Table 1.

Main minerals of bauxite deposits [5].


two corporation networks the Russian possessions (Fria and Débélé) and the US-American and Australian (CBG in Sangaredi and Kamsar) form two business deci-

The alumina refinery plant ACG in Fria converts bauxite into alumina by the

The Bayer process is the name for the hydrometallurgical extraction and refinement of alumina from bauxite. Bauxite ore is ground and then digested in highly

Al2O3.XH2O + 2NaOH 2NaAlO + (x + 1) H2O 135 145°C - <sup>ð</sup>3<sup>Þ</sup>

Gibbsite Al2O3.3H2O + 2NaOH 2NaAlO2 + 4H2O

Boehmite Al2O3.H2O + 2NaOH 2NaAlO2 + 2H2O

Diaspore Al2O3. H2O + 2NaOH 2NaAlO2+ 2H2O (<sup>a</sup>AlO.OH)

2NaOH + SiO2 Na2SiO3 + H2O ð1Þ

Na2SiO2 + Al2O3 Na2O.Al3 SiO2 ð2Þ

135-145°C

ð4Þ

ð5Þ

ð6Þ

( gAI(OH3)

205-245°C

( gAIO.OH)

High pressure

2NaAlO2 + 4H2O Al(OH)3 + 2NaOH ð7Þ

Crystalline alumina hydrate is extracted from the digestion liquor by hydrolysis.

Gangue solids, usually iron oxides, quartz, and other resistant minerals, are separated from the hot sodium aluminate slurry by physical means such as settling and filtration. The solids (red mud and red sand) are countercurrent washed to recover the caustic solutions, then pumped to specially designed impoundment beds. The mud and sand can be intercepted, neutralized, washed, and stored for reuse [2]. The chemical reactions leading to the alumina as final product are given

According to the composition of the parent bauxite and technology applied for processing, the derived RM contains mainly of different amounts of Fe2O3, Al2O3,

The high alkalinity is considered to be one of the principal reasons for the limited success until today in finding applications for RM. Growing awareness has led to a multitude of studies and semi-industrial trials related to the recycle or valorization

sion spaces that overlay with the official political structure in Guinea.

Survey of Bauxite Resources, Alumina Industry and the Prospects of the Production…

Bayer process summarized in as follows.

DOI: http://dx.doi.org/10.5772/intechopen.82413

caustic solutions at elevated temperatures.

The basic digestion reaction is the following:

High temper

Depending on the specific raw mineral:

2.2.1 The Bayer process

above.

77

2.2.2 Red mud

SiO2, TiO2, CaO, and Na2O.

#### Table 2.

Bauxite potential of Guinea (billions of tones) [6, 7].

The bauxite and alumina industry is dominated by three producers: Alumina Compagnie de Guinée (ACG), Compagnie des Bauxites de Guinée (CBG), and Compagnie des Bauxites de Kindia (CBK). CBK and ACG are controlled by the Russian aluminum giant RUSAL. CBG is a joint venture between the American aluminum firm Alcoa Inc., the Canadian aluminum firm Alcan Inc., and the government of Guinea. Its main export markets are North America and Europe. These Survey of Bauxite Resources, Alumina Industry and the Prospects of the Production… DOI: http://dx.doi.org/10.5772/intechopen.82413

two corporation networks the Russian possessions (Fria and Débélé) and the US-American and Australian (CBG in Sangaredi and Kamsar) form two business decision spaces that overlay with the official political structure in Guinea.

The alumina refinery plant ACG in Fria converts bauxite into alumina by the Bayer process summarized in as follows.

#### 2.2.1 The Bayer process

The Bayer process is the name for the hydrometallurgical extraction and refinement of alumina from bauxite. Bauxite ore is ground and then digested in highly caustic solutions at elevated temperatures.

$$2\text{NaOH} + \text{SiO}\_2 \xrightarrow[\text{}]{} \xrightarrow[]{} \text{Na} \text{SiO}\_2 + \text{H}\_2\text{O} \tag{1}$$

$$\text{Na}\_2\text{SiO}\_2 + \text{Al}\_2\text{O}\_3 \xrightarrow[\text{K}]{} \text{Na}\_2\text{O}.\text{Al}\_3\text{ SiO}\_2\tag{2}$$

The basic digestion reaction is the following:

$$\text{Al}\_2\text{O}\_3\text{XH}\_2\text{O} + 2\text{NaOH} \xrightarrow{\text{I}35\text{-I}45\text{°C}} 2\text{NaAlO} + (\text{x} + \text{l})\text{H}\_2\text{O} \tag{3}$$

Depending on the specific raw mineral:

$$\text{Gibbsite Al}\_2\text{O}\_3.3\text{H}\_2\text{O} + 2\text{NaOH} \xrightarrow[(\gamma\text{Al}(\text{OH}3))]{} 2\text{NaAlO} \xrightarrow[(\gamma\text{Al}(\text{OH}3))]{} 2\text{NaAlO} + 4\text{H}\_2\text{O} \qquad (4)$$

$$\text{Bealthite Al}\_2\text{O}\_3\text{H}\_2\text{O} + 2\text{NaOH} \xrightarrow[(\gamma\text{AlO.OH})]{205\text{-}24\text{S}^\circ\text{C}} 2\text{NaAlO}\_2 + 2\text{H}\_2\text{O} \qquad (5)$$

$$\text{Disapore Al}\_2\text{O}\_3.\text{ H}\_2\text{O} + 2\text{NaOH} \xrightarrow[\text{High pressure}]{\text{High temperature}} 2\text{NaAlO}\_2 + 2\text{H}\_2\text{O} \qquad (6)$$

Crystalline alumina hydrate is extracted from the digestion liquor by hydrolysis.

$$2\text{NaAlO}\_2 + 4\text{H}\_2\text{O} \xrightarrow[{}]{} \text{Al(OH)}\_3 + 2\text{NaOH} \tag{7}$$

Gangue solids, usually iron oxides, quartz, and other resistant minerals, are separated from the hot sodium aluminate slurry by physical means such as settling and filtration. The solids (red mud and red sand) are countercurrent washed to recover the caustic solutions, then pumped to specially designed impoundment beds. The mud and sand can be intercepted, neutralized, washed, and stored for reuse [2]. The chemical reactions leading to the alumina as final product are given above.

#### 2.2.2 Red mud

According to the composition of the parent bauxite and technology applied for processing, the derived RM contains mainly of different amounts of Fe2O3, Al2O3, SiO2, TiO2, CaO, and Na2O.

The high alkalinity is considered to be one of the principal reasons for the limited success until today in finding applications for RM. Growing awareness has led to a multitude of studies and semi-industrial trials related to the recycle or valorization

The bauxite and alumina industry is dominated by three producers: Alumina Compagnie de Guinée (ACG), Compagnie des Bauxites de Guinée (CBG), and Compagnie des Bauxites de Kindia (CBK). CBK and ACG are controlled by the Russian aluminum giant RUSAL. CBG is a joint venture between the American aluminum firm Alcoa Inc., the Canadian aluminum firm Alcan Inc., and the government of Guinea. Its main export markets are North America and Europe. These

Location Nr of

Kogon-Tominé

Débélé-Kindia

Dalaba-Mamou

Donghol-Sigon

Bafing-Tinkisso

Littoral-Islands\*

\*Exhausted reserves.

Table 2.

Figure 1.

76

Bauxite train of the CBK.

bowe

Geopolymers and Other Geosynthetics

Proven and probable reserves

Measured resources

Indicated and supposed resources

144 2893 7238 10,129 1593 11,722

49 157 23 69 249 126 375

57 455 465 859 1324

49 703 982 1685 272 1957

Boké 94 913 1945 3053 5911 322 8233

Fatala 115 62 201 1450 1713 4615 6328

Mali 67 277 225 502 622 1124 Labé 85 320 2225 2545 239 2784

Balin-Ko 28 927 927 927 Tougué 111 1428 925 1219 3572 791 4363 Dabola 64 617 95 740 1458 855 690

39 89 89 601

Total 894 3178 7, 398 18,686 29,245 10,895 40,139

4 9 39

Bauxite potential of Guinea (billions of tones) [6, 7].

Total identified resources and reserves

Extra forecasted resources

Bauxite potential of RM as a raw material for different industrial applications. An application in building materials, as a component in OPC, filler material, or geopolymers, seems to be a straightforward approach in terms of high quantity reuses [1]. Generally, the use of geopolymer as an alternative binder drew the attention because of its excellent properties, such as high compressive strength, resistance to acidic solutions, and thermal stability, in combination with their lower CO2 footprint [7].

(iii) evaporation that could originate highly alkaline rainfalls; (iv) visual impact on

Survey of Bauxite Resources, Alumina Industry and the Prospects of the Production…

Chemical analysis shows that red mud contains silicium, aluminum, iron, calcium, titanium, sodium as well as an array of minor elements namely K, Cr, V, Ba, Cu, Mn, Pb, Zn, P, F, S, As and etc. [9]. The variation in chemical composition between red mud worldwide is high. The major chemical composition of red mud for selected countries over the world is presented in Table 2. Chemical analysis shows that red mud contains silicon, aluminum, iron, calcium, titanium, sodium as well as an array of minor elements namely K, Cr, V, Ba, Cu, Mn, Pb, Zn, P, F, S. As and etc. The variation in chemical composition between red mud worldwide is high [9]. The major chemical composition of red mud for selected countries over the

ACG plant rejects 1 ton of mud per ton of alumina produced and that each ton of mud contains on average 15 kilograms of caustic soda (NaOH) which has not been recovered by washing [11]. Moreover this mud is composed on average of 60% iron ore (Fe2O3), lime (CaCO3) with traces of titanium (TiO2). Table 2 shows that RM from ACG/Fria has the highest Fe2O3 content and the lowest Al2O3 one [10].

The increasing need of the industry sectors involving aluminum as metal, entailed the improvement of the Bayer process and the subsequent issue of the management of RM. Despite several years of research on the possible valorization of this waste, there is almost no evidence of a large-scale application of this industrial waste to date. Globally research efforts are focused on three fields for the valoriza-

extensive areas [14].

DOI: http://dx.doi.org/10.5772/intechopen.82413

world is presented in Table 3.

tion or reuse of RM:

Table 3.

79

2.2.3 Prospects for the valorization of RM

• Civil and chemical engineering applications.

• Ecological and biological production purposes.

• Mechanical engineering and Metallurgical applications.

Country Plant Major composition (%)

Australia AWAAK 28.5 24.0 3.11 18.8 3.4 5.26 Brazil Alunorte 45.6 15.1 4.29 15.6 7.5 1.16 Canada ALCAN 31.60 20.61 6.23 8.89 10.26 1.66 France Pechiney 26.62 15.0 15.76 4.98 1.02 22.21 Germany AOSG 44.8 16.2 12.33 5.4 4.0 5.22 Guinea ACG/Fria 53.89 14.68 — 7.06 — 2.1 Guinea Pt Comfort/Texas/US 40 18 — 9.6 2.7 7.6 Italy Eurallumina 35.2 20 9.2 11.6 7.5 6.7 Spain Alcoa 37.5 21.2 11.45 4.4 3.6 5.51 Turkey Seydisehir 36.94 20.39 4.98 15.74 10.10 2.23 UK ALCAN 46.0 20.0 6.0 5.0 8.0 1.0 USA RMC 35.5 18.4 6.31 8.5 6.1 7.73

Chemical composition of red mud generated in alumina plants in various countries adapted from [13].

Fe2O3 Al2O3 TiO2 SiO2 NaO2 CaO

The quantity of alumina produced from bauxite ore depends on the type and the composition of the bauxite ore. Generally authors agree that 1 ton of alumina is produced from 3 ton of bauxite [9]. In average the RM generated per ton of alumina varies between 1 and 1.5 tons, although the amounts from different industrial companies are much broader; it is estimated that over 150 million tons of bauxite residue are produced annually. The quantity of bauxite residue generated at a particular refinery is governed by the processing conditions and bauxite quality [10]. The global inventory of RM stored on land currently is estimated to be over 2.7 billion tons, with an annual growth rate of over 120 million tons.

Over the ACG's 30 years of existence, the quantity of RM produced may very well exceed 20 million metric tons. It should be mentioned that up until the end of the 1980's this mud was simply dumped in the Konkouré river which flows not far from the plant [11].

Figure 2 is a schema allowing the assessment of the accurate amount of alumina and the resulting RM obtainable from crude bauxite.

Bauxite mining and processing have a strong and varied impact on the environment because they entail modifications of the landscape and severe pollution by rejecting wastes into the biosphere (soil, the atmosphere and the water) [13]. Among others RM causes: (i) contamination of water resources with caustic soda and metallic oxide-bearing impurities; (ii) direct contact with fauna and flora;

#### Figure 2.

Calculation scheme for the amount of alumina and red mud that turn out during alumina refinery using chemical and mineralogical data [12].

Survey of Bauxite Resources, Alumina Industry and the Prospects of the Production… DOI: http://dx.doi.org/10.5772/intechopen.82413

(iii) evaporation that could originate highly alkaline rainfalls; (iv) visual impact on extensive areas [14].

Chemical analysis shows that red mud contains silicium, aluminum, iron, calcium, titanium, sodium as well as an array of minor elements namely K, Cr, V, Ba, Cu, Mn, Pb, Zn, P, F, S, As and etc. [9]. The variation in chemical composition between red mud worldwide is high. The major chemical composition of red mud for selected countries over the world is presented in Table 2. Chemical analysis shows that red mud contains silicon, aluminum, iron, calcium, titanium, sodium as well as an array of minor elements namely K, Cr, V, Ba, Cu, Mn, Pb, Zn, P, F, S. As and etc. The variation in chemical composition between red mud worldwide is high [9]. The major chemical composition of red mud for selected countries over the world is presented in Table 3.

ACG plant rejects 1 ton of mud per ton of alumina produced and that each ton of mud contains on average 15 kilograms of caustic soda (NaOH) which has not been recovered by washing [11]. Moreover this mud is composed on average of 60% iron ore (Fe2O3), lime (CaCO3) with traces of titanium (TiO2). Table 2 shows that RM from ACG/Fria has the highest Fe2O3 content and the lowest Al2O3 one [10].

#### 2.2.3 Prospects for the valorization of RM

of RM as a raw material for different industrial applications. An application in building materials, as a component in OPC, filler material, or geopolymers, seems to be a straightforward approach in terms of high quantity reuses [1]. Generally, the use of geopolymer as an alternative binder drew the attention because of its excellent properties, such as high compressive strength, resistance to acidic solutions,

and thermal stability, in combination with their lower CO2 footprint [7].

billion tons, with an annual growth rate of over 120 million tons.

and the resulting RM obtainable from crude bauxite.

far from the plant [11].

Geopolymers and Other Geosynthetics

Figure 2.

78

chemical and mineralogical data [12].

The quantity of alumina produced from bauxite ore depends on the type and the composition of the bauxite ore. Generally authors agree that 1 ton of alumina is produced from 3 ton of bauxite [9]. In average the RM generated per ton of alumina varies between 1 and 1.5 tons, although the amounts from different industrial companies are much broader; it is estimated that over 150 million tons of bauxite residue are produced annually. The quantity of bauxite residue generated at a particular refinery is governed by the processing conditions and bauxite quality [10]. The global inventory of RM stored on land currently is estimated to be over 2.7

Over the ACG's 30 years of existence, the quantity of RM produced may very well exceed 20 million metric tons. It should be mentioned that up until the end of the 1980's this mud was simply dumped in the Konkouré river which flows not

Figure 2 is a schema allowing the assessment of the accurate amount of alumina

Bauxite mining and processing have a strong and varied impact on the environment because they entail modifications of the landscape and severe pollution by rejecting wastes into the biosphere (soil, the atmosphere and the water) [13]. Among others RM causes: (i) contamination of water resources with caustic soda and metallic oxide-bearing impurities; (ii) direct contact with fauna and flora;

Calculation scheme for the amount of alumina and red mud that turn out during alumina refinery using

The increasing need of the industry sectors involving aluminum as metal, entailed the improvement of the Bayer process and the subsequent issue of the management of RM. Despite several years of research on the possible valorization of this waste, there is almost no evidence of a large-scale application of this industrial waste to date. Globally research efforts are focused on three fields for the valorization or reuse of RM:



• Ecological and biological production purposes.

Table 3.

Chemical composition of red mud generated in alumina plants in various countries adapted from [13].

This chapter addresses specifically the use of RM for the production of geopolymers for construction and other engineering applications.
