A novel nanofiltration membrane with [MimAP][Tf2N] ionic liquid for utilization of lithium from brines with high Mg2+/Li+ ratio

In order to utilize lithium from brines with high Mg 2+ /Li + ratio, a positively charged nanofiltration (NF) membrane was prepared by grafting amine-functionalized ionic liquid 1-(3-aminopropyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([MimAP][Tf 2 N]) onto the surface of polyamide (PA) membrane. The effects of [MimAP][Tf 2 N] contents on the chemical composition, surface morphology , surface charges and separation properties of the modified PA membranes were discussed. The results of chemical composition analyses indicated reaction of the amine group of [MimAP][Tf 2 N] with the residual acyl chloride groups, which was existed on the surface of the nascent PA membrane. The surfaces of all the modified PA membranes were positively charged at pH = 6.4 due to the quaternary ammonium group of [MimAP][Tf 2 N]. In the separation process, the resulting membrane presented high water permeance (37.8 L/(m 2 ⋅h)) and mono-/divalent cation selectivity (Li + and Mg 2+ ) with much higher MgCl 2 rejection (83.8%) than LiCl rejection (24.4%). For a simulative brine with a Mg 2+ /Li + ratio of 20, the rejections to Mg 2+ and Li + by the optimized membrane (NF-IL-2.0%) were around 81.9% and −45.2%, respectively, where the permeate with the Mg 2+ /Li + ratio of 3.5 was obtained and the selectivity ( S Li,Mg ) was 8.12. Additionally, the optimized membrane exhibited a stable performance for Mg 2+ /Li + separation. Therefore, there is a very possibility for utilization of lithium from brine with high Mg 2+ /Li + ratio by using the optimized NF membrane.