Hydrothermal conversion of Ti-containing minerals in system of Na2O-Al2O3-SiO2-CaO-TiO2-H2O

Titanium has a great effect on the digestion of bauxite in the Bayer process because it reacts readily at high temperatures in alkaline sodium aluminate solution. Under this consideration, the hydrothermal conversion of Ti-containing minerals in the system of Na2O-Al2O3-SiO2-CaO-TiO2-H2O with increased temperatures was studied based on the thermodynamic analysis and systematic experiments. The results show that anatase converts to Al4Ti2SiO12 at low temperatures (60-120 A degrees C), which is similar to anatase in crystal structure. As the temperature continues to rise, Al4Ti2SiO12 decomposes gradually and converts to Ca3TiSi2(Al2Si0.5Ti0.5)O-14 at 200 A degrees C. When the temperature reaches 260 A degrees C, CaTiO3 forms as the most stable titanate species for its hexagonal closest packing with O2- and Ca2+. The findings enhance the understanding of titanate scaling in the Bayer process and clarify the mechanism of how additive lime improves the digestion of diaspore.