Biochemistry of sulfur extraction in bio-corrosion of pyrite by Thiobacillus ferrooxidans

By adding a small amount of the aminoacid cysteine in acidic solution exposed to pyrite, the duration of the lag phase in the growth of Thiobacillus ferrooxidans is minimized and the leaching rate of this sulfide is increased three times compared to the normal process without this biochemical additive. In the presence of cysteine, pyrite can be oxidized in absence of oxygen or bacteria with a leaching rate comparable with that attained by bacteria under normal leaching conditions. It seems that the sulfhydril group of cysteine participates in a binding process with pyrite. Free-SH groups from the pyrite surface would be the counterpart for the formation of the corresponding disulfide. This thiol-disulfide reaction means that cysteine is consumed by the pyrite surface with the subsequent release of iron-sulfur species. This result is accounted for by the fact that pyrite without bacteria can be completely oxidized. Bacteria would take advantage of this abiotic corrosion process by uptake and oxidation of the released species which are continuously supplied to the thiobacilli-biotope. The reactivity of this thiol biochemical compound with the pyrite surface, which improves the bacterial corrosion rate, suggested the investigation of other mono-thiol molecules with the aim to mask the SH pyritic groups. Tert-butyl mercaptan [(CH3)(3)C-SH: TBM] can be applied to the pyrite surface to stop the bacterial corrosion. Permanent disulfide bonds between pyrite and the blocking SH-agent are the cause for this protection.