Electrospun polyphenylquinoxaline fibrous membrane: a versatile filtering medium for separation of highly alkaline aqueous red mud pollutant

Abstract

Electrospun polyphenylquinoxaline (PPQ) ultrafine non-woven fibrous membrane (UFM) has been successfully used as the filtering medium for the separation of highly alkaline aqueous red mud (RM) slurry (pH = 13.0 at 21.5 °C), known as the industrial waste during production of alumina. For this purpose, the PPQ solution was prepared by dissolving the PPQ resin derived from 1,4-bis(4-benzilyloxy)benzene (DBOB) and 3,3′,4,4′-tetraaminodiphenylether (TADPE) in N-methyl-2-pyrrolidone (NMP) at a solid content of 8 wt%. Then, the PPQ UFM was fabricated by a one-step ES procedure. For comparison, the polyimide (PI) UFM, poly(pyromellitic dianhydride-co-4,4′-oxydianiline) (PMDA-ODA, PI-ref) was made by a two-step ES procedure. The obtained flexible and tough PPQ UFM was used as the filter for the separation of highly alkaline aqueous RM slurry. During the separation process, the PPQ UFM exhibited excellent stability in the aqueous alkaline environments of RM slurry either at room temperature (pH = 13.0 at 21.5 °C) or at higher processing temperature (pH = 12.1 at 60.5 °C). RM powder was efficiently separated from the slurry via the PPQ UFM and easily stripped from the membrane. Water contact angle (WCA) measurements revealed the hydrophobic nature of the PPQ UFM (WCA = 113.4° for pure water and WCA = 128.4° for aqueous sodium hydroxide solution at a solid content of 20 wt%). Comparatively, PI-ref (PMDA-ODA) UFM exhibited poor stability in the high-temperature alkaline environment.