Effects Of The Anolyte Concentration And Composition On The Electrokinetic Remediation Of Chromium-contaminated Soil

The remediation of heavy-metal-contaminated soil is not only a worldwideproblem, but also a pressing one. In China, because of the environmental policy ofremoving negative-environment-impact industries from the center city to the suburbanor industrial estates, the remain sites are usually brown fields and need to be remediated,and among those pollutions, heavy-metal pollution is a great one. Electrokineticremediation is a developing technology of in situ soil remediation, and because of thelow-cost and environmental-friendly characteristics, it has caught very specialattentions.Previous studies usually considered that low pH would increase the removalefficiency of heavy metal. However, hexavalent chromium usually appears as anion likeHCrO₄^-、Cr₂O₇^2-and CrO₄^2-, migrating of H⁺into the soil would not increase theremoval efficiency, on the contrary, it will decrease the efficiency due to high ionicmobility of H⁺, and more energy will be consumed. High concentration of anolytes andtypes of anolytes would also impact the energy efficiency of hexavalentchromium-contaminated soil.In this study, hexavalent chromium contaminated kaolinite or kaolin-gysum mediawere used to investigate the impacts of the concentration of anolytes, H⁺migrating intothe soil and types of anolytes on the electrokinetic remediation，and trying to find someoptimum solutions to increase the energy efficiency of the remediation.This study includes two parts of experiments, and the main conclusions of thisstudy are as followed:1)In the electrokinetic remediation of hexavalent chromium-contaminated soil,high concentration of anolyte will seriously cause focusing phenomenon, thussignificantly decrease the energy efficiency.2)In high-anolyte-concentration condition, low pH could aggravate the focusingphenomenon and consume more energy.3)In the condition of low concentration of anolytes, the migration of H⁺into thesoil will increase the energy consumption, but no apparent focusing phenomenon wasobserved.4)Low ionic mobility of the cations in the anolyts will increase the energyefficiency. 5)Optimum solutions for the electrokinetic remediation of hexavalent chromiumcontaminated soil could be low concentration of anolytes, low ionic mobility ions andneutral pH value of anolytes.