Evolution law of carbon and oxygen groups on coal surface with increasing metamorphic grade and its effect on wettability

Carbon and oxygen elements were studied to explore the effect of structural differences on wettability of coal dust. Surface distribution characteristics of carbon and oxygen groups in 6 coal dusts with different metamorphic grades were examined through NMR and XPS. The evolution of different types of carbon and oxygen groups was obtained using distance analysis. With increasing metamorphic degree a kind of group changes along with variation of other groups in most case, which is a process of clustering. The carbon in Ar-C, -COOH, CH₂ and Ar-O (R-O) has the similar evolution law, the oxygen in -OH and C-O-C is the same case. Factor analysis was used to know effect of group evolution on wettability of coal dust. It is found that Ar-C, as the common factor covering 95.366% to explain coal dust wettability (contact angle), is the main factor of carbon groups; while -OH covering 94.818% is the main factor of oxygen groups.