Abstract
The effect of oxidation rate and addition of Cu2+ or PO43− ion on the oxidation of Fe(II) hydroxo-complexes in aqueous solutions were investigated by means of measurements of the infrared and Mössbauer’s spectra and the X-ray diffraction of oxidation products.The results obtained are summarized as follows:(1) The rapid oxidation of Fe(II) hydroxo-complexes in solutions with the addition of H2O2 resulted in the formation of δ-FeOOH. The oxyhydroxide was obtained also by removing water from the Fe(II) complexes and leaving them in air to be oxidized.(2) The size of δ-FeOOH crystallite formed by the oxidation of Fe(OH)2 with H2O2 is determined by the size of particle of the starting compound. The broad absorption band at 450 cm−1 shifted to 480 cm−1 with the increase in crystallite size. The shift of the absorption band probably corresponds to the increase in force constant of vibration, which may result from the increase of crystallite size, i.e. the decrease in interatomic distance.(3) Green Rust I was converted to Fe3O4 by the slow oxidation in solution.(4) In the presence of Cu2+ or PO43− ion, freshly precipitated Fe(II) hydroxo-complexes were oxidized to amorphous δ-FeOOH with air in solutions. This transformation is considered to be caused by the catalytic effect of Cu2+ or PO43− ion in the oxidation of the Fe(II) complexes.
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