Aqueous complexes for efficient size-based separation of americium from curium

Area of Science:

• Coordination Chemistry
• Nuclear Chemistry
• Radiochemistry

Background:

• Separating adjacent actinide ions like americium(III) and curium(III) is crucial for nuclear waste management.
• Developing selective ligands is key to efficient separation processes.

Purpose of the Study:

• To investigate the complexation of americium(III) and curium(III) using the ligand N,N'-bis[(6-carboxy-2-pyridyl)methyl]-1,10-diaza-18-crown-6 (H2bp18c6).
• To quantify and characterize the americium/curium selectivity of the H2bp18c6 ligand.

Main Methods:

• Liquid-liquid extraction and spectrophotometric titration were employed to study complex formation.
• Competitive complexation experiments were used to determine stability constants.
• Density functional theory (DFT) calculations provided insights into selectivity mechanisms.

Main Results:

• The ligand H2bp18c6 forms both fully deprotonated and monoprotonated complexes with americium(III) and curium(III).
• Stability constants revealed a reversed selectivity, with americium(III) forming more stable complexes than curium(III) (log β101 Am = 15.49, log β101 Cm = 14.88).
• The H2bp18c6 ligand exhibits the highest reported Am/Cm selectivity (4.1) for binary actinide(III)-ligand complexes.

Conclusions:

• The H2bp18c6 ligand demonstrates exceptional selectivity for americium(III) over curium(III), surpassing previously reported ligands.
• Steric constraints within the crown ether ring and enhanced 5f orbital character contribute to the ligand's size-selectivity for larger cations.
• This ligand shows significant potential for application in nuclear waste treatment and separation processes.