The influence of cyanide on the flotation of pyrite from Witwatersrand gold leach residues

A significant portion of the gold in Witwatersrand ores may occur in the pyritic fraction, which seldom comprises more than 4% of the ore. Consequently, pyrite recovery through flotation offers the opportunity to improve gold recoveries through further treatment of the pyritic concentrate. The traditional processing routes are no longer economically viable due to the high cost of acid treatment to overcome the depressing influence of cyanide on xanthate flotation. Amines were identified as possible alternative collectors for pyrite flotation in the presence of cyanide. In this work the influence of cyanide on pyrite flotation with dodecylamine (DDA) acetate was investigated by means of electrochemical impedance measurements, flotation tests, and in-situ Raman spectroscopy. Cyanide was found to act as a slight depressant, or no depressant at all, for the flotation of pyrite with dodecylamine acetate, a much smaller effect than that which cyanide has on pyrite flotation with xanthate. In pH 11 solutions, pyrite electrodes exhibited a lower interfacial capacitance in the presence of DDA acetate, reflecting the formation of a layer on the electrode surface by the adsorption of the cationic (amine) collector on the pyrite surface. At cyanide concentrations typical of gold leaching, this capacitance decrease is not observed, probably reflecting an inhibiting effect of cyanide on amine adsorption. Raman spectroscopical measurements demonstrated a strong pH effect on amine adsorption, and little effect of cyanide, in broad agreement with the flotation tests and electrochemical impedance measurements.