The effect of electrolyte composition on the cathodic reduction of CuFeS 2

Abstract

The electrochemical reduction of CuFeS 2 mineral electrodes has been investigated by performing cathodic polarization curves, constant potential experiments, and cyclic polarization curves in various electrolytes. The effects of H 2SO 4, Fe 2+ and Cu 2+ concentrations have been examined as well as the effects of various dissolved gases, air, O 2, H 2S and N 2. Decreasing H 2SO 4 only shifts the curve to more negative potentials but initial concentrations of 0.36 M Fe 2+ cause up to a ten-fold enhancement in the observed current. The presence of oxygen or Cu 2+ also leads to an increase in the reduction current but in either case further increases in current are observed when Fe 2+ is added to the electrolyte. Chalcocite (Cu 2S) or djurleite (Cu 1.96S) have been identified as products of reaction, although it is possible that a thin layer of a different copper-iron sulfide may form as an intermediate based on the color changes which appear after cathodic excursions. In addition, scanning Auger microprobe analyses of these surfaces show an increasing Cu:Fe ratio as the time at potential is increased. The results also indicate that the solid product layer is porous. A mechanism which accounts for the observed current increase in the presence of Fe 2+ is proposed which involves a redox reaction between dissolved Fe 2+ and cupric ion in the copper sulfide product layer.