Factors affecting the kinetics of the heterogeneous oxidation of ammonium sulfite

Absorption of oxygen into 0.09 – 0.7 M solutions of ammonium sulfite was measured by utilizing a stirred cell. The concentration ranges of the cobalt sulfate catalyst was 5.5 × 10^?5 – 4.7 × 10^?3 M and that of oxygen in the gas phase 21 – 100%. The theory of absorption with fast pseudo-nth order reaction was used to find the order of intrinsic rate of reaction with respect to reactants and the catalyst. Above a critical sulfite concentration the order in sulfite is zero, in O₂ is 0.4 – 1, and in CoSO₄ is 1. Under those conditions a proposed reaction mechanism yields orders of zero, 1, and 1, respectively. Below the critical point the order in sulfite is 2, indicating that another reaction mechanism is applicable. Although an increase of the ionic strength enhances the reaction rate slightly, an increase of pH from 7.6 to 8.5 causes a 1.4 fold increase. Under oxidative conditions deactivation of the catalyst and insoluble precipitate formation is observed.