Thermal And Chemical Stability Of Baseline And Improved Crystalline Silicotitanate

Abstract

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. vii ABSTRACTThe Savannah River Site (SRS) has been evaluating technologies for removing radioactive cesium ("'Cs) from the supemate solutions stored in the high-level waste tanks at the site. Crystalline silicotitanate (CST) sorbent (IONSIV IE-9118, UOP LLC, Des Plaines, IL), which is very effective at removing cesium from high-salt solutions, was one of three technologies that were tested. Because of the extremely high inventory of 137Cs expected for the large columns of CST that would be used for treating the SRS supemate, any loss of flow or cooling to the columns could result in high temperatures from radiolytic heating. Also, even under normal operating conditions, the CST would be exposed to the supernates for up to a year before being removed. Small-scale batch and column tests conducted last year using samples of production batches of CST showed potential problems with CST clumping and loss of cesium capacity after extended contact with the simulant solutions. Similar tests-using samples of a baseline and improved granular CST and the CST powder used to make both granular samples-were performed this year to compare the performance of the improved CST. PThe column tests, which used recirculating supemate simulant, showed that the baseline CST generated more precipitates of sodium aluminosilicate than the improved CST. The precipitates were particularly evident in the tubing that carried the simulant solution to and fi-om the column, but the baseline CST also showed higher concentrations of aluminum on the CST than were observed for the improved CST. Recirculating the simulant through just a section of the tubing (no contact with CST) also produced small amounts of precipitate, similar to the amounts seen for the improved CST column. The sodium aluminosilicate formed bridges between the CST granules, causing clumps of CST to form in the column. Clumps were visible in the baseline CST column after 1 month of operation and in the improved CST column after 2 months, For the baseline CST column, the clumps were routinely dispersed by backwashing the column with simulant. After 96 days of operation, a thin hard layer of CST formed on the bottom screen of the baseline column that restricted flow through the column. The bottom cap was removed and the CST was scraped from the screen to restore the...

Cesium Removal from Tank Waste Simulants Using Crystalline Silicotitanate at 12% and 100% TSCR Bed Heights

“…The colloidal solids were most likely a sodium phosphate phase (see Appendix E) and the plugging phase was most likely a combination of alumino-silicate phase (cancrinite) and sodium phosphate phase. Cancrinite formation in the CST bed had been previously observed with a 5.6 M Na simulant solution (Taylor and Mattus 2001).…”

Heat Transfer Analysis for Fixed CST and Rf Columns

“…3. Thermal and material properties for the packed materials and the column wall were obtained from the literature [4][5][6][7]10,11].…”

“…The model was created boundary for the present analysis of the 28-in OD column with a 6-in sch. 40 pipe imbedded at its center (annular packed bed dimensions: 27.375" OD, 6.625" ID).…”

“…If engineering designs cannot handle this thermal load, hot spots may develop locally which could degrade the performance of the ion-exchange media. Performance degradation with regard to cesium removal has been observed between 50 and 80 o C for CST [5,6] and at 65 o C for RF resin [7]. In addition, the waste supernate solution will boil around 130 o C. If the columns boiled dry, the sorbent material could plug the column and lead to replacement of the entire column module.…”

Desorption of Sorbates From Mst, Mmst, and CST Under Various Conditions

“…Previous work examined the Cs capacity of CST after storing at elevated temperature (80 °C) in SRS average supernate simulant (without Cs). 6 Samples of CST that had been stored in the simulant at 80 °C for six months showed a decrease in Cs capacity of approximately 15% compared to samples of CST that had been stored in the simulant at 23 °C for the same length of time. All loading tests to determine the Cs capacity were performed at 23 °C.…”