| Coal is an important fossil energy,and uranium is an important strategic resource for the country.For the occurrence condition of coal and intergrowth uranium represented by Ordos Basin,for safe,efficient and environmental mining the resources of coal and uranium,and to reduce the adverse impact on the mining of coal and uranium and environment,it is necessary to study the occurrence environment of coal and uranium,and to carry out research on the mechanism and characteristics of mutual disturbance of coordinated mining of coal and uranium,and put forward safety evaluation criteria for the coordinated mining of coal and uranium and optimization of mining technology.Because the sandstone-type uranium is deposited in the uranium mineralization aquifer above the coal seam,the process of in-situ leaching mining involves the chemical reactions of leaching solution and uranium oxide,solute physical movement.For the solute physical movement that the horizontal and vertical migration of leaching solution happened under the influence of seepage,molecular diffusion and flow dispersion based on water differential pressure.The whole process of in-situ leachinguraniumminingis a dynamic coupling process of solute reaction-transportation.The coal seam mining is a dynamic coupling process of stress field,fracture field and seepage field.In other words,coordinated mining of coal and uranium is the dynamic coupling process of stress field,fracture field,seepage field and solute reaction-transportation.Based on the occurrence environment of coal and uranium,the micro-pore morphology and material composition of coal,sandy mudstone and conglomerate were analyzed.Indoor stress-seepage experiment was completed for intact sandstone,sandy mudstone,fractured sandstone,fractured sandy mudstone and large scale conglomerate porous media.Based on the experiment results,the FLAC3D-CFD simulator was used to simulate the solute reaction-transportation process in uranium ore-bearing aquifer and the stress-seepage-solute transportation coupling process in single and double fracture of sandy mudstone.The experimental and numerical model of coordinated mining of coal and uranium were established.Moreover,the transparent material and FLAC3D-CFD simulator were used to simulate the coordinated mining of coal and uranium including synchronous mining,uranium-first mining and coal-first mining.The coupling characteristics of stress field,fracture field,seepage field and solute reaction-transportation were monitored.The preliminary standard for the safety grade of coal and uranium coordination mining was established.And the technical concept of coal-uranium mining corridor and the coal-uranium isolation corridor was developed.The main conclusions of the paper are as follows:?1?Sandy mudstone is composed of the feathered matrix,and the pore and fissure are nearly undeveloped and its permeability is weak,and its permeability was dominated by the macroscopic fissure and micro-dissolution.The conglomerate is composed of matrix and pore,and its pore distribution is sparse and the porosity is low.Its main components are matrix,which has a poor permeability.Sandy mudstone is mainly composed of quartz and kaolin.And different types of sandy mudstone have a different concentration of kaolin.The higher content of kaolin,the more densify of the internal structure of sandy mudstone.The existence of the kaolin means that sandy mudstone has a certain water-absorbable and swell-able properties.The stratified green sandstone,gray green sandstone and gray sandstone are interphase distribution with each other in uranium mine,the permeability of uranium deposit is represented by anisotropy.?2?In the permeability experiment of sandstone,sandy mudstone,and porous media of conglomerate aquifer,hydraulic pressure and confining pressure present an important role on the permeability changes of intact rock mass,fractured rock mass and the porous media.With the increase of hydraulic pressure and the reduction of confining pressure,the permeability gradually increases.In contrast,the permeability gradually decreases,compared with the intact rock mass,crack and porous medium are more sensitive to the change of hydraulic pressure and confining pressure.The permeability of sandstone media with double fractures is 2 to 4 times than the sandstone media with single fracture,and the permeability of sandy mudstone with multi-crack is one to two higher magnitude to the sandy mudstone with single fracture.Compared with medium sandstone,the permeability of sandy mudstone and porous media is related to the content of swelling mineral and mixed components,the effect of crack expansion in sandy mudstone,the transport effect of porous media under low stress and the crushing effect under high stress significantly affect the fluid state and the characteristics of seepage.And under the interaction of stress and composition,the effect of wall and wedge appear in porous media of conglomerate aquifer.?3?The accuracy of porous media and fracture medium numerical model of FLAC3D-CFD is verified by the test data.The rate of leaching uranium is positively related with the solution concentration,and the residual amount of uranium is exponential with the mining time.The grade of uranium has important influence on uranium leaching.The higher the grade of uranium,the higher the mining speed is.The permeability of the porous medium in uranium deposit is enhanced and the chemical dissolution effect of the leaching solution is accelerated under the effect of stress disturbance.The distribution of stress and seepage in the rough fracture surface present anisotropy,and the crack width is related to the confining pressure in negative exponential form.The fracture conductivity is positively correlated with the effective void,and negatively correlated with the gap degree and the asperity height of the fissure surface.The velocity of fracture solute transport is positively correlated with crack width and fissure seepage velocity,solute concentration is negatively correlated with fissure width and seepage velocity compared with the velocity of solute transport.At the same time,the concentration of solute is high and the fracture solute decreases with the negatively exponential form of larger fissure surface and smaller effective void.In the rock mass with double fractures,the low concentration solute is concentrated at the intersection of fissures,and the eddy current and inertia flow are obvious under high velocity seepage.?4?Silica gel powder mixed with mineral oil can be formulated into the layer of coal and uranium deposit.Under the disturbance of overlying pressure,the white area can be formed due to the automatic oil separation,which can simulate the fracture zone formed by the disturbance of coal seam mining,and saturated oil-red O has good dyeing effect,which can effectively track the migration of uranium leaching solution in transparent soil.The maximum height of fracture field is about 90m with the apperance of the"arch-crack"fissure interface.In the scenario of uranium mining first,uranium leaching solution will not flow into coal seam during uranium mining.In the scenario of synchronous mining of coal and uranium,the leaching solution of uranium ore will not seep into the working face in short-term period.In the scenario of coal mining first,the leaching solution of uranium ore is mainly kept horizontal movement in short-term period,and the vertical seepage phenomenon is not obvious.For a long time,it is possible to penetrate the protective layer,penetrate into the fissure zone,and accelerate the seepage velocity under the convection effect of the fissure zone.?5?The fracture geometric zone of loose conglomerate aquifer considering the situation of fully coal mining and after fully coal mining was developed,and the spatiotemporal dynamic coupling process of the stress field,seepage field,fracture field and solute reaction-transport field was simulated by FLAC3D-CFD.When the working face advanced 160m,the largest main stress shell was formed around the fracture field,and the maximum principal stress shell is broken when working face advanced 280m,and a new stress shell was formed with the stress concentration zone in the middle of stope.Coal seam stress dis tribution was seriously disturbed by coal mining,conglomerate aquifer is general and uranium deposit is slight.The diffusion depth of the leaching solution is negatively correlated with the injection velocity and the ratio of injection and drainage in exponential form,and positively correlated with the diffusion coefficient,and is increasing rapidly after 1×10-4 m2/s in vertical direction.Corresponding to stope connecting the atmosphere and working face connecting the atmosphere,in the scenario of ura nium mining first,the leaching solution is infiltrated into stope with"funnel-like"and"asymmetric saddle-shaped"form in a certain period,and under the condition of coal mining first,the leaching solution is infiltrated into the goaf with"saddle-style"and"inclined funnel-shaped"shape under the lower extraction ratio in a certain period.Under the condition of synchronous mining of coal and uranium,there is no obvious infiltration in the leaching solution during the short period of mining,and the leaching solution does not appear under completely sealed stope. |
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