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The structures of CyMe4-BTBP complexes of americium(III) and europium(III) in solvents used in solvent extraction, explaining their separation properties

Christian Ekberg (Institutionen för kemi och kemiteknik, Kärnkemi) ; Elin Löfström Engdahl (Institutionen för kemi och kemiteknik, Kärnkemi) ; Emma Aneheim (Institutionen för kemi och kemiteknik, Kärnkemi) ; Mark Foreman (Institutionen för kemi och kemiteknik, Kärnkemi) ; A. Geist ; D. Lundberg ; M. Denecke ; I. Persson
Dalton Transactions (1477-9226). Vol. 44 (2015), 42, p. 18395-18402.
[Artikel, refereegranskad vetenskaplig]

Separation of trivalent actinoid (An(III)) and lanthanoid (Ln(III)) ions is extremely challenging due to their similar ionic radii and chemical properties. Poly-aromatic nitrogen compounds acting as tetradentate chelating ligands to the metal ions in the extraction, have the ability to sufficiently separate An(III) from Ln(III). One of these compounds, 6,6'-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzol[1,2,4]triazin-3-y l)-[2,2]bipyridine, CyMe4-BTBP, has proven to be resistant towards acidic environments and strong radiation from radioactive decomposition. EXAFS studies of the dicomplexes of CyMe4-BTBP with americium(III) and europium(III) in nitrobenzene, cyclohexanone, 1-hexanol, 1-octanol and malonamide (DMDOHEMA) in 1-octanol have been carried out to get a deeper understanding of the parameters responsible for the separation. The predominating complexes independent of solvent used are [Am(CyMe4-BTBP)(2)(NO3)](2+) and [Eu(CyMe4-BTBP)(2)](3+), respectively, which are present as outer-sphere ion-pairs with nitrate ions in the studied solvents with low relative permittivity. The presence of a nitrate ion in the first coordination sphere of the americium(III) complex compensates the charge density of the complex considerably in comparison when only outer-sphere ion-pairs are formed as for the [Eu(CyMe4-BTBP)(2)](3+) complex. The stability and solubility of a complex in a solvent with low relative permittivity increase with decreasing charge density. The [Am(CyMe4-BTBP)(2)(NO3)](2+) complex will therefore be increasingly soluble and stabilized over the [Eu(CyMe4-BTBP)(2)](3+) complex in solvents with decreasing relative permittivity of the solvent. The separation of americium(III) from europium(III) with CyMe4-BTBP as extraction agent will increase with decreasing relative permittivity of the solvent, and thereby also with decreasing solubility of CyMe4-BTBP. The choice of solvent is therefore a balance of a high separation factor and sufficient solubility of the CyMe4-BTBP ligand.

Nyckelord: radiolytic stability, actinide(iii)/lanthanide(iii) separation, donor, ligands, lanthanides, sanex, actinides, diluents, btbp, thermodynamics, quadridentate, Chemistry

Denna post skapades 2015-11-20. Senast ändrad 2015-12-11.
CPL Pubid: 226105


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Institutionen för kemi och kemiteknik, Kärnkemi



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