Infrared Evaluation of Composition and Structure of Ethyl Xanthate Monolayers Produced on Chalcopyrite, Tetrahedrite, Tennantite at Controlled Potentials

Abstract

Spectroscopic studies of the interaction of ethyl xanthate solution (C2H5OCS2−) with mineral samples of chalcopyrite (CuFeS2), tetrahedrite (Cu12Sb4S13), and tennantite (Cu12As4S13) at different potentials were carried out by infrared reflection spectroscopy. The formation of the adsorbed products was investigated at potentials from open circuit potential (OCP) for each mineral to values about 200 mV higher than OCPs, i.e., in range 180–420 mV (SHE). The experimental results were compared with simulated data of hypothetical surface layers with assumed compositions, structures, and thicknesses in order to quantitatively evaluate the produced surface monolayers on all minerals. The adsorption product observed spectroscopically on these three minerals was the cuprous ethyl xanthate complex (C2H5OCS2Cu). Ethyl dixanthogen (dimmer, (C2H5OCS2)2) as the second adsorption product was only observed on chalcopyrite. Cuprous ethyl xanthate was found as the most stable product on these minerals in an amount from submonolayer to a few statistical monolayers. The dixanthogen which was observed only at the chalcopyrite surface was produced at a potential about 100 mV higher than that calculated from the thermodynamic data. There are thermodynamic and kinetic limitations of ethyl dixanthogen formation on these minerals. Diffusion of copper atoms to mineral-solution interface plays an important role in the formation of surface products. These findings are very different from those observed for amyl xanthate when amyl dixanthogen was produced simultaneously with cuprous amyl surface complex on these minerals. The difference between the interactions of ethyl xanthate with oxidized and “fresh” samples of these three minerals was discussed in detail and mechanisms of ethyl xanthate adsorption on different mineral surfaces were proposed.