Atomic-scale structure of ferric oxyhydroxide formed from Fe-Si alloy in aqueous solutions containing different salts

摘要

Quantitative X-ray structural analysis coupled with reverse Monte Carlo (RMC) simulation was performed for characterizing the atomic-scale structure of y-FeOOH (lepidocrocite) particles. These particles were formed by dipping pure iron or Fe-2mass percent Si alloy into aqueous solutions containing Na_2SO_4 or NaCl. The realistic atomic-scale structures of gamma-FeOOH particles were estimated by fitting ordinary interference functions through the RMC simulation technique. The results revealed that the fundamental FeO_6 octahedral structural units and their linkages were distorted in the gamma-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 gamma-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 gamma-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 gamma-FeOOH particles in the solutions was influenced by the addition of silicon to iron.