Crystallization of δ-Na2Si2O5-rich layered silicates from sodium silicate solutions: seeding and temperature programmed δ-phase embryo creation

The effect of seed composition on the crystalline layered sodium disilicate phase development using a sodium silicate solution (SiO2/Na2O molar ratio=2.1) has been investigated. To obtain δ phase-rich products, it is necessary that the α phase content in the seed be as low as possible. High temperatures (700 °C) and absence of any α phase in the initial seed substantially promote the amorphous phase→δ phase transformation reaction even if the seed contains up to 15.0 wt.% β phase. It has been shown that pretreatment in the temperature range 150–200 °C promotes significantly δ phase nucleation. Low temperature nucleation has been observed for the sodium silicate solution modulus in the range of 1.5–2.1. This finding might be implemented to solve reproducibility problems in the industrial scale production of layered disilicates from water glass. To obtain a minimum calcium binding capacity of 120.0 mg CaO/g , an α phase content of up to 20.0 wt.% is tolerable.