Liquid Extraction of Lithium Chloride with Dibenzo-14-Crown-4 Ether: Complex Formation and Isotope Effect

Abstract Dibenzo-14-crown-4 ether (DB14C4), which exhibits high lithium selectivity, is a promising extractant for lithium recovery from multicomponent systems. The extraction of LiCl with DB14C4 solutions in chloroform was studied, and the thermodynamic parameters of the process were determined, including the enthalpy (–8.1 kJ/mol) and the Gibbs free energy change (13.2 kJ/mol). For the first time, the crystalline complex [Li(DB14C4)Cl]⋅3CHCl3 was isolated and characterized by X-ray diffraction; in this complex, lithium is coordinated by four crown-ether oxygen atoms and a chloride ion. DB14C4 was shown to extract Na+ and K+ only negligibly, which favorably distinguishes it from the benzo-15-crown-5 ether analogs. The 6Li/7Li isotope separation factor was 1.020 ± 0.008, which is lower than that for systems based on B15C5, but this is compensated by the high lithium selectivity. The results demonstrate the potential of DB14C4 for the development of cost-effective and safe technologies for the selective extraction of lithium.