A scanning electrochemical microscopy (SECM) study of the interfacial solution chemistry at polarised chalcopyrite (CuFeS2) and chalcocite (Cu2S)

[Display omitted] •The interfacial chemistry of chalcopyrite and chalcocite has been probed using SECM.•Incomplete chalcopyrite oxidation leads to variations in copper stripping peaks.•Sulfide-derived Cu species deposited on the SECM tip marks chalcopyrite passivation. Chalcopyrite (CuFeS2) passivation during hydrometallurgical copper extraction is attributed to multiple competing mechanisms that are still not completely understood. Here we have studied the interfacial solution chemistry in situ at polarised chalcopyrite and chalcocite, using scanning electrochemical microscopy (SECM). It was observed that the copper species detected at an ultramicroelectrode (UME) positioned at the mineral:solution interface vary between the two minerals, and are dependent upon both the potential of the mineral and the polarisation time. Cu species formed in the presence of sulfide, derived from incomplete oxidation of chalcopyrite, are observed on the UME tip positioned above chalcopyrite under conditions where passivation may occur, in contrast to Cu(II) in the presence of sulfate under conditions where leaching is facile. Only Cu(II) in the presence of sulfate is observed at the interface of chalcocite. These observations via interfacial voltammetry provide experimental support to mechanistic studies on chalcopyrite leaching, and provide new information to complement previous in situ studies which have mostly focused on interfacial solids.