Study On Formation Mechanism And Influence Of Acid Water In The Old Goaf In Shandi River Basin Of Yangquan City

China is rich in coal resources,and the main mode of mining is underground mining.As a result,the problem of coal mining is relatively more,especially in the mined area of coal mine,the problem of water accumulation in the goaf is more prominent.Before and after the integration of coal mines,there existed underground space such as small coal mines exploitation,various private acquisitions and mined-out areas formed by normal coal mining.These spaces generally lack detailed mining data and become the storage space of groundwater.In the process of groundwater convergence,there will be various physical and chemical effects and the role of microorganism in the goaf of coal seam.The gob area water gradually formed the characteristics of the old kiln acidic water.At the same time,the continuous gathering of groundwater and the rising of water level lead to the formation of the gob of acidic water in the proper position to form a flow point.The excreted old kiln water easily pollutes the regional environment and the surrounding river water system,and also has the risk of seepage pollution to the regional groundwater.This paper is based on the research background of the Shandi river basin in Yangquan,Shanxi province,through the collection of data,field investigation,laboratory experiments,field sampling and other means to analyze the formation of acidic water in the Shandi river basin.We mainly understand the general situation of the basin,the geological and hydrogeological conditions in the basin range,the distribution of coal mines and the characteristics of the coal quality.The coal mine integration and mining situation in the area is analyzed.Defining the distribution of goaf areas in coal mines.The amount of water in the old coal mines in the basin is estimated and calculated.The forming conditions of the acidic water in the old goaf were analyzed to explore the water filling factors of each coal mine in the basin.In this paper,the factors influencing the formation of acidic old empty water were analyzed.The formation process of water chemistry of calcium sulphate-type old kiln acidic water is explored.Through the laboratory experiment,the samples of the collected pyrite,No.12 coal and No.15 coal were oxidized and dissolved.The water quality and pollution of different sections of the river are analyzed by sampling and testing.Soil samples were collected from the arable land flowing through the old kiln acidic water in the Liugou at the Shandi river basin to analyze soil characteristics and the distribution of sulfate ions.Through calculation,we can see that the coal seams of various coal mines have different degrees of water accumulation.The largest water accumulation area is Qianniushan coal mine up to 2.45 square kilometer,the largest amount of water accumulation is 2.658 million cubic meter.And the minimum water area is Yankan coal mine up to 0.21 square kilometer,and the minimum amount of water accumulation is 0.2139 million cubic meter.When the solid-liquid ratio is 1:100,1:50,1:20,the overall pH value tends to increase,the overall Eh value shows a decreasing trend and the EC value shows a decreasing trend.Regardless of the solid-liquid ratio,the bivalent iron ion concentration is higher than the ferric ion concentration,and the bivalent iron ion concentration,trivalent iron ion concentration and total iron concentration are both increasing with the solid-liquid ratio increasing.The reaction rate of pyrite was 0.016524mg/h,0.025284 mg/h and 0.048624 mg/h respectively when the solid-liquid ratio of pyrite was 1:100,1:50 and 1:20.The reaction rate of No.12 coal was 0.004464mg/h,0.006408 mg/h and 0.010464 mg/h respectively when the solid-liquid ratio of pyrite was 1:100,1:50 and 1:20.The reaction rate of No.15 coal was 0.001368mg/h,0.002376 mg/h and 0.003192 mg/h respectively when the solid-liquid ratio of pyrite was 1:100,1:50 and 1:20.Therefore,the greater the solid-liquid ratio,the greater the release rate of iron.The content of reactants affects the speed of reaction.The larger the content,the larger the contact area,and the greater the reaction rate.By comparing the same solid-liquid ratio of different materials,regardless of the solid-liquid ratio,the pH value is an upward trend,Eh overall decline and EC relatively flat decline.The concentrations of Fe²⁺,Fe³⁺and total iron are all the highest in pyrite,followed by No.12 coal and the smallest is No.15 coal.Through calculation,the reaction rate of pyrite is the largest,followed by No.12 coal and the smallest is No.15 coal.It can be seen that the content of FeS₂ in the sample affects the reaction rate and the concentration of SO₄^2-.According to the results of water quality monitoring,Cl^-,CN^-,volatile phenol,As,Cr⁶⁺and Pb pollution were not found in the basin,but other indicators showed different degrees of pollution.Among the over standard ions,the lowest single pollution index of ferric ion is 1.2,the highest is 4253.3.The lowest single pollution index of ferrous ion was 14.3,the highest was 4546.7.And the lowest single pollution index of sulfate ion was 2.5,the highest was 79.3.According to the results of soil sample test,the content of SO₄^2-in cultivated land is high,and the content of Zn,Cl^-and NO₃^-is relatively high,while the contents of other ions and heavy metals were relatively low.The distribution of SO42-concentration in the AB and CD sections in the horizontal and vertical directions is analyzed.Because of the diffusion and adsorption,the farther the horizontal distance is,the lower the concentration is.The lower the depth is,the lower the concentration is.