Remediation Of Heavy Metals And Organic Compounds Co-contaminated Soil By Electrokinetics Coupled With Flushing

In the process of accelerated development of industrialization,soil pollution is worsening.The dismantling of WEEE has resulted in severe co-contamination of heavy metals and organic compounds for soil.Electrokinetic remediation technology（EK）is one of the green technologies in recent decades,which has several advantages such as short remediation time,low cost and high removal rate,etc.However,many factors limit the remediation effects,such as the electric field strength,soil characteristics,pH of the electrolytes and the remediation time.In this paper,removing of contaminates from the soil polluted with heavy metals（cadmium,copper and lead）and organic compound（pyrene）,and the soil in the e-waste dismantling plant by electrokinetics coupled with flushing（EK-Flushing）was studied.The contents of experiments included the following main aspects:（1）the treatment of heavy metals spiked in soil by EK-Flushing,and during the experiments the effects of several operating parameters on the remediation efficiency,including the field strength,the materials of electrodes and the concentration of EDTA-2Na,the migration mechanism of heavy metals,the change of the speciation of heavy metals,and the correlation between the speciation of heavy metals and the soil characteristics were analyzed;（2）the treatment of heavy metals and organic compound spiked in soil by EK-Flushing,and the feasibility of EK-Flushing on the remediation of the soil co-contaminated by heavy metals and organic compound was investigated;（3）the treatment of heavy metals and organic compounds in soil from electronic waste dismantling plant by EK-Flushing,which provide reference for remediation of contaminated soil from WEEE dismantling area.The main results are listed as follows:（1）The EK-Flushing process was found to be effective for the removal of Cd,Cu,Pb spiked in soil simultaneously.These three heavy metals were removed by electromigrating from the anode to the cathode under the experimental condition.（2）The soil was pre-acidified using HNO₃ before the EK-Flushing treatment.Maintaining a slightly acidic soil condition was beneficial for the removal of the heavy metals.Compared to the other studies,the electric conductivity of the soil was higher since the soil was pre-acidified.In this experiment,the removal efficiency of heavy metals was relatively high since the electric current was particularly high.（3）During the EK-Flushing treatment,the EDTA-2Na reacted with heavy metals to form metal-chelate complexes that improved the removal efficiency.The ionic complexes were removed by the electromigration,and the neutral complexes were removed by the electroosmotic flow（EOF）.（4）With the increase of voltage gradient,the removal efficiency of heavy metals was enhanced.Under the voltage gradient of 1.0 V/cm,the removal efficiency of Cd,Cu and Pb reached 91.09%,80.34%and 72.38%,respectively.（5）Before the experiment,the main fraction of Cd,Cu and Pb in the soil was residual.The residual form of heavy metals in the soil was transformed to the other fractions easier to be removed due to the function of EK and EDTA-2Na flushing.（6）The desorption experiments were performed to select the flushing reagent in EK treatment.The maximal desorption of the contaminants from the soil was obtained when EDTA-2Na and Brij-35 were used.（7）The EK-Flushing process was found to be effective for the removal of Cd,Cu,Pb and pyrene spiked in soil simultaneously.Under the experimental conditions,heavy metals migrated to the cathode by the electromigration and the organic compound migrated to the anode by the EOF.（8）The EK-Flushing process was found to be effective for the removal of Cd,Cu,Pb and PAHs in soil from the electronic waste dismantling plant simultaneously.In this experiment,the cationic heavy metals migrated to the cathode by the electromigration,however,the reaction of heavy metals with EDTA-2Na formed anionic and neutral metal-chelate complexes under the slightly alkaline soil condition that migrated toward the anode by the electromigration and the reversed EOF respectively,and the PAHs migrated toward the anode due to the reversed EOF.（9）The cost of EK-Flushing for remediating the multiple heavy metals contaminated soil was mainly due to the use of HNO₃ solution.The cost of EK-Flushing for treating the heavy metals and organic compounds co-contaminated soil was mainly due to the use of Brij-35solution.The selection of efficient and cheap eluents will be the development direction of EK-Flushing in the future.