Environmental Geochemistry Of Selenium In Huainan And Huaibei Coalfield

Selenium is a health-related volatile thus environmentally sensitive one among many of the trace elements in coals, which could be released into environment easily during coal consumption especially the combustion. Recently the potential harm to health of exposure to volatile elements from coal has generated more concerns, especially after widely occurred haze and smog. It is of great significance to study the distribution and form of occurrence of trace elements in coal from typical coalfield, especially for the evaluation and prediction of environmental impacts from consumption of coal.The research employed 520 coal samples from 29 selected explorationboreholes in Juji-Huainan coalfield, and 123 samples from 7 mining layers in Huaibei coalfield. The research employed 520 coal samples from 29 selected exploration boreholes in Juji-Huainan coalfield, and 123 samples from 7 mining layers in Huaibei coalfield. Based on the sedimentary conditions, geologic setting, coal properties and elemental analysis, the concentration, distribution and form of occurrence of selenium have been studied in Huainan and Huaibei mining area. The comparison of different samples revealed the sources and factors that impact the enrichment of selenium. The facts of exceeding standards have also been studied. According to the annual discharge of selenium from typical coal-fired power plant in Huainan and peat/gangue-fired power plant in Huaibei, the estimated annual discharge of selenium have been studied and put forward some control measures. The distribution and accumulation of Se in surface environment of low-heating value power plant during 2009-2015 has been studied, providing the basis for the safety assessment of the mining area environment.(1) Content, distribution and mode of occurrence of Se in Huainan and Huaibei coalfieldThe Se content in Huainan coals ranges from bdl (below the detection limit) to 26.17μg/g. Se content in Shanxi formation, Low-shihezi formation and Up-shihezi formation is 7.60、5.28 and 6.91μg/g, respectively. The big gaps of Se content in different coal seams in shihezi formations caused by the uneven input of terrigenous matters. The Se content in 123 coal samples of Huaibei coalfield ranged from 2.38μg/g to 12.01μg/g with a arithmetic mean value of 6.63μg/g. Se content in Shanxi formation, Low-shihezi formation and Up-shihezi formation is 7.31,6.42 and 7.09μg/g, repectively. The Se content varied with the lithological characters, higher in carbon mudstone and lower in sandstone and conglomerate.(2) The evaluation and cause analysis of high-Se content in Huainan and Huaibei coalfieldThe Se content in Huainan and Huaibei coalfield have both high exceed multiple and exceed ratio relative to different indexes. The coal-forming age, active volcanic activities, abundant hydro-thermal fluid and fault, high sulfur content are all contribute on the high Se content in coals from studied coalfield. The similar geological environment makes it easy to explain the enrichment of Se in Huaibei coalfield through the analysis of the drill samples from Huainan coalfield.(3) Environmental risk and countermeasures for Se element release in the power plantAccording to the capacity and the releasing property of selenium of different type of coal-fired power plant, the total annual emissions of selenium is estimated up to 9.08 t by power plants in Huainan coalfield, and about 4.41t in huaibei mining area. The analysis of selenium content in supergene environment surrounding a pithead power plant in Huaibei coalfield shows that, from 2009 to 2015, selenium content in soil and sediment showed a trend of enrichment, the pollution level of selenium increased with time. The content of selenium in water does not change significantly. Considering the remarkable influences of power plant coal-combustion to the accumulation of selenium in regional environment, the corresponding pretreatment of coal is very necessary before using; such as adding of the appropriate adsorption (catalyst) which could work with the dust removal and desulfurization/denitration device for the removal of selenium.