Oxidation of tungstate-containing green rust (Cl-) in aqueous solution

The influence of tungstate on the oxidation of green rust [GR(Cl)], which contains both Fe(II) and Fe(III), was investigated by synthesizing suspensions of GR(Cl) containing tungstate and oxidizing them via injection of N2 gas containing O2. XRD and TEM analyses were used for characterizing the solid particles formed during synthesis and oxidation. The results showed that the formation of fine a-FeOOH was enhanced by the addition of tungstate to the GR(Cl) suspensions, while GR(Cl) without tungstate was transformed primarily into ?-FeOOH. The pH, oxidation-reduction potential (ORP), and dissolved oxygen (DO) values of the aqueous solution were measured during oxidation of GR(Cl) with and without tungstate. The results showed that whereas the pH value of the solution was decreased and the ORP value was increased monotonically by oxidation of GR(Cl), the pH and ORP values during oxidation the GR(Cl) suspension containing tungstate revealed characteristic changes with time. XAS was also used for characterizing the chemical state and local structure of tungstate in the oxidized particles. The results indicated that the local structure of WO?42 was essentially retained in the particles precipitated from GR(Cl) suspensions.