(193d) Reduced Temperature Crystalline Silicotitanate Ion Exchange Performance on Cesium Removal in Various Dilutions of Hanford Tank Waste.

Treatment of AP tank farm supernate to produce immobilized low-activity waste has been initialized at the Hanford Site with the deployment of the Tank-Side Cesium Removal (TSCR) system. Suspended solids and cesium are removed through the utilization of dead-end filtration and crystalline silicotitanate (CST) ion exchange unit operations, respectively. The aqueous waste is fed directly through TSCR from underground storage tanks in preparation for vitrification and long-term storage. Washington River Protection Solutions, which manages the Hanford tank farms and TSCR, requested Pacific Northwest National Laboratory perform bench-scale tests analogous to the full-scale TSCR filtration and ion exchange processes at 16 °C. Current TSCR operations prepare the waste for processing by diluting the highly caustic (>8 M Na) streams with Columbia River water to target a sodium molarity of 5-6 M Na. As part of an effort to reduce river water usage, tests using 5.5 M Na and 7 M Na AP-105 waste were performed using TSCR-prototypic operating conditions to compare CST performance on Cs removal. Each test was performed in a lead-lag column format with a polish column to be added if Cs-137 effluent breakthrough exceeded the waste acceptance criteria (WAC) of 3.18E-5 Ci ¹³⁷Cs/mol Na. Significant improvement in system performance was observed when processing the diluted (5.5 M Na) AP-105 waste supernate. Testing suggested the throughput capacity of the ion exchange system is increased by 10-20% when the feed is diluted to 5.5 M Na rather than 7 M Na when normalized for Na throughput of the system. The increased performance of the ion exchange system in dilute feed streams can reduce the amount of CST (i.e. number of columns) needed thus reducing the associated operational costs for processing the waste.