The enhanced As(III) removal by Fe-Mn-Cu ternary oxide via synergistic oxidation: Performances and mechanisms

Mn-oxide-containing adsorbents have shown outstanding performances for the removal of As(III) through an “oxidation-adsorption” process. In this study, a new adsorbent of Fe-Mn-Cu ternary oxide (FMCTO) was fabricated to improve the redox reaction rate and to enhance the recovery of oxidative ability. FMCTO exhibited a stronger ability for As(III) removal than most of other adsorbents, because it has better oxidative capability for As(III) oxidation. The state of dynamic equilibrium for As(III) removal by FMCTO could be basically achieved within 3 h, and the As removal efficiency reached 98.9% at time = 24 h. The Langmuir As adsorption capacity of FMCTO was determined to be 204.8 mg/g. The As(III) removal efficiency of FMCTO was further boosted by 7% through oxygen gas aeration and decreased by 19% with nitrogen gas in the ambient during the first 3 h, indicating the positive effect of oxygen on As(III) oxidation. EPR and UV spectra methods were used to confirm the generation of superoxide radical (O₂[rad]⁻) and the enhanced production of Mn(III) soluble species on FMCTO surfaces, thus achieving a better As(III) oxidation performance. The XPS analysis results showed that the electron transfer from Cu(I) to Mn(IV) could improve the stability of Mn(III) within FMCTO. Meanwhile, Mn(II) ions could be oxidized to Mn(III) by O₂[rad]⁻. Hence, the formation of a redox cycle between Mn(II) and Mn(III) along with the production of O₂[rad]⁻ plays a vital role in the upgraded As(III) removal mechanisms. This study provides new insights into the promotion of the capability of Mn-containing adsorbents for achieving the improved removal of As from As(III)-contaminated water.