Positively-charged nanofiltration membrane constructed by polyethyleneimine/layered double hydroxide for Mg2+/Li+ separation

As an important resource, lithium is abundant in Salt Lake. The high Mg2+/Li+ ratio is the main obstacle to lithium extraction. Positively-charged nanofiltration membrane has shown great potential in the separation of Mg2+/Li+. Herein, we report a facile method to construct positively-charged nanofiltration membrane by polyethyleneimine (PEI) and layered double hydroxide (LDH) nanosheets on hydrolyzed polyacrylonitrile ultrafiltration membrane. Subsequently, the PEI-LDH composite membrane was crosslinked with glutaraldehyde (GA) to improve its stability. The incorporation of LDH could improve the positive charge of the membrane. Then, the obtained PEI-LDH/GA membrane showed an enhanced separation performance for separating Mg2+/Li+ in an aqueous solution. When the Mg2+/Li+ ratio was 10, the membrane showed a separation factor (SMg2+/Li+) of 18.7. Moreover, the membrane could maintain the separation performance for 100 h, which exhibited a potential application in Mg2+/Li+ separation.