Remediation of Heavy Metal Contamination in Calcareous Soil by Washing with Reagents: A Column Washing

AbstractThis paper presents an evaluation of different dose of HCl and Na2EDTA for the removal of Cd and Pb contaminated calcareous soil in the column mode. The field soil contained high concentrations of DTPA-extractable Cd (12.82mg kg-1) and Pb (105.38mg kg-1). Both HCl and Na2EDTA were found to be effective on removing DTPA-extractable Cd, but low concentration of HCl was ineffective on removing DTPA-extractable Pb and the highest removal efficiency of DTPA-extractable Pb washed by optimal dose of Na2EDTA was only 45.39%. In order to effectively and economically remove both metals from the contaminated soil, a sequential use of the optimal dose of HCl followed by the optimal dose of Na2EDTA was tested and 87.3% and 73.2% removal efficiency were obtained for DTPA-extractable Cd and Pb, respectively. Compared to using single washing agent, the removal efficiencies of DTPA-extractable Cd and Pb for the sequential washing with HCl followed by Na2EDTA were increased more than 8.3% and 27.92%, respectively. Results of soil extractions experiments revealed that the predominant fraction of the removed Cd and Pb were Fe/Mn oxide fraction and carbonate fraction. Trace metals in leachate collected from sequential washing was successfully precipitated and the leachate was safe for discharge