Synchronous Migration-reduction Enhanced Electrokinetic Remediation Of Chromium Contamination Soil

Chromium（Cr）is one of the main heavy metals in the environment.Cr in soil mainly comes from industries such as electroplating and leather production.Compared with Cr（III）,Cr（VI）has high toxicity（such as teratogenicity,carcinogenicity,and mutagenicity）,high solubility,and mobility in the environment,which poses a great threat to the ecological environment and human health.The application of electrokinetic remediation technology in the remediation of Cr contaminated soil has been proven to be safe,effective,and economical.Traditional electrokinetic remediation technology has drawbacks such as low repair efficiency and difficulty in promotion.In order to improve the efficiency of electrokinetic remediation of soil Cr-contaminated soil,this study adopts the method of increasing the volume of the anode chamber for electrokinetic remediation,and connecting an auxiliary circuit（i.e.reduction circuit）with the circuit passing through the soil chamber（i.e.migration circuit）in the enlarged anode chamber to form a synchronous migration reduction electrokinetic remediation system.And,on the basis of the synchronous migration reduction electrokinetic remediation system,the study of enhanced electrokinetic remediation of Cr-contaminated soil is carried out by changing the parameters of the reduction circuit and other methods.The research results indicate that:（1）Increasing the volume of the anode chamber increases the current of the circuit,when the voltage gradient is 2.0 V/cm,the initial value and peak value of the current for increasing the anode chamber volume electrokinetic remediation are 60.60 m A and 80.24 m A,respectively,which are higher than the initial value（56.20 m A）and peak value（74.31 m A）of the current for traditional electrokinetic remediation at a voltage gradient of 2.0 V/cm.Adopting 0.5 V/cm,1.0 V/cm,and 2.0 V/cm as voltage gradients for electric repair,the concentration of Cr（VI）in the anolyte of the increased anode chamber volume electrokinetic remediation（EKL）group was 94.78,244.19,and 271.01 mg/L at three voltage gradients,respectively,lower than the185.89,332.55,and 747.75 mg/L of the traditional electrokinetic remediation（EKT）experimental group.The total Cr concentration in the EKL anolyte under three voltage gradients is 115.8,298.7,and 478.8 mg/L,respectively,which is lower than the 260.75,388.43,and 1023.88 mg/L of the EKT group.Increasing the volume of the anode chamber improved the removal efficiency of Cr（VI）in the soil chamber.Under three voltage gradients,the concentrations of Cr（VI）in the soil chamber of the EKL group were 243.28,145.00,and 39.21 mg/kg,respectively,lower than the 294.75,272.86,and 43.77 mg/kg of the EKT group.At voltage gradients of 0.5 V/cm,1.0 V/cm,and 2.0 V/cm,the removal rates of Cr（VI）by EKL were 31.32%,58.3%,and 88.93%,respectively,which were higher than the Cr（VI）removal rates of 16.8%,22.98%,and 87.56%by EKT under the same voltage gradient.（2）In the synchronous migration reduction electrokinetic remediation system（EKD）,at a voltage gradient of 2.0 V/cm,the removal rate of Cr（VI）in the soil chamber reached 90.67%,which is higher than the removal rates of Cr（VI）in the EKT and EKL experimental groups（87.56%and 88.93%,respectively）at the same voltage gradient of 2.0 V/cm.The cathode of the reduction circuit has a reducing effect on Cr（VI）migrated to the anode chamber,effectively reducing the concentration of Cr（VI）and total Cr in the anolyte.Compared with the EKT group,the concentrations of Cr（VI）and total Cr in the anolyte of the EKD group decreased by 98.65%and 78.49%respectively.Compared with the EKL group,the concentrations of Cr（VI）and total Cr in the anolyte of the EKD group decreased by 98.16%and 51.04%,respectively.When the migration circuit is 2 V/cm,the removal rate of soil Cr（VI）and total Cr is the highest.Therefore,the migration circuit uses a voltage gradient of 2 V/cm for enhanced reduction process electrokinetic remediation.（3）Based on the synchronous migration reduction electrokinetic remediation system,the e electrokinetic remediation of Cr contaminated soil is strengthened by controlling the current of the reduction circuit（EKC）,changing the voltage gradient of the reduction circuit（EKV）,and changing the cathode electrode of the reduction circuit to manganese dioxide modified graphite felt electrode（EKM）.After electric remediation,the concentrations of Cr（VI）and total Cr in the EKC soil chamber were 22.68mg/kg and 206.85 mg/kg,respectively;The concentrations of Cr（VI）and total Cr in the EKV soil chamber were 1.57 mg/kg and 195.31mg/kg,respectively.The removal rates of Cr（VI）and total Cr in the EKV soil chamber were higher than those of other e electrokinetic remediation experimental groups,with removal rates of 99.56%and 65.55%,respectively.（4）The MnO₂ modified electrode effectively increases the current of the circuit in the device,reduces the energy loss of electrokinetic remediation,and reduces the concentration of Cr（VI）and total Cr in the anode chamber.The voltage gradient parameters of EKM and EKV are consistent,but the peak current of the EKM reduction circuit is 95.66 m A,which is significantly higher than the 41.15 m A of EKV;The energy consumption and utilization efficiency of EKM are 13.05 k Wh and 6.07 k Wh,respectively,lower than the17.70 k Wh and 5.62 k Wh of EKV.After the experiment,the concentrations of Cr（VI）and total Cr in EKM anode solution were 3.94 mg/L and 155.84 mg/L,respectively.