The competitive adsorption of cyanide and ethyl xanthate on pyrite and pyrrhotite surfaces

Abstract

Ultraviolet-visible (UV-vis) and Fourier Transform Infrared (FTIR) Spectroscopy have been employed to determine the kinetics of ethyl xanthate adsorption onto pyrite and pyrrhotite at pH 9 in the presence and absence of cyanide. In the absence of cyanide, the rate and extent of ethyl xanthate adsorption increased with the pulp electrochemical potential ( Eh). For both pyrite and pyrrhotite, there was a dramatic increase in adsorption above an Eh of +200 mV, corresponding to the oxidation potential of ethyl xanthate to diethyl dixanthogen. In-situ and ex-situ FTIR studies using attenuated total reflectance (ATR) and single-reflection modes have confirmed the presence of dixanthogen on pyrite and pyrrhotite. The influence of cyanide on the adsorption kinetics of ethyl xanthate depends on Eh as well as the order of reagent addition. In general, cyanide reduced the rate and extent of ethyl xanthate adsorption onto the iron sulphide minerals; this was more pronounced for pyrrhotite. The preadsorption of cyanide dramatically enhanced this depressant action. Furthermore, the addition of cyanide to preadsorbed ethyl xanthate led to a desorption of ethyl xanthate from the surface, but the desorption was short-lived. FTIR and XPS studies confirmed this behaviour and showed the presence of surface cyano-species, apparently as insoluble ferrous and ferric hexacyano complexes. The competitive adsorption of cyanide in the presence of ethyl xanthate is an important mechanism in the depression of pyrite and pyrrhotite.