[Adsorption Effect and Mechanism of Aqueous Arsenic on FeMnNi-LDHs]

Removing As(Ⅲ)from water steadily and efficiently is still a challenging global issue. In this study, novel FeMnNi-LDHs were prepared by a co-precipitation method using Fe, Mn, and Ni as lamellar cations, and the structure were characterized by XRD, TEM, FT-IR, and XPS techniques, and the adsorption performance and mechanism of As(Ⅲ)was explored. The results showed that FeMnNi-LDHs have typical characteristic peaks of layered double hydroxides, with sharp peaks and high crystallinity. The TEM images also show obvious layered structures. The adsorption kinetics of As(Ⅲ)on FeMnNi-LDHs agree with the quasi second-order kinetic model, and the isotherm adsorption curve agrees with the Freundlich isotherm equation. The maximum adsorption capacity at 45℃ was 240.86 mg·g^-1, which is significantly higher than other similar layered double hydroxides. Acidity had little effect on the adsorption performance of As(Ⅲ), and it had a good adsorption effect in the range of pH 2-9. The coexistence of PO₄^3- and CO₃^2- ions in water showed adverse effects on the As(Ⅲ) adsorption capacity, and NO₃^-, Cd²⁺, and Pb²⁺ had less influence. The adsorption mechanism of FeMnNi-LDHs for As(Ⅲ) includes ion exchange, oxidation, and coordination complexation, in which Mn plays a major role in the oxidation process of As(Ⅲ). The prepared FeMnNi-LDHs exhibited good application potential in the adsorption of As(Ⅲ) from water and toxicity control.