Stability study of the As(V)-Fe(III) oxyhydroxide coprecipitate over a broad pH range: Characteristics and mechanism

Fe(III)-oxyhydroxide composites are efficient adsorption materials, however, their detailed geometrical structures and adsorption mechanisms in a broad pH range are still unclear. In this study, the structures of arsenic (V) adsorbed on Fe(III)-oxyhydroxide adsorption complexes were investigated using hybrid density functional theory calculations together with experimental Fourier transform infrared (FT-IR) spectroscopy. Adsorption experiments showed higher arsenic(V) removal rates in the range of pH 5.0-10.0. FT-IR and X-ray diffraction (XRD) revealed that arsenic(V) is stably adsorbed by Fe(III)-oxyhydroxide complexes. The formation of monomeric As (V) appears to be favored in the 1.0-4.0 pH range, while dimeric and trimeric As(V)-Fe(III) oxyhydroxide complexes are preferably formed at higher pH (4.0-10.0). Namely, dimeric and trimeric Fe(III)-oxyhydroxides exhibited good removal efficiencies for arsenic(V) over a wide pH range. Interestingly, the stabilities of the complexes formed between As(V) and monomeric, dimeric and trimeric Fe(III)-oxyhydroxides follow the orders: As(V) trimer > As(V) dimer > As(V) monomer; these complexes are also interconvertible. (C) 2021 Published by Elsevier B.V.

Automated summary

This study investigated the structures and mechanisms of arsenic(V) adsorbed on Fe(III)-oxyhydroxide adsorption complexes using hybrid density functional theory calculations and experimental FT-IR spectroscopy. Experimental results showed higher removal rates of arsenic(V) in the pH range of 5.0-10.0. Additionally, the stabilities of different As(V)-Fe(III)-oxyhydroxide complexes were revealed and found to be interconvertible.