Waste-to-Resource Strategy To Fabricate Highly Porous Whisker-Structured Mullite Ceramic Membrane for Simulated Oil-in-Water Emulsion Wastewater Treatment

Industrial waste coal fly ash, containing hazardous metal oxides, poses potential threats to the environment and humans. Efficient recycling of such kind of solid state waste is highly desired yet still challenging. This work addressed waste-to-resource fabrication of a highly porous whisker-structured mullite ceramic membrane for separation of simulated oil-in-water emulsion wastewater by recycling of waste fly ash and natural bauxite with addition of WO₃. The formation and characterizations of membranes were systematically studied including reaction mechanism, dynamic sintering behavior, open porosity, mechanical property, pore size distribution, microstructure, and pure water flux. The results show mullite formation temperature was decreased about 100 °C with addition of 20 wt % WO₃, whereas open porosity significantly increased with WO₃ content due to the formation of a highly porous interlocked whisker structure. Even without any pore formers, interestingly, the membrane with addition of 20 wt % WO₃ possessed an open porosity as high as 51.9 ± 0.3% after sintering at a high temperature of 1400 °C whereas its mechanical strength (68.7 ± 6.1 MPa) was still improved. An oil-in-water emulsion dead-end microfiltration experiment indicates a significantly improved oil rejection as high as 99% was also obtained for W20 membrane, as compared to that (83%) of the W0 membrane.