Bioenhanced Gold Extraction from Refractory Ores

Abstract

The continuing depletion of high grade oxide gold deposits has created a need for new, economically viable and environmentally safe methods to treat refractory sulphidic ores. One of the alternative leaching processes uses micro-organisms, Thiobacillus ferro-oxidans, partially to oxidise pyrite and/or arsenopyrite containing finely disseminated, submicrometre sized native gold particles. During the bioleaching process, the solid sulphide matrix is converted to sulphate, which is soluble in the leach medium. After solid/liquid separation, the leach residue containing liberated gold particles is rendered alkaline by addition of lime and subjected to cyanide leaching, in which gold is dissolved. This technology has already been applied on a commercial scale in Brazil and South Africa, while intensive pilot plant evaluation of the process is in progress in other countries.