Unraveling the Role of Mn(VI) and Mn(V) Species in Contaminant Abatement by Permanganate

Mn(VI) and Mn(V) (Mn(VI/V)) were reported to be reactive to organic contaminants containing electron-rich moieties and some inorganic contaminants. It remained unclear whether Mn(VI/V) contributed to contaminant abatement by Mn(VII). This study developed two methods (methanol method and kinetics method) to identify the contributions of Mn(VI/V) during contaminant oxidation by Mn(VII). It was verified that methanol was a suitable probe for Mn(VI/V), and HCHO was the major oxidizing product of methanol. By determining the influence of methanol on the stoichiometric ratio of contaminant to Mn(VII) and the generation of HCHO, Mn(VI/V) were found to play a remarkable role during the abatement of As(III), methyl phenyl sulfoxide (MPSO), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate), and phenol by Mn(VII). However, Mn(VI/V) scarcely contributed to carbamazepine degradation by Mn(VII). The difference between the apparent second-order rate constant of MPSO oxidation by Mn(VII) determined in the presence of excess MPSO and that determined in the presence of excess Mn(VII) further verified the contributions of Mn(VI/V) during MPSO degradation by Mn(VII). Natural organic matter in real water samples could also induce the generation of Mn(VI/V) and thus accelerate MPSO abatement by Mn(VII). This study gained deep insights into the overlooked role of Mn(VI/V) in contaminant abatement during the Mn(VII) oxidation process.