Recycling of High Ferrous Bauxite Reducing Slag for Synthesis of CaAl2Si2O8-Al2O3-CaAl12O19 Composite

CaAl2Si2O8-Al2O3-CaAl12O19 (CAS2-A12O3-CA6) composite was synthesized through reaction sintering alumina and bauxite reducing slag. The CAS2-Al2O3-CA6 composite was mainly composed of α-Al2O3, CAS2, and CA6. Gehlenite (Ca2Al2SiO7, C2AS) phase was effectively transformed to CAS2 and CA6 through high-temperature reaction sintering under weak oxidizing atmosphere at 1400 °C for 4 h. SEM (scanning electron microscopy) and EDS (energy dispersive spectroscopy) analysis indicated that black and needle-shaped A12O3, rhombic or irregular polygonal-shaped FeAl2O4, and glassy phase Ca2Al2SiO7 disappeared after the reaction sintering. The light gray and flaky hexagon crystals of CaAl12O19 (10 µm) and the grainy particles of A12O3 (2 – 7 µm) were observed in the CAS2-A12O3-CA6 composite. The gray crystals of CAS2 act as the binding phase and are distributed around CA6 and A12O3. CAS2-A12O3-CA6 composite exhibits high refractoriness and service temperature, which are 1650 °C and 1450 °C, respectively. Reaction sintering of alumina and bauxite reducing slag is a feasible method for the synthesis of CAS2-A12O3-CA6 composite.