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. Crown Copyright (C) 2014 Published by Elsevier Ltd. All rights reserved.