Dye Oxidation in Aqueous Phase by Using Zero-Valent Iron as Persulfate Activator: Kinetic Model and Effect of Particle Size

Abstract

Persulfate (PS) activated by zero-valent iron (ZVI) to generate sulfate radicals (SO4•–) 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 °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 sulf...