The anodic behaviour of chalcopyrite in chloride solutions: Voltammetry

This paper summarizes the results of a voltammetric study of the anodic characteristics of chalcopyrite in the potential region relevant to heap leaching in concentrated chloride solutions. Distinct peaks in the potential region of 0.7 to 0.85 V have been observed in the voltammograms, the magnitude of which depend on the chloride concentration and, particularly, the pH in the range 1 to 3. Three peaks are observed at low chloride concentrations that merge into one peak at higher concentrations. The anodic reactivity increases with increasing pH but shows a complex dependence on the chloride concentration while in the presence of added copper(II) ions, the mixed potential shifts to more positive potentials and only one peak is observed. Hysteresis between the forward and backward-going sweeps has confirmed the transient nature of the processes except at potentials below about 0.75 V in which region the system approaches steady-state behaviour. The voltammetric characteristics of chalcopyrite in this system appear to be very similar to those of covellite. Measurements of the initial rates of dissolution (in the range 1–5 × 10^{− 10} mol cm^{− 2} s^{− 1} depending on the conditions) have been made that confirm the voltammetric trends and compare well with previously published rates. Linear free energy relationships have been used to estimate the thermodynamic properties (Gibbs free energy − 100.7 kJ/mol) of the simplest polysulfide, namely CuS₂ and possible mechanisms for the various steps in the anodic dissolution and passivation of chalcopyrite have been suggested that are consistent with the thermodynamic predictions.