Title: Extraction of water and speciation of trivalent lanthanides and americium in organophosphorus extractants

Abstract

Complexes of the trivalent lanthanides and Am with di-2-ethylhexylphosphoric acid (HDEHP) dissolved in an aliphatic diluent were probed with UV–vis, X-ray absorption fine structure, and time-resolved fluorescence spectroscopy while the water concentration was determined by Karl Fischer titrations. In particular, our work focuses on the Nd-hypersensitive UV–vis absorbance region to identify the cause of changing absorbance values at 570 and 583 nm in relation to the pseudooctahedral Nd environment when coordinated with three HDEHP dimers. In contrast to recently reported interpretations, we establish that while impurities have an effect on this electronic transition band, a high water content can cause distortion of the pseudooctahedral symmetry of the six-coordinate Nd, resembling the reported spectra of the seven-coordinate Nd compounds. Extended X-ray absorption fine structure analysis of the Nd in high-concentration HDEHP solutions also points to an increase in the coordination number from 6 to 7. The spectral behavior of other lanthanides (Pr, Ho, Sm, and Er) and Am^III as a function of the HDEHP concentration suggests that water coordination with the metal likely depends on the metal’s effective charge. Fluorescence data using lifetime studies and excitation and emission spectra support the inclusion of water in the Eu coordination sphere. Further, themore » role of the effective charge was confirmed by a comparison of the Gibbs free energies of six- and seven-coordinate La-HDEHP–H₂O and Lu-HDEHP–H₂O complexes using density functional theory. In contrast, HEH[EHP], the phosphonic acid analogue of HDEHP, exhibits a smaller capacity for water, and the electronic absorption spectra of Nd or Am appear to be unchanged, although the Pr spectra show a noticeable change in intensity as a function of the water content. As a result, electronic absorption extinction coefficients of Am^III, Nd^III, Pr^III, Sm^III, Er^III, and Ho^III as a function of the HDEHP concentration are reported for the first time.« less

Authors:

Gullekson, Brian J. ^[1]; Breshears, Andrew T. ^[2]; Brown, M. Alex ^[3]; Essner, Jeremy B.  ^[4];

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Baker, Gary A. ^[4]; Walensky, Justin R. ^[4]; Paulenova, Alena ^[1]; Gelis, Artem V.  ^[3]

• Search DOE PAGES for author "Gelis, Artem V."
• Search DOE PAGES for ORCID "0000-0002-5487-1472"

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+ Show Author Affiliations

1. Oregon State Univ., Corvallis, OR (United States)
2. Univ. of Missouri, Columbia, MO (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
3. Argonne National Lab. (ANL), Argonne, IL (United States)
4. Univ. of Missouri, Columbia, MO (United States)

Publication Date:

Tue Nov 29 00:00:00 EST 2016

Research Org.:

Argonne National Laboratory (ANL), Argonne, IL (United States)

Sponsoring Org.:

USDOE Office of Nuclear Energy (NE)

OSTI Identifier:

1362294

Grant/Contract Number:  

AC02-06CH11357

Resource Type:

Accepted Manuscript

Journal Name:

Inorganic Chemistry

Additional Journal Information:

Journal Volume: 55; Journal Issue: 24; Journal ID: ISSN 0020-1669

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY