Sodium and Potassium Anion Effects on Cesium-137 Removal by Crystalline Silicotitanate as Applied to Simulated Liquid Hanford Tank Waste

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ROBB-THESIS-2025.pdf (2.75 MB)
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Robb, Abigail Marie
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https://hdl.handle.net/1853/78662
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Treatment of approximately 56 million gallons of stored tank waste at Hanford Site in Washington State represents one of the world’s largest radiological clean-up efforts. One of the first steps in that process involves the treatment of tank waste supernate to remove cesium-137, thus enabling the disposition of that waste as contact handled low activity waste. The Tank Side Cesium Removal (TSCR) process was recently started up in January of 2022 to achieve that separation. This process relies on crystalline silicotitanate (CST) ion exchange media for the separation of cesium from the sodium-laden supernatant. While it is readily recognized that other period 1 cations will impact CST’s capacity for cesium, it is less well known that the anion composition of the supernate can significantly impact the cesium capacity due to the high ionic strength of the solutions. This indicates that the quantity of CST eventually required for treatment of 21-million gallons of liquid tank waste at Hanford can vary substantially depending upon the ionic composition of the supernate that is being processed. Batch contacts were performed with a variety of anion matrices at a typical sodium concentration of 5.3 ± 0.3 M (with and without K+ present). The results demonstrated that the anion composition and potassium concentration can significantly affect the amount of cesium loaded onto the CST when NaOH, NaNO3, Na2CO3, NaNO2, KNO3, and KCl varied. The trends seen as salt concentrations varied were combined into a simple equation that can model the distribution coefficient, Kd, based on the concentrations of the anions and cations that have the largest impact on cesium removal. The equation showed high agreeability with experimental and benchmark results for high salt simple simulants with and without potassium, and for complex sodium salt simulants.
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2025-06-02
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