FORMATION OF MG-BEARING FERRITE BY THE AIR OXIDATION OF AQUEOUS SUSPENSIONS

When the Mg**2** plus /Fe//t//o//t//a//l molar ratio in the initial aqueous suspension is below 0. 1 at pH 9. 0 and 65 degree C, almost all Mg**2** plus is incorporated into the spinel type ferrite by the air oxidation of Fe(OH)//2. The chemical composition of the Mg-bearing ferrite thus obtained is not stoichiometric, and is expressed as the MgFe//2O//4-Fe//3O//4- gamma -Fe//2O//3 system. At pH 8. 0, a small amount of the Mg**2** plus is incorporated into the ferrite, between pH 9. 0 and 10. 0 only the Mg-bearing ferrite is formed, and at pH 11. 0, the alpha -FeOOH type compound is formed together with the Mg-bearing ferrite.