Fundamental Study On Electrokinetic Remediation Of Soils Polluted By Cu/Cr

Electrokinetic technology is a new technology to remove contaminants fromsoil, has been the focus of attention because of the merit of low cost, withoutseeondary pollution, high economical efficiency in the field of solving heavy metalpollution. In electrokinetic remediation process, however, many factors haveinfluence on the restorative effects, such as the applied voltage and current, soiltexture, moisture content, pollutant concentration, and remediation time. In thispaper, the electrokinetic technique for removing heavy metals in soils was examined.And the copper and chromium were, respectively, taken as the target pollutant. Thepaper reveals heavy metal migration discipline under electric field, providestechnical guidance for the practical application of electrokinetic remediation ofheavy metal pollution soils. Experimental results show that:In electrokinetic technique experiments of copper contaminated soils, theelectrolyte distribution has greatly influence upon Cu migration.When adding0.1MKCl as electrolyte distribution, the migrated mass of Cu has reached its maximum.Using cathode cleaning fluid of citric acid-citric acid sodium buffer pH=5is the bestone, which can reach a high removal rate of Cu to83.60%. This illustrated that theelectrokinetic technology can effectively remove the copper. During the inspectionof the effect of voltage gradient on the removal rate, this paper respectively discussedthe copper removal rate in each several part of soils after the voltage gradient0.5V·cm^-1、1.0V·cm^-1、2.0V·cm^-1、、3.0V·cm^-1、4.0V·cm^-1. Two factors: removal rateand the economic costs are taken into account, the best of the voltage gradient is2.0V.cm^-1. Takingexperiment time as one influencing factor, results show that experiment timeis correlativity with the removal efficiencyof copper. When the experiment timeis4d, theefficiencies increase signmcantly, the efficiency reachs up to80.82%.The efficiency ofremove increases along with the time, but slowly. In the study of the initial Cuconcentration impact, this paper respectively discussed the copper removal rate ineach several part of soils after initial Cu concentration500mg·kg^-1、800mg·kg^-1、1100mg·kg^-1、1300mg·kg^-1and1500mg·kg^-1. The removal rate are56.97%、71.61%、78.71%、47.28%and45.57%。The infections of electrolyte, cathode cleaning fluid, the voltage gradient, the repair time and the initial concentration on the removal rate of total chromium,hexavalent chromium, and Cr morphological are also studied in the soil repairexperiment. Experimental results show that using0.1M KH2PO4as electrolyte, theremoval rate of total chromiumis the best. In the study of cathode cleaning fluidimpact, results indicated that adding cathode cleaning can improve the removalefficiency significantly. Adding HAc-NaAc buffer solution was the most effectivemethod, with removal efficiency of total chromium up to50.80%. With the cleaningfluid pH values from3.5,5.5,7.5to9.5, the total chromium removal rate are29.89%,38.28%,50.80%and60.94%, all of the removal rates of hexavalent chromium aremore than90%.The order of removal ratesof heavymetals by electrokinetics in itsdifferent speciations was exchangeable fraction> carbonates> Fe/Mnoxides>organic/sulfides> residual fraction. When the voltage gradient is2.0V·cm^-1, theefficiency of total chromium reachs up to80.82%.The efficiency of remove increasesalong with voltage gradient, but slowly. The removal rate of total chromium,hexavalent chromiu is ideal with the repair time of4d. The pollutants initialconcentration of270mg·kg^-1,550mg·kg^-1,800mg·kg^-1,1050mg·kg^-1and1400mg·kg^-1, total chromium removal efficiency are33.89%,60.99%,59.07%,41.57%,30.81%. This indicates that the initial concentration is between550to800mg·kg^-1,total chromium distribution does not significantly change.