Cooperative Lanthanide Solvation in an Ionic Liquid for Critical Materials Separations

Area of Science:

• Materials Science
• Separation Science
• Coordination Chemistry

Background:

• Critical material separation, particularly lanthanides, is essential for numerous applications.
• Liquid-liquid extraction (LLE) is the standard method, with selectivity influenced by metal coordination.
• Ionic liquids (ILs) offer unique solvent properties for enhanced extraction.

Purpose of the Study:

• To investigate the coordination behavior of Europium (Eu) with a malonamide extractant in an ionic liquid (IL).
• To elucidate the role of the IL anion and extractant in Eu solvation during liquid-liquid extraction.
• To understand the structural basis for improved extraction efficiency in IL-based systems.

Main Methods:

• Systematic titrations of water and extractant concentrations.
• Time-resolved fluorescence spectroscopy for coordination analysis.
• Extended X-ray fine structure (EXAFS) spectroscopy for coordination number determination.
• Molecular dynamics (MD) simulations for structural insights.

Main Results:

• Observed cooperative solvation of Eu by both the malonamide extractant and the IL anion.
• Confirmed strong extractant coordination and no water coordination in the extracted Eu complex.
• Determined a coordination number of 10 for Eu, including IL anion coordination.
• MD simulations corroborated EXAFS findings and revealed IL anion participation.

Conclusions:

• Eu solvation involves both extractant and IL anion, leading to a water-free coordination sphere.
• IL anion coordination, despite weaker ligand strength, enhances Eu extraction efficiency in LLE.
• Tuning metal coordination within unique IL solvent systems presents opportunities for optimizing critical material separations.