Enhanced anti-fouling and selective performance of GO-modified nanofiltration membranes for lithium extraction from salt lake brine

Abstract

Nanofiltration (NF) is a promising method in lithium extraction from salt lake brine with a high Mg2+/Li+ mass ratio. However, membrane fouling challenges its applicability and productivity. This study incorporated graphene oxide (GO) into the polyamide (PA) selective layer of NF membranes to enhance anti-fouling properties and improve lithium extraction from brine. Membrane structure analyses revealed that 0.002 wt% and 0.01 wt% GO facilitated the interfacial polymerization reaction. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) results indicated that the PA selective layers in the GO-0.002 % and GO-0.01 % membranes were denser, smoother, and thinner. In contrast, the addition of 0.05 wt% GO resulted in the Turing structures on the membrane surface. Adsorption kinetics indicated pollutant adhesion in the following order: GO-0.05 % > GO-0 % > GO-0.002 % > GO-0.01 %, which was attributed to calcium-carboxyl complexation, as directly measured by AFM and consistent with carboxyl density. The GO-0.002 % and GO-0.01 % NF membranes demonstrated excellent anti-fouling properties in brines, with lower initial fouling rates and higher flux recovery after cleaning, underscoring the significant role of calcium-carboxyl complexation in membrane fouling. The retention of Mg2+ increased to 95 %, while that of Li+ decreased to below −28 % for GO-0.002 % and GO-0.01 % membranes, indicating promising potential for Mg and Li separation. This study provides valuable insights into developing NF membranes with high Mg/Li selectivity and anti-fouling capabilities for lithium extraction from salt lake brine.