TABLE ik.39. Test C.5, Sterile Supernatant Data in Determination of Characteristics of Nickel Sulphide. (Values in ppm.)

Transcription

1 A.3.3. TABLE A.38. Test C.5, Example of Sampling Data for Inoculated System in Determination of Bioleach Characteristics of Nickel Sulphide. Sampling Procedure is Discussed in the Appendix Figures A.5 and A.6. Day: Sample Supernatant Day: Sample Supernatant 0,75 30,09 g 29,62 g 2,75 30,12 g 29,75 g -29,5 ml 29,0 ml I Wet Solid 29,5 ml I Wet Solid 29,0 ml Wash 0,51 g i Pulp ----* Wash Water Wash - 0,40 g Pulp - Wash Water Water 30,11 g 29,69 g Water 30,38 g 30,03 g 30,0 ml 30,2 ml 15% HC1 Washed Solid 0,43 g i Pulp -* HC1 Extract 31,55 g 31,19 g 15% HCl Washed Solid 0,38 g 1 Pulp -*> HCl Extract 33,05 g 32,68 g 29,1 ml 30,8 ml Wash - Water Extracted Solid 0,48 g 1 Pulp ----> Wash Water 29,43 g ^8,93 g 29,0 ml Wash - Water Extracted Solid 0,39 g Pulp ---- Wash Water 37,26 g 36,74 g 37,0 ml V Washed Solid 0,43 g Washed Solid 0,40 g I Acid Digestion 2 ppm Ammonium in 50 ml Acid Digestion 2 ppm Ammonium in 50 ml 166

2 A.3.3. TABLE ik.39. Test C.5, Sterile Supernatant Data in Determination of Characteristics of Nickel Sulphide. (Values in ppm.) Bioleach DAY Fe Fe2+ Ni P Mg Ca so<2- K n h 4+ 0, ,6 1, , ,5 4,5 1, , ,6 4,5 1, , ,9 5,3 1, , ,6 4,6 < , ,7 4,9 1, ,0 78 6, ,8 5,0 1, , ,8 5,0 1, ,5 76 8, ,8 5,0 1, ,7 71 9, ,8 5,1 1, , , ,9 5,2 < , , ,9 5,2 < , , ,9 5,1 < ,

3 A.3.3. TABLE A.40. Test C.5, Inoculated Supernatant Data in Determination of Bioleach Characteristics of Nickel Sulphide. (Values in ppm, Bugs = (no of bacteria in solution)/ (cm-3 X 10 B )) DAY Fe Fe 2+ Ni P Mg Ca SO 2-4 K n h 4 + Bugs 0, ,14 0, ,4 4,6 1, ,389 1, ,5 4,6 1, ,59 2, ,5 4,6 1, ,20 3, ,6 4,9 1, ,31 4, ,6 4,9 1, ,69 5, ,6 5,2 1, ,19 6, ,6 5,1 1, ,49 7, ,6 5,2 1, ,8 65 5,83 8, ,6 5,2 1, ,4 62 6, 14 9, ,6 5,3 1, ,0 59 7,51 10, ,8 5,4 < ,2 60 8,97 11, ,8 5,5 < ,6 51 8,75 13, ,8 5,3 < ,9 49 7,80 168

4 A.3.3. TABLE A.41. Test C.5, Sterile HCl Extract Data (see Appendix A.2.4.2) in Determination of Bioleach Characteristics of Nickel Sulphide. DAY Fe Ni P K q Ca S042" K N H / 0,75 4,0 18 1,7 1,7 2,2 0,04 2,75 4,4 14 1,5 1,4 1,7-0,05-4, ,5 1,5 1,7-0,32-6, ,1 1,5 1,5-52 <2 8, ,9 2,2 1,5 1,7 0,52 56 <2 10, ,3 1,6 1,5 1,6 0, , ,5 1,6 1,4 1,7 0, TABLE A. 4 2 Test C.5, Inoculated HCl Extract Data (see Appendix A.2.4.2) in Determination of Bioleach Characteristics of Nickel (Values in ppm. Sulphide. DAY Fe Ni P Mg Ca so42- K N H / 0,75 5,1 23 1,7 1,8 2,2-0,07 2,75 4,5 12 1,5 1,4 1,7-0, 08-4, ,6 1,7 2,1-0, 66-6, ,2 1,6 1,6-52 <2 8, ,3 1,6 2,0 0, <2 10, ,6 1,5 1,7 0, , ,0 1,6 1,5 1,6 0,

5 A.3.3. TABLE A.43 Tests 2.4 and C. 5, Ammonium Balances for Inoculated Systems in Determination of Bioleach Ch& acteristics of Nickel Sulphide. rest 2.4 Test 2.5 Day Sol. Jar. Free Att. T.B. T.N. Sol. Jar. Free Att. T.B. T.N. 0, ,7 0,0 1, ,6 0,0 1,6 84 0, ,82 0,0 0, ,54 3,3 3,8 79 1, , , , ,2 0,0 8, ,4 3,3 7,7 90 3, , , , ,1 3,3 8,4 80 5, , , , <2 7,6 3, , , , , <2 8,5 5, , , ," , , , Sol.: Ammonium ions remaining in the solution. Jar.: Ammonium ions locked in jarosite. Free: Ammonium ions consumed by the unattached bacteria. Att.: Ammonium ions consumed by the bacteria attached to sol id material. T.B.: Ammomium ions consumed by all the bacteria. T.N.: Total original concentration of ammonium in the system. 170

6 A A READINGS IN DEDUCTION OF EFFECT OF HYDROGEN PEROXIDE ON CHEMICAL LEACHING OF NICKEL SULPHIDE IN ABSENCE OF BACTERIA TABLE A.44. Test D.1, Data for Deduction of Effect of Hydrogen Peroxide on Chemical Leaching of Nickel sulphide. (10,00 g Solid in 1,5 Litre, 5 ml 98% H 2S04 / 1 initially) Day Time Temp PH Redox Sample Dried Iron Cone. Ni2+ SO2" 4 vol. Macs so; i,t IV I T o t,i! C mv ml g g g/i g/i g/i g/i 1 15h , _ 15h h h , ,98 0, 08 0,30 8,95 0, 15 23,2 17h h h , , 10 0, 13 1, 65 9, 12 0,75 24,8 18h h h , ,30 0, 14 3,05 9, 10 1,51 24, 8 17h h h , ,91 0, 16 3,95 9, 00 1,99 25,3 19h h (*) 09h , , 00 0, 12 4,50 8,98 2,29 26,6 2 OhOO h , , 14 4,80 8,78 2,60 25,4 7 07h h , ,21 0, 13 5,15 8,98 2,86 25, h h , ,72 5,35 8, 80 3,07 26,0 (*) : Add 10 ml of 200 g (98% H 2S04) / 1 171

7 A.3.4. A READINGS IN DEDUCTION OF EFFECT OF HYDROGEN PEROXIDE ON CHEMICAL LEACHING OF NICKEL SULPHIDE Tl'i ABSENCE OF BACTERIA TABLE A.44. Test D. 1, Data for Deduction of Effect of Hydrocen Peroxide on Chemical Leaching of Nickel sulphide. (10,00 g Solid in 1,5 Litre, 5 ml 98% H 2S04 / 1 initially) Day Time Temp PH Redox Sample Dried Iron Cone. Ni2+ SO2" 4 Vol. r > Solid ' T ii C mv ml g g g/i g/i g/i g/i 1 15h00 37,0 1, h05 37, h30 37, h00 37,0 1, ,98 0,08 0,30 8,95 0, 15 23,2 17h30 37, h30 37, h00 37,0 1, , 10 0,13 1, 65 9, 12 0,75 24,8 18h00 37, h30 37, h00 37,0 1, , 30 0,14 3, 05 9, 10 1,51 24,8 17h30 37, h30 37, h00 37, 0 1, ,91 0,16 3,95 9, 00 1, 99 25,3 19h00 37, h30 37, (*) 09h00 37,0 1, , 00 0, 12 4,50 8,98 2,29 26,6 2 OhOO 37,0-4 ] h00 37,0 1, , 14 4, 80 8, 78 2,60 25,4 7 07h30 37, _ 09h00 37, 0 1, ,21 0, 15 5, 15 8,98 2,86 25,8 8 07h30 37, _ 09h00 37,0 1, ,72 5,35 8, 80 3,07 26,0 (*) : Add 10 ml of 200 g (98% H 2S04) / 1 171

8 A.3.4. I TABLE A.45. Test D.2, Data for Deduction of Effect of Hydrogen Peroxide on Chemical Leaching of Nickel sulphide. (10,00 g Solid in 1,5 Litre, 5 ml 98% H 2S04 / 1 initially) T... Day Time Temp PH Redox Sample Dried Iron Cone. NiJ+ 1 o CO Vol. Mass ; <»!.. i 1 t I ' Total C mv ml g g g/1 g / i g / i g / i 1 15h00 37,0 1, a. 15h05 37, h30 36, h00 j6,0 1, ,90 0, 10 0,30 8,92 0,15 23,4 17h3 0 38, h30 36, h00 36,0 1, ,24 0, 12 1,80 8,90 0,84 24,6 18h00 37, h30 38, h00 37,0 1, , 14 0, 18 3,23 9, 10 1,74 25,0 17h30 37, h30 37, h00 37,0 1, ,97 0, 12 4,2C 9, 12 2,08 24,9 19h00 37, (*) 08h3 0 37, h00 37,0 1, , 82 0,11 4,70 8, 85 2,45 26,0 2 OhOO 37, h00 36,0 1, , 13 5, 15 8,90 2,79 25,6 7 07h30 37, h00 37,0 1, , 22 0, ,90 3, 06 25,b 8 07h3 0 37, h00 37,0 1, , 53 0, 10 5, 55 8,80 3, 16 25,6 (*) : Add 10 ml of.700 g (98% H 2S04) / 1 172

9 A.3.5. A.3.5. GRAPHICAL REPRESENTATION OF DATA OF TWO SETS OF PARALLEL TESTS OF TYPE C Data is presented for Tests C.4 and C.5. The following nomenclature is employed: Sterile: Refers to the parallel sterile control. The redox potential in the system is controlled by the addition of nydrogen peroxide. Inoculated: Refers to the inoculated systum. Here the redox potential is determined by the oxidizing activity of the bacteria. Total: Refers to the sum of all the relevant r.pecies in the system, be it in soluble or precipitated form. Soluble: Refers to the relevant species that have remained in aqueous solution. Precipitated: Refers to the relevant species that has precipitated as jarosite. 173

10 A.3.5. FIGURE A.7: Test C.4, Variation of Redox Potential (vs SCE G 3 7 C) with Time in Bioleaching of Ni3S 2 and Parallel Sterile FIGURE A.8: Test C.5, Variation of Redox Potential (vs SCE 0 37 C) with Time in Bioleaching of Ni3S 2 and Parallel Sterile (Experimental Conditions: Impollor Speeds 200 r.p.m.; 9 g/1 Soluble Iron; ph Levels of 1,6 and Temperatures of 37 C.) 174

11 A.3.5. FIGURE A.9: Test C.4, Nickel Recoveries vs Time in Bioleaching of Ni3S 2 and Parallel Sterile Control. FIGURE A.10: Test C.5, Nickel Recoveries vs Time in Bioleaching of Ni3S 2 and Parallel Sterile Control. (Experimental Conditions: Impellor Speeds 300 r.p.m.; 9 g/1 Soluble Iron; ph Levels of 1,6 and Temperatures of 37 C.)

12 A.3.5. FIGURE A.11: Test C.4, Iron Balance in Sterile Leaching of Ni3S 2. i FIGURE A.12: Test C.4, Iron Balance in Bioleaching of Ni3S 2..*> O' \ c o H Vn K e y * T o t a l. r o n \ o S o lu b le p c0)0 c 0 o f r e! f o u s.'ron " 1. f * - r - -*t * i " ' l 1! ' «96 1U! (Experimental Conditions: Impellor Speeds 300 r.p.m.; 9 g/1 Soluble Iron; ph Levels of 1,6 and Temperatures of 37 C.) 176

13 A.3.5. FIGURE A.13: Test C.5, Iron Balance in Sterile Leaching of Ni3S 2. FIGURE A.14: Test C.5, Iron Balance in Bioleaching of Ni3S2. *.... #. «... ^ o ~o *7". ~r. -v- o t K e y : ' * rote! Iron o Soluble x Precioitcled Ferrous Iron K ^ «f <* i 1 0 «96 I #!92 2X) 288 D 6 (Experimental Conditions: Impellor Speeds 300 r.p.m.; 9 g/1 Soluble Iron; ph Levels of 1,6 and Temperatures of 37 C.) 177

14 A.3.5. FIGURE Ni3S : Test C.4, Ammonium Balance in Sterile Leaching of 6 P4 04 c o H Pflj P c<uo C o u FIGURE Ni 3S 2 ^.16: Test C.5, Ammonium Balance in Sterile Leaching of B a \ e o H U +J c<uo c o u (Experimental Conditions: Impellor Speeds 300 r.p.m.; 9 g/1 Soluble Iron; ph Levels of 1,6 and Temperatures of 37 C.) 178

15 A.3.5. FIGURE Ni3S 2..17: Test C.4, Ammonium Consumption in Bioleaching of FIGURE NijSj..18: Test C.5, Ammonium Consumption in Bioleaching of E aa o H V0- e 3 U1co u (Experimental Conditions: Impellor Speeds 300 r.p.m.; 9 g/1 Soluble Iron; ph Levels of 1,6 and Temperatures of 37cC.) 179

16 A.3.5. FIGURE A. 19: Test C.4, Ammonium Balance in Bioleaching of N i 3S 2. B 04 Q, <0 U P C a c co u i36 FIGURE A.20: Test C.5, Ammonium Balance in Bioleaching of Ni3S J K e a 60 N s. w ' / n c t 0 H 4J(0GS (l>» U 1 o 20- «Tote: nmonium o Solub : r Toto! Bocteric! Precipitated V> V * «« J 268 (Experimental Conditions: Impellor Speeds 300 r.p.m.; 9 g/i Soluble Iron; ph Levels of 1,6 and Temperatures of 37 C.) 180

17 A.3.5. FIGURE A.21: Of N i 3S E ft o. c eo- o H 4J ij«c Q) O C 3 20 Test C.4, Other Concentrations in Sterile Leaching. ; : : : * Soluble Potassium : o Magnesium x PhopHorus h n r ' 1 + ' Precipitated Potassium " * : > - r... Y...[... j... \ /. \ / - \ r-.g/-. rf - «f r- ", FIGURE A.22: Ni3S 2. Test C.4, Other Concentrations in Bioleaching of c o H P u -p c<uu c o > m y : Soluble Potassium Magnesium PhopHorus n e tiy iiu ie u ro lassium ft /, : \ / /. \, 4 \ y * - f -r? -r h r / **yjk T - 1» f « (Experimental Conditions: Impellor Speeds 300 r.p.m.;? g/l Soluble Iron; ph Levels of 1,6 and Temperatures of 37 c.) 181

18 A.3.5. FIGURE A. 23: Test C.5, Other Concentrations in Sterile Leaching of NljS j t... Soluble Potassium... o Magnesium : x Phophorus + Precipitated Potassimr FIGURE A.24: Ni3S c 60 o H P u 0) u c o u ts S Test C.5, Other Concentrations in Bioleaching of V - zf*! / ' s..* ir './. _# - ^ / /. / : y..\. Key:» Soluble Potas sium o Magnesium x Phophorus + Precipitated Potassiimr - * - ~* *t 1 ' ^ J U Loaching Time / hr (Experimental Conditions: Impellor Speeds 300 r.p.m.; 9 g/1 Soluble Iron; ph Levels of 1,6 and Temperatures of 37 C.) 182

19 A FIGURE A.25: Test C.4, Acid Consumptions (200 g/1 98% H 2S04) in Bioleaching of Ni3S 2 and Parallel Sterile Control. t FIGURE A.26: Test C.5, Acid Consumptions (200 g/1 98% H 2S04) in Bioleaching of Ni3S 2 and Parallel Sterile Control. (Experimental Conditions: Impollor Speeds 300 r.p.m.; 9 g/1 Soluble Iron; ph Levels of 1,6 and Temperatures of 37 C.) 183

20 A.4. MODELLING OF REDOX POTENTIAL AND ph PREDICTION IN ABSENCE OF NICKEL SULPHIDE In this section, the theory outlined in Section 2.1 is utilized. Initially the values of the equilibrium constants for the complexes in solution were chosen to be those shown in Table A.46. The computer program given in Appendix A.5.1 was used to calculate redox potential and ph levels from the average iori concentration data of Tests A (Tables A.14 to A.17) which were performed in the absence of nickel sulphide. The calculated values are compared with the experimental data points in Figure A.27. Here the potential values are relative to the standard calomel electrode at 37 C. The effect of excluding complex no 6 (Fe(S04)2"), i.e. setting K(6) 0, is also shown. For both values of K(6) similar observations can be made: The calculated redox potential is seen to be higher than that obtained experimentally, and the calculated ph values are also higher than the value at which the ph was controlled in the experiments, with the error increasing as more iron converted to the ferric form. This appears to indicate that more hydroxide species form than are accounted for in the above equilibrium constants. As the error in ph is larger at high percentage ferrous oxidation, it seems that the hydroxide species which additionally forms is some or other ferric hydroxide complex. 184

21 TABLE A.46 Equilibrium Constant 37 C of Complexes Used in Initial Calculation of Redox Potential and ph Levels in Solutions of Experiments of Type A Constant no Complex Equilibrium Constant K(l)* FeSO/ K(2)* FeHS K(3)** *eoh2+ 5,65 X 1011 K (4)* * Fe(OH)** 2,00 X 1022 K(5)** Fe 2(OH)j 4 + 4,37 X K (6)** Fe(S04) K(7) * FeS K (8) * FeHS04* K(9)* * HS04" 138 K(10)*** Niso4 230 * Values from Dry19* ** Values from Smith and Martell (26) *** The Equilibrium Constant for this Complex is Required in Redox Potential Prediction for Experiments of Type C, and was also Obtained from Smith and Martell*26 185

22 FIGURE A.27. Modelling Redox Potential and ph Levels in Tests of Type A, Using Equilibrium Data from the Literature (Table A.46). (Experimental Conditions: No Sulphide Mineral; 9 g/1 Soluble Iron; ph Levels of 1,6 and Temperatures of 37 C.) Redox Potential / mv Average of Tests A.l - A Modelling with K (6) Modelling with K(6)

23 FIGURE A. 28. Modelling Redox Potential and ph Levels in Tests of Type A, but Changing a Single Hydroxide Equilibrium Constant at a Time from its Literature Value (Table A.46). (Experimental Conditions: No Sulphide Mineral; 9 q/1 Soluble Iron; ph Levels of 1,6 and Temperatures of 3 7 C.) Redox Potential / mv --- K (3) x 200 (K (4) & K (5) as in Table 5.1) --- K (4) x 333 (K(3) & K(5) as in Table 5.1) --- K (5) x (K(3) & K(4) as in Table 5.1) 187

24 It can be seen that by increasing K (4) the ph values calculated are far too low at high percentage ferrous oxidation. The redox potential fit is relatively poor if K(5) is increased, although the ph is reasonably predicted. Increasing K(3), however, results in reasonable ph and redox prediction. At low percentage ferrous oxidation, the calculated ph value is 1,74, and this slowly decreases and bottoms out at 1,65 at higher percentage ferrous oxidation. Assuming that the complex FeOH2+ should have a larger eguilibrium constant therefore results in much more accurate redox potential and ph prediction. The predictions seemed to be promising when the value of K (3) was increased by 200-fold. It was therefore decided to put more effort into obtaining a value for K(3) which would model the experimental results as closely as possible. K(3) was multiplied by various factors, while the other hydroxide equilibrium constants were kept as in Table A.46. The error for a given calculated point was taken to be the absolute of the difference between the calculated value and the experimental value. The results for K(6) - 0 are shown on Figure A.29. If the value of K(3) in Table A.46 is multiplied by 160, the average error is minimized, and is equal to 4,6 mv. The predicted values, using the new K (3), are compared with the ex erimental data in Figure A.30. Most of the error seems to be incurred at low percentage ferrous oxidation. The ph prediction is from 1,74 to 1,67, which is reasonable when compared with the experimental error of ±0,05 ph units (the ph was controlled at 1,60). 188

25 A similar minimizing procedure was followed to determine the smallest average error when including the complex Fe(S04)2~» This error was found to be 4,8 mv as opposed to the 4,6 mv obtained when setting K(6) = 0. It was therefore decided to accept Dry's rejection of this complex, as it did not lead to any improvement in the predictions. This complex is therefore excluded from further calculations. FIGURE A.29. Multiplying K(3) by Various* Amounts to Find the Value of K (3) Which Gives the Smallest Average Error in Prediction of Redox Potentials Recorded in Tests A. ( K ( 6 ) = 0 ) Average Error M B0 J2P Literature Value of K (3) multiplied by 189

26 FIGURE A.30. Modelling Redox Potential and ph Levels in Tests of Type A by Multiplying the Literature Value of K(3) (Table A.46) by 160. (Experimental Conditions: No Sulphide Mineral; 9 g/1 Soluble Iron; ph Levels of 1,6 and Temperatures of 37 C.) Redox Potential / mv -----, r --- ' r Iron in Ferric State / % * Average of Tests A.l - A.4 Calculated Values 190

27 It was appreciated that further work would be required to confirm the accuracy of the higher equilibrium constant (perhaps some other ferric hydroxide species could be involved as well), but this was considered to be outside the scope of this project. The relative amounts of ions in solution are given in Figures A.31 and A-32 for ferric and ferrous ion species respectively. Here K(6) - 0 and the new value of K(3) is used. Complexes that contain less than 1% of the total respective iron concentrations are not shown. The relative amounts of all the species in solution may be obtained in Appendix A.6.1 where the computer printout, from which the data for Figures A.30, A.31 and A.32 were obtained, is given. 191

28 FIGURE A.31. Tests A, Major Ferric Species Obtained When Modelling With K(3) - 9,04 x 1013 and K(6) - 0. Key : FeOH Feso.4 Fo14 i i i a b n Tron In Forrlc Stnta / t FIGURE A.32. Tests A, Major Ferrous Species Obtained When Modelling With K(L) - 9,04 x 1013 and K(6)» 0. Kay. -- Fe1* -- FeS04 TeHSO/ 0 V «U B «Iron in Ferric State / \ (Experimental Conditions: No Sulphide Mineral; 9 g/1 soluble Iron; ph Levels of 1,6 and Temperatures of 37 C.) 192

29 A.5. COMPUTER PROGRAMS A.5.1. Section A.5.1: Redox Potential and ph Prediction. Section A.5.2: Determination of Electrochemical Model Constants. Section A.5.3: Prediction of Extraction in Sterile Leaching. A.5.1. REDOX POTENTIAL AND ph PREDICTION Flowsheet: 193

30 Author Huberts Robert Name of thesis Application Of Electrochemical Kinetics To Elucidate The Leaching Mechanism In The Bio-oxidation Of A Synthetic Nickel Sulphide PUBLISHER: University of the Witwatersrand, Johannesburg 2013 LEGAL NOTICES: Copyright Notice: All materials on the University of the Witwatersrand, Johannesburg Library website are protected by South African copyright law and may not be distributed, transmitted, displayed, or otherwise published in any format, without the prior written permission of the copyright owner. Disclaimer and Terms of Use: Provided that you maintain all copyright and other notices contained therein, you may download material (one machine readable copy and one print copy per page) for your personal and/or educational non-commercial use only. The University of the Witwatersrand, Johannesburg, is not responsible for any errors or omissions and excludes any and all liability for any errors in or omissions from the information on the Library website.