In this work, a simple kinetic model was used to study the azo dye Orange II (O-II) degradation using Fenton's reagent, in the Fenton-like stage. The effects of pH, temperature. Cl- concentration and initial concentrations of O-II, hydrogen peroxide (H2O2) and ferrous ion catalyst (Fe2+) on the degradation rate have been investigated in a batch reactor. The apparent kinetic constants, k(ap), for O-II degradation were determined in the following ranges of experimental conditions: 2.0 <= pH <= 4.0, 283 K <= T <= 323 K, 0M <= C-cl- <= 1 x 10(-2) M, 3 x 10(-5) M <= C-Ollo <= 1 x 10(-4) M, 1 x 10(-4) M <= C-H2O2o <= 1 x 10(-3) M and 2.5 x 10(-6) M <= C-Feo(2+) <= 2 x 10(-5) M. A pseudo first-order reaction rate with respect to O-II concentration was found to be adequate to fit the data in these experiments, in which k(ap) depends on the initial conditions following a power-law dependency (at optimum pH of 3 and absence of chloride ions). This equation, without further fitting parameters, was successfully used to validate experiments performed in a continuous stirred tank reactor (CSTR). The ability of the model predictions was also checked by performing experiments in the CSTR out of the above-mentioned ranges (used for the kinetic study). (c) 2008 Elsevier B.V. All rights reserved.