Synthesis, characterization and performance studies of kaolin-fly ash-based membranes for microfiltration of oily waste water

The present study deals with the synthesis, characterization, and performance evaluation of low-cost porous ceramic microfiltration membranes for separation of oily waste water. Ceramic membranes were synthesized following paste-casting method using three different ratios of kaolin to coal fly ash, in combination with a few selected suitable pore - formers and binders like calcium and sodium carbonate, boric acid, and sodium metasilicate. The synthesized membranes were characterized using the field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), atomic force microscopy (AFM), thermogravimetric analysis (TGA), and water permeation tests with the objective of investigating the influence of sintering temperature (750 °C–900 °C) and precursor ratio on the microstructural evolution of the fabricated membranes. Three varying concentrations of oil-in-water (O/W) emulsions (100, 200, and 300 mg/L) prepared using a typical crude oil collected from an oil field located in Digboi, India was used as a representative sample and tested for the microfiltration studies. A fabricated membrane with a porosity (~34.36–39.0%), pore size (~0.65–1.81 μm) showed an excellent separation efficiency of 96.7–99.5% with a permeate flux around ~ 24.3 × 10−5 m3 m−2 s−1. The flux decline mechanism was analyzed using the pore blocking models, and it was observed that the cake filtration model followed by the intermediate pore-blocking model were the best - fitted models as compared to others to describe the permeate flux data. The fabricated kaolin-fly ash-based membranes exhibited good permeability and separation efficiency characteristics, which suggest its suitability for microfiltration of oily waste water from oil exploration and refinery industries.