Nanofiltration Membranes Modified with a Clustered Multiquaternary Ammonium-Based Ionic Liquid for Improved Magnesium/Lithium Separation

Abstract

Lithium separation is of great significance to overcome the lithium supply shortage resulting from a heightened demand in the energy sector. The low selectivity of polymer nanofiltration membranes for lithium extraction from concentrated Mg/Li mixtures caused by miniaturized pore structures and weak and unstable positive surface charges limits their practical implementation. To address the surface charge strength and stability, a novel ionic liquid monomer, N1-(6-aminohexyl)-N1,N1,N6,N6,N6-pentamethylhexane-1,6-diaminium bromide (denoted as DABIL), is first synthesized and covalently anchored on a pristine polyamide thin-film composite (TFC) membrane via a secondary amidation reaction for improved selective lithium separation from Mg/Li mixtures. DABIL modification of the polyamide network contributes to increased surface hydrophilicity, an enlarged membrane pore structure, and reinforced Donnan exclusion effects. Molecular dynamics simulation confirmed that the difference of the interaction energies between water and the multication groups dominates the surface properties. The DABIL membrane exhibits sixfold enhancement of water permeability compared to the unmodified membrane and outperforms the recently reported state-of-the-art positively charged membranes. It presents an improved Li+/Mg2+ selectivity of 26.49, suggesting the membranes’ potential for lithium recovery. Moreover, the membrane shows efficient antibacterial activity for mitigating biofilm formation. We establish that functionalization of TFC membranes with ionic liquids containing multication side chains could be a promising approach to achieve improved and sustainable permselectivity for the recovery of critical metal resources.

Lithium Pyrene Squarate Covalent Organic Frameworks for Efficient Lithium and Magnesium Separation from Salt Water

“…Various membrane-based technologies like membrane electrodialysis, reverse osmosis, liquid-based or supported membranes, and nanofiltration methods have been investigated to separate Mg 2+ and Li + ions from each other. The current state-of-the-art methods for the separation of Mg 2+ /Li + require large amounts of harmful and corrosive chemicals, produce significant waste materials, and are energy-intensive throughout the process. − Finding a sustainable solution to separate the two similar ions while using less solvent and producing less waste is desirable.…”

“…9,10 The techniques currently used for Li + mining from salt-lake brines containing high Mg 2+ -to-Li + ratios include calcination, adsorption, and extraction. 11 Various membrane-based technologies like membrane electrodialysis, reverse osmosis, liquid-based or supported membranes, and nanofiltration methods have been investigated to separate Mg 2+ and Li + ions from each other. The current state-of-the-art methods for the separation of Mg 2+ /Li + require large amounts of harmful and corrosive chemicals, produce significant waste materials, and are energy-intensive throughout the process.…”

Ionic liquids membranes for liquid separation: status and challenges

“…The addition of DABIL allowed for the creation of a nanoheterogeneous microenvironment, leading to improved local ion concentration and membrane properties such as hydrophilicity, water permeance, selectivity, and antimicrobial properties. 100 Moreover, the bis-quaternary ammonium salt (QEDTP), multiamino quaternary ammonium salt (3,5-dimethylhydrazide-benzyl trimethyl ammonium bromide, DHTAB), and triquaternary ammonium-based ionic liquid (TQAIL) were also used for the preparation of ILPMs. 97,101,102 ILs modification introduces nanoscale structural heterogeneity, which improves the surface hydrophilicity of the membrane and reduces internal resistance within the selective layer.…”

“…152 Soyekwo and coworkers figured out the effect of the concentration of DABIL on the properties of the membranes, which affected the roughness, hydrophilicity, charge, and further stability in the separation process. 100 In general, the larger the mass fraction of ILs, the less the proportion of the support skeleton, thus resulting in decreasing stability. Thus, further work is expected to balance the loading amount of IL, separation performance, and stability.…”

Electric Field-Driven Ultraefficient Li+/Mg2+ Separation through Graphyne Membrane

“…Recently, the emerging membrane technology has attracted great attention in the lithium extraction field and has been widely used as an effective separation method to recover lithium due to its advantages of low-energy cost, easy operation, and high efficiency. − For example, Li et al synthesized a high positively charged nanofiltration membrane through interfacial polymerization, and the obtained membrane with an average pore size of 4.76 Å was employed to conduct Mg 2+ /Li + separation under an electric field. It is found that the membrane can almost completely reject Mg 2+ ions and fulfill a high permeance of 0.55 mol·m –2 ·h –1 for Li + ions, with a separation factor S Li/Mg up to 7199.…”