Extraction and enrichment of lead from contaminated soil using chelation reactions

Abstract

Heavy metals such as lead (Pb) are significantly harmful to human health and may have disastrous effects on the ecosystem. Consequently, Pb-contaminated soil necessitates remediation to bring Pb levels below the standard threshold of 150 mg/kg. This study aimed to devise processes for extracting and enriching Pb using chelation reactions. Pb was effectively extracted from the soil using EDTA as the chelating agent, forming a complex ([Pb-HEDTA]-) that is solubilized in the solution. Extraction efficiency increased with higher EDTA/Pb molar ratios, remaining relatively constant at 100 or above. Elevated temperatures also enhanced Pb extraction; concentrations below 150 mg/kg were achieved at 25 °C or higher. The desorption of Pb followed the Langmuir equation, indicating uniform one-to-one Pb desorption. The addition of the chelating flocculant diethyldithiocarbamic acid (DDTC) concentrated Pb in the solid phase, reducing sludge volume. Pb transfer rate rose with increasing DDTC/[Pb-EDTA]2− ratio, peaking at 90 % with a ratio of 50. The presence and extraction of other elements (Fe, Cu, and Zn) did not impede Pb extraction and enrichment. Therefore, this study and its findings could provide the basis for further development of the Pb extraction process and mitigate the problem of Pb-contaminated soil when designing Pb extraction plants.