A positively charged PI nanofiltration membrane with good separation for Li+ and Mg2+

A positively charged PI/PDA/PEI nanofiltration membrane was prepared in this study by crosslinking between polyethyleneimine (PEI) and poly(dopamine) (PDA) on the polyimide (PI) support membrane for separating Mg 2+ and Li + from MgCl 2 /LiCl mixed solution, and its chemical structure, surface properties, and separation performance were investigated. The results indicate that the PI/PDA/PEI membrane has a thin positively charged layer and shows excellent rejections against many inorganic salts [MgCl 2 (93.1%) > MgSO 4 (86.5%) > Na 2 SO 4 (74.7%) > LiCl (37.6%)]. More importantly, the membrane exhibits long-term stability and good separation of Mg 2+ and Li + , and the Mg/Li ratio of the permeate of brine obtained from West Taijnar salt lake can be reduced from 65.3 to 5.0 at pH 6.5 by filtration.