Enhancing Silicate Dissolution Kinetics in Hyperalkaline Environments

The dissolution of silicate minerals and glasses in aqueous solutions is important in many natural and engineered contexts including mineral weathering, nuclear waste stabilization, cementation, and infrastructure degradation. The influences of electrolytes on dissolution rates have been extensively studied, but previous studies have used widely varying minerals and electrolytes, experimental conditions, and measurement techniques. Comparatively fewer studies have been conducted in hyperalkaline solutions that are encountered in concrete, geopolymers, and nuclear stabilization systems. This study seeks to control many of these variables to isolate the effects of electrolyte composition on altering the degree of dissolution of a soda lime silicate glass in hyperalkaline electrolyte solutions. A glass powder is dissolved in one of a series of static solutions having 10 mmol L–1 NaOH (pH 12) at (25 ± 0.2) °C and either an organic or an inorganic electrolyte at a concentration of 1 or 10 mmol L–1. The solution series was designed to reveal qualitatively how ion identity and concentration alter the glass’ degree of dissolution after prescribed exposure times. The results indicate that a relative dissolution enhancement of no greater than about 2.4 times can be induced at pH 12, with the greatest enhancements being observed for Na-benzoate, Na-citrate, and Na-malonate. The degree of dissolution is unaffected by most of the other salts examined. Broadly, the nucleophilic attack by OH– on Si–O bonds and the formation of O––Na+ surface complexes appear to be the most important factors influencing the dissolution rate at high pH. The adsorption and the influence on dissolution of other electrolyte ions are comparatively weak.