Surface analysis of sulfur speciation on pyrite bioleached by extreme thermophile Acidianus manzaensis using Raman and XANES spectroscopy

Sulfur speciation on the surface of pyrite leached by extreme thermophile Acidianus manzaensis YN-25 was investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and sulfur K-edge X-ray absorption near edge structure spectroscopy (XANES). SEM micrographs showed leaching products with numerous holes were formed into the surface of leached pyrite. XRD spectra indicated that the leach residues were mainly composed of pyrite and jarosite. The sulfur K-edge XANES indicated that elemental sulfur, thiosulfate and/or thiosulfate-like species and jarosite were formed on the mineral surface. Raman spectroscopy further verified the presence of jarosite, elemental sulfur and thiosulfate. Jarosite formed in pyrite leaching appeared much later than in chalcopyrite leaching by the same strain. Jarosite on the mineral surface may account for the passivation of pyrite oxidation, with the passivation effect of elemental sulfur which is less important. In addition, the thiosulfate detected in this study provided novel evidence for surface-bound thiosulfate involved in the stepwise oxidation of pyrite by the extreme thermophile A. manzaensis.