Scholarly record

BIOOXIDATION OF FERROUS IRON IONS IN A PREGNANT SOLUTION OF OXIDATIVE LEACHING

А. Г. Булаев

Abstract

Despite biohydrometallurgy is widely used worldwide, new approaches are developed to increase its efficiency, for example, two-stage biohydrometallurgical processing of sulfide concentrates. In the first stage, raw material is leached with ferric sulfate solution at high temperature. In the second stage, Fe3+ ions in the pregnant solution should be regenerated using microorganisms. Screening of the microorganisms, which are capable of active ferrous iron concentration, is important for the development of novel biohydrometallurgical technologies. In this study, biooxidation of Fe2+ ions in pregnant solution of copper-zinc concentrate leaching containing (g/L) 3.4 Fe3+, 16.2 Fe2+, 1.6 Cu2+, and 11.9 Zn2+ was studied. Experiments were performed with moderately thermophilic and thermotolerant strains Sulfobacillus thermosulfidooxidans SH 10-1, S. thermotolerans Kr1T, Acidiplasma sp. MBA-1, A. aeolicum V1T, A. cupricumulans BH2T, mesophilic strain Acidithiobacillus ferrooxidans TFBK, and population of microorganisms from bioleach reactor, in which S. benefaciens and Ferroplasma acidiphilum were predominant. The strains were cultured on a shaker (200 rpm) in bottles with the solution at optimum temperatures for 16 days. The initial cell number was about 1?107 cell/mL. The effect of mineral salts ((NH4)2SO4, KCl, MgSO4, K2HPO4) and an organic carbon source (0.01% stillage and 0.01% molasses) addition on oxidation rate was studied. A. cupricumulans BH2T oxidized of 45 to 75% of iron, most rapidly iron was oxidized in solution with mineral salts and organic substrates (75%). In the case of A. aeolicum V1T, addition of mineral salts and organic carbon sources did not allow to increase oxidation rate (33?43% of iron was oxidized), and iron was most rapidly oxidized in the pregnant solution without additional components (43%). The addition of mineral salts and organic substrates increased the rate of oxidation by the strain Acidiplasma sp. MBA-1 (in the solution with mineral salts and organic substrates 76% of iron was oxidized), and about 40% of Fe2+ was oxidized in a solution without additional components. S. thermosulfidooxidans SH 10-1 oxidized about 30% of Fe2+ in all experiments. In experiments with the S. thermotolerans Kr1T, 17 and 19% of Fe2+ were oxidized in solutions without additional components and with organic substrates, respectively, while in the solutions with mineral salts, as well as with salts and organic substrates, 26 and 29% of ferrous iron were oxidized. A. ferrooxidans TFBK oxidized in solution with mineral salts about 32% of Fe2+, while in other variants rate of oxidation was about 15%. Mixed culture oxidized iron completely in the experiment with the solution without additional components, while in other variants, of 39 to 51% of ferrous iron was oxidized. The most rapid Fe2+oxidation by mixed microbial population can be explained by the long-term adaptation to high concentrations of metal ions during biooxidation of the concentrate.

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