Selective flotation of gold from pyrite under oxidizing conditions

Abstract

Abstract The differential flotation of free gold from sulphide minerals can be interesting for both economic and environmental reasons. The use of hydrogen peroxide as an oxidizing agent in the selective flotation of gold from pyrite with potassium amyl xanthate was studied by contact angle and electrophoretic mobility measurements carried out under similar conditions. Hydrogen peroxide by itself rendered both gold and pyrite surfaces very hydrophilic. However, the subsequent adsorption of xanthate on gold produced a fairly hydrophobic surface (j ∼ 60°), whereas pyrite was maintained hydrophilic at pH 10 and higher, indicating a pH range where selective separation by flotation could be achieved. The electrophoretic measurements showed that the pyrite surface is completely oxidized by hydrogen peroxide, with an isoelectric point at pH 5.5. By contrast, the hydrophilic character of the gold surface is apparently enhanced simply by the leaching action of the hydrogen peroxide. The charge of the gold particles is pH-dependent and their isoelectric point in chlorine media is around pH 2. Bench-scale flotation tests confirmed the feasibility of selective separation of gold from pyrite by using hydrogen peroxide as an oxidizing agent and amyl xanthate as collector. At values of pH 8 depression of pyrite increased significantly, while the high recovery of gold remained practically unchanged.