Rapid purification of As(III) in water using iron-manganese composite oxide coupled with sulfite: Importance of the SO radicals.

Manganese (Mn)-containing composite metal adsorbents are very effective at removing arsenite (As(III)) from contaminated water, however, the low removal speed and oxidation efficiency have limited their further application. In this study, a nonhomogeneous catalytic oxidation-adsorption system was constructed by coupling iron-manganese composite oxide (FeMnO) with sulfite (S(IV)) to enhance the recovery of oxidative capacity and accelerate the removal of As(III). Experimental results showed that the FeMnO/S(IV) system decreased the As(III) concentration from 1079 to <10 µg/L within 10 min and almost completely oxidized As(III) to As(V). In contrast, FeMnO alone removed only 82.4% of As(III) within 30 min, and 60.0% of the adsorbed As(III) was not oxidized. Meanwhile, the adsorption capacity of FeMnO/S(IV) system for As(III) was considerably higher than that of the only-FeMnO system (76.5 > 46.3 mg/g). The efficient and fast As(III) removal was attributed to the SO radical generated by S(IV) acting as the driving force for the redox cycle between As(III) and Mn(II/III/IV). Several environmental factors (e.g., solution pH and inorganic anions) and the reusability and practicality of FeMnO were systematically investigated, and the results further confirmed the superiority of the FeMnO/S(IV) system in As(III) removal. In particular, the proposed FeMnO nanocellulose aerogel effectively purified arsenic-contaminated groundwater using a fixed-bed column. Thus, FeMnO-S(IV) coupling is very promising for the purification of arsenic-contaminated water bodies.