ENHANCED ELECTROKINETIC REMEDIATION OF A REAL LEAD-CONTAMINATED SOIL BY CHELATING AGENT ADDITION

The use of ethylenediaminetetraacetic acid disodium salt (Na₂EDTA) as a chelating agent presents ideal characteristics to be used for the removal of lead from a contaminated site. Batch experiments together with a simple local equilibrium model were carried out to evaluate the role of EDTA as enhancing agent in electrokinetic remediation of a Pb-contaminated soil. According to preliminary results, Pb removal was close to 85% after 9 hours. Hence, electrokinetic experiments were designed implementing a pH control system at both electrode-compartments. From first experiments, no important Pb recovery was obtained probably due to the counteracting effect of the electroosmotic and electromigration movement of Pb-species. The use of an iron anode instead of a platinum anode involved the recovery of a high percentage of Pb (80%) at the cathode. These results were associated with the behavior of the iron as a sacrificial anode. Furthermore, the formation of Fe(EDTA)^- hinders the formation of Pb(EDTA)^2-, which entails the dissolution of the contaminant as Pb²⁺. Therefore, the Pb species are transported toward the cathode by electromigration and electroosmosis. Furthermore, the competition between the oxidation of iron and the water electrolysis entailed a lower consumption of NaOH to control pH value at the anode compartment.

Keywords:
electrokinetic; soil remediation; lead; complexing agent; sacrificial anode