Chalcopyrite leaching in novel lixiviants

Abstract

Chalcopyrite (CuFeS2) makes up a large and increasing fraction of the world's future copper resources, but is highly refractory to leaching with common lixiviants. Novel lixiviants, less common reagents recently proposed for chalcopyrite leaching and reviewed here, show varying chemical effectiveness and economic potential. The fastest overall extraction is achieved through leaching with ionic liquids, a class of solvents mainly based on imidazolium (C3H5N2). These show rapid reaction-controlled kinetics and up to 98% extraction, but require high concentrations of ionic liquid and oxidant, making them expensive in practice. A cheaper option, the simple amino acid glycine (CH2NH2COOH), shows diffusion control in most studies with H2O2, Fe2(SO4)3, or dissolved O2 as oxidants, but slower kinetics and lower total extraction than ionic liquids (< 78.5%). Glycine leaching of chalcopyrite in practice would also face high reagent consumption, variable performance across ore types, the need for fine grinding, and aeration requirements. Another relatively cheap option, methanesulfonic acid (HCH3SO3), extracts up to 100% Cu from chalcopyrite at high H2O2, Fe2(SO4)3, or FeCl3 concentrations and temperatures, with diffusion-controlled rates. However, all studies of methanesulfonic acid so far have indicated a requirement for fine grinding or very high oxidant concentrations to achieve >50% recovery, and its natural decomposition over time would inhibit recycling. A similar problem affects leaching with salts containing ClO− ion, which rapidly dissolve up to 92.5% of Cu from chalcopyrite without additional oxidant by diffusion-controlled (HClO) or mixed-control (NaClO) reactions. These hypochlorites are cheap and leach Cu effectively at low concentrations, but decompose over time, particularly with heat, light, and dissolved metals. Ammoniacal lixiviants dissolve up to 95% of chalcopyrite-hosted Cu at surface reaction-controlled rates under mildly alkaline pH with Cu2+ as oxidant, but evaporate at prohibitive rates in heap conditions. Hypochlorites are the only novel lixiviant studied that performs comparably to baseline ferric chloride without very high reagent and oxidant concentrations, elevated temperatures, and/or very fine grain size. For the others, reaction rates and total extraction are comparable to ferric sulfate, and generally less than ferric chloride. However, the leaching systematics of all these novel lixiviants offer valuable insight into the dissolution behavior of chalcopyrite in various chemical systems, and point the way for future research.