INFLUENCE OF ELECTROCHEMICAL ENVIRONMENT ON THE FLOTATION BEHAVIOR OF MT ISA COPPER AND LEAD ZINC ORE

The flotation of a copper and a lead-zinc sulphide ore from Mt. Isa has been studied in the absence and presence of specific collectors and depressants over a range of grinding and flotation Eh conditions. The surface composition of the products of flotation has been determined by X-ray photoelectron spectroscopy. It is shown that a substantial proportion of the iron sulphide minerals is naturally floatable as a result of a surface coating of graphitic carbon formed during ore genesis. In addition, an overlayer of ferric hydroxides and carbonates reduces the exposure of the sulphide minerals at the surface to low levels. Both chalcopyrite and galena exhibit only moderate collectorless flotation properties. Flotation of both ores with collector show a strong dependency on Eh. The collector selectively removes the ferric hydroxides and carbonates from the surface of the chalcopyrite. Significant collector-induced flotation of the iron sulphide minerals occurred which was largely reduced by the addition of cyanide. Grinding in an oxidising environment reduced selectivity due to increased flotation of the iron sulphide minerals. The influence of the ferric hydroxide and carbonate layers on selective flotation is discussed. It is argued that the addition of complexing depressants during grinding in a reducing environment enhances selectivity by minimising mineral interactions. Implications for flotation practice are considered.