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/Fe(2+)and PS/Fe3+) and the oxidation of Acid Red 18 (AR18). A complete removal was attained after 90 min in both PS/Fe(2+)and PS/Fe(3+)processes with the persulfate concentration of 6 mM. High concentrations of PS, Fe2+, and Fe(3+)promoted the AR18 degradation in both processes and the optimized pH were 3 and 3.3 for PS/Fe(2+)and PS/Fe(3+)processes, respectively. The mechanism of PS activation by Fe(3+)was also investigated. It was found that hydroxyl radical (HO center dot) and sulfate radical (SO4-center dot) were formed and acted as dominating radicals in both processes. It is also deduced that Fe recycle offers Fe(2+)for PS activation in PS/Fe(3+)process to produce HO center dot and SO4-center dot. The less radical side reactions lead to a higher contribution of HO center dot and SO4-center dot on AR18 degradation in PS/Fe(3+)process.