The decoloration of an azo dye reactive brilliant orange (X-GN) by a heterogeneous Fenton system using activated carbon–FeOOH catalyst (AC–FeOOH) and H2O2 was studied. Under typical conditions (pH 7.0, H2O2 10 mmol/L, AC–FeOOH 1.0 g/L and 30 °C), 98% decoloration rate of X-GN was achieved in 240 min. The decoloration efficiency of X-GN increased with higher H2O2 dosage, higher AC–FeOOH dosage and higher reaction temperature. Though the catalytic reaction was an acid driven process, a sufficient decoloration performance was still obtained in neutral and alkaline conditions. Kinetic studies suggested that the decoloration of X-GN followed a pseudo-first order reaction and the activation energy was 17.2 kJ/mol. Iron leaching from AC–FeOOH occurred during the reaction, but the decoloration efficiency of X-GN was still higher than 80% after four runs. The AC–FeOOH has a good stability and can be reused. Besides, the generation of massive iron-containing sludge can be avoided after reaction as the remaining ferric ions in the solution were less than 1 mg/L in this combined H2O2 and AC–FeOOH process.
