Hydrothermal formation and conversion of calcium titanate species in the system Na2O–Al2O3–CaO–TiO2–H2O

The hydrothermal formation and conversion of titanate species in the system Na2O–Al2O3–CaO–TiO2–H2O was investigated based on the thermodynamic calculation and systematic experiments. Experimental results show that the reaction product of anatase with aluminate solution is sodium tri-titanate (Na2O·3TiO2), and that kassite (CaO·2TiO2·H2O) is formed by the reaction of sodium tri-titanate with calcium hydroxide (Ca(OH)2) and sodium aluminate solution with high free caustic concentration at elevated temperatures. The results also show that there are two reaction paths for the formation of perovskite (CaTiO3), one is the direct reaction of sodium tri-titanate with calcium hydroxide, and the other is the conversion of kassite with calcium hydroxide and sodium aluminate solution at elevated temperatures. In addition, the aluminum species in the sodium aluminate solution play a very important role in the process of kassite formation and its conversion to perovskite. The findings provide a potential method for the efficient preparation of titanate species and enhance the understanding of the scaling of heat exchanger surfaces in the Bayer process alumina refinery which is a result of titanate formation.