4.2 Comprehensive utilization processes of iron-rich red mud

During the past decades, extensive work has been done by a lot of researchers to develop various economic ways for the utilization of red mud. Such as the red mud from sintering process, containing some reactive substance such as β-2CaOSiO2, can be used to produce construction materials directly [49, 61]. However, in Bayer process, Al2O3 is dissolved depending on sodium hydroxide from high-iron, highaluminum boehmite and gibbsite bauxite without calcination. Thus, there is less pozzolanic active substance in the Bayer red mud. It is not feasible to use red mud from Bayer process as construction materials directly [62]. Tsakiridis et al. [43] reported the research work on Bayer red mud addition in the raw meal for the production of Portland cement clinker. However, only 3–5% red mud can be mixed with other raw materials, and it is not an effective way compared with the huge amount of the produced red mud. Pontikes et al. [63] did some research work on the thermal behavior of clay mixtures with bauxite residue for the production of heavyclay ceramics, which has potential utilization of red mud in industries. However, this method does not give full play to the potential value of red mud, and the

valuable metals in red mud are not utilized effectively. Some techniques of recovery of rare elements from red mud are not applied because of the complicated procedure and high cost, although some useful production such as gallium (Ga), titanium

Aluminum Mineral Processing and Metallurgy: Iron-Rich Bauxite and Bayer Red Muds

As the high-iron content of the Bayer red mud, there are many techniques that have been intensively investigated for practical implementation with the purpose of recovering valuable components from this waste, such as combined pyrometallurgy and hydrometallurgical process [67], solid-state carbothermic reduction and magnetic separation [68], acid leaching [67] and smelting in a blast furnace [69]. A new concept of using red mud directly for ironmaking/smelting gives further promise. A combined pyrometallurgical and hydrometallurgical process could also be employed to recover aluminum, iron and titanium elements [67]. The process flowsheet is shown in Figure 10. It can be seen that the red mud was first dried and then mixed with coal, lime and sodium carbonate. The mixture is reduced and sintered at 800–1000°C. The sintered products underwent water leaching at 65°C for 1 h and 89% aluminum involved in the products was leached out. The filtrate obtained can be recycled in the Bayer process, and the residue was subjected to high-intensity magnetic separation. The titanium in the non-magnetic portion was taken to the solution by leaching with sulfuric acid. The titanyl sulfate was filtered and then hydrolyzed to metatitanic acid. This acid was then roasted to form TiO2 (87–89% grade). At last, the magnetic portion was smelted at 1480°C and a product

Li et al. [68] carried out stepwise extraction of valuable components like Fe2O3, Al2O3 and SiO2 from reduced red mud by magnetic separation and sulfuric acid leaching. During the reductive roasting of red mud, sodium played an important role in reducing the dispersity of iron and hence increased the efficiency of magnetic separation. They found that the red mud was reduced at 1050°C for 60 min in

dioxide (TiO2) and scandium (Sc) can be obtained [64–66].

DOI: http://dx.doi.org/10.5772/intechopen.78789

containing 93–94% Fe, 4.5% C, was obtained.

Figure 12.

25

Process flowsheet for metal recovery from red mud [67].

#### Aluminum Mineral Processing and Metallurgy: Iron-Rich Bauxite and Bayer Red Muds DOI: http://dx.doi.org/10.5772/intechopen.78789

valuable metals in red mud are not utilized effectively. Some techniques of recovery of rare elements from red mud are not applied because of the complicated procedure and high cost, although some useful production such as gallium (Ga), titanium dioxide (TiO2) and scandium (Sc) can be obtained [64–66].

As the high-iron content of the Bayer red mud, there are many techniques that have been intensively investigated for practical implementation with the purpose of recovering valuable components from this waste, such as combined pyrometallurgy and hydrometallurgical process [67], solid-state carbothermic reduction and magnetic separation [68], acid leaching [67] and smelting in a blast furnace [69]. A new concept of using red mud directly for ironmaking/smelting gives further promise.

A combined pyrometallurgical and hydrometallurgical process could also be employed to recover aluminum, iron and titanium elements [67]. The process flowsheet is shown in Figure 10. It can be seen that the red mud was first dried and then mixed with coal, lime and sodium carbonate. The mixture is reduced and sintered at 800–1000°C. The sintered products underwent water leaching at 65°C for 1 h and 89% aluminum involved in the products was leached out. The filtrate obtained can be recycled in the Bayer process, and the residue was subjected to high-intensity magnetic separation. The titanium in the non-magnetic portion was taken to the solution by leaching with sulfuric acid. The titanyl sulfate was filtered and then hydrolyzed to metatitanic acid. This acid was then roasted to form TiO2 (87–89% grade). At last, the magnetic portion was smelted at 1480°C and a product containing 93–94% Fe, 4.5% C, was obtained.

Li et al. [68] carried out stepwise extraction of valuable components like Fe2O3, Al2O3 and SiO2 from reduced red mud by magnetic separation and sulfuric acid leaching. During the reductive roasting of red mud, sodium played an important role in reducing the dispersity of iron and hence increased the efficiency of magnetic separation. They found that the red mud was reduced at 1050°C for 60 min in

Figure 12. Process flowsheet for metal recovery from red mud [67].

4.2 Comprehensive utilization processes of iron-rich red mud

Aluminium Alloys and Composites

Figure 11.

24

Process flowsheet for reduction, roasting and magnetic separation process of red mud [68].

During the past decades, extensive work has been done by a lot of researchers to develop various economic ways for the utilization of red mud. Such as the red mud from sintering process, containing some reactive substance such as β-2CaOSiO2, can be used to produce construction materials directly [49, 61]. However, in Bayer process, Al2O3 is dissolved depending on sodium hydroxide from high-iron, highaluminum boehmite and gibbsite bauxite without calcination. Thus, there is less pozzolanic active substance in the Bayer red mud. It is not feasible to use red mud from Bayer process as construction materials directly [62]. Tsakiridis et al. [43] reported the research work on Bayer red mud addition in the raw meal for the production of Portland cement clinker. However, only 3–5% red mud can be mixed with other raw materials, and it is not an effective way compared with the huge amount of the produced red mud. Pontikes et al. [63] did some research work on the thermal behavior of clay mixtures with bauxite residue for the production of heavyclay ceramics, which has potential utilization of red mud in industries. However, this method does not give full play to the potential value of red mud, and the

the presence of 6% Na2CO3 and 6% Na2SO4. In the enrichment of TiO2 by sulfuric acid leaching, 94.7% Fe, 98.6% Al and 95.9% Si were extracted and left behind a material having 37.8% TiO2. The process flowsheet for reduction, roasting and magnetic separation process of red mud is shown in Figure 11.

Piga et al. [67] used the acid leaching process to dispose the red mud, and they found that the titanium is soluble in sulfuric acid but not in hydrochloric acid. This process increased the recovery of TiO2 content in the residue from 31 to 58%. The solids were then leached with sulfuric acid at 270°C, followed by hydrolysis and roasting. The TiO2 content obtained was 96%. The product can be used directly as TiO2 pigment or chlorinated to form TiCl4. The process flowsheet for TiO2 recovery from red mud is shown in Figure 12.
