Reactions of Ammonium Hydrogen Fluoride with Oxides of Iron in Solid State

The reactions of ammonium hydrogen fluoride with three oxides of iron, viz., a-Fe2O3, Fe3O4 (magnetite) and γ-Fe2O3 (maghemite) in the solid state at room temperature and at slightly higher than the ambient have been studied. The products were characterised by powder XRD, TG/DTA, chemical analysis and Mössbauer techniques. In all the cases, the product of reaction was [NH4]3FeF6.1.5H2O. This shows that although magnetite contains both ferrous and ferric species, reaction with ammonium hydrogen fluoride in the solid state brought about by mere physical mixing at room temperature in air results in oxidation of Fe(II) to Fe(III).