| China's Ordos Basin is a large-scale energy base where there are large-scale coalfields and world-scale sandstone uranium deposits.The uranium and coal resources overlap and coexist in this region thus forming complex mineral arrangement.The uranium deposit is located about 100 m above the coal mine.In-situ leaching mining of uranium mine is carried out,and long-wall method for mining is adopted in coal mine.In order to ensure the safety of the roof in coal mining,the top aquifer must be regularly drained and depressurized to ensure safe roof during construction,and coal mine drainage water will inevitably lead to drop in the water level of the leaching solution for uranium deposits.The planned coordinated mining methods are as follows: the coal mine is mined westward from the first mining area;after the underground uranium mining ends,the coal mine is mined eastward from the first mining area.Co-development of these resources may bring out a series of safety and environmental problem.When the coal mines dredge the water again,the water barriers between uranium coal mines will be cut off and artificial funnels come into being,which will result in migration of Radon solution in the region to the direction of coal mine drainage and will cause a lot of security risks.For example,radioactive radionuclide(Radon)containing higher concentrations migrate to hydrophobic areas of coal mines and diffuse into the coal mine roadway along the air with porous media so that the Radon concentration in the working environment of coal mines increases,thus the risk of radiation hazards increases.According to the characteristics of Radon migration to coal mine roadway,the rock layer is simplified into porous medium.According to the principle of solute transport in porous medium,it is divided into two stages: leaching mining accompanied by drainage and exhalation from Radon-containing solution.The first mathematical model of saturated/unsaturated migration in a porous medium immersion solution is established;and the second mathematical model is to establish Radon exhalation model of radon-containing solution under different temperature and humidity conditions,and finally to predict the concentration of Radon in the coal mine,providing design parameters for coal mine ventilation and theoretical basis for control.This is also an important basic research topic of radiation environmental safety in the coordinated mining of uranium coal.It has important theoretical significance and practical significance for promoting coal mine safety production and realizing comprehensive exploitation and rational development of two resources.This paper intends to establish a saturated/unsaturated Radon migration model in coal mining areas under in-situ leaching uranium mining and Radon exhalation model of radon-containing solution during discharging so as to simulate the migration process of Radon from uranium-bearing rock formations to coal seam roadways.The migration law in the process of water discharge can predict the Radon exhalation in the coal seam roadway,which will provide a theoretical basis for the design of the ventilation drainage system and the Radon reduction system in the coordinated mining of uranium coal.This paper intends to establish a saturated/unsaturated Radon migration model in coal mining areas under in-situ leaching uranium mining and Radon exhalation model of radon-containing solution during discharging so as to simulate the migration process of Radon from uranium-bearing rock formations to coal seam roadways.The migration law in the process of water discharge can predict the Radon exhalation in the coal seam roadway,which will provide a theoretical basis for the design of the ventilation drainage system and the Radon reduction system in the coordinated mining of uranium coal.This paper is based on the theory of gas-liquid two-phase migration in porous media,the diffusion-seepage migration theory of Radon,and the Radon exhalation theory between two phases.Research on the Radon migration of coal mining areas under in-situ leaching uranium mining to coal seam roadways have been carried out by means of theoretical analysis,model tests,regression design,inversion design,numerical simulation and engineering application.The main contents of the thesis are as follows:(1)According to the actual working conditions,the mathematical model of one-dimensional saturated/unsaturated migration of Radon-containing solution in coal mining areas under in-situ leaching uranium mining and draining water has been established.Based on this mathematical model,each hydraulic parameter has been established respectively.(2)The one-dimensional saturated/unsaturated transport test device and measurement method for the Radon-containing solution in the process of leaching mining and draining water were investigated,and the experimental study on the saturated state of the Radon-containing solution in the leaching mining saturation/unsaturated conditions of the drainage water were carried out.According to the test results,the hydraulic parameters(seepage rate,diffusion coefficient,delay factor and Radon fluid factor)and the Radon concentration under saturated/unsaturated conditions were obtained under one-dimensional conditions.(3)According to the relevant parameters of the Radon-containing solution in the porous media under one-dimensional conditions,the three-dimensional Radon-containing solution in the porous media migration model has been established.According to the actual topography and geomorphology,migration parameters of Radon in the saturated/unsaturated porous medium leaching solution were studied by inversion method.Permeability,diffusion coefficient and retardation coefficient were analyzed by orthogonal test,taking the inversion results as parameters,and regression model was used to fit the mathematical model of the diffusion coefficient and retardation coefficient relative to the permeability.(4)Mathematical model of liquid-gas exhalation for one-dimensional Radon-containing solution has been established.Corresponding indoor experiments were carried out to study Radon exhalation rate and transfer velocity between two phases under different temperature and humidity(specific environmental conditions of coal mine,temperature 15-35°C,humidity 65%-95% RH)were measured.And the mathematical model of temperature and humidity relative to the Radon exhalation rate and transfer velocity has been established.(5)According to the Ansys CFX software based on the finite volume method,the resource areas in which the uranium coal overlaps in the Nalingou uranium mine and the Taran Gale mine were investigated.The working conditions were leaching mining of uranium mines and regular discharging of water in coal mines.The actual physical transient analysis model of Radon-containing solution transported in porous media has been established and the migration law and concentration distribution of uranium mine and coal mine during coordinated mining has been obtained,which can provide a theoretical basis for the control and discharge of Radon. |
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