Minimizing the aggregation of diglycolamide reverse micelles in the n-dodecane phase with bis-(2-ethylhexyl)phosphoric acid “reactive” phase modifier

Abstract

Phase modifiers have been added to the solvent phase to prevent the undesirable third phase formation during the course of solvent extraction. Bis(2-ethylhexyl)phosphoric acid (HDEHP) has been explored as a phase modifier during the extraction of Nd(III) from nitric acid medium in a binary solution of tetra-bis(2-ethylhexyl)diglycolamide (TEHDGA) and HDEHP in n-dodecane (n-DD). To unravel the peculiar role of HDEHP in this binary solution, the reverse micellar aggregates formed in the organic phase upon nitric acid and Nd(III) extraction were probed by Dynamic Light Scattering (DLS) and Fourier Transform Infrared (FTIR) spectroscopy. The aggregate size and its distribution in the organic phase increased with an increase in the concentration of nitric acid and Nd(III) in the aqueous phase. The limiting aggregate size for the formation of a third phase in 0.2 M TEHDGA/n-DD was determined to be ∼30 nm in 1 M nitric acid. The effect of HDEHP concentration on the aggregate size was studied and the concentration of HDEHP needed for preventing third phase formation during the course of Nd(III) extraction from 4 M nitric acid medium was optimized. The results revealed that employment of about 0.25 M HDEHP in 0.2 M TEHDGA/n-DD not only prevented third phase formation during the extraction of trivalent metal ions from nuclear wastes but also facilitated the extraction of trivalents into the binary solution, due to synergism.