The extraction and separation performance of two amide-acid ligands toward actinides

Abstract

Actinide separation is pivotal to resolving spent nuclear fuel reprocessing bottlenecks for nuclear power development, and the development of efficient and environmentally friendly extraction technology is crucial to meet the growing demands. This work investigates how different central atoms between oxygen and nitrogen in amide-acid ligands affect their extraction performance for actinides, aiming to facilitate the design and development of advanced ligands for the selective separation of actinides. For this purpose, N,N-di(2-ethylhexyl) diglycolamic acid (HDEHDGA, HA) and N,N-di(2-ethylhexyl)-N-methyliminodiacetic acid monoamide (HDEHNDGA, HB) were synthesized. Their extraction behaviors toward key actinides, U(VI), Pu(IV) and Am(III), were evaluated via slope analysis, FT-IR and DFT calculations. At HNO₃ concentrations in the range of 0.01–1 M, the distribution ratio of HA in 1-octanol extracting Pu(IV) can reach 113, with separation factors of 500 for Pu(IV)/U(VI) and 120 for Pu(IV)/Am(III). For HB, the Pu(IV)/Am(III) and U(VI)/Am(III) separation factors are as high as 4000 and 750. Spectroscopic and thermodynamic studies revealed distinct coordination modes and thermal behaviors of HA and HB: HA binds via CO and C–O–C in an exothermic process, whereas HB coordinates through CO without the central nitrogen atom in an endothermic manner. These findings clarify the coordination properties of amide-acid ligands and provide a foundation for advancing actinide separation technologies.