Catalytic Ozonation of Oxalic Acid in Aqueous Solution in the Presence of Manganese Ions

Abstract

The kinetics of mineralization of oxalic acid Н₂С₂О₄ under the action of ozone in acidic aqueous solution (С(НClО₄) = 0.1 M, pH ~ 1) with the addition of ${\text{MnO}}_{4}^{ - }$ or Mn²⁺ ions was studied. It was found that manganese ions are effective catalysts for the reaction of O₃ with oxalic acid. Regardless of the manganese species (${\text{MnO}}_{4}^{ - }$ or Mn²⁺) added to the solution, it was converted into an oxalate complex of tetravalent manganese in the course of the reaction, and this complex was the stable form of the catalyst in the system under consideration. The kinetics of release of carbon dioxide—a product of the reaction of Н₂С₂О₄ with О₃—was determined depending on the concentrations of ozone in the gas stream and oxalic acid and manganese in the solution. A basic scheme of the catalysis of the test reaction by manganese ions was proposed, and a kinetic model was constructed to adequately describe the experimental results. The reaction scheme is based on the fact that oxalate is oxidized to CO₂ in the course of a complex decomposition reaction of the oxalate complex of tetravalent manganese; in this case, Mn(IV) is reduced to Mn²⁺. The complex is regenerated by the oxidation of Mn²⁺ to Mn(IV) with ozone.