Ultrathin Microporous Poly(quaternary ammonium) Membrane for Lithium Extraction and Recovery

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Efficient lithium recovery from diverse sources like salt lake brines and battery leachates is critical.
• Existing nanofiltration (NF) membranes often lack the required pH resistance and performance for these applications.
• Poly(quaternary ammonium) (PQA) membranes show promise but suffer from issues like thick layers and broad pore size distribution.

Purpose of the Study:

• To design and synthesize a novel PQA-based NF membrane with enhanced pH resistance and separation performance.
• To overcome limitations of conventional PQA membranes, such as low monomer reactivity and uncontrolled diffusion.
• To enable efficient lithium extraction from challenging industrial streams.

Main Methods:

• Development of a branched tertiary amine monomer (tris(2-dimethylaminoethyl)amine) to accelerate reaction rates.
• Incorporation of sodium dodecyl sulfate (SDS) to control monomer distribution and diffusion.
• Fabrication and characterization of the PQA-T membrane, evaluating its thickness, pore size, water permeance, and ion rejection.
• Testing the membrane's performance in separating lithium from magnesium and cobalt under various pH conditions (acidic and alkaline).
• Demonstration of large-area membrane fabrication and application in two-stage NF processes for real samples.

Main Results:

• The PQA-T membrane achieved an ultralow thickness of ~15 nm and a narrow pore size distribution.
• Exceptional water permeance (30.8 L m⁻² h⁻¹ bar⁻¹) and high MgCl₂ rejection (99.2 ± 0.4%) were obtained.
• High lithium/magnesium separation factors (S_Li/Mg up to 136) were achieved, outperforming existing membranes.
• The membrane maintained excellent separation performance under both acidic (pH 2) and alkaline (pH 10) conditions.
• Successful large-area fabrication (~625 cm²) with consistent performance was demonstrated.

Conclusions:

• The developed PQA-T membrane offers a promising solution for efficient lithium recovery from high-pH brines and acidic leachates.
• The novel monomer design and SDS incorporation effectively addressed limitations of previous PQA membranes.
• The membrane's robust performance under harsh conditions highlights its potential for industrial applications in lithium extraction and recycling.