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 HSO 3 − 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)/HSO 3 − process at pH 7.0 within 20 s, while negligible CBZ was degraded by Mn(III) or HSO 3 − alone. The reactive species responsible for pollutant abatement in the Mn(III)/HSO 3 − process were SO 4 •− and HO • . The treatment efficiency of the Mn(III)/HSO 3 − process is highly related to the dosage of HSO 3 − because HSO 3 − acted as both the radical scavenger and precursor. The reaction of Mn(III) with HSO 3 − follows second-order reaction kinetics and the second-order rate constants ranged from 7.5 × 10 3 to 17 M −1 s −1 under the reaction conditions of this study, suggesting that the Mn(III)/HSO 3 − process is an effective process for producing SO 4 • − . The pH and PP:Mn(III) ratio affect the reactivity of Mn(III) towards HSO 3 − . The water background constituents, such as Cl − and dissolved organic matter, induce considerable loss of the treatment efficiency in different ways.