Electro-kinetic Remediation Of Chromium Contaminated Soil By Three-dimensional Electrode Coupled With A Permeable Reactive Barrier

Electro-kinetic remediation is an in situ soil remediation technology with potential applications.In this paper,three-dimensional electro-kinetic remediation of Cr contaminated soil is investigated by coupling it with permeable reactive barrier(PRB)with the graphite electrode as the third electrode,in order to explore the feasibility of the combined system.In this paper,the soil samples were collected from Chongqing.The physical and chemical properties of soil samples showed that the major elements in the soil sample are O,Ca,Si and Cr,and the relative content of Cr in soil was 9.40%.Cr was mostly found as inorganic Cr oxide.The contents of total Cr and Cr(VI)in the original soil samples were 10512.50 mg/kg and 423.16 mg/kg,and the leaching toxicity of Cr(VI)was 38.85 mg/L with sulfuric and nitric acid method.Three experimental conditions i.e.two dimensional electro-kinetic remediation with and without PRB,and three dimensional electro-kinetic remediation with PRB are used for the remediation of simulated kaolin and actual contaminated soil,respectively.In the three-dimensional coupled system,the results shows that the removal rate of hexavalent chromium has doubled from that in traditional electro-kinetic remediation,both removal rate of total chromium and leaching efficiency of hexavalent chromium have also been significantly improved.Based on the three-dimensional electro-kinetic remediation coupled with PRB,graphite dosage ratio with respect to soil sample(0%,5%,10%,15%,and 20%)was selected as variable factor in single factor experiments.It shows that the addition of three-dimensional electrode has a significant effect on the chromium remediation in soil samples,and 5% dosage ratio is optimum for remediation of Cr contaminated soil.In order to further improve the remediation effect of Cr contaminated soil,three-dimensional electro-kinetic remediation coupled with PRB was conducted under citric acid pretreatment.Citric acid concentration(0 mol/L,0.05 mol/L,0.1 mol/L),voltage gradient(1 V/cm,1.5 V/cm,2 V/cm)and repair time(4 d,8 d,12 d)was selected as the main design index.The results showed that the optimum levels were obtained with citric acid of 0.05 mol/L,voltage gradient of 1.5 V/cm and repair time of 12 d in this remediation system.Optimum removal rate of hexavalent chromium(50.31%),total chromium(23.81%)and leaching efficiency of hexavalent chromium(74.04%)were achieved in orthogonal experiments.