Remediation of arsenic contaminated soil using soil washing with an acidic and reducing solution

Soil contamination with arsenic (As) is a serious environmental concern due to its highly toxicity and carcinogenic property. Iron oxides are known to be the most important factor for controlling As concentration in soil pore water. They adsorb large amount of As and coprecipitate with As. We tried to develop a new washing method of As contaminated soil by the dissolution of iron oxide and desorption of As employing pH and redox potential adjustment. An As contaminated soil sample was collected at a rice paddy field near a copper smelter, Korea. The As concentration of the soil sample was determined with an aqua-regia extraction method. Washing solutions were prepared to be 0.001-0.1N HCl and 0-3% Na-dithionite. The soil and washing solution were mixed at 1:4 ratio and the mixtures were reacted for 15, 30, 45 and 60 minutes. After the reaction, the soil and washing solution were separated with a centrifugation. The pH, Eh and concentrations of As, Fe and Mn of the washing solution were determined and the As concentration of the washed soil sample was also determined. The separated washing solution was treated with H₂O₂, CaCl₂ 2H₂O and cationic organic polymer to remove As. The soil washing with the 0.01N HCl-3% Na-dithionite solution for 30 minutes was the most effective in the As removal from the soil reducing As concentration from 43 mg/kg to 18 mg/kg. The As concentration of the washing solution was reduce from 19.2 mg/L to 0.76 mg/L after the waste water treatment.