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.

Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Acid bake-leach process is promising for the treatment of enargite concentrates. ► Arsenic release to the gas phase was much less than the roasting process. ► Enargite transforms to copper sulfate and a soluble arsenic compound. ► ~ 90% Cu and ~ 61% As released to the leach solution. ► Only < 1% of arsenic released to the gas phase.