Dynamics for oxidation of Fe3O4, Fe2CoO4 and Fe2NiO4

Abstract The kinetics for oxidation of CRUD model compounds (Fe 3 O 4 , Fe 2 CoO 4 , and Fe 2 NiO 4 ) by IrCI 6 2 - and MnO 4 - 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 Fe 3 O 4 , Fe 2 CoO 4 and Fe 2 NiO 4 reacting with IrCl 6 - 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 MnO 4 - . The reactivity of the metal oxides is in the order Fe 2 CoO 4 > Fe 3 O 4 > Fe 2 NiO 4 for both oxidants. Unlike previous studies on oxidation of UO 2 , 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.