Solvent Extraction Separation of Trivalent Americium from Curium and the Lanthanides

Abstract

The sterically constrained, macrocyclic, aqueous soluble ligand N,N′-bis[(6-carboxy-2-pyridyl)methyl]-1,10-diaza-18-crown-6 (H₂BP18C6) was investigated for separating americium from curium and all the lanthanides by solvent extraction. Pairing H₂BP18C6, which favors complexation of larger f-element cations, with acidic organophosphorus extractants that favor extraction of smaller f-element cations, such as bis-(2-ethylhexyl)phosphoric acid (HDEHP) or (2-ethylhexyl)phosphonic acid mono(2-ethylhexyl) ester (HEH[EHP]), created solvent extraction systems with good Cm/Am selectivity, excellent trans-lanthanide selectivity (K_ex,Lu/K_ex,La = 10⁸), but poor selectivity for Am against the lightest lanthanides. However, using an organic phase containing both a neutral extractant, N,N,N’,N’-tetra(2-ethylhexyl)diglycolamide (TEHDGA), and HEH[EHP] enabled rejection of the lightest lanthanides during loading of the organic phase from aqueous nitric acid, eliminating their interference in the americium stripping stages. In addition, although it is a macrocyclic ligand, H₂BP18C6 does not significantly impede the mass transfer kinetics of the HDEHP solvent extraction system.

Keywords:

• americium
• curium
• actinide-lanthanide separation
• crown-ether

Additional information

Funding

Work at Argonne (contract number DE-AC02-06CH11357) and University of Wisconsin–Milwaukee was supported by the U.S. Department of Energy, Assistant Secretary of the Office of Nuclear Energy, Fuel Cycle Research and Development Program. Adrián Roca-Sabio, Andrés de Blas, and Teresa Rodríguez-Blas thank Xunta de Galicia (CN 2012/011) for generous financial support.