Effective remediation of cadmium and zinc co-contaminated soil by electrokinetic-permeable reactive barrier with a pretreatment of complexing agent and microorganism

The combination of electrokinetic-permeable reactive barrier (EK-PRB) is considered as a promising technology for the remediation of heavy metal contaminated soils. In this study, considering the convenient operation and recycling, a new sheet PRB material of sodium alginate/polyvinyl alcohol/attapulgite was prepared and characterized using scanning electron microscopy, X-ray diffraction and fourier transform infrared spectra. Subsequently, the effect of a pretreatment of citric acid (CA) and Shewanella oneidensis (MR-1) on zinc (Zn (Ⅱ)) and cadmium (Cd (Ⅱ)) removal from soils by EK-PRB was investigated. Results showed that Zn (Ⅱ) and Cd (Ⅱ) gradually migrated from anode to cathode in electric field within 8 days’ EK-PRB remediation. The simultaneous addition of CA and MR-1 resulted into the highest electric current, the lowest pH and the more negative soil zeta potential. Correspondingly, the highest removal efficiency of Zn (Ⅱ) and Cd (Ⅱ) also occurred in CA + MR-1 group. The new sheet PRB material effectively captured Zn (Ⅱ) and Cd (Ⅱ) from soils, and the most adsorption occurred in CA + MR-1 group: 1108.36 mg/kg Zn (Ⅱ) and 53.84 mg/kg Cd (Ⅱ) nearby the cathode after 8 days’ remediation. Specifically, for both Zn (Ⅱ) and Cd (Ⅱ), the CA + MR-1 group showed the greatest reduction in exchangeable and carbonate fractions and the highest increase in Fe-Mn oxidation and residual fractions. Overall, with a pretreatment of CA and MR-1, the residual Zn (Ⅱ) and Cd (Ⅱ) in soils were greatly reduced after EK-PRB remediation, due to the migration in the electric filed and the adsorption of the new sheet PRB material.