Phase Transformation and Process Optimization for High-Temperature Calcification Dissolution of Gibbsitic Bauxite

Abstract

As the main method of alumina production in the world, Bayer process emits a large amount of high alkaline red mud, which poses a very serious threat to the ecological environment. In this study, the high-temperature calcification transformation method based on source blocking was used to treat the Guinea gibbsite from the perspective of mineral phase reconstruction. A new type of structural red mud with almost no alkali was obtained while achieving efficient dissolution of alumina at high temperature. Single-factor tests (180–280°C, C/S = 1.25–2.5, 60 min, 240 g L^–1 Na₂O) showed that temperature and CaO/SiO₂ ratio jointly control extraction yield and Na₂O content of the residue. Characterization revealed that rising temperature converts boehmite to well-crystallized hydrogarnet while suppressing sodium aluminosilicate. Al₂O₃ dissolution increases from ~76% at 180°C to ~88% at 260–280°C; excess CaO drops yield. Na₂O in slag falls continuously with higher C/S, reaching 0.41 wt % at 280°C and C/S = 2.5. The optimum compromise among yield, energy and equipment pressure is 240°C, C/S = 2.0, 60 min, giving 85% Al₂O₃ extraction and <0.8 wt % Na₂O in residue.