Migration and Stabilization of Multiple Heavy Metals in an Aged Contaminated Soil under a Constant Voltage Electric Field

With the aim of metal decontamination, migration and stabilization of multiply heavy metals in an aged contaminated soil under a constant 1 V cm^?1 parallel-plate electric field were investigated through monitoring the metal migration in the anolyte, as well as analyzing their species distribution residual in soil. Besides anionic Cr(VI), cationic metals were also found in the anolyte, primarily by the concentration-gradient-driven diffusion of free ions, especially when the produced H⁺ considerably increased their levels in the soil. After 295 h, parts of Cu, Cr, Ni, and Zn were found to electro-migrate into the intermediate area, but no obvious Pb migration was observed, likely ascribed to its own great inertia and precipitation with the present Cr(VI). However, in the whole, only 5.3% of Zn and 2.7% of Ni were separated, while the release of other heavy metals was almost ignorable. Although Pb mobility in the soil near the anode even increased three times, the overall metal mobility in all sample locations was found to significantly reduce under the electric field, indicating an effective stabilization approach. Moreover, compared with the bottom soil, the top soil near the anode was found to have a lower pH, higher moisture, lower heavy metal concentrations, and less soil oxidant demand; these phenomena may be due to a faster electro-migration of charged ions, especially H⁺, in the top soil. Therefore, such a divergence may considered to improve the current simulation approach for a realistic estimation of the actual metal and H⁺ electro-migration rate and the associated behavior under an electric field.