EDTA-Enhanced Washing for Remediation of Pb- and/or Zn-Contaminated Soils

The effects of the operating conditions, the initial concentrations of heavy metals in soils, and the competition among heavy metals during ethylenediaminetetraacetic acid (EDTA)-enhanced soil washing were extensively investigated using batch experiments with Pb- and/or Zn-contaminated soils aiming to determine the heavy-metal removal for different types of contaminations and to optimize the process parameters. Pb or Zn removal efficiency was found to be dependent on contact time, pH, concentrations of EDTA, and their initial concentrations in contaminated soils. The experimental results showed that the heavy-metal removal efficiency increased with a higher initial concentration of heavy metals in soils, and the concentrations of heavy metals in the solutions after washing were linearly correlated with their initial concentrations in soils. The study of the competition among heavy metals indicated that when EDTA was present in solution with the concentration less than the stoichiometric requirements, Pb removal efficiency was higher than that of Zn; on the other hand, when EDTA concentration was greater, Pb and Zn removal efficiencies were almost the same.