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 As(2)O(3) and R-AsOOH. At 20°C, 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°C, extraction efficiencies increased to 75-91% and 94-103%, respectively, regardless of the extraction reagent used. Control experiments with subcritical water at 300°C showed complete extraction of As from the soil. Arsenic species in the solution extracted at 300°C 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.