Element concentration and enrichment patterns in Carboniferous coal from coal-burning endemic area, Yunnan province
With the principal aim of understanding the element variations in Carboniferous coal from eastern Yunnan province of China, the concentration of 48 elements in 16 coal samples were determined. It was found that, (1) Se (0.76–5.13 mg/kg), Mo (0.29–46.71 mg/kg), As (0.96–25.38 mg/kg), Cr (3.89–1152 mg/kg), Li (2.92–109.00 mg/kg), and U (0.09–39.23 mg/kg) in the studied coal samples are 2–43 times more than those of the upper continental crust (UCC). (2) Arithmetic mean of Cr, Sc, Mo, As, Ga, U, V, and Cu are higher than those in China coals average, while Na, P, Al, Ti, Ba, Bi, Tl, and Sr are lower. The average content of Cr in the studied coals is 352 mg/kg, which is 22.49, 20.37, and 23.09 times higher than that of China coals average, World hard coals and USA coals average, respectively. (3) In terms of the correlation between element concentration and ash yield, all the elements were accordingly divided into five groups. In addition, three coal samples (No. KM50, KM64 and LM61) were found to have relatively high Cr concentration as 1055, 1072, and 1152, respectively. Analysis of these three coal samples shows an M-type REE enrichment pattern (UCC normalized), with positive Eu abnormlies of 2.96, 2.52, and 3.96, respectively. This pattern is similar to that in Carboniferous ophiolite and primitive mantle, suggesting that they may have the same source of matter. High Cr coal has a potential harmful impact on the environment and human beings during the coal combustion and utilization. Besides, Se and Mo are 2.12 and 8.65 mg/kg on average, respectively, which are 7.31 and 5.08 times more than those in Chinese soil average, thus Carboniferous coal with low Cr-As but high Se-Mo should be considered as potential fertilizer for local crops.