Sequestration of heavy metals in soils from two polluted industrial sites: Implications for remediation

This study was conducted to determine the distribution of heavy metals in two different contaminated field soils, and to assess its influence on remedial performance. The two field soils were obtained from two different polluted industrial sites in the Metropolitan Chicago area and were characterized for physical and chemical properties. The soils were referred to as silty sand and silty clay, based on their particle-size distribution. A five-step sequential liquid-solid extraction procedure was used to speciate the heavy metals into: (1) easily exchangeable; (2) carbonate bound; (3) Fe/Mn oxide bound; (4) organic bound; and (5) residual fractions. These results showed that all the metals except mercury were predominantly distributed as the Fe/Mn-bound form in silty sand. In contrast, they were distributed as the residual form in silty clay. Results indicated that the metals in both soils were in the forms that are not easily amenable to soil washing using water. Therefore, batch extraction tests with varying concentrations of ethylenediaminetetraacetic acid (EDTA) (0.05, 0.1 and 0.2 M) and acetic acid (0.5, 0.1 and 2 M) were conducted to identify an optimum soil-washing-based remediation system for both silty sand and silty clay. Ethylenediaminetetraacetic acid was found to be effective for the remediation of silty sand, while acetic acid was found to be suitable for the removal of metals that existed in residual form in silty clay. Based on these results, total removal efficiency was found to follow the order sand + EDTA > clay + acetic acid > sand + acetic acid > clay + EDTA. This study showed that the speciation and remediation of heavy metals in soils depend on the sitespecific soil composition, and this should be carefully considered in the selection of an efficient remedial method. © 2010 EPP Publications Ltd