The solvent-based extraction of used nuclear fuel uses designer ligands dissolved in an organic phase to extract ligand-complexed metal ions from an acidic aqueous phase. These extractions will be performed in highly radioactive environments, and quantitatively understanding the radiation chemistry of these complexants and their diluents is essential in determining extraction efficiency, separation factors, and solvent-recycle longevity. Although there has been considerable effort investigating ligand damage occurring in acidic water radiolysis conditions, only minimal fundamental kinetic and mechanistic data has been reported for the degradation of extraction ligands in the organic phase. The radiolysis of organic diluents (dodecane, TPH, kerosene) produces a mixture of radical cations (R●+), carbon-centred radicals (R●), solvated electrons (e-solv), and molecular products such as hydrogen (H2). Typically, the radical species and electrons will react with the dissolved oxygen present to produce relatively inert peroxyl radicals. The alkane radical cation species, R●+, thus is the major radiolytically-produced species that can react with, and degrade, extraction agents in this phase. Recently, we have performed kinetic studies for organic radical cation reactions with various nitrogen-containing ligands. Fast kinetics were observed for dodecane radical cations, highlighting the importance of this mechanistic pathway. Minimal impact on acid-contact was found for these kinetics. We report here kinetic parameters for a wide variety of diluents and ligands which will allow a full, fundamental, understanding of the impact of radiation on solvent extraction based separation processes to be achieved.

Role of organic radical cation chemistry in separation ligand degradation

253rd National Meeting (2017)

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