AbstractThe radioactivity of the Hanford site waste tanks is primarily from 137Cs and 90Sr, of which can both be selectively removed from solution using a crystalline silicotitanate (CST) ion exchanger. We are currently seeking waste forms alternative to borosilicate glass for Cs-CSTs. In order to obtain a fundamental basis for the development of an alternative waste form, we are investigating synthesis and characterization of CST component phases, namely Cs-Si-Ti-O phases. Two novel Cs-Ti-Si-O phases (one porous, one condensed) have been hydrothermally synthesized, characterized and evaluated as waste form candidates based on chemical and thermal stability, leachability, and ion exchange capabilities.
ABSTRACTFundamental data are provided for the potential use of hydrous TiIV-si oxide (TS) and hydrous TiIV-Zr oxide (TZ) as the solidification media of radioactive Cs+ and Sr2+. The sorption capacity for Cs+ and Sr2+, at various conditions, and the structure and the composition of the exchangers in these ionic forms, at high temperature, were investigated, followed by measuring the leaching rate from the calcined exchangers into water at room temperature. TS uptakes more Cs+ and Sr2+ than TZ does. The leaching rate from calcined TS is much lower than that from calcined TZ, due to the formation of titanium silicates of Cs+ or Sr2+. Based on these results, TS is considered to be superior to TZ, in sorption capacity, and the fixation capability of Cs+ and Sr2+, on the exchanger matrix.
Anastasiia P. Topnikova, Elena L. Belokoneva, Anatoly S. Volkov
et al.
Abstract New silicate-germanates (K2.9Cs0.1)(Sc0.7In0.3)[(Si2.95Ge0.05)O9]·H2O and (K2.16Cs0.84)Bi[(Si0.5Ge0.5)3O9]·H2O have been synthesized in multi-component systems under mild hydrothermal conditions. The new compounds are classified as new representatives of close related K3ScSi3O9·H2O parent structure, sp. gr. Pmn21. Their structural and isomorphic peculiarities are compared with it as well as with earlier investigated K1.46Pb1.54Сa[(Ge0.23Si0.77)3O9](ОН)0.54·0.46Н2О. Together with other known compounds, silicate-germanates form the extensive family A3M[T3O9]·H2O, A = K, Cs, Ca, Pb; M = Ho, Sc, Lu, Tb, Er, Y, Bi, Pb, In; T = Si, Ge, with a mixed microporous framework combined of M-octahedra and T-tetrahedra. Large alkali metal or/and Ca, Pb cations fill broad framework channels with cross-section up to 7.3 Å. Because of wide isomorphic substitution in the channels, and in tetrahedra and octahedra, ion exchange properties in the family are expected. Due to polar symmetry, all the crystals possess second-order nonlinearity which was confirmed with positive SHG tests for four compositions. Powder SHG experiments demonstrated moderate second harmonic intensities of order of α-quartz standard signals.
A. L. M. Zanelatto, E. M. S. Ribeiro, R. d. J. Napolitano
We present triplet and singlet scattering lengths for X–Cs133 collisions (X=Li6,7, Na23, K39,40,41, and Rb85,87). We consider the short-range potential-energy curves based on high-quality ab initio calculations and the long-range potential described by accurate dispersion coefficients available in the literature. Using a Fermi function to smoothly connect the short- and long-range terms we construct the potential for all R and evaluate the scattering length for each mixed species X–Cs. In particular, we predict that the cross section for inelastic processes between Na23 and Cs133 and between K40 and Cs133 will be small as compared with the respective elastic cross sections.