Chelator-Enhanced nanofiltration process for selective lithium extraction and Magnesium utilization from salt lake brines

• CEN enables selective Li + /Mg 2+ separation and multi-resource recovery. • HEDTA 3− balances binding strength and selectivity, solubility, and regeneration. • Two-pass filtration enriches Li + /Mg 2+ ratio from 0.0284 to 13.04 in Dongtai brine. • CNE produces battery-grade Li 2 CO 3 and high-purity Mg products. Membrane-based separation processes represent a promising approach for lithium (Li) extraction from salt lake brines. In this study, we developed a chelator-enhanced nanofiltration (CEN) process that synergically integrates selective complexation, membrane separation, and chelator regeneration to simultaneously recover and utilize Li and magnesium (Mg) from high-salinity, multiple-component salt lake brines. Through systematic screening evaluating critical parameters including binding strength, complexation selectivity, separation efficiency, water solubility, and regeneration potential, (2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA) emerged as the suitable chelator, forming negatively-charged complexes with Mg 2+ while leaving Li + unbound in salt lake brines. The CEN process exhibited excellent Li + /Mg 2+ separation factors across various operating and brine conditions and maintained stable performance during 15 days of continuous operation with minimal membrane fouling observed. A two-pass filtration configuration was used to treat a simulated Dongtai Lake Brine with a salinity of 280.76 g●L −1 . The Li + /Mg 2+ ratio increased from 0.0284 to 13.04, a nearly 480-fold enhancement, thereby directly fulfilling industrial Li + precipitation range of 10–30. Furthermore, the integrated CEN system achieved efficient chelator regeneration (99.78 %) while simultaneously producing multiple valuable products: battery-grade Li 2 CO 3 (99.91 % purity), hexagonal nanostructured Mg(OH) 2 (99.49 % purity), and high-purity MgO (99.31 % purity). This multiple-product approach effectively enhanced resource valorization of salt lake brines and demonstrated a process-oriented thinking of membrane-based selective ion-ion separation for complex brine treatment and resource recovery.