Efficient extraction of lithium from alkaline solution using the synergistic extractants ethylhexyl salicylate and trialkylphosphine oxide in kerosene and stripping with acid

Efficient separation of lithium from alkaline solution with high Na/Li ratio is of great importance for the development of batteries for new energy industry. This work proposes the use of a novel extraction system composed of ethylhexyl salicylate (ES) and trialkylphosphine oxide (TRPO). The equilibrium experiment revealed that the order of metal ions extracted by ES/TRPO extraction system is Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺ > K⁺. A recovery process including extraction, scrubbing, and stripping was designed to recover lithium from a solution of 3.25 g/L Li, 52 g/L Na and 0.8 mol/L OH⁻. More than 99% of lithium could be extracted to the organic phase. After stripping, a lithium-rich solution containing 25 g/L Li was obtained, and the system showed good stability in the cycling experiments. The FT-IR analysis and DFT calculation were conducted to investigate the extraction mechanism. The results demonstrated that ES mainly coordinates with metal ions through Ph-O and CO bonds to form a hexatomic ring complex, thereby allowing metal ions to enter the organic phase. The calculated binding energies of the complex are highly consistent with the equilibrium experiment. The present work may provide a novel extraction system to efficiently recover lithium from alkaline solution with high Na/Li ratio.