Characterization of Reaction of Green Rust with Foreign Ions using X-ray Absorption Fine Structure

Abstract

Measurements of X-ray absorption fine structure (XAFS), that is X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), were performed for characterizing the reactions of hydrosulphate green rust (GR) with copper or nickel sulphate ions. Fe K edge XANES spectra showed that a part of Fe(II) in GR2 was oxidized by the addition of copper sulphate ions, while Fe(II) in GR was not oxidized by the addition of nickel sulphate ions. Cu K edge and Ni K edge XANES spectra showed that copper sulphate ions were reduced to zero charge copper in the GR suspension, whereas nickel sulphate ions were not reduced. Radial structural functions for iron obtained from Fe K edge EXAFS spectra indicated that the structure of GR consisted of corner sharing of structural units formed by FeO6 octahedra. Radial structural functions for copper and nickel also indicated that copper sulphate ions were transformed to metallic copper with the face-centered cubic structure in the GR suspension, whereas the local structure of nickel sulphate ions were unchanged. XANES and EXAFS data of GR oxidized by a H2O2 solution were also investigated for comparison.