Advancing the field of chemical separations is important for nearly every area of science and technology. Some of the most challenging separations are associated with the americium ion Am(III) for its extraction in the nuclear fuel cycle, 241 Am production for industrial usage, and environmental cleanup efforts. Herein, we study a series of extractants, using first-principle calculations, to identify the electronic properties that preferentially influence Am(III) binding in separations. As the most used extractant family and because it affords a high degree of functionalization, the polypyridyl family of extractants is chosen to study the effects of the planarity of the structure, preorganization of coordinating atoms, and substitution of various functional groups. The actinyl ions are used as a structurally simplified surrogate model to quickly screen the most promising candidates that can separate these metal ions. The down-selected extractants are then tested for the Am(III)/Eu(III) system. Our results show that π interactions, especially those between the central terpyridine ring and Am(III), play a crucial role in separation. Adding an electron-donating group onto the terpyridine backbone increases the binding energies to Am(III) and stabilizes Am−terpyridine coordination. Increasing the planarity of the extractant increases the binding strength as well, although this effect is found to be rather weak. Preorganizing the coordinating atoms of an extractant to their binding configuration as in the bound metal complex speeds up the binding process and significantly improves the kinetics of the separation process. This conclusion is validated by the synthesized 1,2-dihydrodipyrido [4,3b;5,6-b]acridine (13) extractant, a preorganized derivative of the terpyridine extractant, which we experimentally showed was four times more effective than terpyridine at separating Am 3+ from Eu 3+ (SF Am/Eu ∼ 23 ± 1).

The americium-241 ( 241 Am) radioisotope has valuable nuclear properties that find broad industrial usage. Ensuring stable supplies of 241 Am is critical for supporting (and expanding) the existing 241 Am-application space and enabling emerging 241 Amtechnologies that are important for economic growth, energy, and national security. Unfortunately, the United States halted 241 Am production in 1984 and the existing inventory was depleted in the early 2000s. This situation recently changed when the U.S. Department of Energy Isotope Program established 241 Am recovery at Los Alamos National Laboratory. Today, large-scale quantities of 241 Am are now obtained using the Chloride Extraction and Actinide Recovery (CLEAR) process. This method uses a resin that has the di-(4-t-butylphenyl)-N,N-di-iso-butylcarbamoylmethylphosphine oxide (m-CMPO) extractant adsorbed on a resin bead to harvest 241 Am from plutonium-containing waste streams. To maintain and improve CLEAR processing of 241 Am, we have evaluated the extraction of 241 Am by m-CMPO as a function of three important processing relevant variables: (1) HCl concentration, (2) metal contaminant concentration, and (3) contact time. The performance of the m-CMPO resin was additionally compared against commercially available resins, namely, rare earth (RE) resin and a selected series of diglycolamide (DGA) resins. Our results suggested that the m-CMPO resin outperformed most of the commercially available alternatives. However, tetraoctyl-DGA (TODGA) and tetraethyl-hexyl-DGA (TEHDGA) prevailed on several fronts. The TODGA and TEHDGA resins quantitatively released 241 Am at low HCl concentrations (<0.5 M), were less susceptible to deleterious side effects from metal contaminants in the mobile phase and bound 241 Am faster. Based on these results, we concluded that 241 Am recovery yields have the potential to improve if TODGA or TEHDGA is used in place of m-CMPO for large-scale CLEAR processing of 241 Am.

Improving control over radiolysis would advance nuclear technologies, spanning from radiotherapeutics to national security. Herein, we studied the effects of radiolysis on large-scale production of Am-241.