Experimental and theoretical studies on actinide extraction: dibutyl phenyl phosphonate versus tri-n-butyl phosphate

Abstract

Dibutyl phenyl phosphonate (DBPP) was synthesized by the reaction of phenyl phosphorochloridate with 1-butanol in dichloromethane, in the presence of pyridine as a base. The product was characterized by 13C and 31P NMR, mass spectra and FT-IR spectroscopic techniques. The variation in density of 1.1 M solution of DBPP in xylene was estimated as a function of nitric acid concentration. The conditional acid uptake constant (KH) is a measure of basicity of the ligand. This parameter was evaluated for DBPP and is reported in this paper. Extraction of U(VI), Th(IV) and Am(III) by a 1.1 M solution of DBPP in xylene was studied as a function of nitric acid concentration at 298 K. The distribution ratios of the metal ions in the DBPP/xylene system were compared with that of the tri-n-butyl phosphate (TBP)/n-dodecane system. The stoichiometry of uranyl solvate was evaluated to be 1:2. The extraction studies of some fission products with 1.1 M DBPP/xylene were performed and the distribution ratios (D) were determined. As a final step, we have applied quantum chemical calculations to understand the electronic structure of DBPP and the respective uranium complex, [UO2(NO3)2]·2DBPP. By applying the computationally accurate DLPNO-CCSD(T) methodology, we were able to derive the lowest-energy geometry for [UO2(NO3)2]·2DBPP, where both the nitrate groups are in trans-orientation. The Mulliken population and NBO analysis indicated that for both ligands (TBP and DBPP) the electronic charge is more polarized towards the oxygen atom of P = O group. The net charge at P = O group is positive with a large value estimated for TBP ligand.