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