Controllable preparation and synthetic mechanism of mullite from the bauxite with Fe-rich oxide content

To realize reuse of the bauxite with Fe-rich oxide content (w (Fe2O3)≥5.0%), ferric oxide in the bauxite must enter into some phases with high melting point such as mullite and aluminium titanium, avoiding its enrichment and transformation into phases with low melting point. In this paper, controllable preparation of mullite was attained using the bauxite with Fe-rich oxide content as raw materials, by adjusting its mass ratio of (Fe2O3+Al2O3)/SiO2 to about 2.57 based on the theoretical design of Fe2O3-Al2O3 binary diagram and Al2O3-SiO2-TiO2 ternary diagram. Phase and synthetic mechanism of mullite from the Fe-rich bauxite have been characterized and analyzed by XRD, SEM, EDS and TOPASS refinement software. The results show that Fe3+ and Ti4+ ions enter into aluminum titantate and mullite in the form of solid solution. Crystal phases of the bauxite with Fe-rich oxide content after sintering are composed of mullite solid solution, aluminum titantate solid solution and cristobalite. A very little of amorphous phase exists between mullite crystals, and aluminum titantate solid solution is distributed dispersively and surrounded by mullite solid solution.