Leaching of heavy metals from contaminated soils using EDTA

Ethylenediaminetetraacetic acid (EDTA) extraction of Zn, Cd, Cu and Pb from four contaminated soils was studied using batch and column leaching experi ments. In the batch experiment, the heavy metals extracted were virtually a ll as 1:1 metal-EDTA complexes. The ratios of Zn, Cd, Cu and Pb of the extr acted were similar to those in the soils, suggesting that EDTA extracted th e four heavy metals with similar efficiency. In contrast, different elution patterns were obtained for Zn, Cd, Cu and Pb in the column leaching experi ment using 0.01 MEDTA. Cu was either the most mobile or among the most mobi le of the four heavy metals, and its peak concentration corresponded with t he arrival of full strength EDTA in the leachate. The mobility of Zn and Cd was usually slightly lower than that of Cu. Pb was the least mobile, and i ts elution increased after the peaks of Cu and Zn. Sequential fractionation s of leached and un-leached soils showed that heavy metals in various opera tionally defined fractions contributed to the removal by EDTA. Considerable mobilisation of Fe occurred in two of the four soils during EDTA leaching. Decreases in the Fe and Mn oxide fraction of heavy metals after EDTA leach ing occurred in both soils, as well as in a third soil that showed little F e mobilisation. The results suggest that the lability of metals in soil, th e kinetics of metal desorption/dissolution and the mode of EDTA addition we re the main factors controlling the behaviour of metal leaching with EDTA. (C) 2001 Elsevier Science Ltd. All rights reserved.