Title: Investigation of copper, iron and sulfur speciation during bioleaching of chalcopyrite by moderate thermophile Sulfobacillus thermosulfidooxidans
Abstract: The copper, iron and sulfur speciation of chalcopyrite leached by moderate thermophile Sulfobacillus thermosulfidooxidans was investigated by combining synchrotron radiation X-ray diffraction (SR-XRD) and X-ray absorption near edge structure (XANES) spectroscopy. Leaching experiment showed that the leaching rate of copper was 73.6% after 20 days bioleaching. Results of scanning electron microscopy of leaching residues showed that the surface of chalcopyrite was gradually corroded. Results of SR-XRD showed that orthorhombic form α-S8, jarosite and chalcocite were produced at day 4; the bioleaching residue contained jarosite, covellite and α-S8 besides chalcopyrite from day 8. The Cu, Fe and S K-edge XANES spectra quantitatively analyzed the copper, iron and sulfur species compositions of leaching residues, and the fitted results showed similar trend to SR-XRD results. According to both SR-XRD and XANES study, bornite and amorphous elemental sulfur μ-S were not found during bioleaching of chalcopyrite by S. thermosulfidooxidans. By conclusion, it indicated that iron-deficiency sulfide chalcocite first formed at the initiation of bioleaching with a low Eh value, and it then gradually transformed to covellite at a high Eh value. Meanwhile, α-S8 and jarosite were produced as the predominant intermediates. By combining SR-XRD and XANES, it was useful for better understanding the dissolution mechanism of chalcopyrite during bioleaching by qualitatively and quantitatively analyzing in situ the surface chemical composition of the minerals.