Acid bake-leach process for the treatment of enargite concentrates

As an alternative to roasting, low-temperature (100–200 °C) sulfuric acid baking of an enargite concentrate followed by water-leaching has been evaluated. Results indicate the thermal transformation of enargite and pyrite during sulfuric acid baking. By acid baking of an enargite concentrate at 200 °C for 7 h, ~ 90% Cu and ~ 61% As were released to the leach solution, with < 1% of arsenic being released to the gas phase. The effects of time and temperature were studied on the baking reactions. Extended reaction times (24 h) at lower baking temperatures (170 °C) resulted in lower Cu and As extraction and higher As release to the gas phase (~ 11%). The pH of the water leach solution was always ~ 0.8–2 after extraction due to residual acid, making it suitable for subsequent copper recovery. The oxidation-reduction potential (ORP) of the leach solution fell within the range 491–566 mV (vs. SHE) depending on the baking conditions. The ratio of ferric/ferrous ions in the leach solution showed considerable dependence to reaction time and temperature. Based on this study, some reactions are proposed for the sulfuric acid baking of enargite.