Catalytic Combustion of Biodiesel Wastewater on Red Mud Catalyst

The resource utilization of red mud (RM) has attracted widespread attention for achieving the waste-to-waste treatment goal. In this work, the RM catalysts were synthesized at different calcination temperatures by a simple method. The calcination temperature had a great effect on catalyst activity in the catalytic combustion of biodiesel wastewater. The RM catalyst calcined at 350 °C (RM350) exhibited the best catalytic activity. The chemical oxygen demand (COD) and COD removal rate of the treated wastewater reached almost 0 mg/L and 100%, respectively. The COD removal rate was significantly higher than 90.703% of the catalyst prepared by α-Fe₂O₃ at the same calcination temperature. Characterization results showed that the RM catalyst exhibited a high specific surface area of 60.03-64.15 m²/g and a well-developed mesoporous structure, as the calcination temperature did not exceed 400 °C, which was beneficial for adsorption and diffusion. Meanwhile, most of the Fe₂O₃ in the catalyst existed in an amorphous form and was abundantly presented on the catalyst surface, significantly lowering the reduction temperature of the catalyst and enhancing its reducibility. Furthermore, the α-Fe₂O₃ in the catalyst had higher dispersion, leading to an increase in utilization efficiency.