Enhancing Electrokinetic Remediation Of Cr-contaminated Soil By Chemical Enhancers Coupled With A Permeable Reactive Barrier

With the rapid and sustainable development of the social economy,the problem of heavy metal pollution in the soil has become increasingly serious.At present,electrokinetic remediation as an in-situ repair technology is showing great potential in solving soil pollution problems.This paper used the chromium-contaminated soil which was collected from a chemical plant in Chongqing as the research object.Based on the traditional electrokinetic remediation technology,the enhancement effect of permeable reactive barrier(PRB)and chemical enhancers were discussed.The basic physical and chemical analysis of the collected soil samples were obtained: there were particles of different sizes and irregular shapes on the surface of the soil,with more internal pores and larger specific surface area.The main elements in the soil are O,Ca,Si,Cr,Fe,and the proportion of Cr was 7.73%.Through the full analysis of heavy metals,the contents of total Cr and Cr(VI)in the soil were 36475.52 mg/kg and 504.00 mg/kg,and the Cr(VI)leaching toxicity was 12.55 mg/kg.The form of chromium in the soil was mainly dominated by the residual state.Zeolite is widely used as a adsorbent material in EKR process.In the experiments,the zeolite was modified with cetyltrimethylammonium bromide(CTMAB)according to the properties of Cr(VI).The modification mechanism was explained by the physicochemical properties(SEM 、 Specific surface area 、 FTIR 、 Zeta)of zeolite(CTMAB-Z and UM-Z).Besides these,the static adsorption experiments showed that the adsorption capacity of modified zeolite for Cr(VI)was much better than that of unmodified artificial zeolite.In the EKR experiments,six groups of contrast experiments were designed by adding PRB(modified zeolite,zero-valent iron)and chemical enhancers(DL-tartaric acid,Tween 80)as enhancing techniques.The results showed that both PRB and chemical enhancer can improve the removal rate of Cr(VI)to different extents.Among them,organic acid-DL tartaric acid can achieve better results than surfactant-Tween 80.In order to better remediate the chromium contaminated soil,this paper selected the repair time(4 d,6 d,8 d),voltage gradient(1.5 V/cm,2.0 V/cm,2.5 V/cm),DL-tartaric acid concentration(0.05 mol/L,0.1 mol/L,0.15 mol/L)as the main index.The range analysis showed that the optimum level of these factors regarding remediation efficiency of Cr(VI)in this study was summarized as A3(8 days repair time),B3(2.5 V/cm of voltage gradient)and C3(0.15 mol/L dl-tartaric acid concentration).In other words,the highest Cr(VI)removal rate(80.92%)and leaching efficiency(85.25%)were achieved after treating the samples at a voltage gradient of 2.5 V/cm for 8 days in presence of 0.15 mol/L concentration of dl-tartaric acid.