Leaching of chalcopyrite with ferric ion. Part III: Effect of redox potential on the silver-catalyzed process

This study examines the effect of redox potential on silver-catalyzed chalcopyrite leaching. Leaching tests were carried out in stirred Erlenmeyer flasks with 0.5 g chalcopyrite mineral, 1 g Ag/kg Cu and 100 mL of a sulphate solution of Fe³⁺/Fe²⁺ (with redox potential ranging between 300 and 600 mV Ag/AgCl) at pH 1.8, 180 rpm and 35°C or 68 °C. Unlike uncatalyzed leaching, an increase of the redox potential increased copper dissolution in the presence of silver ions, as the regeneration of Ag⁺ requires a high concentration of oxidizing agent, Fe³⁺. Additionally, the high reactivity of the mineral surface when silver was present could have been responsible for inhibiting the nucleation of hydrolysis products of Fe³⁺ on it. Excessive addition of silver transformed the chalcopyrite surface into copper-rich sulphides such as covellite, CuS, and geerite, Cu₈S₅, preventing the formation of CuFeS₂/Ag₂S galvanic couple and the recycling of silver ions.