| With the development of China’s industrial and agricultural production, soilpollution becomes more and more serious. Therefore, people have developed a varietyof restoration techniques. In the last decade, the development of ecologicalremediation technologies–electrokinetic remediation showed great prospect..Electrokinetic remediation has been successfully applied to the actual heavy metalsoil pollution in some overseas countries, and will become the mainstream soilremediation technology. In this paper, heavy metal Cr (Ⅵ), as a common pollutant incontaminated soil and groundwater, were set as the targeted pollutant. In laboratoryexperiments, the carbon electrodes were used to remediate Cr (Ⅵ) and the feasibilitywere studied. The experimental parameters were used in the chromium-contaminatedsite. And according to the experimental results, we proposed programs to the pilottests and practical applications, explored the feasibility of electrokinetic remediationin the field of application and discuessed the related parameters. The experimentalresults were as follows:(1)Chromium could be removed from kaolin through electrokinetic remediation,and the removal efficiency increased with increasing reaction time. When the appliedvoltage was increased to1V/cm, the best removal rate occurred, which was94.27%.In the first batch of kaolin, the removal rates were studied under differentexperimental conditions. The average removal rate reached over75%, which showedgood effect.(2)Cr (Ⅵ) in soil, which existed as oxyanion, migrated to the anode inelectrokinetic remediation. In the process, part of the Cr (Ⅵ) was reduced to Cr(Ⅲ).(3)OH-generated by electrolysis at cathode had great effect on the chromiumremoval efficiency. The removal rate could be improved by replacement of the anodeand cathode fluid regularly or by neutralization of cathode fluid with acetic acid/hydrochloric acid.(4)The content of chromium in the chromium-contaminated site was farexceeded the national standard, and the content amount of Cr (Ⅵ) and total chromium in the heaviest polluted area reached over1000mg/kg and5000mg/kg, respectively.Cr (Ⅲ) was the main pollutant. For speciation distribution, chromium in the soil wasmainly bound to organic matter(38.0%) and residual(54.4%).(5)For soil samples over a10-mesh sieve, the mass distribution of soil samples ofvarious particle was almost uniform. The content of Cr (Ⅵ) and total chromium wasthe highest in the50-100mesh sieve, and the lowest in coarse grained soil sampleswith a <20mesh sieve.(6)For the soil samples in the chromium-contaminated site, after a4~6daysremediation with1V/cm DC voltage, Cr (Ⅵ) in soil, which existed as oxyanion,migrated to the anode, and the removal efficiency reached32%~44%, while theremoval efficiency of Cr(T) reached only5.1%~8.7%. It was mainly because thatmost of Cr(Ⅲ) in the soil existed as Cr(OH)3, which was hard to migrate underelectric field.(7)Chromium in soil could be removed through electrokinetic remediation. Thetechnology could be used in soils with different permeability, and the removalefficiency was mainly depended on the soil and the type of pollution. Thepermeability the lower was, the better the removal rate was. Chromium which wasweak acid extractable was removed more easily. Chromium bound to iron andmanganese decreased a little, and the same to which bound to organic matter andresidual. The residual chromium was almost not affected by electrokineticremediation.(8)Initial valence of chromium in contaminated soil had great effect on theremoval efficiency. After the Cr (Ⅵ) contaminated kaolin experiment, Cr (Ⅵ) washardly detected at the cathode side.(9)Different valence of chromium affected the speciation of chromium in soil aswell. After the test, chromium in Cr(Ⅵ) contaminated soil was mainly weak acidextractable, while in Cr(Ⅲ) contaminated soil was mainly bound to organic matter. |
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