XPS characterization of chalcopyrite, tetrahedrite, and tennantite surface products after different conditioning .1. Aqueous solution at pH

Characterization of the surface products formed by the interaction of aqueous solution at pH 10 with mineral samples of chalcopyrite (CuFeS2), tetrahedrite (Cu12Sb4S13), and tennantite (CU(12)AS(4)S(13)) was carried out by X-ray photoelectron spectroscopy(XPS). The experimental data collected directly after treatment with aqueous solution and after successive sputtering have led us to determine the in-depth distribution of the different types of surface products formed by the diffusion of metal atoms from the bulk structure to the interface and their interaction with aerated water. In general, the following in-depth surface composition was found for the investigated mineral samples: (i) the outermost thin layer consists of hydrophilic species, mainly ferric or cupric (depending on the mineral sample) oxides/hydroxides and adsorbed water, (ii) the next layer is a sulfur-enriched structure with a gradually changing composition with hydrophobic properties which vary significantly among the minerals, and (iii) the innermost layer has a bulk mineral composition and structure. In the case of chalcopyrite the separation between the outermost hydrophilic layer (iron oxides/hydroxides) and the internal hydrophobic sulfur-rich layer is more pronounced than for other mineral samples. This is the reason that the outermost hydrophilic thin layer can be relatively easily removed mechanically and/or by dissolution during a strong agitation. This involves a strong increase in the hydrophobicity of chalcopyrite. In the case of tetrahedrite and tennantite the outermost hydrophilic layer consists mainly of copper oxides/hydroxides and it is not well separated from the rest of the surface structure. This implies that the two minerals remain hydrophilic. Tetrahedrite forms the copper oxides/hydroxides product much more quickly with a major amount of cupric species, whereas tennantite oxidation, under the same conditions, yields a small amount of cuprous surface species, The differences in surface composition of these three minerals, caused by the different mobilities of copper atoms in their crystalline structures, are vitally important for their separation in the presence of surfactants. It should be noted that although tetrahedrite and tennantite contain a significant amount of other elements, they are not concentrated in the outermost layer. On the contrary their surface concentrations are several times lower than those found for the bulk composition.