Antagonism in the aggregation behaviour of N,N,N′,N′-tetraoctyldiglycolamide in n-dodecane upon adding N,N-dioctylhydroxyacetamide during trivalent metal extraction

The solvent phase composed of tetraoctyl diglycolamide (TODGA) in n-dodecane (n-DD) undergoes the undesirable organic phase splitting during the solvent extraction of trivalent actinides and lanthanides from nitric acid medium. To overcome this limitation a neutral extractant namely the N,N-dioctyl hydroxyacetamide (DOHyA), which was half the molecule of TODGA, has been added to the solvent phase and evaluated for the extraction of Nd(III) from nitric acid medium. Since the reverse micellar aggregates of the extracted species in the organic phase was responsible for organic phase splitting, the aggregation behaviour of the organic phase was probed by dynamic light scattering (DLS) technique. The results have been compared with the individual solvent systems, namely DOHyA/n-DD and TODGA/n-DD. The investigations revealed that the extraction of nitric acid and loading of Nd(III) in organic phase increased upon adding DOHyA, but the size of aggregates formed in the organic phase decreased remarkably with DOHyA addition, which was in contrast to the expected behaviour of increase in aggregate size with increase of extraction in the organic phase. To understand the unexpected behaviour of aggregation, the extracted organic phase was further probed by UV–visible and luminescence spectroscopy. The results further revealed that DOHyA in the binary solution served as a reactive organic phase modifier and induced antagonistic effect on aggregation when mixed with TODGA, which was, in fact an advantage for the extraction of trivalent actinides from high-level nuclear waste.