Dynamics for oxidation of Fe3O4, Fe2CoO4 and Fe2NiO4

The kinetics for oxidation of CRUD model compounds (Fe3O4, Fe2CoO4, and Fe2NiO4) by IrCI62- and MnO4- has been studied using aqueous suspensions of metal oxide powder. The second order rate constants at room temperature were determined to 3.6(±0.3) × 10−6, 1.2(±0.2) × 10−5 and 3.3(±0.5) × 10−6 min−1 m for Fe3O4, Fe2CoO4 and Fe2NiO4 reacting with IrCl6-2 and to 1.5(±0.2) × 10−6, 1.2(±0.1) × 10−6 and 6(±1) × 10−7 min−1 m for the reactions with MnO4-. The reactivity of the metal oxides is in the order Fe2CoO4 > Fe3O4 > Fe2NiO4 for both oxidants. Unlike previous studies on oxidation of UO2, there is no linear relation between the logarithm of the rate constant, ln k, and the one-electron reduction potential of the oxidants for the metal oxides studied here. This discrepancy is explained in terms of differences in the reorganization energy of the metal oxides giving rise to different curvature in accordance with the Marcus theory for electron transfer.