Extraction of Nitric Acid and Uranium with DEHiBA under High Loading Conditions

The mechanism by which high concentrations (1.5 M in n-dodecane) of N,N-di-2-ethylhexyl-isobutyramide (DEHiBA) extracts HNO₃ and UO₂(NO₃)₂ is under examination. Most prior studies have examined the extractant and the mechanism at a concentration of 1.0 M in n-dodecane; however, under the higher loading conditions that can be achieved by a higher concentration of extractant, this mechanism could change. Increased extraction of both nitric acid and uranium is observed with an increased concentration of DEHiBA. The mechanisms are examined by thermodynamic modeling of distribution ratios, ¹⁵N nuclear magnetic resonance (NMR) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy coupled with principal component analysis (PCA). Speciation diagrams produced through thermodynamic modeling have been qualitatively reproduced through PCA of the FTIR spectra. The predominant extracted species of HNO₃(DEHiBA), HNO₃(DEHiBA)₂, and UO₂(NO₃)₂(DEHiBA)₂ are in good agreement with prior literature reports for 1.0 M DEHiBA systems. Evidence for an additional species of either UO₂(NO₃)₂(DEHiBA) or UO₂(NO₃)₂(DEHiBA)₂(HNO₃) also contributing to the extraction of uranium species is given.