The adsorption of carbon disulphide and potassium ethylxanthate on partially oxidised lead sulphide
The gas phase chemisorption of carbon disulphide on lead sulphide surfaces, at near room temperatures, has been investigated. The effects of changes in the semiconductor properties of the lead sulphide, brought about by partial oxidation of the surface, have been studied. Both the initial rate and the heat of adsorption of carbon disulphide were shown to vary with the semiconductor properties, and reached a maximum for a slightly p-type sample. Further oxidation resulted in the formation of surface oxidation product layers, on which little chemisorption took place. Multilayer physical adsorption took place on all surfaces. Desorption of the strongly chemisorbed carbon disulphide resulted in the breakdown of the molecule, giving sulphur, which remained on the surface, resulting in a change in the surface properties, and CS, which was desorbed. The adsorption of potassium ethyl xanthate from aqueous solution, on lead sulphide has been studied and correlated with the carbon disulphide adsorption behaviour. No adsorption was detected on a freshly prepared n-type sample. The chemisorption on partially oxidised samples was limited to a monolayer, and the heat of adsorption showed a maximum in a similar manner to that observed for carbon disulphide adsorption. On heavily oxidised surfaces, xanthate was removed from solution by reaction with the oxidation product layers. The results suggest that measurements of the rate of carbon disulphide adsorption may be used to determine optimum quantities of oxidation for strong xanthate adsorption on sulphide minerals.