3. Iron-rich bauxite processing and metallurgy

Iron-rich bauxite ore usually contains over 40 wt% iron oxide [11, 12], huge reserves are found in Australia, Guinea, Brazil, Laos, Vietnam and China, but they have not yet been used effectively. It is worth noting that more than 1.5 billion tons of iron-rich bauxite resources have been explored over the last 20 years in western Guangxi, China [13–15], which belong to the high-iron, low-aluminum silicon ratio type bauxite. These bauxites are very difficult to be leached by the Bayer process also and cannot be used as blast furnace burden. Iron-rich bauxite contains large amounts of silica and iron oxide with complex mineralogical composition and characteristics, which limit the use of this material as feedstock for conventional processes.

China's bauxite reserves are only 3% of the world's bauxite reserves, mainly deposited in Shanxi, Guizhou, Henan and Guangxi provinces. However, the ironrich bauxite accounts for more than 30% of China's total bauxite resources, which has a great deal of economic value, and more than 1.5 billion tons have been explored in the last 20 years. The typical iron-rich bauxite deposited in Guigang of Guangxi, China is shown in Figure 3.

#### 3.1 Mineralogical characteristics of iron-rich bauxite

The typical iron-rich bauxite ore was provided by the Guigang Mine of Guangxi, China. The chemical composition of the iron-rich bauxite is shown in Table 1. It can be seen that the iron-rich bauxite mainly consisted of 40.42 wt% Fe2O3, 11.70 wt%

Figure 3.

The typical iron-rich bauxite ore (a) and mineral powder (b) deposited in Guigang of Guangxi, China.


Table 1.

Chemical composition of iron-rich bauxite sample.

SiO2, and 26.53 wt% Al2O3. The particle size distribution of iron-rich bauxite is shown in Figure 4(a) which was obtained with the Malvern Mastersizer 2000 particle size analyzer. The analysis results show that the average particle diameter and specific surface area of mixtures are 88.431 μm and 0.149 m<sup>2</sup> /g, respectively. The mineral phase composition of iron-rich bauxite was identified by X-ray diffraction (XRD) as shown in Figure 4(b). It can be seen that the gibbsite [Al(OH)3], diaspore [AlO(OH)], goethite [FeO(OH)], hematite (Fe2O3) and kaolin (Mg2Si3O82H2O) are major mineral components in bauxite ore, the anatase (TiO2) and quartz (SiO2) are minor components.

from K-feldspar and clay minerals during laterization processes, and it is characterized by a small crystal size. The gibbsite with relatively perfect crystals was commonly formed via precipitation from Al-rich solutions within the bauxite horizon. Anatase commonly precipitated in a reducing condition in the formation of the

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

The heterogeneous minerals in iron-rich bauxite are treated with conventional techniques, such as gravity concentration [18], magnetic separation [19], flotation [20], roasting followed by magnetic separation [21, 22] and chemical leaching [23, 24]. All of these conventional techniques cannot recover iron and aluminum from iron-rich bauxite effectively. The reverse flotation process of iron-rich bauxite cannot achieve effective separation of Al2O3 and SiO2, because it is characterized by a high content of Al2O3 and SiO2 and a low ratio of Al2O3 to SiO2 (m(Al2O3)/m (SiO2) = A/S, usually 2–3) [25]. In order to produce a raw material suitable for sponge, the microwave reduction roasting and wet magnetic separation process of red mud was reported, only the total iron concentration of 35.15 and metallization

degree of 69.3 wt% were obtained in the process [21]. The lateritic bauxite hydrochloric acid leaching process showed that when the ore granularity was less than 55 μm, the liquid/solid ratio (L/S ratio) was 100:7, the leaching temperature was 373–383 K, the leaching time was 120 min and the HCl concentration was 10%, both the leaching rates of Al and Fe were over 95% [26]. But the hydrochloric acid leaching process was very expensive and caused serious environment pollution. However, the high-temperature reduction and smelting process exhibit a lot of advantages for ironmaking [27, 28]. In this processes, carbon composite pellets are reduced and smelted to produce metallic iron, which is then separated from slag at a furnace temperature of 1573 K or higher. High-quality iron nuggets are an ideal feed material for steelmaking and can be used for electric arc furnace charging or as a basic oxygen furnace coolant [29, 30]. Zhang et al. [31] successfully obtained iron nuggets and autogenously pulverizable calcium aluminate slag from iron-rich bauxite through a high-temperature reduction and smelting process. The flow diagram for recovering iron and autogenously pulverizable slag from iron-rich bauxite

3.2 Comprehensive utilization processes of iron-rich bauxite

karst bauxite deposit [16, 17].

The microphotographs of typical iron-rich bauxite sample.

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

Figure 5.

is shown in Figure 6.

19

The ore microscope observation shows that the mineral components in the bauxite ores are cryptocrystalline diaspore, hematite, ferrihydrite, kaolinite, anatase, vanadium titanomagnetite and chamosite (Figure 5(a)–(f)). It can be seen that most of the diaspores are cryptocrystalline with a small particle size and mainly coexists with ferrihydrite (Figure 5(d) and (f)). Kaolinite is the major clay mineral in the iron-rich bauxite. Kaolinite mainly coexists with gibbsite and anatase, and the edges of the gibbsite that are adjacent to the kaolinite show clear corrosion (Figure 5(b)), suggesting that kaolinite may have formed partially at the expense of gibbsite. Although most of the gibbsite are lamellar (Figure 5(a)), small amounts of euhedral-hypidiomorphic gibbsite (50–300 μm) could be discovered in the matrix of the bauxite ores (Figure 5(b)). Most of the gibbsite in nature was transformed

Figure 4. The particle size distribution (a) and XRD pattern (b) of typical iron-rich bauxite sample.

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

Figure 5. The microphotographs of typical iron-rich bauxite sample.

from K-feldspar and clay minerals during laterization processes, and it is characterized by a small crystal size. The gibbsite with relatively perfect crystals was commonly formed via precipitation from Al-rich solutions within the bauxite horizon. Anatase commonly precipitated in a reducing condition in the formation of the karst bauxite deposit [16, 17].

#### 3.2 Comprehensive utilization processes of iron-rich bauxite

The heterogeneous minerals in iron-rich bauxite are treated with conventional techniques, such as gravity concentration [18], magnetic separation [19], flotation [20], roasting followed by magnetic separation [21, 22] and chemical leaching [23, 24]. All of these conventional techniques cannot recover iron and aluminum from iron-rich bauxite effectively. The reverse flotation process of iron-rich bauxite cannot achieve effective separation of Al2O3 and SiO2, because it is characterized by a high content of Al2O3 and SiO2 and a low ratio of Al2O3 to SiO2 (m(Al2O3)/m (SiO2) = A/S, usually 2–3) [25]. In order to produce a raw material suitable for sponge, the microwave reduction roasting and wet magnetic separation process of red mud was reported, only the total iron concentration of 35.15 and metallization degree of 69.3 wt% were obtained in the process [21]. The lateritic bauxite hydrochloric acid leaching process showed that when the ore granularity was less than 55 μm, the liquid/solid ratio (L/S ratio) was 100:7, the leaching temperature was 373–383 K, the leaching time was 120 min and the HCl concentration was 10%, both the leaching rates of Al and Fe were over 95% [26]. But the hydrochloric acid leaching process was very expensive and caused serious environment pollution.

However, the high-temperature reduction and smelting process exhibit a lot of advantages for ironmaking [27, 28]. In this processes, carbon composite pellets are reduced and smelted to produce metallic iron, which is then separated from slag at a furnace temperature of 1573 K or higher. High-quality iron nuggets are an ideal feed material for steelmaking and can be used for electric arc furnace charging or as a basic oxygen furnace coolant [29, 30]. Zhang et al. [31] successfully obtained iron nuggets and autogenously pulverizable calcium aluminate slag from iron-rich bauxite through a high-temperature reduction and smelting process. The flow diagram for recovering iron and autogenously pulverizable slag from iron-rich bauxite is shown in Figure 6.

SiO2, and 26.53 wt% Al2O3. The particle size distribution of iron-rich bauxite is shown in Figure 4(a) which was obtained with the Malvern Mastersizer 2000 particle size analyzer. The analysis results show that the average particle diameter

The typical iron-rich bauxite ore (a) and mineral powder (b) deposited in Guigang of Guangxi, China.

Fetot Fe2O3 FeO SiO2 Al2O3 TiO2 MnO MgO CaO LOI 28.29 40.42 0.20 11.77 26.53 1.57 1.21 0.48 1.38 16.42

The mineral phase composition of iron-rich bauxite was identified by X-ray diffraction (XRD) as shown in Figure 4(b). It can be seen that the gibbsite [Al(OH)3],

(Mg2Si3O82H2O) are major mineral components in bauxite ore, the anatase (TiO2)

The ore microscope observation shows that the mineral components in the bauxite ores are cryptocrystalline diaspore, hematite, ferrihydrite, kaolinite, anatase, vanadium titanomagnetite and chamosite (Figure 5(a)–(f)). It can be seen that most of the diaspores are cryptocrystalline with a small particle size and mainly coexists with ferrihydrite (Figure 5(d) and (f)). Kaolinite is the major clay mineral in the iron-rich bauxite. Kaolinite mainly coexists with gibbsite and anatase, and the edges of the gibbsite that are adjacent to the kaolinite show clear corrosion (Figure 5(b)), suggesting that kaolinite may have formed partially at the expense of gibbsite. Although most of the gibbsite are lamellar (Figure 5(a)), small amounts of euhedral-hypidiomorphic gibbsite (50–300 μm) could be discovered in the matrix of the bauxite ores (Figure 5(b)). Most of the gibbsite in nature was transformed

/g, respectively.

and specific surface area of mixtures are 88.431 μm and 0.149 m<sup>2</sup>

and quartz (SiO2) are minor components.

Chemical composition of iron-rich bauxite sample.

Aluminium Alloys and Composites

Figure 3.

Table 1.

Figure 4.

18

diaspore [AlO(OH)], goethite [FeO(OH)], hematite (Fe2O3) and kaolin

The particle size distribution (a) and XRD pattern (b) of typical iron-rich bauxite sample.

(52.83 wt%), and the mineral constituent mainly comprised Ca2SiO4 and Ca12Al14O33, with small amounts of FeAl2O4, CaAl2O4 and Ca2Al2SiO7.

The cement clinker of autogenously pulverizable slag. (a) R = 3.60, (b) R = 3.85, (c) R = 4.10.

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

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

Figure 8.

faster hydration rate, promoted the hydration activity of β-C2S.

4. Iron-rich red mud processing and metallurgy

result in even greater social and economic damage.

21

is a feasible method to recover iron and alumina from iron-rich bauxite.

Red mud is the solid waste residue generated from the alumina refining of bauxite ore, primarily by the Bayer process which utilizes caustic soda to dissolve the aluminum silicate. Approximately, 35–40% of the processed bauxite ore goes into the waste as alkaline red mud slurry which consists of 15–40% solids, and 1.0– 1.5 tons of red mud is generated per ton of alumina produced [37]. It is estimated that annually 70 million tons of red mud is produced all over the world, with 0.7 million tons in Greece, 2 million tons in India, 30 million tons in Australia, nearly 30 million tons in China [38, 39] and presently it has been already accumulated in well over 4.0 billion tons [40]. With the quick development of alumina industry, the disposal of red mud has caused serious environmental problems mainly due to its large quantities and strong alkalinity (pH 10.0–12.5) [41]. At present, only little red mud is used to produce construction materials and calcination cement [42, 43]. Most of the red mud is directly placed in landfill, deep sea and storage in settling ponds, as shown in Figure 9. Despite the harmful impact that these methods pose on our environment, the risks of failure of a poorly engineered storage dam can

In addition, Zhang et al. [32] found that the autogenously pulverizable slag (calcium aluminate slag) cement clinker has a higher reactivity during the early stage of the hydration process, and the cement clinker of autogenously pulverizable slag is shown in Figure 8. After hydration for 28 days, the hydration products of autogenously pulverizable slag are mainly composed of killalaite (Ca3.2(H0.6Si2O7) (OH)), calcium silicate hydrate (Ca1.5SiO3.5xH2O) and calcium aluminates hydroxide (3CaOAl2O3Ca(OH)218H2O, Ca12Al13.86Fe0.14(OH)2). With the increase of w (CaO)/w(SiO2) ratios, the killalaite disappeared, the 3CaOAl2O3Ca(OH)2<sup>18</sup>H2O and Ca12Al13.86Fe0.14(OH)2 amounts increases gradually as a function of w(CaO)/w (SiO2) ratio. The C3A and C12A7 have very exothermic hydration characteristic and

The autogenously pulverizable slag (calcium aluminate slag) can also be applied to leach alumina with Na2CO3 and Na2C solutions [33, 34]. The ideal composition of calcium aluminate slags is 12CaO7Al2O3 and γ-2CaOSiO2 [35]. The slag reacts with sodium carbonate solution and yields an alumina leaching efficiency of 85% [36]. Therefore, the high-temperature reduction, smelting and alkaline leaching process

#### Figure 6.

The flow diagram for recovering iron and autogenously pulverizable slag from high-ferrous bauxite.

#### Figure 7.

The photos of iron nuggets and calcium aluminate slag obtained under the optimized process conditions. (a) metallized pellets surfaces, (b) metallized pellets bottoms, (c) EDS map of an iron nugget.


#### Table 2.

Chemical composition of the iron nuggets and autogenously pulverizable slag.

They found that the optimized process conditions were bauxite/anthracite/ slaked lime weight ratio of 100:16.17:59.37, reduction temperature at 1450°C and reduction time of 20 min. Under these conditions, high-quality iron nuggets and calcium aluminate slag were obtained and shown in Figure 7. The largest size and the highest recovery rate of iron nuggets were 11.42 mm and 92.79 wt%, respectively. The chemical composition of the iron nuggets and autogenously pulverizable calcium aluminate slag is shown in Table 2. It can be seen that the iron nuggets mainly consist of Fe, C and Mn. The total iron content exceeds 93.28 wt%, and the C and Mn contents are 4.17 and 1.60 wt%, respectively. Almost no harmful elements are present, specifically S and P. The chemical composition of autogenously pulverizable slag mainly consisted of Al2O3 (27.21 wt%), SiO2 (13.69 wt%) and CaO

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

Figure 8. The cement clinker of autogenously pulverizable slag. (a) R = 3.60, (b) R = 3.85, (c) R = 4.10.

(52.83 wt%), and the mineral constituent mainly comprised Ca2SiO4 and Ca12Al14O33, with small amounts of FeAl2O4, CaAl2O4 and Ca2Al2SiO7.

In addition, Zhang et al. [32] found that the autogenously pulverizable slag (calcium aluminate slag) cement clinker has a higher reactivity during the early stage of the hydration process, and the cement clinker of autogenously pulverizable slag is shown in Figure 8. After hydration for 28 days, the hydration products of autogenously pulverizable slag are mainly composed of killalaite (Ca3.2(H0.6Si2O7) (OH)), calcium silicate hydrate (Ca1.5SiO3.5xH2O) and calcium aluminates hydroxide (3CaOAl2O3Ca(OH)218H2O, Ca12Al13.86Fe0.14(OH)2). With the increase of w (CaO)/w(SiO2) ratios, the killalaite disappeared, the 3CaOAl2O3Ca(OH)2<sup>18</sup>H2O and Ca12Al13.86Fe0.14(OH)2 amounts increases gradually as a function of w(CaO)/w (SiO2) ratio. The C3A and C12A7 have very exothermic hydration characteristic and faster hydration rate, promoted the hydration activity of β-C2S.

The autogenously pulverizable slag (calcium aluminate slag) can also be applied to leach alumina with Na2CO3 and Na2C solutions [33, 34]. The ideal composition of calcium aluminate slags is 12CaO7Al2O3 and γ-2CaOSiO2 [35]. The slag reacts with sodium carbonate solution and yields an alumina leaching efficiency of 85% [36]. Therefore, the high-temperature reduction, smelting and alkaline leaching process is a feasible method to recover iron and alumina from iron-rich bauxite.

### 4. Iron-rich red mud processing and metallurgy

Red mud is the solid waste residue generated from the alumina refining of bauxite ore, primarily by the Bayer process which utilizes caustic soda to dissolve the aluminum silicate. Approximately, 35–40% of the processed bauxite ore goes into the waste as alkaline red mud slurry which consists of 15–40% solids, and 1.0– 1.5 tons of red mud is generated per ton of alumina produced [37]. It is estimated that annually 70 million tons of red mud is produced all over the world, with 0.7 million tons in Greece, 2 million tons in India, 30 million tons in Australia, nearly 30 million tons in China [38, 39] and presently it has been already accumulated in well over 4.0 billion tons [40]. With the quick development of alumina industry, the disposal of red mud has caused serious environmental problems mainly due to its large quantities and strong alkalinity (pH 10.0–12.5) [41]. At present, only little red mud is used to produce construction materials and calcination cement [42, 43]. Most of the red mud is directly placed in landfill, deep sea and storage in settling ponds, as shown in Figure 9. Despite the harmful impact that these methods pose on our environment, the risks of failure of a poorly engineered storage dam can result in even greater social and economic damage.

They found that the optimized process conditions were bauxite/anthracite/ slaked lime weight ratio of 100:16.17:59.37, reduction temperature at 1450°C and reduction time of 20 min. Under these conditions, high-quality iron nuggets and calcium aluminate slag were obtained and shown in Figure 7. The largest size and the highest recovery rate of iron nuggets were 11.42 mm and 92.79 wt%, respectively. The chemical composition of the iron nuggets and autogenously pulverizable calcium aluminate slag is shown in Table 2. It can be seen that the iron nuggets mainly consist of Fe, C and Mn. The total iron content exceeds 93.28 wt%, and the C and Mn contents are 4.17 and 1.60 wt%, respectively. Almost no harmful elements are present, specifically S and P. The chemical composition of autogenously pulverizable slag mainly consisted of Al2O3 (27.21 wt%), SiO2 (13.69 wt%) and CaO

FeO Al2O3 SiO2 CaO MnO TiO2 MgO 1.28 27.21 13.69 52.83 1.35 1.74 0.85

The flow diagram for recovering iron and autogenously pulverizable slag from high-ferrous bauxite.

The photos of iron nuggets and calcium aluminate slag obtained under the optimized process conditions. (a) metallized pellets surfaces, (b) metallized pellets bottoms, (c) EDS map of an iron nugget.

Fe C Si S P Mn 93.28 4.17 0.12 0.0043 0.0064 1.60

Chemical composition of the autogenously pulverizable slag/wt%

Chemical composition of the iron nuggets and autogenously pulverizable slag.

Figure 6.

Aluminium Alloys and Composites

Figure 7.

Table 2.

20

Chemical composition of the iron nuggets/wt%

Country Plant Major composition (wt%) Ref. No.

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

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

Italy Eurallumina 20.00 35.2 11.6 9.20 6.70 7.50 1.72 [52] Turkey Seydisehir 20.39 36.94 15.74 4.98 2.23 10.10 1.30 [53] UK ALCAN 20.00 46.00 5.00 6.00 1.00 8.00 4.00 [54] Canada ALCAN 20.61 31.60 8.89 6.23 1.66 10.26 2.32 [55] Australia Tomakomai 19.78 46.14 10.92 9.79 6.15 7.14 1.81 [56]

Brazil Alunorte 15.1 45.60 15.60 4.29 1.16 7.50 0.97 [58] Germany AOSG 16.20 44.80 5.40 12.33 5.22 4.00 3.00 [58] USA RMC 18.4 35.50 8.50 6.31 7.73 6.10 2.16 [58]

India Damanjodi 17.01 62.99 7.36 4.25 2.87 5.52 2.31 [59]

China Chinalco 19.08 36.13 28.19 0.77 2.84 12.99 0.68 [60]

Process flowsheet for metal extraction from red mud by a combined pyro- and hydrometallurgical process [67].

Major chemical composition of iron-rich red mud generated in alumina plants in various countries.

Table 4.

Figure 10.

23

Al2O3 Fe2O3 SiO2 TiO2 CaO Na2O A/S

Pinjarra 19.77 41.85 27.51 4.51 4.51 1.85 0.72 [57]

Point Comfort 20.67 46.44 11.13 9.85 8.79 3.12 1.86 [56]

Belgaum 21.57 50.00 7.87 15.17 0.90 4.49 2.74 [59]

#### Figure 9.

The traditional disposal method of red mud.


#### Table 3.

Typical chemical composition and metal content of red mud [37, 45, 46].

### 4.1 Mineralogical characteristics of iron-rich red mud

Red mud is mainly composed of coarse sand and fine particles of mud. Its composition, property and phase vary with the origin of the bauxite and the alumina production process, and will change over time when stocked [44]. No matter what the production process is, the chemical composition of red mud contains six major constituents. Chemical analysis shows that red mud contains Si, Al, Fe, Ca, Ti, Na, as well as an array of minor elements, namely U, Ga, V, Zr, Sc, Cr, Mn, Ni, Zn etc. [37, 45, 46]. The variation in chemical composition between red mud worldwide is very high. Typical chemical composition and metal content of Bayer process red mud are shown in Table 3. The calcium oxide (CaO) and silica (SiO2) are the major constituents for red mud from the sintering process, but the contents of Fe2O3 in red mud from the sintering process and combined process are much lower than that from the Bayer process. The major chemical composition of ironrich red mud generated in alumina plants in various countries over the world is presented in Table 4.

Generally, the major mineralogical constituents of iron-rich red mud from the Bayer process are gibbsite (Al(OH)3), boehmite (γ-AlOOH), hematite (Fe2O3), goethite (FeO(OH)), quartz (SiO2), rutile (TiO2), anatase (TiO2) and calcite (CaCO3) [47, 48], and the principal mineralogical constituents of red mud from the sintering process are β-2CaOSiO2, calcite (CaCO3), aragonite (CaCO3), hematite (Fe2O3), gibbsite (Al(OH)3) and perovskite (CaTiO3) [49, 50]. Red mud is a very fine grained material with an average particle size <10 μm. Typical values for particle size distribution are 90 wt% below 75 μm [51]. The specific surface area (BET) of red mud is between 10 and 30 m<sup>2</sup> /g, depending on the degree of grinding of bauxite.


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

Table 4.

4.1 Mineralogical characteristics of iron-rich red mud

Typical chemical composition and metal content of red mud [37, 45, 46].

presented in Table 4.

Figure 9.

Table 3.

Chemical composition

The traditional disposal method of red mud.

Aluminium Alloys and Composites

Concentration (wt%)

Major elements

Fe2O3 30–65 Fe 4.52–50.6 U 50–60 Al2O3 10–20 Al 4.42–16.06 Ga 60–90 SiO2 3–30 Si 2.16–14.86 V 730 Na2O 2–10 Na 0.98–7.79 Zr 1230 CaO 2–8 Ca 0.39–16.72 Sc 54–120 TiO2 Trace-15 Ti 0.98–5.34 Cr 497

Concentration (wt%)

Minor elements Concentration (mg/kg)

of bauxite.

22

(BET) of red mud is between 10 and 30 m<sup>2</sup>

Red mud is mainly composed of coarse sand and fine particles of mud. Its composition, property and phase vary with the origin of the bauxite and the alumina production process, and will change over time when stocked [44]. No matter what the production process is, the chemical composition of red mud contains six major constituents. Chemical analysis shows that red mud contains Si, Al, Fe, Ca, Ti, Na, as well as an array of minor elements, namely U, Ga, V, Zr, Sc, Cr, Mn, Ni, Zn etc. [37, 45, 46]. The variation in chemical composition between red mud worldwide is very high. Typical chemical composition and metal content of Bayer process red mud are shown in Table 3. The calcium oxide (CaO) and silica (SiO2) are the major constituents for red mud from the sintering process, but the contents of Fe2O3 in red mud from the sintering process and combined process are much lower than that from the Bayer process. The major chemical composition of ironrich red mud generated in alumina plants in various countries over the world is

Generally, the major mineralogical constituents of iron-rich red mud from the Bayer process are gibbsite (Al(OH)3), boehmite (γ-AlOOH), hematite (Fe2O3), goethite (FeO(OH)), quartz (SiO2), rutile (TiO2), anatase (TiO2) and calcite (CaCO3) [47, 48], and the principal mineralogical constituents of red mud from the sintering process are β-2CaOSiO2, calcite (CaCO3), aragonite (CaCO3), hematite (Fe2O3), gibbsite (Al(OH)3) and perovskite (CaTiO3) [49, 50]. Red mud is a very fine grained material with an average particle size <10 μm. Typical values for particle size distribution are 90 wt% below 75 μm [51]. The specific surface area

/g, depending on the degree of grinding

Major chemical composition of iron-rich red mud generated in alumina plants in various countries.
