Pollution Characteristics Of Heavy Metal And Environment Risk Assessment In Soil Of Tiefa Mining In Liaoning Province

As the largest producer and consumer of coal in the world, the proportion of coal in the Chinese energy consumption structure is above 70%. As large-scale coal exploitation and utilization provides energy security for economic development, it also does serious damage to the mining environment. During the process of coal mining, processing and utilization, the heavy metal elements in the coal will be migrated and transformed, resulting in the pollution of atmosphere, water and soil, which affects the people's health in the mining. The heavy metal pollution has become one of the severe environmental problems in the coal mining.In this thesis, the largest power coal production base in the northeast of China Tiefa mine area in Liaoning province is chosen as the research area. Through field investigation, and soil sampling, processing and testing, heavy metal content and distribution characteristics, and combination characteristics and sources of heavy metal elements in soil of coal-mine area are analyzed by the integrated thery and methods of analytical chemistry, geochemical chemistry and environmental chemistry. Then the pollution situation is evaluated by enrichment factor index and fuzzy comprehensive assessment model. On these bases, environment risk assessment is perfromed by potential ecological risk index and the health risk assessment model. The main conclusions are drawn as follows:1. The content and distribution characteristics of soil heavy metal in coal mining area. Cd Cr As content in soil of Tiefa mining area exceeds standard ,pollution is relativly serious. The variation coefficient of all kinds of heavy metal elements in soil of Tiefa mining is between 0.41 and 0.77, and belong to strong variation,which indicate that the content of soil heavy metals is seriously affected by human activities. Along with the growth of exploitation time, Co and Th content is gradually increasing, while Cr content is gradually decreased, but the decrease is not obvious. As and Cd content at every coal-mining area is close, relatively stable, except that As content in soil of Daming mining area is obviously higher than that in others. Cu and Zn content has a certaint similarity in every mining area, the mining area with high soil Cu content has high soil Zn content. On the vertical section, surface gathered phenomenon of Cu,As,Se,Cr,Zn are more signifcant, while surface gathered phenomenon of Th, Cd, Co are not significant.2. Combination characteristics and source judgment of Heavy metal elements in mining soil. Through the correlation analysis, principal component analysis and cluster analysis, the main conclusions are drawn as follows: Th, Cd and Co mostly come from the soil parent material, and they are less affected by coal exploitation. The content of Zn and Cu are mainly affected by coal exploitation and transportation system, the content of Se, Cr, Cd and As are controlled by both soil parent material and coal exploitation.3. The soil heavy metal pollution evaluation in the mining. Firstly, the enrichment degree is analyzed by enrichment factor index, and the results shows that the soil of all mining area is polluted by Cd in the certain degree, the pollution scope of As, Se, Cr and Th are large too, the whole order of enrichment degree is that Daming > Dalong > Xiaonan > Xiaoming > Daxing > Xiaoqing, which means that the mining area with longer exploitation has the more serious heavy metal enrichment. Then the soil heavy metal pollution in every mining area and the whole coal mining are evaluated by the fuzzy comprehensive evaluation model. It can be found that: Cd, Cr and As are main impact factors in Tiefa coal mine. Soil of Daming mining area belongs to light pollution), soil of Dalong and Xiaoming minng area belong to basic cleaning, soil of Xiaonan, Xiaoqing and Daxing mining area all belong to clean, which shows that the soil heavy metal pollution in Tiefa mining is not serious, the environment quality mainly belong to basic cleaning level.4. The ecological risk assessment of the soil of mine area. The ecological risk of Cd is more prominent than others', and belongs to high level. Those of other heavy metal elements are at low level potential Ecological risk following an order of Cd > Cr > As > Cu > Zn. Comparison among all mining areas, the potential ecological risk in Daming, Xiaoming, Dalong, Xiaonan mining area is higher than Xiaoqing and Daxing mining area.The new mining area is slighter than the old. All of mining areas belong to slight ecological risk level, but the sources of Cd need to control because the potential ecological risk of Cd in all mining areas is high.5. The assessment of health risk from soil heavy metal in mining area. The health risk from the soil heavy metal pollution in mining area is evaluated by health risk assessment model. The results indicate that Cd content in soil of Tiefa mine area is higher than the background value of Liaoning province and the national 1st standard, but it does not result in the high health risk value, the threat of human body is small. The mining area with longer mining time has higher personal average risk value. the annual risk value of carcinogenic heavy metal is higher than that of non-carcinogens, the health risk of three carcinogenic heavy metals in turn is Cr6+>As>Cd, so Cr should be primary control index of environment management. The values of annual health risk for adult belong toⅠand II two grades, in same district the level of annual risk for children is generally higher two grades than the adults', it is deduced that the impaction of soil heavy metal on adult body is mild, but the health harm to children is serious, so the impact from soil heavy metal in mining area on children should be focused by related department and soiety.