| The greenhouse effect has always been a problem of wide concern in the world.As the greenhouse gas second only to carbon dioxide,methane has a global warming potential more than 20 times that of carbon dioxide,which has a huge impact on the greenhouse effect.Our country as a big coal producing country,in the process of coal mining will produce a large amount of coal gangue,but coal gangue that has not been comprehensively used will form a landfill.Based on actual measurement,the flux of methane discharge for gangue is far greater than the soil.The base number of coal gangue sites in our country is huge,so the methane discharge of coal gangue sites can not be ignored.Based on this,methane emission rules and mechanisms of coal gangue dumps under different ecological restoration measures are studied in this thesis,aiming to make contributions to the formulation of ecological restoration strategies for coal gangue dumps and the mitigation of greenhouse effect.In order to explore the methane emission rule of coal gangue and the relationship between its methane emission and basic properties,the experiment firstly uses the coal gangue of coal mines in Shanxi,Yunnan and Shandong（SX,YN,SD）to construct the coal gangue dumps,and determines the methane emission of coal gangue dumps and the basic properties of coal gangue.It is found that the methane emission rate of the open pit coal gangue landfill gradually decreases with time,and the overall methane emission rate is in the order of SX>YN>SD.The average methane emission rate of coal gangue has a very significant positive correlation with Ro,max,organic maceral and fixed carbon content（P≤0.01）,and a very significant negative correlation with ash content（P≤0.01）.There was a significant positive correlation with vitrinite（P≤0.05）,and a significant negative correlation with inertinite,volatile matter and total pore volume（P≤0.05）.After that,the influence of environmental factors on methane emission from coal gangue dump was explored by using small bottle experiment.It is found that the overall effect of temperature on methane emission of coal gangue is promoting,and the overall effect of water on methane emission of coal gangue is inhibiting.Both acidic and alkaline conditions can change the pore structure of coal gangue surface and promote methane emission.In a certain range,the stronger the acidity or alkalinity is,the more obvious the promotion effect is.In order to explore the methane emission characteristics and mechanism of coal gangue dumps under different ecological restoration measures,the experiment uses coal gangue from a coal mine in Shanxi to construct coal gangue dumps with different measures,and determines the methane emission,soil physical and chemical properties and enzyme activities of coal gangue dumps.It was found that the methane emission flux of each gangue dumps decreased by more than 80%within 14 days,and the overall methane emission reduction effect was as follows:vegetation>shotcrete>soil cover>CK gangue.The thicker the soil cover was,the better the methane emission reduction effect was,while layered soil cover had little effect on methane emission reduction.The ecological restoration measures mainly affect the oxidation process of methane in soil through affecting the physical and chemical properties of soil and enzyme activity,and ultimately affect the emission reduction effect.The soil methanogenesis process has little impact on the methane emission from storage dumps.In order to explore the influence of different ecological restoration measures on methanogens and methanotrophs,the activity,copy number of functional genes and community structure of methanogens and methanotrophs were determined in soil of gangue dumps and coal gangue of blank control group.It is found that the methane emission from the gangue layer of the coal gangue dumps can inhibit the activity of methanogens and promote the activity of methanotrophs in the soil.Vegetation coverage can not only significantly improve the activity of methane functional bacteria in soil,but also increase the copy number of methane functional genes.Among them,there is a greater increase in the activity of methanotrophs and the copy number of pmo A genes,leading to a stronger promoting effect on the methane oxidation process.The final results of this experiment show that soil cover+vegetation cover has the best effect on methane emission reduction of gangue dumps.Considering the factors such as fire fighting and spontaneous combustion prevention of coal gangue,comprehensive measures of soil cover+shotcrete+vegetation cover can be adopted for ecological restoration of newly discharged gangue timely in practical projects,which can effectively reduce methane gas emission.There are 42 figures,21 tables and 141 references in this thesis. |
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