Adsorption behavior of Mg–Al layered double hydroxide on Pb(Ⅱ), Zn(Ⅱ), Cd(Ⅱ), and As(V) coexisting in aqueous solution

Abstract

MgAl-layered double hydroxide（MgAl-LDH）was synthesized via hydrothermal method, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption-desorption, energy dispersive spectrum (EDS). The results proved that the prepared MgAl-LDH exhibited a well-defined layered structure and mesoporous morphology with a large specific surface area, which endowed them with abundant adsorption sites and diffusion mass transfer channels for heavy metal ions. Subsequently, the MgAl-LDH was used to evaluate the adsorption efficiency for Pb(Ⅱ), Zn (Ⅱ), Cd (Ⅱ), and As(V) coexisting in aqueous solutions by batch equilibrium experiments. The results showed favorable adsorption performance of MgAl-LDH toward four coexisting ionic species, with competitive adsorption among the heavy metal ions. Under the experimental conditions, the removal rates of Pb(Ⅱ), Zn (Ⅱ), Cd (Ⅱ), and As(V) ions were 96.7%, 97.1%, 65.2%, and 98.7%, respectively, and the selective order for cation adsorption followed Pb(Ⅱ) > Zn (Ⅱ) > Cd (Ⅱ). Furthermore, the adsorption mechanisms of Pb(Ⅱ), Zn (Ⅱ), Cd (Ⅱ) and As(V) by MgAl-LDH were detailed conducted by XRD, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis, and could be ascribed to the surface complexation, precipitation and isomorphic replacement for Pb(Ⅱ), Zn (Ⅱ), Cd (Ⅱ) while surface complexation, ion exchange and electrostatic adsorption for As(V).