Ozone-enhanced oxidation of oxalic acid in water with cobalt catalysts.: 2.: Heterogeneous catalytic ozonation

Ozone and a Co3O4/Al2O3 catalyst have been used to remove oxalic acid from water at acidic pH. The influence of different variables, including the initial oxalic acid and ozone gas concentrations, the catalyst mass, and the temperature, has been investigated under conditions of chemical control. The ozone efficiency was found to reach values of up to 40%, which are higher than those found in homogeneous catalysis (see also the first part of this work, which immediately precedes this paper in this issue), and the mean stoichiometry was determined to be 0.8 mol of ozone consumed per mole of oxalic acid consumed. Metal leaching was also followed to check the stability of the catalyst. As a result, ozonation of oxalic acid was found to be due to both heterogeneous and homogeneous catalytic ozonation. The average contribution of heterogeneous catalytic ozonation for the removal of oxalic acid was found to be 75%. A kinetic study taking into account both catalytic contributions is also presented. The experimental heterogeneous catalysis was found to be first-, one-half-, and zeroth-order with respect to catalyst, dissolved ozone, and oxalic acid, respectively. A mechanism is also proposed to account for the kinetic results.