Effect of cysteine on the electrochemical dissolution of chalcopyrite

Abstract

The effect of cysteine on the electrochemical dissolution of chalcopyrite (CuFeS2) in sulfuric acid solutions in the presence and absence of ferric sulfate has been studied.The effect of cysteine on the dissolution current density of the CuFeS2 electrode was different depending on the presence or absence of ferric sulfate. In the absence of ferric sulfate cysteine inhibited the dissolution process due to different factors: the adsorption of cysteine on the surface of the electrode that resulted in 80% losses of the active area, an increase in thickness of the film formed on the surface of CuFeS2 and an increased resistance to the solid-state diffusion of metallic ions within this film.In the presence of ferric sulfate cysteine was oxidized to cystine. Cystine acted as an oxidant for CuFeS2 and increased the dissolution current density. Reduction of cystine on the surface of CuFeS2 may have resulted in its dissociative adsorption to yield two adsorbed molecules of cysteine. In the presence of ferric sulfate these adsorbed molecules could also have enhanced the electron transfer between the CuFeS2 and the aqueous Fe3+ species. In the presence of ferric sulfate, cysteine (or cystine) decreased the thickness of the film formed on the surface of CuFeS2 and facilitated the transport of ions at the electrolyte/electrode interface.