Abstract
Fe–Mn binary oxide is a promising material for As(III) removal through a combined oxidation and adsorption process. To improve its applicability in column or other flow-through systems, we developed a new nanocomposite motivated by the Donnan membrane principle, i.e., Fe–Mn binary oxide encapsulated within a polystyrene anion exchanger D201 (designated D201-Fe/Mn), for efficient As(III) removal from water. As compared to single Fe(III) oxide-loaded D201, the resultant D201-Fe/Mn was less sensitive to pH variation in the range of 4–10 and exhibited higher As(III) capacity. X-ray photoelectron spectroscopy (XPS) analysis confirmed that As(III) was oxidized to As(V) by Mn(IV) oxide during its sequestration by D201-Fe/Mn, whereas Mn(IV) was reduced to MnOOH* and consequently to Mn(II) simultaneously. The exhausted D201-Fe/Mn could be regenerated by NaOH–NaCl–NaClO solution for repeated use without any significant capacity loss, where the adsorbed As species was effectively desorbed to solution and the Mn(II) species was oxidized back to Mn(IV). High-level phosphate and silicate would pose strong competition for As(III) adsorption by D201-Fe/Mn, while sulfate and chloride did not show significant competition under similar conditions. Fixed-bed adsorption further validated that D201-Fe/Mn would be of considerable potential in As(III) removal from contaminated waters.
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