Hydrothermal Dissolution of Reactive Silica Materials in Sodium Hydroxide Lyes

Reactive silica materials like vitreous silica or cristobalite were dissolved at temperatures between 100 and 220 °C for up to 7 days in NaOH lyes. The liquid and solid reaction products were analyzed chemically. Sodium water glasses with silica concentrations of up to 27 wt % and molar SiO₂/Na₂O ratios of up to 3.7 were obtained. The experimental data were evaluated by an approximation algorithm. The initial size reduction rates ranged between 0.1 and 7 µm h⁻¹, depending on the temperature and the choice of starting materials. Correlations between thermodynamics and kinetics were discussed.