Comparative study of the solubility of the crystalline layered silicates α-Na2Si2O5 and δ-Na2Si2O5 and the amorphous silicate Na2Si2O5

The solubility of a crystalline layered silicate, delta-Na2Si2O5, has been evaluated and compared with that of a crystalline alpha phase (alpha-Na2Si2O5) and an amorphous silicate of the same composition. Experiments were carried out at 293, 313, and 333 K. It was found that on raising the temperature from 293 to 333 K, a large increase in solubility occurred for all silicates studied, whereas increasing the time from 30 to 180 min had a less marked effect. Interactions between the silicates and deionized and tap water are discussed. The solubility in tap water was determined taking into account the alkaline earth metal (Ca2+ and Mg2+) binding capacity of the solid phases. A model aimed at understanding the reaction of delta-Na2Si2O5 in deionized water has been proposed on the basis of species identified in solution (Na+, Si4+). A good reproduction was achieved between the amount of NaOH predicted by the model and the pH measured in situ at each temperature studied.