Kinetics and mass transfer effects in the oxidation of ferrous sulfate over doped active carbon catalysts

Ferric sulfate is used in water purification. The oxidation of ferrous sulf ate, FeSO4, to ferric sulfate in acidic aqueous solutions of H2SO4 over fin ely dispersed active carbon particles was studied in a vigorously stirred b atch reactor. Molecular oxygen was used as the oxidation agent and two kind s of catalysts were utilized: active carbon, doped active carbon. Both acti ve carbon and doped active carbon catalysts enhanced the oxidation rate con siderably. Systematic kinetic experiments were carried out at the temperature and pres sure ranges of 60-100 degreesC and 3-10 bar, respectively. The results reve aled that both non-catalytic and catalytic oxidation of Fe2+ take place sim ultaneously. The experimental data were fitted to rate equations, which wer e based on a plausible reaction mechanism: adsorption of dissolved oxygen o n active carbon, electron transfer from Fe2+ ions to adsorbed oxygen and fo rmation of surface hydroxyls. A comparison of the Fe2+ concentrations predi cted by the kinetic model with the experimentally observed concentrations i ndicated that the mechanistic rate equations were able to describe the intr insic oxidation kinetics of Fe2+ over pure active carbon and doped active c arbon catalysts. (C) 2001 Elsevier Science B.V. All rights reserved.