Proposing "Dual-site synergistic coordination model" for regulating lithium selectivity of OPEs in simulated high Mg/Li brines

• Revelation of the structure-acidity-coordination synergy in OPEs. • Quantitative selectivity order: TOP>TIBP>TBP ≫ acidic OPEs. Salt lake brines, key lithium resources, face challenges in efficient lithium extraction due to high Mg/Li ratios. This study investigated six organophosphorus extractants (OPEs) across neutral and acidic types. Using simulated high Mg/Li brines, it first proposed a "dual-site synergistic coordination model" to clarify how OPEs’ molecular structure, acidity, and coordination mode regulate lithium selectivity. Neutral OPEs (TOP>TIBP>TBP) outperformed acidic ones in extraction efficiency/selectivity by forming stable [LiLn]+[FeCl4]- complexes, while acidic OPEs showed poor performance due to Fe³⁺ chelation and H⁺/Mg²⁺ exchange. TOP enhanced Li⁺ selectivity by 20% vs TBP. This work establishes structure-acidity-performance correlations, guiding commercial extractant optimization and addressing high Mg/Li bottlenecks.