A novel thermal spraying technique to fabricate fly ash/alumina composite membranes for oily emulsion and spent tin wastewater treatment

Ceramic membranes with asymmetric structures play an important role in treating wastewater in the chemical engineering industry. However, the asymmetric structure requires repetitive “coating-drying-sintering” processes to achieve a ceramic membrane with satisfactory separation accuracy, which in turn requires a long fabrication period and has limited the widespread application of such membranes. Herein, a single-step coating preparation for a high-performance asymmetric ceramic membrane using macroporous fly ash supports has been developed using a thermal spraying technique. The novel coating process can not only prevent the penetration phenomenon and avoid the need for intermediate layers, but also significantly lower the fabrication time and cost of the ceramic membranes. Based on theoretical calculations using the Hagen-Poiseuille (H-P) and Darcy equations, the resistance of the supports and fabricated membrane layer accounted for 8.5% and 91.5% of the total resistance, respectively. The resistance distribution indicates a reasonable membrane structure, with the resistance being mainly concentrated on the membrane. This indicates that the supports only provide high bending strength and do not have an adverse effect on the permeability performance. The fly ash/alumina composite membranes (FACMs) fabricated under the optimized conditions had pore diameters of approximately 100 nm and a permeability of approximately 445 L m⁻² h⁻¹ bar⁻¹ (at 0.1 MPa). In the treatment of oily emulsions and spent tin wastewater, the FACMs showed good total organic carbon (TOC) retention (above 99%) and a high rejection for stannic acid (above 99.9%) in industrial spent tin wastewater from the printed circuit board industry. The technique of combining low-cost fly ash supports and the optimized membrane structure could significantly decrease the membrane cost and serve as an efficient method for wastewater treatment.