Highly selective deep eutectic solvents for the recovery of lithium from high sodium concentration aqueous solutions

Abstract

Efficient and selective extraction of lithium from sodium-rich systems is crucial for meeting the growing demand for lithium and achieving green development goals. In this study, we synthesized three hydrophobic deep eutectic solvents (HDES) using trioctylphosphine oxide and β-diketones for the separation of alkali metal ions. Experimental results indicated that the chosen extractants exhibit excellent Li+ extraction capability under alkaline conditions, and the extraction capacity of HDES for Li+ is superior to that of their components. Thermodynamic function calculations revealed that the Li+ extraction reaction is exothermic. A study of the factors affecting Li+ extraction efficiency and separation coefficients, and the recyclability of HDES, was conducted, achieving efficient recovery of lithium from solutions. Additionally, Fourier-transform infrared spectroscopy analysis and quantum chemical calculations elucidated the extraction mechanism. This study aims to provide a theoretical basis and a green approach for the selective recovery of Li+ from high Na/Li aqueous solutions.