Mossbauer spectroscopic evidence of a ^IVFe³⁺ intermediate in the oxidation of Fe(Oh)₂ to α-FeOOH

Abstract

Mossbauer spectroscopy was used to study the oxidation of Fe(OH)2 under high pH conditions with the aim of detecting the formation of Fe(OH)3. The Mossbauer spectral parameters indicated that a small IVFe3+ component was initially present in the Fe(OH)2. The Mossbauer spectra were recorded at 77 K, thus any Fe species in solution would also be observed in the frozen state. The small IVFe3+ component increased progressively with the oxidation of the Fe(OH)2, maximizing with the onset of á-FeOOH formation. As á-FeOOH formation increased, the IVFe3+ component decreased, with á-FeOOH being the final sole phase. It is suggested that the Mossbauer spectral parameters indicate that a component such as Fe(OH)2 may form at high pH values as used in this study. Furthermore, any Fe3+ produced by the initial oxidation of Fe(OH)2 is exsolved from the solid and at the high pH of the surrounding liquid produces Fe(OH)-4 until the formation of the more stable á-FeOOH begins. This suggests Fe(OH)2 could be the building blocks for á-FeOOH in alkaline solution. No apparent Fe(OH)3 phase was observed as anticipated.