Migration Mechanism Of Coal Gangue Leachate In Geosynthetic Clay Liners And Pollutant Removal Performance

A large number of coal gangue were produced in coal mining and washing process,which accounted for about 10%¹5%of the output of coal.According to the statistics,the cumulative amount of coal gangue is more than 6 billion tons.Due to the effect of weathering and precipitation eluviation,coal gangue with high sulfur content could produce a series of physical,chemical and biological reaction,forming coal gangue acid leachate in the open air.Under the action of erosion of precipitation,coal gangue acid leachate not only polluted the surface water and soil around the mining area,also could infiltrate into the groundwater through various hydraulic connection,which has made serious impact on the groundwater around the mining area.Based on this,this study proposed source control technology of acid leachate from coal gangue based on Geosynthetic clay liners（GCL）,analyzing systematically the migration rule of coal gangue leachate in geosynthetic clay liners and its pollutant removal performance.And it was also analyzed that the permeability of GCL to loess leachate,evaluating the technical feasibility of GCL as the bottom liner system and top cover system of coal gangue disposal site.The specific work and main conclusions of this article are as follows.（1）The permeability test of coal gangue leachate as permeable solution was carried out by using the flexible wall permeameter,which studied the changes of the permeability of natural sodium bentonite（GCL-N）and sodium artificial bentonite（GCL-S）.The results show that the hydraulic conductivity of GCL to coal gangue leachate is related to the effective stress.When the effective stress was 10 kPa,the permeation of the leachate would lead to a significant increase in the hydraulic conductivity of GCL,while the hydraulic conductivity of GCL was not affected by coal gangue leachate as the effective stress was 200 kPa.In addition,under the same effective stress condition,GCL-N often has a lower hydraulic conductivity than GCL-S.（2）It was analyzed that the diffusion ability of heavy metals and sulfate from coal gangue leachate in GCL-S（Sodium-activated bentonite）and finite layer method POLLUTE V7 was used to draw the fitting curve of pollutant changing with time in the diffusion device,which calculated the diffusion coefficient of contaminants in GCL.It can be seen from the data that the diffusion coefficient in GCL was lower than that in compacted clay liners,So GCL could control the diffusion and migration of pollutants more effectively.（3）Batch tests were conducted to determine the adsorption capacity of bentonites sandwiched in GCLs for Zn²⁺and Mn²⁺prior to using in situ.In this study,the parameters evaluated were solid:solution ratio and the pH of solution.The test results showed that the solid:solution ratio and the pH of solution have a significant effect on the adsorption capacity of bentonite.However,while under most extreme conditions,the adsorption capacity of bentonite is higher than that of most other clay soils.Therefore,GCLs can be used as a liner material for the coal gangue disposal site from the angle of adsorption capacity.（4）According to the test data and analysis results in penetration test,diffusion test and adsorption test,finite layer method simulation software POLLUTE V7 was used to simulate the migration process of coal gangue leachate in GCL,analying the breakdown time of pollutants of coal gangue leachate in the bottom liner layer under different conditions,and evaluating the pollutant removal performance of coal gangue leachate in GCL.The simulation results showed that the pollutant removal performance of GCL to Zn²⁺is better than that of the compacted clay liner.（5）The permeability tests were conducted to study the change of permeability of GCL-N and GCL-S to loss leachate.The results of this test indicated that the continuous infiltration of loess leachate will lead to an increase in the hydraulic conductivity of GCL.And increases in effective stress can minimize the detrimental effect of loess leachate permeation on hydraulic performance of GCLs;however,in order to make the GCL satisfy the requirement,the thickness of the surface loess layer must be higher than 5.0 m.