Electric field-assisted positively charged nanofiltration membranes for efficient Mg2+/Li+ separation

Electric field-assisted nanofiltration (ENF) has emerged as a promising technology for Mg 2+ /Li + separation from salt lake brines. However, integrating ENF process with widely used negatively charged membranes induces a non-uniform distribution of reconstructed positive charge. This leads to reduced separation efficiency under high feed concentrations due to charge shielding effects. To overcome this limitation, we developed a strategy employing a positively charged nanofiltration (NF) membrane under an applied electric field. This configuration facilitates both the dehydration of hydrated Li + and a more uniform distribution of positive charges on the membrane surface. The optimized system demonstrated a remarkable separation performance, achieving nearly 100% rejection of Mg 2+ and − 176% rejection of Li + . The separation factor ( S Li, Mg ) represents a 162-fold improvement over the system without an electric field. The ENF process successfully separated Mg 2+ and Li + even in real Yiliping salt lake brine. Furthermore, the permeate stream containing high-purity Li + enabled the production of battery-grade Li₂CO₃ with 99.9% purity. This study demonstrates a pragmatic and efficient approach for Mg 2+ /Li + separation, showcasing considerable promise for high-purity Li + extraction from salt lakes.