High-permeance polyurethane-polyester nanofiltration membrane for extreme acidic wastewater treatment

Polyurethane-polyester nanofiltration membranes were prepared by interfacial polymerization. • The NF membrane shows over 98.5% rejection of MgCl 2 at pH 7 and membrane water permeability can reach 15 L m −2  h −1 ·bar −1 . • The membranes exhibit excellent acid stability in 20 wt% sulfuric acid solution. • DFT calculations confirm superior stability of urethane and ester groups over amide. Developing acid-resistant nanofiltration (NF) membranes that combine high permeability with long-term stability remains a critical challenge in hydrometallurgical wastewater treatment. Herein, we report a novel molecular design strategy involving Mannich reactions and quaternization to develop quaternary ammonium functionalized monomers. These monomers exhibit excellent water solubility, which exhibit exceptional aqueous solubility under alkali-free conditions. These monomers were then reacted with 3,5-diisocyanatobenzoyl chloride (DBC) via interfacial polymerization to fabricate a polyurethane-polyester composite nanofiltration membrane. The optimized membrane achieved a MgCl 2 rejection of over 98.5% and a water permeance of 15 L m −2  h −1 ·bar −1 under neutral conditions, achieving an effective balance between permeability and selectivity. Acid durability tests demonstrated that the membrane retained > 93% of its MgCl 2 rejection after 100 days of immersion in 20 wt% H 2 SO 4 . Furthermore, continuous operation in simulated industrial acidic wastewater (1 wt% H 2 SO 4 containing Fe 3+ , Cu 2+ ) for 500 h revealed no significant rejection decline, confirming its stability under complex conditions. Density functional theory (DFT) calculations were performed to provide a molecular-level mechanistic understanding of the exceptional acid stability exhibited by the polyurethane–polyester NF membranes. The proposed composite membrane design strategy, which combines hydrophilic functional groups with acid-resistant aromatic networks, provides a novel solution for efficient treatment of wet-process metallurgical wastewater. Download: Download high-res image (332KB) Download: Download full-size image