Surfactants intervened construction of NF membranes for lithium extraction in high Mg2+/Li+ ratio and high concentration environments

Abstract

Nanofiltration (NF) membranes offer notable benefits for Li⁺/Mg²⁺ separation, but their efficiency tends to diminish when exposed to mixed salt solutions with elevated Mg²⁺ concentrations or high Mg²⁺/Li⁺ ratios (MLR), restricting their practical applications. This study employed the surfactant-assisted interfacial polymerization (SIAIP) method to incorporate sodium dodecyl sulfate (SDS) and dodecyl phosphate (DDP), leading to the creation of two NF membranes with opposite surface charge characteristics. SDS promoted the trans-interfacial diffusion of the amine monomer while simultaneously limiting its escape from the bulk-phase solution, which was crucial for developing positively charged membranes. Conversely, DDP predominantly influenced the interfacial diffusion of the amine monomer, resulting in a membrane with a reduced pore size and a negatively charged active layer. SIAIP-DDP membranes exhibited excellent stability (S _{Li, Mg} > 110) in environments with high MLR and Mg²⁺ concentrations, highlighting their potential for application in harsh salt-lake brine. This work presents a detailed mechanistic analysis of the surfactant-induced interfacial polymerization process, offering new insights into the efficient separation of Li⁺/Mg²⁺ under high MLR and high concentration conditions.