Electric Field-Regulated Proton Gradient for Efficient Recovery of Li+ via Polymer Inclusion Membranes

The selective separation of Li+ from Na+ in high-salinity solutions remains a challenge. Although polymer inclusion membranes (PIMs) are promising, their application is hindered by the rapid dissipation of the proton gradient, which requires continuous acid/base addition. Herein, we present an electric field-assisted PIM-electrodialysis (PIM-ED) process that overcomes this limitation by using in situ water electrolysis to generate and sustain a stable proton gradient, eliminating chemical additives. Mechanistic investigations reveal that this electrically sustained proton gradient is a necessary condition for achieving efficient Li+ transport through the Li+/H+ counter-transport mechanism in the PIM process. Under optimized conditions, the Li+ permeability coefficient reached 3.50 μm·s–1, an order of magnitude higher than in PIMs, with excellent selectivity (separation factor Li+/Na+ > 31). When applied to the real Li2CO3 mother liquor, the process produced purified Li+ with a concentration of 21.17 g·L–1, meeting industrial feedstock requirements.