Dissolution of nickel and chromium from Ni-Cr-Fe-O oxide by oxidative treatment with permanganate

Ni-Cr-Fe mixed oxides (NiCrxFe2-xO4) are formed as a corrosion oxide films on structural material surface of coolant or heat transport circuit in water-cooled nuclear reactors. Study on the dissolution behavior of these oxides forms a critical part in development of an efficient chemical decontamination process for the nuclear industry. The present study describes release of Ni and Cr in permanganate medium from the chromium substituted nickel ferrite and also on the mechanistic aspects of oxide dissolution. These oxides were synthesized by combustion method and characterized by the XRD, XPS and Raman spectroscopy. The dissolution kinetics of oxide in permanganate medium was modeled by Shrinking Sphere Model and General Kinetic law Equation. The rate constant for oxide dissolution increased with the Cr substitution in nickel ferrite. Presence of chromium in the oxide lattice affect the release of nickel and also a minimum chromium concentration in the lattice is required for the release of nickel from the oxide lattice during the permanganate treatment. However, when the chromium substitution (x) is increased to 0.6 and above, the nickel release was lowered.