Synthesis and ion exchange properties for Cs+ of ammonium-type mordenite

Cesium content in the seawater is 3.0 × 10−4mg·L-1, and ammonium-type mordenite was used to exchange cesium from cesium source. K-type mordenite was obtained by hydrothermal synthesis method. After ammonium-modified, ion exchange properties such as saturated ion exchange capacities and selectivity coefficients for alkali metal ions were determined. At the same time, ion exchange isothermal curves of ammonium-type mordenite for Cs+ and NH4+ were determined at 25 °C. Pitzer electrolyte solution theory was used to work out activity coefficients of the system, and the Kielland diagram of the ion exchange system was obtained. The calculated equilibrium constant (Ka) and ion free enthalpy (ΔG0) of mordenite for Cs+ and NH4+ are 1.455 and −930.3 J·mol−1, respectively, indicating that ion exchange process of ammonium-type mordenite for cesium is a spontaneous process.