Experimental and theoretical studies on solvent extraction of uranium(VI) with hexapropyl and hexabutyl phosphoramide extractants

Abstract

ABSTRACT Two phosphoramide extractants, namely, hexapropyl phosphoramide (HPPA) and hexabutyl phosphoramide (HBPA), were developed in our laboratory for their application toward actinide separations. Preliminary studies on actinides with phosphoramides revealed that they are potential extractants for actinide recovery. However, the knowledge of extraction and stripping of U(VI), Th(IV), and Pu(IV) is essential for deploying it to plant-level reprocessing applications. In this context, the extraction behavior of U(VI) by 1.1 M solution of HBPA in n-dodecane and HPPA in xylene was studied. To gain insights into the U(VI) extraction behavior with phosphoramides, we have applied density functional theory (DFT) calculations on ligands and the corresponding metal complexes. Our estimates indicate that the ν(P = O) is red-shifted upon complex formation, which implies a moderate weakening of the P = O bond. A considerable amount of charge is transferred from the P = O group to U(VI) during complex formation. In addition to this, the computed extraction behavior was consistent with the trend established by experimental distribution ratios. These studies are useful for developing solvent extraction-based separation procedures to separate and purify actinides using a phosphoramide-based solvent.