Interfacial polymerization of poly(quaternary ammonium) membranes with extreme acid stability for phosphorus recovery from phosphogypsum leachate

Abstract

Phosphogypsum leachate, a phosphorus-rich wastewater, poses significant threats to aquatic ecosystems. Nanofiltration represents a promising approach for phosphorus recovery from such leachate by selectively allowing phosphorus permeation while rejecting multivalent cations. However, the widespread application of conventional polyamide nanofiltration membranes in phosphogypsum leachate treatment is constrained by their poor acid stability. Herein, To address this limitation, an acid-resistant, highly positively charged nanofiltration membrane was fabricated by synthesizing a crosslinked poly(quaternary ammonium) selective layer on a polysulfone support via a temperature-regulated interfacial polymerization between N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDTA) and 1,3,5-Tris(bromomethyl)benzene (TBB). Remarkably, elevating reaction temperature not only enables the formation of an ultrathin selective layer (30 nm) with dense cross-linking (MWCO = 471 Da) but also achieves rapid synthesis within 2 min. The poly(quaternary ammonium) membranes achieved a high MgCl₂ rejection (97.17 %) and a high P permeation (88.16 %) owing to the exceptionally strong positive charge provided by quaternary ammonium groups. Moreover, the “C–N⁺” bonds within the poly(quaternary ammonium) structure contribute to exceptional acid stability. The membranes remain stable after prolonged immersion in 1.5 M H₂SO₄ for 40 days (MgCl₂ rejection >95 %). This breakthrough combination of ultrafast reaction, high cation selectivity and outstanding acid stability positions the poly(quaternary ammonium) membrane as a highly viable candidate for phosphogypsum leachate treatment applications.