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 (K _a) and ion free enthalpy (ΔG ⁰) 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.