This paper describes a novel process, hematite involved roasting − alkaline leaching − Bayer digestion, to extract silica and alumina from high-alumina coal gangue (HACG). The phase transformations during roasting were investigated through X-ray diffraction, X-ray photoelectron spectroscopy, scanning electronic microscope, and energy-dispersive spectrometer. The silica and alumina extraction were carried out through alkaline leaching. Results shown that, by reductively roasting with hematite, kaolinite converted into hercynite (FeAl₂O₄), and cristobalite solid solution (SiO₂), which dispersed as the form of fine grain dissemination. During cooling in oxidizing atmosphere, the cristobalite solid solution showed insignificant change. In contrast, the hercynite oxidized into α-Fe₂O₃ and α-Al₂O₃ through the conversion of intermediate products of Fe₃O₄, γ-Fe₂O₃, and γ-Al₂O₃. The migration of iron oxides to hercynite surface during cooling process prevented the formation of Al–Si compounds. > 96% of silica and > 97% of alumina were extracted by alkaline leaching at 110 °C and Bayer digestion at 260 °C, respectively. This work demonstrates a new process to treat and recover the high-value components in HACG and decrease the red mud output through recycling the hematite.

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