The anodic behaviour of chalcopyrite in chloride solutions: Overall features and comparison with sulfate solutions

Abstract

The anodic behaviour of chalcopyrite at high potentials (transpassive region) in both sulfate and chloride solutions has been compared. It has been shown that the apparent plateau in the current/potential curve for the oxidation of chalcopyrite in dilute sulfuric solution at high potentials as observed in a recently published study has not been confirmed by several similar studies including the present one.Anodic oxidation at high potentials occurs at lower potentials in sulfate than in chloride solutions. Anodic oxidation in concentrated chloride solutions is more rapid at low potentials but severely inhibited relative to dilute chloride or sulfate solutions at high potentials. The behaviour in sulfate and chloride solutions has been confirmed by the results obtained from the oxidation of fine chalcopyrite particles that showed current peaks in the same potential regions as found using the bulk electrodes.The stoichiometry of anodic dissolution in both sulfate and chloride solutions at high potentials has confirmed published data of a consistent value of 6.5–6.7F/mol copper dissolved that is independent of the source of the mineral, potential and solution composition. An alternative mechanism involving initial oxidation to H2S2O2 and subsequent disproportionation to elemental sulfur and sulfate ions has been proposed that is consistent with the above stoichiometry and the yield of elemental sulfur.A possible explanation for slow oxidation in concentrated chloride solutions has been proposed that involves the formation of an inhibiting layer of S2Cl2 on the surface.