The semiconductor mechanism of dissolution and the pseudo-passivation of chalcopyrite

The dissolution of chalcopyrite has received a significant amount of attention. The predominant paradigm of investigation is that its rate of dissolution is limited or passivated by a surface coating or film of material. The common candidates for such a passivating coating are numerous: polysulphide coating, metal deficient layers, copper sulphide coating, bornite layers, jarosite precipitates, and elemental sulphur films. While this line of explanation, that is, the explanation based on passivation, seems to have won some form of consensus with researchers, there is another explanation for the results that can account for all the results observed. Crundwell(1) proposed that the solid state properties of chalcopyrite, in particular, the semiconducting properties, are responsible for the observed behaviour of chalcopyrite. This paper outlines the semiconductor mechanism of dissolution, shows how this mechanism accounts for the dissolution behaviour of chalcopyrite, and provides clear reasoning for the slow dissolution kinetics of chalcopyrite. In particular, an explanation is provided for: (i) the shape of the current-voltage curve, (ii) for the flat region between 0.3 and 0.6 Vv. SCE; (iii) the onset of the active region from 0.6 Vv. SCE onwards; (iv) the reactivity of redox couples; and (v) for the preferential dissolution of iron. In addition, the explanation makes a prediction for the effect of light, for which results are presented.