The influence of silver ion on the electrochemical response of chalcopyrite and other mineral sulfide electrodes in sulfuric acid

Abstract

The electrochemical behavior of chalcopyrite electrodes in H 2SO 4 solutions with and without silver ion has been investigated and has provided additional information concerning the enhanced or catalyzed leaching rates previously observed for the ferric sulfate leaching of CuFeS 2 in the presence of Ag +. A careful analysis of the cyclic voltammetry for CuFeS 2 electrodes in the presence of silver ion, indicates the formation of Ag 2S and metallic silver on the chalcopyrite surface, and that cyclic voltammetry for CuFeS 2 in solutions containing Ag + is an integration of the electrochemical responses for CuFeS 2 and Ag 2S. Consistent with previously reported leaching responses, additions of Ag + up to an optimum of approximately 10 -3M result in higher anodic currents for CuFeS 2 electrodes Concentrations of 10 -3M and larger cause a decrease in current which is attributed to the precipitation of Ag 2SO 4. The effect of Ag + on the individual anodic and cathodic half cell reactions has also been examined by means of a dual cell apparatus and has shown that added silver affects the anodic dissolution reaction and has no effect on the cathodic half cell, i.e. the Fe 2+/Fe 3+ couple. These results along with mass balances performed at constant anodic potential are considered in the context of reactions between CuFeS 2 and added silver which are indicated. The apparent catalysis is believed to occur through a change in morphology or conductivity of the normally protective sulfur layer which forms on CuFeS 2 through reactions involving Ag 2S or elemental silver. A preliminary exploration of other systems in which catalysis or enhancement may be found has also been briefly investigated using ZnS and PbS electrodes.