Aggregation and organic phase splitting behavior of a synergic extractant system probed by dynamic light scattering spectroscopy

Abstract

A synergic solution of N,N-di-n-octyl-2-hydroxyacetamide (DOHyA) and bis-(2-ethylhexyl)diglycolamic acid (HDEHDGA) in n-dodecane has been proposed for the single-cycle separation of Am(III) and Cm(III) from high-level nuclear waste containing chemically similar lanthanides in 3–4 M nitric acid medium. The reverse micellar aggregation behavior of the binary extractants in n-dodecane has been studied in the synergic extraction regime (>1 M nitric acid) by dynamic light scattering (DLS) spectroscopy. The results were compared with the individual extractants in n-dodecane. The aggregation of reverse micelles increased with increase in the loading of nitric acid and Nd(III) in the organic phase in all organic solutions. The organic phase underwent splitting into two phases, with the lighter one “diluent-rich” and the heavier one “aggregate rich” at a particular limiting value of Nd(III) and nitric acid loading in the organic phase. Accordingly, the limiting reverse micellar aggregate size in organic phase for third phase formation was determined, and it was found to increase with increase in the polarity of the ligand in organic phase. Studies with simulated nuclear waste revealed that the binary solution composed of (0.2 M DOHyA +0.1 M HDEHDGA)/n-DD would not undergo phase splitting as the aggregate size formed in organic phase was much lower than the limiting aggregate size of 15 nm for phase splitting in the present case.