Present situation of salt-lake lithium resources and research progress of lithium extraction technology

Motivated by the electric vehicle revolution, the demand for lithium (Li) has significantly increased during the last decade. Li is the key strategic resource in energy structure transformation to be extensively employed in several fields, such as new energy vehicles, electronic products, and energy storage. For sustainable Li supply, developing cost-effective and green methods to extract Li from various sources is urgently needed. Due to the abundant reserves and low cost, the recovery of Li from salt-lake brines has garnered immense attention globally. China is rich in salt-lake resources; among them, brine Li resources are mainly distributed in Qinghai and Xizang, but the separation is difficult because of low concentration and high Mg/Li ratio. Moreover, the composition of salt lakes in different regions varies, and the poor technical universality restricts the development of Li extraction from salt lakes in China. This review summarizes the major developments in Li recovery from brines. An overview of the Li distribution, endowment characteristics, extraction methods, and development direction is presented, concentrating on the mechanisms, operation and development of precipitation, solvent extraction, adsorption, membrane separation, and electrochemical Li extraction. The advantages and disadvantages, separation effects, and applicable conditions of the extraction methods are examined. Although the prevalent precipitation, extraction, and adsorption methods are appropriate for the mass extraction of Li from brine sources with low Mg/Li ratios, they are not ecofriendly and typically show low Li recovery. For example, precipitation and extraction methods have issues with large dosages of chemicals and severe environmental effects; meanwhile, adsorption methods have drawbacks of intensive water use and easy dissolution of adsorbents, greatly limiting industrial application. The emerging membrane separation and electrochemical methods have good separation effects, limited requirements for additional chemicals, minimal waste production, wide applicability, and outstanding performance in Mg/Li or Na/Li separation, thereby demonstrating broad application prospects. However, these methods are limited by the poor technical maturity for large-scale lithium recovery. We underscore the most pressing challenges that these technologies encounter, including limited electrode capacity, poor electrode stability, and limited Li selectivity between homovalent ions. Then, potentially effective strategies are systematically described to overcome these challenges. Finally, future development directions and research focus on Li extraction technology from salt-lake brines are prospected.