Titanium silicates, M3HTi4O4(SiO4)3·4H2O (M=Na+, K+),with three-dimensional tunnel structures for the selective removal of strontium and cesium from wastewater solutions

The ion exchange behavior of a sodium and a potassium titanosilicate towards Cs⁺ and Sr²⁺ was studied. The materials of interest in this study are titanium and silicon structural analogs of the mineral pharmacosiderite. Pharmacosiderite is a non-aluminosilicate molecular sieve with the framework composition [Fe₄(OH)₄ (AsO₄)₃]⁻.5H₂O. For the titanosilicate analogs, the framework arrangement of silicate tetrahedra and titanium octahedra create three-dimensional structures with water molecules and charge-neutralizing cations located in the face-centers. Distribution coefficient (K_d) measurements showed that the potassium titanosilicate removed at least 97% of the Sr²⁺ from a groundwater simulant that also contained ppm levels of Ca²⁺, Mg²⁺, K⁺, Cs⁺ and Na⁺. Similarly, the sodium phase removed about 98% Cs⁺ from the groundwater solution. These preliminary K_d values provide an indication that these exchangers may act as potential Cs⁺ and Sr²⁺ sorbers for groundwater remediation applications. The sodium and potassium phases were also tested as potential exchangers for Cs⁺ and Sr²⁺ in different nuclear waste simulants. While the sodium phase showed little to no preference for Cs⁺ in highly acidic or basic solutions containing large concentrations of NaNO₃, the potassium phase yielded a Sr²⁺ K_d of around 7100 ml g⁻¹ in 2.5 M NaNO₃/l M NaOH solutions, and a K_d of 3500 ml g⁻¹ for a solution containing 5 M NaNO₃/l M NaOH.