Light and trace element composition of Carboniferous coals from the Donets Basin (Ukraine): An electron microprobe study
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External Organisational units
- College of Geoscience and Surveying Engineering, China University of Mining and Technology, Beijing, China
The Ukrainian Donets Basin (Donbas) is one of the major coal mining provinces worldwide. While the depositional Setting of Donbas coals is well-studied, information on modes of trace element occurrence and changes in element composition with increasing maturation is lacking. Within the frame of the present study, both major (light) elements (C, O, S) and trace elements (e.g. As, Cu, Hg, Mo, Pb) were investigated using the electron microprobe (EPMA), which allows in-situ determination of the chemical composition of a maceral or mineral phase. Deviating maturity trends in C, O and S contents were found for different maceral groups. In relatively immature samples (< 0.7%Rr), S contents are generally higher in liptinite than in vitrinite and inertinite macerals. In liptinites and vitrinites, S contents decrease with increasing coalification, whereas S contents in inertinites remain constantly low. In mature samples (> 0.9%Rr), S contents of vitrinites and liptinites are comparable, but lower in inertinite macerals. Vitrinites in a marine-influenced coal host a higher amount of organic S, whereas the trace element concentrations are lower than in the investigated non-marine coals. As expected, a trend of increasing C and decreasing O contents was observed for vitrinite macerals within a maturity range from 0.5 to 1.4%Rr, referred to a decrease in volatile compounds during thermal maturation. The light element composition generally tends to higher homogenity with increasing coal rank. Highly variable trace element concentrations of ash residues were determined for Donbas coals, with measured As contents up to several thousand ppm. Despite enrichment in epigenetic pyrite, a clearly isolated inorganic source could not be identified, suggesting that trace element storage in macerals is an important factor. EPMA measurements revealed an organic matter affinity for at least part of the investigated elements (e.g. Hg, Mo, Pb).