Effective and Eco-friendly Lithium Recovery from High Mg/Li Ratio Brine by DEHEHP and P507

Abstract The global surge in lithium demand, driven by the lithium-ion battery (LIBs) industry, has intensified the need to develop domestic resources. In China, the focus has turned to the salt lakes of the Qinghai-Tibet Plateau. However, their high Mg/Li ratio has prevented commercial extraction. While cost-effective, the solvent extraction method faces industrial limitations due to extractant loss and the need for acidic stripping. This study introduces an eco-friendly extraction system using di(2-ethylhexyl)-2-ethylhexyl phosphonate and di-(2-ethylhexyl) phosphoric acid (DEHEHP-P507). In this system, DEHEHP minimizes dissolution loss, while P507 enables efficient stripping with water. A process involving eight-stage extraction and two-stage stripping was tested on brine from the Daqai dam salt lake, achieving a lithium recovery rate of >97.5%. The Li+ concentration was enriched by approximately 6-fold in the stripping liquor, while the Mg/Li ratio was drastically reduced from 87.89 to 1.41, a 62-fold decrease. Finally, Li2CO3 with a purity of >98% was produced. By completely avoiding contact with acids and alkalis, the DEHEHP-P507 system proves to be an efficient and sustainable method for lithium recovery from high Mg/Li ratio brines, demonstrating significant industrial potential.