硫酸-セリウム (IV) 溶液中におけるニッケルフェライトの溶解挙動

抄録

The oxidative dissolution of NiFe₂O₄ in sulfuric acid-cerium (IV), SC, solution has been investigated in comparing with previous works on the reductive dissolution of nickel ferrites. Each dissolution rate of Ni and Fe components in the oxide of NiFe₂O₄ greatly depends on the redox potential of the SC solution. The magnitude of their rates is in the following order: Fe>Ni in 0.25M H₂SO₄ without Ce⁴⁺ or with the addition of ascorbic acid in the SC solution, and Ni>Fe in the SC solution, indicating that the rate of Ni increases in an oxidative solution. Both the rates mainly depend on temperrature (40-90°C), but are little affected by Ce⁴⁺ concentration (1.3-10×10^-3M) and H₂SO₄ concentration (0.25-0.5M). A little consumption of Ce⁴⁺ was observed only at the initial stage of the dissolution. This shows that the dissolution is not due to redox reactions, but is catalyzed by Ni³⁺ formed in the oxide by the oxidation of Ce⁴⁺ in the SC solution. The overall dissolution rate of NiFe₂O₄ is dominated by the rate of Fe in a reductive solution and by the rate of Ni in an oxidative solution.