Two-phase calorimetry. II. studies on the thermodynamics of cesium and strontium extraction by mixtures of H+CCD- and PEG-400 in FS-13

P. R. Zalupski, R. S. Herbst, L. H. Delmau, L. R. Martin, D. R. Peterman, K. L. Nash

Research output: Contribution to journalArticlepeer-review

21 Scopus citations

Abstract

Thermochemical characterization of the partitioning of cesium and strontium from nitric acid solutions into mixtures of the acid form of chlorinated cobalt dicarbollide (H+CCD-) and polyethylene glycol (PEG-400) in FS-13 diluent has been completed using isothermal titration microcalorimetry and radiotracer distribution methods. The phase transfer reaction for Cs+ is a straightforward (H+ for Cs+) cation exchange reaction. In contrast, the extraction of Sr2+ does not proceed in the absence of the co-solvent molecule PEG-400. This molecule is believed to facilitate the dehydration of the Sr2+ aquo cation to overcome its resistance to partitioning. The phase transfer reactions for both Cs+ and Sr2+ are enthalpy driven (exothermic), but partially compensated by an unfavorable entropy. The results of the calorimetry studies suggest that the PEG-400 functions as a stoichiometric phase transfer reagent rather than acting simply as a phase transfer catalyst or phase modifier. The calorimetry results also demonstrate that the extraction of Sr2+ is complex, including evidence for both the partitioning of Sr(NO3)+ and endothermic ion pairing interactions in the organic phase that contribute to the net enthalpic effect. The thermodynamics of the liquid-liquid distribution equilibria are discussed mainly considering the basic features of the ion solvation thermochemistry.

Original languageEnglish
Pages (from-to)161-183
Number of pages23
JournalSolvent Extraction and Ion Exchange
Volume28
Issue number2
DOIs
StatePublished - Mar 2010

Funding

Work by PRZ was supported under subcontract number 11W-2452-0742 with the Idaho National Laboratory, the Laboratory Director’s Research and Development program.

Keywords

  • Calorimetry
  • Cesium
  • Chlorinated cobalt dicarbollide
  • FS-13
  • Polyethylene glycol
  • Solvent extraction
  • Strontium
  • Thermochemistry

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