Selective Am(III)/Eu(III) Separation by C-N Coupling Phenanthroline-Derived Bis(pyrazole) Ligands

Area of Science:

• Nuclear Chemistry
• Radiochemistry
• Separation Science

Background:

• Separation of trivalent actinides (An(III)) from lanthanides (Ln(III)) is essential for nuclear waste management and advanced fuel cycles.
• Existing methods face challenges in achieving high efficiency and selectivity, particularly in acidic environments.

Purpose of the Study:

• To develop and evaluate novel tetradentate N-donor ligands for selective An(III)/Ln(III) separation.
• To investigate the extraction efficiency, selectivity, and coordination behavior of these ligands in acidic media.

Main Methods:

• Synthesis of four N-donor ligands (L1-L4) via C-N coupling of 2,9-dichloro-1,10-phenanthroline and pyrazole derivatives.
• Liquid-liquid extraction experiments in HNO3 media.
• Spectroscopic techniques (UV-vis titration, ESI-MS) and single-crystal X-ray diffraction for structural analysis.
• Slope analysis to determine metal-to-ligand stoichiometry.

Main Results:

• Ligands L1-L4 demonstrated exceptional Am(III) extraction efficiency and selectivity over Eu(III), with separation factors (SFAm/Eu) exceeding 220.
• A 1:1 metal-to-ligand (M/L) stoichiometry was confirmed for the extracted species.
• Stability constants for Eu(III) varied based on ligand structure, with L3 showing the highest stability, influenced by inductive effects and steric hindrance of alkyl substituents.

Conclusions:

• C-N-coupled bis(pyrazole)phenanthroline ligands are highly effective for An(III)/Ln(III) separation in acidic conditions.
• The ligand structure significantly impacts extraction performance and stability, offering a pathway for optimizing separation processes.
• These findings support the development of advanced nuclear waste treatment and recycling technologies.