Decontamination of arsenite by a nano-sized lanthanum peroxide composite through a simultaneous treatment process combined with spontaneously catalytic oxidation and adsorption reactions

Arsenic is a well-documented element that is extremely harmful to humans. Among major arsenic species in nature, arsenite (As(III)) has higher mobility and toxicity, and is more difficult to be treated by such technologies as coagulation or adsorption than arsenate. As such, its decontamination is greatly challenging. Herein, a new nano-sized lanthanum peroxide composite (LPC) with H₂O₂-to-La³⁺ molar ratio of 1:1 developed through a simple precipitation method can simultaneously oxidize and adsorb arsenite. The LPC exhibited rapid arsenite oxidation and adsorption kinetics in pH 4.5–10.8 and the uptake was completed at time = 60 min; it had a strong selectivity in the presence of competing matters. Moreover, the LPC had a superior As(III) adsorption capacity of 123.2 mg-As/g, outperforming many reported adsorbents. Both As(III) and As(V) in simulated arsenic-polluted reservoir waters were rapidly removed and the rigorous arsenic standard of 10 μg/L was met. Our mechanism studies showed that the oxidation of arsenite to arsenate was ascribed to the La-O-O- groups and the derived [rad]OH generated through the self-catalytic process via the electron transfer within internal peroxo groups. The formed arsenate was bonded to the LPC surface, forming stable inner-sphere complexes via electrostatic attraction and ligand exchange with surface hydroxyls. The study reported here demonstrates that the LPC is promising for the simultaneous oxidation and removal of arsenite from aqueous solutions.