SELECTIVE SEPARATION OF EUROPIUM USING POLYMER-ENHANCED ULTRAFILTRATION

The U.S. Department of Energy (DOE) is actively pur suing new and impr oved separation techniques for the cleanup of past nuclear defense pro duction sites. Research and production activities at DOE's Hanford Sit e in Richland, Wash., have created large volumes of waste streams cont aining hazardous and toxic chemicals along with radioactive materials. Many of these wastes will require processing for segregation into hig h-level, transuranic, and/or low-level waste for permanent disposal. A process to selectively remove actinides, such as americium, from liqu id radioactive waste was investigated for potential use at Hanford and other contaminated DOE sites. The objective of this research was to d etermine the effectiveness of polymer binding followed by ultrafiltrat ion for removal of europium (Eu), a nonradioactive surrogate for triva lent actinides such as americium. A commercially available polyacrylic acid (PAA) and a Pacific Northwest Laboratory (PNL) synthesized copol ymer were tested. Both polymers significantly increased Eu removal. A cation exchange mechanism was implied by examination of the Eu-to-RCO( 2)(-) functional groups that comprise the acrylic acid monomer. The we ight ratios of Eu-to-polymer needed to achieve 85% rejection of Eu wer e 1:6 for PAA and 1:10 for the PNL copolymer. Addition of sodium to th e feed solution at a concentration three orders of magnitude greater t han Eu did not adversely affect rejection of Eu; this showed the high selectivity of both polymers for Eu. Polymer binding of metals followe d by ultrafiltration also has potential applications for selective sep aration of metals from various industrial process streams. The formati on of metal hydroxide precipitates is also a possibility unless pH is controlled; these could be separated as well by ultrafiltration but de feat the intent of polymer addition. For the polymers tested, pH had t o be above the pK(a) (4.25) of the ionizing functional groups but belo w a pH of 6 where precipitation may interfere.