A Comparative Study on Oxidation of Acidic Red 18 by Persulfate with Ferrous and Ferric Ions

Ferrous and ferric salts were tested for the persulfate activation (PS/Fe2+ and PS/Fe3+) and the oxidation of Acid Red 18 (AR18). A complete removal was attained after 90 min in both PS/Fe2+ and PS/Fe3+ processes with the persulfate concentration of 6 mM. High concentrations of PS, Fe2+, and Fe3+ promoted the AR18 degradation in both processes and the optimized pH were 3 and 3.3 for PS/Fe2+ and PS/Fe3+ processes, respectively. The mechanism of PS activation by Fe3+ was also investigated. It was found that hydroxyl radical (HO•) and sulfate radical (SO4−•) were formed and acted as dominating radicals in both processes. It is also deduced that Fe recycle offers Fe2+ for PS activation in PS/Fe3+ process to produce HO• and SO4−•. The less radical side reactions lead to a higher contribution of HO• and SO4−• on AR18 degradation in PS/Fe3+ process.