Scanning photoelectron microscopy studies of freshly fractured chalcopyrite exposed to O2 and H2O

It is possible that the mechanism of SO42− formation on chalcopyrite is similar to the electrochemical mechanisms proposed for pyrite involving attack by O2 at surface Fe sites resulting in formation of Fe-O species (cathodic reaction) and electron withdrawal from neighbouring surface sites (anodic reaction). This induces dissociation of H2O attached at adjacent Fe sites resulting in the release of H+, and nucleophilic attack of the resultant OH− group onto the electron depleted surface S, to form SO moieties. The oxidation state of Cu on freshly fractured and moderately oxidised chalcopyrite surfaces examined in this study remains as +1, no evidence for the formation of Cu2+ was found.