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

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][NTf 2 ] 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 6 Li/ 7 Li obtained in the present study was 1.025, indicating that the lighter isotope 6 Li was enriched in organic phase while the heavier isotope 7 Li 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.