Clumping behavior and cesium loading results for crystalline silicotitanate and zeolite in SRS dissolved salt simulants

A small-column treatment system, using either crystalline silicotitanate (CST) or IE-96 zeolite sorbent, is being evaluated for treating low-activity dissolved salt cake from the high-level waste tanks at the Savannah River Site (SRS). Previous work at Oak Ridge National Laboratory (ORNL) has shown that CST could form clumps after long-term storage in the high-hydroxide, high-aluminum supernate from the SRS waste tanks. The proposed small-column treatment system would have processing times of less than 2 weeks between column change-outs. Column and batch tests were conducted for over 1 month to examine potential clumping problems in four dissolved saltcake simulants (early, middle, late and average) that bounded the expected compositions of the actual waste streams. Cesium loading tests were also conducted in the bounding waste compositions to verify model predictions for column design. No clumping was detected during the first 2 weeks. After 3 weeks, both CST and zeolite showed very weak clumps in average simulant at 35°C. After 4 weeks, the zeolite in middie simulant at 35°C also showed very weak clumps. After 7 weeks, zeolite showed weak clumps in early, middle, and average simulants and CST showed weak clumps in average simulant at 35°C. No clumps were detected in the other simulants at 35°C or in any of the simulants at 23°C. The clumps that were formed were very weak and would not be expected to interfere with sluicing the sorbent from a column. Column tests using CST and two simulant compositions showed a small clump in the bottom of one column after 38 days. The cesium loading tests using CST matched the ZAM ¹ model predictions for all of the simulant compositions tested. Zeolite had much lower cesium capacity in these simulants. Some of the zeolite particles broke apart in the early simulant, which had the highest concentration of sodium hydroxide.