Lithium extraction from aqueous medium using hydrophobic deep eutectic solvents

Because lithium resources are becoming increasingly scarce, their recovery is an urgent problem that needs to be solved. In this paper, an environmentally friendly process for the recovery of lithium ions from water resources by liquid-liquid extraction (LLE) is proposed. Menthol (DLM) was used as a hydrogen bond acceptor (HBA), and octanoic acid, decanoic acid, and lauric acid (LA) were used as hydrogen bond donors (HBDs) to form nine hydrophobic deep eutectic solvents (HDESs). The HDESs synthesized using DLM and LA had the best effect and thus were selected for the lithium extraction experiment. The single extraction efficiency of lithium ions was 80.69 %, with optimized rotational speed, equilibrium time, pH, molar ratio of organic phase to inorganic phase (O/L), and initial concentration of different lithium complexes of 660 rpm, 30 min, 12, 3:1, and 0.5 g/L, respectively. In addition, the regeneration cycle experiment of the HDES was further investigated. The possible extraction mechanism was demonstrated by Fourier-transform infrared spectroscopy and slope method. The separation factor (β) of Li/Na and Li/K obtained from the experimental results was 18.72 and 84.25, showing that 2DLM/LA can selectively extract lithium ions from systems containing Li, Na and K. This will be beneficial to design potential green HDESs for recovering lithium resources from aqueous solutions.