Regulating And Intervening Of The Transformation Of Cr Speciation In Soil Electrokinetic Remediation

In recent years,with the rapid development of industry and agriculture,the problem of heavy metal pollution in soil has become increasingly serious,especially Cr-contaminated soil on industrial sites has a great environmental risk.Electrokinetic remediation technology(EKR)has been used for remediation of low-permeability soils contaminated by heavy metals,but the transformation of heavy metal chemical speciation during the electrokinetic remediation process and its impact on the repair effect still need further study.In this paper,artificial Cr contaminated soil and real Cr contaminated soil collected from industrial sites are used the research object,and different electrolytes(citric acid,ammonium citrate,sodium dodecyl sulfate,and ultrapure water)are selected.By increasing electrolyte concentration and soil pretreatment as regulating measures and the electrolyte circulation and moving cathode as intervening act to to conduct electrokinetic remediation experiments.The transformation,migration and distribution of Cr speciation during electrokinetic remediation and its influence on the repair effect are discussed.The results show that:(1)Increasing the electrolyte concentration and soil pretreatment as regulating measures can effectively reduce the pH of the catholyte and anolyte and the soil pH,and the regulating measure of soil pretreatment will reduce the buffer capacity of the catholyte and shorten the time of OH~-migration from cathode chamber to soil chamber.(2)When 0.1M citric acid,1M citric acid,1M ammonium citrate,and 0.05M sodium dodecyl sulfate(SDS)is used as the electrolyte,both 0.1M citric acid and ammonium citrate are beneficial to the generation of electroosmotic flow during EKR.The regulation of soil pretreatment and intervention of mobile cathode will reduce the electroosmotic flow during remediation and reduce the migration of Cr into the cathode chamber.(3)In real Cr-contaminated soil and artificial Cr-contaminated soil,regulating measures and intervening act can increase the transformation of Cr speciation effective time and enhance the migration of easily migrated speciation(exchangeable and bound to carbonates)from the soil chamber to the electrode chamber.However,the low water content of some soil areas during EKR will lead to accumulation of easily migrated speciation and reduce the removal efficiency of Cr.(4)Compared with the use of low concentration(0.1M)citric acid,increasing the electrolyte concentration and soil pretreatment can enhance the transformation of Cr residual(RES),bound to organic matter(OC)and bound to Fe/Mn oxides(FM)to exchangeable(EXC)and bound to carbonates(CAR).Intervening act that increase electrolyte circulation and move the cathode on the basis of using the same electrolyte can more effectively promote the transformation of the FM to the easily migrated speciation and improve the removal efficiency.