Crown Ether Chemistry of Polydentate Complexing for Lithium Isotope Separation

The two naturally occurring isotopes of lithium, 6 Li and 7 Li, have important roles in the nuclear energy industry.Among many techniques for the separation of lithium isotopes, high isotope separation factors are usually realized with the polydentate complex method.Crown ethers, for their selective-complexing ability with metal cations, have been regarded as perhaps the most effective extractants for lithium isotope separation.This review summarizes the application of crown ether and crown ether chelating resin for lithium isotope separation based on polydentate complexing method, exemplify recent developments in complexation of metal-containing crown ethers with metal cations, and prospect their potential in separation of lithium isotopes.Keywords lithium isotope separation; polydentate complex; crown ether; crown ether chelating resin; metal-containing crown ethers 在核能工业中, 锂的两种同位素锂-6 和锂-7 具有不 同的核反应性能.锂-6 受热中子轰击后产生的氚(T), 是 未来可控热核聚变反应堆必不可少的核聚变燃料.锂-7 在裂变反应堆中具有重要用途, 氢氧化锂( 7 LiOH)可用 于控制压水堆 pH 值, 减缓压力容器壁的腐蚀; 氟化锂 ( 7 LiF)可作为新一代熔融盐反应堆(MSR)冷却剂的重要 组分, 提高反应堆的安全性和效率 [1] .锂同位素的分离方法很多, 如化学交换法(锂汞齐 法)、离子交换法、电迁移/熔岩电解法、热扩散/分子蒸 馏法、激光/电磁分离法、以及萃取、分级结晶、分级沉 淀等 [2～4] .其中已用于工业生产的只有锂汞齐法 [5] , 但 此工艺大量的使用金属汞, 严重危害人体和环境安全 [6] ,