A novel approach for metal extraction from metal sulfide ores with NH4Cl: A combined DFT and experimental studies

Abstract Chalcocite (Cu2S) is the main source for metallurgical production of copper worldwide but it usually co-exist with nickel sulfide in nature. To develop an efficient and green process for the separation and extraction of valuable metals from high-grade matte, we performed density functional theory (DFT) calculations and experimental studies to elucidate chlorination mechanism of Cu2S with ammonium chloride (NH4Cl). First, NH4Cl can react with Cu2S directly in the absence of O2, leading to the formation of H2S and NH3 with negative adsorption energies. Second, O2 can promote the chlorination process by providing adsorbed O and promoting the dissociation of HCl decomposed from NH4Cl, leading to the formation of H2O and CuCl species eventually. Besides, SO2 generated at the Cu2S surface after O2 dissociative adsorption, may leading to the generation of Cl2. Finally, the chlorination can also be achieved by the interaction between Cu2S and Cl2, which is favored thermodynamically and kinetically. Based on the computational results, low-temperature roasting experiments were performed. Cu2S was successfully converted into the corresponding metal chloride (CuCl) by NH4Cl in the absence of O2, but the chlorination process is incomplete with unreacted Cu2S. However, the conversion from Cu2S to CuCl is complete under air atmosphere, consistent with our computational results. Furthermore, metallic copper was successfully obtained at the cathode through electrodeposition with CuCl. The present study reveals detailed reaction mechanism between Cu2S and NH4Cl, and shows the chlorination of Cu2S by NH4Cl followed by electrodeposition of the resulting CuCl as a highly efficient and green process.