Study On The Service Performance Of Geomembrane Composite Vertical Barrier Bottom Sealing Materials For Chromium Contaminated Sites

Chromium salt is an important chemical basic material,mainly used in industries such as metallurgy,dyes,and leather.However,some non compliant chromium salt factories have been shut down,leaving behind a large number of polluted sites.Due to the high solubility of hexavalent chromium compounds in water and their toxicity,carcinogenicity,and easy migration to the surrounding environment,the remediation of chromium contaminated sites has become a hot topic of concern.At present,the commonly used treatment method for chromium contaminated sites is to build vertical barriers around the site.Geomembrane composite anti fouling barriers have been widely used in the treatment of contaminated sites due to their low permeability and strong corrosion resistance.However,there may be gaps between the geomembrane and weakly permeable bedrock,and pollutants can easily flow around the joints.Therefore,a sealing material is needed to bond the gaps between the two.In response to the above engineering problems,this article selects a sealing material made of a mixture of attapulgite soil and cement to bond the geomembrane with weakly permeable bedrock.The main research content is as follows:(1)By combining flowability tests,unconfined compressive strength tests,and permeability tests,the flowability,strength,and impermeability of sealing materials with different ratios were studied.The test results showed that when the water cement ratio was constant,adding a certain amount of attapulgite can increase the flowability of the sealing material,reduce bleeding,improve unconfined compressive strength,and reduce hydraulic conductivity;When the content of attapulgite soil is constant,reducing the water cement ratio can improve the unconfined compressive strength and reduce the hydraulic conductivity.(2)Through the direct shear test of bedrock sealing material interface and the tensile test of geomembrane sealing material,the bonding performance of sealing materials with different ratios to bedrock and geomembrane is studied.The test results show that when the water cement ratio is constant,increasing the content of attapulgite can improve the bonding performance of sealing materials to bedrock and geomembrane;When the content of attapulgite soil is constant,reducing the water cement ratio can improve the bonding performance of the sealing material with the bedrock and geomembrane.(3)Optimize the ratio of sealing materials,select a type with high fluidity,low hydraulic conductivity,and high compressive strength,which can effectively bond with bedrock and geomembrane.Using hexavalent chromium as a pollutant,based on Batch adsorption experiments,study the adsorption performance of sealing materials on hexavalent chromium solution at different p H conditions.The results show that when hexavalent chromium solution is acidic,The maximum adsorption capacity of the sealing material for hexavalent chromium solution is greater than that of alkaline solution,and the stronger the acidity of the solution,the greater the maximum adsorption capacity and the higher the removal rate.(4)Using soil column tests,the effect of hydraulic gradient on the migration characteristics of hexavalent chromium solution in sealing materials was studied.The results showed that as the hydraulic gradient increased,the dispersion coefficient increased and the retardation factor decreased.The dispersion was influenced by the hydraulic gradient.The service life of the composite vertical barrier was calculated to be 37.67 years using finite element simulation software.