(115f) Alternate Methods for Eluting Cesium from Spherical Resorcinol-Formaldehyde Resin

A Small Column Ion Exchange (SCIX) system has been proposed for removing cesium from high level waste at the Savannah River Site (SRS). The SCIX system could use spherical resorcinol-formaldehyde (RF), a regenerable resin, to remove the cesium. The standard method for eluting cesium from resin involves 15-20 bed volumes (BV) of 0.5 M nitric acid. The nitric acid eluate containing radioactive cesium would be combined with waste tank sludge and vitrified at the Defense Waste Processing Facility (DWPF). The standard amount of nitric acid to elute the RF resin exceeds the capacity of DWPF to destroy nitrate ions and maintain the required chemical-reducing environment in the glass melt.

Alternate methods for eluting the resin have been tested, including using lower concentrations of nitric acid, other acids, and changing the flow regimes. All of these laboratory-scale tests used a 1.5-cm inside diameter column with a resin height of 10.5 cm, the same aspect ratio as the planned SCIX columns. The resin was loaded with 9.5 g Cs/L of resin prior to elution, which is the maximum expected loading for RF resin treating the waste at SRS.

The alternative method that used 4 BV of 0.5 M HNO3 followed by 13 BV of 0.05 M HNO3 used 164 g of nitrate per liter of resin (35% of the standard elution) and removed >99.996% of the cesium. Formic acid was slightly less efficient than nitric, but 20 BV of 0.5 M HCOOH removed 99.98% of the cesium.