Thermal and Chemical Stability of Crystalline Silicotitanate Sorbent

Abstract

The Savannah River Site (SRS) is evaluating technologies for removing cesium-137 (137Cs)horn the supemate solutions stored in the high-level waste tanks at the site. Crystalline .&licotitanate sorbent (IONSIV IE-9 11', UOP Molecular SievesYMt. Laurel, NJ) is very effective for removing cesium from high-salt solution, such as the SRS supemates, and is currently being used at Oak Ridge National Laboratory to remove radioactive cesium from similar solutions. Because of the extremely high loading of 137CS that would be expected for the large columns of crystalline silicotitanate (C ST) that would be used for treating the SRS supemate, any loss of flow or cooling to the columns could result in high temperatures within the column from radiolytic heating. The ability of CST to retain previously loaded cesium while in contact with SRS tank supernates at various temperatures was determined by performing bench scale simulant tests using CST samples that were loaded with stable cesium and radioactive cesium tracer. These results were compared with those obtained fi-om loading tests at the same temperatures.. .

Influence of Water Addition on Crystalline Silicotitanate Column Operation

“…1 Several studies examined the cesium removal efficiencies, along with chemical and thermal stability of the CST. 2,3 During previous testing of the CST sorbent, several events of column plugging occurred. 4 Most plugging events related to precipitates containing niobium 5 or solids resulting from silicon leaching.…”

“…6 An inadvertent addition of water to a fully loaded CST ion exchange column may have detrimental impact to the facility operations. The most likely plugging scenario would result from precipitation of aluminum hydroxide Al(OH) 3 caused by a rapid pH change. Previous studies provide evidence of aluminum hydroxide precipitation including the work by Steele, et al, 7 and Walker.…”

Pilot-Scale Test of Counter-Current Ion Exchange (CCIX) Using UOP IONSIV IE-911

“…Previous experiments showed that aluminosilicate precipitates rather quickly from SRS-average simulant in the presence of IE-911 (Taylor and Mattus 2001). Therefore, a three-week test was planned to pass SRS-average simulant through a pilot-scale CCIX ® column packed with IE-911.…”

Structural Stability Study of Crystalline Silicotitanate Dispersed in Caustic Solutions for Extended Periods

“…1 ORNL completed several extensive studies of CST clumping in the early 2000s and showed evidence of agglomeration of CST beads when stored in various simulant solutions for prolonged periods and especially at elevated temperatures. 2,3 In the first set of experiments CST beads, which had been pretreated by recirculating dilute NaOH for 24 hours to reach a pH of ~13, were exposed to four different simulant solutions: SRS Average simulant, a high hydroxide version of the simulant, a high nitrate version of the simulant, and finally a simple salt solution containing only sodium hydroxide and sodium nitrate with a total sodium concentration of 5.6 M (the same as the other more complex simulants). 2 Samples of engineered CST were contacted with these various solutions at temperatures of 23 °C, 30 °C, 35 °C, 50 °C, and 80 °C.…”