Dissolution kinetics of silica between 5 and 35 °C. Application of a titrimetric method

Abstract

The dissolution kinetics of a sample of commercial Fontainebleau sand consisting of >99.6% silica are studied at 25 °C and an ionic strength of 0.01 mol dm^–3 in the pH range 2.9–10.9. The sample was not pretreated with concentrated sodium hydroxide to expose the quartz substrate and so the results apply to the dissolution of the surface layer of amorphous silica or vitreous silica. The results at 25 °C obtained by two methods are compared and the calculated rate constants for the dissolution reaction are interpreted using a surface-speciation model previously described for quartz dissolution.

A titrimetric method for measuring the rate of silica dissolution over a temperature range of 5–35 °C at constant pH = 10 is compared with direct measurement of the change in silica concentration in solution. The results lead to Arrhenius activation energies of 83.2 and 80.6 kJ mol^–1, respectively, and an estimate of the first dissociation constant of silicic acid, K₁, between 15 and 35 °C of pK₁=–3.543 + 3885/T.