Mössbauer spectra at 77 K of products formed during transformation of Fe(OH)2 to Fe3O4 in aqueous suspension by air oxidation

Mossbauer spectra at 77 K of the products formed during the aerial oxidation of aqueous iron(II) hydroxide suspensions, combined with X-ray powder diffraction and electron micrograph data have suggested that at pH 9.0, Fe(OH)2 and Fe3O4 are formed. [During the initial stage, iron(III) hydroxide oxide, γ-FeO(OH), is also formed.] It has been also suggested that at pH 7.0, only ‘green rust II’ is formed in the second stage, followed by the formation of Fe3O4, while the content of Fe2+ ion in the supernatant gradually decreases. The Mossbauer data suggest that the FeII : FeIII mol ratio in green rust II is 2 : 1.