Mechanistic study of arsenate adsorption on lithium/aluminum layered double hydroxide

Lithium/aluminum layered double hydroxide intercalated by chloride (Li/Al LDH-Cl) was considered as a superior adsorbent for anionic compounds. This study aimed to establish the adsorption behavior of arsenate on Li/Al LDH-Cl by employing X-ray absorption spectroscopy (XAS) and adsorption kinetics. The XAS analysis demonstrated that inner-sphere complexes were the dominant arsenate adsorption configurations on the planar surfaces and edges of Li/Al LDH-Cl. Based on a kinetic study, arsenate adsorption on Li/Al LDH-Cl could be separated into fast and slow reactions. This biphasic arsenate adsorption behavior was partially attributable to: (i) two different adsorption sites associated with Li, exposing on planar surfaces, and Al, existing on the edges of double hydroxyl layers, and (ii) micropore adsorption sites within the Li/Al LDH-Cl surfaces. Activation energies derived by the Arrhenius equation indicated that the diffusion process was the rate-limiting step of arsenate adsorption on Li/Al LDH-Cl.