Caustic Recycle from Hanford Tank Waste Using NaSICON Ceramic Membranes

Abstract

Abstract A sodium (Na) Super Ion Conductor (NaSICON), has been studied at Pacific Northwest National Laboratory (PNNL) to investigate its ability to separate sodium from radioactively contaminated sodium salt solutions for treating U.S. Department of Energy (DOE) tank wastes. Ceramatec Inc. developed and fabricated a membrane disk containing a proprietary NAS-GY material formulation that was electrochemically tested in a bench-scale apparatus with both a simulant and a radioactive tank-waste solution to determine the membrane performance when removing sodium from DOE tank wastes. Implementing this sodium separation process can result in significant cost savings by reducing the disposal volume of low-activity wastes and by producing a 19 M NaOH feedstock product for recycle into waste treatment processes such as sludge leaching, regenerating ion exchange resins, inhibiting corrosion in carbon-steel tanks, or retrieving tank wastes. In actual waste tests, average sodium transport rates of 10.3 kg/day/m2 were achieved at average sodium transport efficiencies of 99%. The membrane was found to be highly selective to sodium ions resulting in no detectable cation transport except Na and a small quantity (0.04% to 0.06%) of 137Cs. An average decontamination factor of 2000 was observed with respect to 137Cs. As expected, Gibbsite precipitation was observed as OH− ions were depleted from the tank waste. Keywords: Alkalinecaustic recycleceramicelectrochemistryinorganicmembraneNaSICON ACKNOWLEDGMENTS The authors would like to acknowledge the following people for their significant contributions: Marilyn Steele (PNNL), Susan Jones (PNNL), Jagan Bontha (PNNL), and Mark Flinders (Ceramatec Inc.). This work is funded through a sub-contract from Ceramatec Inc. who is funded by the Office of Science and Technology within the U.S. Department of Energy's Office of Environmental Management under contract DE-FG07–04ID14622. Pacific Northwest National Laboratory is operated for the U.S. Department of Energy by Battelle under Contract DE-AC05–76RL01830. Notes Concentrations less than 0.5 were rounded to zero. No material was added to simulant for elements with "–" TIC = Total Inorganic Carbon (calculated from recipe) TOC = Total Organic Carbon (calculated from recipe). nd = not detected. Df = Decontamination Factor.