Activation of Bisulfite with Pyrophosphate-Complexed Mn(III) for Fast Oxidation of Organic Pollutants

Aqueous complexes of Mn(III) ion with ligands exist in various aquatic systems and many stages of water treatment works, while HSO₃^- is a common reductant in water treatment. This study discloses that their encounter results in a process that oxidizes organic contaminants rapidly. Pyrophosphate (PP, a nonredox active ligand) was used to prepare the Mn(III) solution. An approximate 71% removal of carbamazepine (CBZ) was achieved by the Mn(III)/HSO₃^- process at pH 7.0 within 20 s, while negligible CBZ was degraded by Mn(III) or HSO₃^- alone. The reactive species responsible for pollutant abatement in the Mn(III)/HSO₃^- process were SO₄^•- and HO^•. The treatment efficiency of the Mn(III)/HSO₃^- process is highly related to the dosage of HSO₃^- because HSO₃^- acted as both the radical scavenger and precursor. The reaction of Mn(III) with HSO₃^- follows second-order reaction kinetics and the second-order rate constants ranged from 7.5 × 10³ to 17 M^-1 s^-1 under the reaction conditions of this study, suggesting that the Mn(III)/HSO₃^- process is an effective process for producing SO₄^•-. The pH and PP:Mn(III) ratio affect the reactivity of Mn(III) towards HSO₃^-. The water background constituents, such as Cl^- and dissolved organic matter, induce considerable loss of the treatment efficiency in different ways.