Raman study of the microbially mediated dissolution of pyrite by Thiobacillus ferrooxidans

Raman spectroscopy was applied to the microbially mediated dissolution of pyrite by high density (more than 10(9) cells) of Thiobacillus ferrooxidans. In the range 600-200 cm(-1), peaks corresponding to secondary minerals such as elemental sulfur and jarosite were observed in addition to those of pyrite. Small amounts of elemental sulfur and poorly crystalline jarosite were detected by Raman spectroscopy, but are undetectable by X-ray diffraction and Fourier transform infrared spectroscopy. Ammoniojarosite was predominantly formed in microbially mediated dissolution of pyrite with a high density of cells, whereas jarosite was formed in the sterilized control. This finding is probably ultimately due to the much greater amount of jarosite precursors (Fe3+ sulfate complexes) formed by the bacterial oxidation of iron. Initially, and in both cases, the kinetically favored jarosite appeared, but in the presence of bacteria, there was so much precursor present that the available potassium was exhausted. Ammoniojarosite subsequently was formed. In the sterilized control, precursors were less readily formed, and jarosite formed. There was no evidence for direct involvement of bacteria in the formation of jarosite. The changes in mineral compositions are correlated with those in the solutions. Raman spectroscopy was used to follow compositional changes in minerals during the microbially mediated dissolution of pyrite.