A nanofiltration membrane with positively and negatively charged groups by grafted p-aminosalicylic acid-Fe(III) chelation for Li+/Mg2+ efficient separation

Abstract

High-performance nanofiltration (NF) membrane plays a key role in Li+/Mg2+ separation process. In this work, a new NF membrane with positively and negatively charged groups was prepared by grafting p-aminosalicylic acid (AS) onto the surface of polyamide (PA) membrane followed by chelation with Fe3+ ions for Li+/Mg2+ separation. The AS grafting (PA-g-AS) and Fe3+ chelating (PA-g-AS-Fe) NF membranes had almost same surface and section structure and surface pore size as the PA membrane. But Zeta potential (about −8 mV at pH 7) of the obtained PA-g-AS-Fe membrane was improved in comparison with the PA and PA-g-AS NF (about −20 mV at pH 7) membranes due to Fe3+ addition, suggesting that there were positively and negatively charged groups on the membrane surface. The PA-g-AS-Fe membrane showed a high Mg2+ rejection of 97.7% and high Li+ permeation (negative rejection of −87.6%); while a high Li+/Mg2+ separation factor (SLi,Mg) of about 81.5 was achieved, which is much higher than those for PA and PA-g-AS NF membranes and surpassed those of the results reported in literature. The fluxes of three membranes were about the same. The results demonstrated the NF membrane with positively and negatively charged groups was suitable for efficient separation of Li+/Mg2+ and would have promising applications in recovery of lithium from brine.