Phase Transformation of Hercynite During the Oxidative Roasting Process

Abstract

Converting the aluminum in hercynite into a readily soluble state in alkali solution is significant for extracting alumina from hercynite. Thermodynamic analysis shows that the aluminum in hercynite is insoluble in alkali solution and that it can be chemically separated from iron through oxidative roasting. X-ray diffraction combined with x-ray photoelectron spectroscopy analysis indicates that, during oxidative roasting, hercynite first decomposes into γ-Al2O3 and Fe3O4 with lattice distortion. With increasing temperature, the former subsequently converts into α-Al2O3 while the latter into γ-Fe2O3 followed by α-Fe2O3. Hercynite can be completely converted into alumina and iron oxides through treatment at > 1173 K for 20 min. Alumina in the oxidized hercynite obtained at 1173 K to 1373 K can be efficiently digested by the Bayer digestion at 513 K and 533 K, with an alumina digestion ratio of ~ 96% and ~ 98%, respectively. This work lays the foundation for alumina extraction from hercynite.