Characterization of Formation and Oxidation of Green Rust (Cl−) Suspension

Abstract

Green rust (GR) containing both ferrous (Fe(II)) and ferric (Fe(III)) ions is formed in an aqueous solution with a relatively low electrochemical potential. In this study, in order to understand the formation and oxidation of GR, a suspension of GR containing chloride ions (GR(Cl−)) was synthesized and subsequently oxidized by injecting nitrogen gas containing oxygen under different conditions. X-ray diffraction (XRD) measurements were performed for identifying the solid particles formed under different conditions. The results show that the GR(Cl−) suspension was formed from specific concentrations of hydroxyl, ferrous, and ferric ions. The pH values and oxidation-reduction potential (ORP) of the aqueous solution were measured during oxidation of the GR(Cl−) suspension. It was observed that because of oxygen injection, GR(Cl−) was transformed into iron oxides such as α-FeOOH, γ-FeOOH, and Fe3O4. These iron oxide and oxyhydroxide species formed by oxidation were dependent on the oxidation conditions such as temperature. This suggested that conditions of aqueous solution are crucial for the transformation of GR(Cl−) into different iron oxides and oxyhydroxides.