Highly Selective Lithium Recovery from High-Mg/Li Brines via A Novel DPOP-P204-DES System: From Molecular Selectivity Design to Process Co-optimization

Driven by surging global lithium demand, highly selective lithium separation from magnesium-rich brines is urgently required. This work systematically investigated the structure–performance relationship of four aryl-substituted phosphates (TOP, DPOP, IPPP, TPP). Moderate aryl substitution widened the coordination difference between Li + and Mg 2+ through electron-withdrawing effects, and DPOP exhibited the optimal balance of extraction capacity and selectivity. A ternary synergistic extraction system was fabricated with DPOP as the primary extractant, P204 to immobilize Fe 3+ , and eco-friendly diethyl succinate (DES) as a polar modifier. DES inhibited third-phase formation at DPOP contents of 10–50 vol.% and produced synergistic solvation via carbonyl groups. Under optimized conditions, the single-stage Li + extraction efficiency achieved ∼73%, and the Li/Mg separation factor reached 1630, nearly 80 times that of the traditional TBP–FeCl 3 system. Synergistic coordination of P204 and DES stabilized Fe 3+ in the organic phase, realizing quantitative lithium stripping with deionized water and avoiding concentrated acid and saponification. The organic phase maintained over 80% extraction efficiency after ten cycles. Slope analysis and FT-IR confirmed the extracted complex LiFeCl 4 •2DPOP•0.1DES. This work transforms DPOP into a sustainable, low-cost, closed loop industrial solution for lithium recovery from high Mg/Li brines.