Chemical Engineering Journal, Vol.362, 183-189, 2019
Enhanced oxidation of aniline using Fe(III)-S(IV) system: Role of different oxysulfur radicals
In this paper, the efficiency of Fe(III)-S(IV) system used for advanced oxidation processes (AOPs) has been investigated using aniline as a pollutant model compound in water. The chemical kinetics, influencing factors, and mechanism of aniline oxidation are examined with an emphasis on the contribution of the different oxysulfur radicals (mainly SO4 center dot- and SO5 center dot-). Our results show a significant enhancement in the efficiency of aniline oxidation observed at pH 4.0 with 1.0 mM S(IV) and 0.1 mM Fe(III) concentrations. Moreover, the degradation efficiency drastically decreases to 10% in the absence of oxygen indicating the significant role of oxygen in this type of process. Through competition kinetic experiments and radical scavenger experiments, it is shown that SO5 center dot- is responsible for about 60% of the aniline oxidation in the Fe(III)-S(IV) system under the typical conditions investigated in this work. For the first time we have determined the second order rate constant between SO5 center dot- and aniline (5.8 +/- 0.6x10(6) M-1 s(-1) (at pH 3.0) and SO4 center dot- and aniline 7.7 +/- 0.5x10(9) M-1 s(-1) (at pH 3.0)). Sequential experiments with successive additions of sulfite drastically improve the oxidation efficiency. These findings may provide a precise understanding of the overall mechanism and may have promising implications in developing a new cost-effective technology for the treatment of organic compounds-containing water. Furthermore, the results of this work help to understand the relevance and mechanism of organic contaminants oxidation by SO5 center dot-, which has not been given much attention in conventional SR-AOPs using peroxymonosulfate.