Identifying chemisorption in the interaction of thiol collectors with sulfide minerals by XPS: adsorption of xanthate on silver and silver sulfide

The adsorption of ethyl xanthate on silver and sulfidised silver surfaces at controlled potentials has been investigated by X-ray photoelectron spectroscopy (XPS). Silver/xanthate and silver sulfide/xanthate were chosen as model systems for investigating the identification of chemisorption of thiol collectors on sulfide minerals by means of core electron energy shifts. There was no discernible effect from submonolayer adsorption on either substrate on the corresponding Ag(MNN) spectrum, even when the presence of adsorbed xanthate was clearly evident from the S 2p spectrum. It was confirmed that the Ag(MNN) electron energies for multilayer silver xanthate were significantly different from those for silver and silver sulfide. The basis for the general proposition, that chemisorption of thiol collectors on sulfide mineral surfaces might not necessarily give rise to discernible substrate core electron energy shifts, was examined in the context of previously reported investigations of chemisorption of adsorbates from the vapour phase. It was concluded from this appraisal, and from the experimental results for the interaction of xanthate with silver and silver sulfide, that substrate core electron energy shifts on chemisorption are not always large enough to be detectable by conventional XPS. By contrast, core electron energy shifts for multilayer metal-collector compound formation are clearly discernible.