Marcus Walter

Contrasting immobilization behavior of Cs+ and Sr2+ cations in a titanosilicate matrix

ETS-10 titanosilicate was tested as an adsorbent for the removal of Cs+ and Sr2+ cations from radioactive waters, considering both the ion exchange and the behaviour of the loaded adsorbent during thermal conditioning. The studies indicate that ETS-10 has a high and similar affinity for both Cs+ and Sr2+ cations reaching the ion exchange capacity of ETS-10 at a concentration of about 50 milliequivalents gram per liter. Thermal treatment of Cs+- and Sr2+-exchanged ETS-10 materials results in melting at approximately 700 °C. The melting temperature increases with the initial Cs+ and Sr2+ concentration and is higher for Sr2+ than for Cs+ exchanged ETS-10. Recrystallisation occurs only in the presence of Sr2+ as evidenced by the exothermic effects between 800 and 900 °C. After calcination of Cs+- and Sr2+-exchanged ETS-10 in air at 800 °C, two types of materials were obtained: an amorphous glass material with homogeneous Cs+ distribution and a strontium fresnoites glass–ceramic material.

Improvement of retention capacity of ETS-10 for uranyl ions by porosity modification and their immobilization into a titanosilicate matrix

The retention capacity of ETS-10 titanosilicate for uranyl ions was improved by generation of additional intra-crystalline porosity with formation of an extended silica-rich surface area. Chemical bonds between uranyl groups and [SiO4] tetrahedra were found. By calcination at 800 °C, the uranium-loaded ETS-10 transforms into a inert titanosilicate matrix that encapsulates uranium.