Chemical Nanobubbles Controlled Guanidyl-Incorporated Nanofiltration Membrane with High Flux in Mg/Li Separation

Abstract

Inspired by the simultaneous increase of permeability and selectivity by introducing physical nanobubbles, this study firstly proposed a chemical nanobubbles controlled guanidyl-incorporated double layer nanofiltration (NF) membrane for Mg/Li separation in salt-lake brine. As a bridge, 1,3-diaminoguanidine released nanobubbles rapidly and uniformly by pH control while polymerization with trimesoyl chloride (TMC) during interfacial polymerization, followed by polyethyleneimine (PEI) secondary reaction, which effectively changed the solute transportation to obtain the shortest pathways in horizontal and normal directions. Compared with conventional PEI-TMC membrane, the water flux of guanidyl-incorporated PEI (G-PEI) membrane was obviously increased by 54.28% while separation factor of Li/Mg (S_Li/Mg) enhanced by 63.27% in the initial 1 h, indicating chemical nanobubble interlayer effectively broke Trade-off effect by increasing the effective filtration area. After separation of Mg/Li mixture for at least 5 h, G-PEI-NF membrane exhibited an excellent S_Li/Mg of approximately 60, lower MLR of 0.31 and Li⁺ purity of 99.5 with the stable flux of 19–20 L/m²·h. This study expected to provide a novel chemical nanobubble interlayer NF membrane with high filtration performance for Mg/Li separation in salt-lake brine.