In seam variation of element-oxides and trace elements in coal from the eastern Ordos Basin, China

Abstract

This paper investigated the mineralogical and geochemical compositions of the upper Pennsylvanian coal from Hedong Coalfield, in the eastern Ordos basin, China, using SEM, XRD, ICP-MS, ICP-CCT-MS, DMA-80 and ISE methods. The bituminous coal samples were collected form Nos. 3 and 4 Coal, which had low ash yield and were medium volatile, and had low sulfur content and low hazardous trace elements concentrations (Be, F, As, Hg, U and Pb). Maceral compositions were dominated by vitrinite (up to 90.2%), and to a lesser extent by inertinite and liptinite, all subgroups were detected in the coal samples. Minerals included quartz, clay minerals, sulfide and other oxide minerals. SiO2 and Al2O3 were the dominant major elements-oxides in both coal seams with much higher concentrations than in Chinese coal, while other major elements-oxides (Na2O, K2O, Fe2O3, MgO) had average values compared to Chinese coal. No. 3 Coal was enriched in Li and Zr, and No. 4 Coal was enriched in Li, Be, Cu, Se, and In. Elemental occurrence was studied using statistical methods, and Li, Rb, Zr, Cs, Ba, Hf, Tl, Pb, and Th were inorganic affinities, while F, V, Cr, Ga, Ni, As, In, Ta occurred as inorganic–organic affinities and Fe and S may have occurred in pyrite. Coal facies indicators (GI, TPI, GWI, and VI) plots suggested that the two coal seams were deposited in different environments: No. 3 Coal was deposited in a wet forest swamp, while No. 4 Coal was formed in a mesotrophic to ombrotrophic environment. The geochemistry of these coal samples (Al2O3/TiO2, TiO2/Zr, Zr/Sc and Th/Sc ratios) indicated that the coal samples sediment was sourced from intermediate and felsic igneous rocks.