Efficient As(III) removal by macroporous anion exchanger-supported Fe-Mn binary oxide: Behavior and mechanism

摘要

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-NaCIO 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.