THE COMPETITIVE ADSORPTION OF CYANIDE AND ETHYL XANTHATE ON PYRITE AND PYRRHOTITE SURFACES

Ultraviolet-visible (UV-vis) and Fourier Transform Infrared (FTIR) Spe ctroscopy have been employed to determine the kinetics of ethyl xantha te adsorption onto pyrite and pyrrhotite at pH 9 in the presence and a bsence of cyanide. In the absence of cyanide, the rate and extent of e thyl xanthate adsorption increased with the pulp electrochemical poten tial (E(h)). For both pyrite and pyrrhotite, there was a dramatic incr ease in adsorption above an E(h) of +200 mV, corresponding to the oxid ation potential of ethyl xanthate to diethyl dixanthogen. In-situ and ex-situ FTIR studies using attenuated total reflectance (ATR) and sing le-reflection modes have confirmed the presence of dixanthogen on pyri te and pyrrhotite. The influence of cyanide on the adsorption kinetics of ethyl xanthate depends on E(h) as well as the order of reagent add ition. In general, cyanide reduced the rate and extent of ethyl xantha te adsorption onto the iron sulphide minerals; this was more pronounce d for pyrrhotite. The preadsorption of cyanide dramatically enhanced t his depressant action. Furthermore, the addition of cyanide to preadso rbed ethyl xanthate led to a desorption of ethyl xanthate from the sur face, but the desorption was short-lived. FTIR and XPS studies confirm ed this behaviour and showed the presence of surface cyano-species, ap parently as insoluble ferrous and ferric hexacyano complexes. The comp etitive adsorption of cyanide in the presence of ethyl xanthate is an important mechanism in the depression of pyrite and pyrrhotite.