Evaluating acids and chelating agents for removing heavy metals from contaminated soils

The prevalence of heavy metal soil contamination at Army facilities poses a serious threat to human health and the environment. To address this problem, the US Army Engineer Waterways Experiment Station in Vicksburg MS is developing a mobile piot-scale soil washing treatment facility that can be used to remove metals from the contaminated soils. To support this project, laboratory studies were conducted on both acids and chelating agents to evaluate their ability in extracting heavy metals from contaminated soils. Eight soils contaminated with lead, cadmium, and chromium were selected for use in this study. Contaminant concentrations in the various soils ranged from 4,000–30,000 mg/kg lead, 40–1,000 mg/kg cadmium, and 500–2,000 mg/kg chromium. The results indicated that, before a full-scale clean-up is initiated, a preliminary investigation is needed to determine principal contaminants of concern, their concentrations, and soil type followed by treatability studies to determine optimal reagent and concentrations of reagents for cleanup. Specific results from this study also indicated that Cd was the easiest metal to remove from soils followed by Pb and Cr. The results also suggested that the strong acids and chelating agents were both effective extracting agents, and the latter group of compounds may be more useful in soil washing because they are less harmful to the soil environment. Finally, higher initial concentrations of metal contaminants in the soil resulted in greater metal removal efficiencies using the reagents.