Nanofiber Production Equipment| Lithium recovery from seawaterdesalination brines using ion-sieveelectrospun nanofibrous membranes: therole of nanofiber design

Professor Wang Rong's Team at Nanyang Technological University Singapore: Electrospun Nanofiber Membranes Integrated with Lithium Ion-Sieves for Efficient Lithium Extraction from Desalination Brine

With the surging demand for lithium resources from electric vehicles, grid energy storage systems, and portable electronics, conventional lithium extraction methods are increasingly facing bottlenecks in both production capacity and environmental sustainability. Meanwhile, global desalination plants discharge approximately 150 million cubic meters of brine daily, containing lithium concentrations about twice that of seawater (0.34 ppm). However, efficient lithium separation and recovery have remained challenging due to interference from competing ions such as sodium, magnesium, calcium, and potassium.

Professor Wang Rong's team innovatively combined electrospun nanofiber membranes with lithium ion-sieves to construct a separation platform with exceptional selectivity and flux performance, demonstrating remarkable advantages in extracting trace lithium from brine. This breakthrough may open new pathways for sustainable lithium resource development.

Recently, Professor Wang Rong's team at the Singapore Membrane Technology Centre (SMTC) of Nanyang Technological University published their latest research in Chemical Engineering Journal, titled "Lithium recovery from seawater desalination brines using ion-sieve electrospun nanofibrous membranes: the role of nanofiber design". The study focuses on efficient lithium recovery from desalination brine using ion-sieve electrospun nanofibrous membranes, with in-depth investigation of the critical role of nanofiber structural design in selective separation processes. Doctoral candidate Naeem Nadzri served as first author, with Dr. Lin Yujie as co-first author.The research team utilized electrospinning technology to prepare self-supporting, lightweight, and highly elastic fibrous membranes, embedding two lithium-selective materials - H1.6Mn1.6O4 (HMO) and H₂TiO₃ (HTO) - into polyacrylonitrile (PAN)-based composite membranes. To investigate the impact of different fiber structures on lithium recovery performance, the team designed and evaluated three heterogeneous membrane types: Direct blending (DB), Mesoporous (MP), and Electrospin-electrospray (ES) (Fig. 1).Among these, the mesoporous HMO/PAN membrane demonstrated superior lithium adsorption performance due to its optimized pore structure and highly distributed active sites, outperforming traditional powder-packed bed methods in both capacity and selectivity. This study provides new insights for efficient lithium recovery from desalination brine and may advance sustainable lithium utilization technologies.

Fig. 1. Schematic diagrams of three nanofiber membrane structures: Direct blending (DB), Mesoporous (MP), and Electrospin-electrospray (ES).

The mesoporous membrane, formed by adding structural pore-forming agents, features larger and clearer pore channels that significantly enhance lithium ion transport pathways and contact area. Its adsorption capacity increased by 3.7 times compared to traditional powder materials, achieving an 82.7-fold lithium enrichment effect in initial testing while maintaining high selectivity against competing ions (Na⁺, Mg²⁺, Ca²⁺, K⁺). Multi-cycle tests further verified its excellent reusability and large-scale application potential.

Fig. 2. Structural morphology comparison of blank PAN membrane with three electrospun membrane types (DB, MP, ES).

The DB membrane was prepared by directly blending adsorbents into the electrospinning solution. Due to thicker fiber shells and larger overall fiber diameter, some adsorbents became embedded within the fibers, preventing effective contact between most active sites and the solution, thereby affecting adsorption performance (Fig. 2).The MP membrane introduced PVP-type pore-forming agents into the system, followed by chemical cleaning and heat treatment to form distinct macroporous structures (Fig. 2d), significantly increasing total adsorption area and lithium ion transport channels.The ES membrane adopted a bilayer design, with adsorbents uniformly distributed on the first PAN support membrane surface via electrospraying, using fine glass fiber beads formed by electrospinning low-concentration PAN solution as the support layer. Although the ES membrane exposed the most surface adsorbents, particle aggregation reduced its effective adsorption area. SEM statistics (Fig. 2f) showed an average fiber diameter of 1969 nm.Elemental analysis confirmed successful embedding of lithium-selective adsorbents HMO and HTO into all membrane structures.

Fig. 3. Comparison of lithium elution performance among HMO, HTO membranes and packed bed components after first-cycle testing.

 After continuous treatment of seawater reverse osmosis (SWRO) brine, lithium-enriched membrane components were regenerated using 0.5 M hydrochloric acid to obtain concentrated lithium eluate.

Results showed the mesoporous HMO/PAN membrane exhibited optimal elution capability, with lithium concentration reaching 7.78 mg/L, significantly outperforming traditional packed beds (2.12 mg/L) and other membrane types (Fig. 3). These results not only verify its exceptional adsorption performance but also highlight its outstanding lithium desorption and enrichment capabilities under real application conditions.In contrast, electrospray membranes showed weakest elution effects due to surface adsorbent aggregation and insufficient active site exposure. HTO-based membranes generally underperformed HMO-based membranes in lithium recovery efficiency.

Fig. 4. Multi-cycle adsorption-elution stability and lithium selectivity analysis of mesoporous HMO/PAN membrane.

The mesoporous HMO/PAN membrane maintained excellent lithium recovery performance through six consecutive adsorption-elution cycles, demonstrating outstanding operational stability and ion selectivity (Fig. 4b). Throughout the process, eluted lithium concentration remained stable with minimal performance degradation. The separation factors of Li⁺ relative to Na⁺, Mg²⁺, Ca²⁺, and K⁺ remained consistently high, reflecting excellent selective separation capability (Fig. 4d).Furthermore, the Bohart-Adams model's predicted dynamic adsorption capacity closely matched experimental results, further validating the membrane's reliability in continuous operation. These results fully demonstrate the membrane's excellent cycling stability, making it highly suitable for integration into desalination systems for efficient, sustainable lithium resource recovery.This study emphasizes the critical role of nanofiber structure in enhancing lithium recovery efficiency. These membrane materials are not only lightweight and scalable for production but can also be efficiently coupled with existing desalination processes, providing a novel solution for low-energy, high-selectivity lithium extraction.

Paper link: https://doi.org/10.1016/j.cej.2025.162886