Lithium recovery from seawater desalination brines using ion-sieve electrospun nanofibrous membranes: the role of nanofiber design

The increasing demand for lithium (Li) necessitates sustainable extraction from alternative sources such as desalination brines. This study developed and evaluated electrospun nanofibrous membranes with lithium ion-sieves, H_1.6Mn_1.6O₄ (HMO) and H₂TiO₃ (HTO), for lithium recovery from seawater reverse osmosis (SWRO) brines. Three distinct nanofiber morphologies, namely – direct-blend, mesoporous, and electrospray – were fabricated to optimize adsorbent distribution and accessibility. Mesoporous membranes enhanced adsorption by creating accessible pores via sacrificial polymer elution, achieving 13.5 % capacity increase over powder adsorbents. Electrospray membranes, despite maximizing adsorbent surface exposure, showed a 25.6 % capacity reduction due to particle agglomeration. Static tests demonstrated HTO's higher lithium selectivity, but slower kinetics compared to HMO. Dynamic experiments revealed mesoporous HMO/PAN membranes as optimal, achieving a 82.7-fold lithium enrichment (from 0.34 to 28.11 mg L⁻¹) and a dynamic capacity of 2.11 ± 0.16 mg g⁻¹ over six cycles. Mesoporous HMO/PAN membranes were able to concentrate 3.7 times more lithium in the first cycle compared to the HMO packed bed configuration (7.78 mg L⁻¹ eluted compared to 2.12 mg L⁻¹). High separation factors (4198 for Na⁺, 4131 for Mg²⁺, 1829 for Ca²⁺, and 1113 for K⁺) underscored exceptional selectivity of the ion-sieve embedded membranes. Continuous adsorption–desorption tests confirmed the membranes’ robustness and reusability. These results demonstrate the critical role of nanofiber design in optimizing adsorption capacity, selectivity, and kinetics, enabling scalable lithium recovery from desalination brines.