Characterizing Extraction Chromatography for Large-Scale Americium-241 Processing

The americium-241 (241Am) radioisotope has valuable nuclear properties that find broad industrial usage. Ensuring stable supplies of 241Am is critical for supporting (and expanding) the existing 241Am-application space and enabling emerging 241Am-technologies that are important for economic growth, energy, and national security. Unfortunately, the United States halted 241Am 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 241Am recovery at Los Alamos National Laboratory. Today, large-scale quantities of 241Am 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 241Am from plutonium-containing waste streams. To maintain and improve CLEAR processing of 241Am, we have evaluated the extraction of 241Am 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 241Am at low HCl concentrations (<0.5 M), were less susceptible to deleterious side effects from metal contaminants in the mobile phase and bound 241Am faster. Based on these results, we concluded that 241Am recovery yields have the potential to improve if TODGA or TEHDGA is used in place of m-CMPO for large-scale CLEAR processing of 241Am.