Multi-step leaching of Pb and Zn contaminated soils with EDTA

The efficiency of multi-step leaching of heavy metal contaminated soils was evaluated in a laboratory scale study. Four different soils contaminated with Pb (1136 ± 16–4424 ± 313 mg kg−1) and Zn (288 ± 5–5489 ± 471 mg kg−1) were obtained from industrial sites in the Mežica Valley, Slovenia and Príbram district, Czech Republic. Different dosages (2.5–40 mmol kg−1) of ethylenediamine tetraacetate (EDTA) were used to treat soils in 1–10 leaching steps. Higher EDTA dosages did not result in a proportional gain in Pb and Zn removal. EDTA extracted Pb more efficiently than Zn from three of four tested soils. The percentage of removed Zn did not exceed 75% regardless of the soil, EDTA dosage and leaching steps. Significantly more Pb (in three of four soils) and Zn were removed from soils when the same amount of EDTA was applied in several leaching steps. The interference of major soil cations Fe and Ca with EDTA complexation as a possible factor affecting Pb and Zn removal efficiency with multi-step heap leaching was examined and is discussed. The results of our study indicate that, for some soils, using multi-step leaching instead of the more traditionally used single dose EDTA treatment could improve heavy metal removal efficiency and thus the economics of soil remediation.