Preparation of novel porous ceramic microfiltration membranes from fly ash, kaolin and dolomite mixtures

Abstract

In the present work, low-cost ceramic membranes were prepared by using kaolin (KA), fly ash (FA) and dolomite. The effects of sintering temperature and raw materials composition (i.e., 0–100 wt% of KA in the mixture of KA + FA) on the membrane properties (strength, porosity, pore size, permeability, etc.) were studied. The raw material mixtures were subjected to TGA and the prepared membranes were characterized by SEM, XRD, liquid permeation, mechanical strength and chemical stability tests. The SEM analysis evidenced that the membranes were free of defects and had homogeneous surface structure with evenly distributed pores of similar sizes. A sintering temperature of 900 °C was found to be optimum for both kaolin-based and fly ash based membranes. Addition of 20% dolomite provided sufficient porosity to all membranes (28–51%). The porosity, strength and stability increased, while the pore diameter decreased with an increase in the kaolin content (M0–M100). The sintered mixture with a kaolin content of 75% (M75) was identified as the best membrane among others based on the pore characteristics (mean pore diameter 0.62 μm and porosity 46.3%). When applied to oil-water separation, M75 showed excellent filtration performance with good separation efficiency (up to 97.4% for 100 mg/L oil and up to 98.8% for 200 mg/L oil). The average permeate quality obtained at 1.03 bar pressure difference was found to be within the safe discharge limit (<10 mg/L). Although, the permeate flux declined steadily with time, it has been recovered through membrane regeneration. Model fitting to the flux data indicated the formation of a cake layer because of concentration polarization at the membrane surface during dead-end filtration.