The effect of galvanic interaction on the behaviour of free and refractory gold during froth flotation

Abstract

This paper provides new information towards the effect of galvanic contact between metallic iron and free gold, and gold locked in refractory iron sulphide minerals such as pyrite and pyrrhotite. Galvanic interaction between pyrite, pyrrhotite and other sulphide minerals has been studied before and is well documented in the literature but there is no evidence that the effect of galvanic interaction on the recovery of free and refractory gold has been investigated. In this study, milling in a mild steel environment has been simulated by adding different dosages of metallic iron powder to a ceramic mill during grinding, and flotation has been performed using three different collector regimes. The results show that the overall gold recovery increases as more metallic iron is added to the ore prior to milling regardless of whether potassium amyl xanthate (PAX), a trithiocarbonate or a combination of the two collectors is used. When PAX is used by itself or in combination with a trithiocarbonate collector, a greater dosage of metallic iron added prior to milling causes the rest potential of the pyrrhotite to decrease and its flotation recovery increases. The decrease in the pyrrhotite rest potential means that there would be a reduction in the extent of oxide and hydroxide film formation on the mineral surface which typically prevents copper activation and flotation of the pyrrhotite. In most cases, the greatest amount of sulphide material is recovered when 5 kg/t of metallic iron is added to the ore prior to milling which is mainly a result of an increase in froth stability. Due to this increase in froth stability, it was found that more water and solids could be entrained and in most cases a greater recovery of free gold was obtained.