Kinetics of Chlorine Dioxide Oxidation of Benzidine in Tannery Wastewater

Reaction kinetics of benzid ine oxidation with ClO 2 in the wastewater was investigated systematically by detecting concentrations of benzid ine with HPLC at regular intervals. The results show that the reaction was firstorder with respect to both ClO2 and benzid ine, and the entire reaction was of second-order. Under condition of pH 6.5 and water temperature 298K, the second-order reaction rate constant k was 5.721×10-4L/(mmol·s). The reaction activation energy was 51.1kJ ·mol -1, revealing that the reaction could take place under usual water treatment conditions. The rate constants first increased with the increasing reaction pH value, and then decreased. Diphenoquinonediimine, diphenoquinonedioxime and diphenoquinone were detected by GC-MS as intermediates of the protonated benzid ine-ClO2 reaction, however, hydrazobenzene, azobenzene and para-benzoquinone as intermediates of the free benzid ine-ClO 2 reaction. The end product of the free and proton state benzid ine oxidized by ClO2 was unsaturated organic diacid. The two possible pathways for the benzid ine-ClO2 reaction were proposed based on the mechanism of the single electron transfer (SET).