Bioleaching

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.

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⁺):

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