Studies on the Uptake and Column Chromatographic Separation of Eu, Th, U, and Am by Tetramethylmalonamide Resin

Abstract

A tetramethylmalonamide-functionalized resin (TMMA resin) has been developed and investigated for its ability to separate trivalent, tetravalent, and hexavalent actinide elements. As a fundamental study of the extraction mechanism and to design a chromatographic separation scheme, distribution coefficients (K d) for partitioning of Eu(III), Th(IV), U(VI), and Am(III) onto the resin from HNO3, NaNO3, HCl, and NaCl solutions have been determined. The partitioning of HNO3 onto the resin was also evaluated. The order of the K d values was Th(IV) > U(VI) > Am(III) = Eu(III) in all tested solutions. The competition between metal extraction and HNO3 extraction was confirmed by the extraction data and FT-IR spectra. The loading capacities of Eu(NO3)3 and UO2(NO3)2 at 3 M HNO3, determined by a dynamic method with TMMA resin (TMMA in the resin was 2.05 mmol/g), were 0.83 mmol/g and 1.6 mmol/g, respectively, implying that M:TMMA stoichiometry was 1:2 for Eu(III) and 1:1 for U. Because the K d values for Th(IV) and U(VI) were greater than 100 in all solutions tested, the influence of organic acids on the K d values of Th(IV) and U(VI) from 3 M and 0.01 M HNO3 solutions was studied to identify potential stripping agents. The effects of Na, Al, K, Ca, Cr, Ni, and Fe (potential constituents of low-level radioactive waste) on the K d values of Am(III) were also studied. Although the K d values for Am(III) decreased in the presence of 0.01 M Fe(III), the influence of the other ions was negligible. Based on these fundamental experimental results, an extractive chromatographic scheme for actinide isolation was designed and demonstrated.