The surface properties of pyrite coupled with gold in the presence of oxygen

Gold often exists with pyrite and there is an urgent need to separate the low-gold-content pyrite from the high gold -content pyrite when gold is recovered from refractory pyritic ores. This separation may be achieved by exploring the change of surface properties on pyrite upon contact with gold. For the first time, the current study investigated the galvanic interaction between gold and pyrite in the presence of oxygen as well as the oxidation products formed on pyrite surfaces with and without the galvanic coupling. It was interesting to find that gold was slightly more active than pyrite under ambient conditions, and the coupling of gold with pyrite generated a low negative galvanic current. However, under oxygen-enriched conditions, gold became much nobler than pyrite, and the coupling of gold with pyrite generated a high positive galvanic current resulting in an oxidation layer on pyrite. It is evident that oxygen can change the surface reactivity of gold and enhance the galvanic interaction between gold and pyrite. A combination of cyclic voltammetry measurements and Cryo-XPS (X-ray Photoelectron Spectroscopy) analyses was used to characterize pyrite surfaces after self-oxidation and galvanically induced oxidation. Additional oxidation products consisting of elemental sulphur, iron hydroxyl-oxide and iron sulphate, in particular the latter two, formed on pyrite surfaces when coupled with gold especially under oxygen-enriched conditions. This indicates that gold can alter pyrite surface properties once in contact with pyrite under oxygen-enriched conditions. This study provides new insights into the electrochemistry of base metal and precious minerals as well as the separation of different types of pyrite during the process of gold recovery.