Control of iron and sulfur oxidation activities of Thiobacillus ferrooxidans and bacterial leaching of metals from sulfide ores

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Harahuc, Lesia
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'Thiobacillus ferrooxidans' is a dominant member of the bioleaching community responsible for mineral solubilization. In order to capitalize on its natural ability to solubilize metal sulfides this study began with a detailed analysis of the bacteria's iron and sulfur oxidation pathways. Only those cells grown in the presence of high iron concentrations retained the ability to oxidize ferrous iron. Sulfur oxidation was faster in sulfur grown cells but in both the iron and sulfur grown cells it proceeded via a sulfur oxidizing system which used molecular oxygen as the terminal acceptor. Iron grown 'T. ferrooxidans' oxidized sulfite by a free radical mechanism initiated by Fe3+ on the cell surface, with cytochrome oxidase involved in the regeneration of Fe3+ by the normal Fe2+ oxidizing system. Metal extraction from mineral ore by 'Thiobacillus ferrooxidans ' is achieved through two reactions: the oxidation of ferrous iron to ferric and that of sulfide/sulfur to sulfuric acid. The oxidation of either ferrous iron or sulfur by 'Thiobacillus ferroxidans' was selectively inhibited or controlled by various anions, inhibitors and osmotic pressure. Bacterial leaching of sulfide ores using 'Thiobacillus ferooxidans, Thiobacillus thiooxidans' or a combination of the two was studied under various anionic concentrations. Selective zinc and copper solubilization was obtained by inhibiting iron oxidation without affecting sulfur/sulfide oxidation. Phosphate reduced iron solubilization from a pyrite (FeS2 ) - sphalerite (ZnS) mixture without significantly affecting zinc solubilization. Copper leaching from a chalcopyrite (CuFeS2) sphalerite mixture was stimulated by phosphate, while chloride accelerated zinc extraction. In a complex sulfide ore containing pyrite, chalcopyrite and sphale ite both phosphate and chloride reduced iron solubilization and increased copper extraction, while only chloride stimulated zinc extraction. Mineral solubilization under natural conditions is a combination of chemical and biological reactions. The chemical or indirect method of mineral solubilization involved the use of bacteria in the regeneration of ferric iron as oxidizing agent. In order to maximize ferric iron production 'T. ferrooxidans ' was grown on a variety of cell carriers to increase cell concentrations. (Abstract shortened by UMI.)