Synthesis, characterization, and thermodynamic study of selected Na-based zeolites

Abstract

Zeolites are crystalline aluminosilicates with three-dimensional framework structures that can form in alkali-activated cements, Roman cements, and the interaction zone of cements and clays. However, their stability domains are uncertain due to their high structural variability and the lack of experimental solubility data. Thermodynamic data were here determined for selected Na-based zeolites built from six different secondary building units that could possibly form in the interaction zones of cement/clay. The zeolites were synthesized by hydrothermal methods and full-scale characterized with respect to framework structures, extra-framework cations, Si/Al ratios, and water contents. Their thermodynamic properties were determined based on the experimental solubility products at different temperatures using GEMS. Predominance diagrams of zeolite-clay/mica-SiO2/Al(OH)3 minerals in the chemical sub-systems of Na2O-SiO2-Al2O3-H2O were successfully established using PHREEQC-PhreePlot code. The experimentally derived thermodynamic data provide insights on the early stage of the zeolite ageing and predicting zeolite stability domains during cementitious material hydration.