X-ray photoelectron spectroscopy study of oxidized coals with different sulphur content

The aim of the study reported was to determine the effect of oxidation on the surface composition of coal as studied by X-ray photoelectron spectroscopy (XPS) method. Five coals characterized by a different degree of coalification and different amounts of sulphur were subject to oxidation with peroxyacetic acid (PAA). The process of oxidation was carried out for coal samples demineralised by the Radmacher method. Carbon, oxygen, sulphur and nitrogen peaks were registered and analysed. The effect of oxidation depended on coal rank. In case of S 2p, three or four peaks were found for the oxidized samples, corresponding to tiophene, sulphoxides (Ph2–SO type), sulphonic acids and in some cases, more oxidized forms of sulphur, possibly inorganic sulphates. The surface sulphur content increased upon oxidation. A possible reason could be the mobility of the S-containing species.