Geochemistry of elements associated with Late Permian coal in the Zhongliangshan mine, Chongqing, Southwest China

Abstract

The enrichment and geochemical significance of elements associated with Late Permian coals in Southwest China have always gained widespread interest in the field of coal geology. The present study focuses on the geochemical characterization of Late Permian coal in the Zhongliangshan mine. Twenty-three samples were collected from the K1a coal seam of the Zhongliangshan mine, and the major and trace elements in the coal were analyzed by using X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma mass spectrometry. The composition of minerals in the Zhongliangshan coal, and the modes of occurrence of coal-associated elements, especially those with elevated contents, were studied through a combination of microscopic analyses, X-ray powder diffraction, and scanning electron microscope -energy dispersive X-ray spectrometer. The minerals in coal mainly consist of kaolinite, pyrite, calcite, and quartz, as well as small amount of gypsum and anatase. Compared with the average elemental concentrations in world coal, the Zhongliangshan coal is enriched in Cr, and slightly enriched in Li, U, Sr, V and Ag. Combining the correlation analysis and sequential chemical extraction experiments, it can be inferred that many trace elements in the Zhongliangshan coal have both inorganic and organic affinities. The elements Cr, Li, and V mainly occur in clay minerals, and also are related to organic matter in the coal. Uranium presents firstly in the organic and then silicate states. Strontium shows multiple modes of occurrence including carbonate, silicate, and exchangeable ion states, and Ag primarily occurs in sulfides followed by silicates. The terrigenous debris input from the Emeishan basalt is the major reason for the enrichment of above elements in the Zhongliangshan coal.

Mineralogy and Geochemistry of High-Sulfur Coals from the M8 Coal Seam, Shihao Mine, Songzao Coalfield, Chongqing, Southwestern China

“…Moreover, other elements, such as Li, Cs, Ag, Re, etc., have also been sporadically reported in different coalfields. Meanwhile, the elevated environmentally sensitive elements, especially As, Se, Sb, Hg, Pb, Cr, V, Co, Cu, U, and Th, have been detected in the above and other coalfields in Southwestern China [9,10,26,27]. As was concluded from the available literature, relatively high concentrations of elements in Late Permian coals from Southwestern China are generally caused by various geological factors.…”

“…The coalbearing sequence of P 2 l in this area was developed and formed on the residual weathering crust caused by the Dongwu Movement, one of the essential tectonic events in Southwestern China [30]. The sedimentary environment of the P 2 l is the tidal flat of restricted seacarbonate platform of the continental-marine transitional environment [27]. The lithology of the P 2 l primarily includes limestone, siltstone, mudstone, sandy mudstone, argillaceous limestone, fine sandstone, argillaceous sandstone, aluminum mudstone, and several coal seams (Figure 1d) [32].…”

“…The cell-filling kaolinite has a lamellar structure under a high magnification (Figure 2b). Discrete and zonal kaolinite may indicate its derivation from syngenetic clastic sediments [27]. Cell-filling and wormy structured kaolinites are of epigenetic origin [44,45].…”

Uranium Sources, Uptake, Translocation in the soil-plant System and Its Toxicity in Plants and Humans: A Critical Review

“…The source of contamination of Uranium varies greatly. A certain amount of Uranium is found in the coals [38][39][40][41][42][43][44][45] , mining, extraction, and disposal of U-containing products or their by-products are considered the anthropogenic sources of U contamination of soils 46,47 . Phosphorous fertilizers made from natural rocks in agriculture are another potential source of U enrichment in soils 48 .…”