In situ polyamide nanofiltration coatings for enhanced lithium extraction from high Mg/Li brines

Lithium manganese oxide (LMO) ion sieves are promising for lithium extraction due to their high adsorption capacity. However, their practical application is often limited by structural degradation from manganese leakage, reduced lithium uptake, and poor Li + /Mg 2+ selectivity, especially in brines with high Mg/Li ratios. To overcome these challenges, we in-situ synthesized polyamide (PA) nanofiltration membranes on the surface of LMO using two distinct amine monomers, polyethyleneimine (PEI) and piperazine (PIP), to create novel composite adsorbents LMO@PA(PEI) and LMO@PA(PIP). Both the coated materials demonstrated improved lithium uptake capacity and cyclic stability in adsorption-desorption cycles in simulated brine. More importantly, under a challenging Li/Mg ratio of 1:50 in binary ion solutions, the separation factors (α) of HMO@PA(PEI) and HMO@PA(PIP) were 2.23 and 4.55 times higher than that of uncoated HMO, showcasing excellent Li + /Mg 2+ selectivity. These findings highlight that polyamide nanofiltration layers successfully endow LMO with enhanced capacity, selectivity, and long-term stability, presenting a promising and scalable approach for direct lithium extraction from high‑magnesium salt lakes.