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

Abstract

A novel zero-valent iron loaded biochar (ZVI-CSC) was synthesized in this study for the remediation of As( ) and Cd(II) contamination. The impact of ZVI-CSC on the adsorption performance of As( ) and Cd(II) in solution, as well as their migration properties in soil, were investigated through adsorption kinetics and soil column leaching experiments, respectively. The results showed that the adsorption capacity of As( ) by ZVI-CSC was signi cantly improved to 14.42 g•kg -1 at pH=3, compared with unmodi ed biochar.However, the adsorption capacity of Cd(II) was not improved. In the leaching experiments, the addition of ZVI-CSC to As( )-contaminated soil resulted in a signi cant reduction of cumulative As( ) release rate from 32.26% to 3.11%, compared with CSC. Moreover, the role of ZVI in As(V)/Cd(II) remediation was analyzed. nZVI forms ≡Fe-OH and ≡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 group (C=O, C-O-C, -OH and -COOH) and their bond dissociation enthalpy (BDE) with As( ) 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 modi ed to improve its adsorption performance of As( ) and Cd(II).Highlights ZVI-CSC exhibited extraordinary performance of As(V) adsorption in solution.The migration of As(V) in soil was greatly reduced by ZVI-CSC.The shell structure of nZVI oxidation is the main cause of As(V) adsorption.-OH has better adsorption for As(V), while C-O-C is optimal for Cd(II). To improve the simultaneous remediation of As( ) and Cd( ) by ZVI-CSC, the ESP of biochar with different functional groups (C = O, C-O-C, -OH and -COOH) was analyzed based on DFT calculation. According to the results of ESP calculation, the O atom changes the electrostatic potential of biochar edge, promoting the electrostatic attraction and the complexation of AsO 4 3− and Cd 2+ .Moreover, the interaction between As( )/Cd( ) and these functional groups on biochar were also analyzed based on DFT calculation. The results showed that C = O and -COOH can be used for simultaneous adsorption of As(V) and Cd(II),and -OH showed the best adsorption effect for As( ) (ΔE=-147.91 kcal/mol, bond length 2.805Å). C-O-C showed the best adsorption effect for Cd( ) (ΔE=-111.46 kcal/mol, bond length 3.105Å).