The U.S. Department of Energy (DOE) is actively pursuing new and improved separation techniques for the cleanup of past nuclear defense production sites. Research and production activities at DOE's Hanford Site in Richland, Wash., have created large volumes of waste streams containing hazardous and toxic chemicals along with radioactive materials. Many of these wastes will require processing for segregation into high‐level, transuranic, and/or low‐level waste for permanent disposal. A process to selectively remove actinides, such as americium, from liquid radioactive waste was investigated for potential use at Hanford and other contaminated DOE sites.
The objective of this research was to determine the effectiveness of polymer binding followed by ultrafiltration for removal of europium (Eu), a nonradioactive surrogate for trivalent actinides such as americium. A commercially available polyacrylic acid (PAA) and a Pacific Northwest Laboratory (PNL) synthesized copolymer were tested.
Both polymers significantly increased Eu removal. A cation exchange mechanism was implied by examination of the Eu‐to‐RCO2− functional groups that comprise the acrylic acid monomer. The weight ratios of Eu‐to‐polymer needed to achieve 85% rejection of Eu were 1:6 for PAA and 1:10 for the PNL copolymer. Addition of sodium to the feed solution at a concentration three orders of magnitude greater than Eu did not adversely affect rejection of Eu; this showed the high selectivity of both polymers for Eu. Polymer binding of metals followed by ultrafiltration also has potential applications for selective separation of metals from various industrial process streams. The formation of metal hydroxide precipitates is also a possibility unless pH is controlled; these could be separated as well by ultrafiltration but defeat the intent of polymer addition. For the polymers tested, pH had to be above the pKa (4.25) of the ionizing functional groups but below a pH of 6 where precipitation may interfere.

The U.S. Department of Energyis activelypursuingnewand improvedseparationtechniquesto " concentratehigh-levelliquidradioactivewaste,particularlyat the HanfordSite, inorderto minimizethe waste volumerequiringvitrification. A processto selectivelyremove24tAmfromliquidradioactivewaste was investigatedas an actinideseparation methodthatcouldbe applicableto Hanfordandother waste sites. The experimentalproceduresinvolvedremovalof Eu, a nonradioactivesurrogatefor:41Am,from aqueoussolutionsat pH 5 using organicpolymersin conjunction with ultrafiltration.Commercially availablepolyacrylicacid (60,000 MW)and PacificNorthwestLaboratory's ! (PNL) synthesizedE3 copolymer(-10,000 MW)were tested. Test solutionscontaining10_tg/mLof Eu were dosed with each polymerat various concentrationsin orderto bindEu (i.e., by complexationand/orcation exchange)for subsequentrejectionby an ultrafiltration coupon. Test solutionswere filteredwith and withoutpolymerto determineif enhancedEu separationcouldbe achieved_om polymertrealanent.Both polymers significantly increasedEu removal. The optimumconcentrationswere20 gtg/mLof polyacrylicacid and 100 _tg/mLof E3 for 100%Eu rejectionby the AmiconPM10membraneat 55 psi. In additionto enhancementof removal,the polymersselectivelybound Eu overNa, suggesting that selective separation of Eu was possible. _. The results of this studysuggest that polymer-enhancedultrafiltration is a potential process for separationof 241Am fromHartfordtank waste. Thus, furtherinvestigationof binding agents and membraneseffective under conditions similarto the tank waste (e.g., very alkaline and high ionic strength) is warranted. This process also has potentialapplications for selectiveseparationof metals from industrial 1Operated for the U.S. Departmentof Energyby Battelle MemorialInstitute underContract DE-AC06-76RLO 1830. 111 process streamsandthe use of the polymersevaluatedinthis studyandotherhigh molecularweight bindingagentsthatexhibitan affinityforregulatedtoxic metalsshouldbe furtherexamined.