(528c) Small Scale Testing of a Floating Ion Exchange Bed for Nuclear Waste Treatment

Technetium-99 is a waste isotope that is being consdered for separation in high level nuclear waste at Department of Energy sites like Hanford in Washington state and Savannah River in South Carolina.  Technetium-99 has a half-life of 211,000 years and is highly mobile in groundwater.   Ion exchange of the liquid wastes is one processing option to remove the technetium that is present in solution as pertechnetate.

SuperLig® 639 (IBC Advanced Technologies) resin was tested under challenging conditions in the current work.   A nonradioactive surrogate waste solution containing perrhenate ion as the trace representative for pertechnetate was used, its sodium molarity being atypically high at 8 M (such wastes are typically 5-6 M).  The higher molarity would allow more efficient throughput in a large process.  The current work was done at the bench scale with a 10 mL resin bed.  One goal of the work was to examine bed behavior when it floats during loading (feed specific gravity 1.34), and sinks when eluted with water at 65 °C.  Feed upflow was found to float the bed upward as a single and stable unit.  The work saw 50% breakthrough after more than 50 bed volumes at 3 bed volumes per hour.   The resin bed was then smoothly sunk with a downflow of water.  Elution at about 1 BV/hr produced an output peak of perrhenate concentration greater than 20 times the feed concentration.

The work is a first demonstration that the ion exchange process can be operated at high feed sodium molarity with SuperLig® 639 resin.  Further work will be at larger scale.  Savannah River National Laboratory has an ion exchange modeling capability to relate this performance to that of resin separating pertechnetate from actual waste.