Inner-Shell Spectroscopy and Imaging of a Subbituminous Coal: In-Situ Analysis of Organic and Inorganic Microstructure Using C(1s)-, Ca(2p)-, and Cl(2s)-NEXAFS

Inner-shell microspectroscopy has been used to provide in-situ microanalysis of organic and inorganic constituents within Wyodak subbituminous coal (APCS No. 2). Two specimens were prepared, one loaded with Ca super(2+) and the other rinsed in HCl. Carbon NEXAFS spectroscopy was used to determine the chemical structure of liptinitic and huminitic macerals. Liptinite was characterized by an abundance of aliphatic carbon, evident by the intensity of absorption assigned to the transition from carbon's 1s orbital to a mixed valence/Rydberg state; a low concentration of aromatic carbon, evident by low-intensity absorption associated with a 1s- pi transition; and an appreciable quantity of carboxylic functionality, evident through a relatively intense absorption associated with a 1s- pi transition due to C identical with O. The huminite exhibits fine structure indicative of an abundance of both aromatic and aliphatic carbon. The presence of polyhydroxylated aromatic carbon and carbonyl associated with carboxylic acids is also clearly indicated. In addition to carbonaceous heterogeneities, chlorine-rich inclusions were also identified. These were observed to strongly absorb in the energy range near 270 eV corresponding to Cl's 2s absorption edge. The inclusions are anticipated to be inorganic chlorides, precipitates which formed following the rinse in dilute HCl. Imaging and spectroscopy on the calcium's 2p absorption edge reveals that the chloride's cation is not calcium, although calcium is detected in the huminite of the Ca super(2+)-loaded coal.