Geochemical research of the impact of Se-Cu-Mo-V-bearing coal layers on the environment in Pingli County, Shaanxi Province, China

This paper presents a geochemical study on the impact of Se-Cu-Mo-V-bearing coal layers on the environment in Pingli County, Shaanxi Province, China. Analysed samples for environmental geochemical study (rock, soil and edible plant) were collected from the abandoned Dragon Village coal mine on the northern bank of the Pingli River, and the Shanliya coal mine area still in exploitation. Experiments on coal combustion were made in order to determine the amount of Se released from coal burned by local inhabitants. There are three main ways by which coal beds enhance Se, Cu, Mo, and V in the environment in the study area. First of all, supergene geological processes involving soils derived from the Se-bearing rocks and the weathering of coal are the main control on the redistribution of Se, Mo, and other trace elements in Pingli County. Coal seams in the Shanliya contain as much as 48 mug g(-1) Se, 452 mug g(-1) Mo, and 335 mug g(-1) Cu, whereas the soil has 0.85-7.10 mug g(-1) Se, 46-227 mug g(-1) Cu, and 8-29 mug g(-1) Mo. Selenium is enriched in the weathering crust of coal beds with values of 88.4 mug g(-1) Se in a calcareous sinter from the top of the weathering zone. Therefore, edible plants possible may accumulate Se, Zn, Cu, and Mo, for instance, with value above 20 mug g(-1) Cu from sesame and peanut growing in the area. Second, coal beds in the Dragon Village coal mine contain 96 mug g(-1) Se while the Se concentration of soils is high, ranging from 27 to 29.5 mug g(-1) Se. As a result, some plants have high Se contents (0.08-28 mug g(-1) Se). Variations in Se and Mo contents of the same plant species are due to large-scale geographical variations in environmental Se and Mo of soils and rocks. Finally, it is proposed that most of Se in the coal is released into atmosphere after combustion. The percentage of Se released from coal combustion containing 52.8-53 mug g(-1) Se from the Shanliya mine is 78% on average, whereas that from the coal containing 73-85 mug g(-1) Se from Dragon Village is 98%. Whenever it rains, the Se released in the atmosphere could recycle back to soils and plants on the ground. (C) 2003 Elsevier Science B.V. All rights reserved.