Titanium silicates, M3HTi4O4(SiO4)(3)center dot 4H(2)O (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 [Fe-4(OH)(4) (AsO4)(3)](-).5H(2)O. 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 mi g(-1) for a solution containing 5 M NaNO3/1 M NaOH. (C) 1997 Elsevier Science B.V.