This study investigated the use of blast furnace dust (BFD) as a catalyst to degrade an azo dye (RR195) by photo-Fenton-like processes. This waste contains hematite, magnetite and maghemite as iron sources, and its dissolution provides more Fe3+ than Fe2+ for the Fenton reaction in solution. The effect of hydrogen peroxide concentration and catalyst dosage on the kinetics of hydrogen peroxide decomposition and dye decolorization was also studied. The photo-Fenton-like process was compared to Fenton-like (using BDF without irradiation), Fenton and photo-Fenton (using FeSO4 as iron source), UV/H2O2 and UV processes. The results indicated that BFD can be effectively used as a catalyst in the photocatalytic process because it was able to completely degrade H2O2 via an adjusted Langmuir-Hinshelwood model. Although the photo-Fenton-like reaction with BFD showed the same decolorization efficiency of RR195 as the homogeneous photo-Fenton process (using FeSO4), the catalyst considerably increased the reaction rates (more than five times) according pseudo-first-order kinetics. The results of the irradiated systems using BFD can be more efficient in dye decolorization due to greater hydroxyl radical production through Fe2+/Fe3+ cycling and by the occurrence of homogeneous and heterogeneous reactions. The practical use of the steel waste is promising, because it increases the reaction rates and its high density and magnetic proprieties enable an easy solid-liquid separation and reuse, making it a versatile material for environmental applications. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.