Composite anti-scaling membrane made of interpenetrating networks of nanofibers for selective separation of lithium

Abstract

The selective separation and extraction of lithium from salt lakes is compromised by the high salt concentration and the presence of competing ions. In this study, a class of novel cation exchange membranes based on Kevlar aramid nanofibers (KANFs) was designed via interpenetrating networks of poly(4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA) and amide reaction of 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (ATTO). Membranes with different PSSMA content were fabricated, and the final membrane denoted as A#PSSMA@KANF-2 achieved a ~1.2 mmol g−1 ion exchange capacity, ~28% water content, ~4.5% swelling rate and ~1.8 Ω cm2 surface electrical resistance. The thin A#PSSMA@KANF-2 membrane (~8 μm thickness) also exhibited a high membrane limiting current density of 32.0 mA cm−2 (in 0.1 M NaCl solution) and an exceptional desalination efficiency (99.9% for NaCl) in electrodialysis. Moreover, compared to some commercial monovalent selectivity cation exchange membranes (CSO and CIMS membranes, which are two commercial monovalent cation selective membranes), the A#PSSMA@KANF-2 membrane was found functional for the separation of Li+/Mg2+ and to have an excellent anti-scaling performance. As the selectivity has potential to be as high or higher as that of commercial membranes, this work provides a promising method to develop membranes with anti-scaling performance for the extraction of lithium from high salt concentrations in salt lakes.