Nanofiltration Membrane Based on LDH Intermediate Layer and Its Magnesium Lithium Separation Performance

Achieving the separation of magnesium and lithium in Salt Lake brine has become a huge challenge in the process of lithium extraction from salt lakes. Developing nanofiltration membranes with high magnesium lithium separation performance has become a key issue that needs to be urgently solved. In this study, porous layered double hydroxide (LDH) nanosheets were obtained by chemical etching, which were then deposited on the surface of polyacrylonitrile membrane as an intermediate layer. Then, the positively charged polyamide nanofiltration membranes were prepared on the surface of LDH by interfacial polymerization of polyethylenimine and trimesoyl chloride. The intermediate layer of LDH not only enhances the positive charge of the membrane surface, but also induces the formation of a coffee ring structure in the polyamide layer, improving the roughness of the membrane surface, thereby synchronously improving the selectivity and permeability of the membrane. When separating a mixture with a magnesium lithium ratio of 20, the LDH/polyamide nanofiltration membrane has a magnesium lithium separation factor of 17 with the permeance of 1.15×10^-4 L/(m²·h·Pa). Moreover, the separation performance of the membrane was stable within 100 h, demonstrating good prospects for magnesium lithium separation applications.