REACTIVITY OF CHROMIUM-OXIDE IN AQUEOUS-SOLUTIONS .1. OXIDATIVE DISSOLUTION

Chromium(III) oxide, alpha-Cr2O3, is dissolved in aqueous media in the presence of Ce4+, MnO4-, BrO3-, and S2O8-/Ag+ species in a process preceded by the formation of surface Cr-O-X complexes. The last cited reactant causes oxidation of Cr(III) by Ag2+ attack on the surface complex, whereas the other three additives promote dissolution by the formation of Cr(VI) through an internal redox process within the surface complex. Langmuir-type conditional constants for the formation of the surface complexes are presented and discussed, together with the rate constants that describe their evolution to dissolved Cr(VI). The analogy between these heterogeneous oxidations of alpha-Cr2O3 and oxidations of dissolved Cr(H2O)6(3+) is discussed.