XPS CHARACTERIZATION OF COAL SURFACES - STUDY OF AERIAL OXIDATION OF BROWN COALS

XPS was used to determine the surface concentrations of different elements present in two Spanish brown coals. Sputtering with Ar+ ions followed by XPS analysis permitted depth concentration profiles in both, fresh and oxidized coals, to be obtained, and show that aerial oxidation brought about a redispersion of the organic matter onto the mineral phase. Analysis of C 1s band shape together with Fourier transform infrared (FTIR) study of organic functional groups show that loss of hydroxyl groups from the organic phase occurs by thermal decomposition during the first stages of oxidation, leading to an increase of the hydroxyl groups in the mineral phase by proton transfer. At higher temperatures, oxidation gives rise to formation of new carboxyl groups. The usefulness of XPS and some bulk characterization techniques used for studying coal oxidation is compared.