Efficient Metal Cutting Fluid Wastewater Separation of Polyacrylonitrile Ultrafiltration Membranes Enabled by Metal Ion Cross-Linking

Abstract

Polymer ultrafiltration (UF) membranes are critically needed in oily wastewater separation. However, oily wastewaters, e.g., metal cutting fluid wastewater, have complex components and properties, and it is necessary to investigate the interactions between them and the membrane pore structure and the surface properties and to achieve efficient oily wastewater separation. Herein, a novel polyacrylonitrile (PAN) UF membrane was fabricated through metal ion Cu2+ cross-linking of the as-generated -COO– groups on PAN chains. Compared to the pristine PAN membrane, the obtained Cu2+@HPAN membranes with the appropriate addition of Cu2+ (0.32 atom %) show better hydrophilicity (water contact angle of ∼0°), a larger ζ potential on the surface, and an optimized pore structure (stable small pores and high porosity), which are responsible for efficient oily wastewater separation. The changes in the pore structure and surface properties of Cu2+@HPAN have been investigated during filtration of the simulated oily wastewaters with different oils, coexisting ions, pH, and temperature. Cu2+ in the PAN membranes remains stable during long-term filtration. Cyclic filtration demonstrates that Cu2+@HPAN retains a high flux recovery rate (>90%) by simple water washing. The highly efficient separation (rejection of >96%, flux of ∼80 L m–2 h–1) toward the practical metal cutting fluid wastewater suggests the promise of the application of Cu2+@HPAN in practical oily wastewater treatment.