Quaternary phosphonium-polyamide membranes for efficient lithium extraction from brine sources

Lithium extraction from brine sources such as salt lakes, seawater, and produced water from oil/gas fields is garnering increasing interests from the academic and industrial sectors due to its cost-effectiveness and reduced environmental impact. A critical technological challenge is the efficient separation of Mg 2+ and Li + ions. Many researchers have reported the preparation of positively charged nanofiltration membranes with quaternary ammonium groups, yet investigations about quaternary phosphonium groups are scarce. In this work, positively charged nanofiltration membranes were prepared utilizing polyethyleneimine as the aqueous phase monomer, trimesoyl chloride as the organic phase monomer, and 3-bromopropyl triphenyl phosphonium bromide as the functionalizing monomer. The TFC-P + membranes, enriched with a high density of quaternary phosphonium groups and an enhanced Donnan effect, achieve a MgCl 2 rejection of 98.9 %, a Mg 2+ /Li + selectivity of 81.6, and a water flux of 50 LMH under 0.5 MPa. The membranes possess an enhanced comprehensive separation capability that exceeds that of the majority of nanofiltration membranes documented in scholarly articles. Additionally, the membranes exhibit outstanding anti-fouling and anti-bacterial characteristics, essential for their industrial applications. The preparation method proposed herein is simple and conducive to continuous production processes. In light of the abundant produced water reserves from oil and gas extraction, future work will focus on pilot-scale lithium extraction experiments.