Assessment of soil washing for heavy metal contaminated paddy soil using FeCl3 washing solutions.

In this study, soil washing is applied for the remediation of heavy-metal (Pb, Cu and Zn) contaminated paddy soil located near an abandoned mine area. FeCl3 washing solutions were used in bench-scale soil washing experiments at concentrations in the range of 0.1 to 1 M. The strong acid, HCl was also used in this study for comparison. The washing process was performed at room temperature, mixing at 200 RPM for 1 h and a liquid to solid ratio of 2. A sequential extraction technique was performed to evaluate the chemical fractions of Pb in the soils. The soil washing effectiveness was evaluated and compared against regulations applicable to residential districts (Korean warning standards). The soil washing results showed that the heavy metal concentrations were reduced with increasing concentrations of FeCl3. Moreover, the lowest heavy metal concentrations were obtained with a 1 M FeCl3 washing solution. In the case of Pb removal, a 0.3 M FeCl3 washing solution was required to comply with the Korean warning standard of 200 mg/kg. The lowest Pb concentration of 117 mg/kg was obtained with 1 M FeCl3. Similar washing results were also obtained with HCl. The initial total concentrations for Cu and Zn were below the Korean warning standards of 150 and 300 mg/kg, respectively. Consequently, the reduction in Cu and Zn from the contaminated paddy soil using FeCl3 washing solutions was rather limited. The sequential extraction results showed that the exchangeable and weak acid-soluble fractions of Pb were significantly reduced upon FeCl3 washing.

Assessment of Young Dong tributary and Imgok Creek impacted by Young Dong coal mine, South Korea.

An initial reclamation of the Young Dong coal mine site, located in northeastern South Korea, was completed in 1995. Despite the filling of the adit with limestone, acid rock drainage (ARD) enters Young Dong tributary and is then discharged to Imgok Creek. This ARD carries an average of 500 mg CaCO(3)/l of mineral acidity, primarily as Fe(II) and Al. Before spring runoff, the flow of Imgok Creek is 3.3-4 times greater than that of the tributary and has an alkalinity of 100 mg CaCO(3)/l, which is sufficient to eliminate the mineral acidity and raise the pH to about 6.5. From April through September 2008, there were at least two periods of high surface flow that affects the flow of ARD from the adit. Flow of ARD reaches 2.8 m(3)/min during spring runoff. This raised the concentrations of Fe and Al in the confluence with Imgok Creek. However, by 2 km downstream the pH of the Imgok Creek is 6.5 and only dissolved Fe is above the Korean drinking water criteria (0.30 mg/l). This suggests only a minor impact of Young Dong Creek water on Imgok Creek. Acid digestion of the sediments in Imgok Creek and Young Dong Tributary reveals considerable abundances of heavy metals, which could have a long-term impact on water quality. However, several water-based leaching tests, which better simulate the bioavailable metals pool, released only Al, Fe, Mn, and Zn at concentrations exceeding the criteria for drinking water or aquatic life.