Environmental Behaviors Of The Whole Life Cycle Of Coal And Their Effects On Land Resources

Coal resource is an important material foundation for the sustainable development of national economy,and its development and utilization processes have an obvious life cycle.There are different production and utilization mode of coal resources at different life cycle phases,which leads to different pollution forms and levels on the ecological environment,also with different environmental impact behavior characteristics.In this thesis,the whole life cycle of coal was divided,the pollutants contribution and distribution characteristics at different phases were investigated,the gas carbon source and soil carbon sink on the coal mining phase were evaluated,the distribution characteristics of soil heavy metals on coal utilization phase were analyzed,the environmental impact behavior and the cumulative effect on soil environmental and the accumulation characteristics of land damage at different life cycle phases were also assessed based on the definition of the whole life cycle of coal.The main results are as follows:1.The coal whole life cycle was divided into five phases: coal mining,coal processing,coal transportation,coal utilization and waste disposal.This phase division of the whole life cycle of coal reflects the integrity of the coal life cycle and the difference among each phase characteristics better,which is conducive to systematic study of the coal ecological risk assessment.It is also pointed out that coal mining and utilization are the two important phases of coal environmental risk potential release.2.The calculation models of the greenhouse effect potential of gas carbon source and the carbon sink of regional ecosystem were established respectively,and the carbon source/carbon sink effects caused by the change of land use on the coal mining phase of Jiawang mining area in Xuzhou were investigated.The research results show that:(1)The greenhouse effect potential per ton coal in China was estimated as108.11 kg CO2 equivalently,while it is 12679 k ton CO2 equivalently in Jiawang in the studied period,which reaches 6.76 times of the regional vegetation-soil carbon sink(1874.90 k ton CO2 equivalently).(2)The carbon sink capability is weakened obviously due to the coal mining activities,and the annual vegetation-soil carbon sink is decreased by 10.23% in Jiawang from 1990 to 2010,while it is stable in the same period in Xuzhou.(3)Coal mining activities have influences on regional ecological types,and the effects on negative carbon sink are greatly enhanced.The negative carbon sink in water area is increased by 3.51% per year,and the total incrementreaches 73.79% in Jiawang,contrary to a decreased trend in Xuzhou.(4)Water area and construction area increase monotonically during the mining process,however,the decay trend for carbon sink is not weakened after mine closing,and an upward trend still exists in the negative carbon sink of water area.The annual carbon sequestration is decreased by 4.10% and 6.39%,and the negative water carbon sinks is increased by55.33% and 11.89% respectively during the period of coal mine expansion from 1990 to 2000 and the subsequent closure of coal mines in the following 10 years in Jiawang area.3.The distribution characteristics of seven kinds of heavy metals in the soil in Xuzhou at the coal utilization phase were analyzed.(1)The contents of Cd,As and Zn are below National Soil Quality Level 2 and the soil background value of Xuzhou;also below National Soil Quality,while lager than the soil background value of Xuzhou for Cr,Cu,Hg and Pb.(2)The main impact factors of the relativistic heavy pollution Cr and light pollution Cd include the mining activities,coal combustion in brick factory and the wind direction.(3)The relationship between relativistic heavy pollution Cr content in a small scale and the impact factors including pH value,organic matter,organic carbon,the distances to mining area,to city and to rivers was analyzed quantitatively,and the regression models heavy about relatively severe,moderate and mild pollution Cr were established.Among them,the correlation coefficients of pH value,organic matter and organic carbon in relativistic severe polluted area are estimated as 0.7262,0.6914 and 0.6891 respectively;the correlation coefficients of the distance to mining area,the distance to city and the distance to river in moderate polluted area estimated as-0.6775,-0.7216 and-0.6263 respectively;and the correlation coefficients of pH value,organic matter and organic carbon are in mild polluted area estimated as 0.9745,0.476 and 0.471 respectively.The soil physical and chemical properties in severe and mild polluted areas have significant effects on the content distribution of heavy metal Cr,while the distances to the mining area,city and rivers are the important factors on the content distribution of heavy metal Cr in moderate polluted area.4.Geoaccumulation index and Potential risk index were used to analyze the cumulative effects of coal environmental behaviors in Xuzhou,and the results show that:(1)Cumulative risk degree of Cd and Hg from raw gas and that of Cd from net flue gas in coal combustion are higher;cumulative risk degree of Cr and Pb from raw gas and Hg and Pb from net flue gas is medium,while those of As from raw gas andCr and As from net flue gas do not present the ecological risk characterization.(2)Potential hazard degree to soil environment in heavy metals in slag and ash from coal combustion is relatively higher,the damage of heavy metals in coal is medium.For the damage to soil environment,it is the highest for Hg element,relatively higher for Cd element,and relatively lower for Pb,As and Cr elements.5.The environmental effects at various phases in coal whole life cycle were analyzed,specific measures to improve the environmental behavior of coal in Xuzhou were put forward,regional characteristics also with the internal and external factors of environmental behavior in China were analyzed,and the ideas concerning of establishing green collaborative development of coal life cycle,strengthening the investigation of natural conditions and developing new energy and specific response strategies of negative effects of coal environmental behavior were proposed.