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A highly selective adsorbent for multivalent cationic species based on a sitinakite-type titanosilicate was prepared from a leucoxene ore enrichment waste. The synthesized material was used as for the selective removal of alkali-earth strontium (II) and barium (II) cations as well as for the cationic species based on the natural isotopes of uranium, radium, and thorium from aqueous solutions. The influence of such parameters as the pH, the initial concentration of the ions, the presence of other electrolytes on the sorption parameters was investigated. The sorption capacity of the synthesized material at ambient conditions is 80 and 110 mg/g for Sr 2+ and Ba 2+ , respectively, and it rises with increasing temperature. Furthermore, the material shows a high selectivity towards radionuclides of radium, uranium, and thorium. By using the current titanosilicate materials, the extracting degree of over 99% could be achieved when extracting these species from their respective standard aqueous solutions. The origin of the high adsorption selectivity for cationic complexes of thorium and uranium is rationalized based on periodic density functional theory calculations. The obtained results indicate that the described materials could be promising and inexpensive sorbents for the selective extraction of radioactive isotopes and particularly those of Sr, Ba and U, Th, Ra.

The microporous titanosilicate sitinakite, KNa2Ti4(SiO4)2O5(OH)·4H2O, was first discovered in the Khibiny alkaline massif. This material is also known as IONSIV IE-911 and is considered as one of the most effective sorbents for Cs+ and Sr2+ from water solutions. We investigate a mechanism of cooperative crystal chemical adaptation caused by the incorporation of La3+ ions into sitinakite structure by the combination of theoretical (geometrical–topological analysis, Voronoi migration map calculation, structural complexity calculation) and empirical methods (PXRD, SCXRD, Raman spectroscopy, scanning electron microscopy). The natural crystals of sitinakite (a = 7.8159(2), c = 12.0167(3) Å) were kept in a 1M solution of La(NO3)3 for 24 h. The ordering of La3+ cations in the channels of the ion-exchanged form La3+Ti4(SiO4)2O5(OH)·4H2O (a = 11.0339(10), b = 11.0598(8), c = 11.8430(7) Å), results in the symmetry breaking according to the group–subgroup relation P42/mcm → Cmmm.