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 1056M^-1s and 2248M^-1s when Fe(II) dosage were 0 and 0.9mM, respectively. The optimum O₃/Fe(II) combination was 2mgL^-1min^-1 ozone dosage rate with initial Fe(II) dosage of 0.9mM when RR2 dye initial concentration was 0.45mM 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 E_a of 26.3kJmol^-1. A possible degradation mechanism between ozone and RR2 dye in O₃/Fe(II) process was discussed.