A positively charged composite nanofiltration membrane modified by EDTA for LiCl/MgCl2 separation

For efficient recovery of lithium from brines, a composite nanofiltration (NF) membrane with positively charged skin layer (PA-B) was first synthesized via interfacial polymerization between branched poly(ethylene imine) (BPEI) and trimesoyl chloride (TMC) on the support of crosslinked polyetherimide, and the separation performance was assessed for simulative brine of mixed LiCl/MgCl2 solution. To improve the permselectivity of Li+ against Mg2+, then we adopted EDTA to modify the as-prepared positively charged PA-B NF membrane. The optimal EDTA modified NF membrane PA-B2-E3 showed the separation factor SLi,Mg about 9.2 for the LiCl/MgCl2 mixed solution with a Mg2+/Li+ mass ratio of 24, with excellent stability within 36 h filtration, which would have promising applications in the recovery of Li from brine.