EVALUATION AND TESTING OF INORGANIC ION EXCHANGE SORBENTS FOR THE REMOVAL OF CESIUM-137 FROM ACTUAL IDAHO NUCLEAR TECHNOLOGY AND ENGINEERING CENTER ACIDIC TANK WASTE

Abstract

Three inorganic ion exchange sorbents were evaluated for 137Cs removal from the Idaho Nuclear Technology and Engineering Center (INTEC), acidic tank waste. A commercially available, Russian manufactured, potassium copper hexacyanoferrate (FS-2), crystalline silicotitanate (IONSIV IE-911), manufactured by UOP, and ammonium molybdophosphate-polyacrilonitrile composite sorbent (AMP-PAN), produced at the Czech Technical University, Prague, were tested. Approximately 800 mLs of actual radioactive tank waste were used to evaluate the FS-2 and IONSIV IE-911 sorbents. Feed flowrates of 6-7 mLs/hr through a 1 cm3 column were used for both tests. Initial 137Cs breakthrough with IONSIV IE-911 was observed at approximately 100 mLs and 50 % breakthrough was observed at 660 mLs. A 137Cs breakthrough of 20 % was observed after 775 mLs of waste was processed through the column containing FS-2. Tests were also performed with both of these sorbents using simulated tank waste. Results for the IONSIV IE-911 compare well for both tests; however, there are some slight discrepancies with the FS-2 results. These discrepancies are believed to be the result of mercury sorption arising from different mercury speciation between the actual and simulated waste feeds. Over 80 wt% of the cesium loaded onto the FS-2 sorbent was eluted with 8 M HNO3, while no attempt was made to elute cesium from the IONSIV IE-911 sorbent. The AMP-PAN test used a 1.5 cm3 column, 1600 mLs of actual radioactive waste, and a flowrate of 40 mLs/hr (26 bed volumes/hr). Initial 137Cs breakthrough was observed after processing 600 mLs, and 0.15 % breakthrough was observed after processing 1550 mLs of waste. Over 83 % of the cesium was eluted using 44 mLs of 5 M NH4NO3. Two loading and elution cycles were performed with simulated waste and AMP-PAN. Approximately 4800 mLs (3200 BV) of simulant were processed before 50 % breakthrough was observed. Over 70 % of the cesium was eluted in 85 mL (57 BV). Only 4050 mLs (2700 BV) of simulant were processed before 50 % breakthrough was observed in the second loading cycle and 50 % of the cesium was eluted in 117 mL (78 BV). The results indicate that AMP-PAN has the highest capacity for cesium and sorption appears to not be affected by the presence of mercury in the waste, giving it clear advantages over IONSIV IE-911 and the FS-2 sorbent. The AMP may also be easily dissolved from the PAN binder using sodium hydroxide.