Review on the application and development of red mud-based photocatalytic materials for degradation of organic pollutants in water

Red mud is a strong alkaline solid waste that is discharged from alumina production process. Its cumulative storage and annual emission are huge with about 0.8–1.5 t of red mud emitted for 1 t of alumina produced. As of 2018, the global cumulative emissions of red mud were about 4 billion t and increased by 120 million tons annually. In China, about 100 million tons of red mud are discharged annually and the comprehensive utilization rate of red mud is about 4%, which is mainly stored in the Red Mud Dam. This often causes serious damage to the surrounding environment, as the red mud with high alkalinity and radioactivity raises the alkalization of soil and leaching into the groundwater through diffusion and infiltration. The comprehensive utilization of red mud is mainly to prepare building materials, ceramics materials, new functional materials, and recover valuable metals. As a low-cost, efficient, and safe environment-friendly environmental purification technology, photocatalytic technology is considered to be one of the best solutions to the severe energy crisis and environmental pollution problems that the world is currently facing. Semiconductor photocatalytic materials (such as Fe₂O₃, TiO₂, ZnO) have been widely studied in the degradation of organic pollutants in water. Red mud is rich in iron oxides and has a high specific surface area and pore structure. In recent years, red mud-based photocatalytic materials have attracted much attention in the photocatalytic degradation of organic pollutants in water. In this paper, the characteristics of red mud were introduced. The preparation methods of red mud-based photocatalytic materials were summarized and its application in the photocatalytic degradation of organic pollutants in water was summarized. The mechanism of red mud-based photocatalytic materials for degradation of organic pollutants in water was described, and the existing problems of these materials were discussed. Finally, the future development trend of red mud-based photocatalytic materials was proposed based on previous research results.