Thermochemistry and kinetics of silica dissolution in NaOH solutions: Effect of the alkali concentration

• Silica was dissolved in 8 and 11 wt% NaOH solutions at 80–130 °C.
• Dissolution was followed thermochemically by a C80 Setaram calorimeter.
• The dissolution was modelized by a two successive first-order reactions.
• Isoconversional model suggests a variation of Ea over the conversion fraction.

The silica (α-cristobalite) dissolution in 8 and 11 wt% of sodium hydroxide solutions (2.17 or 3.08 mol L−1, respectively) was followed by microcalorimetry at temperature ranging between 80 and 130 °C. The global enthalpies of the process are equal to −15.13 and −17.51 kJ mol−1, respectively. A kinetic scheme based on two successive first-order reactions has been proposed, and thermochemical and kinetic parameters were iteratively deduced. The former are generally in accordance with the experimental values. The isoconversional model showed that the activation energy of silica dissolution varies with the conversion degree and ranges in the interval 72–97 kJ mol−1. It reaches a maximum corresponding to a minimum dissolution speed, which moves toward lower conversion fraction values when the concentration of NaOH solution increases.