Highly selective extraction of Pu (IV) and Am (III) by N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline ligand: An experimental and theoretical study

Abstract

The group actinide extraction ligand, N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen) has been successfully developed in our laboratory recently. In this work, the extraction behaviors of the tetradentate Et-Tol-DAPhen toward Am(III) and Pu(IV) by using 1-(trifluoromethyl)-3-nitrobenzene as the diluent were systematically explored. The effects of HNO3 and ligand concentration as well as temperature were studied in detail. In addition, the selectivity of this ligand towards actinides and the stripping performance of the extraction system were also investigated to assess its potential application for group actinide separation over trivalent lanthanides (Ln(III)). According to our results, Et-Tol-DAPhen exhibits large distribution ratios for both Am(III) and Pu(IV) with high separation factors over Pm(III) in a wide range of acidity. Moreover, Am(III) and Pu(IV) can be efficiently stripped into the aqueous phase via three stages of batch back extraction. In addition, density functional theory (DFT) calculations suggest that the ligand selectivity towards actinides over Ln(III) probably results from the higher covalency of An-N bonds. The consistency between calculated thermodynamic parameters and experimental observations demonstrates the reasonability of the proposed extraction mechanism. Our findings afford insightful extraction parameters of Et-Tol-DAPhen towards actinides with different oxidation states and justify its versatile coordination abilities with respect to group actinide separation over lanthanides.