Ozone-Enhanced Oxidation of Oxalic Acid in Water with Cobalt Catalysts. 1. Homogeneous Catalytic Ozonation

Oxalic acid in water has been treated with ozone in the presence of a Co(II) salt at acidic pH. The influence of different variables, including the initial oxalic acid, cobalt(II), and ozone gas concentrations and the temperature, has been investigated. The experimental stoichiometric ratio varied between 0.7 and 1.4 mol of ozone consumed per mole of oxalic acid consumed, while the ozone efficiency reached values as high as 25%. At any conditions applied, nearly total mineralization was achieved. The process developed between the slow and moderate kinetic regimes of ozone absorption. Experiments in the slow kinetic regime allowed for the experimental determination of the reaction kinetics, which was found to be first order with respect to oxalic acid and catalyst. For the case of ozone, nearly one-half-order kinetics was found. A mechanism that involves the participation of cobalt−oxalate complexes is also discussed.