Study On Electrokinetic Remediation Of Pb And Cd Contaminated Soil

Soil heavy metal contamination and its remediation have become the focus of global attention to environmental study.Since the technology of electrokinetic remediation has a good adaptability to the low-permeability soil contaminated by heavy metals and can be used in combination with other remediation technologies,it has attracted wide attention.The technology is in its infancy in China.In this paper,Pb and Cd composite contaminated soil was taken as the research object,and the influence of the types and concentrations of electrolyte,soil type,leaching solution and other factors on the removal efficiency of heavy metals in electrodynamic remediation was mainly discussed.The main results are as follows:（1）EDTA（0.05M）and citric acid（anode 0.3M,cathode 0.1M）were selected as electrolyte for heavy metal contaminated soil.When EDTA was electrolyte,the average removal efficiency of Cd and Pb was 17.8%and 13.2%respectively,and the power consumption was 26.9 KW·h/g.Cd and Pb were removed by complexing with EDTA^4-to CdEDTA^2-and PbEDTA^2-migrating to the anode under the action of an electric field,and the change of soil pH was small and the secondary pollution was small.When citric acid was electrolyte,the average removal efficiency of Cd and Pb was 18.3%and 10.3%,respectively,and the power consumption was 35.1 KW·h/g.When citric acid was used electrolyte,it can provide a lower soil pH environment.The main forms of Cd in the S1 and S5 areas were Cd²⁺and Cd-（Citrate）₂^4-,respectively,and they migrate toward the cathode and the cathode;The main form in the soil was Pb-Citrate-,which migrated to the anode under the action of an electric field.（2）Different soils have different heavy metal removal rates due to their differences in physical and chemical properties.With a voltage gradient of 2 V/cm and a repair time of 4 d,the best electrolyte in red soil was citric acid,and the removal rates of Cd and Pb were 33.8%and 20%,respectively.The best electrolyte in black soil For EDTA,the removal rates of Cd and Pb are 19%and 24%,respectively;citric acid can accelerate soil acidification,desorb heavy metals from the surface of soil particles,and also form negatively charged complexes with metal ions.The removal effect of Pb was better than that of Pb;and EDTA mainly forms complexes with negative charges by complexing with heavy metals.The removal effect of Pb in soil was better than that of Cd.（3）The regulation and mechanism of Pb and Cd polluted soil by electrokinetic combined leaching were investigated.0.3M citric acid was selected as the leaching solution.Because EDTA^4-preferentially selected Fe³⁺to form complexes,it competed with Cd²⁺and Pb²⁺for adsorption sites.The electrokinetic and leaching combined remediation technology can significantly improve the removal rate of heavy metals Pb and Cd in the soil.The best remediation solution was citric acid,and the average removal rate of Cd and Pb was 84.16%and 79.44%,respectively.