Kinetic Modeling of Manganese(II) Oxidation by Chlorine Dioxide and Potassium Permanganate

Oxidation of Mn(II) by potassium permanganate and chlorine dioxide was investigated for the environmental conditions of pH, temperature, and initial Mn(II) concentrations typically observed in water treatment. For the conditions examined, oxidation reactions are rapid, with completion of the reactions within ˜30 s. A kinetic model based on solution-phase oxidation, adsorption, and surface oxidation mechanisms was developed that successfully simulates experimental data. The model was capable of simulating the experimental data (r² = 0.90 and 0.75 for KMnO₄ and ClO₂, respectively) over a range of solution pH (5.5-8), temperature (2-25 °C), and initial Mn(II) concentrations (0.4-1.25 mg/L). The kinetic model was solved numerically, and rate constants and activation energies (10-50 kJ/mol) were derived for the three mechanisms simulated. For reactive oxidants such as KMnO₄ and ClO₂, adsorption of Mn(II) to the oxide surface is the rate-limiting step. Because of rapid surface oxidation reactions, concentrations of adsorbed Mn(II) were predicted to be low for the conditions studied. This result is in contrast to less reactive oxidants where surface adsorption is rapid relative to solution and surface oxidation reactions.