Direct extraction of copper from copper sulfide minerals using deep eutectic solvents

Abstract

Copper is predominantly recovered from sulfide ores by pyrometallurgy – an energy intensive process requiring capture and treatment of released SO₂. Whilst some copper ores are amenable to hydrometallurgy, chalcopyrite, the main copper mineral, is challenging to process in aqueous solutions due to surface passivation. The chalcopyrite surface may be less prone to passivation in non-aqueous solvents such as Ionic Liquids. Here we provide the first demonstration that electrochemistry in Deep Eutectic Solvents can solubilise and directly recover high purity copper from solution from three copper sulfide minerals: covellite (CuS), chalcocite (Cu₂S) and chalcopyrite (CuFeS₂). Cyclic voltammetry supported by EXAFS identifies the metal speciation in solution. In a choline chloride-ethylene glycol DES the main copper species present after dissolution of chalcocite and covellite was [CuCl₄]²⁻. In the solution formed from chalcopyrite, a mix of Cu^II and Cu^I species were formed instead. In a choline chloride-urea DES, copper had a mixed chloride/O- or N-donor coordination, potentially altering electrochemical behaviour. Sulfide in the mineral is oxidised to sulfate without the generation of SO₂ or H₂S. The best selective recovery of copper (99 at%) from chalcopyrite was obtained with a mixed DES of 20 wt% choline chloride-oxalic acid and 80 wt% choline chloride-ethylene glycol. This demonstrates how design of the Deep Eutectic Solvents can enable increased selectivity of copper over iron in the electrowinning stage by changing solute speciation and redox properties.