Toni TRATNJEK (LNER) will defend his Ph.D. dissertation titled "Development of silicotitanates with hierarchical porosity for Strontium capture" on Friday, December 9, 2022 at 9.00 a.m. (ICSM Auditorium).
Strontium (90Sr) is present in the nuclear fuel cycle, particularly following the uranium and plutonium recycling stages after which large volumes of aqueous solutions are generated. 90Sr requires special attention due to its high specific activity (4.59 x 1014 Bq/mol) and its half-life (T1/2 = 28.8 years). The main objective of this work is to develop materials for Sr adsorption in a column process with the sitinakite phase (Na2Ti2O3SiO4.2H2O). This phase was selected because its structure is composed of microporous tunnels in which the alkaline earth cation Sr2+ sorbs selectively in the aqueous medium. For this purpose, sitinakite powders obtained by hydrothermal synthesis using liquid precursors were characterized to obtain reference materials. Next, sitinakite powders were fabricated using solid precursors in order to prove the feasibility of transforming pre-formed objects into objects with the sitinakite phase. Finally, granules and monoliths with the sitinakite phase were synthesized based on the accumulated knowledge of the previous systems. Thus, sitinakite powders, granules and monoliths with increasing crystallite sizes and tunnel sizes were obtained. The ion exchange properties towards Sr2+ and the most problematic competitor cation (Ca2+) were evaluated for the different materials. Sorption kinetics curves of the selected materials were performed with and without the presence of the Ca2+ cation to determine the contact times required to reach thermodynamic equilibrium, depending on the properties of the materials. The sorption isotherms of Sr2+ with and without the presence of Ca2+ were also plotted to determine the maximum sorption capacities of Sr2+ in a simplified aqueous medium, free of Ca2+, and in an aqueous medium with strong ionic competition.
Keywords: Decontamination; Strontium; Silicotitanates; Sitinakite; Monoliths; Porous