Decolorization efficiency and kinetics of typical reactive azo dye RR2 in the homogeneous Fe(II) catalyzed ozonation process

The decolorization efficiency and gas–liquid reaction kinetics of Reactive Red 2 (RR2, C.I. 18200) dye by ferrous catalyzed ozonation process (O3/Fe(II)) in a semi-batch reactor were evaluated. The results indicate that RR2 dye ozonation is an irreversible second order reaction. Danckwerts surface renewal theory was used to specify the gas–liquid mass transfer progress and to determine the second order reaction rate constant k2. It is also found that Fe(II) can enhance the degradation efficiency of RR2 dye, and the k2 values were 1056 M−1 s and 2248 M−1 s when Fe(II) dosage were 0 and 0.9 mM, respectively. The optimum O3/Fe(II) combination was 2 mg L−1 min−1 ozone dosage rate with initial Fe(II) dosage of 0.9 mM when RR2 dye initial concentration was 0.45 mM at pH 7. Increasing of the ozone inlet gas concentration and gas flow rate will increase the mass transfer coefficients and therefore increase k2. Furthermore, k2 is observed associate with temperature and can be expressed by a modified Arrhenius Equation with activation energy Ea of 26.3 kJ mol−1. A possible degradation mechanism between ozone and RR2 dye in O3/Fe(II) process was discussed.