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 t he pyritic fraction, which seldom comprises more than 4% of the ore. C onsequently, pyrite recovery through flotation offers the opportunity to improve gold recoveries through further treatment of the pyritic co ncentrate. The traditional processing routes are no longer economicall y viable due to the high cost of acid treatment to overcome the depres sing influence of cyanide on xanthate flotation. Amines were identifie d as possible alternative collectors for pyrite flotation in the prese nce of cyanide. In this work the influence of cyanide on pyrite flotat ion with dodecylamine (DDA) acetate was investigated by means of elect rochemical impedance measurements, flotation tests, and in-situ Raman spectroscopy. Cyanide was found to act as a slight depressant, or no d epressant at all, for the flotation of pyrite with dodecylamine acetat e, a much smaller effect than that which cyanide has on pyrite flotati on with xanthate. In pH II solutions, pyrite electrodes exhibited a lo wer interfacial capacitance in the presence of DDA acetate, reflecting the formation of a layer on the electrode surface by the adsorption o f the cationic (amine) collector on the pyrite surface. At cyanide con centrations typical of gold leaching, this capacitance decrease is not observed, probably reflecting an inhibiting effect of cyanide on amin e 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 meas urements.