Mass transport mechanisms insights of selective sodium/magnesium separation through nanofiltration membranes

This study investigates the selective ion separation capabilities of interfacially polymerized nanofiltration (NF) membranes, focusing on the effect of piperazine (PIP) and trimesoyl chloride (TMC) concentrations on Na⁺/Mg²⁺ selectivity. By varying the concentrations of PIP and TMC during interfacial polymerization (IP), we altered the membranes’ physicochemical characteristics and assessed their performance. The Donnan Steric Pore Model with Dielectric Exclusion (DSPM-DE) was used to explore the correlations between the DSPM-DE input parameters and the partitioning mechanisms and transmembrane fluxes of Na⁺ and Mg²⁺ in terms of the monomer concentrations. Our findings reveal that variations in the thickness-to-porosity ratio and the effective membrane charge density, influenced by higher PIP and lower TMC concentrations, enhance the Na⁺/Mg²⁺ separation capabilities of the membranes. This study provides a mechanistic understanding of selective Na⁺/Mg²⁺ separation in terms of PIP and TMC concentrations, elucidating the underlying transport and exclusion mechanisms. These insights are important for optimizing membrane fabrication by IP and designing NF membranes for efficient Na⁺/Mg²⁺ separation, which is essential due to the importance of magnesium as a critical raw material.