Membrane technologies for Li+/Mg2+ separation from salt-lake brines and seawater: A comprehensive review

Recent years have seen rapid improvement of technology and large-scale applications of lithium-ion batteries, which leads to an increasing market demand for lithium. Since the land lithium resources are diminishing drastically, the sources of lithium extraction have shifted to the large amount of water resources containing salt-lake brines and seawater. Among the varieties of aqueous recovery approaches, membrane technology seems to have huge development potential and good application prospect. This is because the membrane technologies exhibit excellent Li/Mg separation selectivity, with low energy consumption and green process owing to no addition of chemicals. The present work reviews the latest advances in various membrane technologies, including nanofiltration membrane, electrodialysis, membrane capacitive deionization approaches, solid electrolyte electrolysis-based technology, etc. The recent developments in positively charged nanofiltration membrane are discussed in terms of the preparation methods, membrane properties, and Li/Mg separation coefficient. In addition, the effects of several factors on electrodialysis for lithium extraction and relevant mechanisms in both simple and actual saline systems are discussed, including applied voltage, VC/VD, and coexisting ions. The applications of electrodialysis with novel selective membrane involving nanofiltration membrane as well as solid electrolyte membrane and perspectives for further investigation are proposed.