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Bioleaching is the extraction of metals from their ores through the use of living organisms. This is much cleaner than the traditional heap leaching using cyanide. Bioleaching is one of several applications within biohydrometallurgy and several methods are used to recover copper, zinc, lead, arsenic, antimony, nickel, molybdenum, gold, silver, and cobalt. == Process == Bioleaching can involve numerous ferrous iron and sulfur oxidizing bacteria, including ''Acidithiobacillus ferrooxidans'' (formerly known as ''Thiobacillus ferrooxidans'') and ''Acidithiobacillus thiooxidans '' (formerly known as ''Thiobacillus thiooxidans''). As a general principle, Fe3+ ions are used to oxidize the ore. This step is entirely independent of microbes. The role of the bacteria is the further oxidation of the ore, but also the regeneration of the chemical oxidant Fe3+ from Fe2+. For example, bacteria catalyse the breakdown of the mineral pyrite (FeS2) by oxidising the sulfur and metal (in this case ferrous iron, (Fe2+)) using oxygen. This yields soluble products that can be further purified and refined to yield the desired metal. Pyrite leaching (FeS2): In the first step, disulfide is spontaneously oxidized to thiosulfate by ferric ion (Fe3+), which in turn is reduced to give ferrous ion (Fe2+): :(1) spontaneous The ferrous ion is then oxidized by bacteria using oxygen: :(2) (iron oxidizers) Thiosulfate is also oxidized by bacteria to give sulfate: :(3) (sulfur oxidizers) The ferric ion produced in reaction (2) oxidized more sulfide as in reaction (1), closing the cycle and given the net reaction: :(4) The net products of the reaction are soluble ferrous sulfate and sulfuric acid. The microbial oxidation process occurs at the cell membrane of the bacteria. The electrons pass into the cells and are used in biochemical processes to produce energy for the bacteria while reducing oxygen to water. The critical reaction is the oxidation of sulfide by ferric iron. The main role of the bacterial step is the regeneration of this reactant. The process for copper is very similar, but the efficiency and kinetics depend on the copper mineralogy. The most efficient minerals are supergene minerals such as chalcocite, Cu2S and covellite, CuS. The main copper mineral chalcopyrite (CuFeS2) is not leached very efficiently, which is why the dominant copper-producing technology remains flotation, followed by smelting and refining. The leaching of CuFeS2 follows the two stages of being dissolved and then further oxidised, with Cu2+ ions being left in solution. Chalcopyrite leaching: :(1) spontaneous :(2) (iron oxidizers) :(3) (sulfur oxidizers) net reaction: :(4) In general, sulfides are first oxidized to elemental sulfur, whereas disulfides are oxidized to give thiosulfate, and the processes above can be applied to other sulfidic ores. Bioleaching of non-sulfidic ores such as pitchblende also uses ferric iron as an oxidant (e.g., UO2 + 2 Fe3+ ==> UO22+ + 2 Fe2+). In this case, the sole purpose of the bacterial step is the regeneration of Fe3+. Sulfidic iron ores can be added to speed up the process and provide a source of iron. Bioleaching of non-sulfidic ores by layering of waste sulfides and elemental sulfur, colonized by ''Acidithiobacillus'' spp., has been accomplished, which provides a strategy for accelerated leaching of materials that do not contain sulfide minerals.〔Power, I.M., Dipple, G.M., and Southam, G. (2010) ''Bioleaching of ultramafic tailings by Acidithiobacillus spp. for CO2 sequestration'', http://pubs.acs.org/doi/abs/10.1021/es900986n Environmental Science & Technology. 44: 456-462.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bioleaching」の詳細全文を読む スポンサード リンク
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