Extraction of lithium from Chinese salt-lake brines by membranes: Design and practice

Interests on lithium extraction from the Chinese salt-lake brines have regained momentum due to the growing demand of lithium for application in electric vehicles. Characterized by a high Mg2+/Li+ ratio (MLR), the Chinese salt-lake brine has troubled scientists and engineers for decades. Recent progress has shown significant advantages of membrane technologies. This review summarizes the membrane technologies utilized for lithium extraction, including membrane extraction (ME), nanofiltration (NF), lithium ion-sieve (LIS), electrodialysis (ED), and forward osmosis (FO). The fundamental concepts and separation mechanisms of ME and chemical exchange are introduced. Positive NF membranes, ion-selective ED membranes are discussed in detail in terms of materials design for high permselectivity. Maintaining the high selectivity and adsorption capacity are discussed for LIS membranes. Solutions to design single ion-selective separation membranes by hybrid of mobility and affinity are discussed for the urgent lithium extraction problem. Carbon neutral FO is proposed for the concentration of lithium-enriched brines with a focal on a low structure parameter substrate and a high rejection for highly saline brine. The fundamental and engineering strategies for lithium extraction from high MLR brine will be of strong interest for the harvesting of valuable metal resources from complicated brine.