Interactions between sulphide minerals and alkylxanthate ions. Part 1.—A vibrational spectroscopic study of the interactions between sphalerite and synthetic zinc(II) and cadmium(II) sulphides, and ethylxanthate ions in aqueous and acetone solutions
The crystal structures of zinc(II) and cadmium(II) sulphides are not affected by the stoichiometry of metal and sulphide ions at the precipitation of the two compounds. The composition and structure of the ultimate surface layers, and thereby the chemical properties of the particles, are on the other hand sensitive to the stoichiometry at the preparation. Chemisorbed ethylxanthate complexes are formed at metal ion sites on the surfaces of sphalerite and synthetic zinc(II) and cadmium(II) sulphides at metal and ethylxanthate ion concentrations where the solubility product of zinc(II) or cadmium(II) ethylxanthate is not exceeded. Two different types of ethylxanthate species co-ordinated to the surfaces have been found. These have been assigned to mono- and bi-dentate co-ordination of the ethylxanthate ion to the surface. Surface complexes are most probably enthalpy stabilized, and the bond(s) between the metal ion site in the surface and the ligand must contain some degree of covalency, as the entropy contribution to the formation of a chemisorbed complex on a surface is small. The stability of complexes of this kind is expected to increase with increasing softness of metal site and ligand. This is indicated as the ethylxanthate and EDTA surface complexes on cadmium(II) sulphide seem to be more stable than the corresponding complexes on zinc(II) sulphide surfaces. The stability of the surface complex is dependent on the solvent used, and seems to be a function of the solvation properties of the solvent.