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 Sr2+ and Ba2+ 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 Sr2+ to high equivalent fraction of Sr2+ on solid phase. In case of Ba2+ 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 Ba2+ 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 Sr2+ and Ba2+ from nuclear waste solutions.

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► Ion exchange properties of Na-titanosilicates were probed for removal of Sr and Ba.
► Na-ETS-4 and Na-titanosilicate showed high selectivity and capacity for Sr2+.
► Na-ETS-4 was selective for Ba2+ unlike Na-titanosilicate.
► Na-ETS-4 is excellent for selective uptake of both Sr and Ba from nuclear waste.