In-situ probing of electrochemical dissolution and surface properties of chalcopyrite with implications for the dissolution kinetics and passivation mechanism

Abstract

Hypothesis: The anodic dissolution of chalcopyrite (CuFeS2) encounters the problem of surface passivation, which significantly affects the copper extraction efficiency. So far, there is no agreement on the passivation mechanism and composition of passive layer, which could be studied by using in-situ scanning electrochemical microscopy (SECM).Experiments: SECM was applied for the in-situ probing of chalcopyrite dissolution under mild oxidation potentials. The surface hydrophobicity and nanoscale distribution of hydrophobic domains were analyzed by static water contact angle measurement and atomic force microscope (AFM) force mapping, respectively. The surface conductivity was characterized by SECM feedback mode.Findings: The concentrations of released species Fe2+, Cu2+ and soluble copper sulfide species (CuxS) generally increased with the potential of chalcopyrite. In the active region (low potentials), Fe2+ was preferentially released, and the metal-deficient sulfide layer that was rich in copper relative to iron started to form as the passive layer. While the release of Fe2+ and Cu2+ was impeded in the passive region, the detected CuxS became pronounced in this region and the following transpassive region, which suggested that the existence of CuxS was a result of passive layer dissolution. The nanoscale distribution of hydrophobic domains suggested that the formation of hydrophobic passive layer initiated in the active region and this layer almost completely covered the chalcopyrite surface at the beginning of passive region. The surface conductivity of chalcopyrite decreased with potential due to the formation of less conductive metal-deficient sulfide layer and possibly insulating elemental sulfur (in the transpassive region). This work provides a new approach for the in-situ probing of chalcopyrite dissolution and useful insights into its dissolution kinetics and passivation mechanisms, with implications for similar electrochemical processes of other mineral surfaces.