Unraveling the role of phase modifiers in the extraction of Nd(III) from nitric acid medium in tetra-bis(2-ethylhexyl)diglycolamide in n-dodecane containing long chain aliphatic alcohols

Abstract

Tetra-bis(2-ethylhexyl)diglycolamide (TEHDGA) alone in n-dodecane (n-DD) is unsuitable for the solvent extraction of trivalent actinides from high-level liquid waste due to the occurrence of third phase formation during the course of solvent extraction. Significant concentration of long chain aliphatic alcohols ranging from 5% to 15% (V/V) have been added to the solvent phase, TEHDGA/n-DD, to control the undesirable third phase formation. The alcohols investigated were n-octanol, n-decanol, and isodecanol. To understand the role of alcohols in controlling the third phase formation, the extraction behaviour of the trivalent metal ion, Nd(III), from nitric acid medium was studied in a solution of 0.2 M TEHDGA + 1 M alcohol in n-DD. The equilibrium concentration of Nd(III) and nitric acid present in organic and aqueous phases were determined. The organic phase obtained after extraction was subjected to dynamic light scattering studies to unravel the role of alcohol phase modifiers in organic phase. The aggregate size and their distribution in organic phase was determined as a function of various parameters such as concentrations of nitric acid, Nd(NO3)3 and the nature of alcohol. The results revealed that the presence of long chain alkyl aliphatic alcohols interact with the polar acid-solvates and metal-solvates by solvation and prevents these solvates undergoing aggregation in organic phase. In view of this, the aggregate size was controlled much below the limiting aggregate size required for third phase formation by these alcohol phase modifiers. Even though all the alcohols investigated in the present study could bring down the aggregate size much below the limiting value, n-decanol was found to be superior to other alcohols.