Evaluation of the Hydrophilic Complexant N,N,N’,N’-tetraethyldiglycolamide (TEDGA) and its Methyl-substituted Analogues in the Selective Am(III) Separation

ABSTRACT

N,N,N’,N’-tetraethyldiglycolamide (TEDGA) is used in the French EXAm (extraction of americium) process to separate Am(III) from Cm(III) and Ln(III). In this study, the complexation behavior of TEDGA towards actinides(III) and lanthanides(III) was compared to its methyl-substituted derivatives Me-TEDGA and Me₂-TEDGA under experimental conditions applying to the EXAm process. Using the EXAm solvent, 0.6 mol/L N,N’-dimethyl-N,N’-dioctyl-hexylethoxymalonamide (DMDOHEMA) and 0.45 mol/L bis(2-ethylhexyl)-phosphoric acid (HDEHP), An(III) and Ln(III) distribution ratios increase in the order TEDGA < Me-TEDGA < Me₂-TEDGA. This is explained by differences in the strength of complexation in the aqueous phase: Conditional stability constants for the formation of [Cm(DGA)_x]³⁺ complexes decrease in the order TEDGA > Me-TEDGA > Me₂-TEDGA, as shown by time-resolved laser fluorescence spectroscopy (TRLFS). TRLFS measurements verified the exclusive existence of [Cm(DGA)₃]³⁺ complexes in the aqueous phase. Both the homoleptic [Cm(DMDOHEMA)_n]³⁺ and the heteroleptic [Cm(DGA)_x(DMDOHEMA)_y]³⁺ complexes were detected in the organic phase, as postulated in the literature.^[14]

KEYWORDS:

• TEDGA
• Me-TEDGA
• Me₂-TEDGA
• diglycolamides
• EXAm process
• time-resolved laser fluorescence spectroscopy
• actinide separation
• solvent extraction

Additional information

Funding

The research was supported by the European Commission under project SACSESS, Contract number [FP7-Fission-2012-323-282]; by the German Federal Ministry of Education and Research under Contract number [02NUK020E] and by the Ministry of Science and Higher Education of Poland under statutory research co-financed from the funds for science.