The effect of gold coupling on the surface properties of pyrite in the presence of ferric ions

The surface properties of gold-associated pyrite play a determining role in pyrite dissolution in gold extraction. However, the surface properties of pyrite have been always studied without the consideration of gold coupling. In this study, the reactivity, surface speciation and topography of pyrite after its oxidation with and without gold coupling in the presence of Fe³⁺, a strong oxidant widely used in the industry, were studied and compared using EIS (Electrochemical Impedance Spectroscopy), Cryo-XPS (X-ray Photoelectron Spectroscopy at-145 °C) and AFM (Atomic Force Microscopy), respectively. It was interesting to find that gold could catalyse Fe³⁺ reduction and gold coupling significantly enhanced pyrite oxidation with more oxidised iron species such as Fe₃O₄/Fe₂O₃ and FeOOH and oxidised sulphur species such as S_n²⁻/S₈ and SO₃²⁻ formed on the pyrite surface. Gold coupling also resulted in a much rougher and larger surface area of pyrite, appreciably increasing the electrochemical reactivity of pyrite for its successive oxidation and dissolution. These findings provide insights into the physicochemical properties of gold-associated pyrite, which can be exploited to improve the gold extraction process.