Polyamide/polyethylene thin film composite (PA/PE-TFC) NF membranes prepared from reverse-phase interface polymerization (RIP) for improved Mg(II)/Li(I) separation

Polyamide/polyethylene thin film composite (PA/PE-TFC) NF membranes were prepared from reverse-phase interface polymerization (RIP) for improved Mg(II)/Li(I) separation. RIP processes between 1,3,5-benzenetricarbonyl chloride (TMC) in bottom organic phase and piperazine (PIP) in upper aqueous phase were developed to form continuous and intact surface PA separation layers on PE porous substrates thinner than traditional polysulfone (PSF) based substrates. After activation with isopropyl alcohol (IPA), PA/PE-TFC-IPA NF membranes were formed, whose NF performance could be tuned by adjusting the preparation conditions. When TMC concentration was kept at 0.15 % w/v, RIP with low PIP concentration (0.025 wt%) yield PA/PE-TFC-IPA NF membranes with negatively charged surfaces, high Na2SO4 rejection rate (95 % ± 3 %) and water permeance (13–19 L·m−2·h−1·bar−1). RIP with high PIP concentration (0.3 wt%) formed PA/PE-TFC-IPA NF membranes with less negative surfaces, high MgCl2 rejection rate (94.3 ± 0.7 %), low water permeance (4.8 ± 0.3 L·m−2·h−1·bar−1), and high Mg(II)/Li(I) separation coefficient SLi/Mg (18 ± 1) for 1000 ppm LiCl and MgCl2 mixed solution. PA/PE-TFC-IPA NF membranes also showed good long-term stability and improved anti-fouling performance for positively charged pollutants, bearing high potential for applications in the lithium extraction processes.