Lithium Isotope Separation Using the 15-Crown-5 Ether System and Laboratory-Made Membranes

Area of Science:

• Materials Science
• Chemical Engineering
• Isotope Separation

Background:

• High enrichment of ⁶Li isotopes (from 7.6% to >59%) is essential for next-generation green technologies and climate change mitigation.
• Current methods for lithium isotope separation face challenges in efficiency and scalability.

Purpose of the Study:

• To develop and evaluate custom laboratory-made organic membranes for lithium isotope separation.
• To investigate the performance of non-impregnated (AI-1) and LiNTf₂-impregnated (AI-2) membranes under varying electromigration conditions.

Main Methods:

• Fabrication of two types of organic membranes: AI-1 (non-impregnated) and AI-2 (impregnated with LiNTf₂), both synthesized with ionic liquid and crown ether.
• Electromigration experiments were conducted using these membranes to separate lithium isotopes from a lithium-loaded organic phase in an aqueous solution.
• Varied parameters included applied potentials, migration time, and organic solution concentration in the anode chamber; isotope separation was analyzed using ICP-MS.

Main Results:

• AI-2 membranes showed increased ⁶Li enrichment in initial stages, with effectiveness decreasing after 25 hours.
• Lithium isotope enrichment efficiency correlated positively with applied potential, migration time, and organic solution concentration.
• A specific ionic solution (0.5 mol/L LiNTf₂ with 0.1 M TBAP in acetonitrile) significantly improved Li isotope separation compared to aqueous environments.

Conclusions:

• Laboratory-engineered membranes demonstrate the ability to impart isotope selectivity and enhance permselectivity for singly charged ions.
• Optimal conditions for migration efficiency and Li isotope separation in the catholyte were identified (minimum 9 V and 6 h migration time).
• The developed membrane technology is valuable and potentially commercially feasible for future lithium isotope research, particularly in nuclear technology.