(158d) Surface Modification of PEI-TMC Membrane with Oligoethers for Simultaneous Enhancement of Membrane Permeability and Li+/Mg2+ Separation

In recent years, with the rapid development of new energy vehicles and energy storage technology, the market demand for lithium resources is expected to grow sharply at a rate of 20% per year. Recovery of lithium from brines can reduce costs by 30%-50% compared to lithium extraction from ores. But the existence of high concentration of Mg²⁺ and other competing cations in the salt lake severely reduces the efficiency of lithium extraction. Positively charged nanofiltration membranes have received much attention due to their higher rejection of multivalent cations. However, the thicker selective layer and the lower affinity for lithium ions results in lower separation efficiency of the membranes. Here, PEI-P membranes with highly efficient Li⁺/Mg²⁺ separation performance are prepared by introducing highly lithophilic 4,7,10-Trioxygen-1,13-tridecanediamine (DCA) on the surface of PEI-TMC membranes using a post-modification method. Characterization and experimental results demonstrate that the introduction of DCA reduces the thickness of the active layer by about 35% and presents a unique coffee-ring structure that ensures excellent water permeability of the membrane. The ion-dipole interaction of the ether chain with Li⁺ facilitated Li⁺ transport and improved the Li⁺/Mg²⁺ selectivity (S_Li,Mg = 23.3). In a three-stage nanofiltration process treating simulated salt lake water (Mg²⁺/Li⁺ mass ratio: 40), the PEI-P membrane demonstrates the capability to decrease the Mg²⁺/Li⁺ ratio of the lake water to 0.09 and produce Li₂CO₃ with a purity surpassing 99.5%, showcasing its potential for application in lithium extraction from salt lakes.