The influence of oxidation with air in comparison to oxygen in sodium carbonate solution on the surface composition of coals of different ranks

The influence of oxidation on surface composition of coals of different rank and different sulphur content were studied. Coal samples untreated or oxidized with oxygen in 0.5 N Na2CO3 aqueous solution or air at 125 °C were investigated by X-ray photoelectron spectroscopy XPS. The comparison of surface O/C ratios with those of the bulk allows to indicate the faster of two competing processes—chemisorption of oxygen or gasification. Where the formation of oxygen containing surface species is concerned, the use of oxygen in gaseous mixtures at moderate temperatures (125 °C) is preferable to oxygen in low temperatures in aqueous media. Mild oxidants such as oxygen in gaseous mixtures at moderate temperatures (125 °C) lead to some decrease in the content of pyritic sulphur. Additionally, relatively small amounts of organic sulphur may be removed in contrast to the application of aqueous solution of peroxyacetic acid which was much more efficient in that matter.