PNNL

Abstract

The diglycolamide extractant, T2EHDGA, has proven promising for the separation of lanthanides and minor actinides in high-level nuclear waste reprocessing. This neutral extractant has shown significant extraction capacity for HNO3 into the non-polar organic phase, along with hyper-stoichiometric nitrate dependence on extraction of trivalent f-elements. The transport behavior of T2EHDGA/n-dodecane toward trivalent lanthanides is not well understood. This work found a significant increase in distribution measurements for Eu(III) extracted from aqueous HNO3 media as compared to NaNO3. The extraction of Eu(III) from HNO3 results in a different thermodynamic product than predicted by classic solvent extraction of 3:1 ligand-metal complex as observed with NaNO3 in FTIR and UV-vis spectroscopy. Experimental distribution measurements in conjunction with the solvent extraction modeling program, SXLSQI, suggest participation of 1- to 2 HNO3 molecules in the Eu(III)/T2EHDGA complex when extracted from HNO3 media, indicative of a mechanism change responsible for the enhanced extraction behavior toward lanthanides in the presence of HNO3.