Positively charged nanofiltration membrane based on (MWCNTs-COOK)-engineered substrate for fast and efficient lithium extraction

Abstract

Both high flux and Mg2+/Li+ separation capability of nanofiltration (NF) membrane are essential for high efficiency lithium extraction from salt-lake brine. Herein, we proposed a potassium carboxylate functionalized multi-walled carbon nanotubes (MWCNTs-COOK)-engineered substrate membrane to regulate the NF membrane for fast and efficient separation of Li+ and co-existing Mg2+ in brines. Results proved that the fixed MWCNTs-COOK strengthened the connection between the substrate and the formed polyamide layer, and it endowed both the substrate and the final NF membrane with higher water permeability. The membrane performance characterization indicated that with a low MWCNTs-COOK content of 0.012 wt% in the NF membrane, the difference between rejections of Mg2+ and Li+ reached up to 86.94%. Note that the modified NF membrane showed a high flux of 11.46 (L/m2hbar), which was 2.28 times as high as that of the NF membrane without MWCNTs-COOK. Moreover, the NF membrane also performed stable during the long-time filtration due to the improved structure and hydrophilicity of membrane. Such MWCNTs-COOK-modified NF membrane is a promising approach for fast and efficient lithium extraction from salt-lake brines that loaded with high concentration of Mg2+.