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

Abstract

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.