Abstract: Red mud is a kind of strong alkaline solid waste discharged in the process of alumina production. The annual emission is huge and the utilization rate is low,which causes serious waste of resources and environmental pollution. How to effectively recycle and utilize red mud is an urgent problem to be solved. Based on the hazard,physical and chemical properties and comprehensive utilization status of red mud,the application research progress of red mud-based adsorbents is reviewed in detail. Red mud has a fine particle size,high specific surface area and porosity,and contains a variety of active ingredients, which is suitable for treating wastewater containing pollution. However,if red mud is directly applied to sewage treatment,its treatment capacity is limited,and if highly alkaline red mud is directly used to treat sewage,the pH value of the solution will increase. Therefore,a series of activation processes are often used to activate red mud to prepare red mud-based adsorbents. The activation process not only improves the adsorption performance of red mud-based adsorbents,but also prevents secondary pol-lution caused by red mud to a certain extent. At present,the commonly used activation process of red mud mainly includes acid activation process,thermal activation process and neutralization activation process. The acid activation process can significantly improve the adsorption effect of red mud on anions. The thermal activation process can reduce the mass transfer resistance,high temperature pore-forming and mineral transformation,but the cost is high. Neutralizing activated red mud is often used to treat metal cations. The combined activation technology can comprehensively utilize the advantages of single activation process mentioned above,so that the activated red mud has better adsorption performance. However,the combined activation technology has more complicated operation and higher cost,which makes it difficult to be applied on a large scale in industry. At present,red mud-based adsorbents have been studied for the treatment of non-metallic anions,metal cations and organic pollutants in wastewater. In this paper,the examples of removing anions and heavy metal cations in wastewater by red mud-based adsorbents are listed,and the removal mechanism is expounded. Red mud-based adsorbents show good adsorption performance for some specific pollutants in wastewater,such as PO3- 4 ,F- ,AsO3- 4 ,etc. ,which mainly remove anionic pollutants in wastewater through surface complexation,ion exchange and precipitation. The red mud after activation modification can effectively remove heavy metal cations such as lead,copper,chromium and other heavy metal cations in water. For different target cations,the removal mechanism is also different,mainly including ion exchange,coprecipitation,electrostatic attraction," cation-π" interaction, complexation and physical adsorption. However,the removal mechanism of various pollutants by red mud-based adsorbents has not been fully clarified,and there are few studies on the competitive adsorption system in the presence of multiple pollutants. In summary,it is pointed out that in the future research of red mud-based adsorbents,it is an important research direction to find a convenient and cheap activation process to prepare new,efficient and environmentally friendly adsorbents and improve the adsorption performance of red mud-based adsorbents. At the same time,in the study of the preparation of red mud-based adsorbents and the treatment of waste,the research on the preparation mechanism and adsorption mechanism should be strengthened to provide theoretical guidance for the production and industrial application of red mud-based adsorbents.

Key words: red mud,resource utilization,adsorbents,waste water