Recent advances in magnesium/lithium separation and lithium extraction technologies from salt lake brine

Over the past few decades, the demand for lithium resources has increased significantly with the rapid development and extensive application of lithium-ion batteries. Extracting lithium from salt lake brine is of significance because of its abundance in brines. Numerous endeavours have addressed the challenges of magnesium/lithium separation from salt lake brines having high Mg/Li ratios with the aim of efficiently and sustainably recovering lithium resources. This review focuses on the latest advances in magnesium/lithium separation and lithium recovery from salt lake brines, including extraction, adsorption, membrane, and electrochemical methods as well as reaction-coupled separation technology. The features and adaptabilities of various methods are analysed from the viewpoint of the chemical structures of related materials, reaction mechanisms, properties, and applications. Among the available techniques, adsorption methods have great potential to be widely used. However, membrane methods have attracted attention owing to their low energy consumption and high separation rates; the advantages and limitations of nanofiltration, electrodialysis, bipolar membranes, and membrane capacitive deionisation are therefore summarised in this review. As representative electrochemical methods, the lithium ion capturing system and the rocking-chair battery system are reviewed, and the roles of various electrode materials in lithium recovery are analysed. Recently, reaction-coupled separation technology has emerged as an advantageous method for magnesium/lithium separation and lithium extraction. The ability of this technology to realise highly efficient magnesium/lithium separation while simultaneously preparing high-value magnesium-based functional materials from magnesium resources is discussed. The development of such methods that can comprehensively utilise the magnesium and lithium resources in salt lake brine is essential for resource sustainability.