SUBMONOLAYER ADSORPTION OF ALKYL XANTHATES ON GALENA

The interaction of n-butyl xanthate with galena has been studied by X-ray photoelectron spectroscopy using fresh surfaces formed by fracture of the mineral under xanthate solutions in equilibrium with air, or abraded surfaces held at controlled potentials. For the former treatment, and for surfaces held at potentials below the reversible value of the galena/lead xanthate couple, the S(2p) spectrum was characterised by a single additional doublet shifted by 1.4 eV from that for galena, a binding energy that is 0. 3-0.4 eV less than expected for lead xanthate. The assignment of the shifted component to chemisorbed xanthate was supported by the 0 (1s) and C ( 1s) spectra. The corresponding Pb (4f) spectrum was indistinguishable from that of galena itself and it is concluded that xanthate is chemisorbed to lead atoms in the outer layer of the mineral lattice and is not present as an adsorbed lead xanthate species. S (2p) spectra of surfaces held at potentials above the reversible value of the galena/lead xanthate couple, and from oxidised sur-faces treated with xanthate, contained a second shifted doublet which was assigned to multilayer lead xanthate. Lead-oxygen species were also identified on the surface held at positive potentials.