XANES and XRD study of the effect of ferrous and ferric ions on chalcopyrite bioleaching at 30 C and 48 C

The effect of Fe²⁺/Fe³⁺ ratio on chalcopyrite bacterial and chemical leaching has been studied by X-ray absorption near edge structure (XANES) spectroscopy, X-ray diffraction (XRD) and Raman spectroscopy. The leaching results indicate a high Fe²⁺/Fe³⁺ ratio, which keeps the Eh at a relatively low range (350-480 mV vs. Ag/AgCl), can significantly promote the dissolution of chalcopyrite during either bioleaching or chemical leaching. Jarosite was found as a major leaching product that accumulated more rapidly with higher initial Fe²⁺/Fe³⁺ ratio and at higher temperature. Elemental sulfur was also found as an intermediate that was effectively eliminated by sulfur-oxidizing bacteria. Passivation of chalcopyrite dissolution occurred in the late stages of leaching and was observed under all conditions. However, the results suggest that neither jarosite nor elemental sulfur seems to be the primary passivation factor. During chalcopyrite dissolution a covellite-like phase was detected, which is likely to be an intermediate formed in chalcopyrite direct oxidation or converted from chalcocite at low redox potential.