per e" 1 Oxidation of elemental sulphur (6 electrons): S° + 1.5 0 2 + H 2 0 -> H2SO4 -624 (-104 pere" 1 1 enthalpy values extracted from the HSC Chemistry v4.1 (© Outokumpu Research Oy, Pori, Finland, A. Roine) database On the basis of these assumptions, the task of calculating the total heat generated is relatively straightforward. First, the amounts of sulphidic zinc, lead, and iron extracted are determined by subtracting the oxide fractions and tails assays for each metal from the head assays. Each 86 Chapter 4: Experimental Results species is assumed to be in its zero-valence state within every sulphide mineral. Hence, the rules in Table 4-6 apply: Table 4-6. Redox reactions and their associated heat generation values Species Redox reaction Heat generated (kJ per mol e _) Z n 2 + Zn(S) -> Z n 2 + + 2 e" 200 P b 2 + Pb(S) -> P b 2 + + 2 e" 200 F e 2 + Fe(S) -> F e 2 + + 2 e _ 200 S 0 4 2 - S(S) + 4 H 2 0 -> S 0 4 2 " + 8 H + + 6 e" 600 s° S(S) -> S° 0 The resulting heat generated from each column can now be calculated from the solids assay. This analysis is illustrated in the following example: Ex.: Heat Generation Determination for Experiment Number 1 (30°C, single pass, 1-ft) A n overall mass balance is conducted on each of the four replicate columns that constitute this experiment. Table 4-7 outlines the assay data that was received for experiment number 1 and Table 4-8 illustrates how this data is incorporated into the overall mass balance for replicate 1. 87 Chapter 4: Experimental Results Table 4-7. Assay data for replicate number 1 of experiment number 1 Head,% Replicate Z n P b Fe , S T S ° S 2 SsCM 1-4 15 03 •• n 6 39 14.49 0.17 13.62 0.60 Tails, % IjfliSJIBBillllF Replicate Z n " " " P b S T * ' " ~ S ° " ' ' S J Ss04 1 1260 4.68 " ' 5 87 14.22 0.76 12 76 • 0.55 2 9.62 5.39 5.38 13.31 2.73 9.89 0.67 3 6.61 4.27 5.02 10.82 2.47 7.60 0.57 4 4.82 5.93 3.39 12.23 5.42 5.78 0.83 Table 4-8. Mass balance incorporating assay data for replicate 1 of experiment number 1 M A S S B A L A N C E M a s s in = 4196.15 g M a s s O u t = 3929.07 g Zn Extn R e p l i c a t e 1 in, in. g out, out g change, g moles 21.50% Z n 15.03 630.68 12.60 495.06 -135.62 -2.074 Fe/Pb Extn F e 6.39 268.13 5.87 230.64 -37.50 -0.671 13.98% P b 4.31 180.85 4.68 183.88 3.03 0.015 -1.67% S t o t 14.49 608.02 14.22 558.71 -49.31 -1.538 S:" Conv. S ° 0.17 7.13 0.76 29.86 22.73 0.709 12.28% s-2 13.62 571.52 12.76 501.35 -70.17 -2.188 toS" so4-2 0.60 25.18 0.55 21.61 -3.57 -0.111 32.39% where: Zn Extraction = 1 - M » ™ = 1 - ^ = 22.29% MZn(in) 630.68 Ma.Aout) 50135 S~2 Conversion = 1 s — — - = 1 - ^ £ 1 = 12.28% M s _ 2 (m) 571.52 and, to S°= S°(out)-S\in) _ 29.86-7.13 _ 3 2 3 9 , S-\out)-S-\in) 501.35-571.52 Integration of the mass balance into the heat generation analysis is accomplished by util izing the heat associated with each of the redox reactions given in Table 4-6. By subtracting the oxide fractions and tails assays for each metal from the head assays we can determine the heat 88 Chapter 4: Experimental Results associated with the oxidation of the metal sulphides. The layout for these calculations is shown in Table 4-9. Table 4-9. Heat analysis of replicate 1 of experiment number 1 H E A T A N A L Y S I S R e p l i c a t e 1 mol kg ' T o t a l Z n 15.03 2.299 Z n ( o x i d e ) 0.17 0.025 T o t a l F e 6.39 1.144 F c ( o x i d e ) 0.11 0.019 T o t a l P B 4.31 0.208 S= 13.62 4.247 total l e a c h e d Z n 21.50 0.494 s u l f i d i c Z n 99.83 0.469 Hea t G e n e r a t e d 28.13 93.782 total l e a c h e d F e 13.98 0.160 s u l f i d i c F e 99.89 0.141 H e a t G e n e r a t e d 8.44 28.141 total l e a c h e d P b o o o : 0.000 s u l f i d i c P b 100.00 0.000 H e a t G e n e r a t e d 0.00 0.000 total o x i d i z e d S 12.28 0.521 to S ° 32 39 0.169 to S O / ' 67.61 0.353 H e a t G e n e r a t e d 63.43 211.517 T o t a l Hea t G e n e r a t e d , k J / k g o f O r e 333.440 O v e r a l l R a t e o f Hea t G e n e r a t i o n , W / m 3 o f O r e 153.792 calculating values for zinc, Z n . (Head Grade (Zn)) = O1503 W _ ^ £ j M W . Zn 65.39 g mol g 2.299 mol 4.5 Total Leached Zn = Zn Extraction • Total Zn = 2 L 5 Q % • 2.299 — = 0.494 100% kg mol ~kg 4.6 89 Chapter 4: Experimental Results Sulfidic Zn = Total Leached Zn - Zn (oxide) - 0.494 - 0.025 = 0.469 — 4.7 kl mnl kJ kJ Heat Generated = Sulfidic Zn • 200 — = 0.469 — • 200 = 93.78 — 4.8 mol kg mol kg Once the heat generation terms are determined for the oxidation reactions of each of the sulfide minerals, they are summed to yield the total heat generated for that column (333.4 kJ k g - 1 for replicate 1 of experiment number 1). The overall rate of heat generation can then be determined: 332743 — Rate = p . ^ = 1752.86 ^ = 153.47 4.9 8 t m 43.99 c / . 24 ^ - 3 6 0 0 - m d hr where: p is the packing density of the column (mass of loaded ore / volume of column) 5H is the change in heat generated between two consecutive replicates and, 8t is the change in time on-stream between two consecutive replicates (from the point of bacteria inoculation) Figure 4-8 shows the resulting heat generation plots for experiment number 1. 90 Chapter 4: Experimental Results 1600 1400 O 1200 o TO)1000 Tf 800 0) ro a> c 600 a) O S 400 X 200 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e on S t ream (s ince inoculat ion) , d Figure 4-8. Heat generated by four replicate columns operating at 30°C A l l four replicates for experiment number 1 exhibited similar leaching behavior. The extraction profiles (Figure 4-3), the pH (Figure 4-4), and the O R P (Figure 4-5) all behaved similarly for the duration of the 305 day experiment. From Figure 4-4, it can be seen that the system was initially acid consuming. The columns did not become acid neutral until approximately 140 days on stream. At this point the pregnant leach solution was exiting the columns at a pH equal to that of the entering leach solution (pH =1.10). It should be noted that the very low pH values recorded during the initial stages of the experiment reflect the flushing of the acid used to agglomerate the ore. From Figure 4-5, it can be seen that all four replicate columns had a potential dramatically higher than the entering leach solution (475 vs. Ag /AgC l ) . This very high solution potential of 700 ±50 m V vs. A g / A g C l was attained after a lag period of approximately 40 days; this 91 Chapter 4: Experimental Results strongly supports the assertion made in section 2.4 that mesophilic bacteria are strong iron oxidizers. As shown in Table 4-1, the only column which did not exhibit a close correlation between the two methods of determining zinc extraction was replicate number 2. According to the mass balance for zinc, Table 4-2, this column experienced a fairly poor close on its balance. Since more zinc is recovered than what when into the system, this error is likely due to the accumulation of error in that replicate solution assays. The overall mass balance of experiment number 1 is shown in Table 4-3. It can be noted that the closure on the individual replicates increases with the amount of time that the respective columns remained on stream. The initial rate of zinc oxidation during the first 117 days of leaching was determined to be 2667 mg Zn d" 1 . After this point the rate decreased to 888 mg Zn d _ 1 . A s can be seen in Figure 4-7, the bacterial population in solution has a relatively constant value of 10 5 m L - 1 during the first 100 days of the experiment. After this point the population rose two orders of magnitude to a value of 10 7 m L - 1 . The cells attached to mineral surfaces also experienced a similar increase. Cel l populations on solids increase over the course of the experiment from a value of 2 x 10 9 m L - 1 to 4 x 10 1 0 m L - 1 . As shown in Figure 4-8, the maximum amount of heat generated by a single replicate over the course of the study was approximately 1400 kJ k g - 1 of ore. 92 Chapter 4: Experimental Results 4.1.2 Results of Experiment Number 2 - Four Replicates at 50°C The dissolved zinc and iron concentrations with time, as determined by A A S , for four replicate columns operating at 50°C (experiment number 2 as summarized in Table 3-6) are shown in Figure 4-9 and Figure 4-10, respectively. 5500 5000 4500 4000 3500 !_l 0)3000 E ^ 2 5 0 0 L i 2000 1500 1000 500 0 ' O n . o O I A • - A -- ° - — T T C A - A ^ M - . . 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n St ream, d o Replicate 1 o Replicate 2 o Replicate 3 A Replicate 4 Figure 4-9. Zinc concentration in solution for four replicate columns operating at 50°C 93 Chapter 4: Experimental Results 2000 O) E £ . 1000 500 • A ^& ^ A \ / o O A A O 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 Time on Stream, d o Replicate 1 • Replicate 2 o Replicate 3 A Replicate 4 Figure 4-10. Iron concentration in solution for four replicate columns operating at 50°C note: the entering leach solution contained 1 g L'1 dissolved iron The corresponding zinc extraction profile for this experiment is shown in Figure 4-11. The respective columns were taken offline after being leached for 56, 119, 236, and 307 days. When the last column was taken offline, the maximum extraction achieved was 51.9%. The p H and potential (ORP) of the four replicates are shown in Figure 4-12 and Figure 4-13, respectively. 94 Chapter 4: Experimental Results m 40 c N >0 A • A, A A £ 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 32 T i m e on S t ream, d o Replicate 1 o Replicate 2 o Replicate 3 A Replicate 4 Figure 4-11. Zinc extraction in solution for four replicate columns operating at 50°C (based on solution assays) 2.0 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n S t ream, d o Replicate 1 • Replicate 2 o Replicate 3 A Replicate 4 Figure 4-12. p H for four replicate columns operating at 50°C Figure 4-14 illustrates the zinc extraction based on solids analysis (ICP) and Table 4-10 summarizes these extraction values. 95 Chapter 4: Experimental Results 800 750 700 O 650 < D) 600 < § 550 > E 500 0." O 450 400 -g 350 300 C P " 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e on S t ream, d o Column 1: Eh • Column 2: Eh o Column 3: Eh A Column 4: Eh Figure 4-13. O R P of four replicate columns operating at 50°C 100 90 80 70 c - 60 o ra 50 x UJ c N 40 30 20 10 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 Time on St ream, d Figure 4-14. Zinc extraction of four replicate columns operating at 50°C (based on solids assays) 96 Chapter 4: Experimental Results Table 4-10. Extraction values obtained by solution and solids analysis for four replicate columns operating at 50°C Replicate Time on Stream Zinc Extraction, % Number days Solution (AAS) Solids (ICP) 1 56 26.49 22.32 2 119 39.09 37.72 3 236 42.34 46.39 4 307 51.87 51.57 Figure 4-15 illustrates the results of bacterial enumeration of samples collected from the last column in the four-column series and the solids from all four columns. 1E+11 1E+10 1E+09 1E+08 c •£ 1E+07 </) 1E+06 1E+05 ID = 1E+04 U 1E+03 1E+02 1E+01 1E+00 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 Time on Stream (s ince inoculation), d A Bacteria in Solution x Bacteria on Solids Figure 4-15. Bacterial cell counts for four replicate columns operating at 50°C Table 4-11 summarizes the mass balance for zinc and Table 4-12 summarizes the overall mass balance for experiment number 2. 97 Chapter 4: Experimental Results Table 4-11. Zinc mass balance for four replicate columns operating at 50°C Replicate Head Tails Solution Total Out Close Number g g g g % 1 622.05 483.36 164.75 648.12 -4.19 2 622.72 387.99 243.45 631.43 -1.40 3 632.49 339.18 267.78 ' 606.96 4.04 4 634.19 307.22 334.35 641.57 -1.16 Table 4-12. Overall mass balance for four replicate columns operating at 30°C Replicate Mass In Mass Out Difference Close Number g g g % 1 4138.70 3969.29 169.41 4.09 2 4143.21 3924.52 218.69 5.28 3 4208.16 3489.17 428.71 10.19 4 4219.49 3959.91 259.57 6.15 Table 4-15 summarizes the chemical analysis of the tailings from each of the replicates. Table 4-13. Chemical analysis of tailings from four replicate columns operating at 50°C Replicate Zn Pb Fe S T S° s-2 Ss04 Number % % % % % % % 1 12.74 4.84 5.55 14.19 0.89 12.35 0.66 2 10.59 5.37 5.42 13.32 1.67 10.91 0.60 3 9.72 4.23 5.38 11.76 0.83 10.16 0.51 4 8.56 5.70 5.03 13.63 3.46 9.12 0.84 98 Chapter 4: Experimental Results Figure 4-16 shows the resulting heat generation plots for experiment number 2. 1400 1200 o 1000 o 800 •o & 2 600 <D c o o •S 400 flj o X 200 0 -I 1 , 1 1 , ! 1 1 1 1 1 1 . 1 . 1 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n St ream (s ince inoculat ion) , d Figure 4-16. Heat generated by four replicate columns operating at 50°C A l l four replicates for experiment number 2 exhibited similar leaching behavior. The extraction profiles (Figure 4-11), the pH (Figure 4-12), and the O R P (Figure 4-13) all behaved similarly for the duration of the 307 day experiment. Comparing the extent of zinc extraction (Table 4-10) it can be observed that the extractions based on solution assays overestimated the true amount of zinc oxidation in replicate number 1 and underestimated it in replicate number 3. This is also pronounced in Table 4-12 where the close on the mass balance for replicate number 3 is 10.19%. This discrepancy is attributed to the error incurred during the analysis of the solution samples; this error accumulates over the duration of the experiment. 99 Chapter 4: Experimental Results The initial rate of zinc oxidation during the first 92 days of leaching was determined to be 2376 mg Zn d - 1 . After this point the rate decreased to 453 mg Zn d _ 1 . From Figure 4-12, it can be seen that the system within each replicate was initially acid consuming. The columns did not become acid neutral until approximately 100 days on stream. A t this point the pregnant leach solution was exiting the columns at a p H equal to that of the entering leach solution (pH = 1.10). From Figure 4-13, it can be seen that all four replicate columns had a potential of 425 m V vs. A g / A g C l , which is slightly lower than that of the entering leach solution potential (475 m V vs. Ag /AgC l ) . This suggests that the moderate thermophiles that were operating in this temperature regime were not strong iron oxidizers. As can be seen in Figure 4-15, the bacterial population in solution exhibited a relatively constant value of 5 x IO5 m l / 1 over the entire duration of the experiment. Cel l populations attached to the solid surfaces remained •steady at 5 x 1 0 9 m L _ 1 . As shown in Figure 4-16, the maximum amount of heat generated by a single replicate over the course of the study was approximately 1150 kJ k g - 1 of ore. 100 Chapter 4: Experimental Results 4.1.3 Results of Experiment Number 3 - Four Replicates at 70°C The dissolved zinc and iron concentrations with time, as determined by A A S , for four replicate columns operating at 70°C (experiment number 3 as summarized in Table 3-6) are shown in Figure 4-17 and Figure 4-18, respectively. 5500 5000 4500 4000 3500 L 0)3000 E ^ 2 5 0 0 N 2000 1500 1000 500 0 ' A O An oa 3±. 00 - f i -cr A • ^1 A A _C8A_ ol cpcP° o - °^ Orfy, ^ A° n ° . . 0 _ _ - " O O AAO ° ^ ~ 0 o O CD A O „ A ° A A A A O O AAAO A A A A A 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n St ream, d o Replicate 1 • Replicate 2 o Replicate 3 A Replicate 4 Figure 4-17. Zinc concentration in solution for four replicate columns operating at 70°C 101 Chapter 4: Experimental Results 2500 2000 7 1500 _1 o i . 1000 A £ - o ° -^ A A A A O O M A A A 500 0 O A O 0 -I , , , , , , , , , , , , , , , J 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 Time on Stream, d © Repl icate 1 • Repl icate 2 o Repl icate 3 A Repl icate 4 Figure 4-18. Iron concentration in solution for four replicate columns operating at 70°C note: the entering leach solution contained I g L'1 dissolved iron The corresponding zinc extraction profile for this experiment is shown in Figure 4-19. The respective columns were taken offline after being leached for 54, 117, 234, and 305 days. When the last column was taken offline, the maximum extraction achieved was 73.1%. 102 Chapter 4: Experimental Results 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n S t ream, d o Replicate 1 • Replicate 2 o Replicate 3 A Replicate 4 Figure 4-19. Zinc extraction in solution for four replicate columns operating at 70°C (based on solution assays) The p H and potential (ORP) of the four replicates are shown in Figure 4-20 and Figure 4-21, respectively. 2.0 1.8 1.6 1.4 1.2 £ 1.0 0.8 0.6 0.4 0.2 0.0 A 0 * , i A m • a o O A _ A A A A 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n S t ream, d o Replicate 1 o Replicate 2 o Replicate 3 A Replicate 4 Figure 4-20. p H for four replicate columns operating at 70°C 103 Chapter 4: Experimental Results 800 750 700 O 650 at "3)600 < $ 550 > E 500 Q." O 450 400 350 300 ^ ^ ° 0 C O g g S > A A A ~ A ~ * 6 ^ A A A A ~ A A -AA 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e on St ream, d © Replicate 1 • Replicate 2 o Replicate 3 A Replicate 4 Figure 4-21. O R P of four replicate columns operating at 70°C Figure 4-22 illustrates the zinc extraction based on solids analysis (ICP) and Table 4-14 summarizes these extraction values. 100 90 80 70 3^ c 60 o act 50 X LU 40 C N 30 20 10 0 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e on St ream, d Figure 4-22. Zinc extraction of four replicate columns operating at 70°C (based on solids assays) 104 Chapter 4: Experimental Results Table 4-14. Extraction values obtained by solution and solids analysis for four replicate columns operating at 70°C Replicate Time on Stream Zinc Extraction, % Number days Solution (AAS) Solids (ICP) 1 54 23.89 22.51 2 117 36.10 30.57 3 234 63.19 51.51 4 305 73.06 70.68 Figure 4-23 illustrates the results of bacterial enumeration of samples collected from the last column in the four-column series and the solids from all four columns. 1E+11 -I 1E+10 -1E+09 -1E+08 -c o 1E+07 -o </) 1E+06 • !_l E 1E+05 -V) 1E+04 -~o O 1E+03 -1E+02 -1E+01 -1E+00 -Pa r J ^ • 5" • o • 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e on St ream (s ince inoculat ion) , d • Bacteria in Solution x Bacteria on Solids Figure 4-23. Bacterial cell counts for four replicate columns operating at 70°C Table 4-15 summarizes the mass balance for zinc and Table 4-16 summarizes the overall mass balance for experiment number 3. 105 Chapter 4: Experimental Results Table 4-15. Zinc mass balance for four replicate columns operating at 70°C Replicate Head Tails Solution Total Out Close Number g g g g % 1 635.75 492.65 151.91 644.56 -1.39 2 636.21 441.70 229.64 671.35 -5.52 3 635.85 308.35 401.78 710.13 -11.68 4 636.17 186.55 464.81 651.36 -2.39 Table 4-16. Overall mass balance for four replicate columns operating at 70°C Replicate Mass In Mass Out Difference Close Number g g g % 1 4229.87 4102.91 126.96 3.00 2 4232.92 3748.58 237.35 5.61 3 4230.53 3865.93 364.60 8.62 4 4232.69 3824.42 408.27 9.65 Table 4-17 summarizes the chemical analysis of the tailings from each of the replicates. 106 Chapter 4: Experimental Results Table 4-17. Chemical analysis of tailings from four replicate columns operating at 70°C Replicate Zn Pb Fe St S° s-2 Ss04 Number % % % % % % % 1 12.54 4.70 4.93 14.39 0.50 13.01 0.70 2 11.78 5.42 5.62 12.63 0.66 11.03 0.69 3 9.11 4.10 4.45 10.55 0.97 8.71 0.45 4 5.73 6.23 3.20 10.79 3.62 5.87 1.07 Figure 4-24 shows the resulting heat generation plots for experiment number 3. 1800 1600 £ 1 o 4— o •a a c <u U ra Q> X 400 • 200 000 800 600 400 200 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e on S t ream (s ince inoculat ion) , d Figure 4-24. Heat generated by four replicate columns operating at 70°C A s can be noted in Figure 4-17 (zinc in the effluent), Figure 4-20 (pH of the effluent), and Figure 4-21 (ORP of the effluent), there is a great deal of scatter in the results of experiment number 3. In addition, there is a significant divergence in the data reported in Table 4-14. 107 Chapter 4: Experimental Results The conversion of sphalerite based on solution assays is considerably higher than that determined by ICP analysis for replicates 2 and 3. Replicates 1 and 4, despite the scatter of the interim data, exhibited a close correlation between the solution and solid assays. It should be noted that both solution and solids assays for the entire experiment have been repeated with no significant change from the data being reported. The following general observations can be made about experiment number 3. The system remained slightly acid consuming for the duration of the experiment. The potential of the replicates was generally low (400 to 450 m V vs. Ag /AgC l ) , although replicate number 4 did have a period of high potential (60 to 180 days on stream) which was followed by a sharp drop in solution potential. As could be expected from these results, the mass balances that were performed on this experiment showed a very good close on replicates 1 and 4, while replicates 2 and 3 are notably poor. A s can be seen in Figure 4-23, the bacterial populations in solution gave a relatively constant value of 5 x 10 5 mLT 1 over the entire duration of the experiment. Cel l populations attached to the solid surfaces had a steady value of 7 x 10 8 mLT 1. There does not appear to be any significant fluctuation in the bacteria counts, thereby establishing that changes in bacterial populations is not a likely explanation for the scatter observed in the data. The initial rate of zinc oxidation during the first 55 days of leaching was determined to be 2481 mg Zn d _ 1 . After this point the rate decreased to 1137 mg Zn d _ 1 . 108 Chapter 4: Experimental Results As can be seen in Figure 4-24, the maximum amount of heat generated by a single replicate over the course of our study was approximately 1650 kJ k g - 1 of ore. A n average of the extraction results was calculated from the four replicate columns used in each respective experiment. This average data, coupled with the extraction based on solids assays, is shown in Figure 4-25. As can be expected, there are sharp rises and falls in the plot that coincide with the removal of a column from the set. For instance, it can be noted that between days 119 and 236 for experiment number two (50°C), the average of the data is skewed by the average of replicates 3 and 4. Since replicate 3 lagged behind the other three columns with respect to zinc extraction (as determined by solution assays), there is a corresponding decrease in zinc extraction. open marker = solution assays 0 20 40 60 80 100 120 140 160, 180 200 220 240,260 280 300 320 340 T i m e on S t ream, d o Experiment 1 (30°C) A Experiment 2 (50°C) o Experiment 3 (70°C) Figure 4-25. Summary of zinc extraction, based on both solution and solid assays, for experiments one, two, and three. 109 Chapter 4: Experimental Results 4.1.4 Results of Experiment Number 4 - Four Columns in Tandem at 30°C The dissolved zinc concentration with time, as determined by atomic A A S , for four columns operating in tandem at 30°C (experiment number 4 as summarized in Table 3-6) is shown in Figure 4-26. The amount of zinc in solution appears to be dramatically greater than shown in Figure 4-1. However, it should be noted that the concentration of zinc is accumulating after passing through each consecutive column. The dissolved iron concentration for these columns is shown in Figure 4-27. 22000 20000 18000 16000 14000 !_l 0)12000 E ^ 1 0 0 0 0 N 8000 6000 4000 2000 0 % A D A A >AO-A A A ; AA . _3u> a rf^o0 -J * ^ - 2 ^ co-• Q Q - p A ^ ^ A A a , A A • 0 Q J £ * D 0 6 D o " o 0 8 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 T i m e o n St ream, d ©1-ft • 2-ft 0 3-ft A4-ft Figure 4-26. Zinc concentration in solution for four columns operating in tandem at 30°C 110 Chapter 4: Experimental Results 3500 3000 2500 !_l 2000 o> E £ 1500 500 • • a „ . AAA A AsA AAA AAA J ^ W ^ c o o ^ o _J2 CEO ° 0 _ Q _ A 6 o O O O A 4*r c o o O o • • o o x P ~ ©o o o ° & 8 * > ° A ° 6 Q A 6 A AD . * D 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 Time on Stream, d 0 1-ft • 2-ft 0 3-ft A4-ft Figure 4-27. Iron concentration in solution for four columns operating in tandem at 30°C note: the entering leach solution contained 1 g L~' dissolved iron (fed to the 1-ft column) The corresponding zinc extraction profile for this experiment is shown in Figure 4-28. The respective columns were taken offline after being leached for 320 days. When the last column was taken offline, the maximum extraction achieved was 67.5%. This can be contrasted against the value of 74.3%, which was achieved in experiment number 1. I l l Chapter 4: Experimental Results 100 90 80 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 T i m e on St ream, d Figure 4-28. Overall zinc extraction in solution for four columns operating in tandem at 30°C (based on solution assays) The p H and potential (ORP) of the four columns are shown in Figure 4-29 and Figure 4-30, respectively. x a 3.6 3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -rj> % A A - A - A -20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 T i m e o n S t r e a m , d ©1-ft 0 2-ft o3-ft A4-ft Figure 4-29. p H for four columns operating in tandem at 30°C 112 Chapter 4: Experimental Results 800 750 700 0 650 U) < at 600 < 1 550 > E 500 0." O 450 400 350 300 " - ^ C A ^ g o 4 4 « 8 „ o -o-<A A O 0 Cb 0 o ° CO Pa <Y) n g R « B 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 T i m e o n S t ream, d o 1 -ft • 2-ft 0 3-ft A4-ft Figure 4-30. O R P of four columns operating in tandem at 30°C Figure 4-31 illustrates the zinc extraction based on solids analysis (ICP) and Table 4-18 summarizes these extraction values. 100 -[ 90 80 20 : : 10 0 \ ; 1 • ^ : ; 1 2 3 ' 4 Depth , ft Figure 4-31. Zinc extraction of four columns operating in tandem at 30°C (based on solids assays) 113 Chapter 4: Experimental Results Table 4-18. Extraction values obtained by solution and solids analysis for four columns operating in tandem at 30°C Column Time on Stream Zinc Extraction, % Number days Solution (AAS) Solids (ICP) 1 320 69.66 2 320 72.93 3 320 68.58 4 320 67.52 76.71 Figure 4-32 illustrates the results of bacterial enumeration of samples collected from both solution and solids for the last column in the four-column series. 1E+10 -1E+09 -1E+08 -c 1E+07 -o "3 1E+06 -o CO 1 1E+05 • _l E 1E+04 -a> o 1E+03 -1E+02 -1E+01 -1E+00 -o o 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 Time on Stream (since inoculat ion), d o Bacteria in Solution x Bacteria on Solids Figure 4-32. Bacterial cell counts for four columns operating in tandem at 30°C Table 4-19 summarizes the mass balance for zinc and Table 4-20 summarizes the overall mass balance for experiment number 4. 114 Chapter 4: Experimental Results Table 4-19. Zinc mass balance for four columns operating in tandem at 30°C Column Head Tails Solution Total Out Close Number g g g g % 1 643.95 195.38 17.69 213.07 2 644.12 173.17 14.78 187.95 3 642.92 200.55 21.20 221.75 4 580.05 135.08 1635.60 • 1770.69 T O T A L 2511.05 704.18 1689.27 2393.45 4.68 Table 4-20. Overall mass balance for four columns operating in tandem at 30°C Column Mass In Mass Out Difference Close Number g g g % 1 4284.46 3525.15 759.32 17.72 2 4285.59 3488.22 797.38 ' 18.61 3 4277.61 3558.68 718.93 16.81 4 3859.28 5075.32 -1216.04 -31.51 T O T A L 16706.95 15647.37 1059.58 6.34 Table 4-21 summarizes the chemical analysis of the tailings from each of the replicates. Table 4-21. Chemical analy sis of tailings from four columns operating in tandem at 30°C Replicate Zn Pb Fe S T S° s- 2 Ss04 Number % % % % % % % 1 5.58 5.61 4.02 13.85 5.84 7.04 0.73 2 4.99 5.88 4.33 12.94 6.06 5.88 0.84 3 5.68 5.81 4.51 10.88 3.74 5.98 0.93 4 4.25 6.33 5.38 10.41 3.41 5.50 1.40 115 Chapter 4: Experimental Results Figure 4-33 shows the resulting heat generation plots for experiment number 4. 1600 1400 o 1200 >*— o 1000 J£ ~> •6 800 a> 2 a> c 600 a> O +J re 0) 400 X 200 Depth, ft Figure 4-33. Heat generated by four columns operating in tandem at 30°C The overall zinc extraction, as summarized in Table 4-18, shows very close agreement between solution assays and the solid assays. Because the solution exiting the bottom of each column was pumped to the top of the next column, it was impossible to accurately track zinc extraction on a per column basis by solution assays. One can, however, determine zinc recovery based on the solids analysis. The zinc extraction value (based on solution assays) shown in Table 4-18 was determined as a composite of all of the intermediate solution samples throughout the length of the multiple four-foot column. A n average zinc extraction, based on solids, of 72.0% was achieved. This can be compared against the final zinc extraction attained in experiment number 1 discussed in section 4.1.1 (74.6%). 116 Chapter 4: Experimental Results From Figure 4-29, it can be seen that system remained acid consuming for the duration of the experiment. The effect of acid consumption with depth is readily seen, with the pH consistently reaching values of 2.0 to 3.0. Figure 4-30 shows a steady increase in the potential of the P L S exiting each of the columns in experiment number 4. It can be seen that all four columns achieved a potential dramatically higher than that of the entering leach solution (475 m V vs. Ag /AgCl ) . It is felt that the rate of increase in solution potential of columns 3 and 4 was higher than in 1 and 2 due to the experimental apparatus. The P L S exiting each column was collected in a small 100 m L container such that it could be pumped to the top of the next column in the series. This created an opportunity for the solution to be oxidized by atmospheric oxygen and may have resulted in the increase in solution potential that can be observed in Figure 4-30. A s was the case in experiment number 1, the mesophilic bacteria were very active in oxidizing ferrous iron. A s shown in Figure 4-32, the bacterial populations in the effluent have an initial value of 10 6 m L - 1 and a final value of 3 x 10 8 mL" 1 . Cel l populations attached to the surface of the solids had a final value o f 8 x 10 9 m L - 1 . A s shown in Table 4-19, there was a very good close on the mass balance for experiment number 4 (4.68%). The overall mass balance is shown in Table 4-20. The mass balance on the individual columns is notably poor. This discrepancy can be attributed to the mass of zinc 117 Chapter 4: Experimental Results which was put into solution, and which reports to the total mass in column number 4. The mass of zinc in solution totaled 1636 g at the end of the 320 day experiment. The overall close on the mass balance, with this movement of mass from each column to the last column taken into consideration, is 6.34%. The initial rate of zinc oxidation during the first 180 days of leaching was determined to be 1767 mg Zn d - 1 . After this point the rate decreased to 546 mg Zn d - 1 . As can be seen in Figure 4-33, the maximum amount of heat generated by a single column over the course of our study was approximately 1580 kJ k g - 1 of ore. Although these columns should have similar heat generation profiles, there is a notable difference. Considering the heat generated by the conversion of the respective sulphide minerals, Table 4-22, there is a dramatic increase in the conversion of sulphide to sulphate from column 1 to 4. Table 4-22. Heat analysis of experiment number 4 HEAT ANALYSIS Column 1 Column 2 Column 3 Column 4 mol kg'' %" ' mol kg" % ,/>'K mol kg % mol kg"' Total Zn 15.03 2.299 15.03 2.299 15.03 2.299 15.03 2.299 Zn(oxide) 0.00 0.000 0.00 0.000 0.00 0.000 1.01 0.154 Total Fe 6.39 1.144 6.39 1.144 6.39 1.144 6.39 1.144 Fe(oxidc) 0.00 0.000 0.00 0.000 0.00 0.000 0.54 0.097 Total Pb 4.31 0.208 4.31 0.208 4.31 0.208 4.31 0.208 13.62 4.247 13.62 4.247 13.62 4.247 13.62 4.247 total leached Zn 69.66 1.601 73.12 1.681 68.81 1.582 76.71 1.763 sulfidic Zn 100.00 1.601 100.00 1.680 100.00 1.581 98.99 1.609 Hoat Generated 30.72 320.177 27.72 336.050 21.18 316.231 20.34 321.812 total leached Fe 48.52 0.555 45.18 0.517 41.82 0.478 30.80 0.352 sulfidic Fe 100.00 0.555 100.00 0.517 100.00 0.478 99.46 0.255 Heat Generated 10.65 110:989 8 53 103 358 6.41 95.656 3 22 51.010 total leached Pb 0.00 0:000 0.00 0.000 0.00 0.000 0.00 0.000 sulfidic Pb 100.00 0.000 100.00 0.000 100.00 100.00 0.000 Heat Generated 0 00 0.000 0.00 0.000 0.00 0.000 0.00 0.000 total oxidized S 57.78 2.454 65 07 2.764 63.81 2.710 66.81 2.837 toS 1.436 • • • s i l o 1.476 33.49 0.908 28 96 0.822 to SO.- - 41.50 1.018 46 60 1.288 66.51 1.802 71.04 2.016 Heat Generated 58.63 610.940 63.75 772.706 72.42 1081.398 76.44 1209.307 Total Heat Generated , kJ /kg of Ore (from t = 0) 10421105 1212.113 1493 285 1582.128 Overal l Rate of Heat Generat ion, W / m 3 of Ore (from t = 0) 68.286 79.447 97.694 93 384 118 Chapter 4: Experimental Results 4.1.5 Results of Experiment Number 5 - Four Columns in Tandem at 50°C The dissolved zinc and iron concentrations with time, as determined by A A S , for four columns operating in tandem at 50°C (experiment number 5 as summarized in Table 3-6) are shown in Figure 4-34 and Figure 4-35, respectively. Once again, the zinc concentration is increasing as the solution is pumped from the first column to the last. 30000 28000 26000 24000 22000 20000 T j 18000 0)16000 _^ 14000 C i 12000 10000 8000 6000 4000 2000 0 _ C Q _ -<b-_ A A _ dAA AO A A. A A A n ^ A. . _ . y _ n . r f T r > . — J AA AAA A A A - C A -_ 0 _ A A 8 ° B OO 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 T i m e on St ream, d 0 1-ft • 2-ft 0 3-ft A4-f t Figure 4-34. Zinc concentration in solution for four columns operating in tandem at 50°C 119 Chapter 4: Experimental Results 4500 4000 3500 3000 ' i 2500 E •S1 2000 It 1500 1000 500 A^t^AAA O O ^ ° COAE! 0<fXXiO /wP • j n J r m ^AAAgggj— A A A O o a t P V * * o * O O 0 O X O C O 0 5 0 ° CD % A 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 Time on Stream, d o1-ft • 2-ft 0 3-ft A4-ft Figure 4-35. Iron concentration in solution for four columns operating in tandem at 50°C note: the entering leach solution contained 1 g L~' dissolved iron (fed to the I-ft column) The corresponding zinc extraction profile for this experiment is shown in Figure 4-36. The respective columns were taken offline after being leached for 308 days. When the last column was taken offline, the maximum extraction achieved was 59.5%. This is can be compared to the value of 51.9% which was achieved in experiment number 2. 120 Chapter 4: Experimental Results 100 90 80 70 c 60 o act 50 i_ x UJ 40 c N 30 20 10 0 A A A A A A " . A * ,A* .AA' .AA "3* AA' ,AA' 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 T i m e o n S t r e a m , d Figure 4-36. Overall zinc extraction in solution for four columns operating in tandem at 50°C (based on solution assays) The pH and potential (ORP) of the four columns are shown in Figure 4-37 and Figure 4-38, respectively. 3.6 3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 o a 4o 2 „ r ^AA A o - O H — A -~o—s> Q A - A _ O a 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 T i m e o n S t ream, d o Column 1: pH • Column 2: pH o Column 3: pH A Column 4: pH Figure 4-37. p H for four columns operating in tandem at 50°C 121 Chapter 4: Experimental Results 800 750 700 O 650 < D) 600 < A A A A A A Q 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 T i m e o n S t ream, d o Column 1: Eh • Column 2: Eh o Column 3: Eh A Column 4: Eh Figure 4-38. O R P of four columns operating in tandem at 50°C Figure 4-39 illustrates the zinc extraction based on solids analysis (ICP) and Table 4-23 summarizes these extraction values. 100 i - , 90 I 80 20 10 0 -I 1 1 1 2 3 4 Depth , ft Figure 4-39. Zinc extraction of four columns operating in tandem at 50°C (based on solids assays) 122 Chapter 4: Experimental Results Table 4-23. Extraction values obtained by solution and solids analysis for four columns operating in tandem at 50°C Column Time on Stream Zinc Extraction, % Number days Solution (AAS) Solids (ICP) 1 308 55.60 2 308 57.17 3 308 66.88 4 308 59.46 67.09 Figure 4-41 illustrates the results of bacterial enumeration of samples collected from both solution and solids for the last column in the four-column series. 1E+10 1E+09 1E+08 c 1E+07 o 1E+06 O <n T 1E+05 _l E w 1E+04 o o 1E+03 1E+02 1E+01 1E+00 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 T i m e on Stream (since inoculat ion), d A Bacteria in Solution x Bacteria on Solids Figure 4-40. Bacteria cell counts for four columns operating in tandem at 50°C Table 4-24 summarizes the mass balance for zinc and Table 4-25 summarizes the overall mass balance for experiment number 5. 123 Chapter 4: Experimental Results Table 4-24. Zinc mass balance for four columns operating in tandem at 50°C Column Head Tails Solution Total Out Close Number g g g g % 1 642.24 285.16 6.04 . 291.21 2 641.29 274.64 7.97 282.61 3 643.70 213.19 17.05 230.24 4 645.27 212.38 1498.54 1710.92 T O T A L 2572.51 985.37 1529.61 2514.97 2.24 Table 4-25. Overall mass balance for four columns operating in tandem at 50°C Column Number Mass In g Mass Out g Difference g Close % 1 4273.08 3550.78 722.30 16.90 2 4266.75 3592.00 674.76 15.81 3 4282.73 3598.34 684.40 15.98 4 4293.24 5282.95 -989.71 -23.05 T O T A L 17115.81 16024.06 1091.74 6.38 Table 4-26 summarizes the chemical analysis of the tailings from each of the replicates. Table 4-26. Chemical analysis of tailings from four columns operating in tandem at 50°C Replicate Zn Pb Fe S T S° s -2 Ss04 Number % % % % % % % 1 8.05 6.23 5.49 12.62 3.57 8.04 0.82 2 7.67 5.53 4.73 12.96 3.53 8.39 0.83 3 5.96 5.49 4.20 11.55 3.84 6.68 0.78 4 6.05 6.03 5.34 12.12 5.02 5.41 1.50 124 Chapter 4: Experimental Results Figure 4-41 shows the resulting heat generation plots for experiment number 5. 1600 1400 'o>1000 J£ -5 JC •a 800 — a> ra k_ cu C 600 — 0> O *-i a 400 X 200 — — 0 \ 1 1 1 1 2 3 4 Depth, ft Figure 4-41. Heat generated by four replicate columns operating in tandem at 50°C The overall zinc extraction, as summarized in Table 4-23, shows very close agreement between solution and solid assays. The zinc extraction value (based on solution assays) shown in Table 4-23 was determined as a composite of all of the intermediate solution samples throughout the length of the multiple four-foot column. A n average zinc extraction, based on solids, of 61.7% was achieved. This can be compared to the final zinc extraction attained in experiment number 2 discussed in section 4.1.2 (51.6%). The dramatic increase in zinc concentration in the effluent of column 3 over the period of TOS 112 to 151 as shown in Figure 4-34 is believed to be the result of a pump failure. This is also reflected as an increase in pH (Figure 4-37) and O R P (Figure 4-38) during the same time period. 125 Chapter 4: Experimental Results From Figure 4-37, it can be seen that the system remained acid consuming for the initial 110 days of the experiment (with the exception of column 3). Figure 4-38 shows a steady increase in the potential of the P L S exiting each of the columns in experiment number 5. A l l four columns behaved similarly and there was a steady increase in solution potential from 350 m V vs. A g / A g C l at the beginning of the experiment to a potential of 475 m V vs. A g / A g C l at the end of the experiment. As shown in Figure 4-40, the bacterial populations in solution have an initial value of 4 x 10 5 mLT 1 and a final value of 2 x 10 6 mLT 1. Cel l populations attached to the solid surfaces had a final value of 2 x 10 9 mLT 1. As shown in Table 4-24, there was a very good close on the mass balance for experiment number 5 (2.24%). The overall mass balance, shown in Table 4-25, is 6.38%. The initial rate of zinc oxidation during the first 126 days of leaching was determined to be 1913 mg Zn d _ 1 . After this point the rate decreased to 756 mg Zn d _ 1 . A s can be seen in Figure 4-41, the maximum amount of heat generated by a single column over the course of our study was approximately 1345kJ k g - 1 of ore. 126 Chapter 4: Experimental Results The zinc extraction (based on solution) for the last column from experiments four and five are plotted with the average zinc extraction (based on solids) in Figure 4-42. Figure 4-42. Summary of zinc extraction, based on both solution and solid assays, for experiments four and five 127 Chapter 4: Experimental Results 4.1.6 Results of Experiment Number Six - Two Replicates at 70°C with 100% Oxygen As was discussed in section 3.2, experiment number 6 was identical to experiment number 3, with the notable exception that the air feed was replaced with 100% oxygen. The dissolved zinc and iron concentrations with time, as determined by A A S , for two replicate columns operating at 70°C with 100%) oxygen gas feed are shown in Figure 4-43 and Figure 4-44, respectively. 7000 6500 6000 5500 5000 4500 '-i 4000 Q) E 3500 N 3000 "2500 2000 1500 1000 500 0 o o o • -a o-D • • • • 20 40 60 80 100 120 140 160 180 200 T i m e o n S t ream, d o Replicate 1 a Replicate 2 Figure 4-43. Zinc concentration in solution for two replicate columns operating at 70°C with 100%o oxygen 128 Chapter 4: Experimental Results 3500 3000 2500 2000 E £ 1500 1000 500 • • • • • 20 40 60 80 100 120 140 160 180 Time on Stream, d 200 o Replicate 1 • Replicate 2 Figure 4-44. Iron concentration in solution for two replicate columns operating at 70°C with 100% oxygen note: the entering leach solution contained 1 g LT1 dissolved iron The corresponding zinc extraction profile for this experiment is shown in Figure 4-45. The respective columns were taken offline after being leached for 68 and 190 days. When the second column was taken offline, the maximum extraction achieved was 46.6%. 129 Chapter 4: Experimental Results UJ 40 )0 • • • ° ° ° D D „ o ° o • • a 0 p a 0 0 20 40 60 80 100 120 140 160 180 2t T i m e o n S t ream, d o Replicate 1 • Replicate 2 Figure 4-45. Zinc extraction in solution for two replicate columns operating at 70°C with 100% oxygen (based on solution assays) The p H and potential (ORP) of the four replicates are shown in Figure 4-46 and Figure 4-47, respectively. 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -a—o-20 40 60 80 100 120 140 160 180 200 T i m e o n S t ream, d o Replicate 1 o Replicate 2 Figure 4-46. p H for two replicate columns operating at 70°C with 100% oxygen 130 Chapter 4: Experimental Results 800 750 700 O 650 O) < "5)600 < > E 500 O 450 400 350 300 0 ©o oo oO o Da • — C L n o do -0--q—o— 20 40 60 80 100 120 140 160 180 200 T i m e o n St ream, d o Replicate 1 • Replicate 2 Figure 4-47. O R P of two replicate columns operating at 70°C with 100% oxygen Figure 4-48 illustrates the zinc extraction based on solids analysis (ICP) and Table 4-27 summarizes these extraction values. 100 90 80 70 C 60 o act 50 k_ "S w 40 c N 30 20 10 0 20 40 60 80 100 120 140 T i m e o n S t ream, d 160 180 200 Figure 4-48. Zinc extraction of two replicate columns operating at 70°C with 100% oxygen (based on solids assays) 131 Chapter 4: Experimental Results Table 4-27. Extraction values obtained by solution and solids analysis for two replicate columns operating at 70°C with 100% oxygen Replicate Time on Stream Zinc Extraction, % Number days Solution (AAS) Solids (ICP) 1 68 39.42 41.01 2 190 46.56 51.50 Figure 4-49 illustrates the results of bacterial enumeration of samples collected from the second column in the two-column experiment and the solids from both columns. 1E+09 1E+08 1E+07 O 1E+06 OT1E+05 g1E+04 VI »1E+03 1E+02 1E+01 1E+00 o o o 0 20 40 60 80 100 120 140 160 180 200 T i m e o n St ream (s ince inoculat ion) , d o Bacteria in Solution x Bacteria on Solids Figure 4-49. Bacteria cell counts for two replicate columns operating at 70°C with 100%) oxygen Table 4-28 summarizes the mass balance for zinc and Table 4-29 summarizes the overall mass balance for experiment number 6. 132 Chapter 4: Experimental Results Table 4-28. Zinc mass balance for two replicate columns operating at 70°C with 100% oxygen Replicate Head Tails Solution Total Out Close Number g g g g % 1 633.49 373.68 249.69 623.37 1.60 2 626.30 303.78 291.61 595.38 4.94 Table 4-29. Overall mass balance for two replicate columns operating at 70°C with 100% oxygen Replicate Mass In Mass Out Difference Close Number g g g % 1 4214.82 3981.90 232.92 5.53 2 4166.99 3887.36 279.63 6.71 Table 4-30 summarizes the chemical analysis of the tailings from each of the replicates. Table 4-30. Chemical analysis of tailings from two replicate columns operating at 70°C with 100% oxygen Replicate Zn Pb Fe St S° s-2 Ss04 Number % % % % % % % 1 10.18 5.14 4.76 14.09 2.72 10.40 0.80 2 8.76 5.67 4.54 13.14 3.53 8.90 0.52 Figure 4-50 shows the resulting heat generation plots for experiment number 6. 133 Chapter 4: Experimental Results 1000 900 800 •a 500 a> ra cu 400 c a> 300 ra a> 1 200 100 20 40 60 80 100 120 140 160 180 200 Time on Stream (since inoculation), d Figure 4-50. Heat generated by two replicate columns operating at 70°C with 100% oxygen The overall zinc extraction, as summarized in Table 4-27, shows very close agreement between solution and solid assays. The final zinc extraction, based on solids, of 51.50% can be compared against experiment number 3, which had an equivalent zinc extraction at day 190, based on solids, of approximately 43%. It can be noted in Figure 4-45 that there is a sharp change in the leaching rate o f the system at day 40. It is felt that replicate number 2 may have failed due to bacterial breakdown as a result of the lack of carbon dioxide in the system. Figure 4-47 shows a steady increase in the potential of the P L S exiting each of the columns in experiment number 6 for the first 40 days of the experiment from a value of 350 to a value of 440 m V vs. A g / A g C l . This is comparable to the potentials which were observed in experiment number 3 (Figure 4-21). 134 Chapter 4: Experimental Results As shown in Figure 4-40, the bacterial populations in solution have an average value of 9 x 10 5 m L - 1 . Ce l l populations attached to solid surfaces had a final value of 5 x 10 8 m L - 1 . The initial rate of zinc oxidation during the first 43 days of leaching was determined to be 5833 mg Zn d - 1 . After this point the rate decreased to 538 mg Zn d _ 1 . Figure 4-51 illustrates the dramatic increase in zinc extraction at 70°C at an elevated oxygen concentration. Although this increased rate was not sustained, there was a 235% increase in the rate of zinc extraction (from 2481 mg Zn d _ 1 to 5833 mg Zn d _ I ) . As shown in Figure 4-50, the maximum amount of heat generated by a single replicate over the course of the study was approximately 948 kJ k g - 1 of ore. Figure 4-51. Comparison of zinc extraction under low oxygen (air + 1%>C02) and high oxygen (100%) 02) conditions 135 Chapter 4: Experimental Results 4 . 2 Results of Controlled Potential, Isothermal, Chemical Leaching Experiments Figure 4-52 shows the results for the variable temperature experiments ( T l , T2, and T3) and Figure 4-53 shows the results for the variable potential experiments (PI , P2, T l , and P3) based on the assay of the solution samples which were taken during the respective experimental runs. Table 4-31 summarizes the chemical analysis of the tailings residue from each of the experiments and Table 4-32 summarizes the overall zinc extracted during the controlled potential, isothermal, chemical leaching experiments. It should be noted that zinc extraction based on solution assays are based on the zinc head assay as determined by ICP and summarized in Table 3-7. The complete results for the controlled potential, isothermal, chemical leaching experiments can be found in Appendix B. 100 90 80 70 c 60 x * 1 a • g • • o 50 UJ 40 c N 30 6 -20 10 10 100 T i m e o n St ream, hr 1000 .xT1 (70°C, 1:1) • T2 (55°C, 1:1) bT3 (40°C, 1:1) -Figure 4-52. Zinc extraction by solution assay for constant potential experiments (temperature, Fe 3 + :Fe 2 + ra t io ) 136 Chapter 4: Experimental Results 100 -90 • 80 • 70 • 60 -50 40 30 20 10 0 0 O X _ Q B X X a A - A * — o X B 4 6 8 T i m e on St ream, hr 10 12 oP1 (70"C, 100:1) •P2(70°C, 10:1) xT1 (70°C, 1:1) A P3 (70°C, 1:10) Figure 4-53. Zinc extraction by solution assay for constant temperature experiments at (temperature, Fe : Fe ratio) Table 4-31. Chemical analysis of tailings from the controlled potential, isothermal, chemical leaching experiments Experiment Zn Pb Fe S T S° s -2 Ss04 Number % % % % % % % T l 0.49 12.40 1.49 23.23 18.71 1.58 2.69 T2 0.63 12.25 1.66 23.57 18.07 2.55 2.63 T3 0.94 11.10 4.78 23.96 16.09 5.34 2.43 PI 0.28 11.26 2.61 20.34 16.11 0.61 3.17 P2 0.37 11.23 0.68 21.17 17.61 0.53 2.66 P3 0.47 10.97 0.95 23.42 19.07 1.44 2.54 137 Chapter 4: Experimental Results Table 4-32. Summary of results for the controlled potential, isothermal, chemical leaching experiments Experiment Temperature Time on Stream Zinc Extraction, % Number °C hours Solution (AAS) Solids (ICP) T l 70 46 93.18 98.55 T2 55 195 90.11 98.15 T3 40 193 90.62 96.99 PI 70 84 92.70 99.06 P2 70 53 89.71 98.89 P3 70 165 96.25 98.60 Table 4-33 summarizes the mass balance on zinc for these experiments. Table 4-33. Zinc mass balance for controlled potential, isothermal, chemical leaching experiments Experiment Head Tails Solution Total Out Close Number g g g g % T l 4.539 0.066 4.277 4.343 4.33 T2 4.539 0.084 4.271 4.355 4.05 T3 4.537 0.137 4.225 4.362 3.87 PI 4.538 0.043 4.336 4.379 3.51 P2 4.538 0.050 4.171 4.221 6.68 P3 4.538 0.063 4.513 4.576 -0.84 138 Chapter 4: Experimental Results 4.2.1 Modeling Potentiostatic Data The leaching data presented in Figure 4-52 and Figure 4-53 cannot be fitted with conventional shrinking core models (i. e., the shrinking core model with surface reaction control {kt = 1 - ( l - a ) 1 / 3 j after Venkatachalam and Soman [ 1 5 0 ] , Perez and Dutr izac [ 2 7 ] , and Romankiw and De B r u y n [ 1 3 2 ] , or the shrinking core model with product diffusion control ( 2 ^ kt = 1 — a - ( l - a)2/i after M i s ra [ 1 4 6 ] ) as these methods are only applicable to those V 3 J systems that employ a constant particle size. Attempts were then made to fit the data using a multi-convolution integral approach using Gauss-Laguerre quadrature after D i x o n . [ l 5 1 ' 1 5 2 1 Acceptable fits could not be established for this data using any of the three approaches detailed by Dixon (a linear M C I , a parabolic M C I , nor a added-resistance shrinking-core MCI ) . Successful fitting of the data was ultimately achieved when a variable order approach was employed, after D ixon and Hendr ix . [ 1 5 3 ] With this approach, each set of experimental data was fitted with the following expression: i \-X = {\-(\-f)kty* 4.10 where: X = fraction unreacted tf> = reaction order k = rate constant t = time 139 Chapter 4: Experimental Results A best fit for the data was established by minimizing the global error between the model and the data while simultaneously solving for a global value of <j> and data specific values of k. Table 4-34 summarizes the values obtained when the error was minimized for this data set and Figure 4-54 through Figure 4-59 illustrate the fits that were achieved. Table 4-34. Variable order fit parameters for potentiostatic experiments Experiment Number k <t> T l 1.06 2.30 T2 0.44 2.30 T3 0.15 2.30 PI 1.47 2.30 P2 1.30 2.30 P3 0.59 2.30 140 Chapter 4: Experimental Results Figure 4-54. Variable order fit for experiment number T l 100 90 80 70 60 50 40 30 20 10 0 0 2 4 6 , 8 10 12 14 16 18 20 22 24 26 28 30 T i m e on St ream, hr • Data - Model Figure 4-55. Variable order fit for experiment number T2 141 Chapter 4: Experimental Results 90 80 70 C 60 o ra 50 0 2 4 T i m e o n St ream, hr o Data — M o d e l Figure 4-56. Variable order fit for experiment number T3 100 20 — — — ' 10 — — 0 -I ———. 1 1 < ' 0 2 4 6 8 10 T i m e on St ream, hr o Data — M o d e l Figure 4-57. Variable order fit for experiment number PI 142 Chapter 4: Experimental Results 1U 0 2 4 6 8 10 T i m e o n S t ream, hr 12 14 16 a Data — Model Figure 4-58. Variable order fit for experiment number P2 100 90 80 0 2 4 6 T i m e o n S t ream, hr A Data — M o d e l Figure 4-59. Variable order fit for experiment number P3 143 Chapter 4: Experimental Results 4.2.2 Determination of Activation Energy The determination of activation energy can be accomplished by using the Arrhenius rate expression and conducting experiments at different temperatures while keeping all other conditions static (i.e., F e 3 + : F e 2 + ) . Therefore, we can use the data from experiments T l , T2, and T3 to perform our calculations. Arrhenius's rate law relates the magnitude of the reaction rate constant to absolute temperature, thus: f E ^ kT=k0exp\--j^;J 4.11 where: kj = reaction rate constant E = activation energy (kJ mo l - 1 ) R = universal gas constant (8.3143 J m o l - 1 KT 1) T = absolute temperature The activation energy is determined by plotting In k vs. Tx, which has a slope oi-E R~\ The reaction rate constant, kr, was evaluated using the method discussed in section 4.2.1 and is summarized in Table 4-34. Thus, plotting kr vs. Tx, Figure 4-60, we can solve for the activation energy of this sphalerite ore. The activation energy was determined to be 58.23 kJ m o l - 1 . This is consistent with the values established by Perez and Dutr izac [ 2 7 ] (41 - 72 kJ m o f 1 ) , and Verbaan [ 1 4 8 ] (56.64 kJ mol" 1). 144 Chapter 4: Experimental Results 0.5 T y = -7003 .9X + 20.496 ,2 -2.0 0.0029 0.0030 0.0030 0.0031 0.0031 0.0032 0.0032 1 IT K -1 o Data — Linear (Data) Figure 4-60. Arrhenius plot 4.2.3 Determination of Ferric and Ferrous Dependency Determining this ores dependency on ferric and ferrous ions can be achieved by seeking a linear relationship of In k vs. In [Fe 3 +] and In k\s. In [Fe 2 +] for experiments P I , P2, T l , and P3. Upon doing so, a linear relationship was observed for ferric ions, and is shown in Figure 4-61. It should be noted that this dependency did not extend to the high ferric concentration (experiment P I , 100:1) and the resulting value of 0.342 is based on F e 3 + : F e 2 + ratios of 10:1, 1:1, and 1:10. No such relationship was observed for F e 2 + ions. 145 Chapter 4: Experimental Results -2.4968 -1.9968 -1.4968 -0.9968 -0.4968 0.0032 In [Fe 3 + ] o Data — Linear (Data) Figure 4-61. Dependency on F e 3 + ions Thus, combining all of these values yields a proposed grain model for this ore: dX , — = «n«exp dt 0 v ( 4.12 146 Chapter 5: Modeling Experimental Results and Discussion 5. M O D E L I N G OF SHORT C O L U M N D A T A A N D DISCUSSION Equation Section (Next)An attempt was made to fit the experimental data generated in experiments 1, 2, and 3 of the bacterially assisted short-column experiments. Parameters determined from the controlled potential, isothermal experiments were used to help calibrate the model. The individual algorithms of the mathematical model have received extensive treatment by Bouffard and Dixon, Dixon, and Peterson and D i x o n J 1 5 4 - 1 5 6 1 A n excellent description and significance of each of the following parameters can be found in Bouffard's thesis. [ 1 5 7^ Furthermore, parameters for the pyrite leach kinetics were adopted from Bouffard's thesis. During this modeling exercise, it was assumed that each experiment was assisted by only those bacteria which had their optimal cardinal temperature at the experiments operating temperature. Therefore, experiment number 1 (30°C) was assisted by mesophiles, experiment number 2 (50°C) was assisted by moderate thermophiles, and experiment number 3 (70°C) was assisted by extreme thermophiles. Table 5-1 through Table 5-4 summarizes the model parameters which were used in all three modeling exercises. 147 Chapter 5: Modeling Experimental Results and Discussion Table 5-1. Column parameters A c t i v e H e a p H e i g h t 0 . 3 m D r a i n a g e L a y e r T h i c k n e s s 0 . 0 m A c t u a l D r a i n a g e L a y e r T h i c k n e s s 0 . 0 0 m T o t a l H e a p H e i g h t 0 . 3 0 m O r e P a c k e d D e n s i t y 1 7 6 6 k g / m 3 I n i t i a l /Se t H e a p T e m p e r a t u r e 3 0 ° C S t a g n a n t B e d M o i s t u r e 8 % t w a t e r / t o r e Table 5-2. Column operational parameters A i r B l o w i n g R a t e ( v o l u m e ) 7 . 6 3 9 N m 3 / m 2 - h r A i r B l o w i n g R a t e ( m a s s ) 9 . 2 k g / m 2 - h r A i r In let T e m p e r a t u r e 2 0 ° C A i r In let R e l a t i v e H u m i d i t y 6 0 % % S o l u t i o n A p p l i c a t i o n R a t e 5 . 3 L / m 2 - h r S o l u t i o n T e m p e r a t u r e 2 0 ° C S i d e - B r a n c h L e n g t h ( D r i p p e r 1/2 S p a c i n g ) 0 . 0 2 m Table 5-3. Agglomeration parameters A g g l o m e r a t i o n S o l u t i o n A d d e d 3 . 9 % t w a t e r / t o r e A c i d A d d e d d u r i n g A g g l o m e r a t i o n 1 1 . 5 k g a c i d / t o r e A c i d A d d e d d u r i n g A g g l o m e r a t i o n 0 . 1 1 7 m o l / k g o r e 148 Chapter 5: Modeling Experimental Results and Discussion Table 5-4. Mineral leach parameters Number of Minerals Mineral No Name Goslarite Melanterite 2 1 Marmatite 2 Pyrite Zinc Grade from Assays (mass % Zn) 0.30% 15.03% mass % Zn Iron Grade from Assays (mass % Fe) 0.10% 2.97% mass % Fe y, Marmatite Mole Fraction Fe 5.00% mole % Fe Mineral Grade from Assays (mass % min) 0.74% 0.27% 23.46% 6.39% mass % Formula Molecular Mass (g/gmol) 161.44 151.91 96.96 119.97 g/mol Mineral Grade to Program (mol/kg heap) 0.0459 0.0179 2.4199 0.5326 mol/kg heap Rate Constant @ T 0 0.00018 0.0002 1/hr T 0, Rate Reference Temperature 25 55 °C Activation Energy 59260 74340 J/mol Exponent on Fraction Unreacted 2.1 3.2 n, Ferric Reduction Exponent 0.5 0.5 mol/L KA, Ferric Mass Transfer Parameter 0.00001 0.00001 mol/L KB, Ferric Reduction Parameter 0.005 0.00001 mol/L Passivation Potential (mV vs Ag/AgCl) 2000 2000 mV Pyrite abiotic elemental sulfur yield 1 mol S°/mol 5.1 Results of Modeling Experiment Number 1, Replicate 4 Attempts to fit the data generated from experiment number 1, replicate 4, as described in Table 3-6, were unsuccessful until an initial concentration of bacteria was assumed to exist on the agglomerated ore (prior to inoculation). A concentration of 1.00E+04 cells LT1 of mesophilic iron oxidizers and 1.00E+02 cells L _ I of mesophilic sulphur oxidizers was found to yield the best results. The bacterial rate parameters which were established for the mesophilic bacteria are summarized in Table 5-5. The model results are shown in Figure 5-1 through Figure 5-6. 149 Chapter 5: Modeling Experimental Results and Discussion Table 5-5. Bacterial rate parameters for mesophilic bacteria C o m p o n e n t N u m b e r 5 8 N a m e m e s o F e O m e s o S u O G r o w t h R a t e C o n s t a n t , k g 0.11 0 . 0 0 7 1/hr O p t i m u m T d o u b l i n g t i m e = l n ( 2 ) / k g 6 . 3 9 9 . 0 h r D e c a y R a t e M u l t i p l i e r , k e / k g 1 % 1 % 1/hr G r o w t h M o n o d F a c t o r s , K g ( F e ) o r K g ( S ) 1 . 0 0 E - 0 5 1 . 0 0 E - 0 2 m o l / L G r o w t h M o n o d F a c t o r , K g ( 0 2 ) 5 . 0 0 E - 0 5 5 . 0 0 E - 0 5 m o l / L G r o w t h I nh ib i t i on F a c t o r , K g ( Y ) 1 0 0 1 0 0 t e r a c e l l s / L A c i d L i m i t 0 . 0 0 7 m o l / L C e l l Y i e l d p e r m o l e F e o r S ° 2 0 2 0 t e r a c e l l s / m o l M a i n t e n a n c e R a t e C o n s t a n t , k m 0 0 1 /hr S o l i d - L i q u i d P a r t i t i o n C o e f f i c i e n t 1 . 0 0 E + 0 3 1 . 0 0 E + 0 3 a t t a c h e d / f r e e A d s o r p t i o n M a x i m u m 1.5 1.5 t e r a c e l l s / L A d s o r p t i o n C o n s t a n t 6 6 6 . 6 6 6 7 6 6 6 . 6 6 6 7 L / t e r a c e l l M i n i m u m V i a b l e T e m p e r a t u r e , T m i n 1 5 1 5 ° C M a x i m u m V i a b l e T e m p e r a t u r e , T m a x 4 2 4 2 ° C O p t i m u m T e m p e r a t u r e , T o p t 3 8 3 8 ° C T e m p e r a t u r e F u n c t i o n S k e w P a r a m e t e r 0 . 0 8 9 0 . 0 8 9 Figure 5-1. Model ing the zinc concentration in column effluent for experiment number 1, replicate 4 150 Chapter 5: Modeling Experimental Results and Discussion 5 D) 0 o u ° CO CO o 0 0 ^ ! ^ ^ ^ °°oo ^ r r ^ C^ -TS^OcP^ - - -___0C000C003C0C0COCCo O ° \ ^ £ , O ° n u 0 o 0 cCk u O c r o 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n St ream, d I o Data Model Figure 5-2. Model ing the iron concentration in column effluent for experiment number 1, replicate 4 note: the entering leach solution contained 1 g L~' dissolved iron 90 80 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n S t ream, d o Data — M o d e l Figure 5-3. Model ing the overall zinc extraction for experiment number 1, replicate 4 151 Chapter 5: Modeling Experimental Results and Discussion Figure 5-4. Model ing the p H in column effluent for experiment number 1, replicate 4 Figure 5-5. Model ing the O R P in column effluent for experiment number 1, replicate 4 152 Chapter 5: Modeling Experimental Results and Discussion 0. 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n S t ream, d o Data — Model Figure 5-6. Model ing the bacterial populations in column effluent for experiment number 1, replicate 4 As shown in the above figures, the model was able to predict the general trends observed in the experimental data, with the notable exception of the bacterial populations, where the magnitude of the model is approximately four orders of magnitude higher than the data in the first 120 days of the experiment, and approximately two orders of magnitude higher in the last 200 days of the experiment. From the above figures, it can be observed that there is a notable shift in the solution's potential (Figure 5-5) and pH (Figure 5-4) after approximately 40 days on stream. This coincides with a dramatic increase in the concentration of zinc in the column's effluent (Figure 5-1). It was first believed that this 40 day lag period was a result of bacterial 153 Chapter 5: Modeling Experimental Results and Discussion acclimation and population growth; however this is not reflected in either the model output or the experimental data (Figure 5-6). A plot of marmatite and pyrite extraction with time, Figure 5-7, indicates that there is a significant increase in the rate of pyrite conversion after approximately 90 days on stream; this coincides with a dramatic decrease in the rate o f zinc solubilization. However, from Figure 5-2 it can be noted that the iron concentration in the column's effluent remains elevated for the remainder of the experiment. This suggests that the system has undergone a transition from selectively leaching marmatite to selectively leaching pyrite. The bacteria now have an abundant source of ferrous iron to oxidize and hence there is a considerable solution potential that is sustained for the remainder of the experiment. 100 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n S t ream, d - Marmatite - Pyrite Figure 5-7. Model predictions of marmatite and pyrite for experiment number 1, replicate 4 154 Chapter 5: Modeling Experimental Results and Discussion If this is indeed the situation, then the kinetics of pyrite leaching is now impacting upon the rate at which marmatite is being oxidized. Furthermore, elemental sulphur formed during the oxidation of marmatite and pyrite is also consuming oxidant as it is being converted to sulphide. Although in this situation it is clear that there is sufficient oxygen to fuel the bacterial oxidation of ferrous iron to ferric iron, as indicated by the very high solution potentials observed in Figure 5-13, we can nonetheless look at the model predictions for oxygen concentration in solution, Figure 5-8. It can be observed that after 41.4 days (each line progression represents 13.8 days) the dissolved oxygen content of the column is less than 2 ppm. This 2 ppm limit, or 25% of saturation, is approaching the 20% limit set as the bacteria's growth Monod factor, as determined by the following expression: Oxygen Saturation = 8 ppm = 2.5 x mol L 1 Growth Monod Factor ( K g ( 0 2 ) ) = 5.0 x 10~5 mol L" - i 5.1 5.0 x 10 2.5 x 10 ,-5 Critical Oxygen Limit = ,-4 = 20% of Saturation 155 Chapter 5: Modeling Experimental Results and Discussion 9.0 8.0 0.0 -I 1 1 1 1 1 1 0.00 0.05 0.10 0.15 0.20 0.25 0.30 Depth, m Progression with each line: 13.8 days Figure 5-8. Model ing the dissolved oxygen concentration in column depth with time for experiment number 1, replicate 4 5.2 Results of Modeling Experiment Number 2, Replicate 4 Attempts to fit the data generated from experiment number 2, replicate 4, as described in Table 3-6, were unsuccessful until an initial concentration of bacteria was assumed to exist on the agglomerated ore (prior to inoculation). A significant concentration of 1.00E+08 cells LT 1 of moderate thermophilic iron oxidizers and 1.00E+05 cells LT1 of moderate thermophilic sulphur oxidizers was found to yield the best results. The bacterial rate parameters which were established for the moderate thermophilic bacteria are summarized in Table 5-6. The model results are shown in Figure 5-9 through Figure 5-14. 156 Chapter 5: Modeling Experimental Results and Discussion Table 5-6. Bacterial rate parameters for moderate thermophilic bacteria C o m p o n e n t N u m b e r 6 9 N a m e m o d F e O m o d S u O G r o w t h R a t e C o n s t a n t , k g 0 . 0 6 0 . 0 0 9 1/hr O p t i m u m T d o u b l i n g t i m e = l n ( 2 ) / k g 1 1 . 6 7 7 . 0 h r D e c a y R a t e M u l t i p l i e r , k e / k g 1 % 1 % 1/hr G r o w t h M o n o d F a c t o r s , K g ( F e ) o r K g ( S ) 1 . 0 0 E - 0 5 1 . 0 0 E - 0 2 m o l / L G r o w t h M o n o d F a c t o r , K g ( 0 2 ) 1 . 0 0 E - 0 4 4 . 0 0 E - 0 5 m o l / L G r o w t h Inh ib i t i on F a c t o r , K g ( Y ) 1 0 0 1 0 0 t e r a c e l l s / L A c i d L i m i t 0 . 0 0 7 m o l / L C e l l Y i e l d p e r m o l e F e o r S ° 2 0 2 0 t e r a c e l l s / m o l M a i n t e n a n c e R a t e C o n s t a n t , k m 0 0 1/hr S o l i d - L i q u i d P a r t i t i o n C o e f f i c i e n t 1 . 0 0 E + 0 4 1 . 0 0 E + 0 4 a t t a c h e d / f r e e A d s o r p t i o n M a x i m u m 1.5 1.5 t e r a c e l l s / L A d s o r p t i o n C o n s t a n t 6 6 6 6 . 6 6 6 7 6 6 6 6 . 6 6 6 7 L / t e r a c e l l M i n i m u m V i a b l e T e m p e r a t u r e , T m i n 2 5 2 5 ° C M a x i m u m V i a b l e T e m p e r a t u r e , T m a x 5 5 5 5 ° C O p t i m u m T e m p e r a t u r e , T o p t 4 5 4 5 ° C T e m p e r a t u r e F u n c t i o n S k e w P a r a m e t e r 0 . 3 6 7 0 . 3 6 7 Figure 5-9. Model ing the zinc concentration in column effluent for experiment number 2, replicate 4 157 Chapter 5: Modeling Experimental Results and Discussion o - i , 1 . 1 1 1 1 1 1 ' 1 1 1 ' ' i 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e on St ream, d [ o Data — M o d e l Figure 5-10. Model ing the iron concentration in column effluent for experiment number 2, replicate 4 note: the entering leach solution contained 1 g LT1 dissolved iron 90 80 T i m e on S t ream, d o Data — M o d e l Figure 5-11. Model ing the overall zinc extraction for experiment number 2, replicate 4 158 Chapter 5: Modeling Experimental Results and Discussion 0 o ° ^ w ^ U (^J '3 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n S t ream, d Figure 5-12. Model ing the pH in column effluent for experiment number 2, replicate 4 Figure 5-13. Model ing the O R P in column effluent for experiment number 2, replicate 4 159 Chapter 5: Modeling Experimental Results and Discussion 1E+13 1E+12 1E+11 1E+10 1E+09 1E+08 1E+07 1E+06 in = 1E+05 <t> ° 1E+04 1E+03 1E+02 1E+01 1E+00 o o 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 Time o n S t ream, d o Data -Model Figure 5-14. Model ing the bacterial populations in column effluent for experiment number 2, replicate 4 As shown in the above figures, the model was able to predict the general trends observed in the experimental data, with the exception of the bacterial populations. In this modeling exercise the model predicts a bacteria population that is approximately 4 orders of magnitude greater than that observed during the experiment. In addition to the poor bacteria fits, it can be noted that after day 90 there is a steady decline in solution potential, p H , and bacteria population, which was not observed in the experimental data. After day 180 there is a dramatic shift in the rate of zinc solubilization and, as shown in Figure 5-15, the rate of pyrite conversion; this is accompanied by a large increase in solution potential. It is believed that there is a shift in the selective rate of leaching from marmatite to pyrite. 160 Chapter 5: Modeling Experimental Results and Discussion 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e on S t ream, d - Marmatite - Pyrite Figure 5-15. Model predictions of marmatite and pyrite for experiment number 2, replicate 4 This model behavior can be understood by looking at the dissolved oxygen concentration within the column, Figure 5-16. 0.00 0.05 0.10 Progression with each line: 13.8 days 0.15 Depth, m 0.20 0.25 0.30 Figure 5-16. Model ing the dissolved oxygen concentration in column depth with time for experiment number 2, replicate 4 161 Chapter 5: Modeling Experimental Results and Discussion As shown in Figure 5-16, the oxygen concentration drops below the critical oxygen limit for the bacteria (1.6 ppm dissolved oxygen) at approximately 96.6 days (7 line progressions at 13.8 days per line). This concentration represents an oxygen limitation for bacterial oxidation of ferrous iron to ferric iron and hence, the rate of leaching of marmatite decreases, as shown in Figure 5-15. The oxygen returns to an acceptable limit after approximately 193.2 days (14 line progressions) and hence, a return to a faster rate of leaching. 5.3 Results of Modeling Experiment Number 3, Replicate 4 As was the situation in the first two modeling attempts, the data generated from experiment number 3, replicate 4, as described in Table 3-6, could not be satisfactorily fitted until an initial concentration of bacteria was assumed to exist on the agglomerated ore (prior to inoculation). A concentration of 1.00E+05 cells LT 1 of moderate thermophilic iron oxidizers and 1.00E+05 cells LT1 of moderate thermophilic sulphur oxidizers was found to yield the best results. The bacterial rate parameters which were established for the moderate thermophilic bacteria are summarized in Table 5-7. The model results are shown in Figure 5-17 through Figure 5-22. 162 Chapter 5: Modeling Experimental Results and Discussion Table 5-7. Bacterial rate parameters for extreme thermophilic bacteria C o m p o n e n t N u m b e r 7 1 0 N a m e e x t r F e O e x t r S u O G r o w t h R a t e C o n s t a n t , k g 0 . 1 5 0 . 0 9 1/hr O p t i m u m T d o u b l i n g t i m e = l n ( 2 ) / k g 4 . 6 7 . 7 h r D e c a y R a t e M u l t i p l i e r , kjkq 1 % 1 % 1/hr G r o w t h M o n o d F a c t o r s , K g ( F e ) o r K g ( S ) 1 . 0 0 E - 0 5 1 . 0 0 E - 0 2 m o l / L G r o w t h M o n o d F a c t o r , K g ( 0 2 ) 5 . 0 0 E - 0 5 5 . 0 0 E - 0 5 m o l / L G r o w t h I nh ib i t i on F a c t o r , K g ( Y ) 1 0 0 1 0 0 t e r a c e l l s / L A c i d L i m i t 0 . 0 0 7 m o l / L C e l l Y i e l d p e r m o l e F e o r S ° 2 0 2 0 t e r a c e l l s / m o l M a i n t e n a n c e R a t e C o n s t a n t , k m 0 0 1/hr S o l i d - L i q u i d P a r t i t i o n C o e f f i c i e n t 1 . 0 0 E + 0 3 1 . 0 0 E + 0 3 a t t a c h e d / f r e e A d s o r p t i o n M a x i m u m 1.5 1.5 t e r a c e l l s / L A d s o r p t i o n C o n s t a n t 6 6 6 . 6 6 6 7 6 6 6 . 6 6 6 7 L / t e r a c e l l M i n i m u m V i a b l e T e m p e r a t u r e , T m i n 5 0 5 0 ° C M a x i m u m V i a b l e T e m p e r a t u r e , T m a x 8 0 8 0 ° C O p t i m u m T e m p e r a t u r e , T o p t 6 8 6 8 ° C T e m p e r a t u r e F u n c t i o n S k e w P a r a m e t e r 0 . 5 5 3 0 . 5 5 3 163 Chapter 5: Modeling Experimental Results and Discussion 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e on St ream, d o Data -Model Figure 5-17. Model ing the zinc concentration in column effluent for experiment number 3, replicate 4 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n St ream, d o Data -Model Figure 5-18. Model ing the iron concentration in column effluent for experiment number 3, replicate 4 note: the entering leach solution contained 1 g L~' dissolved iron 164 Chapter 5: Modeling Experimental Results and Discussion Figure 5-19. Model ing the overall zinc extraction for experiment number 3, replicate 4 Figure 5-20. Modeling the pH in column effluent for experiment number 3, replicate 4 165 Chapter 5: Modeling Experimental Results and Discussion Figure 5-21. Model ing the O R P in column effluent for experiment number 3, replicate 4 1E+13 1E+12 1E+11 1E+10 c 1E+09 33 1E+08 3 O to 1E+07 '>_, 1E+06 = 1E+05 o ° 1E+04 1E+03 1E+02 1E+01 1E+00 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 T i m e o n St ream, d o Data — Model Figure 5-22. Model ing the bacterial populations in column effluent for experiment number 3, replicate 4 166 Chapter 5: Modeling Experimental Results and Discussion A s shown in the above figures, the model was able to predict the general trends observed in the experimental data, however, the fits are not as good as in the previous exercises. The p H is the only plot where the model was able to simulate both the magnitude and the shape of the experimental data. As in previous runs, model predicts a bacteria population that is approximately 4 orders of magnitude greater than that observed during the experiment. It should be noted that slightly better fit of zinc extraction was achieved by assuming a slightly larger sphalerite rate constant (0.00024 hr - 1 ) . However, the remaining fits were virtually unchanged. As was the case at 50°C, there is a significant change in the respective rates of mineral leaching; at 190 days on stream the rate of pyrite leaching accelerates, as shown in Figure 5-23. This further supports the belief that there is a shift from the selective leaching of marmatite to that of pyrite. Additionally, the irregular behavior demonstrated in the experimental data suggests that a complex interplay exists between the oxidation of the three primary elements which exist in the system (zinc, iron, and sulphur). The oxygen available for the biooxidation of ferrous iron in this system is notably low, as shown in Figure 5-24. The bacteria are starved for oxygen and, as the model suggests, may have perished in the actual experiments. 167 Chapter 5: Modeling Experimental Results and Discussion 100 Figure 5-23. Model predictions of marmatite and pyrite for experiment number 3, replicate 4 6.0 7 0.00 0.05 0.10 0.15 0.20 0.25 0.30 Depth, m Progression with each line: 13.8 days Figure 5-24. Model ing the dissolved oxygen concentration in column depth with time for experiment number 3, replicate 4 168 Chapter 6: Conclusions 6. C O N C L U S I O N S Equation Section (Next)From this experimental program a number of useful conclusions can be drawn. The results of the controlled potential, isothermal experiments illustrated that on a fine particle scale (sub 400 mesh) this material follows a variable order model after D ixon and Hendr ix . [ 1 5 3 ] In addition, the material was found to have an activation energy of 58.23 kJ m o l - 1 , a reaction order of 2.30 and a dependency on ferric ions of 0.342. It is proposed that the grain model for this particular ore follows the expression: f = Vexp(-I^).[F^r.( ,-Xr From the results of the bacterially assisted short column experiments it has been concluded that the systems were limited by the availability of dissolved oxygen. A dramatic increase in the initial rate of zinc extraction (235%) was observed when air was replaced with oxygen gas. It can also be concluded from the results of the modeling exercise that the mathematical model, at its current stage of development, is insufficient to accurately describe the leaching of this ore. In addition to being oxygen mass transport limited, the system is hindered by a complex interplay between the three competing elements (zinc, iron, and sulphur) for oxidant. A s such, these elements wi l l not only compete with each other for F e 3 + ions, but there wi l l also be galvanic interactions that wi l l take place through simple physical contact. As observed by Murr and Mehta, these galvanic interactions coupled with the catalytic effect created from the 169 Chapter 6: Conclusions presence of bacteria can produce a system that has complex chemistry. Furthermore, the utilization of the oxidant wi l l vary with the kinetics of the respective mineral and are subject to change as the system shifts in mineral selectivity. In addition, it can be concluded that a superior understanding of each mineral's intrinsic kinetics is required to properly perform a fitting exercise with the current model. To appreciate the switch in selective leaching which was observed in the data these kinetics need to be quantified. A n additional observation that can be made of the bacterially assisted, short-column experiments is that there is a one order of magnitude decrease in the number of cells attached to the solids for every increase in cardinal temperature. This is to say that the cell counts dropped from approximately 4 x 10 1 0 mL" 1 at 30°C to 5 x 10 9 m l / 1 at 50°C to 7 x 10 8 m l / 1 at 70°C. 170 Chapter 7: Recommendations 7. R E C O M M E N D A T I O N S Equation Section (Next)This multiminerallic material (marmatite, pyrite, and sulphur) is very difficult to describe without a better understanding of the individual mineral kinetics. Therefore, it is recommended that a hybrid experiment be developed whereby the control of solution potential and the minimization o f mass transfer control of the Appl ikon experiments is married with the large particle sizes and controlled temperature of the short-column experiments. This wi l l allow for careful solution assays to be taken for a system that has conditions designed to minimize jarosite precipitation while operating at a potential below that of pyrite. In addition, it is felt that more experiments need to be performed to investigate the effect of elevated oxygen on the extraction of zinc for the respective systems studied in these experiments. Furthermore, it is felt that further validation of the model with additional short column experiments needs to be conducted. It is also felt that although the fits that were generated yielded reasonable results, it is unknown whether they are exclusive. 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Results of experiment number 1, replicate 1 Time on Stream, Zn Zn Fe d pH Eh, mV PPm Extraction, % ppm 2.36 0.82 410 11220 1.1% 9651 5.73 1.38 438 2342 1.8% 1492 9.76 1.14 469 1575 2.7% 941 12.67 1.24 470 2017 3.6% 875 16.61 1.18 475 2259 4.8% 934 19.66 1.27 449 2358 5.8% 875 23.65 1.25 443 2477 6.3% 1162 26.67 1.26 440 2562 7.3% 969 30.68 1.30 442 2799 8.7% 1031 33.66 1.36 470 2970 9.8% 1091 37.80 . 1.44 522 3742 11.8% • ' 1221 40.68 1.45 654 3798 13.2% 1181 44.74 1.63 622 4176 15.3% 1231 47.67 1.77 605 4443 17.0% 1306 51.74 1.85 600 4456 19.3% 1551 53.67 1.78 722 4742 20.5% 1646 Fe Extraction, 1.7% 2.0% 1.9% 1.8% 1.6% 1.5% 0.5% 0.5% 0.5% 0.5% 0.9% 1.1% -- 1.3% 1.5% 2.2% 2.8% Table A 2. Results of experiment number 1, replicate 2 Time on Stream, d PH Eh, mV 2.36 0.85 409 5.73 1.32 448 9.76 1.11 449 12.66 1.19 519 16.63 1.24 472 19.66 1.26 454 23.65 1.23 451 26.67 1.26 441 30.67 1.31 440 33.65 1.31 455 37.76 1.38 476 40.68 1.44 533 44.68 1.48 566 47.67 1.64 537 51.73 1.65 522 54.70 1.49 576 58.70 1.68 654 61.70 1.57 671 65.72 1.63 699 68.69 1.75 582 72.75 1.52 679 75.63 1.53 692 79.67 1.71 655 82.65 1.58 691 86.67 1.53 696 89.66 1.35 706 93.70 1.28 700 96.64 1.30 651 100.72 1.21 718 103.65 1.20 714 107.75 1.16 743 110.65 1.21 721 114.67 1.41 721 116.74 1.49 743 Zn Zn Fe Fe ppm Extraction, % ppm Extraction, % 6046 1.6% 4270 2.0% 1714 2.4% 1001 2.0% 1381 3.2% 911 1.9% 1947 3.6% 885 1.1% 2069 4.9% 952 1.0% 2360 6.0% 788 0.7% 2316 7.4% 1156 0.9% 2430 8.6% 948 0.8% 2708 10.2% 980 0.8% 2655 11.3% 1054 0.8% 3242 13.2% 1118 0.9% 3660 14.7% 1240 1.1% 3762 16.9% 1287 1.4% 4070 18.6% 1329 1.9% 3986 21.0% 1467 2.6% 4075 22.8% 1606 3.1% 4485 25.1% 1548 3.8% 4956 27.3% 1497 4.3% 4925 29.3% 1590 4.8% 4590 30.9% 1782 5.4% 4240 33.1% 1613 6.2% 3834 34.5% 1598 6.7% 3605 36.7% 1622 7.6% 3863 38.4% 1574 8.1% 3937 40.3% 1672 8.9% 2439 41.6% 1287 9.2% 2517 43.1% 1528 10.0% 2370 44.2% 1499 10.5% 2674 45.7% 1364 11.0% 2505 46.7% 1451 11.4% 2253 48.0% 1452 12.0% 2439 48.9% 1715 12.6% 4092 50.1% 1758 13.1% 2380 51.0% 1801 14.0% 185 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 3. Results of experiment number 1, replicate 3 Time on Stream, Zn Zn Fe Fe d pH Eh, mV ppm Extraction, % ppm Extraction, % 2.36 1.08 419 5116 1.0% 3355 1.0% 5.72 1.36 429 2392 1.7% 1253 1.2% 9.75 1.31 431 2254 2.3% 961 1.1% 12.65 1.40 439 3733 3.0% 970 1.1% 16.61 1.18 482 2413 4.4% 942 1.0% 19.66 1.31 445 2502 5.5% 897 1.0% 23.65 1.29 437 2713 6.9% 942 0.6% 26.66 1.31 431 2983 8.0% 978 0.6% 30.65 1.40 427 3270 9.5% 1032 0.7% 33.65 1.41 449 3283 10.7% 976 0.7% 37.80 1.52 479 4449 12.6% 1195 0.8% 40.67 1.69 505 5027 14.1% 1161 0.9% 44.67 1.80 495 4884 16.1% 1344 1.2% 47.66 1.91 479 4981 17.6% 1413 1,4% 51.72 1.66 470 - 4490 19.9% 1539 2.0% • 54.70 1.54 489 4627 21.6% 1499 2.4% 58.69 1.73 510 4770 23.9% 1694 3.3% 61.69 1.75 597 4678 25.6% 1698 3.8% 65.72 1.55 680 4684 27.8% 1402 4.3% 68.69 1.43 738 3355 29.4% 1395 4.7% 72.74 1.38 663 3720 31.2% 1501, 5.3% 75.63 1.40 693 3376 32.7% 1421 5.7% 79.67 1.59 674 2777 34.3% 1336 6.2% 82.64 1.43 679 3111 35.9% 1329 6.6% 86.67 1.29 719 2677 37.6% 1318 7.1% 89.66 1.30 700 2810 38.7% 1272 7.3% 93.69 1.35 697 2771 40.0% 1555 7.9% 96.64 1.21 657 2491 41.1% 1388 8.3% 100.73 1.25 711 3027 42.9% 1575 9.5% 103.66 1.25 711 2904 43.8% 1539 10.0% 107.77 1.21 720 2041 45.0% 1342 10.4% 110.68 1.16 682 2165 45.8% 1558 11.0% 114.68 1.32 730 2228 47.0% 1577 11.7% 117.71 1.25 715 2119 47.8% 1596 12.2% 121.68 1.24 702 1842 48.8% 1553 12.9% 124.65 1.25 707 1724 49.5% 1553 13.4% 128.69 1.20 719 1838 50.4% 1510 13.8% 131.65 1.17 687 1384 51.0% 1502 14.4% 135.74 1.19 707 1432 51.7% 1502 15.0% 138.65 1.12 704 1668 52.4% 1493 15.5% 142.75 1.24 675 1310 53.1% 1478 16.1% 145.69 1.22 656 1191 53.7% 1478 16.7% 149.65 1.23 1399 54.3% 1463 17.2% 152.69 1.07 699 872 54.8% 1394 17.7% 156.67 1.17 680 868 55.3% 1394 18.3% 159.72 1.02 708 958 55.8% 1324 18.6% 163.71 1.24 719 1148 56.4% 1364 19.1% 166.67 1.19 712 860 56.8% 1364 19.5% 170.74 1.20 714 1083 57.4% 1364 20.0% 173.85 1.17 711 732 57.8% 1403 20.4% 177.69 1.10 693 1023 58.3% 1354 20.9% 180.66 1.22 709 906 58.7% 1354 21.3% 184.70 1.21 702 930 59.3% 1304 21.8% 187.71 1.06 677 1065 59.8% 1313 22.1% 191.73 1.08 694 858 60.3% 1313 22.5% 194.65 1.05 677 936 60.7% 1321 22.8% 198.67 1.11 678 918 61.2% 1305 23.3% 201.67 1.06 679 937 61.6% 1305 23.6% 205.66 1.03 673 820 62.2% 1289 24.1% 208.70 1.17 674 550 62.5% 1305 24.5% 212.77 1.10 668 466 62.7% 1305 24.9% 215.84 0.99 678 681 63.1% 1321 25.3% 219.89 1.07 684 500 63.4% 1257 25.7% 222.83 1.04 671 765 63.8% 1257 26.0% 226.65 1.04 678 584 64.0% 1193 26.2% 229.77 1.08 691 1070 64.6% 1252 26.5% 233.65 1.05 672 872 65.1% 1310 26.8% 186 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 4. Results of experiment number 1, replicate 4 Time on Stream, Zn Zn Fe Fe d pH Eh, mV ppm Extraction, % ppm Extraction, % 2.36 1.14 422 6268 1.6% 4283 1.9% 5.70 1.30 453 1952 2.5% 1076 2.0% 9.75 1.20 453 1567 3.4% 819 1.7% 12.65 1.29 446 2161 4.4% 960 1.6% 16.61 1.18 470 2469 5.9% 826 1.3% 19.65 1.26 451 2053 7.0% 923 1.2% 23.64 1.24 440 2298 8.4% 948 1.1% 26.66 1.26 434 2611 9.6% 861 0.8% 30.65 1.32 431 2701 11.3% 1027 1.1% 33.64 1.33 449 2719 12.5% 1111 1.1% 37.79 1.32 458 3108 13.9% 1239 1.3% 40.66 1.36 453 4182 15.6% 1280 1.4% 44.65 1.40 468 3559 17.7% 1085 1.5% 47.64 1.65 478 4278 19.4% 1448 1.9% 51.71 1.77 491 4566 21.9% 1640 2.7% 54.70 1.60 518 4612 23.7% 1659 3.2% 58.69 1.66 522 4126 25.8% 1675 4.0% 61.69 1.66 622 4136 27.5% 1654 4.7% 65.71 1.48 676 4175 29.8% 1571 5.4% 68.68 1.23 683 2910 31.4% 1355 5.8% 72.74 1 37 688 3305 33.3% 1400 6.4% 75.62 1 61 677 4715 34.5% 1786 6.8% 79.67 1.77 657 3940 35.6% 1611 7.2% 82.64 1.46 608 3022 37.3% 1367 .7.7% 86.65 1.36 702 2586 38.7% 1345 8.1% 89.65 1.25 694 2230 39.9% 1204 8.4% 93.69 1.24 689 1985 40.9% 1420 8.9% 96.63 1.26 669 2362 42.3% 1385 9.4% 100.73 1.16 722 2049 43.4% 1355 9.9% 103.67 1.22 725 2583 44.6% 1438 10.3% 107.78 1.16 740 1792 45.5% 1248 10.6% 110.68 1.23 720 2417 46.7% 1652 11.3% 114.71 1.27 676 1981 47.8% 1649 12.2% 117.71 1.24 708 2264 48.8% 1645 12.9% 121.71 1.22 740 1802 49.7% 1585 13.6% 124.66 1.32 700 2458 50.7% 1585 14.1% 128.70 1.19 737 1779 51.8% 1524 14.8% 131.66 1.17 711 1703 52.5% 1512 15.3% 135.75 1.16 712 1705 53.5% 1512 16.0% 138.67 1.15 687 1628 54.1% 1499 16.5% 142.75 1.21 676 1613 55.1% 1728 17.5% 145.69 1.23 675 1484 55.3% 1728 17.7% 149.66 1.27 3319 56.4% 1957 18.5% 152.69 1.04 728 1185 56.9% 1766 19.3% 156.68 1.20 708 1776 57.4% 1766 19.8% 159.72 1.08 749 1498 58.2% 1574 20.5% 163.71 1.24 729 1301 59.0% 1471 21.1% 166.67 1.14 733 971 59.4% 1471 21.6% 170.74 1.18 725 1206 60.0% 1471 22.1% 173.86 1.16 717 903 60.4% 1368 22.5% 177.70 1.10 738 1020 61.1% 1352 23.1% 180.66 1.16 723 978 61.6% 1352 23.5% 184.71 1.12 724 1008 62.2% 1335 23.9% 187.71 1.07 688 840 62.6% 1331 24.3% 191.73 1.07 691 1018 63.2% 1331 24.7% 194.65 1.05 683 979 63.6% 1327 25.1% 198.67 1.14 679 925 64.2% 1350 25.6% 201.68 1.00 680 1057 64.7% 1350 25.8% 205.67 1.00 656 1108 65.2% 1372 26.1% 208.67 1.12 680 702 65.6% 1356 26.5% 212.77 1.10 669 667 66.0% 1356 27.0% 215.84 1.01 680 762 66.4% 1340 27.4% 219.90 1.06 681 765 66.8% 1328 27.8% 222.84 1.03 670 803 67.2% 1328 28.1% 226.66 1.03 684 785 67.6% 1315 28.6% 229.77 1.05 692 777 68.0% 1299 28.9% 233.66 1.00 670 681 68.4% 1282 29.3% 243.69 1.05 720 674 69.5% 1291 30.3% 253.76 1.01 683 552 70.3% 946 30.0% 263.69 1.07 693 456 71.0% 1033 30.1% 273.77 1.13 657 341 71.6% 1119 30.6% 283.92 1.12 303 72.1% 1094 30.9% 293.89 1.08 615 391 72.7% 1069 31.1% 187 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 5. Results of experiment number 2, replicate 1 Time on Stream, Zn Zn Fe Fe d pH Eh, mV ppm Extraction, % ppm Extraction, % 1.00 397 10640 2.1% 6858 2.7% 4.78 1.32 434 2225 3.5% 1011 2.7% 7.66 1.25 431 2466 4.7% 906 2.6% 11.76 1.36 428 3408 6.5% 941 2.5% 14.66 1.41 ' 420 3690 8.0% 1034 2.5% 18.63 1.42 419 3791 10.1% 965 2.4% 21.68 1.42 414 3650 11.7% 1222 2.5% 25.65 1.34 410 3297 13.8% 1020 2.6% 28.68 1.38 406 3458 15.5% 1073 2.6% 32.76 1.33 401 2801 17.2% 1121 2.8% 35.76 1.35 407 3211 18.7% 1159 2.9% 39.90 1.37 407 3066 20.7% 1119 3.1% 42.79 1.28 412 2904 21.9% 1054 3.1% 46.82 1.24 413 2499 23.4% 1154 3.3% 49.79 1.28 411 2371 24.4% 1056 3.3% 53.73 1.23 408 2269 25.7% 1069 3.4% 55.87 1.23 416 2155 26.5% 1007 4.0% Table A 6. Results of experiment number 2, replicate 2 Time on Stream, Zn Zn Fe Fe d PH Eh, mV ppm Extraction, % PPm Extraction, % 1.00 395' 10340 2.0% 7110 2.7% 4.78 1.32 433 2594 3.6% 1104 2.8% 7.66 1.22 • 424 2924 4.8% . 976 27% 11.75 1.36 427 3364 5.4% 974 2.0% 14.65 1.42 419 4301 7.0% 1190 1.9% 18.64 1.43 417 4477 9.5% 1217 2.1% 21.67 1.40 415 3973 11.1% 1380 2.3% 25.65 1.31 413 3613 13.1% 1242 2.4% 28.67 • 1.35 411 4368 14.9% 1292 2.5% 32.76 . 1.31 407 3218 16.7% 1249 2.7% 35.76 1.33 412 3586 18.1% 1311 2.7%' 39.88 1.35 415 3524 19.8% 1408 2.9% 42.78 1.24 404 3766 21.3% 1559 3.2% 46.82 1.17 417 2363 22.6% 1193 3.4% 49.78 1.28 407 2526 23.7% 1140 3.4% 53.72 1.24 412 2348 25.1% 1100 3.5% 56.72 1.08 416 2476 26.1% 1147 3.6% 60.71 1.16 405 1763 27.2% 1086 3.7% 63.70 1.19 420 1462 27.9% 1021 3.7% 67.73 1.14 427 1645 28.9% 1018 3.7% 70.68 1.19 440 1640 29.6% 1021 3.7% 74.76 1.13 424 1615 30.6% 1065 3.8% 77.64 1.10 418 1272 31.2% 802 3.5% 81.69 1.37 419 1131 31.9% 871 3.4% 84.66 1.25 411 1206 32.6% 1062 3.4% 88.69 1.17 422 1116 33.2% 1042 3.4% 91.68 1.16 402 1789 34.0% 1243 3.7% 95.69 1.17 411 1350 34.9% 1168 3.9% 98.66 1.07 401 1401 35.6% 1245 4.1% 102.80 1.09 410 1282 36.4% 1226 4.4% 105.75 1.07 419 1298 36.9% 1111 4.5% 109.86 1.05 425 1108 37.6% 1133 4.7% 112.78 1.09 417 1051 38.1% 1320 5.0% 116.79 1.16 420 858 38.7% 1297 5.5% 118.77 1.33 429 957 39.1% 1297 6.3% 188 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 7. Results of experiment number 2, replicate 3 Time on Stream, Zn Zn Fe Fe d PH Eh, mV PPm Extraction, % ppm Extraction, % 1.00 0.61 403 9029 1.7% 6256 2.2% 4.78 1.37 426 2173 2.8% 1072 2.2% 7.65 1.19 445 2073 3.9% 991 2.2% 11.74 1.36 453 3320 5.4% 982 2.0% 14.64 1.36 442 4328 7.0% 1344 2.2% 18.64 1.47 425 3799 9.2% 1291 2.4% 21.67 1.48 419 4060 10.9% 1414 2.6% 25.65 1.26 417 3220 12.7% 1176 2.7% 28.67 1.21 412 3431 14.1% 1282 2.7% 32.77 1.23 409 2702 15.7% 1210 2.9% 35.75 1.29 412 2834 16.6% 1305 3.1% 39.88 1.32 403 2607 17.9% 1123 3.1% 42.78 1.15 403 2578 18.9% 1239 3.1% 46.81 1.24 420 2125 20.0% 1221 3.1% 49.78 1.32 431 3007 20.3% 1123 3.1% 53.72 1.21 402 2264 21.5% 1269 3.3% 56.72 ' , 1.06 424 ' 2140 22.4% 1148 3.4% 60.70 1.15' 405 1616 23.3% 1132 3.6% 63.70 1.17 421 1315 23.8% 1006 3.6% 67.73 1.15 435 1410 24.4% 1006 3.2% 70.68 1.17 445 1480 25.0% 992 3.1% 74.76 1.11 426 1320 25.8% 916 3.0% 77.64 1.07 418 1050 26.3% 789 2.7% 81.69 1.40 419 958 ' 26.9% 857 2.5% 84.66 1.23 417 1215 27.5% 1005 2.5% 88.69 1.18 425 1213 28.3% 996 2.5% 91.68 1.14 411 1328 28.9% 1008 2.4% 95.68 1.11 419 1136 29.6% 1015 2.4% 98.66 1.10 410 1188 30.2% 1202 2.6% 102.80 1.11 419 1116 30.9% 1173 2.8% 105.74 1.09 427 1004 31.3% 1051 2.8% 109.87 1.01 431 334 31.5% 860 2.7% 112.78 1.03 427 346 31.7% 1079 2.7% 116.78 1.10 426 277 31.9% 1098 3.3% 119.76 1.08 435 345 32.0% 1117 3.4% 123.78 1.10 445 304 32.1% 1169 3.5% 126.73 1.16 413 916 32.5% 1169 3.7% 130.76 1.21 424 719 33.0% 1220 4.0% 133.72 1.16 420 795 33.4% 1232 4.2% 137.80 1.07 419 576 33.7% 1232 4.6% 140.85 1.15 421 820 34.2% 1244 4.8% 144.81 1.15 421 884 34.7% 1134 5.1% 147.77 1.20 429 1058 35.0% 1134 4.5% 151.73 1.12 395 543 35.3% 1023 4.5% 154.81 1.06 416 496 35.6% 1155 4.7% 158.75 1.20 423 803 36.1% 1155 4.9% 161.77 1.05 430 872 36.5% 1286 5.2% 165.81 1.23 423 828 37.0% 1272 5.6% 168.74 1.13 420 831 37.4% 1272 5.9% 172.81 1.09 417 818 38.0% 1257 6.6% 175.88 1.09 420 787 38.4% 1133 6.7% 179.76 1.12 407 501 38.8% 1133 7.0% 182.74 1.15 427 260 38.9% 1009 6.9% 186.78 1.09 385 229 39.0% 1032 6.9% 189.76 1.00 388 191 39.1% 1032 6.9% 193.81 1.02 396 273 39.3% 1054 7.0% 196.71 0.98 406 279 39.4% 1078 7.1% 200.72 1.05 395 292 39.6% 1078 7.2% 203.77 0.95 398 274 39.8% 1102 7.3% 207.75 0.98 422 635 40.1% 1144 7.5% 210.73 1.18 419 566 40.4% 1144 7.7% 214.82 1.05 420 521 40.7% 1186 7.9% 217.90 1.04 421 513 41.0% 922 7.8% 221.95 1.08 429 491 41.3% 1050 7.9% 224.89 1.05 422 493 41.5% 1178 8.0% 228.72 1.03 422 482 41.8% 1089 8.2% 231.83 1.04 410 380 42.0% 1089 8.3% 235.73 1.09 316 42.3% 821 8.4% 189 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 8. Results of experiment number 2, replicate 4 Time on Stream, Zn Zn Fe Fe d PH Eh, mV PPm Extraction, % ppm Extraction, % 1.00 0.65 398 8283 1.8% 5195 2.1% 4.76 1.35 427 1975 3.0% 953 2.0% 7.65 1.23 425 2307 ' 4.1% 1048 2.0% 11.74 1.43 428 3267 5.6% 892 1.9% 14.64 1.38 420 3469 7.0% 1057 1.9% 18.63 1.47 422 4306 9.4% 1151 2.1% 21.66 1.53 417 3844 11.1% 1317 2.3% 25.64 1.37 415 3116 13.0% 1122 2.5% 28.67 1.30 421 3502 14.7% 1072 2.5% 32.77 1.31 415 2691 16.4% 1109 2.7% 35.75 1.29 425 2906 17.6% 1234 2.8% • 39.88 1.32 425 2560 18.9% 1303 2.9% 42.77 1.23 414 2696 20.0% 1069 2.8% 46.79 1.18 420 2635 21.4% 1250 3.1% 49.78 1.26 417 2699 22.5% 1270 3.3% 53.71 1.21 413 1764 23.6% 1144 3.5% 56.72 1.04 419 2137 24.5% 1093 3.5% 60.70 1.20 409 1426 25.4% 1045 3.6% 63.70 . 1.19 424 1274 26.0% 1033 3.7% 67.72 1.27 425 1525 27.0% 1029 3.7% 70.67 1.19 442 1520 27.7% 951 3.7% 74.75 1.15 427 1510 28.2% 1032 3.7% 77.64 1.18 415 1845 29.1% 888 3.5% 81.69 1.36 414 1066 29.8% 895 3.4% 84.65 1.25 417 1357 30.5% 1029 3.4% 88.68 1.19 422 1366 31.4% 999 3.4% 91.67 1.15 410 1525 32.1% 1031 3.4% 95.67 1.12 417 1257 32.9% 1012 3.5% 98.65 1.12 410 1363 33.6% 1249 3.7% 102.79 1.17 417 1208 34.3% 1072 3.9% 105.74 1.08 424 1297 34.9% 1107 3.9% 109.87 1.07 433 940 35.5% 1173 4.2% 112.77 1.11 422 1067 36.0% 1324 4.5% 116.77 1.20 424 1017 36.6% 1347 5.0% 119.77 1.09 435 1228 37.0% 1369 5.3% 123.80 1.16 429 884 37.5% 1327 5.8% 126.74 1.16 420 953 38.0% 1327 6.1% 130.77 1.21 427 809 38.4% 1285 6.6% 133.72 1.12 420 882 38.9% 1262 6.8% 137.80 1.05 424 738 39.3% 1262 7.3% 140.85 1.13 421 782 39.7% 1239 7.5% 144.81 1.13 423 916 40.3% 1209 7.6% 147.77 1.07 423 749 40.6% 1209 8.0% 151.74 1.14 399 525 40.9% 1179 7.9% 154.81 0.99 415 512 41.2% 1221 8.1% 158.76 1.16 421 717 41.6% 1221 8.4% 161.78 0.99 429 874 42.0% 1263 8.7% 165.82 1.21 422 783 42.5% 1270 9.0% 168.80 1.12 415 802 42.9% 1270 9.3% 172.81 1.08 419 739 43.3% 1277 9.4% 175.90 1.06 399 425 43.5% 1196 9.7% 179.77 1.11 397 329 43.7% 1196 9.7% 182.74 1.20 422 528 43.9% 1115 9.8% 186.78 1.11 412 820 44.5% 1110 10.0% 189.76 1.06 402 490 44.7% 1110 10.4% 193.82 1.07 405 463 45.0% 1104 10.6% 196.71 0.98 419 500 45.3% 1142 10.7% 200.74 1.10 407 482 45.6% 1142 10.9% 203.78 0.96 411 474 45.8% 1179 11.1% 207.75 0.98 421 648 46.2% 1166 12.1% 210.77 1.11 409 746 46.6% 1166 12.3% 214.83 1.08 419 384 46.9% 1153 12.6% 217.90 1.03 420 545 47.2% 1099 12.7% 221.95 1.03 431 431 47.4% 1162 13.0% 224.89 1.06 421 507 47.7% 1225 13.2% 228.73 1.01 422 427 48.0% 1081 13.4% 231.83 1.03 407 318 48.2% 1081 13.5% 235.74 1.01 415 282 48.4% 936 13.4% 245.77 1.05 427 443 49.1% 1070 13.6% 256.82 0.99 413 160 49.3% 1204 14.4% 265.72 1.09 436 490 50.1% 1043 14.5% 275.82 1.10 419 404 50.7% 882 14.1% 285.97 1.14 391 312 51.1% 948 13.9% 190 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 9. Results of experiment number 3, replicate 1 Time on Stream, Zn Zn Fe Fe d PH Eh, mV ppm Extraction, % PPm Extraction, % 2.77 1.31 404 7659 3.9% 5993 5.9% 5.66 1.31 395 2298 5.0% 1108 5.9% 9.74 1.27 388 2351 6.3% 1145 6.0% 12.64 1.24 386 2642 7.4% 1055 6.0% 16.61 1.12 374 2069 8.5% 1050 6.0% 19.64 1.08 376 2160 9.4% 729 5.6% 23.64 1.06 381 1991 10.5% 1174 5.7% 26.64 1.07 382 2483 11.6% 1109 5.7% 30.69 1.16 389 2604 13.1% 1101 5.7% 33.69 1.21 393 2941 14.4% 1197 5.8% 37.62 1.25 394 3125 16.3% 1300 6.2% 40.72 1.25 395 3967 18.0% 1329 6.5% 44.74 1.24 405 2992 19.8% 1243 6.8% 47.73 1.32 400 4035 21.3% 1485 7.1% 51.70 1.25 396 2673 22.9% 1338 7.6% 53.71 1.31 391 3413 23.9% 1529 8.3% Table A 10. Results of experiment number 3, replicate 2 Time on Stream, Zn Zn Fe Fe d pH Eh, mV ppm Extraction, % PPm Extraction, % 2.76 1.42 402 5500 2.1% 3860 2.4% 5.67 1.41 401 2656 3.2% 1183 2.4% 9.74 1.27 404 3650 4.9% 1268 2.3% 12.64 1.23 403 3848 6.1% 1351 2.3% 16.61 1.13 401 3504 7.6% 1418 2.4% 19.64 1.10 403 3470 8.5% 1152 2.1% 23.64 1.02 403 3770 9.8% 1775 2.1% 26.64 1.05 386 5579 11.5% 1955 , 2.3% 30.69 1.08 393 3930 13.5% 1641 2.8% 33.68 0.93 399 4827 14.4% 2184 2.7% 37.82 0.89 402 6980 15.6% 2944 2.5% 40.71 1.03 389 7871 17.8% 3403 3.7% 44.73 1.19 387 1891 18.9% 1031 3.6% 47.71 1.20 419 1974 19.7% 1105 3.6% 51.70 1.18 385 2381 21.1% 1222 3.9% 54.69 1.04 386 2883 22.2% 1431 4.2% 58.68 1.13 381 1975 23.3% 1154 4.3% 61.68 1.23 398 2314 24.2% 1224 4.4% 65.70 1.15 407 2307 25.6% 1177 4.6% 68.66 1.16 417 2185 26.5% 1190 4.7% 72.73 1.07 404 1870 27.5% 1086 4.9% 75.62 1.07 398 1486 28.3% 945 4.8% 79.66 1.27 384 1114 29.0% 961 4.8% 82.63 1.17 391 1228 29.7% 993 4.7% 86.65 1.11 404 1116 30.4% 965 4.6% 89.64 1.05 392 1385 31.1% 1023 4.6% 93.67 1.05 385 1206 31.8% 1015 4.6% 96.63 1.02 389 773 32.2% 940 4.5% 100.74 1.05 413 2046 33.5% 1144 4.7% 103.69 1.09 418 1998 34.4% 1289 5.0% 107.81 1.01 422 1767 35.5% 1212 5.4% 110.72 1.05 401 445 35.7% 1201 5.6% 114.73 1.11 416 355 35.9% 1143 5.8% 116.73 1.37 423 371 36.1% 1085 6.4% 191 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A l l . Results of experiment number 3, replicate 3 Time on Stream, Zn Zn Fe Fe d pH Eh, mV Ppm Extraction, % ppm Extraction 2.78 1.36 382 8996 3.8% 7071 5.9% 5.67 1.32 398 2536 4.9% 1344 6.1% 9.73 1.22 402 3043 6.3% 1149 5.9% 12.63 1.20 397 3316 7.4% 1233 5.9% 16.61 1.09 396 2878 8.7% 1067 5.6% 19.64 1.02 402 2935 9.5% 1228 5.4% 23.63 1.00 397 3359 10.8% 1702 5.4% 26.65 1.04 379 1951 11.6% 1261 5.5% 30.70 1.08 384 1887 12.7% 1019 5.4% 33.67 1.15 399 2463 13.7% 1119 5.5% 37.82 1.20 396 2895 15.5% 1271 5.8% 40.70 1.17 404 3002 16.7% 1178 5.9% 44.73 1.24 414 3930 18.5% 1453 6.2% 47.74 1.28 396 3210 19.6% 1250 6.3% 51.69 1.22 408 3231 21.2% 1376 6.7% 54.69 1.05 412 3589 22.5% 1708 7.2% 58.68 1.19 427 2388 23.6% 1303 7.4% 61.68 1.32 433 2943 24.6% 1498 7.8% 65.70 1.19 439 3006 26.1% 1517 8.3% 68.66 1.16 455 2550 27.1% 1358 8.6% 72.73 1.09 446 2240 28.2% 1246 8.6% 75.61 1.15 450 1518 29.0% 956 8.5% 79.66 1.29 443 1307 29.8% 1041 8.6% 82.63 1.22 459 1747 30.8% 1096 8.7% 86.65 1.13 465 1614 31.8% 1032 8.7% 89.65 1.12 461 1921 32.6% 1190 8.8% 93.67 1.13 429 1311 33.4% 1226 9.1% 96.63 1.07 390 614 33.7% 930 9.0% 100.74 0.99 402 463 34.0% 845 8.8% 103.68 1.05 417 596 34.3% 943 8.7% 107.78 1.09 413 1997 35.5% 1159 8.9% 110.75 1.11 408 1809 36.3% 1484 9.4% 114.72 1.18 408 1816 37.4% 1488 10.4% 117.71 1.16 418 1866 38.3% 1491 10.9% 121.73 1.14 404 1889 39.3% 1477 11.5% 124.67 1.22 404 1567 40.1% 1477 12.0% 128.70 1.17 412 1498 41.0% 1463 12.7% 131.70 1.13 403 1562 41.7% 1467 13.2% 135.75 1.12 412 1509 42.2% 1467 12.8% 138.67 1.09 404 1746 43.0% 1470 13.3% 142.76 1.17 409 1785 44.2% 1362 13.9% 145.70 1.17 420 1817 45.0% 1362 14.3% 149.67 1.15 407 758 45.4% 1254 14.6% 152.75 1.17 440 1148 46.0% 1444 15.1% 156.69 1.16 454 2044 47.2% 1444 15.6% 159.73 1.08 471 2120 48.2% 1634 16.3% 163.72 1.25 457 2047 49.5% 1616 17.2% 166.68 1.18 454 1778 50.3% 1616 17.8% 170.75 1.14 455 1626 51.3% 1598 18.7% 173.86 1.15 453 2578 52.5% 1596 19.3% 177.70 1.10 452 1452 53.4% 1596 20.0% 180.68 1.24 456 1273 54.0% 1594 20.7% 184.73 1.10 453 1312 54.8% 1590 21.5% 187.71 1.12 438 1501 55.6% 1590 22.2% 191.74 1.03 446 1323 56.4% 1586 23.0% 194.66 1.05 446 1320 56.8% 1605 23.4% 198.67 1.17 444 1640 57.8% 1605 24.3% 201.69 1.06 447 1463 58.5% 1623 25.0% 205.68 1.06 459 1626 59.5% 1602 25.8% 208.67 1.15 456 1437 60.2% 1602 26.5% 212.69 1.09 468 1282 61.0% 1580 27.4% 215.85 1.09 471 1433 61.7% 1337 27.8% 219.90 1.02 425 286 61.9% 1337 28.3% 222.84 0.99 415 1156 62.4% 1093 28.4% 226.65 1.02 421 426 62.7% 1065 28.5% 229.78 1.03 418 490 62.9% 1065 28.6% 233.67 1.09 572 478 63.2% 1037 28.8% 192 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 12. Results of experiment number 3, replicate 4 Time on Stream, Zn Zn Fe Fe d PH Eh, mV ppm Extraction, % ppm Extraction, % 2.77 1.31 385 7935 3.2% 6063 4.8% 5.64 1.33 402 2563 4.3% 1101 4.7% 9.73 1.25 404 3072 5.7% 1150 4.5% 12.62 1.24 404 3448 6.9% 1285 4.5% 16.60 1.11 402 3078 8.4% 1319 4,7% 19.64 1.09 377 2040 9.2% 918 4.5% 23.61 1.06 387 2100 10.4% 1273 4.8% 26.64 1.09 392 2457 11.5% 1130 4.8% 30.70 1.17 399 2798 13.1% 1100 4.8% 33.67 1.19 400 3186 14.5% 1233 4.9% 37.81 1.18. 398 3351 16.5% 1321 • 5.3% 40.70 1.26' 397 3648 . 18.1% 1307 5.6% 44.72 1.25 400 2411 . 19.5% 1052 5.6%, 47.69 1.32 411 3563 21.0% 1178 5.7%' 51.69 1.23 403 3206 22.9% 1396 6.3% 53.68 1.05 408 3399 24.3% 1587 6.8% 58.68 1.18 439 1876 25.4% 1121 6.9% 61.67 1.27 452 2460 26.6% 1162 7.1% 65.69 1.24 464 2561 28.2% 1301 7.5% 68.65 1.19 475 2325 29.3% '1260 7.8% 72.72 1.12 464 1865 30.5% •. 1158 8.3% 75.61 1.09 467 1501 31.2% 964 8.2% 79.65 1.34 458 1163 31.9% 1008 8.2% 82.63 1.17 469 842 32.4% 842 8.0% 86.65 1.15 476 640 32.8% 916 7.9% 89.64 1.12 470 1730 33.6% 1024 7.9% 93.65 1.15 464 2122 34.8% 1345 8.4% 96.62 1.11 459 1135 35.3% 1018 8.4% 100.74 1.19 498 2754 37.1% 1435 9.0% 103.67 1.24 492 3233 38.4% 1601 9.6% 107.81 1.16 512 3041 39.2% 1685 10.0% 110.71 1.23 482 4741 41.5% 1834 10.9% 114.72 1.23 491 2449 42.8% 1814 11.8% 117.72 1.20 501 3102 44.3% 1794 12.6% 121.73 1.21 502 2430 45.8% 1768 13.8% 124.68 1.29 500 2521 47.0% 1768 14.6% 128.71 1.22 506 2212 48.4% 1742 15.8% 131.67 1.18 507 2376 49.6% 1785 16.6% 135.75 1.13 512 2238 51.0% 1785 17.8% 138.79 1.22 514 2600 52.2% 1827 18.7% 142.76 1.21 518 2445 53.8% 1860 20.1% 145.71 1.21 519 2311 54.9% 1860 21.0% 149.68 1.16 438 713 55.3% 1893 22.2% 152.75 1.02 471 879 55.7% 1774 22.9% 156.69 1.09 484 1608 56.6% 1774 23.7% 159.73 1.08 510 1682 57.4% 1655 24.4% 163.73 1.26 498 2080 ' 58.4% 1666 25.2% 166.68 1.16 503 1572 59.1% 1666 25.9% 170.76 1.16 508 1451 60.0% 1676 26.8% 173.86 1.14 511 1463 60.7% 1638 27.5% 177.70 1.11 509 1357 61.5% 1638 28.4% 180.68 1.17 444 516 61.7% 1599 29.0% 184.73 1.08 358 223 61.9% 1358 29.5% 187.72 1.01 330 229 62.0% 1358 29.9% 191.76 1.03 393 387 62.2% 1117 30.0% 194.66 1.03 426 801 62.5% 1329 30.3% 198.68 1.14 437 895 63.0% 1329 30.8% 201.70 0.99 439 1098 63.5% 1540 31.3% 205.69 0.99 452 1277 64.2% 1326 31.7% 208.67 1.10 357 314 64.4% 1326 32.1% 212.70 1.03 381 321 64.6% 1112 32.2% 215.85 1.02 379 294 64.7% 1269 32.5% 219.90 1.04 428 924 65.2% 1269 32.8% 222.84 1.04 441 425 65.3% 1425 33.1% 226.66 1.02 428 1129 66.0% 1301 33.5% 229.78 1.04 423 1097 66.5% 1301 33.8% 233.68 0.99 396 643 66.9% 1176 34.1% 243.72 1.06 443 1143 68.7% 1386 35.5% 253.77 1.02 448 1003 70.2% 1306 36.6% 263.69 1.09 427 406 70.9% 1226 37.4% 273.78 1.11 430 310 71.3% 1163 38.0% 283.93 1.13 428 308 71.8% 1099 38.3% 293.89 1.07 417 336 72.3% 1131 38.8% 193 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 13. Results of experiment number 4, column 1 Time on Stream, Zn Zn Fe Fe d PH Eh, mV ppm Extraction, % PPm Extraction, % 4.29 1.35 451 2484 0.0% 1223 0.0% 7.07 1.41 407 1854 0.0% 1105 0.0% 11.16 1.18 409 1827 0.0% 996 0.0% 14.16 1.36 418 2291 0.0% 1042 0.0% 18.27 1.60 461 4798 0.0% 1207 0.0% 21.20 1.29 428 2339 . 0.1% 939 0.1% 25.24 1.84 448 5076 0.1% 1261 0.1% 28.35 1.49 434 3070 0.1% 1027 0.1% 32.21 2.34 463 6845 0.1% 754 0.1% 35.13 1.47 488 2263 0.1% 905 0.1% 39.26 2.30 468 8325 0.2% 920 0.1% 42.11 1.61 495 3566 0.2% 1155 0.1% 46.26 1.49 . 479 3362 0.2% 1529 0.1% 49.25 1.40 497 2932 0.2% 1301 0.1% 53.25 1.54 484 5085 0.2% 1773 0.2% 56.23 1.41 474 3120 0.2% 1278 0.2% 60.30 2.08 439 6225 0.3% 1353 0.2% 63.07 1.52 470 2595 0.3% 1097 0.2% 67.04 2.20 448 6132 0.3% 1498 0.2% 70.22 1.42 479 2598 0.3% 1542 0.2% 74.25 1.41 488 8065 0.3% 1429 0.2% 77.06 1.40 472 1727 0.3% 1429 0.2% 81.18 1.31 481 2057 0.3% 1429 0.3% 84.12 1.25 493 1071 0.3% 1316 0.3% 88.26 1.26 502 1244 0.4% 1339 0.3% 91.17 1.32 493 1513 0.4% 1339 0.3% 95.17 1.38 502 1651 0.4% 1339 0.3% 98.18 1.21 505 1126 0.4% 1361 0.3% 102.18 1.32 505 1382 0.4% 1412 0.3% 105.13 1.33 505 1591 0.4% 1412 0.3% 109.14 1.29 512 1619 0.4% 1412 0.4% 112.08 1.23 510 2013 0.4% 1462 0.4% 116.17 1.08 540 2335 0.4% 1384 0.4% 119.23 1.17 521 1572 0.4% 1384 0.4% 123.17 1.22 526 1466 0.4% 1384 0.4% 126.17 1.26 528 2627 0.4% 1305 0.4% 130.13 1.21 537 1354 0.4% 1293 0.4% 133.19 1.16 535 1408 0.4% 1293 0.4% 137.18 1.21 547 1342 0.4% 1293 0.5% 140.16 1.12 540 1389 0.4% 1281 0.5% 144.21 1.43 552 1368 0.5% 1251 0.5% 147.18 1.25 542 1436 0.5% 1251 0.5% 151.23 1.19 542 1409 0.5% 1251 0.5% 154.30 1.17 551 992 0.5% 1221 0.5% 158.20 1.23 568 2355 0.5% 1233 0.5% 161.13 1.31 565 587 0.5% 1233 0.5% 165.17 1.38 531 3815 0.5% 1233 0.5% 168.15 1.10 560 1082 0.5% 1244 0.6% 172.19 1.13 590 1394 0.5% 1246 0.6% 175.09 1.05 563 1479 0.5% 1246 0.6% 179.12 1.18 568 1194 0.5% 1246 0.6% 182.17 1.08 600 1233 0.5% 1248 0.6% 186.14 1.04 585 884 0.5% 1757 0.6% 189.13 1.17 595 872 0.5% 1757 0.6% 193.20 1.15 602 892 0.5% 1757 0.7% 196.28 1.16 574 1040 0.5% 2266 0.7% 200.32 1.10 592 952 0.5% 1739 0.7% 203.26 1.07 633 890 0.5% 1739 0.7% 207.10 1.09 600 842 0.5% 1739 0.7% 210.27 1.07 603 868 0.5% 1211 0.7% 214.11 1.04 635 738 0.6% 1191 0.7% 224.25 1.08 690 804 0.6% 1171 0.8% 234.18 1.02 678 808 0.6% 1198 0.8% 244.51 1.21 628 564 0.6% 1225 0.8% 254.19 1.17 630 568 0.6% 2274 0.8% 264.33 1.36 553 4176 0.6% 3322 0.8% 274.30 1.05 591 434 0.6% 2457 0.8% 284.31 1.10 562 786 0.6% 1592 0.8% 294.09 1.02 588 1038 0.6% 1440 0.8% 304.25 1.05 780 532 0.6% 1287 0.8% 320.19 1416 2.7% 1842 1.9% 194 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 14. Results of experiment number 4, column 2 Time on Stream, Zn Zn Fe Fe d pH Eh, mV ppm Extraction, % Ppm Extraction, % 4.29 1.49 447 3035 0.0% 1455 0.0% 7.11 1.43 403 3602 0.0% 1237 0.0% 11.16 1.38 399 3869 0.0% 1223 0.0% 14.16 1.53 406 4653 0.1% 1244 0.0% 18.26 1.64 421 4559 0.1% 1297 0.1% 21.21 1.71 420 4791 0.1% 1171 0.1% 25.25 1.81 429 5333 0.1% 1245 0.1% 28.35 1.95 401 3061 0.1% 1022 0.1% 32.21 1.58 429 3886 0.1% 890 0.1% 35.13 1.84 455 4133 0.2% 1125 0.1% 39.31 2.55 462 9300 0.2% 585 0.1% 42.11 2.61 440 7280 0.2% 741 0.1% 46.26 2.40 432 7657 0.3% 1263 0.1% 49.27 1.81 456 5079 0.3% 1486 0.2% 53.24 2.17 464 11040 0.3% 1196 0.2% 56.23 2.03 440 6435 0.4% 1344 0.2% 60.30 2.55 432 8775 0.4% 590 0.2% 63.07 1.92 446 5145 0.4% 1375 0.2% 67.28 2.23 446 6910 0.4% 1191 0.2% 70.21 1.77 454 5189 0.4% 1871 0.2% 74.25 1.74 487 8306 0.5% 1847 0.2% 77.06 1.78 452 4439 0.5% 1847 0.3% 81.18 1.55 465 4210 0.5% 1847 0.3% 84.12 1.58 474 3449 0.5% 1822 0.3% 88.25 1.53 484 4004 0.5% 1849 0.3% 91.18 1.57 475 4018 0.6% 1849 0.3% 95.18 1.69 475 4350 0.6% 1849 0.3% 98.18 1.40 489 3340 0.6% 1875 0.4% 102.18 1.53 487 3706 0.6% 1792 0.4% 105.13 1.55 489 3778 0.6% 1792 0.4% 109.15 1.46 496 3673 0.6% 1792 0.4% 112.08 1.34 499 3189 0.6% 1709 0.4% 116.17 1.29 493 3827 0.7% 1709 0.4% 119.24 1.36 505 3687 0.7% 1709 0.4% 123.18 1.34 516 3174 0.7% 1709 0.5% 126.17 1.36 518 3076 0.7% 1709 0.5% 130.13 1.34 530 2852 0.7% 1754 0.5% 133.20 1.27 537 2975 0.7% 1754 0.5% 137.18 1.33 571 2817 0.7% 1754 0.5% 140.16 1.19 562 2913 0.7% 1798 0.5% 144.21 1.53 579 2884 0.7% 1759 0.6% 147.18 1.36 565 2827 0.8% 1759 0.6% 151.23 1.27 557 2719 0.8% 1759 0.6% 154.30 1.27 565 2032 0.8% 1719 0.6% 158.23 1.35 592 3632 0.8% 1778 0.6% ' 161.14 1.36 568 1558 0.8% 1778 0.6% 165.16 1.30 652 1578 0.8% 1778 0.7% 168.16 1.22 541 2441 . 0.8% 1836 0.7% 172.20 1.22 . 570 2269 ' 0.8% 1791 0:7% 175.09 1.21 562 ' 2523 0.8% 1791 0.7% 179.12 1.25 565 2301 0.8% 1791 0.7% 182.17 1.16 565 2451 0.9% 1746 0.7% 186.14 1.12 577 1896 0.9% 1517 0.8% 189.13 1.25 583 1806 0.9% 1517 0.8% 193.20 1.23 600 1971 0.9% 1517 0.8% 196.28 1.21 577 2253 0.9% 1288 0.8% 200.32 1.21 595 1908 0.9% 1488 0.8% 203.27 1.15 596 1935 0.9% 1488 0.8% 207.11 1.16 591 1827 0.9% 1488 0.8% 210.27 1.14 612 1923 0.9% 1688 0.8% 214.14 1.11 609 1551 0.9% 1644 0.9% 224.26 1.16 685 1824 0.9% 1599 0.9% 234.18 1.11 609 3714 0.9% 2338 0.9% 244.51 1.32 716 4713 1.0% 3076 0.9% 254.19 1.22 652 1584 1.0% 3199 1.0% 264.33 1.26 559 1341 1.0% 3322 1.0% 274.30 1.06 579 1071 1.0% 2425 1.0% 284.31 1.23 577 1218 1.0% 1528 1.0% 294.10 1.10 596 972 1.0% 1555 1.0% 304.25 1.08 580 1047 1.0% 1581 1.0% 320.19 2040 2.3% 2188 2.3% 195 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 15. Results of experiment number 4, column 3 Time on Stream, Zn Zn Fe Fe d pH Eh, mV ppm Extraction, % ppm Extraction, % 4.29 1.65 434 4163 0.0% 1574 0.0% 7.09 1.64 400 5337 0.0% 1479 0.0% 11.17 1.70 385 5825 0.1% 1358 0.0% 14.17 1.92 393 6699 0.1% 1443 0.1% 18.27 2.05 404 6530 0.1% 1446 0.1% 21.21 2.44 396 6519 0.1% 847 0.1% 25.25 2.31 412 6490 0.2% 1106 0.1% 28.35 3.01 370 5731 0.2% 422 0.1% 32.21 2.38 415 6684 0.2% 923 0.1% 35.13 2.29 445 6050 0.2% 1069 0.1% 39.35 2.63 452 11100 0.3% 142 0.1% 42.11 2.65 474 10780 0.3% 318 0.1% 46.26 2.43 452 7657 0.4% 952 0.1% 49.27 2.19 472 5079 0.4% 1249 0.1% 53.25 2.17 476 21240 0.5% 814 0.1% 56.24 2.32 . 537 10035 0.5% 692 0.1% 60.11 2.53 479 8370 0.5% 1034 0.2% 63.07 2.30 490 7665 0.6% 1083 0.2% 67.28 2.36 661 10410 0.6% 893 0.2% 70.20 2.09 529 7380 0.6% 1686 0.2% 74.28 2.04 520 15540 0.7% 1805 0.2% 77.06 2.03 517 7155 0.7% 1805 0.2% 81.19 1.81 540 6851 0.7% 1805 0.2% 84.12 1.88 526 5942 0.8% 1924 0.3% 88.26 1.75 527 5841 0.8% 2089 0.3% - 91.18 ' 1.74 573 6310 0.8% 2089 0.3% 95.18 1.86 699 7610 0.9% ' 2089 0.3% 98.18 1.58 595 5816 0.9% 2254 0.3% 102.19 1.69 650 6149 0.9% 2228 0.4% 105.13 1.70 597 6378 0.9% 2228 0.4% 109.15 1.63 705 7260 1.0% 2228 0.4% 112.09 1.50 537 5705 1.0% 2201 0.4% 116.17 1.38 • 577 5914 1.0% 2168 0.4% 119.24 1.46 600 5746 1.0% 2168 0.5% 123.18 1.43 617 5450 1.0% 2168 0.5% 126.17 1.46 649 4644 1.1% 2134 0.5% 130.17 1.38 707 4737 1.1% 2176 0.5% 133.20 1.37 700 5175 1.1% 2176 0.5% 137.18 1.40 701 5206 1.1% 2176 0.6% 140.16 1.29 688 5037 1.1% 2218 0.6% 144.21 1.62 695 5292 1.2% 2130 0.6% 147.19 1.42 693 4953 1.2% 2130 0.6% 151.23 1.34 628 4681 1.2% 2130 0.6% 154.30 1.32 678 3630 1.2% 2042 0.7% 158.24 1.41 720 6061 1.2% 2123 0.7% 161.13 1.46 686 3392 1.3% 2123 0.7% 165.17 1.34 663 3799 1.3% 2123 0.7% 168.16 1.28 663 4578 1.3% 2204 0.7% 172.21 1.26 661 3581 1.3% 2251 0.8% 175.09 1.24 659 4521 1.3% 2251 0.8% 179.13 1.32 673 4318 1.3% 2251 0.8% 182.17 1.22 655 4699 1.4% 2297 0.8% 186.15 1.20 643 3354 1.4% 2043 0.8% 189.13 1.28 659 3042 • 1.4% 2043 0.9% 193.20 1.30 656 3204 1.4% 2043 0.9% 196.29 1.26 646 3660 1.4% 1789 0.9% 200.32 1.24 661 3414 1.4% 1933 0.9% 203.27 1.22 684 3570 1.4% 1933 0.9% 207.11 1.23 649 3264 1.5% 1933 1.0% 210.27 1.23 661 3222 1.5% 2076 1.0% 214.14 1.18 676 2748 1.5% 2058 1.0% 224.26 1.22 692 3210 1.5% 2040 1.0% 234.19 1.17 688 2550 1.5% 3008 1.0% 244.50 1.43 700 8160 1.5% 3975 1.1% 254.19 1.23 645 3150 1.5% 3060 1.1% 264.34 1.26 560 2442 1.5% 2145 1.1% 274.30 1.17 586 3210 1.6% 2267 1.1% 284.31 1.22 567 2772 1.6% 2389 1.2% 294.10 1.13 584 1800 1.6% 2130 1.2% 304.25 1.10 585 1566 1.6% 1870 1.2% 320.19 1872 3.3% 2044 3.2% 196 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 16. Results of experiment number 4, column 4 Time on Stream, Zn Zn Fe Fe d PH Eh, mV ppm Extraction, % ppm Extraction, % 4.25 1.76 338 11790 1.6% 7568 2.0% 7,09 1.82 390 5469 2.2% 1689 2.1% 11.18 1.90 382 6979 3.2% 1524 2.3% 14.17 2.28 387 7013 3.9% 1469 2.4% 18.25 2.55 382 7651 5.0% 1466 2.5% 21.20 3.02 373 7860 5.8% 980 2.4% 25.22 2.98 389 7772 7.0% 861 2.4% 28.35 3.03 408 7331 7.8% 360 ' 2.2% 32.22 2.41 429 7002 9.1% 770 ' 2.1% 35.13 2.59 448 6985 10.1% 579 2.0% 39.11 2.70 462 8053 11.4% 401 1.7% 42.36 2.34 534 15400 11.8% 387 1.4% 46.23 2.61 459 13800 12.9% 514 1.3% 49.25 2.45 511 10670 14.2% 710 1.2% 53.23 2.50 597 14205 14.7% 547 1.2% 56.22 2.51 537 15660 16.3% 749 1.1% 60.08 2.66 552 11460 17.9% 910 1.0% 63.05 2.56 613 10350 19.1% 682 0.9% 67.04 2.53 657 9561 20.5% 974 0.9% 70.21 2.20 667 10070 21.6% 1244 0.9% 74.28 2.30 655 11590 22.2% 1635 0.9% 77.05 2.15 613 12380 23.5% 1635 1.1% 81.16 2.03 667 9651 24.9% 1635 1.3% 84.13 2.00 663 7827 25.6% 2026 1.5% 88.26 1.96 647 9652 26.7% 1811 1.6% 91.18 1.91 658 9002 27.7% 1811 1.8% 95.18 1.96 699 6949 29.2% 1811 2.2% 98.18 1.79 684 9862 30.3% 1595 2.3% 102.19 1.85 657 8486 31.5% 2026 2.6% 105.14 1.86 651 10060 32.5% 2026 2.8% 109.15 1.83 663 11050 33.6% 2026 3.0% 112.09 1.70 666 10800 34.3% 2457 3.2% 116.17 1.52 651 8672 35.6% 2459 3.7% 119.24 1.64 661 8715 36.6% 2459 4.1% 123.18 1.56 648 7836 37.7% 2459 4.6% 126.17 1.60 590 7558 38.6% 2460 4.9% 130.14 1.50 464 6586 39.7% 2571 5.5% 133.20 1.50 544 6956 40.4% 2571 5.9% 137.18 1.47 677 6940 41.5% 2571 6.5% 140.17 1.32 703 7318 42.3% 2682 6.9% 144.22 1.68 699 7111 43.4% 2622 7.4% 147.18 1.52 704 7647 44.1% 2622 7.7% 151.24 1.39 694 6964 45.2% 2622 8.3% 154.30 1.45 698 5890 46.0% 2562 8.8% 158.24 1.42 695 5737 46.8% 2811 9.3% 161.13 1.57 703 6659 47.4% 2811 9.6% 165.17 1.33 673 3752 48.1% 2811 10.5% 168.16 1.41 658 7848 48.9% 3060 10.8% 172.21 1.34 638 5678 49.6% 2865 11.4% 175.09 1.30 658 6226 50.3% 2865 11.9% 179.13 1.40 639 6259 51.1% 2865 12.5% 182.17 1.31 651 5982 51.6% 2669 12.7% 186.15 1.32 646 7500 52.8% 2782 13.4% 189.14 1.36 640 4572 53.4% 2782 13.9% 193.20 1.33 664 4734 54.1% 2782 14.6% 196.29 1.34 640 5430 54.7% 2894 15.0% 200.32 1.30 673 5028 55.4% 2776 15.6% 203.26 1.31 679 5088 56.0% 2776 16.0% 207.11 1.27 673 4566 56.6% 2776 16.6% 210.27 1.28 668 4482 57.2% 2657 17.1% 214.14 1.24 678 4278 57.8% 2502 17.5% 224.25 1.22 685 3528 59.1% 2347 18.7% 234.19 1.26 702 5256 60.1% 3029 19.5% 244.50 1.33 693 5448 61.1% 3711 20.1% 254.19 1.21 634 2424 62.0% 3066 22.0% 264.25 1.25 523 2754 62.8% 2420 22.7% 274.30 1.23 592 4560 63.8% 2179 22.9% 284.32 1.22 571 1674 64.3% 1937 23.8% 294.10 1.14 586 2352 65.2% 2195 24.7% 304.25 1.13 587 2748 65.9% 2453 25.4% 320.19 3612 67.5% 3045 26.8% 197 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 17. Results of experiment number 5, column 1 Time on Stream, Zn Zn Fe Fe d PH Eh, mV ppm Extraction, % ppm Extraction, % 4.28 1.63 396 4155 0.0% 1313 0.0% 7.07 1.57 394 4370 0.0% 1175 0.0% 11.15 1.30 394 4520 0.1% 1115 0.0% 14.13 1.80 390 5347 0.1% 1159 0.0% 18.25 1.65 391 4265 0.1% 1138 0.1% 21.20 1.53 398 4321 0.1% 1124 0.1% 25.22 1.52 400 4281 0.1% 1134 0.1% 28.35 1.41 402 6713 0.2% 1374 0.1% 32.15 2.07 430 12700 0.2% 674 0.1% 35.11 1.34 399 2060 0.2% 963 0.1% 39.25 2.35 374 10010 0.3% 931 0.1% 42.13 2.36 370 9802 0.3% 1025 0.1% 46.22 1.74 396 2197 0.3% 1002 0.1% 49.26 1.28 410 1833 0.3% 920 0.1% 53.23 1.25 408 2975 0.3% 1158 0.2% 56.20 1.81 398 1652 0.3% 923 0.2% 60.29 1.61 369 4749 0.3% 1418 0.2% 63.06 1.26 404 1260 0.3% 905 0.2% 67.03 1.38 405 3770 0.4% 1325 0.2% 70.21 1.28 398 1487 0.4% 1397 0.2% 74.28 1.23 403 895 0.4% 1287 0.2% 77.05 1.21 395 1283 0.4% 1287 0.2% 81.16 1.19 398 2994 0.4% 1287 0.2% 84.11 1.06 403 1053 0.4% 1177 0.2% 88.24 1.03 407 1074 0.4% 1213 0.3% 91.21 1.33 409 9809 0.4% 1213 0.3% 95.16 1.35 407 912 0.4% 1213 0.3% 98.17 1.09 402 1091 0.4% 1249 0.3% 102.16 1.17 406 929 0.4% 1227 0.3% 105.11 1.22 401 978 0.4% 1227 0.3% 109.13 1.20 404 878 0.5% 1227 0.3% 112.13 1.24 401 748 0.5% 1205 0.3% 116.16 1.04 408 836 0.5% 1133 0.3% 119.22 1.07 410 783 0.5% 1133 0.4% 123.17 1.13 408 764 0.5% 1133 0.4% 126.15 1.12 409 699 0.5% 1133 0.4% 130.11 1.08 399 418 0.5% 1133 0.4% 133.19 1.05 405 357 0.5% 1061 0.4% 137.13 1.08 419 651 0.5% 1133 0.4% 140.15 0.96 419 749 0.5% 1133 0.4% 144.18 1.23 428 759 0.5% 1133 0.4% 147.17 1.10 410 789 0.5% 1204 0.4% 151.19 1.04 415 740 0.5% 1383 0.5% 154.28 1.07 407 732 0.5% 1383 0.5% 158.13 1.10 398 4613 0.5% 1383 0.5% 161.11 1.27 403 1605 0.5% 1562 0.5% 165.15 1.16 406 444 0.5% 1390 0.5% 168.14 1.02 386 606 0.5% 1390 0.5% 172.19 1.09 391 779 0.5% 1390 0.5% 175.07 1.05 406 614 0.5% 1217 0.5% 179.10 1.07 395 594 0.5% 1213 0.6% 182.15 0.93 402 686 0.5% 1213 0.6% 186.15 1.02 397 714 0.5% 1213 0.6% 189.09 1.09 397 774 0.5% 1209 0.6% 193.19 1.09 419 772 0.5% 1200 0.6% 196.27 1.03 406 686 0.5% 1200 0.6% 200.31 1.07 434 716 0.5% 1200 0.6% 203.25 1.04 410 712 0.5% 1191 0.6% 207.09 1.04 423 602 0.5% 1250 0.6% 210.24 1.06 422 582 0.5% 1250 0.7% 214.10 1.02 418 584 0.5% 1250 0.7% 224.23 1.05 440 1514 0.6% 1308 0.7% 234.17 1.07 431 548 0.6% 1235 0.7% 244.48 1.13 455 456 0.6% 1161 0.7% 254.18 1.14 458 460 0.6% 1440 0.7% 264.33 1.17 401 1958 0.6% 1719 0.7% 274.29 1.12 439 388 0.6% 1307 0.7% 284.29 1.04 361 360 0.6% 894 0.7% 294.08 1.03 418 680 0.6% 1087 0.8% 304.23 1.03 418 646 0.6% 1280 0.8% 308.10 860 0.9% 1378 1.1% 198 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 18. Results of experiment number 5, column 2 on Stream, Zn Zn Fe Fe d pH Eh, mV ppm Extraction, % PPm Extraction, % 4.28 1.87 392 4654 0.0% 1643 0.0% 7.13 3.02 377 7464 0.1% 736 0.0% 11.18 2.83 351 7450 0.1% 612 0.0% 14.14 3.05 360 7371 0.1% 441 0.0% 18.25 2.88 359 7611 0.1% 316 0.0% 21.23 2.62 359 7414 0.2% 456 0.0% 25.26 2.37 369 8495 0.2% 953 0.0% 28.35 2.04 382 2273 0.2% 990 0.1% 32.15 2.10 399 7563 0.2% 1309 0.1% 35.11 1.94 394 4686 0.3% 1450 0.1% 39.27 2.65 410 11350 0.3% 212 0.1% 42.11 2.09 388 8220 0.3% 809 0.1% 46.22 1.94 383 4907 0.4% 1437 0.1% 49.27 1.50 394 3495 0.4% 1301 0.1% 53.22 1.51 386 3918 0.4% 1321 0.1% 56.20 1.48 389 3892 0.4% 1306 0.1% 60.29 2.03 372 7743 0.4% 1427 0.2% 63.06 1.49 402 3255 0.4% 1325 0.2% 67.23 1.58 420 5051 0.5% 1615 0.2% 70.20 1.48 400 4307 0.5% 1849 0.2% 74.27 1.39 396 3476 0.5% 1863 0.2% 77.05 1.55 398 3219 0.5% 1863 0.2% 81.22 1.50 407 5935 0.5% 1863 0.3% 84.11 1.25 407 3229 0.5% 1877 0.3% 88.25 1.18 413 2605 0.5% 1983 0.3% 91.25 1.09 433 9216 0.6% 1983 0.3% 95.16 1.38 415 2194 0.6% 1983 0.3% 98.17 1.12 418 3360 0.6% 2088 0.3% 102.16 1.33 413 2025 0.6% 1938 0.4% 105.11 1.23 412 2184 0.6% 1938 0.4% 109.13 1.21 416 2132 0.6% 1938 0.4% 112.08 1.17 412 2168 0.6% 1787 0.4% 116.16 1.07 413 1897 0.6% 1572 0.4% 119.22 1.13 417 1865 0.7% 1572 0.4% 123.16 1.16 415 1803 0.7% 1572 0.5% 126.16 1.17 406 1624 0.7% 1572 0.5% 130.11 1.10 380 563 0.7% 1572 0.5% 133.19 1.07 417 998 0.7% 1356 0.5% 137.14 1.14 420 1318 0.7% 1378 0.5% 140.15 0.97 421 1419 0.7% 1378 0.5% 144.18 1.24 425 1365 0.7% 1378 0.5% 147.17 1.12 419 1411 0.7% 1399 0.6% 151.21 1.07 428 1355 0.7% 1432 0.6% 154.28 1.13 415 1042 0.7% 1432 0.6% 158.17 1.18 428 1245 0.7% 1432 0.6% 161.11 1.29 413 1214 0.7% 1465 , 0.6% 165.15 . 1.10 417 1117 0.7% 1521 0.6% 168.15 1.05 396 1161 0.7% 1521 0.6% 172.19 1.07 432 1429 0.7% 1521 0.6% 175.08 0.99 411 1491 0.7% 1576 0.7% 179.11 1.06 400 1250 0.7% 1497 0.7% 182.16 0.95 405 1314 0.7% 1497 0.7% 186.12 1.01 412 1388 0.7% 1497 0.7% 189.12 1.11 410 1412 0.8% 1418 0.7% 193.19 • 1.10 420 1396 0.8% 1420 0.7% 196.27 1.06 417 1384 0.8% 1420 0.7% 200.31 1.07 433 1032 0.8% 1420 0.8% 203.25 1.04 421 1236 0.8% 1422 0.8% 207.09 1.05 426 1148 0.8% 1527 0.8% 210.24 1.03 419 1060 0.8% 1527 0.8% 214.10 1.04 426 1070 0.8% 1527 0.8% 224.24 1.04 447 1896 0.8% 1632 0.8% 234.17 1.05 430 1050 0.8% 1553 0.8% 244.51 1.19 450 1026 0.8% 1473 0.9% 254.18 1.13 451 916 0.8% 2489 0.9% 264.33 1.15 420 6330 0.8% 3504 0.9% 274.30 1.12 445 698 0.8% 2459 0.9% 284.31 1.13 426 1646 0.8% 1414 0.9% 294.09 1.11 461 646 0.8% 2299 0.9% 304.24 1.22 416 6078 0.9% 3183 1.0% 308.10 3504 1.2% 2543 1.3% 199 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 19. Results of experiment number 5, column 3 Time on Stream, Zn Zn Fe Fe d pH Eh, mV ppm Extraction, % ppm Extraction, % 4.28 3.21 312 5983 0.0% 2186 0.0% 7.09 3.34 330 8391 0.1% 797 0.0% 11.18 3.58 300 8600 0.1% 233 0.0% 14.14 3.35 322 8215 0.1% 152 0.0% 18.25 3.18 334 8403 0.2% 86 0.0% 21.23 2.92 345 8350 0.2% 124 0.0% 25.22 3.04 338 10480 0.2% 206 0.0% 28.35 3.06 368 12120 0.3% 121 0.0% 32.15 2.24 397 7154 0.3% 1723 0.1% 35.11 2.61 371 6760 0.4% 691 0.1% 39.34 3.04 403 14090 0.4% 33 0.1% 42.36 2.91 403 13820 0.5% 107 0.1% 46.21 2.72 381 7329 0.5% 736 0.1% 49.26 2.00 386 6373 0.5% 1356 0.1% 53.23 1.91 378 5732 0.5% 1577 0.1% 56.23 1.96 386 6728 0.6% 1576 0.1% 60.11 2.02 376 6433 0.6% 1731 0.1% 63.07 1.75 391 5580 0.6% 1848 0.1% 67.15 1.76 391 5967 0.6% . 1781 0.2% 70.20 1.76 395 8219 0.7% 2222 0.2% 74.28 1.68 396 5567 0.7% 2189 0.2% 77.05 1.50 389 5688 0.7% 2189 0.2% 81.22 1.70 395 9079 0.7% 2189 0.2% 84.11 1.45 403 5493 0.8% 2155 0.3% 88.25 1.45 415 4918 0.8% 2256 0.3% 91.22 1.53 429 6752 0.8% 2256 0.3% 95.17 1.47 405 5889 0.8% 2256 0.3% 98.17 1.34 405 6434 0.9% 2356 0.3% 102.17 1.42 405 4003 0.9% 2450 0.4% 105.12 1.38 402 4250 0.9% 2450 0.4% 109.14 1.35 403 3748 0.9% 2450 0.4% 112.08 1.68 396 9970 0.9% 2544 0.4% 116.16 1.65 414 17240 1.0% 2611 0.5% 119.22 1.85 444 20590 1.1% 2611 0.5% 123.17 1.83 462 22560 1.2% 2611 0.5% 126.16 1.92 474 22050 1.3% .2611 0.5% 130.11 1.94 500 22800 1.3% 2611 0.6% 133.19 1.96 622 24260 1.4% 2678 0.6% 137.26 2.07 603 24840 1.5% 2711 0.6% 140.44 1.87 426 28210 1.6% 2711 0.6% 144.18 1.60 410 28340 1.8% 2711 0.6% 147.17 1.40 417 17440 1.8% 2743 0.7% 151.21 1.18 429 7297 1.9% 2459 0.7% 154.29 1.23 433 2527 1.9% 2459 0.7% 158.17 1.20 438 2766 1.9% 2459 0.7% 161.12 1.35 435 2008 1.9% 2175 0.8% 165.15 1.26 439 2372 1.9% 2424 0.8% 168.15 1.12 418 2444 1.9% 2424 0.8% 172.18 1.14 427 2421 1.9% 2424 0.8% 175.08 1.08 424 3212 1.9% 2673 0.9% 179.11 1.14 418 2746 1.9% 2361 0.9% 182.16 1.03 415 2167 1.9% 2361 0.9% 186.14 1.08 424 2838 2.0% 2361 0.9% 189.13 1.16 420 2703 2.0% 2049 0.9% 193.20 1.13 428 2391 2.0% 1994 1.0% 196.28 1.09 421 2193 2.0% 1994 1.0% 200.31 1.11 439 2244 2.0% 1994 1.0% 203.26 1.06 426 2115 2.0% 1938 1.0% 207.09 1.09 427 1920 2.0% 2450 1.0% 210.26 1.06 427 1845 2.0% 2450 1.1% 214.10 1.05 427 1872 2.0% 2450 1.1% 224.24 1.00 437 3192 2.0% 2962 1.1% 234.26 1.07 434 1650 2.0% 2357 1.1% 244.51 1.15 458 1656 2.0% 1752 1.1% 254.18 1.13 455 1380 2.1% 2285 1.2% 264.33 1.21 424 3600 2 1% 2817 1.2% 274.30 1.10 454 1248 2.1% 3241 1.2% 284.31 1.29 426 8010 2.1% 3664 1.2% 294.09 1.05 472 1104 2.1% 3788 1.3% 304.24 1.30 432 9828 2.1% 3911 1.3% 308.10 5586 2.6% 2919 1.6% 200 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 20. Results of experiment number 5, column 4 Time on Stream, Zn Zn Fe Fe d pH Eh, mV ppm Extraction, % ppm Extraction, % 4.28 3.63 238 14800 1.6% 9997 2.2% 7.07 3.59 322 8844 2.5% 1441 2.3% 11.19 3.49 347 9855 3.7% 305 2.0% 14.14 3.33 357 9143 4.5% 134 1.8% 18.25 3.10 382 9478 5.7% 47 1.5% 21.20 2.94 393 9273 6.5% 36 1.3% 25.22 2.91 388 13540 7.8% 254 1.0% 28.34 2.93 388 11860 8.8% 111 0.8% 32.15 2.82 365 10790 9.5% 326 0.5% 35.11 2.94 369 11350 11.4% 258 0.3% 39.10 3.00 360 8438 12.7% 159 0.0% 42.36 3.09 433 10400 13.6% 72 -0.2% 46.20 3.13 376 10752 14.9% 122 •0.5% 49.25 2.77 384 8692 15.9% 440 -0.7% 53.22 2.67 363 8937 17.2% 764 -0.8% 56.19 2.22 388 7963 18.2% 1037 -0.8% 60.08 2.51 373 8314 19.4% 1461 -0.6% 63.05 2.24 403 8595 20.4% 1574 -0.5% 67.03 2.08 388 7868 21.6% 1802 -0.2% 70.20 2.02 386 9907 22.3% 1886 -0.1% 74.10 1.88 393 8850 23.5% 2064 0.3% 77.04 • 1.73 392 8378 24.4% 2064 0.5% 81.22 1.77 402 9177 25.4% 2064 0.7% 84.11 1.77 412 9871 26.3% 2241 1.0% 88.25 1.67 422 10010 27.5% 2264 1.3% 91.22 1.71 425 8289 28.0% 2264 1.5% 95.17 1.75 415 8475 29.2% 2264 2.0% 98.17 1.62 429 10840 29.9% 2287 2.1% 102.17 1.65 424 7268 31.0% 2348 2.6% 105.12 1.60 425 7353 31.7% 2348 2.9% 109.14 1.56 427 7099 32.7% 2348 3.3% 112.08 1.42 429 5211 33.3% 2409 3.7% 116.16 1.28 430 4746 34.0% 2344 4.2% 119.23 1.34 431 4548 34.6% 2344 4.5% 123.17 1.36 415 3814 35.1% 2344 5.0% 126.16 1.30 400 3039 35.5% 2344 5.4% 130.12 1.24 389 1883 35.9% 2344 5.9% 133.19 1.17 407 2246 36.2% 2278 6.3% 137.15 1.20 438 3262 36.7% 2331 6.8% 140.16 1.02 443 4001 37.2% 2331 7.1% 144.20 1.70 438 8583 38.5% 2331 7.6% 147.17 1.51 436 7301 39.3% 2383 7.9% 151.22 1.33 436 6272 40.2% 2522 8.4% 154.28 1.38 436 5650 41.0% 2522 8.9% 158.17 1.33 436 4643 41.6% 2522 9.4% 161.12 1.48 438 6467 42.3% 2661 9.7% 165.16 1.30 423 2914 42.7% 2746 10.4% 168.15 1.29 418 6579 43.5% 2746 10.9% 172.17 1.22 429 5169 44.0% 2746 11.1% 175.08 1.23 432 7546 44.7% 2831 11.5% 179.11 1.33 428 6255 45.3% 2636 11.9% 182.16 1.17 431 4883' 45.8% 2636 12.3% 186.14 1.17 424 4656 46.5% 2636 13.0% 189.13 1.20 429 3906 47.0% 2441 13.3% 193.20 1.21 437 3762 47.6% 2485 13.9% 196.28 1.21 438 4338 48.0% 2485 14.2% 200.31 1.17 447 3606 48.6% 2485 14.8% 203.26 1.19 446 4158 49.0% 2529 15.1% 207.10 1.14 438 3198 49.5% 2449 15.6% 210.24 1.15 448 3432 49.9% 2449 16.0% 214.11 1.13 450 3342 50.4% 2449 16.5% 224.13 1.16 459 3384 51.4% 2368 17.5% 234.18 1.15 470 3330 52.7% 2365 18.7% 244.48 1.22 473 3216 53.8% 2362 19.8% 254.18 1.17 472 2616 54.8% 2330 20.9% 264.33 1.30 471 3948 55.9% 2298 21.7% 274.29 1.16 488 2280 56.8% 2353 22.9% 284.31 1.21 491 3390 57.8% 2408 23.8% 294.09 1.18 505 2142 58.6% 2860 25.6% 304.25 1.21 505 5190 58.7% 3312 25.1% 308.10 10014 59.5% 4104 25.8% 201 Appendix A : Bacterially Assisted, Short-Column Leaching Experimental Data Table A 21. Results of experiment number 6, replicate 1 e on Stream, Zn Zn Fe Fe d pH Eh, mV ppm Extraction, % PPm Extraction, % 5.06 1.62 364 6507 3.9% 3364 3.3% 8.24 2.03 363 6564 7.6% 1590 4.1% 12.00 1.86 379 6164 10.6% 1882 5.2% 15.00 1.75 378 6033 14.4% 1669 6.4% 19.06 1.60 388 5067 17.6% 1711 7.5% 22.01 1.50 397 4728 19.8% 1995 8.6% 26.06 1.50 401 4139 22.5% 1932 10.0% 29.11 1.47 414 3690 24.3% 1919 11.1% 33.23 1.39 430 3294 26.3% 1718 12.1% 36.06 1.34 431 3048 27.7% 1844 13.0% 40.09 1.29 440 2880 29.5% 1882 14.3% 43.06 1.30 436 2778 30.8% 1795 15.1% • 47.05 1.32 436 2070 32.1% 1743 16.2% 50.19 1.32 436 2550 33.4% . 1763 17.0% 54.02 . 1.27 435 2124 34.7% ' 1739 18.0% 57.07 - 1.29 439 2346 35.7% • 1782 18.7% 61.25 1.24 • 440 2082 37.0% 1650 19.6% 64.09 1.30 433 2118 38.0% 1551 20.2% 68.09 1.22 445 2064 39.4% 1632 22.8% Table A 22. Results of experiment number 6, replicate 2 Time on Stream, Zn Zn Fe Fe d PH Eh, mV ppm Extraction, % ppm Extraction, 5.06 2.32 356 6963 4.3%- 1646 1.0% 8.22 2.20 354 6796 8.0% 1539 1.7% 12.00 1.96 380 6288 11.9% 1541 2.5% 15.00 1.79 408 6521 15.2% 1728 3.4% 19.05 1.63 393 5449 18.8% 1756 4.6% 22.01 1.55 408 4832 21.9% 2002 6.5% 26.06 1.52 409 4432 24.8% 1980 8.0% 29.11 1.48 414 3924 26.7% 1970 9.1% 33.23 1.43 420 3150 28.7% 1929 10.5% 36.06 1.30 411 2268 29.7% 2121 11.7% 40.07 1.30 425 2694 31.5% 1867 13.1% 43.06 1.28 418 1458 32.2% 1978 14.2% 47.04 1.16 422 300 32.4% 1621 15.1% 50.15 1.20 416 204 32.5% 1374 15.6% 54.02 1.10 385 156 32.6% 1155 15.8% 57.07 1.29 418 1848 33.2% 1501 16.1% 61.24 1.20 407 1500 34.2% 1408 16.7% 64.09 1.35 403 2844 35.5% 1799 17.6% 68.09 1.14 350 744 36.0% 1172 17.9% 69.00 1.24 355 522 36.1% 1057 16.7% 78.06 1.11 401 1560 38.1% 1542 19.9% 88.21 1.01 404 192 38.4% 974 22.1% 97.97 0.99 392 180 38.7% 1033 24.4% 108.17 1.04 419 738 39.9% 1095 27.1% 118.16 1.09 415 1810 42.7% 1764 32.0% 128.14 1.09 377 276 43.1% 927 34.0% 139.15 1.02 406 578 44.1% 792 35.6% 149.17 0.98 406 690 45.1% 1265 39.1% 159.31 1.00 350 432 45.7% 925 41.0% 169.04 1.03 321 159 45.9% 827 42.9% 179.44 1.10 305 200 46.2% 950 44.9% 190.11 1.10 300 200 46.6% 1050 47.5% 202 Appendix B: Controlled Potential Chemical Leaching Experimental Data A P P E N D I X B : Controlled Potential Chemical Leaching Experimental Data Table B 1. Results of experiment T l Experiment OPERATING PARAMETERS Mass Solids: 20.01 9 Pulp Density: 1.24 % Zn Grade: 22.69 % Zn in Solids: 4.54 g Fe Grade: 6.49 % Fe in Solids 1.30 g Total [Fe]: 0.994 9 [Fe2+1: 0.4846 g/L [Fe3*]: 0.5092 g/L FeS04.7H20: 3.9234 9 Fe2(S04)3.5H20: 3.7071 9 Ratio: 1.0506 Fe3+ / Fe2+ Initial Volume: 1.61 L [H202]: 4 % ORP (setpoint): 525 mV, Ag/AgCl Temperature: 70 •c ORP, mV AAS (Zn) Zn AAS (Fe) Fe Sample Time, hr PH Ag/AgCl mg/L Extraction, % mg/L Extraction 1 0.33 1.11 516 511 18.35 847 29.61 2 0.50 1.13 523 857 30.44 902 35.22 3 0.75 1.16 524 1183 42.02 942 40.21 4 1.00 1.13 523 1366 48.52 923 37.87 5 2.00 1.14 524 1793 64.17 956 42.88 6 3.00 1.12 524 1946 70.17 912 38.21 7 4.00 1.14 524 2279 81.87 1018 51.11 8 5.00 1.15 524 2350 84.42 1028 52.37 9 6.00 1.12 524 2452 88.08 1078 58.65 10 7.83 1.11 524 2531 90.92 1125 64.55 11 21.50 1.02 525 2547 91.84 1268 83.10 12 25.50 1.01 525 2557 92.20 1282 84.66 13 45.50 0.99 528 2584 93.18 1367 95.57 14 46.00 1.00 527 2495 92.20 1311 88.52 PLS + Wash Water 46.00 2112 91.23 1014 76.35 Extraction: Zn by Solution by Solids 91.23 98.55 Extraction; Fe by Solution by Solids 76.35 84.53 Mass Balance: Zn Zn in Solution, g Zn in Solids, g Zn in Head, g 4.277 0.066 4.539 Mass Balance: Fe Fe in Solution, g Fe In Solids, g Fe in Head, g 1.07 0.20 1.30 203 Appendix B: Controlled Potential Chemical Leaching Experimental Data Table B 2. Results of experiment T2 Experiment OPERATING PARAMETERS Mass Solids 20.01 g Pulp Density 1.28 % Zn Grade 22.69 % Zn in Solids 4.54 9 Fe Grade 6.49 % Fe in Solids 1.30 9 Total [Fe] 1.021 g [Fe2+] 0.4978 g'L [Fe3+] 0.5234 g'L FeS04.7H2O 3.9204 9 Fe2(S04)3.5H20 3.7076 g Ratio 1.0515 Fe3+ / Fe2+ Initial Volume 1.57 L [H202] 4 % ORP (setpolnt) 495 mV, Ag/AgCl Temperature 55 •c ORP, mV AAS (Zn) Zn AAS (Fe) Fe Sample Time, hr PH Ag/AgCl mg/L Extraction, % mg/L Extraction, % 1 0.25 1.07 494 366 12.75 961 38.39 2 0.50 1.10 494 573 19.97 968 39.24 3 0.75 1.13 494 747 26.03 973 39.85 4 1.00 1.15 494 855 29.79 971 39.61 5 1.50 1.13 494 1125 39.35 992 42.63 6 2.00 1.12 494 1269 44.39 1000 43.61 7 2.50 1.13 494 1368 47.85 996 43.12 8 3.50 1.13 494 1527 53.41 978 40.92 9 4.50 1.12 495 1663 59.10 1028 47.52 10 8.33 1.19 494 1989 69.57 1047 49.36 11 21.17 1.12 497 2445 86.85 1121 60.53 12 25.83 1.13 495 2505 68.98 1134 62.14 13 49.08 1.15 495 2496 87.98 1083 54.78 14 74.25 1.17 495 2487 87.67 1088 55.40 15 97.00 1.15 495 2526 89.73 1136 62.39 16 117.75 1.16 495 2493 87.88 1299 81.39 17 142.25 1.16 495 2529 88.46 1350 86.40 18 169.17 1.13 497 2577 92.24 1372 92.99 19 188.00 1.12 495 2475 91.17 1333 81.79 20 195.25 1.13 495 2430 91.17 1295 76.61 PLS * Wash Water 195.25 - 2130 90.11 1034 74.21 Extraction: Zn by Solution by Solids 90.11 98.15 Extraction: Fe by Solution by Solids 74.21 82.97 Mass Balance: Zn Zn in Solution, g Zn In Solids, g Zn in Head, g 4.271 0.084 4.539 Mass Balance: Fe Fe in Solution, g Fe in Solids, g Fe In Head, g 1.07 0.22 1.30 204 Appendix B: Controlled Potential Chemical Leaching Experimental Data Table B 3. Results of experiment T3 Experiment T3 OPERATING PARAMETERS Mass Solids 20.00 9 Pulp Density 1.33 % Zn Grade 22.69 % Zn in Solids 4.54 9 Fe Grade 6.49 % Fein Solids 1.30 9 Total [Fe] 1.062 9 [Fe2+] 0.5177 g/L [Fe3+] 0.5441 g/L FeSO4.7H20 3.9226 g Fe2(S04)3.5H20 3.7078 g Ratio 1.0510 Fe3+ / Fe2+ Initial Volume 1.51 L [H202] 4 % ORP (setpoint) 490 mV, Ag/AgCl, 25*C Temperature 40 •c ORP, mV AAS (Zn) Zn AAS (Fe) Fe Sample Time, hr pH Ag/AgCl mg/L Extraction, % mg/L Extraction, % 1 0.28 0.88 488 258 8.64 924 26.39 2 0.50 0.90 487 348 11.66 935 27.68 3 0.75 0.91 489 399 13.37 911 24.87 4 1.00 0.92 488 483 16.11 968 31.09 5 1.50 0.94 488 621 20.63 888 21.34 6 2.00 0.95 489 678 22.53 847 16.58 7 3.00 0.98 489 891 29.60 920 25.05 6 4.00 1.01 489 1047 34.79 903 23.06 9 5.00 1.03 489 1194 39.67 927 25.87 10 21.25 1.13 489 1950 65.59 1001 35.88 11 26.25 1.13 490 2040 68.61 1041 40.58 12 48.08 1.12 490 2304 77.18 1001 35.41 13 70.33 1.12 490 2532 84.82 1038 39.74 14 . 96.42 1.16 490 2595 86.93 1071 43.60 15 166.00 1.14 491 2676 89.64 1124 49.81 16 193.00 1.14 490 2643 90.13 1049 41.03 PLS + Wash Water 193.00 - 2277 90.62 903 43.81 Extraction: Zn by Solution by Solids 90.62 96.99 Extraction: Fe by Solution by Solids 43.81 46.46 Mass Balance: Zn Zn in Solution, g Zn in Solids, g Zn in Head, g 4.225 . 0.137 4.537 Mass Balance: Fe Fe in Solution, g Fe In Solids, g Fe In Head, g 0.65 0.70 1.30 205 Appendix B: Controlled Potential Chemical Leaching Experimental Data Table B 4. Results of experiment PI O P E R A T I N G P A R A M E T E R S Mass Solids 20.00 g Pulp Density 1.25 % Zn Grade 22.69 % Zn in Solids 4.54 g Fe Grade 6.49 % Fe in Solids 1.30 g Total [Fe] 0.998 9 [Fe2+] 0.0100 g/L [Fe3t] 0.9881 g/L F e S 0 4 . 7 H 2 0 0.0808 g Fe2(S04)3.5H20 7.1648 g Ratio 98.5959 Fe3+ / Fe2+ Initial Volume 1.60 L [H202] 4 % O R P (setpoint) 661 mV. Ag/AgCl Temperature 70 •c 7 8 9 10 11 12 13 P L S * Wash Water Time, hr 0.25 0.50 0.75 1.00 1.58 2.08 3.08 4.08 5.08 6.08 8.50 22.58 25.58 84.00 84.00 PH 0.72 0.79 0.95 0.94 1.01 1.05 1.12 1.17 1.14 1.16 1.21 1.15 1.13 1.13 O R P , mV A A S (Zn) Zn A A S (Fe) Fe in Sample A g / A g C l mg/L Extraction, % mg/L mg 656 717 26.06 699 3.50 659 1026 37.29 897 4.49 660 1278 48.01 928 4.64 656 1428 54.03 957 4.79 658 1680 64.47 1020 5.10 660 1830 70.98 1054 5.27 659 2019 79.40 1105 5.53 665 2139 84.70 1061 5.31 665 2232 88 36 1078 5.39 667 2244 88.86 1093 5.47 661 2304 90.61 1134 5.67 671 2367 93.41 1107 5.54 674 2373 93.64 1130 5.65 674 2334 867 4.34 2154 92.70 961 Fe Extraction, % 11.91 37.06 44.96 49.67 59.93 65.99 75.00 69.96 72.31 74.39 78.99 75.80 78.97 38.59 67.66 Extraction: Z n by Solution by Solids 92.70 99.06 Extraction: Fe by Solution by Sol ids 67.66 69.06 Mass Balance: Z n Z n in Solution, g Z n in Sol ids, g Zn in Head, g 4.336 0.043 4.538 Mass Balance: Fe Fe in Solution, g Fe in Sol ids, g Fe in Head, g 0.95 0.40 1.30 206 Appendix B: Controlled Potential Chemical Leaching Experimental Data Table B 5. Results of experiment P2 Experiment P2 O P E R A T I N G P A R A M E T E R S Mass Solids 20.00 9 PulpDensrty: 1.23 % Zn Grade 22.69 % Zn in Solids: 4.54 g Fe Grade 6 49 % Fe in Solids 1.30 0 Tolal [Fe) 0.983 g |Fe2+] 0.0896 g'L [Fe3f] 0.8937 9'L F e S 0 4 . 7 H 2 0 0.7335 9 Fe2(S04)3.5H20 6.5775 g Ratio 9.9707 Fe3 t / Fe2+ Initial Volume 1.63 L [H202] 4 % O R P (setpoint] 580 mV, Ag/AgCl Temperature 70 • c O R P , mV A A S (Zn) Z n A A S (Fe) Fe in Sample Fe Sample Time, hr pH A g / A g C l mg/L Extraction, % mg/L mg Extraction, % 1 0.25 1.05 577 708 25.92 725 3.63 17.04 2 0.50 1.10 576 1050 38.59 750 3.75 20.59 3 0.75 1.14 571 1296 47.80 773 3.87 23.91 4 1.00 1.16 578 1443 53.42 796 3.98 27.26 5 1.50 1.14 579 1620 60.85 805 4.03 29.95 6 2.00 1.14 579 1782 66.94 918 4.59 44.78 7 3.00 1.16 580 1965 73.81 955 4.78 49.64 8 4.00 1.15 580 20SS 78.71 1017 5.09 58.26 9 5.00 1.13 580 2184 82.63 1026 5.13 59.93 10 6.00 1.14 578 2262 85.58 1083 5.42 67.47 11 10.83 1.15 579 2337 89.05 1118 5.59 73.15 12 23.08 1.13 582 2355 90.06 1102 5.51 71.55 13 29.00 1.12 582 2346 89.39 1099 5.50 70.62 14 46.75 1.12 581 2367 89.87 1118 5.59 72.62 15 52.50 1.11 584 2367 89.71 1128 5.64 73.68 P L S • W a s h Water 52.50 2205 89.71 1107 80.10 Extraction: Zn by Solution by Solids 89.71 98.89 Extraction: Fe by Solution by Solids 80.10 92.94 Mass Balance: Zn Zn in Solution, g Z n in Sol ids, g Z n in Head, g 4.171 0.050 4.538 Mass Balance: Fe Fe in Solution, g Fe in Sol ids, g Fe in Head, g 1.11 0.09 1.30 207 Appendix B: Controlled Potential Chemical Leaching Experimental Data Table B 6. Results of experiment P3 OPERATING P A R A M E T E R S Mass Solids 20.00 9 Pulp Density 1.23 % Zn Grade 22.69 % Zn in Solids: 4.54 9 Fe Grade: 6.49 % Fe in Solids 1.30 9 Total [Fe] 0.988 g [Fe2»] 0.8978 g i -[Fe3+] 0.0899 g/L FeS04.7H20 7.3136 , 0 Fe2(S04)3.5H20 0.6587 g Ratio 0.1001 Fe3+ / Fe2* Initial Volume 1.62 L [H202] 4 % O R P (setpoint) 451 mV. Ag/AgCl, 2 5 - C Temperature 70 •c O R P , mV A A S (Zn) Zn A A S (Fe) Fe in Sample Fe Sample Time, hr pH Ag /AgCl mg/L Extraction, % mg/L mg Extraction, % 1 0.25 0.96 451 540 19.34 848 4.24 30.05 2 0.50 1.03 449 711 25.47 978 4.89 46.36 3 0.75 1.08 449 849 30.43 753 3.77 18.25 4 1.00 1.11 452 993 35.58 770 3.85 20.34 5 1.50 1.14 452 1185 42.54 766 3.83 20.03 6 2 00 1.13 455 1347 48.44 777 3.89 21.57 7 3.00 1.13 456 1620 58.38 793 3.97 23.79 8 4.00 1.14 450 1761 63.53 807 4.04 25.67 9 5.00 1.15 450 1956 70.61 823 4.12 27.75 10 21.50 1.20 452 2505 91.68 912 4.56 40.58 11 28.00 1.21 451 2541 92.72 969 4.85 47.50 12 47.00 1.15 454 2556 93.67 1016 5.08 54.05 13 74.17 1.15 452 2634 96.80 1117 5.59 67.39 14 119.17 1.15 451 2697 99.13 1215 6.08 79.99 15 146.33 1.13 500 2595 95.51 1280 6.40 88.56 16 165.17 1.13 507 2607 1329 6.65 94.36 LS + Wash Water 165.17 2358 96.25 1172 91.10 Extraction: Zn by Solution 96.25 by Solids 98.60 Extraction: Fe by Solution 91.10 by Sol ids 90.00 Mass Balance: Zn Zn in Solution, g 4.513 Zn in Solids, g 0.063 Zn in Head, < 4.538 Mass Balance: Fe Fe in Solution, g 1.26 Fe in Sol ids, g 0.13 Fe in Head, j 1.30 208 Appendix C : Analytical Procedures A P P E N D I X C: Analytical Procedures Induction Coupled Plasma The following documentation was provided by International Plasma Laboratory Ltd (IPL) and reflects their procedures for performing an ICP analysis. A l l determination of solid samples used in this study were determined by ICP analysis, and were conducted by IPL. International Plasma Laboratory 2036 Columbia Street Vancouver, B .C. Canada V 5 Y 3 E 1 Method of 30 element analysis by Mult i Acids digestion/ICP (a) 0.50 grams of sample is digested with concentrated H N O 3 , H C I O 4 and H F acid solution in a Teflon beaker by heating on a hot plate until dried, then cooled and re-boiled with a 5% Aqua Regia solution, bulked up to a fixed volume with de-mineralized water, and thoroughly mixed. (b) The specific elements are determined using an Inductively Coupled Argon Plasma spectrophotometer. A l l elements are corrected for inter-element interference. A l l data are subsequently stored onto computer diskette. 209 Appendix C : Analytical Procedures Quality Control The machine is first calibrated using three known standards and a blank. The test samples are then run in batches. A sample batch consists of 38 or less samples: Two tubes are placed before a set. These are an In-house standard and an acid blank, which are both digested with the samples. A known standard with characteristics best matching the samples is chosen and placed after every fifteenth sample. After every 38th sample (not including standards), two samples, chosen at random, are re-weighed and analyzed. A t the end of a batch, the standard and blank used at the beginning is rerun. The readings for these knowns are compared with the pre-rack knowns to detect any calibration drift. Gravimetric Analysis The following documentation was provided by International Plasma Laboratory Ltd (IPL) and reflects their procedures for performing a gravimetric analysis. A l l determination of sulphur species used in this study were determined by gravimetric analysis, and were conducted by IPL. International Plasma Laboratory 2036 Columbia Street Vancouver, B .C. Canada V 5 Y 3 E 1 210 Appendix C : Analytical Procedures Method of Sulfur Group Assays by Gravimetric Analysis Sulfur group elements consist of: S(total) (assay separately); S(elemental); S(sulphide); S (sulphate): S(total) Assays (a) 0.50 to 2.00 grams of sample was weighed accurately into a 150-mL beaker; KCIO3, K B r , B r and HNO3 are added and digested slowly until dry on a warm hot plate. (b) The sample is then removed from the hot plate and cooled. The sample is then boiled in hot water with Na2C03 before filtering off the insoluble matter. (c) The filtrate is then acidified by adding HC1 acid and boiled to remove any excess CO2. (d) B a C b solution is added to form BaSC^. The crystalline BaSC>4 precipitate is then purified by digestion: a process in which the solution from which the precipitate came and the precipitates are heated to dissolve smaller precipitate particles which subsequently re-precipitate on larger particles. The precipitates are then filtered onto an ash-less filter paper. The filter paper is removed in a furnace, and the remaining solids are then removed and allowed to cool. They are then weighed as BaSC^ , the gravimetric factor of S to BaSC^ is then applied and the value is then reported as S(total). 211 Appendix C : Analytical Procedures S(elemental) Assays (e) 0.50 to 2.00 grams of sample is weighed accurately into a 150-mL beaker, tetrachloro-ethylene is added and boiled to dissolve any elemental sulfur in sample. The organic filtrate is then filtered off into a clean beaker. The residue is saved for S(S04) & S(-2) assays. (f) The sample is then slowly evaporated until dry, removed and digested with KCIO3, K B r , Br and HNO3 acid and digested slowly under gentle heat until once again dry on a warm hot plate. (g) The sample is then removed from the hot plate and allowed to cool. It is then boiled in hot water with Na2C03 before filtering off the insoluble matter. (h) The filtrate is then acidified by adding HC1 acid and boiled to remove any excess CO2. (i) B a C b solution is added to form BaS04. The crystalline BaSCM precipitate is then purified by digestion: a process in which the solution from which the precipitate came and the precipitates are heated to dissolve smaller precipitate particles which subsequently re-precipitate on larger particles. The precipitates are then filtered onto an ash-less filter paper. The filter paper is removed in a furnace, and the remaining solids are then removed and allowed to cool. They are then weighed as BaS04, the gravimetric factor of S to BaS04 is then applied and the value is then reported as S(elemental). 212 Appendix C : Analytical Procedures S(sulphate) assays (j) Take the residue from S(elemental) filtration (step e), and boil it in hot water with Na2CC>3 before filtering off the insoluble matter. Save the residue for S(-2) assays. (k) The filtrate is then acidified by adding HC1 acid and boiled to remove any excess CO2. (j) BaCl2 solution is added to form BaSC^i. The crystalline BaSC»4 precipitate is then purified by digestion: a process in which the solution from which the precipitate came and the precipitates are heated to dissolve smaller precipitate particles which subsequently re-precipitate on larger particles. The precipitates are then filtered onto an ash-less filter paper. The filter paper is removed in a furnace, and the remaining solids are then removed and allowed to cool. They are then weighed as BaSC»4, the gravimetric factor of S to BaSC>4 is then applied and the value is then reported as S(sulphate). S(sulphide) assays (m) Take the residue from S(sulphate) filtrate (step j) and add KCIO3, K B r , Br ,HNC>3 and digest slowly until dry on a warm hot plate. (n) The sample is then removed from the hot plate and allowed to cool. It is then boiled in hot water with Na2C03 before filtering off the insoluble matter. 213 Appendix C : Analytical Procedures t (o) The filtrate is then acidified by adding HC1 acid and boiled to remove any excess CO2. (p) B a C h solution is added to form BaSC^. The crystalline BaSC^ precipitate is then purified by digestion: a process in which the solution from which the precipitate came and the precipitates are heated to dissolve smaller precipitate particles which subsequently re-precipitate on larger particles. The precipitates are then filtered onto an ash-less filter paper. The filter paper is removed in a furnace, and the remaining solids are then removed and allowed to cool. They are then weighed as BaSC^ , the gravimetric factor of S to BaSC^ is then applied and the value is then reported as S(sulphide). 214 Appendix C : Analytical Procedures Atomic Adsorption Spectroscopy Determination of dissolved zinc and iron was performed in-house at U B C using the fol lowing procedure. The machine ( U N I C A M 929 A A Spectrometer) was first calibrated using known standards and a blank. The standards used for zinc, 0.2, 0.4, 0.6, and 1.0 ppm, were prepared from a 1000 ppm Zinc Reference Solution (Fisher Scientific CSZ13-500). The standards used for iron, 1, 2, 6, and 6 ppm, were prepared from a 1000 ppm Iron Reference Solution (Fisher Scientific CSI124-500). The test samples were then run in batches of 5. After each set of 5, the machine's calibration was rescaled with the highest concentration standard to account for drift. After another five samples were processed the machine was recalibrated with all of the original standards to ensure that the calibration curve remained accurate. 215 Appendix C : Analytical Procedures Bacteria Culturing Procedure Transfer cultures once a week. Into a clean 250 mL baffled Erlenmeyer flask weigh 2 g of pulverized sphalerite ore and 100 mg of sulphur powder (200 mg of sulphur powder are to be used for culturing Moderate and Extreme Thermophiles). To that add 75 mL of the appropriate medium as detailed in Table 3-2e new flask with a foam stopper and place back in the incubator. Ensure the incubator is set to 30°C for the Mesophiles, 48°C for the Moderate Thermophiles, and 68°C for the Extreme Thermophiles. Do not exceed 150 rpm on the shakers. Discard the remaining cultured solution or transfer into more flasks as required. Wash out the old flask(s). N B : due to the high temperatures in the Extreme Thermophiles incubator, the solution wi l l evaporate quite rapidly. Therefore, refill the flask after 3-4 days with distilled water. 216 Appendix C : Analytical Procedures Protocol For Determination Of Free And Attached Bacteria From the Same Sample (15 mL tube containing fines and liquid) The following documentation was provided by Ms . Amy M . Chan: Amy M . Chan, Research Scientist Earth and Ocean Sciences University of Brit ish Columbia 6270 University B lvd V 6 T 1Z4 A l l enumeration of bacteria in solution in this study was determined by M s . Chan using this method. 1. Re-suspend the solids by inverting/shaking the tube several times by hand 2. Centrifuge for 7 min at 800 x g and 25°C 3. Transfer the supernatant to a new tube using a transfer pipette [free cells] 4. A d d 5 mL of media to the remaining solids and re-suspend the solids by inverting/shaking the tube several times by hand 5. Centrifuge for 7 min at 800 x g and 25°C 6. Transfer the supernatant to the free cell tube 7. Repeat steps 4, 5 and 6 one more time so that you have a tube with 15 mL of free cells. (Prepare a slide from this 'free cel l ' tube. This tube contains the original free cell solution combined with 2 washes with media) [Cell counts need to be multiplied by 3 to get original concentration of cells in leaching solution] 8. Weigh tubes with solids 217 Appendix C : Analytical Procedures 9. Extract attached cells from the solids: Add 4 mL buffer (1% tween 80 in media) to the solids remaining in the tube and vortex on high for 5 sec. 10. Transfer contents to a 50 mL tube using a transfer pipette; rinse any leftover solids from tube with 1 mL buffer and add to the 50 mL tube 11. Shake the tube at 350 rpm for 1 hour 12. ' Weigh empty tubes (get weight of solids by subtraction) 13. Centrifuge for 2 min at 800 x g and 25°C 14. Transfer supernatant to a N E W tube [attached cells] 15. Add 5 mL buffer to the remaining solids and vortex on high for 5 sec. 16. Shake the tube at 350 rpm for 15 min 17. Centrifuge for 2 min at 800 x g and 25°C 18. Transfer the supernatant to the attached cell tube 19. Repeat steps 12, 13, 14, and 15 twice more. Prepare a slide for attached cell count. (This tube contains the first extraction along with 3 washes, with a total volume of 20 mL.) 20. The S Y B R Green and epifluorescence microscopy method used for counting the bacteria is based on the following reference: Noble, R T and J A Fuhrman, 1998. Use of S Y B R Green I for rapid epifluorescence counts of marine viruses and bacteria. Aquatic Microbial Ecology 14: 113-118 218 Appendix C : Analytical Procedures Method for Extraction of Attached Bacteria From A R D Material The following documentation was provided by Ms . Amy M . Chan: Amy M . Chan, Research Scientist Earth and Ocean Sciences University of Brit ish Columbia 6270 University B lvd V 6 T 1Z4 A l l enumeration of bacteria in attached to solids in this study was determined by Ms . Chan using this method. 1. Collect representative sample from column (~15 grams) in 50 m L falcon tubes 2. A d d 10 m L of 10% formalin (made up in mesophile media without Fe) 3. M i x tube content and store at 4 °C 4. When ready to extract bacteria, add 10 mL of 1% tween 80 (made up in mesophile media) and top up with 1 % tween 80 (in mesophile media) so that the ratio of 1 mL per 1.5 grams of ore is maintained 5. Vortex tube contents for a count of five 6. Shake on rotary shaker for min of 60 min at 250 rpm 7. Separate ore from liquid by centrifugation for 5 min at 800 x g in a swinging bucket rotor 8. Pour off supernatant into new 50 mL tube (=extract) 9. Wash bacteria off ore: add 10 mL of 1% tween 80 (in mesophile media) and shake for 15 min at 250 rpm 219 Appendix C : Analytical Procedures 10. Centrifuge tube as in step 6 11. Pour off supernatant into extract tube 12. Repeat steps 8 to 10 twice, pooling all the washes with the extract together in a single tube 13. Vortex the tube contents, sub-sample 1000 u.1 and pellet the fines by centrifugation for 3 min at 500 x g [in a microfuge tube] 14. Prepare a slide using the S Y B R Green Method (filter a minimum of 800 u.1) 15. The S Y B R Green and epifluorescence microscopy method used for counting the bacteria is based on the following reference: Noble, R T and J A Fuhrman, 1998. Use of S Y B R Green I for rapid epifluorescence counts of marine viruses and bacteria. Aquatic Microbial Ecology 14: 113-118 220 Appendix C : Analytical Procedures Trace Elements Solution In fresh deionized water dissolve: Component Concentration, mg L 1 MnCl 2 »4H 2 0 1.8 N a 2 B 4 O 7 ' 1 0 H 2 O 4.5 Z n S 0 4 ' 7 H 2 0 0.22 CuCl 2 »2H 2 0 0.05 VOS0 4 «2H 2 0 0.03 C 0 S O 4 0.01 adapted from the Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH (DSMZ) Medium archive: Medium #88 Adjust p H to 2.0 with 10 N H 2 S 0 4 at room temperature and store in fridge. 221 

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