Remediation of As(V) and Cd(II) Contamination by a ZVI-Biochar: Experimental and DFT Calculation

A zero-valent iron-loaded corn straw char (ZVI-CSC) was synthesized in this study for the remediation of As(V) and Cd(II) contamination. The impact of ZVI-CSC on the adsorption performance of As(V) and Cd(II) in solution, as well as their migration properties in soil, was investigated through adsorption kinetics and soil column leaching experiments, respectively. The results showed that the adsorption capacity of As(V) by ZVI-CSC was significantly improved to 14.42 g center dot kg-1 at pH = 3, compared with unmodified corn straw char (CSC). However, the adsorption capacity of Cd(II) was not improved. In the leaching experiments, the addition of ZVI-CSC to As(V)-contaminated soil resulted in a significant reduction of cumulative As(V) release rate from 32.26 to 3.11%, compared with corn straw char (CSC). Moreover, the role of ZVI in As(V)/Cd(II) remediation was analyzed. nZVI forms equivalent to Fe-OH and equivalent to Fe-OOH due to oxidation, which can form monodentate and bidentate complexes with As(V) via ligand exchange, thus promoting As immobilization. Furthermore, to further improve the adsorption performance of Cd(II), the electrostatic potential (ESP) of biochars with different surface functional groups (C = O, C-O-C, -OH, and -COOH) and their bond dissociation enthalpy (BDE) with As(V) and Cd(II) were calculated based on density functional theory (DFT). The results showed that -OH was the most effective for As(V) adsorption, and C-O-C was the most effective for Cd(II) adsorption. C = O and -COOH can be used to the simultaneous adsorption of As(V) and Cd(II). Therefore, the surface functional groups of ZVI-CSC can be selectively modified to improve its adsorption performance of As(V) and Cd(II).