Extraction, Characterization, and Stability Studies of Bistriazinyl-Derived Carboxylic Acids

Area of Science:

• Nuclear Chemistry and Materials Science
• Radiochemical Separation Processes

Background:

• Recycling used nuclear fuel (UNF) requires efficient separation of An(III) and Ln(III) ions.
• Development of novel CHON (carbon, hydrogen, oxygen, nitrogen) ligands is crucial for waste-free secondary waste production.
• Existing separation processes often rely on sulfonated analogues with potential waste generation.

Purpose of the Study:

• To evaluate the efficacy of a new water-soluble bistriazinyl-octa-carboxylic acid ligand, BTPOA, for selective An(III)/Ln(III) ion separation.
• To investigate the complexation behavior and stability of BTPOA with Cm(III) and Eu(III) ions.
• To assess the radiolytic stability of BTPOA under conditions relevant to UNF reprocessing.

Main Methods:

• Solvent extraction experiments to determine BTPOA's selectivity for Am(III) over Eu(III).
• Potentiometric and time-resolved laser-induced spectroscopy to study metal-ligand complexation and determine stability constants in HClO4 and HNO3 media.
• Electron pulse irradiation to measure absolute rate coefficients for BTPOA's reactions with major UNF radiolysis products.

Main Results:

• BTPOA demonstrated high selectivity for Am(III) over Eu(III) ions, showing good extraction efficiency.
• Complexation studies revealed stepwise formation of Cm(III)-BTPOA species (1:1, 1:2, 1:3) in HClO4 and multiple complexes in HNO3, with stability constants comparable to SO3-Ph-BTP.
• Rate coefficients for BTPOA reactions with hydrated electrons, H atoms, and OH/NO3 radicals were determined, indicating increased radiolytic stability in HNO3.

Conclusions:

• BTPOA is a promising CHON ligand for selective Am(III)/Cm(III) separation in UNF recycling, offering a potential waste-free alternative.
• The ligand exhibits favorable complexation behavior and stability, comparable to existing sulfonated analogues.
• BTPOA's radiolytic stability is enhanced in nitric acid media, suggesting its suitability for reprocessing environments.