Ex-situ remediation of a metal-contaminated Superfund soil using selective extractants

The Superfund Amendments and Reauthorization Act requires the use of remedial technologies that permanently and significantly reduce the volume, toxicity, or mobility of contaminated materials at affected sites. Extractive processes can accomplish the requirements of the Superfund Amendments and Reauthorization Act. Ethylenediaminetetraacetic acid (EDTA), N-2(acetamido)iminodiacetic acid (ADA), pyridine-2,6-dicarboxylic acid (PDA), and hydrochloric acid (HCl) were evaluated over a range of concentrations and reaction times in batch studies for their ability to remove lead (Pb) and cadmium (Cd) from a Superfund soil (Pb-total = 65,200 mg/kg, Cd-total = 52 mg/kg). Lead extraction was limited by a slow overall reaction. The order of Pb removal by extractant was EDTA > ADA > PDA > HCL. The soil was subjected to three repeated 1 h extractions in which a maximum of 86, 84, 70, and 54% of the total soil fb was removed with EDTA, ADA, PDA, and HCl, respectively. The soil was not treated to below the Pb regulatory limit (1,000 mg/kg), even after five extractions with 0.075 M EDTA; however, the remaining Pb occurred in a residual form. All extractants treated the soil below the proposed Cd regulatory limit (40 mg/kg) within 1 h. With three repeated extractions EDTA, ADA, PDA, and HCl removed a maximum of 96, 100, 98, and 100% Cd, respectively. Lead recovery from spent solution was accomplished by hydroxide precipitation in the presence of excess calcium. Recovery at pH 11 was 70, 98, and 97% from the EDTA, ADH, and FDA complexes, respectively. The results indicate that the remediation of weathered, heavily Pb- and Cd-contaminated soils via extractive processes is possible under the appropriate conditions.