Lithium isotope separation effect of N-phenylaza-15-crown-5

Abstract Azacrown ethers contain multiple coordination sites, which show specific complexation to alkali metal ions. In this research, a neoteric liquid-liquid extraction system was investigated for the selective separation of lithium isotope using N-phenylaza-15-crown-5 (Ph-N15C5) as chelating agent and [BMIm][NTf2] and anisole as extraction solvent. The effects of the counter anions of lithium salt, concentrations of crown ether, temperature, extraction equilibrium time and concentrations of lithium salt solution on the separation of lithium isotope with Ph-N15C5 were studied. The maximum extraction efficiency of lithium ions was 41.54% and the maximum single-stage separation factor (α) of 6Li/7Li obtained in the present study was 1.025, indicating that the lighter isotope 6Li was enriched in organic phase while the heavier isotope 7Li was concentrated in the aqueous phase. The complexation ratio of the lithium crown ether complex was determined as 1:1 by the slope analysis method. The lithium ions in the aqueous phase were extracted into the organic phase to form [Li(Ph-N15C5)]+ complex. The thermodynamic data obtained at different temperatures demonstrated that lithium isotope exchange was a spontaneous exothermic process, and lowering the temperature was beneficial to increase the separation factor. In addition, the system reached the extraction equilibrium after 60 min. This high efficiency and green liquid-liquid extraction system has potential application in lithium isotope separation.