Search

[Display omitted] • Coupling of FeMnO with S(IV) improves the removal speed of As(III). • The FeMnO/S(IV) system integrates adsorption and oxidation functions. • Active Mn(III) is mainly responsible for the oxidation of As(III). • The possible activation pathway of S(IV) in the FeMnO/S(IV) system is proposed. • FeMnO has excellent stability and regeneration/recovery ability. The activation of sulfite [S(IV)] by transition metals, a new generation of advanced oxidation processes, has been widely studied for water purification. However, the application of this process to oxidize and remove arsenite [As(III)] from water through Fe-based S(IV) activation and the associated mechanisms are not fully understood. In particular, rapid removal of As(III) and secondary metal contamination have presented challenges. Herein, we develop a novel sea urchin-like magnetic Fe-Mn bimetallic oxides (FeMnO)-activated S(IV) process to address these issues. Under neutral pH, the FeMnO/S(IV) system achieved a 99.2 % removal of As(III) within only 10 min with residual arsenic concentration below 10 µg/L, and the removed As(III) was fully oxidized to arsenate [As(V)]. Additionally, FeMnO was recyclable and capable of treating actual arsenic-contaminated water. Furthermore, the oxidation mechanism of non-radical active trivalent manganese [Mn(III)] was discovered during the reaction between the FeMnO/S(IV) system and As(III). The FeMnO catalyst activated S(IV) to generate oxysulfur radicals (i.e., SO 5 •–, SO 4 •– and SO 3 •–), but they were not the primary oxidizing species for As(III). Instead, As(III) oxidation was mainly attributed to the active Mn(III) generated by the electron transfer between the FeMnO catalyst and SO 5 •– radicals. The discovery of active Mn(III) species in this work may provide a new avenue for developing novel Fe-Mn-type adsorbents to purify arsenic-contaminated water. [ABSTRACT FROM AUTHOR]

• The FeMnO x /S(IV) system has faster removal speed and higher adsorption capacity for As(III) compared to FeMnO x alone. • The As(III) (1079 µg/L) could be decreased to less than 10 µg/L within 10 min. • The SO 5 •− radicals generated by S(IV) acting as the driving force for the redox cycle between As(III) and Mn(II/III/IV). • The possible mechanism of As(III) oxidation and removal for the FeMnO x /S(IV) system was proposed. • The FeMnO x nanocellulose aerogel broadened the scope of FeMnO x /S(IV) system in engineering applications. 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 x) with sulfite (S(IV)) to enhance the recovery of oxidative capacity and accelerate the removal of As(III). Experimental results showed that the FeMnO x /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 x 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 x /S(IV) system for As(III) was considerably higher than that of the only-FeMnO x system (76.5 > 46.3 mg/g). The efficient and fast As(III) removal was attributed to the SO 5 •− 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 x were systematically investigated, and the results further confirmed the superiority of the FeMnO x /S(IV) system in As(III) removal. In particular, the proposed FeMnO x nanocellulose aerogel effectively purified arsenic-contaminated groundwater using a fixed-bed column. Thus, FeMnO x –S(IV) coupling is very promising for the purification of arsenic-contaminated water bodies. [Display omitted] [ABSTRACT FROM AUTHOR]