Actinide Binding by Kläui Ligands: REDOX Speciation and Sorption on an Extraction Chromatography Resin

Journal Article · Mon Dec 01 04:00:00 EST 2008 · Radiochimica Acta, 96(12):805-815

DOI:https://doi.org/10.1524/ract.2008.1524· OSTI ID:949926

Levitskaia, Tatiana G; Sinkov, Sergey I; Lumetta, Gregg J

The sorption of Eu(III) and actinide ions in various oxidation states from nitric acid solutions by an extraction chromatography resin containing 1 wt% of the Kläui ligand Cp*Co[P(O)(OR)2]3– [Cp* = pentamethylcyclopentadienyl, R = –CH2 CH2CH3] on Amberlite® XAD-7HP was examined. At 0.3 M HNO3 and a metal-to-ligand ratio of 0.07, the relative affinity of the resin for the ions investigated followed the order: tetravalent >> hexavalent > trivalent > pentavalent; however, the relative affinity for the trivalent and hexavalent ions can be reversed, depending on the extent of ligand loading and the nitric acid concentration. The sorption of the tetravalent ions was exceptionally strong in the entire range of nitric acid concentration examined (0.2 to 8 M HNO3). Resin samples loaded with various actinide ions were examined spectrophotometrically. No Np(V) and Pu(III) species were identified on the resin; rather, reduction-oxidation (REDOX) reactions occurred during equilibration, resulting in their complete conversion to M(IV) species bound by the Kläui ligand. Similarly, the sorption behavior of Pu(VI) and Np(VI) was complicated by their reduction to M(IV) upon sorption. The observed REDOX processes were apparently driven by the extremely high affinity of the Kläui ligand for the tetravalent ions. The acid-base properties of the methyl derivative of the Kläui ligand were investigated in aqueous solution, and its pKa was found to be highly dependent upon the solution ionic strength. The binding constants of this ligand with various actinide ions measured in a mixed methanol/carbon tetrachloride solvent exhibited qualitative agreement with the sorption selectivity trends.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 949926
• Report Number(s): PNNL-SA-58447; NN2001000
• Journal Information: Radiochimica Acta, 96(12):805-815, Journal Name: Radiochimica Acta, 96(12):805-815 Journal Issue: 12 Vol. 96; ISSN RAACAP; ISSN 0033-8230
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
ACTINIDES
AFFINITY
EUROPIUM
EXTRACTION CHROMATOGRAPHY
Kläui ligand
LIGANDS
NEPTUNIUM
PLUTONIUM
REDOX REACTIONS
RESINS
SORPTION
UV-vis spectral characterization
VALENCE
actinide complexes
separation
sorption