A novel ternary hydrophobic deep eutectic solvent over a wide pH range for lithium recovery

Owing to the crucial role of lithium (Li) in green technology and energy storage, the global demand for Li is constantly increasing. This article provides a new strategy for recovering Li using ternary hydrophobic deep eutectic solvent (HDES). The novel HDES was composed of 2-thiophenyltrifluoroacetone (HTTA), trioctylphosphine oxide (TOPO), and N,N-diethyldecanamide (DDA), and exhibited high efficiency and selectivity for extracting Li from aqueous solutions. This study systematically evaluated the effect of the initial aqueous pH on the Li extraction efficiency, revealing the stable performance of HDES in the pH range 3-13. Compared to the highly alkaline environment required for Li extraction, the pH characteristics of the HDES provide a wider range of applications and a more environmentally friendly alternative. The HDES exhibited rapid extraction kinetics, achieving equilibrium within 10 min and maintaining phase stability without emulsification. The main mechanism of selective Li extraction is the electrostatic interaction between Li(I) and TTA. The interactions between Li(I) and both TOPO and DDA were confirmed by Fourier transform infrared (FT-IR) spectroscopy, thereby improving the selectivity and extraction efficiency. The countercurrent extraction process demonstrated an impressive Li extraction rate of 98.704 % and a Li(I)/Na(I) separation factor of 10643.14 with industrial Li₂CO₃ mother liquor, highlighting the application potential of the ternary HDES. The excellent performance of the HDES over a wide pH range provides more opportunities for its application, and its high efficiency, selectivity, and environmental characteristics may promote Li recovery.