Extraction of Uranium, Thorium, and Certain Lanthanides from Nitric Acid Medium with a Series of Substituted Glutaramides as Novel Extractants

A series of novel structurally related glutaramides (GAs) were synthesized and applied to the extraction and separation of selected actinides and lanthanides from nitric acid medium. The influence of the nature of the alkyl chain on the distribution ratio of U(VI) and Th(IV) was examined. N,N′-Dimethyl-N, N′-dioctylglutaramide (DMDOGA) and N, N′-dihexyl-N, N′-dioctylglutaramide (DHDOGA) were chosen and applied to the selective extraction and separation of U(VI), Th(IV), and selected lanthanides Ln(III) [Nd(III), Eu(III), Gd(III), Sm(III), and Dy(III)]. The distribution ratios of U(VI) and Th(IV) were determined in relation to the diluent type, shaking time, nitric acid concentration, salting-out agents, concentration of substituted glutaramide, and temperature. The extraction of lanthanides is negligible in the entire studied range of HNO3 concentrations (0.1–7 M). With an increase in the HNO3 concentration, the extraction of U(VI) increased up to 5 M HNO3 and then decreased on further increase in the acidity, whereas the extraction of Th(IV) slowly increased with the HNO3 concentration in the entire range studied. The stoichiometry of the U(VI) and Th(IV) extractable species was determined to be UO2(NO3)2·2GA and Th(NO3)4·GA, respectively. The IR spectra of the extracted species were recorded. Both DMDOGA and DHDOGA are more selective to U(VI) compared to Th(IV) in HNO3 solutions. Good separation of U(VI) from Th(IV) can be achieved at 0.1–0.5 M HNO3. The back-extraction of U(VI) and Th(IV) from the organic phase was also studied.