Mn(II)-enhanced oxidation of benzoic acid by Fe(III)/H₂O₂ system

This study investigated the enhanced oxidation of benzoic acid (BA) by Fenton-like system (Fe(III)/H₂O₂) with manganese ion (Mn(II)). Experiments were conducted at pH 3.0, with Fe in the low concentration, H₂O₂ in excess and Mn(II) in a wide range. In all cases, Mn(II), which is very inert to H₂O₂, significantly enhanced the oxidation of BA, accelerated the formation of Fe(II) and the decomposition of H₂O₂. The pseudo-first-order rate constant for the initial lag phase and the half-life of BA were calculated to evaluate the degree of enhancement in the presence of Mn(II). As a primary product, the concentration of p-hydroxybenzoic acid (pHBA) was monitored during the oxidation. The ratio between formed pHBA and oxidized BA indicated that HO dominated the oxidizing process, and this was further confirmed by the inhibition of tert-butanol on the oxidation of BA. Finally, the role of Mn(II) in Fe(III)/H₂O₂ system was analyzed, and a series of reactions including manganese species, HO, HO2/O2- and H₂O₂ were proposed to be the possible reason for the enhancement.