Chemical extraction of arsenic from contaminated soil under subcritical conditions

In this research, we investigated a chemical extraction process, under subcritical conditions, for arsenic (As)-contaminated soil in the vicinity of an abandoned smelting plant in South Korea. The total concentration of As in soil was 75.5 mg/kg, 68% of which was As(+ III). X-ray photoelectron spectroscopy analysis showed that the possible As(+ III)-bearing compounds in the soil were As2O3 and R-AsOOH. At 20 oC, 100 mM of NaOH could extract 26% of the As from the soil samples. In contrast, 100 mM of ethylenediaminetetraacetic acid (EDTA) and citric acid showed less than 10% extraction efficiency. However, as the temperature increased to 250 and 300 oC, extraction efficiencies increased to 75-91% and 94-103%, respectively, regardless of the extraction reagent used. Control experiments with subcritical water at 300 oC showed complete extraction of As from the soil. Arsenic species in the solution extracted at 300 oC indicated that subcritical water oxidation may be involved in the dissolution of As(+ III)-bearing minerals under given conditions. Our results suggest that subcritical water extraction/oxidation is a promising option for effective disposal of As-contaminated soil. - Research highlights: → Extraction efficiency by EDTA, citric acid, and NaOH is limited at room temperature. → Extraction efficiencies increase to 94-103% at 300 oC regardless of the extraction reagent used. → Subcritical water oxidation may be responsible for the dissolution of As(+ III)-bearing minerals.