Ca2+-activated ferrate (VI) to generate reactive species and oxygen for efficient membrane cleaning: Mechanisms and application

Rapid self-decomposition and low reactivity to natural organic compounds with more unsaturated functional groups in alkaline water were the two critical parameters that restricted the practical application of Ferrate (VI). Herein, we reported a novel approach to reactivate the stabilized Fe (VI) for highly efficient membrane cleaning. The Fe (VI) stabilized by bicarbonate/carbonate (HCO3−/CO32−) buffer was reactivated by calcium ions (Ca2+) to facilitate releasement of O2 and generate high-valent iron species with subsequent hydroxyl radicals (•OH). The process was rationally utilized for removal of the membrane foulants, humic acid (HA) coupled with Ca2+, which exhibited excellent cleaning performance with membrane flux recovered from 67% to 98%. The outstanding removal performance of membrane foulants could be mainly attributed to the high-valent iron species and •OH, with their contribution rate ratio being about 7:3. Significantly, the proposed FeO42− + HCO3−/CO32− buffer + Ca2+ strategies paved a novel way for upgrading the Fe(VI) utilization pattern compared with Fe(VI) direct oxidation, which was expected to provide an effective option for Fe(VI)-based membrane cleaning in alkaline water. [Display omitted] •A novel cleaning strategy in alkaline condition using Fe (VI) was proposed.•The stabilized Fe (VI) was reactivated by Ca2+ to facilitate releasement of O2.•Ca2+ could activate stabilized ferrate (VI) for effective membrane cleaning.•High-valent iron species and .•OH radicals were the reactive species for cleaning process.