Thermodynamic features of the complexation of neodymium(III) and Americium(III) by lactate in trifluoromethanesulfonate media

P. R. Zalupski, K. L. Nash, L. R. Martin

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21 Scopus citations

Abstract

The protonation of lactate has been studied in a variety of electrolyte solutions using microcalorimetry to reveal a distinct medium influence imposed on the thermochemistry of the equilibrium. The thermochemistry of lactate protonation, when studied directly in 1.0 mol̇L-1 sodium lactate, agreed well with the studies performed in trifluoromethanesulfonate (triflate). This thermodynamic agreement suggests that the physical chemistry of lactate in the solutions applicable to the TALSPEAK process-a solvent extraction method for separating trivalent actinides from trivalent lanthanides within the scope of used nuclear fuel processing efforts-may be simulated in triflate solutions. Potentiometry, spectrophotometry and microcalorimetry have been subsequently used to study the thermodynamic features of neodymium and americium complexation by lactate using triflate as a strong background electrolyte. Three successive mononuclear lactate complexes were identified for Nd(III) and Am(III). The stability constants for neodymium, β 101=2.60±0.01, β 102=4.66±0.02 and β 103=5.6±0.1, and for americium, β 101=2.60±0.06, β 102=4.7±0.1 and β 103=6.2±0.2, were found to closely agree with the thermodynamic studies reported in sodium perchlorate solutions. Consequently, the thermodynamic medium effect, imposed on the TALSPEAK-related solution equilibria by the presence of strong background electrolytes such as NaClO4 and NaNO3, does not significantly impact the speciation in solution.

Original languageEnglish
Pages (from-to)1213-1229
Number of pages17
JournalJournal of Solution Chemistry
Volume39
Issue number8
DOIs
StatePublished - Oct 2010
Externally publishedYes

Funding

Acknowledgements Support for this work was from the Fuel Cycle Research and Development program (FCR&D), U.S. Department of Energy, Office of Nuclear Energy, under DOE Idaho Operations Office Contract DE-AC07-05ID14517.

Keywords

  • Actinides
  • Calorimetry
  • Lanthanides
  • TALSPEAK process
  • Thermochemistry

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