Titanosilicates: Giant exchange capacity and selectivity for Sr and Ba

Two different microporous Na-titanosilicates with high cation exchange capacities were synthesized and characterized by X-ray diffraction, scanning electron microscopy (SEM) and solid-state ²⁹Si and ²⁷Al magic-angle spinning nuclear magnetic resonance (MASNMR) spectroscopy. The ion exchange properties of Na-ETS-4 (ETS = Engelhard TitanoSilicate) and Na-titanosilicate were investigated for Sr ²⁺ and Ba ²⁺ using isotherms and Kielland plots in order to check the potential for the decontamination of ⁹⁰Sr and ¹³³Ba from nuclear waste solutions. Na-ETS-4 and Na-titanosilicate show high affinity for Sr ²⁺ to high equivalent fraction of Sr ²⁺ on solid phase. In case of Ba ²⁺ the selectivity coefficient of both titanosilicate exchangers rapidly decreased due to the steric hindrance at exchange sites at X _Ba > ∼0.5. However, Na-ETS-4 was still selective for Ba ²⁺ even after the above rapid decrease in selectivity, unlike Na-titanosilicate. Therefore, Na-ETS-4 is one of the best candidates for the removal of both Sr ²⁺ and Ba ²⁺ from nuclear waste solutions.