| Biohydrometallurgy is a technology that refer to the processing of valuable metal dissolution into the leaching solution and metal recovery or dissolution of heavy metals in minerals assisted by microbial activity and microbial oxidation. Its process is relatively low cost, environmental friendly, mild reaction conditions and offers an extensive attention in the pretreatment of refractory gold ores.This study focused on biooxidation process as a pretreatment of arsenopyrite-bearing gold concentrate by using Leptospirillum ferriphilum. Firstly, L. ferriphilum ATCC 49881 was grown in 9K medium to determine the optimum biooxidation activity. The following results as below:1. L. ferriphilum ATCC 49881 growth that investigated in 9K medium demonstrated that: at various initial pH, L. ferriphilum ATCC 49881 exponential growth phase occurred in 12 to 50 hours, while its highest cells density occurred after cultivation for 97 h (about 8.2 x 106 cells/ml,5.6 x 106 cells/ml,6.4 x 106 cells/ml for initial pH 1.6, pH 1.8 and pH 2.0, respectively).2. By using Lineweaver burk linear plotting for the Monod equation, it showed the cell growth kinetics of maximum specific growth rate (μmax) were determined as 0.076 h-1,0.178 h-1,0.020 h-1 for the initial pH 1.6,1.8 and 2.0, respectively and half saturated coefficient (Ks) were determined as 1.048 g·L-1,1.865 g·L-1, and 0.027 g·L-1 for the initial pH 1.6,1.8 and 2.0, respectively. Based on the calculation results, the highest maximum specific growth rate (μmax) occurred at initial pH 1.8, indicated its initial pH 1.8 as the optimum growth condition of L. ferriphilum.3. At the initial pH 1.6,1.8, and 2.0, the maximum biooxidation rates of ferrous ions oxidation, rFe2+max, were determined as 0.156 g·L-1·h-1,0.119 g·L-1·h-1,0.073 g·L-1·h-1, respectively and ferrous ions half saturated coefficient (KFe2+) were determined as 0.327 g·L-1, 0.116 g·L-1, and 0.051 g·L-1 for the initial pH 1.6,1.8 and 2.0, respectively. Determination of ferrous ions oxidation rate of L. ferriphilum culture represents the relationship between microbial oxidation activity and pH solution, when initial pH was increased then the rate of ferrous ions oxidation decreased, indicated biooxidation activity of L. ferriphilum decreased. At higher pH value, ferric iron produced from the ferrous oxidation prefer to form a precipitate.Afterwards, the effect on biooxidation process of arsenopyrite-bearing gold concentrate by L. ferriphilum under variation of chemical compound added to the medium was investigated, the results show:1. The preliminary study demonstrated the capability of the L. ferriphilum in oxidizing arsenopyrite within 6 days which proved by X-ray diffraction (XRD) analyses. The elemental sulfur and ferrous iron produced was used for the subsequent reaction.2. The variation of chemical compounds adding including elemental sulfur, ferrous sulfate and ferric sulfate on biooxidation process of arsenopyrite-bearing gold concentrate by L. ferriphilum showed the elemental sulfur adding in the arsenopyrite-bearing gold concentrate was not affected the biooxidation process of arsenopyrite with L. ferriphilum; the ferric iron and ferrous addition in the arsenopyrite-bearing gold concentrate could enhance the biooxidation process.At last, the kinetics study of L. ferriphilum biooxidation of arsenopyrite-bearing gold concentrate was investigated. Results showed that biooxidation was occurred in the first order reaction kinetics, and indicated the initial ferrous and ferric iron concentration could affect the arsenopyrite biooxidation rates. Results showed that 1% of ferric sulfate addition into the arsenopyrite-bearing gold concentrate was the optimum biooxidation rate which could generate the highest total dissolved arsenic concentration. |
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