New bifunctional anion-exchange resins for nuclear waste treatment

Several new types of bifunctional anion-exchange resin have been designed, synthesized, and tested for their ability to remove Pu(IV) from nitric acid. The functional group present in all of these resins is a pyridinium unit derived from the host poly(4-vinylpyridine) resin. Bifunctionality was achieved by adding a second anion-exchange site to the pyridine nitrogen via an alkylene spacer that encompassed ethylene through hexylene. The attached anion-exchange sites include trimethylammonium, pyridinium, and trimethylphosphonium. The sorption kinetics and distribution coefficients of Pu(IV) from 5 to 9 M nitric acid generally were best when the two anion-exchange sites were separated by a five-carbon spacer. The order of affinity for Pu(IV) from 7 M nitric acid was pyridinium>phosphonium>trimethylammonium. Replacing the central methylene unit in a five-carbon spacer with an ether-oxygen further enhanced the sorption of Pu(IV) onto the trimethylammonium-containing resin. Because these bifunctional resins are modifications of existing commercial Reillex™ resins, they are much easier to prepare than resins that require complete synthesis. We plan to evaluate these and related bifunctional resin structures for their ability to selectively remove other targeted anions from groundwater and industrial waste streams.