Recovery of lithium from geothermal brine with ultrahigh mass ratio of sodium to lithium by solvent extraction: A process study

Lithium has become a strategic resource for the new energy industry, while geothermal water represents a promising supplementary lithium source with low lithium concentration and ultrahigh sodium-to-lithium ratio. The existing extraction studies focus mainly on mechanism and performance rather than integrated process development. This work established a complete solvent extraction process using a β‑diketone synergistic system (HBNA/TRPO) to recover lithium from Jianghan Basin geothermal brine (48 mg/L Li⁺) and prepare battery‑grade lithium carbonate.The process includes calcium/magnesium pre‑removal, lithium extraction, sodium scrubbing, lithium stripping, and lithium carbonate precipitation. Under optimized conditions, Ca and Mg removal reached 96% and 99% with less than 5% Li loss, and lithium extraction efficiency exceeded 95% at 50% saponified organic phase and O/A = 1/2. In the scrubbing process, over 97% lithium remained in the organic phase while sodium was efficiently washed off. In the stripping process, lithium could be concentrated to 4.1 g/L, and to facilitate subsequent lithium carbonate precipitation, the lithium-rich solution is further concentrated by evaporation to 12 g/L. After deep removal of calcium and magnesium, the lithium carbonate with purity of 99.6% was prepared by adding sodium carbonate.Cycling process and techno‑economic analysis shows confirmed stable extraction performance and favorable cost–price margins. This study provides a practical, scalable route for lithium recovery from low‑grade, high‑Na/Li geothermal brines, supporting the development of unconventional lithium resources.