Artificial Cation-Chloride Co-Transporters for Chloride-Facilitated Lithium/Magnesium Separation

Area of Science:

• Materials Science
• Chemical Engineering
• Separation Science

Background:

• Artificial ion sieving materials are crucial for next-generation ion extraction, particularly for lithium ions (Li+).
• Constructing artificial co-transporters with complex ion-sieving properties, like those for cation-chloride transport, remains a significant challenge.
• Existing co-transporters exhibit selective ion transport but lack selectivity between specific ion pairs, hindering efficient separation.

Purpose of the Study:

• To develop a novel method for constructing artificial co-transporters with synchronized ion-sieving properties.
• To achieve high selectivity for lithium ions (Li+) extraction from complex mixtures.
• To demonstrate an improved process for lithium extraction from industrial brines.

Main Methods:

• Fabrication of a porous organic framework membrane with disordered stacking and abundant quaternary ammonium groups.
• Engineering the membrane with extremely narrow pores (~0.3 nm) and minimal surface charge for size-based selectivity.
• Utilizing the membrane's synchronized sieving property to enhance lithium ion (Li+) extraction by co-feeding chloride ions (Cl-).

Main Results:

• The artificial co-transporter membrane exhibited size-based high alkaline ion selectivity against other cations and high chloride ion (Cl-) selectivity against other anions.
• The membrane demonstrated minimal selectivity between alkaline ions and chloride ions, mimicking natural co-transporter behavior.
• Achieved high-flux (0.44 mol m-2 h-1) and high selectivity (185) for lithium ion (Li+) over magnesium ion (Mg2+) separation.
• Successfully reversed the conventional brine-based lithium extraction process by sieving Li+ before NaCl removal.

Conclusions:

• The developed porous organic framework membrane effectively functions as an artificial co-transporter.
• This approach enables efficient and highly selective lithium ion (Li+) extraction, offering a promising alternative to current industrial methods.
• The synchronized ion-sieving property is key to enhancing the extraction of high-value cations like Li+.