In search of nanofiltration membranes for efficient lithium extraction from carbonate-type salt lakes

Carbonate-type salt lakes exhibit low Mg²⁺ to Li⁺ ratio and provide abundant and high-quality lithium resources. Nevertheless, the lithium extraction from carbonate-type salt lakes is rarely studied academically due to the presence of anionic impurities and lithium loss. This work evaluates the feasibility of nanofiltration (NF) membranes for selectively extracting lithium from this kind of real brine. Three commercial NF membranes were systematically characterized and evaluated. Negatively charged NF membrane with a pore radius between the hydrated radius of lithium and carbonate ions were found to simultaneously enhance the removal of divalent anions and the permeation of Li⁺ through pore size sieving and Donnan effect. >90 % of SO₄²⁻ and CO₃²⁻ could be effectively removed from real brine, while maintaining the Li⁺ loss rate below 5 %, thereby providing LiCl for the subsequent process stage. At high concentration brines, this kind of NF membranes achieved excellent separation performance in both Cl⁻/SO₄²⁻ and Cl⁻/CO₃²⁻ systems, with selectivities of approximately 120 and 11, respectively. Consequently, this research paves the way for the development of lithium extraction from carbonate-type lakes and marks a stride in the application of NF membranes for lithium extraction.