Effects of Thermal Pretreatment on the Oxidative Dissolution of Chalcopyrite: Electrochemical Study with Synthetic Minerals

Understanding the leaching mechanism of chalcopyrite from natural resources is important for expanding Cu production via hydrometallurgical processes. This understanding could be effectively achieved by investigating the reaction phenomena using synthetic chalcopyrite with controlled compositions and morphologies. In this study, we prepared bulk samples of synthetic chalcopyrite and investigated the effects of thermal pretreatment on its oxidative dissolution behavior in acidic ferric sulfate solutions. Dense chalcopyrite pellets with a stoichiometric composition (Cu0.25Fe0.25S0.50) were prepared by subjecting the synthetic chalcopyrite powders to pulse current pressure sintering followed by annealing. Thermal pretreatment at 580 °C in a vacuum-sealed quartz ampoule resulted in the precipitation of a small amount of pyrite and a slight compositional change in the chalcopyrite phase. Leaching tests in 0.1 M Fe(SO4)1.5 − 10−4 M FeSO4 − 0.18 M H2SO4 solution at 70 °C revealed that thermal pretreatment increased the Cu extraction rate by approximately one order of magnitude and shifted the corrosion potential to a less noble value. Polarization measurements in 0.18 M H2SO4 solution at 70 °C showed that the anodic dissolution rate significantly increased after thermal pretreatment. We also prepared a nonstoichiometric and pyrite-free chalcopyrite sample and confirmed its high dissolution rate in the acidic ferric sulfate solution. Therefore, we conclude that the enhanced dissolution of chalcopyrite observed after thermal pretreatment is caused not by its galvanic interaction with the precipitated pyrite phase but by the change in its reactivity owing to small compositional changes.