Study On The Law Of Cr(?) Migration In Red Mud Leachate In Compacted Clay Liner

When the artificial impervious layer(geotextile and HDPE membrane)of the red mud yard is damaged or failed,the leachate of the red mud yard will directly penetrate into the compacted clay liner,and then cause pollution to the groundwater.Therefore,it is necessary to study the law of Cr(?)migration in red mud leachate in compacted clay liner to prevent further pollution of Cr(?)to groundwater.At present,a lot of research has been done on the seepage control of landfill leachate at home and abroad.However,there was little research on the migration law of pollutants from strongly alkaline red mud leachate in impervious layer,especially on its impact on the impervious performance of compacted clay liner.In this paper,bentonite was selected as compacted clay liner material.Red mud leachate was taken from a red mud yard.The physical and chemical properties of red mud leachate and compacted clay were studied.The influence of red mud leachate on the permeability characteristics of compacted clay liner and its erosion mechanism were studied by permeability test and scanning electron microscope.The adsorption characteristics of Cr(?)in compacted clay were studied by soil column penetration test.The mathematical model was established and solved by Hydrus-1D.The migration law of Cr(?)in red mud leachate in compacted clay liner was studied.The specific research results were as follows:(1)The p H of red mud leachate was 12.6.The concentration of Na⁺in red mud leachate was 12500mg/L.The concentration of Cr(?)was 1.76 mg/L.Al in red mud leachate exists in the form of Al(OH)₄^-.(2)Through infiltration test,the permeability coefficient of compacted clay was5.43×10^-11m/s with red mud leachate as infiltration solution.The permeability coefficient meets the anti-seepage requirement that the saturated permeability coefficient of compacted clay should not be greater than 1.0×10^-7cm/s in the Standard for Pollution Control of Storage and Landfill of General Industrial Solid Waste(GB18599-2020).Through scanning electron microscope and energy spectrum analysis,the dissolution and adsorption reaction between compacted clay and leachate were occurred.Red mud leachate has a great erosion degree on clay particles.The chemical compatibility between red mud leachate and compacted clay was poor.(3)Through the soil column test,the concentration of Cr(?)in effluent reached 93%of the initial concentration when the adsorption saturation time reached 146d.It takes a long time for Cr(?)in red mud leachate to completely penetrate the compacted clay.Compacted clay liner has a better effect on blocking Cr(?)in red mud leachate.Logistic penetration model,Thomas model and Yoon-Nelson model could well fit the penetration process.The adsorption of Cr(?)by clay at different p H values was simulated by Visual MINTEQ.The adsorption effect of clay on Cr(?)is better under alkaline condition,which shows that compacted clay liner can effectively block the downward migration of Cr(?)in red mud leachate,thus verifying the blocking effect of compacted clay liner on Cr(?)in soil column test.(4)Hydrus-1D was used to simulate the migration of Cr(?)in compacted clay liner.At 7813d(21.4a),the content of Cr(?)seeped from the bottom of compacted clay liner was0.0498 mg/L.According to Groundwater Quality Standard(GB/T14848-2017),when the leakage time exceeded 7813d,the content of Cr(?)leaked from the bottom of compacted clay liner was higher than the limit of Class III standard of groundwater quality,and then the compacted clay liner failed.