Heavy Metal Precipitation Migration Control And Reclamation Evaluation Of Gangue Filling And Reclamation In Mining Sinkhole Areas In Western Ecologically Fragile Mining Areas

Large-scale coal exploitation in arid and semi-arid mining areas in western China has resulted in large area surface collapse,resulting in soil deterioration/water loss,vegetation damage,desertification and other ecological environmental damage problems in the subsidence area.At the same time,the coal gangue produced in the process of coal development is piled up on the ground,which not only occupies a large amount of land,but also causes the pollution of the soil and water environment in the mining area.Therefore,how to minimize the damage of surface subsidence and gangue accumulation on the ecological environment of mining area is an important problem facing the coordinated development of green efficient mining and environmental protection in western ecological fragile mining area.Based on the research background of the typical arid and semi-arid ecologically fragile mining area in Ningdong,this thesis systematically studies the spatio-temporal evolution law of surface subsidence and ground fractures in the typical ecologically fragile mining area by using the research methods of field test,laboratory test,numerical simulation and industrial test,divides the failure types of the subsidence area,and puts forward the method of gangue filling and reclamation in the coal mining subsidence area.The background content of heavy metal elements in gangue backfill materials and the rule of gangue-soil heavy metal precipitation and migration were systematically analyzed.The permeability and stability of soil structure of different gangue backfill reclaimed soil and the control effect of gangue heavy metal were studied and analyzed.The heavy metal migration control method of gangue backfill reclaimed soil in subsidence area was proposed,and the evaluation model of gangue backfill reclamation effect in subsidence area was constructed.It has realized the quantitative evaluation of reclamation effect in the subsidence area.The research results provide theoretical and technical support for the treatment of subsidence and environmental protection of ecologically fragile mining areas in western China.The main achievements are as follows:(1)The D-In SAR technology is used to analyze the temporal and spatial evolution characteristics of surface subsidence during mining in Ningdong typical mining area.It is found that the center of surface subsidence basin gradually moves to the stop-mining line during mining,and there is an obvious "mining lag effect" between surface subsidence and underground mining.Based on the remote sensing images of unmanned aerial vehicle,the distribution characteristics of surface cracks in subsidence area were extracted.Based on the rules of surface subsidence and the development characteristics of ground cracks,the classification system of subsidence failure was established based on the goal-oriented gangue filling and reclamation in subsidence area,and the subsidence zoning was divided into three types: bending subsidence type,fissure-step type and collapse pit type.The reclamation methods for different types of damaged areas using gangue backfill are put forward.(2)Based on field sampling and laboratory testing and analysis,the background content and enrichment coefficient of heavy metal elements in gangue backfill materials were systematically studied.It was found that the enrichment coefficient of heavy metal elements in fresh gangue from large to small was As > Cd > Pb > Cr > Zn > V > Cu >Mn > Hg > Ni.Through the dynamic leaching experiment of gangue,the change of concentration and precipitation rate of heavy metals in gangue under the dynamic leaching condition were revealed,the horizontal and vertical migration of heavy metals from gangue in soil was clarified,the risk assessment of soil heavy metal pollution was carried out,and the main prevention and control scope and object of soil heavy metal pollution were put forward.(3)Based on the reclamation methods of gangue filling soil,gangue separating,gangue separating and gangue separating,the permeability characteristics and stability of reclaimed soil under different compaction conditions are studied.It is found that under the same conditions,the thicker the soil layer is,the lower the permeability of reclaimed soil,the better the isolation effect of reclaimed soil for gangue heavy metals,and the stronger the anti-deformation ability of reclaimed soil.The thicker the isolation layer is,the lower the permeability is,and the stronger the stability of the reclaimed body is.The permeability of soil-gangue structure,soil-isolated layer-gangue structure,soil-gangue isolated layer-isolation structure,soil-isolated layer-gangue isolated layerisolation structure decreases successively,and the soil-isolated layer-gangue isolated layer-structure has the largest compression modulus,the strongest compressibility resistance,and the more stable reclamation body,so the best reclamation scheme in the subsidence area is determined.(4)The control effect of soil-septum-gangue-septum,soil-gangue-septum,soilseptum-gangue,soil-gangue and soil-gangue reclamation structures on the early and late precipitation and migration of heavy metals in gangue filling reclaimed soil was studied through the combination of laboratory soil column leaching test and COMSOL numerical simulation.The mechanism of controlling heavy metal migration by weathering gangue,clay and activated carbon as isolation layer was revealed.The structure type of reclaimed soil for gangue filling based on heavy metal migration control was established,and the control effect of heavy metal in reclaimed soil of bending subsidence type,crack type,step type and collapse pit type was determined.(5)Based on the field engineering test,the content of heavy metal elements such as V,Cr and Mn in the soil before and after the reclamation in the No.13 mining area of Zaoquan Coal Mine in Ningdong was tested,and the control effect of the reclamation scheme on the heavy metal elements in the soil was verified.At the same time,a variety of suitable vegetation such as cat’s head and wolfberry were screened for ecological restoration.Based on Landsat satellite,remote sensing images of pre-mining,midmining,post-mining and post-restoration in the mining area were analyzed for vegetation coverage.It was found that mining activities would reduce the surface vegetation coverage in the mining area,while the surface vegetation treatment and restoration in the subsidence area could reduce the impact of mining activities on the surface vegetation.Improve the surface vegetation coverage;Finally,the fuzzy comprehensive evaluation model of vegetation restoration effect in coal mining subsidence area was built through the fuzzy comprehensive evaluation method to realize the quantitative evaluation of vegetation restoration effect in 13 mining areas.The evaluation results show that the restoration effect in subsidence area is better.There are 99 figures,42 tables and 135 references in this thesis.