Atomic-scale Structure of Ferric Oxyhydroxide Formed from Fe–Si Alloy in Aqueous Solutions Containing Different Salts

Quantitative X-ray structural analysis coupled with reverse Monte Carlo (RMC) simulation was performed for characterizing the atomic-scale structure of γ-FeOOH (lepidocrocite) particles. These particles were formed by dipping pure iron or Fe–2mass%Si alloy into aqueous solutions containing Na2SO4 or NaCl. The realistic atomic-scale structures of γ-FeOOH particles were estimated by fitting ordinary interference functions through the RMC simulation technique. The results revealed that the fundamental FeO6 octahedral structural units and their linkages were distorted in the γ-FeOOH particles formed from the Fe–Si alloy. This distortion was considered to be caused by the incorporation of silicate species into these particles. Transmission electron microscopy and Fourier-transform infrared (FT-IR) spectroscopy were employed for observing the morphology of the particles and for characterizing their bonding structure, respectively. Further, the amount of γ-FeOOH particles formed was measured in order to investigate their formation processes. The changes in the pH and oxidation-reduction potential (ORP) of the solutions were monitored during the formation of γ-FeOOH particles. Inductively coupled plasma analyses were also performed for determining the amounts of iron and silicon in supernatant solutions. The results indicated that the formation process of γ-FeOOH particles in the solutions was influenced by the addition of silicon to iron.