Is Mn(III) a principal oxidant for trace organic contaminant abatement in permanganate/bisulfate process?

Abstract

Combining permanganate (Mn(VII)) with bisulfite (S(IV)) is an emerging advanced oxidation process, while the principal oxidant for ultrafast abatement of trace organic contaminant (TrOC) in the Mn(VII)/S(IV) (MS) process has long been under disputation. In this work, Mn(III) yield, kinetics, stoichiometry, and TrOC abatement by the MS and Mn(VII)/Mn(II) (MM) processes were investigated. The results showed that the yields of Mn(III) were close to the theoretical value of 90% in both processes, and the molar ratio of -Δ[Mn(VII)]/Δ[Mn(III)] was respectively determined to be 1:1 and 1:5 in the MS process and MM process. Although the second-order rate constant of the Mn(III) generation in the MS process (3.0 × 105 M−1 s−1) was about 43 times that of the MM process (7.0 × 103 M−1 s−1), the abatement rate of TrOC in the MS process was 4–5 orders of magnitude higher than that of the MM process. Interestingly, the abatement of bisphenol A was completely inhibited in the absence of dissolved oxygen in both processes, whereas the high yield of Mn(III) still occurred at deoxygenated solutions in the MM process. This indicated that the contribution of Mn(III) to TrOC abatement was limited in both processes. Moreover, it was found that the rate-determining step of TrOC abatement in the MS process was the reduction of Mn(III) by S(IV) by comparing the MS process with the Mn(III)/S(IV) process.