High quality of Jurassic Coals in the Southern and Eastern Junggar Coalfields, Xinjiang, NW China: Geochemical and mineralogical characteristics

Abstract The Junggar coal basin, with enormous coal reserves, is one of the largest coal basins in Xinjiang Province, Northwest China. According to the exploration data, there is one to dozens of workable coal seams developed in the Xishanyao Formation of Middle Jurassic across the whole basin, with the maximum accumulated coal thickness of over 100 m. Ninety-six bulk coal samples from six exploration boreholes in the Southern and Eastern Junggar Coalfields were collected to investigate the coal qualities of the Junggar coals. The mineralogical characteristics of the studied coals were determined by Powder X-ray diffraction (XRD) and geochemical analyses are performed by means of inductively-coupled plasma atomic-emission spectrometry (ICP-AES) and inductively-coupled plasma mass spectrometry (ICP-MS). The Eastern and Southern Junggar bituminous coals are all characterized by low ash yields, low S contents, and low mineral contents. Furthermore, the concentrations of most major and trace elements in both the Eastern and Southern Junggar coals are relatively low with respect to other Chinese and worldwide coals, with the exceptions of Sr and Ba. The results show that elements including K, Li, Ti, Sc, V, Cr, Ga, Rb, Zr, Pb, and rare earth elements (REEs), have aluminosilicate affinities. Ca-bearing and Fe-bearing carbonate affinities are deduced for Ca, Mg, Fe, Mn, Sr, and Ba. Sulfur (Fe), Zn, Pb, Cu, and As show a partial sulfide affinity in some coals. An apatite and/or crandallite affinity is deduced from relatively high correlation of P, Sr, and Ba. The very high coal quality of Junggar coals is attributed to very low detrital supply in very stable shallow-lake sedimentary facies during peat accumulation. Slight differences of peat bog accumulation rate, water table, and oxidizing-reducing condition account for the merging and splitting of coal seams in different coal exploration areas and the slight differences of mineral, S, ash, and trace element contents. In summary, the Eastern and Southern Junggar coals with very enormous reserves are characterized by high quality, which is significantly and environmentally relevant to coal combustion by-products (CCPs) and potential emissions of gaseous pollutants/particulate matter during the large coal consumption in pulverized coal combustion power stations in Xinjiang Province. The high coal quality of the Junggar coals is expected to generate CCPs that can be reused for various purposes with low environmental threat.