Group Separation of Hexavalent Actinides from Lanthanides through Selective Extraction by Sterically Hindered 2-Ethylhexyl Phosphonic Acid Mono-2-ethylhexyl Ester
Xue Dong, Qiang Yan, Zhipeng Wang, Xiaogui Feng, Jing Chen, Chao Xu
Abstract
Group separation of actinides (An, including U, Np, Pu, and Am) from lanthanides (Ln) is of great significance for nuclear resources recycling and long-term radiotoxicity reduction. But this task represents a big challenge due to the chemical complexity of the actinides. In the present work, we proposed a strategy for group An/Ln separation by oxidizing the actinides to hexavalent oxidation states and then selectively extracting them from lanthanides by a sterically hindered ligand, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (EHEHPA). The intrinsic selectivity of EHEHPA to hexavalent actinides over trivalent/tetravalent lanthanides affords single-stage An/Ln separation factors in the range of 102–105, depending on the specific actinides or lanthanides. The selective mechanism of An(VI)/Ln(III/IV) was analyzed by means of UV–vis absorption and mass spectroscopies, which suggests that the Ln(III/IV)/EHEHPA and An(VI)/EHEHPA complexes possess similar metal/ligand stoichiometries but the former one may consist of more hydrophilic nitrate ion or water molecules, thus leading to high selectivity to An over Ln by EHEHPA.