IHEP scientists developed up-to-now the most efficient ligand for the group separation of actinides from fission products in highly acidic solution, which might hold promising applications in the partitioning of High-level Waste (HLW). The results have been published online in Inorganic Chemistry journal on January 10 (Xiao Chengliang, Chai Zhifang*, Shi Weiqun*, et al. Inorg. Chem., 2014, ASAP), a core inorganic chemistry journal of the American Chemical Society.

The studies were conducted by scientists from the Nuclear Energy Radiochemistry Laboratory of IHEP. Since 2011, the laboratory has been devoted to design novel ligands for the separation of actinides over lanthanides by density functional theory and has published a serial of important papers (Inorg. Chem., 2011, 50: 9230; J. Phys. Chem. A, 2012, 116: 504; Coord. Chem. Rev., 2012, 256: 1406; Inorg. Chem., 2013, 52: 196; Inorg. Chem., 2013, 52: 10904.). Based on the accumulated knowledge, they designed and synthesized a phenanthroline-based tetradentate ligand with hard-soft donors combined in the same molecule, N,N’-diethyl-N,N’-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen), for the group separation of actinides over lanthanides in the recent studies.

The synthesis and solvent extraction as well as complexation behaviors of the ligand with actinides and lanthanides were studied experimentally and theoretically. The ligand exhibited excellent extraction ability and high selectivity toward hexavalent, tetravalent, and trivalent actinides over lanthanides in highly acidic solution. The distribution ratios of Th(IV), U(VI), and Am(III) should be determined to be 205, 25, and 6 in 1.0 M HNO₃, respectively. The single-stage separation factors (SF) of Th(IV), U(VI), and Am(III) toward Eu(III) were 2277, 277, and 67 in 1.0 M HNO₃, respectively. With respect to the group separation of actinides using single extractant, the distribution ratios and selectivity for all actinides over lanthanides they achieved in this case were the most competitive compared to previous works.

After the emergence of nuclear power plants, the environmental issues associated with spent fuels accompanying electricity generation are of great concern. Though U and Pu can be recovered by the traditional PUREX (Plutonium and Uranium Recovery by Extraction) process, minor actinides (MA) still remaining in the high-level liquid waste (HLLW) become the predominant long-lived radiotoxic elements and will pose long-term risks toward the environment. The so-called partitioning and transmutation strategy may provide a reasonable approach to achieve the minimization of nuclear waste and to reduce the threat of MA. However, MA(III) and Ln(III) possess similar chemical properties, making the separation of MA(III) from Ln(III) in highly acidic waste very challenging. The ligand reported in this work holds promising applications in the partitioning of High-level wastes.

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http://pubs.acs.org/doi/full/10.1021/ic402784c