Disentangling chemical effects in ionic-liquid-based Cu leaching from chalcopyrite

Hydrometallurgical copper extraction from chalcopyrite is a slow and often incomplete process that relies on corrosive and environmentally unfriendly H2SO4-based leaching systems. Some ionic liquids (ILs), including imidazolium- and ammonium-based ILs, have previously been suggested as better performing alternatives, but at present it is not clear whether the leaching mechanism is different than in H2SO4-based lixiviants. Here, we study a range of different, structurally simple ILs using a robotic screening platform and other methods, to address this question. Indeed, we do find differences between ILs, in that IL-based lixiviants with more polar cations (NH4+, K+, [C1Him]+) appear to show better extraction than those with less polar cations ([C2C1im]+, [C4C1im]+). However, none performed better than aqueous H2SO4, when corrected for differences in pH. Notably, results are qualitatively very similar: three leaching stages were seen in all cases, presumably involving leaching of a Fe rich/Cu poor layer first, followed by leaching of bulk chalcopyrite and eventually passivation. During the second stage, the apparent activation energies in aqueous NH4HSO4, and H2SO4 are similar in that both rates are first order with respect to the proton concentration in both cases. The leaching rate increases with stirring, suggesting some degree of mass transport-control on the leaching process. The poorer leaching performance for [C2C1im]HSO4 and [C4C1im]HSO4 is consistent with physical blocking of the mineral surface, presumably by the IL cation, in accordance with contact angle data.