Effect of diluent on the extraction of europium(iii) and americium(iii) with N,N,N′,N′-tetraoctyl diglycolamide (TODGA)

Solvent extraction of Eu(3+) and Am(3+)via N,N,N′,N'-tetraoctyl diglycolamide (TODGA) dissolved in different molecular diluents was studied. The diluent types used in this work were primary and secondary alcohols, secondary ketones and alkanes. Effects of concentration of extracting agent, temperature, diluent type and its carbon chain length on the extractions were determined. Distribution ratios of Eu(3+) and Am(3+) showed high dependence on the diluent type as well as the carbon chain length within the same type of diluent. The highest distribution ratios for both Eu(3+) and Am(3+) as well as the separation factors of Eu(3+) over Am(3+) were observed in the alkane diluents. Unexpectedly high distribution ratios for Eu(3+) and Am(3+) were observed in polar diluents with 5 carbon atoms in the chain, clearly standing out against the general trends. It was found that Eu(3+) and Am(3+) extraction via TODGA is enthalpy driven in all the studied diluents and that extraction is more exothermic in alkane diluents. Analysis of the stoichiometry of the extracted complexes shows that the average ligand number of TODGA molecules in the extracted complex is lower for Am(3+) compared to Eu(3+) except for with alkane diluents.