Fabrication of Novel Ceramic Membrane Using Coal Fly Ash Blended with Fuller’s Clay for Separation of Technical Lignin

Abstract

In this study, waste coal fly ash was blended with fuller’s clay to fabricate a novel ceramic membrane for the efficient separation of technical lignin from aqueous solutions. A circular ceramic membrane was prepared using the uniaxial compaction method as a value-added product from waste fly ash. The fabricated membrane was sintered at 800°C according to the thermogravimetric analysis (TGA) results. The Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses confirmed the presence of similar compounds and the crystalline structure of the membrane before and after the sintering. The hydrophilic behavior of the membrane was confirmed using contact angle (23.258°) analysis. In addition, the zeta potential (−65.4 mV) showed the negative charge of the sintered membrane. The porous morphology of the membrane was confirmed by scanning electron microscope (SEM) analysis. The presence of more silicon (Si) and aluminum (Al) was established by the energy dispersive X-ray spectroscopy (EDX) results. The atomic force microscopy (AFM) scan exhibits a relatively rough surface, and the average pore diameter was from 71 to 74 nm. The nitrogen (N2) adsorption analysis using the Brunauer–Emmett–Teller (BET) method confirms the surface area of 7.2643 × 10−1 m2/g and total pore volume of 3.1242 × 103 cm3/g, with average pore diameter of 17 nm. The molecular weight cut-off (MWCO) of the fabricated membrane was 8,329.91 Da. The separation of technical lignin from an aqueous solution was carried out at different transmembrane pressures (69–345 kPa), lignin feed concentrations (5–20 g/L), and feed pH (2–12) using a dead-end filtration setup. The increasing concentration increased the lignin separation efficiency from 34.8% to 72.2%, with the highest permeate flux of 18.18 L/m2/h. However, when the applied pressure increased, the lignin separation efficiency decreased from 72.2% to 40.8%. Of interest, the high separation efficiency was achieved at very acidic (pH 2) while the feed pH was varied. The fabricated membrane achieved a pore radius of 57 nm and came under the range of ultrafiltration. Therefore, the fabricated membranes from fly ash could be considered a value-added product for effective lignin separation.