DEMINERALIZATION EFFECTS ON THE EPR PROPERTIES OF ARGONNE PREMIUM COALS

Because of the nature of their collection and handling, Argonne Premium Coals provide a unique opportunity to study the chemistry of the hydrocarbon and mineral species encountered in coal in its native state. Electron paramagnetic resonance (EPR) observations are reported for Argonne Premium Coals before and after demineralization by either a citric acid wash or HCl/HF treatments. Increases in radical density of up to a factor of 3 are observed after citric acid washing (for Beulah-Zap lignite) and up to a factor of 3.3 after HCl/HF demineralization (Upper Freeport). Changes in g values and line widths are also observed. These data suggest that the carbon radicals in the organic material of the coal are interacting with inorganic paramagnetic species which occur in both mineral and ionic forms. This interaction renders some of the carbon radicals unobservable in the EPR experiment and affects the EPR properties (g values, line widths, microwave saturation behavior) of those that are observable. Demineralization is recommended before quantitative EPR studies of coal organic matter.