Superficial compounds produced by Fe(III) mineral oxidation as essential reactants for bio-oxidation of pyrite by Thiobacillus ferrooxidans

In experiment of pyrite bioleaching by Thiobacillus ferrooxidans (DSM 583), the use of a K+ sulfonic resin to exchange ferrous and ferric ions of the medium in order to eliminate soluble bacterial substrate and mineral oxidiz ing agent, showed that the bacterial population does not grow efficiently i f any substrate, except FeS2, is available. On the other hand, if the mediu m is free of any chemical oxidizing agent, the sulfide mineral is not oxidi zed and the leaching does not occur. Moreover, a physico-chemical approach showed that elemental sulfur and ferrous sulfate chemically produced at min eral surface by the action of free ferric ions, are effective substrates fo r the bacteria. These, non fully oxidized superficial phases (Sg, FeSO4) ar e essential reactants because Thiobacillus ferrooxidans is unable to perfor m the direct oxidation of the mineral. Their nature, amount and spatial dis tribution control the kinetics of leaching and the corrosion of pyrite grai ns.