An integrated approach to evaluating the effect of associated minerals on copper ammoniacal thiosulfate leaching of a gold–bearing sulfide concentrate

This work proposes a method for the evaluation of the effect of galvanic interactions between intergrown sulfide-mineral grains present in a thiosulfate leaching system, based on a combination of electrochemical measurements. Several common associated minerals in complex sulfide ore (CSO), as well as high purity sulfide minerals (pyrite, arsenopyrite, chalcopyrite, sphalerite, and galena), were used to develop and test the method. The reactivity of the CSO and each individual sulfide mineral in an ammoniacal thiosulfate solution was determined by voltammetry and chronoamperometry, using carbon paste electrodes and rotating disk electrodes (RDE). Secondary phase formation and the surface alteration of both the individual and associated minerals were evaluated by in-situ Raman spectroscopy and ex-situ cyclic voltammetry in 0.1 M NaNO3 aqueous solution. Chalcocite (Cu2S) and covellite (CuS) were identified as intermediate products of chalcopyrite leaching, while pyrite was oxidized to ferrous hydroxide and later to magnetite. Results showed that pyrite in CSO acts as a cathodic side, promoting the reduction of oxygen. Thus, the oxidation of pyrite was delayed due to the galvanic protection offered by arsenopyrite and chalcopyrite. Mineralogy and evaluation of the mineral textures both of the ore and its modification as a result of leaching were used to validate the method.