Optical Spectroscopic Investigation of Hexavalent Actinide Ions in n-Dodecane Solutions of Tri-butyl Phosphate

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

“…On the addition of greater quantities of U, peaks corresponding to the UO 2 2+ -bound species increase. These include the U­(VI)-bound amide CO stretch at 1568 cm –1 (reported previously at 1573 cm –1 , and 1565 cm –1 ), the U­(VI)-bound nitrate at 1520 cm –1 (1525 cm –1 ), the nitrate symmetric stretch at 1273 cm –1 (1272 cm –1 ), and the overlapping OUO ν asy and N–OH stretch at 935 cm –1 . , The UO 2 2+ -bound CO stretching frequency of DEHiBA also matches well with what has been measured for the lanthanide elements (1570 cm –1 ), Th­(IV) (1558 cm –1 ), and Pu­(IV) (1543 cm –1 ) …”

“…These include the U(VI)-bound amide C�O stretch at 1568 cm −1 (reported previously at 1573 cm −1 , 41 and 1565 cm −1 ), 45 the U(VI)-bound nitrate at 1520 cm −1 (1525 cm −1 ), 41 the nitrate symmetric stretch at 1273 cm −1 (1272 cm −1 ), 41 and the overlapping O�U�O ν asy and N−OH stretch at 935 cm −1 . 37,45 The UO 2 2+ -bound C�O stretching frequency of DEHiBA also matches well with what has been measured for the lanthanide elements (1570 cm −1 ), Th(IV) (1558 cm −1 ), and Pu(IV) (1543 cm −1 ). 49 Of interest is that while the U-bound nitrate vibration appears at 1028 cm −1 as previously reported, 50 a second band grows with increasing uranium loading at 1019 cm −1 which is not present when extraction occurs from LiNO 3 media under significant loading, 46 but is present for solid uranyl nitrate hydrates.…”

“…To better quantify the speciation changes observed in the FTIR spectra, the spectra were analyzed using principal component analysis (PCA). PCA is a multivariate approach to condense complex data sets into several principal components (PC) that can reproduce the initial data set with little data loss. , To emphasize the effect of any (HNO 3 ) n L m complexes, a spectral subtraction approach similar to that used by Lumetta et al was utilized . That is, the baselined and methyl rock-normalized spectrum of n -dodecane was subtracted from the baselined and normalized spectra to give the spectra of DEHiBA and HNO 3 .…”

“…In the samples collected at lower acid concentrations or without contact of an aqueous phase, a strong absorbance band from the C�O stretch of unbound DEHiBA is present at 1648 cm −1 . It should be noted in the interpretation of spectra contacted with nitric acid solutions (with and without U) that a weak nitrate band has been observed at this location for HNO 3 -TBP systems and may contribute to the prominence of this band, 37 particularly at high nitric acid strengths. At low to intermediate HNO 3 concentrations, a weak shoulder band attributed to the C� O stretch interacting with HNO 3 appears at 1617 cm −1 , initially increasing, but then decreasing with increasing HNO 3 concentrations.…”

Innovative Separations Research and Development Needs for Advanced Fuel Cycles

“…The dominant extraction reactions are believed to be those described by Eqs. 3 and 4 (Herbst et al 2011), but recent results suggest that other species are likely involved (Lumetta et al 2021).…”