Histidine-Grafted Polyamide Nanofiltration Membranes with Enhanced Acid Resistance and Electro-Nanofiltration for Lithium Separation from Acidic Lithium-Ion Battery Leachates

Abstract The recovery of lithium from spent lithium-ion battery (LIB) leachates remained challenging because strong acidity and complex ion compositions compromised the stability and selectivity of conventional nanofiltration (NF) membranes. In this work, an acid-resistant membrane was synthesized via covalent grafting of histidine (HIS) onto a polyamide (PA) layer (PA-HIS) through secondary interfacial polymerization (IP). In acidic media, imidazole protonation generated positively charged imidazolium sites that repelled H+, suppressing acid-catalyzed amide hydrolysis. Beyond this protective effect, HIS moieties enhanced surface hydration and water flux. The imidazole groups further promoted multivalent cation coordination and improved ion selectivity. This modified membrane maintained 98.9% Na2SO4 rejection after 28 days at pH = 1, demonstrating excellent chemical durability. When electro-nanofiltration (ENF) based on the PA-HIS membrane was carried out for separating simulated acidic LIB leachates, the rejection of Ni2+, Co2+, and Mn2+ of over 99.8% and Li+ rejection of –35% were achieved to yield a separation factor SLi/(Ni,Co,Mn) of around 600. Continuous operational stability was further confirmed and exhibited exceptionally high ion selectivity (SLi/(Ni,Co,Mn) > 400). These results demonstrated that HIS grafting enhanced acid durability, and electric field regulated ion discrimination, facilitating Li recovery from acidic LIB leachates.