X-ray photoelectron spectroscopy (XPS) studies of potassium amyl xanthate (KAX) adsorption on precipitated PbS related to galena flotation

X-ray photoelectron spectroscopy (XPS) has been used to investigate the fundamental surface chemical reactions involved in the adsorption of potassium amyl xanthate (KAX) on precipitated lead sulphide (PbS). The results have been correlated with Hallimond tube laboratory flotation tests carried out on a high grade sample of natural lead sulphide (galena) and used to interpret the flotation response of the latter. A preoxidised PbS surface was found to be an essential prerequisite for the chemisorption of xanthate collectors onto PbS/galena surfaces. Analysis of the published electrochemical literature indicates, and XPS results confirm, that oxidation by dissolved oxygen in aqueous solution alone is insufficient to provide the degree of surface oxidation necessary for the chemisorption reaction. However, chemical oxidation with hydrogen peroxide, or crushing/grinding pretreatments, do generate enough oxide and sulphate/thiosulphate-like groups on the surface for chemisorption of xanthate to occur via ion-exchange with these species. A layer of lead xanthate is formed, the thickness of which depends on the relative amounts and solubilities of these base compounds. The formation of a lead xanthate layer is necessary to produce a hydrophobic particle surface which is readily floatable. However, this has to be sufficiently thick to overcome the hydrophilicity of the unreacted and/or underlying oxidised surface species.