| Summary: | The separation of lithium and magnesium from salt-lake brines with high Mg<sup>2+</sup>/Li<sup>+</sup> ratios is a main challenge for lithium extraction. In this work, novel polymer inclusion membranes (PIMs) were developed by incorporating 2-ethylhexyl phosphonic acid mono 2-ethylhexyl (P507) and tributyl phosphate (TBP) as the carriers into cellulose triacetate (CTA) polymers. The Li<sup>+</sup> could be stripped from the P507-TBP extracting carriers using pure water eluents without adding concentrated hydrochloric acid, which can help decrease carriers’ leakage risk from membrane matrixes and keep the stability of PIMs. The morphology, composition, and wettability of P507-TBP-based PIMs were characterized systematically, and the carrier content in the PIM was also optimized. In the transport experiment with the feed of 0.1 mol/L LiCl and 4.0 mol/L MgCl<sub>2</sub>, the CTA/P507-TBP60% membrane exhibits a Li<sup>+</sup> permeability of 4.76 × 10<sup>−3</sup> mol·m<sup>−2</sup>·h<sup>−1</sup> and a Li/Mg separation ratio of 10.2. After recycling seven times, the selectivity of the PIM is well-retained (>10), and the permeability of Li<sup>+</sup> decreases slightly (less than 15%). With a decent selectivity and excellent stability, PIMs containing P507-TBP carriers show great potential for sustainable and efficient lithium recovery from brines with high Mg/Li ratios.
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