Polyethyleneimine Modified Two-Dimensional GO/MXene Composite Membranes with Enhanced Mg²⁺/Li⁺ Separation Performance for Salt Lake Brine

As global demand for renewable energy and electric vehicles increases, the need for lithium has surged significantly. Extracting lithium from salt lake brine has become a cutting-edge technology in lithium resource production. In this study, two-dimensional (2D) GO/MXene composite membranes were fabricated using pressure-assisted filtration with a polyethyleneimine (PEI) coating, resulting in positively charged PEI-GO/MXene membranes. These innovative membranes, taking advantage of the synergistic effects of interlayer channel sieving and the Donnan effect, demonstrated excellent performance in Mg²⁺/Li⁺ separation with a mass ratio of 20 (Mg²⁺ rejection = 85.3%, Li⁺ rejection = 16.7%, S_Li,Mg = 5.7) in simulated saline lake brine. Testing on actual salt lake brine in Tibet, China, confirmed the composite membrane's potential for effective Mg²⁺/Li⁺ separation. In the actual brine test with high concentration, Mg²⁺/Li⁺ after membrane separation is 2.2, which indicates that the membrane can significantly reduce the concentration of Mg²⁺ in the brine. Additionally, the PEI-GO/MXene composite membrane demonstrated strong anti-swelling properties and effective divalent ion rejection. This research presents an innovative approach to advance the development of 2D membranes for the selective removal of Mg²⁺ and Li⁺ from salt lake brine.