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EFFECT OF MOLYBDENUM AND MANGANESE ON FERROUS IRON BIOOXIDATION BY ACIDOPHILIC BACTERIUM ACIDITHIOBACILLUS FERROOXIDANS

Khusain Valiev

Abstract

Acidophilic microorganisms oxidizing ferrous iron and sulfur are widely used in hydrometallurgy to extract different metals including copper, zinc, nickel, cobalt, and uranium from sulfide ores. The activity of microorganisms and screening of microbial strains capable of biooxidation of ferrous iron and sulfur compounds under different conditions, i.e. in the present of different toxicants, which may be present in treated ores, are crucial for the development of biohydrometallurgical technologies. Different factors affect rate of biooxidation of ferrous iron, sulfur compounds, and sulfide minerals. It is well known that different metal ions, which may be accumulated in liquid media during biooxidation of different ores, can inhibit microorganisms providing this process. Therefore, it is necessary to evaluate the effect of different toxic ions on the activity of microorganisms to obtain the data on threshold concentrations of metal ions, which should not be exceeded during the bioleaching processes. In the present study, we investigate the effect of molybdate and manganese (Mn2+) ions on biooxidation of ferrous iron by the strain of acidophilic bacterium Acidithiobacillus ferrooxidans isolated from the sample of acid drainage from Vostok uranium deposit (Kazakhstan). These ions were studied because the ore contains up to 0.04% of molybdenum, while pyrolusite (MnO2) is often used as an oxidant for uranium acid leaching. The experiments in ferrous iron biooxidation was performed using mineral liquid medium containing Fe2+. Cultivation of the strain was performed on a rotation shaker at 28°C (the temperature was close to optimum for the studied strain). Effect of molybdenum was studied at a concentration range of 0.0025 to 0.3 g/L. It was demonstrated that molybdenum concentration up to 0.05 g/L did not inhibit biooxidation significantly, while higher concentration depressed the microbial activity. In the same time, manganese, concentrations of which in the medium comprised of 2.5 to 30.0 g/L, almost did not inhibit ferrous iron oxidation. Thus, it was shown that studied ions differed in inhibition activity that should be taken in consideration during bioprocessing of the ores.

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