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.

Influence of amendments and aided phytostabilization on metal availability and mobility in Pb/Zn mine tailings.

A greenhouse experiment was conducted to evaluate the effect of four different amendments, bone mill, bottom ash, furnace slag, and red mud, as immobilizing agents and the plant species Miscanthus sinensis and Pteridium aquilinum in aided phytostabilization of Pb/Zn mine tailings. The effects of amendments and plants on the availability and mobility of heavy metals were evaluated using single extraction, sequential extraction, pore-water analysis, and determination of heavy metal concentrations in plants. The application of Fe-rich amendments significantly reduced the amount of soluble and extractable heavy metals in the tailings (p < 0.05). Furnace slag and M. sinensis reduced CaCl2-extractable heavy metals by 56-91%, red mud and P. aquilinum treatment was the most effective at decreasing bioaccessible Pb, reducing it to 34% of the total Pb. Compared to control, water soluble Cd, Cu, Pb, and Zn were reduced by 99, 99, 98, and 99%, respectively, in the red mud and P. aquilinum tailings. M. sinensis accumulated heavy metals mainly in the root, and had lower translocation factors compared with P. aquilinum. The results of this study suggest that M. sinensis can be used in aided phytostabilization for these types of mine tailings and Fe-rich amendments are effective for the in situ immobilization of metals.