Transformation of green rust (Cl ^-) into different oxyhydroxides in aqueous solution containing molybdenum ions

To investigate the influence of the addition of molybdenum ions on the transformation of green rust GR(Cl ^-) comprising Fe(II) and Fe(III) into different oxyhydroxides, suspensions of GR(Cl ^-) containing molybdenum ions were oxidized by passing nitrogen gas containing oxygen through the suspensions. X-ray diffraction (XRD) was used for identifying the solid particles formed by oxidation. The results showed that in the presence of molybdenum ions, the formation of β-FeOOH and α-FeOOH was enhanced as compared to that of γ-FeOOH in the GR(Cl ^-) suspensions. This implied that the molybdenum ions interacted with the chloride ions obtained from GR(Cl ^-) and induced the formation of β-FeOOH that contained chloride ions. Transmission electron micrographs of the solid particles showed that the particle size of the resulting oxyhydroxides was considerably reduced because of the addition of the molybdenum ions. The pH and oxidation-reduction potential (ORP) of the aqueous solution were also measured during the oxidation. The addition of molybdenum ions was found to cause characteristic changes in the pH and ORP in the initial stage of the oxidation.