Hydrothermal Dissolution of Low‐Quartz in Sodium Hydroxide Lyes: Kinetics and Equilibrium

Abstract

Quartz flours were dissolved at temperatures between 100 and 220 °C for up to 7 d in NaOH lyes. The starting materials were characterized by particle size analysis. Liquid and solid reaction products were characterized chemically and structurally. Sodium water glasses with silica concentrations of up to 20 wt % were obtained. Radius reduction of size distributed particle ensembles was calculated to evaluate the concentration control of the dissolution rate which is due to saturation effects. An equilibrium between low‐quartz and the resulting water glass explains the obtained results.

Hydrothermal Dissolution of Technical Grade Vitreous Silica in NaOH Solutions to Liquid Water Glasses with Higher SiO2:Na2O Ratios

“…SiO 2 content of liquid water glass produced by hydrothermal dissolution at 100 °C as a function of dissolution time t . ○ batch A; □ batch B; Δ batch C; ♦ batch D; — fit to batch A according to numerical simulation in 4; results for batches C and D are nearly identical.…”

“…The analytical results obtained at 100 and 130 °C (Tab. S2) were evaluated with an iterative calculation procedure described in 4: Starting with the particle size distribution of QN‐D50 (Tab. S1) the radius of the particles, which were assumed to be spherical, were reduced with an initial dissolution rate q diss,1 .…”

“…Final SiO 2 contents as function of dissolution temperature T ; □ c ∞, NW calculated according to 4 for QP‐DN50 (batch C); ○ c max for QP‐DN50 (batch C); • literature data reported by Rowe et al 27; ▴ c ∞, NW reported in 4 for low quartz; ▵ c ∞, c (Tab. S5, at 160 and 220 °C identical with ▴).…”

“…The solubility of silica in general was already treated in 5 and the solubility of low quartz in 4. In the present report, the literature concerning and dissolution kinetics of vitreous silica is evaluated.…”

“…Reports on the application of raw materials with a higher reactivity – like cristobalite or vitreous silica – in order to reach higher R m values are published in the patent literature (e.g., 3). Studies on dissolution of opal and low quartz materials to synthesize liquid sodium water glass were presented in 4, 5.…”