Enhanced leaching of chalcopyrite at low potentials in chloride solutions 2. Mechanisms

Abstract

In a previous paper in this series, it was shown that enhanced leaching of chalcopyrite from a number of concentrates in acidic chloride solutions can be achieved by controlling the potential in a range of 560-600 mV (SHE) in the presence of dissolved oxygen. The addition of fine pyrite enhanced the rate of dissolution under these conditions. Based on the results of these leaching experiments and detailed mineralogical analyses of the residues, a mechanism involving non-oxidative dissolution of the mineral coupled to oxidation of the product hydrogen sulfide is proposed. The latter reaction is shown to occur predominately by a copper ion- catalyzed reaction with dissolved oxygen. The results of an independent study of the kinetics of this reaction will be presented which will demonstrate that the rates are consistent with those obtained for the dissolution of the mineral. The possible involvement of a covellite-like surface layer on the chalcopyrite under some conditions will also discussed as it relates to the mechanism. It will also be shown that fine pyrite particles can also act as a catalyst surface for the oxidation of hydrogen sulfide. This mechanism is consistent with the mineralogy which confirmed the formation of secondary sulfur which is not directly associated with chalcopyrite except at high pH (about 2) values but is found as discrete globules and associated with fine pyrite if present. A comparison of this mechanism with those proposed in other more limited studies of the dissolution of chalcopyrite under similar conditions in sulfate solutions has been made