The electrochemistry and kinetics of the oxidative dissolution of chalcopyrite in ammoniacal solutions. Part II – Cathodic reactions

The cathodic reduction of copper(II) and oxygen on the surface of chalcopyrite have been studied in ammonia-ammonium sulphate using cyclic voltammetry and chrono-amperometry. The predominant cathodic reaction in the oxidative dissolution of chalcopyrite in ammoniacal solutions has been established to be that of the reduction of copper (II). The rate of the cathodic reaction is inversely dependent on the total ammonia concentration and although the tetra-ammine copper(II) ion is the most dominant species under these conditions, it is suggested that the tri-ammine complex is the most electroactive under these conditions. It was shown that both the reduction of copper(II) and oxidation of copper(I) occur simultaneously at potentials close to the mixed potentials of chalcopyrite under the conditions of this study and apparent mass transfer limitations observed on the reaction were concluded to be due the outward migration of the product of Cu(I) ions from the mineral surface.