Simulation Of Gas Adsorption Characteristics And Groundwater Quality Response Of Closed Coal Mine

After closing the pit,the high-gas coal mine still has a large amount of gas and groundwater rebound.A three-phase multi-component system of mine water-coal-rock-gas in mine closure is formed.Three-phase reaction may bring the risk of gas leakage and groundwater pollution.Taking the closed coal mine water-rock gas reaction simulation experiment system as the experimental platform to simulate the water-coal-gas interaction process of the closed mine.Then based on the experimental methods of X-Ray fluorescence?XRF?,X-Ray diffraction?XRD?,field emission scanning electron microscopy?FESEM?,mercury intrusion porosimetry,low temperature liquid nitrogen adsorption method,CO₂ adsorption,gas isothermal adsorption,inductively coupled plasma-mass spectrometry?ICP-MS?,ion chromatography and other analytical test methods,analyzed the element content,mineral content,micro-morphology,pore structure,gas adsorption characteristics and changes in groundwater quality of coal under three-phase action.The main research results obtained in this study are as follows:?1?The characteristics of mineral dissolution and element release and the change of microstructure in coal under three phase action are revealed.Under the action of three phases,the content of minerals and elements in coal changes.The reaction on carbonate minerals in coal is the strongest and the calcite decreased the most.Corrosion crystal cone and new crystal faces appear on the surface of calcite.Dolomite is next,and new dissolution ravines are formed on its surface,so Ca and Mg elements in coal have higher mobility.Clay minerals react slowly,The evolution of feldspar to illite,the evolution of primary illite to kaolinite,the decrease of chlorite and illite is small and the content of kaolinite increases.Na and K elements have high mobility,while Al and Si elements have low mobility.The content of minerals such as quartz hardly changes.New mixed carbonate minerals and gypsum minerals are formed on the surface of pyrite and siderite,causing pores and cracks to be blocked.Low mobility of elements such as P,S and Ti.CO₂ gas promotes the dissolution of carbonate minerals.Under the two gas phase reaction conditions of CH₄and CO₂,clay minerals,oxides and sulfide minerals have the same change range.?2?The characteristics of pore structure evolution and gas adsorption under three phase action are revealed.Under the action of three phases,the pore volume of coal sample increases.The total specific surface area of coal samples in Sihe Mine,Zhaozhuang Mine and Maidizhang Mine decreased,and the specific surface area of coal sample in Bakuang Mine increased.The pore size distribution of coal did not change significantly.The number of pores less than 100 nm and more than 30?m increased significantly.High-rank coal has the largest change in pore volume?473.38%?.The change of pores in coal was accelerated by CO₂ gas,and the influence of CO₂ gas on the pores>30?m macropore was greater than that of CH₄ gas.Under the action of three phases,the volumes of the non-effectively interconnected pores of the coal samples greatly increased more than those of the effectively interconnected pores.The pore structure and coal sample connectivity of the pore size of 1.7-200 nm did not change significantly.The gas condition does not determine the change of pore connectivity of coal sample.Under the action of three phases,the adsorption volume of coal sample V_L of sihe mine,zhaozhuang mine and maidizhang mine decreased,while that of coal sample V_L of baishan mine increased,and there was no obvious change rule of coal sample P_L.Under different gas phase conditions,the three-phase reaction should have little influence on the change of coal sample V_L.The three equations can well describe the experimental data of gas isothermal adsorption before and after the three phase reaction of coal.The fitting accuracy of the DA equation and the BET equation to the high-rank coal sample isotherm adsorption experimental data is higher than that of the Langmuir equation,and the Langmuir equation fits the low-rank coal sample with higher accuracy.?3?The water quality of mine closure under three phase action is discussed.In the reaction process with CO₂ as the gas phase,pH value increases,Eh is negatively correlated with pH and decreases gradually.The HCO₃^-increased with the increase of reaction time.The content of SO₄^2-in closed mine water in sihe mine and zhaozhuang mine increased,while that in maidizhang mine and baishan mine decreased.The dissolution of carbonate minerals increases the content of Ca and Mg elements in closed mine water,and the dissolution of clay minerals increases the content of K,Na,Al and Si in the reaction solution.The content of major elements in closed mine water is high under the condition of CO₂ is gas phase.The trace elements in closed mine water are fluctuant,the content of Mn and Ni exceeds the standard of groundwater,so it is necessary to strengthen the monitoring of water quality in mines with high gas closures,so as to avoid the deterioration of water quality and the pollution of shallow groundwater.This thesis contains 43 figures,18 tables and 131 references...