Efficient separation of Mg2+/Li+ using reduced GO membranes modified by positively charged arginine†

Abstract

Nanofiltration has emerged as an effective technique for the selective separation of mono- and divalent ions, such as Mg²⁺/Li⁺ mixtures, and plays a crucial role in lithium extraction from salt lakes. In this study, a graphene oxide (GO) membrane with positively charged channels was prepared by crosslinking arginine (Arg) onto GO nanosheets, followed by vacuum filtration to form the membrane, and then thermal reduction (Arg-rGO). The Arg-rGO membrane exhibits high performance in the ion separation of a typical brine with a Mg²⁺/Li⁺ mass ratio of 20. The separation factor (S_Li/Mg) reached up to 45.6—two times the highest separation factor reported—while maintaining an advanced water permeance of 21.3 L m⁻² h⁻¹ bar⁻¹. Furthermore, the Mg²⁺/Li⁺ mass ratio was reduced from 20 to 0.2 after two-stage crossflow filtration with high flux under high pressure. The observed separation performance can be attributed to the synergistic effect of electrostatic repulsion and size-exclusion. These findings confirmed efficient separation of Mg²⁺/Li⁺ using GO membranes, demonstrating potential for practical application in lithium extraction from salt lakes.