Alkaline high-level waste (HLW) has been generated and stored in underground tanks at the Hanford Site and the Savannah River Site (SRS) for over 50 years. At SRS, HLW is currently treated in two sequential processes: i) Actinide Removal Process (sorption of 90Sr and actinides (An) by monosodium titanate) and ii) Caustic-Side Solvent Extraction process (CSSX; extraction of 137Cs by calixarenes), which was invented at ORNL. Modification of CSSX process by adding new organic ligands containing soft donor sites for combined Cs and An separation from the HLW stream into the organic phase could potentially make the HLW separation process faster and more economical. In this context, we are proposing scorpionate-type tripodal sulfonamide and pyrazole ligands based on alkylaromatic frameworks, with proper N-binding site orientation, thus providing a versatile and robust platform for An(III) complexation. The ligands have various alkyl (ethyl, iso-propyl, tert-butyl, n-decyl) substituents on the aniline or pyrazole components, which significantly improve their lipophilicity and potential applicability for extraction and removal of An from alkaline aqueous media. Binding and extraction of lanthanides in chlorinated organic solvents by some of these ligands has been confirmed by ICP-OES, fluorescence, and NMR titration experiments. DFT calculations of the M(III)-trisulfonamide complexes indicated cation-π interactions with both Sm(III) and Am(III), and shorter bond distances for Am-N bonds compared to Sm-N bonds. We eventually aim to modify these ligands further for compatibility with the CSSX solvent and its components, and test them for combined extraction of Cs and An.

Trivalent f-metal coordination and extraction by tripodal sulfonamide ligands and analogs

253rd National Meeting (2017)

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