Complexation and Extraction Studies of Trivalent Actinides and Lanthanides with Water-Soluble and CHON-Compatible Ligands for the Selective Extraction of Americium
Patrik Weßling, Melina Maag, Giana Baruth, Thomas Sittel, Fynn S. Sauerwein, Andreas Wilden, Giuseppe Modolo, Andreas Geist, Petra J. Panak
Abstract
Novel hydrophilic ligands to selectively separate Am(III) are synthesized: 3,3′-([2,2′-bipyridine]-6,6′-diylbis(1H-1,2,3-triazole-4,1-diyl))bis(propan-1-ol) (PrOH-BPTD) and 3,3′-([2,2′-bipyridine]-6,6′-diylbis(1H-1,2,3-triazole-4,1-diyl))bis(ethan-1-ol) (EtOH-BPTD). The complexation of An(III) and Ln(III) with PrOH- and EtOH-BPTD is studied by time-resolved laser fluorescence spectroscopy. [ML2]3+ is found for both Cm(III) and Eu(III), while [ML]3+ is only formed with Cm(III). Stability constants show a preferential coordination of Cm(III) over Eu(III) with PrOH-BPTD being the stronger ligand. The distribution of Am(III), Cm(III), and Ln(III) between an organic phase containing the extracting agent N,N,N′,N′-tetra-n-octyl-3-oxapentanediamide (TODGA) and aqueous phases containing PrOH-BPTD is studied as a function of time and temperature as well as the TODGA, BPTD, and HNO3 concentrations. A system composed of 0.2 mol/L TODGA and 0.04 mol/L PrOH-BPTD in 0.33–0.39 mol/L HNO3 allows for selective Am(III) back-extraction into the aqueous phase while keeping Cm(III) and Ln(III) in the organic phase, marking PrOH-BPTD as an excellent complexant for an optimized AmSel process (Am(III) selective extraction).