Enargite leaching under ammoniacal media with sodium persulfate and consecutive precipitation of As/Cu with Na2S/NaHS

Enargite ore (Cu3AsS4) is generally processed via pyrometallurgy, with high temperatures that release toxic arsenic (AsxOy) and sulfur (SOx) gases. In seeking alternatives that avoid production of noxious gases, this paper discusses batch leaching experiments of mineral mixtures of enargite and pyrite (Cu3AsS4 and FeS2), agitated under ammoniacal media (NH4OH) using sodium persulfate (Na2S2O8) as an oxidant. The results showed that almost complete leaching of enargite (98%) could be obtained due to the elimination of passivation (S°) by the action of the oxidant. With the help of a deep thermodynamic study and with DRX analysis, it was possible to establish the reaction mechanisms of dissolution of enargite with persulfate in an ammoniacal media. Leaching action selected for enargite, not affecting pyrite present. Enargite leaching can be represented under a heterogeneous kinetic model of reactant diffusion through a porous layer formed at reaction time. Orders of reaction 2.0 and 1.5, for persulfate and ammonium hydroxide concentrations, respectively, were established. Activation energy was calculated at 45.0 kJ/mol. Consecutive evaluations showed that metals present (Cu and As) could be precipitated with sodium sulfide and sodium hydrosulfide at 99% yields, thus generating a solution rich in ammonia that can be re-used in leaching.