Persulfate (PS) activated by zero-valent iron (ZVI) to generate sulfate radicals (SO4 center dot-) was employed in the oxidation of Orange G (OG), an azo dye commonly found in textile wastewaters. Acidic corrosion and direct reaction with persulfate were considered for the oxidation of ZVI to Fe(II), both reactions taking place at the ZVI surface. Effects of pH (1-3.5), PS concentration (0 and 1 mM), and ZVI particle radius (0.030-0.095 cm) were studied. OG (0.1 mM) oxidation was carried out with a 0.5 L batch reactor at 20 degrees C. Using ZVI as activator, Fe(II) is slowly released to the media through a fluid-solid corrosion of ZVI. Therefore, the unproductive consumption of sulfate radicals by Fe(II) can be controlled by changing the particle diameter. A kinetic model capable of describing the evolution of pollutant, oxidant, and iron concentrations (at the different oxidation stages) as well as the mineralization was proposed and validated. To do this, a set of reactions counting for the iron valence change, the sulfate radical production, and the pollutant oxidation and mineralization have been proposed, and the kinetic parameters have been estimated from fitting experimental data. In addition, the model was able to predict data obtained using Fe(II) and Fe(III) as activator. Regeneration of Fe(III) into Fe(II) by the organic matter was also considered as found elsewhere (Rodriguez, S.; et al. Oxidation of Orange G by persulfate activated by Fe(II), Fe(III) and zero valent iron (ZVI). Chemosphere 2014, 101, 86-92).