Electrodialysis with nanofiltration membrane (EDNF) for high-efficiency cations fractionation

A membrane process EDNF was carried out for cations fractionation, in which home-made nanofiltration membrane (NFM) was used instead of cation exchange membrane in conventional electrodialysis. Such process was exemplified by the systems of H+/Zn2+ and Na+/Mg2+. The results showed that the porous structure of NFM could decrease the transfer resistance of ions, enhance the limiting current density and thus improve the ion flux. Especially, the dense layer of NFM synthesized by interfacial polymerization could reject the divalent cations rather than monovalent cations resulting from their different Stokes radius. As a result, higher perm-selectivity and increased mono-valent ion flux were achieved simultaneously. Compared with the standard monovalent-selective CSO membrane, NFM used in EDNF can enable higher demineralization rate and acid recovery in the respective investigating systems. Thus this process is expected to apply in seawater desalination or acid recovery.