Comparative leaching of a sulfidic gold ore in ionic liquid and aqueous acid with thiourea and halides using Fe(III) or HSO5− oxidant

The leaching of gold, silver and base metals from a sulfidic gold ore in the presence of an oxidant (peroxomonosulfate (HSO5−) or iron(III)) and leaching agent (thiourea, chloride, bromide or iodide) is compared in 1-butyl-3-methylimidazolium hydrogen sulfate (bmimHSO4) and chloride (bmimCl) ionic liquids, as well as in aqueous saturated K2SO4 as the solvent medium. Over 85% of gold and silver was recovered in the presence of HSO5−/ thiourea at 25–50 °C in both bmimHSO4 and bmimCl, with silver recovery significantly enhanced compared with that from aqueous sulfate medium. The leaching efficiency with HSO5− was similar to that with Fe(III) as oxidant in bmimHSO4 and was far superior in bmimCl. With HSO5− /halide ion (Cl−, Br−, I−) as leaching agent, gold and silver recovery in bmimHSO4, bmimCl or saturated aqueous K2SO4 improved from Cl− to Br− to I−, but only I− gave a high recovery in the bmimCl ionic liquid due to the particular stability of the iodo complex anion in this medium. However, recovery was significantly higher than in an aqueous medium. Negligible recovery of base metals occurred in the ionic liquid medium, making it highly selective for Au and Ag. Concentration dependence studies with respect to halide and oxidant have defined optimum conditions for gold and silver recovery.