Influence Of Gangue Grouting Backfill On Groundwater In Separation Layer Of Menkeqing Mining Area

Coal gangue is a co-product in the process of coal mining.It is usually piled up on the surface in large quantities,which wastes land resources and also damages the environment.It is also a matter of concern whether the use of gangue to fill the separation space and goaf will have a great impact on the groundwater environment.Based on the national key research and development project“Material and technology for prevention and control of groundwater pollution in coal mining area”,this paper studied the whole process of aquifer pollution from coal seam mining to gangue filling separation space.Firstly,the position and volume of coal seam roof separation were inferred through numerical simulation analysis.Then the composition of gangue was studied,and the leaching rules of different components in gangue were analyzed by immersion tests,and the ions that might cause pollution to the environment were determined.Finally,the GMS software is used to simulate the migration and diffusion of pollutants and judge the influence of gangue filling on aquifer in a long time scale.（1）Based on the geological data,hydrogeological data and mining conditions of Menkeqing mining area,a numerical model was constructed by using 3DEC software to simulate the process of roof separation space generation and the volume after separation stability in the process of 3-1 coal mining.The simulation results show that the stable separation with the potential of water storage is located between the thick medium-grained sandstone and sandy mudstone of Anding Formation in the middle Jurassic.It is observed that the separation space is 180 m in length,100 m in width and 1.7 m in height.（2）Coal gangue from the three Jurassic coal mine areas of Menkeqing Coal Mine,Hongliulin Coal Mine and Xiaojihan Coal Mine were selected on the Yishan slope in the Ordos Basin.According to X-ray diffraction and X-ray fluorescence spectrum analysis,the chemical components of the three kinds of coal gangue are mainly Si O₂,Al₂O₃and Fe₂O₃.The main mineral components of the three coal mines are mainly quartz,clay minerals.（3）A total of 45 coal gangue samples from three mines were soaked,48 indexes were detected,and the leaching differences of each component in gangue under different soaking conditions were studied.It was found that the leaching concentration of As,CD,Hg,Pb,Ni,Cu and Zn was lower than the detection limit,and the pollution was negligible.Comparing the leaching concentration of each component with the groundwater quality standard,it is found that only Na⁺and SO₄^2-exceed the groundwater class III standard under the condition of mine water immersion.The Sr element concentration even exceeds the national mineral water quality standard,and resource utilization can be considered.Based on the above results,it is believed that the separated gangue in Menkeqing mining area will not have a great impact on the environment after grouting and filling.（4）GMS software was used to simulate and predict the long-term impact of separated fillings on aquifers.Na⁺,SO₄^2-and Cr ions are selected as pollutants,and the model only considers convection and dispersion.The simulation results show that the diffusion range of the three ions is about 220m in length,150m in width and 20m in height during 0-20 years.In practice,considering the possible chemical reactions of water-rock interaction,the diffusion distances of these three ions will be further reduced.From the point of view of the whole mining area,separate layer grouting will only affect the local stability group sandstone aquifer.The impact on the water quality of the whole mining area is small and it will not produce significant pollution problems.