‘Green’ leaching: recyclable and selective leaching of gold-bearing ore in an ionic liquid

Abstract

The recovery of gold and silver from ore in an ionic liquid is reported for the first time. The 1-butyl-3-methyl-imidazolium hydrogen sulfate ionic liquid (bmim⁺HSO₄⁻) was employed, with iron(III) sulfate oxidant and thiourea added. Selective extraction of gold (≥85%) and silver (≥60%) from powdered ore (of dominantly chalcopyrite/pyrite/pyrrhotite/sphalerite mineralogy) was achieved at room temperature in 50 h, with other lower-value metals present in the ore (Cu, Zn, Pb, Fe) extracted to only low percentages. Gold extraction was similar to that achieved in aqueous H₂SO₄/thiourea/Fe₂(SO₄)₃, and silver extraction was significantly better. Moreover, the ionic liquid can be recycled following selective stripping of gold and silver on activated charcoal, with reuse in at least four successive treatments leading to neither ionic liquid degradation nor any loss in extraction efficiency.