The Variation Law And Estimation Method Of Permeability Coefficient Of Ore Soil During Leaching Process

At present,the main mining technology of ionic rare earth ore is in-situ leaching method.In the process of mining by in-situ leaching method,the change of pore structure is the direct factor causing the change of permeability coefficient.When the leaching solution is injected into the upper orebody,the ore-soil first enters the saturated state from the unsaturated state.After that,the water and soil chemical action between the leaching solution and the ore soil makes the ore soil particles disperse or agglomerate,and the seepage of the leaching solution will cause the migration of the micro particles at the same time,which makes the pore structure of the ore soil change continuously,resulting in the change of the permeability coefficient of the ore soil.When the injection strength exceeds the effective penetration strength of the ore,it is easy to cause surface landslide accidents.Therefore,it is of guiding significance for the actual production of mines to explore the variation law of soil permeability coefficient in the leaching process.In the process of in-situ leaching,the initial water content of ore soil,the concentration of ammonium sulfate solution and the migration of micro particles in the leaching process will change the pore structure of ore soil,and then affect the permeability coefficient.Therefore,in view of these three factors,this paper carried out laboratory tests respectively,analyzed the variation law and mechanism of permeability coefficient of mine soil,and proposed the estimation method of permeability coefficient of mine soil.Through the above work,the conclusions are as follows :(1)The initial water content of the mine was collected and analyzed,and the constant head column leaching test of the corresponding water content was carried out in the laboratory :When the initial water content of the mine soil is 12 %,15 %,18 % and 21 %,the corresponding distribution frequencies are 17.86 %,24.11 %,37.5 % and 19.64 %,respectively.Under the corresponding conditions,the permeability coefficients of the mine soil are 0.83 m/ d,0.93 m /d,1.37 m/d and 1.14 m/d,respectively.Therefore,the determination of initial liquid injection intensity should consider the influence of initial water content of mine soil.(2)In order to weaken the migration of micro-particles,the short column was used to conduct the constant head column leaching test on the same mineral soil.The leaching solution was ammonium sulfate solutions with different concentrations.When the concentration of ammonium sulfate solution gradually decreases from 3 % to 0 %,the permeability coefficient of the ore decreases from 0.119 m / d to 0.077 m / d.The reason is that when the concentration of ammonium sulfate solution gradually decreases from 3 % to 0 %,the effective porosity of the ore decreases from 39.065 % to 38.027 %.(3)Considering the combined effect of micro-particle migration and ammonium sulfate solution concentration,the long column and ammonium sulfate solutions with different concentrations were used for the column leaching test with constant head.The concentration of ammonium sulfate solution increased from 1 % to 3 %.The overall permeability coefficient of the mine soil increased from 0.056 m/d to 0.103 m/d,because the effective porosity of the mine soil increased from 10.93 % to 15.48 % under the corresponding conditions.(4)The empirical calculation method of permeability coefficient based on K-C equation can be used to estimate the permeability coefficient of mineral soil only considering the influence of leaching agent solution concentration,or considering the combined effect of leaching agent solution concentration and micro particle migration.The calculated results are in good agreement with the measured values.