Introduction

Bauxite residue is the industrial solid waste discharged from the production of alumina by bauxite, which contains a certain amount of ferric oxide in a reddish-brown color, so it is also called “red mud”, and is a typical non-ferrous metallurgical solid waste (Wang et al. 2018; Xue et al. 2022). The varieties of bauxite residue depend on the grade of the bauxite and alumina production process. It can be classified as Bayer method bauxite residue (red mud), sintering method bauxite residue (red mud), and Bayer-sintering combination method bauxite residue (red mud) (Ke et al. 2021; Sutar et al. 2014). Currently, the Bayer process is responsible for more than 90% of the world’s alumina production, so Bayer bauxite residue accounts for more than 90% of all bauxite residue emissions (Lu et al. 2019; Zhang et al. 2020a). The Bayer process of alumina production involves bauxite reacting with NaOH solution under high temperature and pressure to obtain sodium aluminate solution, then adding Al(OH)3 crystals to precipitate Al(OH)3 solid and calcining to produce alumina products. The remaining alkali liquor is reused to treat the next batch of bauxite. The tailing obtained in this process is bauxite residue, which is extremely alkaline and therefore a strong alkaline solid waste (Liu et al. 2009; Mishra and Gostu 2017; Narayan et al. 2021). Bayer method has the incomparable advantages of the sintering method and combined method, low energy consumption, simple process and low cost, so it is widely used.

Due to different grades of bauxite, approximately 2–3 tons of bauxite will be consumed to generate 1–2.5 tons for every 1 ton of alumina produced, and the bauxite residue emission progressively increases with the reduction in the bauxite grade (Agrawal and Dhawan 2021; Jones et al. 2012). The annual emissions of bauxite residue in the world range from 100 million tons to 150 million tons (Habibi et al. 2021). In 2020, global alumina production was 136 million tons, bauxite residue emissions were approximately 176.8 million tons (USGS, 2021), the amount in China exceeded 100 million, and the accumulated stockpile reached 600 million tons. Affected by the distribution of bauxite mining areas, bauxite residue in China is mainly distributed in Henan, Shanxi, Shandong, Guizhou, and Guangxi, with a secondary distribution in Inner Mongolia, Hebei, Chongqing, and Yunnan, as shown in Fig. 1. At present, the global comprehensive utilization rate of is less than 15%, and less than 5% in China (Wang et al. 2018). A large amount of bauxite residue is in the state of stockpiling, including wet treatment and pumping to storage tanks or open storage using semidry or dry technology (Lyu et al. 2021).

Fig. 1
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Distribution of bauxite residue in China

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Massive amounts of bauxite residue are being disposed of and stored, which is becoming a severe environmental issue. Experts at home and abroad have focused their attention on the comprehensive utilization technology of bauxite residue to effectively decrease the threat of bauxite residue accumulation to the environment, and have achieved certain results. This study presents local and international studies on the use of bauxite residue in environmental protection, with the goal of assisting in the reduction and safe application of bauxite residue.

Properties of Bauxite Residue

Characteristics of Bauxite Residue

Depending on the alumina production process, the chemical composition and mineral phase structure of bauxite, the composition of bauxite residue is also different. Table 1 shows the composition comparison of different types of bauxite residue (Nan et al. 2009). According to the different iron contents, bauxite residue can be divided into high iron (Fe2O3: 30−60%) and low iron (Fe2O3: 10−30%).

Table 1 Chemical composition of different types of bauxite residue (wt%)
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Bauxite residue has fine particles with an average particle size of less than 10 μm, and 90% of the particles are less than 75 μm (Rao and Reddy 2017). Bauxite residue has a large specific surface area, which is generally 64.09–186.9 m2/g depending on the degree of bauxite being crushed during the production process, and has similar characteristics to porous materials with a pore ratio of 2.5–3 (Nan et al. 2010). In addition, bauxite residue has a high water content (700–1000 kg/m3), accounting for 79–93% of the total weight, and it has strong compressibility with a plastic index of 17–30. The chemical composition and specific physicochemical properties of bauxite residue determine its broad application potential in many fields.

Hazards of Bauxite Residue

In the past, some coastal alumina producers have taken advantage of their location to discharge bauxite residue into the ocean (Burke et al. 2012). In recent years, with the increase in global environmental awareness, the direct discharge of bauxite residue into the sea has been explicitly restricted. In China, a large amount of bauxite residue is stored in the open air, and most dams are constructed from bauxite residue. Its effective treatment has become a worldwide environmental protection problem, and its main hazards are as follows:

(1) The bauxite residue storage not only occupies a large amount of land to construct the storage yard but also has serious safety risks. Notably, in extreme weather, such as a rainstorm, the leakage of the bauxite residue storage yard will have a devastating impact on downstream farmland.

(2) Bauxite residue contains a large amount of strongly alkaline chemicals, which leads to strong corrosion of biomass, metals, and silica materials (Kannan et al. 2021), and it seeps into underground or surface water, raising the pH value of water and critically polluting water sources (Liang and Chen 2014).

(3) Dehydrated and weathered bauxite residue can easily cause dust pollution. The flying bauxite residue dust not only causes air pollution but also seriously affects the visibility of the storage site.

In recent years, there have been many incidents of bauxite residue yard breaches in alumina production enterprises all over the world. On October 4, 2010, the bauxite residue dam burst at the Ajkai alumina refinery in southwestern Hungary, resulting in the release of 1.0 × 106 cm3 of bauxite residue, causing heavy casualties and sparking panic in many European countries (Burke et al. 2012); On August 8, 2016, a bauxite residue landslide occurred at the dam of an aluminum company’s bauxite residue reservoir in Henan Province, China, resulting in the burying of a huge number of houses, livestock, grain and other properties in a village downstream, affecting more than 300 people (Novais et al. 2018). Obviously, the disposal of bauxite residue has a direct impact on the aluminum industry’s long-term sustainable development.

Utilization of Bauxite Residue

Currently, the technologies for the integrated application of bauxite residue include the following:

(1) Production of building materials (Babisk et al. 2020; Molineux et al. 2016; Somlai et al. 2008). However, this method is not suitable for the treatment of Bayer process bauxite residue, because of the high alkali content of Bayer bauxite residue, the cost of its dealkalization is expensive, and the small transportation radius;

(2) The production of decorative tiles, door filler materials, etc. (Xu et al. 2019). The main drawback of this method is that the amount of use is relatively small, which cannot be achieved for the large-scale elimination of Bayer bauxite residue.

(3) Extraction of valuable metal elements (Li et al. 2016; Wang et al. 2021; Zhu et al. 2019). The main technologies include two types: one is to recover valuable components such as aluminum, iron, and scandium by acid leaching, which has technical problems such as high operation costs, large equipment investment, and secondary pollution caused by acidic slag. The other is to recover the iron, but this kind of technology is only applicable to the treatment of bauxite residue discharged from alumina production areas using high-iron bauxite.

(4) Environmental treatment and ecological restoration, such as water purification, flue gas purification, soil improvement, bauxite residue reclamation, and preparation of environmental restoration materials, as shown in Fig. 2. (Wang and Liu 2021; Zhang et al. 2021; Zhang et al. 2020b).

Fig. 2
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Research progress in the environmental application of bauxite residue

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Research Status of Application in Ecological Environmental

Application in Wastewater Treatment

Bauxite residue is utilized as an adsorbent for water treatment because of its large specific surface area and porosity, as well as its strong adsorption capacity, which allows it to filter and remove pollutants from wastewater. Currently, the main applications are the preparation of wastewater clarifiers for the removal of toxic heavy metals or quasi-metallic ions such as Cu (II), Cr (V), As (V), Cd (II) (Danış 2005; Nadaroglu et al. 2010), inorganic anions such as PO4 3−, F−, NO3 − and organic pollutants from wastewater (Çengeloğlu et al. 2002). Lu et al. (2021) investigated the use of bauxite residue to treat wastewater discharged from a non-ferrous smelter, and the results showed that bauxite residue could remove nearly 100% of As from the wastewater at room temperature, with a maximum arsenic removal capacity of 101.5 mg/g at a ratio of bauxite residue to wastewater of 40 g/L. Gao et al. (2021) studied the use of bauxite residue and corn straw pyrolysis to prepare functional biochar composites to treat acid dye wastewater, the results showed that the material prepared at 600 ℃ contained CaO for acid neutralization, Fe0 for magnetic material collection, and biomass carbon for adsorption, and had good wastewater treatment capacity. Shi et al. (2020) explored the preparation of bauxite residue/g-C3N4 composites by one-step thermal polymerization of bauxite residue and melamine to treat the organic matter in wastewater and found that the optimal 0.8% bauxite residue/g-C3N4 composite had good antibiotic (TC, OTC, and CTC) and dye (MB and MG) removal ability in the synergistic action of adsorption and photocatalysis.

Application in Soil Remediation

Bauxite residue can be used to restore contaminated soil, upgrade acidic soil and soil lacking in nutrients because of its special physicochemical properties (Brennan et al. 2019; Xue et al. 2021). Zhang et al. (2021) studied the rapid transformation of bauxite residue into a soil matrix by co-hydrothermal carbonization with biomass waste, and the results showed that the elimination of bauxite residue alkalinity could be achieved by this technique, the soil properties of tailings were improved, and ryegrass grew well in this soil substrate. Li et al. (2018) investigated the use of bauxite residue, diatomaceous earth, and lime (5:3:2) as passivation agents to remediate acidic Cd-contaminated rice fields, and the results showed that the application of bauxite residue -based passivation agents reduced the cadmium concentration and increased the pH value in acidic soils and improved rice yields. Ujaczki et al. (2016) evaluated the potential use of red mud-soil mixture (RMSM) as a surface additive for landfills and showed that the incorporation of RMSM at 20% w/w into the subsoil could be used as a surface layer for landfill covering systems. Wang et al. (2021; 2019) studied the extraction of alumina and sodium oxide from bauxite residue by the calcification-carbonization method, and the tail residue was remediated for soil reclamation. The main process of this technology is illustrated in Fig. 3. The basic principle is to complete the calcification transformation of bauxite residue by adding CaO and obtaining the calcification residue with hydrogarnet as the main phase. Following that, the calcified residue was carbonized by passing CO2 through it, yielding the carbonized residue containing CaCO3, xCaO·ySiO2, and Al(OH)3. Last, the low-concentration alkaline solution is used to dissolve the carbonized residue under low-temperature conditions to obtain tailings with lower Na2O and Al2O3 contents, where the Na2O content does not exceed 1%, which meets the general soil indicators.

Fig. 3
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Process diagram of bauxite residue treatment by calcification-carbonization-tailings soil reclamation technology

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Application in Flue Gas Purification

Bauxite residue is rich in alkaline substances and has good absorbability, which makes it widely used in flue gas purification treatment of SOx, H2S, NOx, COx, and so on (Sahu et al. 2011). Yang et al. (2018) researched the removal of elemental mercury from flue gas using various potassium halides modified bauxite residue, and the findings revealed that KI modified bauxite residue had the best Hg0 removal efficiency. Nie et al. (2019) researched the use of bauxite residue for flue gas desulfurization, and the results showed that bauxite residue has good desulfurization ability and that desulfurized tailings can be used as a chemical activator, in which C-grade fly ash was added to produce a high-quality product. Yadav et al. (2010) studied the sequestration of CO2 gas by bauxite residue, and the results showed that bauxite residue with a 4.57% weight%, 1.8 g/cm3 relative density, and an average size of 30 μm could capture CO2 more effectively, reaching 5.3 g CO2/100 g bauxite residue, which makes an important contribution to carbon emission reduction.

Conclusions

Bauxite residue as bulk solid waste from the aluminum industry poses a great threat to the ecological environment as well as human life safety. This paper describes the applications of bauxite residue for wastewater treatment technology, soil remediation technology, and flue gas purification technology, which have made some research progress in terms of adsorption mechanisms and optimization techniques. The current status of the integrated utilization of bauxite residue treatment in the environment is reviewed, which provides a research basis for the large-scale disposal of bauxite residue in industry. In general, putting these technologies into actual industrial production deserves further development and research to contribute to the reduction of bauxite residue.

In conclusion, the treatment of bauxite residue and the improvement of its comprehensive utilization rate are urgent problems to be resolved. This research indicates that it is feasible to produce mineral compound fertilizer with bauxite residue according to its chemical composition and special physicochemical properties. Bauxite residue can be used on a large scale in this way, which has the advantages of low cost and easy industrial production. On the one hand, it can improve the utilization rate of bauxite residue and decrease the threat to ecological environmental safety. On the other hand, it can alleviate the deficiency of soil trace elements, provide nutrition for crop growth and reduce the pressure on the fertilizer industry.