Separation of Lithium Ions from Aqueous Solutions Using Membrane Aided Separation Techniques

Abstract

Lithium production is crucial for sustainable development. Lithium ions have been used in battery technology, ceramics, and polymer production. Membrane processes like reverse osmosis and electrodialysis are trending for lithium recovery. However, high energy consumption is still a challenging problem in lithium recovery. To reduce the cost and membrane fouling, the present study focused on the development of PAN-Fe₂O₃ membranes. The chemical structure, surface morphology, and chemical compounds of a commercial HPA50 membrane and fabricated PAN-Fe₂O₃ membranes were characterized by XRD, SEM and FTIR respectively. Lithium ions are separated by micellar enhanced ultrafiltration with sodium dodecyl sulfate (SDS) surfactant employing commercial hydrophilized polyamide membrane and PAN membranes blended with varying concentrations of iron nanoparticles (0.005%, 0.01%, and 0.1%). Experiments were conducted by varying the feed concentration and operating pressure. The chemical structure was confirmed by XRD analysis, which showed peaks at 20°, 23°, and 25° for HPA50 membrane at 18°, 23°, and 26° for PAN-Fe₂O₃ membranes. FTIR analysis identified amide functional groups for the HPA50 membrane and nitrile groups for PAN-Fe₂O₃ membranes. Additionally, SEM analysis confirmed the uniform and stable attachment of particles on the surface of both HPA50 and PAN-Fe₂O₃ membranes. HPA50 membrane, utilized for lithium-ion separation, exhibited rejection rates of 40%, 85%, and 83.9% at operating pressures of 0 bar, 1 bar, and 2 bar, respectively, when employed with a LiCl aqueous feed solution. Subsequently, experiments conducted with LiCl and SDS surfactant yielded higher rejection rates of 89.40%, 93%, and 83.90%. There is no rejection observed in PAN-Fe₂O₃ membranes due to large pore sizes. The HPA50 membrane rejection rates indicate that the separation of Li⁺ ions from pure aqueous solutions is more difficult than the separation from divalent ions in mixed solutions.  ICP-MS of reject samples showed a higher peak area, indicating separation. Addition of SDS to the feed with HPA50 membrane enhanced lithium ion rejection. PAN-Fe₂O₃ membranes are found to be ineffective due to large pore sizes for concentrating lithium ions.