Oligoether-Functionalized Covalent Organic Framework Membranes For Lithium/Magnesium Separation

The global demand for lithium is greatly increased due to the widespread use of lithium batteries.In China,lithium resources are concentrated in salt lakes,most of which have a high magnesium-lithium ratio.However,lithium and magnesium are very similar in physical and chemical properties,so it is particularly necessary to develop an efficient separation method for lithium and magnesium.Covalent organic framework（COFs）membranes have uniform adjustable pore size and easy to customize functional sites,and rigid structure is conducive to the uniform distribution of functional groups in ion channels,which is an ideal material for lithium/magnesium separation.Suitable pore size and functional sites make it highly selective in lithium/magnesium separation.In addition,ordered pore structure can make it have high permeability flux.To realize the efficient separation of lithium and magnesium.In this paper,four kinds of COF membranes modified with oligoether chains were designed and synthesized for the separation of lithium and magnesium in the process of lithium extraction from salt lake.All the four membranes have certain selectivity of lithium and magnesium,among which LZU-627-PET-12 and LZU-628-PET-18 membranes have good lithium/magnesium separation effect,especially the selectivity of Li⁺/Mg²⁺in LZU-628-PET-18 membrane reaches 159.28,The infiltration rate of Li⁺is 0.115 mol h^-1m^`.In addition,in artificial simulated salt lake water with high magnesium/lithium ratio,LZU-627-PET-12 and LZU-628-PET-18 membranes still have lithium magnesium selectivity,and after single penetration into the second penetration chamber through LZU-628-PET-18membranes,the molar ratio of Li⁺/Mg²⁺is≈33.53:1,which is close to the battery level purity.These results indicate that the synthesized membrane has the potential of extracting lithium from salt lake.