Investigations on Preferential Pu(IV) Extraction over U(VI) by N,N-Dihexyloctanamide versus Tri-n-butyl Phosphate: Evidence through Small Angle Neutron Scattering and DFT Studies

Abstract

Straight chain amide N,N-dihexyloctanamide (DHOA) has been found to be a promising alternative extractant to tri-n-butyl phosphate (TBP) for the reprocessing of irradiated uranium- and thorium-based fuels. Unlike TBP, DHOA displays preferential extraction of Pu(IV) over U(VI) at higher acidities (≥3 M HNO3) and poor extraction at lower acidities. Density functional theory (DFT) based calculations have been carried out on the structures and relative binding energies of U(VI) and Pu(IV) with the extractant molecules. These calculations suggest that the differential hardness of the two extractants is responsible for the preferential binding/complexation of TBP to uranyl, whereas the softer DHOA and the bulky nature of the extractant lead to stronger binding/complexation of DHOA to Pu(IV). In conjunction with quantum chemical calculations, small angle neutron scattering (SANS) measurements have also been performed for understanding the stoichiometry of the complex formed that leads to relatively lower extraction of Th(IV) (a model for Pu(IV)) as compared to U(VI) using DHOA and TBP as the extractants. The combined experimental and theoretical studies helped us to understand the superior complexation/extraction behavior of Pu(IV) over U(VI) with DHOA.

Speciation analysis the complexation of uranyl nitrate with tri-n-butyl phosphate in supercritical CO2

“…The most predominant species were 1 : 1 and 1 : 2. The structure of UO 2 (NO 3 ) 2 -$2TBP was similar to that reported in the literature, 35 in which two TBP molecules coordinated with uranyl moiety O]U]O at the equatorial plane. For the 1 : 1 species, TBP also coordinated to the uranium from the equatorial plane of the uranyl moiety, and the angle of N/U/N was approximately 153 , bending towards the side without TBP.…”

Speciation of uranium‐mandelic acid complexes using electrospray ionization mass spectrometry and density functional theory

“…[30,31] A similar combination of functional and basis sets was previously used to predict accurate geometries and energetics for several uranyl complexes. [24,[32][33][34][35][36][37][38][39] To verify whether the obtained structures correspond to the potential energy minima, analytical frequency calculations were carried out using the AOFORCE module as implemented in TURBOMOLE version 6.3.1 (Karlsruhe, Germany). [40] Finally, binding free energies were calculated at 298.15 K after incorporating thermal and non-thermal corrections into the electronic energies.…”

Selective Separation of HNO3 and HCl by Extraction: The Investigation on the Noncovalent Interaction between Extractants and Acids by Density Functional Theory

“…Correspondingly, through DFT calculations, Chandrasekar et al found that the selectivity of tri- sec -butyl phosphate (TsBP) for U­(VI) is much higher than that for Th­(IV), which is related to the combination of structural and electronic effects near the binding site. Likewise, Kong, Verma, and Wang et al , examined the interactions between various extractants and elements in spent nuclear fuel by DFT. Mechanisms of extractants to selectively separate plutonium, uranium, actinides, and lanthanides are explained from the microscopic level by analyzing the electronic structure and bonding nature of complexes.…”