Extraction of Lanthanides with N,N′‐Dimethyl‐N,N′‐diphenyl‐malonamide and ‐3,6‐dioxaoctanediamide

Abstract

The extraction properties of the trivalent lanthanides (Ln(III)) with the bidentate N,N′‐dimethyl‐N,N′‐diphenyl‐malonamide (MA) and the tetradentate N,N′‐dimethyl‐N,N′‐diphenyl‐3,6‐dioxaoctanediamide (DOODA) were investigated. These diamides formed by coupling two amide groups with methylene and/or ether groups are bidentate for the MA and tetradentate for the DOODA. By adding a previous data regarding the tridentate N,N′‐dimethyl‐N,N′‐diphenyl‐diglycolamide (DGA), these extraction results enabled us systematically study an effect of number of oxygen donor on its extraction behavior of Ln(III). The change in the distribution ratios (Ds) of Lu(III) with an increase in the HNO3 concentration is greater than that of La(III) in both the MA and DOODA systems. Therefore, the relationship between the D and atomic number, i.e., the lanthanide pattern, changes with the HNO3 concentration: the Ds decrease with an increasing atomic number at lower HNO3 concentrations. The Ds of the lighter Ln(III) are similar to the Ds of the heavier Ln(III) at higher HNO3 concentrations. The number of the extractant in the extracted species for La(III) and Lu(III) obtained from slope analysis at 4 M HNO3 in the MA system are about 3, while those in the DOODA system are quite different, i.e., 2 for La(III) and 1.5–3 for Lu(III). The comparison of the extractability of Ln(III) by MA, DOODA, and DGA shows that the magnitude of the Ds is in the sequence of MA < DOODA ≪ DGA. This suggests the introduction of one ether oxygen atom to the principal chain in the diamides leads to a good extractability for the Ln(III) from HNO3 solution.