Conversion of ferric oxide to magnetite byhydrothermal reduction in Bayer digestion process
(1. School of Metallurgy and Environment, Central South University, Changsha 410083, China;
2. Zhongzhou Aluminum Corporation Limited of Aluminum Corporation of China (CHALCO), Jiaozuo 454000, China)
2. Zhongzhou Aluminum Corporation Limited of Aluminum Corporation of China (CHALCO), Jiaozuo 454000, China)
Abstract: Digesting aluminum-bearing minerals and converting ferric oxide to magnetite simultaneously in Bayer digestion process is crucially important to deal with high-iron diasporic bauxite economically for alumina production. The reaction behaviors of hydrothermal reduction of ferric oxide in alkali solution were studied by both thermodynamic calculation and experimental investigation. The thermodynamic calculation indicates that Fe3O4 can be formed by the conversion of Fe2O3 at proper redox potentials in alkaline solution. The experimental results show that the formation ratio of Fe3O4 either through the reaction of Fe and Fe2O3 or through the reaction of Fe and H2O in alkaline aqueous solution increases remarkably with raising the temperature and alkali concentration, suggesting that Fe(OH)3- and Fe(OH)4- form by dissolving Fe and Fe2O3, respectively, in alkaline aqueous solution and further react to form Fe3O4. Moreover, aluminate ions have little influence on the hydrothermal reduction of Fe2O3 in alkaline aqueous solution, and converting iron minerals to magnetite can be realized in the Bayer digestion process of diasporic bauxite.
Key words: Bayer process; digestion; hydrothermal reduction; ferric oxide; magnetite