Impact of the Nature of Exchangeable Cations on LTA-Type Zeolite Hydration

Due to their high cation-exchange ability as well as to their molecular sieve properties, natural zeolites are widely used in industry. In this work, we used molecular simulation to comprehensively explore at the microscopic scale the hydration process in aluminum-rich (Si/Al ratio = 1) LTA-type zeolites with different compositions of charge balancing sodium and calcium cations. The results reveal the nature of the cation to be more influential than the density of the cations, which is detectable in both the adsorption isotherms, and the energetic and structural descriptions of system interactions. The higher affinity of water to calcium cations in relation to sodium cations leads to a more hydrophilic character of Ca-containing zeolites, and the water clustering proceeds differently during the adsorption process. However, the extra-framework cations negligibly influence on the hydrogen-bonded network of the adsorbed water at saturation, when a dense phase is formed, as well as on cation-water interactions.