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 degrees 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 mu m h-1, depending on the temperature and the choice of starting materials. Correlations between thermodynamics and kinetics were discussed. Reactive silica materials like vitreous silica or cristobalite in NaOH lyes approach transient concentration limits when dissolved under hydrothermal conditions. The resulting sodium water glasses comply with the targeted composition, especially at temperatures <= 160 degrees C. image