Extraction Behavior of Ln(III) Ions by T2EHDGA/n-Dodecane from Nitric Acid and Sodium Nitrate Solutions

ABSTRACT

The diglycolamide extractant T2EHDGA has proven to be 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 nonpolar 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 ratios for Eu(III) extracted from aqueous HNO₃ media compared with that from 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 mass-action modeling using the solvent extraction modeling program SXLSQI suggest participation of 1 to 2 HNO₃ molecules in the Eu(III)/T2EHDGA complex upon extraction from HNO₃ media, indicative of a mechanism change responsible for the enhanced extraction behavior toward lanthanides in the presence of HNO₃.

KEYWORDS:

• ALSEP
• T2EHDGA
• speciation model
• trivalent actinides and lanthanides
• extraction constant

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Erratum

Acknowledgments

This work was supported by U.S. Department of Energy, Office of Nuclear Energy, through the Nuclear Technology Research and Development Program. Pacific Northwest National Laboratory is operated by Battelle Memorial Institute for the U.S. Department of Energy under contract DE-AC05-76RL01830.

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Funding

This work was supported by U.S. Department of Energy, Office of Nuclear Energy, through the Nuclear Technology Research and Development Program.