In situ measurements of X-ray absorption spectra at an Fe K absorption edge were carried out during the transformation of chloride-containing green rust (GR(Cl -)) to oxyhydroxide (that is, lepidocrocite (γ -FeOOH)), by oxidation via aqueous solution. Results showed that the Fe K absorption edge in X-ray absorption near-edge structure (XANES) spectrum shifted toward the higher energy side with increasing oxidation time. The factor analysis of the XANES spectra, using reference data, implied

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... dissolution of GR(Cl -) and precipitation of γ -FeOOH occur simultaneously. The fraction of γ -FeOOH in the suspension increased continuously with increasing oxidation time, in response to the continuous decrease of the fraction of GR(Cl -). The results lead us to conclude that GR(Cl -) transforms to γ -FeOOH during oxidation under the present experimental conditions.