STRUCTURAL EFFECTS IN<i>N</i>,<i>N</i>-DIALKYL AMIDES ON THEIR EXTRACTION BEHAVIOR TOWARD URANIUM AND THORIUM

Abstract

Extraction behavior of four N,N-dialkylamides with varying alkyl substituents on the α carbon atom with respect to carbonyl group, viz. di-(2-ethylhexyl)acetamide (D2EHAA), di-(2-ethylhexyl)propionamide (D2EHPRA), di-(2-ethylhexyl)isobutyramide (D2EHIBA), and di-(2-ethylhexyl)pivalamide (D2EHPVA) toward nitric acid, U(VI), and Th(IV) has been investigated. The conditional acid uptake constant (K H) values for 1:1 species predominant in the acidity range 0.5–3 M HNO3 are in the following order: D2EHAA (0.28±0.03) > D2EHPRA (0.20±0.01) > D2EHIBA (0.15±0.04) > D2EHPVA (0.06±0.002). The stoichiometry of the extracted species of uranium conforms to UO2(NO3)2·2A (where A = amide). The conditional extraction constants (K ex.) for uranium were found to vary in the following order: 34.0±2.0 (D2EHAA) > 5.6±0.4 (D2EHPRA) > 1.2±0.1 (D2EHIBA)>0.51±0.03 (D2EHPVA). Third phase has been observed in the case of D2EHAA (≥1 M HNO3) and D2EHPRA (≥3 M HNO3) in the presence of macro concentration of thorium (220 g/L). The separation factor (S.F.=,D U/D Th) values of D2EHPVA are distinctly larger as compared to other amides as well as to TBP. An attempt has also been made to correlate the observed distribution data with the electronic charge parameter of the amide extractants.