Extraction separation of lithium isotopes with Bromobenzene-15-crown-5/ionic liquids system: Experimental and theoretical study

Controlled fusion energy is considered to be one kind of sustainable energy source with clean and green properties. The fusion process requires a large number of lithium isotopes, but the naturally stable lithium isotopes 6 Li and 7 Li cannot be directly applied to the fusion process and must be further enriched. In this paper, a system for the separation of lithium isotopes by extraction was investigated, which mainly consists of bromobenzene-15-crown-5 and ionic liquids. The effects of ionic liquids, lithium salts, crown ether concentration, and temperature on the separation performance of lithium isotopes were explored. It was found that 6 Li was enriched in the organic phase and the single-stage separation factor reached 1.032. It was proved by the temperature experiment that the exchange of lithium isotopes was a spontaneous and exothermic process. The complexation ratio of crown ether and lithium ions was 1:1. The optimized complexation model and the interaction of crown ether and lithium ions were calculated by DFT and Multiwfn. Lithium ions were weakly bonded to the crown ether and strongly bonded to the water molecule as demonstrated by the non-bonded interactions and Mayer bond order of Li-O. Meanwhile, the mechanism of lithium isotope separation with crown ether was clarified by mutual verification of experiment and theoretical calculations.