The structures of CyMe4-BTBP complexes of americium(III) and europium(III) in solvents used in solvent extraction, explaining their separation properties
Artikel i vetenskaplig tidskrift, 2015

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.

ligands

thermodynamics

radiolytic stability

btbp

actinide(iii)/lanthanide(iii) separation

lanthanides

donor

Chemistry

quadridentate

diluents

actinides

sanex

Författare

Christian Ekberg

Chalmers, Kemi och kemiteknik, Energi och material, Kärnkemi

Elin Löfström Engdahl

Chalmers, Kemi och kemiteknik, Energi och material, Kärnkemi

Emma Aneheim

Chalmers, Kemi och kemiteknik, Energi och material, Kärnkemi

Mark Foreman

Chalmers, Kemi och kemiteknik, Energi och material, Kärnkemi

A. Geist

Karlsruher Institut für Technologie (KIT)

D. Lundberg

Sveriges lantbruksuniversitet (SLU)

M. Denecke

University of Manchester

I. Persson

Sveriges lantbruksuniversitet (SLU)

Dalton Transactions

1477-9226 (ISSN) 1477-9234 (eISSN)

Vol. 44 18395-18402

Ämneskategorier

Subatomär fysik

DOI

10.1039/c5dt02859k

PubMed

26426842