TITANIUM SILICATES, M3HTI4O4(SIO4)(3)CENTER-DOT-4H(2)O (M = NA-DIMENSIONAL TUNNEL STRUCTURES FOR THE SELECTIVE REMOVAL OF STRONTIUM AND CESIUM FROM WASTE-WATER SOLUTIONS(, K+), WITH 3)

The ion exchange behavior of a sodium and a potassium titanosilicate t owards Cs+ and Sr2+ was studied. The materials of interest in this stu dy are titanium and silicon structural analogs of the mineral pharmaco siderite. Pharmacosiderite is a non-aluminosilicate molecular sieve wi th the framework composition [Fe-4(OH)(4) (AsO4)(3)](-).5H(2)O. For th e titanosilicate analogs, the framework arrangement of silicate tetrah edra and titanium octahedra create three-dimensional structures with w ater molecules and charge-neutralizing cations located in the face-cen ters. Distribution coefficient (K-d) measurements showed that the pota ssium titanosilicate removed at least 97% of the Sr2+ from a groundwat er simulant that also contained ppm levels of Ca2+, Mg2+, K+, Cs+ and Na+. Similarly, the sodium phase removed about 98% Cs+ from the ground water solution. These preliminary K-d values provide an indication tha t these exchangers may act as potential Cs+ and Sr2+ sorbers for groun dwater remediation applications, The sodium and potassium phases were also tested as potential exchangers for Cs+ and Sr2+ in different nucl ear waste simulants. While the sodium phase showed little to no prefer ence for Cs+ in highly acidic or basic solutions containing large conc entrations 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.