Investigation of SOMS and Their Related Perovskites

Abstract

We are evaluating new metal niobate and silicotitanate ion exchangers for Cs and Sr removal and their related condensed phases as potential ceramic waste forms. The goal of the program is to provide the U.S. Department of Energy (DOE) with alternative materials that can exceed the solvent extraction process for removing Cs and Sr from high-level wastes and with technical alternatives for disposal of silicotitanate and niobate based ion exchange materials. One class of the new phases, which are Na 2 Nb 2 -,M IV x6-x(OH) x .H 2 O (M IV = Ti, Zr, x = 0.04 ∼ 0.4, SOMS) and their thermally converted Sr loaded perovskites Na 2-x Sr x Nb 1.6 Ti 0.4 O 5.8+0,5x (0 ≤ x≤ 0.4), have been synthesized and characterized. SOMS exhibits very high Sr selectivity with Kd larger than 99,800 mL/g in the absence of competitive ions such as Na in solution, and about 10 3 mL/g when 0.1M Na presented in solution. This class of SOMS is easily converted to perovskites through low-temperature heat treatment (500 to 600 °C). The thermally converted perovskites exhibit extremely low Sr leach rates, ranging from 2.4 x 10 -7 to 1 x 10 -6 g/m 2 day for 5% to 20% Sr loading over a 7-day leaching period. Fractional Sr release FR% is 0.001% to 0.02% for 5% to 20%Sr loading over the 7-day leaching period. These results indicate SOMS could potentially be used for separating Sr from high-level waste and that their related perovskites could be used as potential ceramic waste forms.