1. Introduction

Bauxite deposits in Guinea are characteristically gigantic and of higher grade than commercial deposits in other parts of the world. Out of Africa's five producer countries, only Guinea has significantly contributed to worldwide production. The only African alumina refinery is located in Fria, Guinea, and has produced about 1% of world output since the start of production in 1960. In the Bayer process for alumina production, huge quantities of the insoluble by-product called red mud RM are generated. Per ton of produced alumina, about 1–1.5 tons of bauxite RM is generated. Management of RM is a first-priority issue for all alumina plants. The high alkalinity is considered to be one of the principal reasons for the limited success until today in finding applications for RM. An application in building materials, as a component in Ordinary Portland Cement (OPC) or geopolymers, seems to be a straightforward approach in terms of high quantity reuse. 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 [1].

2.2 Bauxite mining and alumina industry in Guinea

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

for more than one-third of the world's known reserves.

distance of 130 km to the Port of Conakry.

Guinea's exports and generate a quarter of its tax revenues [8].

Several concepts are used to define the content of a geological deposit: resource, reserve, potential, etc. No matter definitions used, taking into account its identified bauxite deposits both in tonnage and grade, it appears from all studies that Guinea is the country the most endowed with bauxite in the world [6]. The country account

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

As shows Table 2 its potential is about 40 billion tons. Its production of bauxite, sourced from three mines located at Sangarédi, Kindia and Fria, is among the largest in the world. At present, crude bauxite and alumina constitute about 60% of

However, Guinea has not realized the full potential of its mineral resources. Annual production of bauxite is very low considering the proven reserves. A comparison of the country's bauxite reserves and production pattern with other major world producers shows that whereas Guinea has the largest known bauxite reserves in the world it has the lowest alumina to bauxite production ratio of all the major bauxite and alumina producing countries. The country has only one alumina refinery plant which has a production capacity of about 0.6 million tons, hence, more than 95% of the bauxite is exported raw. Among others a reason for the poor performance of the sector is insufficient emphasis on local transformation. Power supply constraints and a generally weak investment climate are other possible reasons for low growth in the sector [8]. Power supply, which is vital to production of alumina and aluminum, is a major constraint in Guinea. Poor transport infrastructure and lack of human capital and organizational capacity are also serious concerns. Figure 1 shows a train transporting bauxite from Débélé (Kindia) on a

Name Composition

Hematite α-Fe2O3 Goethite α-FeOOH Magnetite α-Fe3O4 Siderite FeCO3 Ilmenite FeOTiO3 Anatase TiO2 Rutile TiO2 Brookite TiO2

Halloysite Al2O3.2SiO23H2O Kaolinite Al2O3.2SiO22H2O

Quartz SiO2

Table 1.

75

Main minerals of bauxite deposits [5].

Gibbsite γ-AI(OH3) α-Al2O3.3H2O (Hydrargillite) γ-AIOOH, α-AhO].H Boehmite γ-AIOOH, α-Al2O3.3H2O Diaspore α-AIOOH, β-Al2O3.3H2O

The primary function of a geopolymer is to act as a binder and replace OPC in concrete manufacture or provide complementary products [2]. Some of the advantages that geopolymers have over OPC are their high compressive and flexural strength, their very high temperature resistance, a high resistance to acid, and the ability to utilize multiple waste or byproduct streams [2] Geopolymers binders have the potential to incorporate cations, anions, and organic species within their threedimensional structure. A significant ecological and marketing benefit reported for geopolymer binder over OPC is the reduction in CO2; OPC releases 0.55 ton of CO2 emissions. One ton of CO2 from the calcination of limestone and the combustion of carbon-based fuel for heat and power generation produces an average additional 0.40 t of CO2. Comparatively, geopolymer production creates only between 0.2 and 0.5 ton of CO2 per ton of product, depending on inclusion of life cycle and transport factors [2].

#### 2. Bauxite potential and outlook

Aluminum (Al) is the most plentiful metal in earth's crust, representing more than 7% by weight, and is the third most abundant element after silicon and oxygen. Because aluminum is highly reactive, it is mostly found in oxidized form, of which approximately 250 different minerals exist [3]. Bauxite is the main source of the world's aluminum, supplying 99% of metallic aluminum [1]. Bauxite is a member of the family of lateritic rocks. It is characterized by a particular enrichment of aluminum-hydroxide minerals, such as gibbsite, boehmite and/or diaspore. Bauxite is formed as a weathering product of low iron and silica bedrock. About 90% of bauxite resources in the world can be found in tropical areas while the rest in other latitudes have been exposed to prolonged weathering in their geological past [4]. Bauxite is the principle ore for the production of alumina and aluminum metal. Via a two-stage process that involves the refining of bauxite to alumina by the Bayer process, wet chemical caustic leach process and the electrolytic reduction of alumina to aluminum metal.

#### 2.1 Nature and occurrence

Bauxite is a naturally occurring heterogeneous material and composes of one or more aluminum hydroxide minerals, principally gibbsite [Al(OH)3], boehmite [γ-AlO(OH)] and diaspore [α-AlO(OH)]4. In addition, other compounds are also found in bauxite such as hematite [Fe2O3], goethite [FeO(OH)], quartz [SiO2], rutile/anatase [TiO2], kaolinite [Al2Si2O5(OH)4] with impurities in traces, as shows Table 1. Most commercial bauxite has a minimum Al2O3 content of 50–55% [5]. Based on mode of occurrence and parent rock, bauxite deposits can be subdivided into two major groups.


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

### 2.2 Bauxite mining and alumina industry in Guinea

be a straightforward approach in terms of high quantity reuse. 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

The primary function of a geopolymer is to act as a binder and replace OPC in concrete manufacture or provide complementary products [2]. Some of the advantages that geopolymers have over OPC are their high compressive and flexural strength, their very high temperature resistance, a high resistance to acid, and the ability to utilize multiple waste or byproduct streams [2] Geopolymers binders have the potential to incorporate cations, anions, and organic species within their threedimensional structure. A significant ecological and marketing benefit reported for geopolymer binder over OPC is the reduction in CO2; OPC releases 0.55 ton of CO2 emissions. One ton of CO2 from the calcination of limestone and the combustion of carbon-based fuel for heat and power generation produces an average additional 0.40 t of CO2. Comparatively, geopolymer production creates only between 0.2 and 0.5 ton of CO2 per ton of product, depending on inclusion of life

Aluminum (Al) is the most plentiful metal in earth's crust, representing more than 7% by weight, and is the third most abundant element after silicon and oxygen. Because aluminum is highly reactive, it is mostly found in oxidized form, of which approximately 250 different minerals exist [3]. Bauxite is the main source of the world's aluminum, supplying 99% of metallic aluminum [1]. Bauxite is a member of the family of lateritic rocks. It is characterized by a particular enrichment of aluminum-hydroxide minerals, such as gibbsite, boehmite and/or diaspore. Bauxite is formed as a weathering product of low iron and silica bedrock. About 90% of bauxite resources in the world can be found in tropical areas while the rest in other latitudes have been exposed to prolonged weathering in their geological past [4]. Bauxite is the principle ore for the production of alumina and aluminum metal. Via a two-stage process that involves the refining of bauxite to alumina by the Bayer process, wet chemical caustic leach process and the electrolytic reduction of alu-

Bauxite is a naturally occurring heterogeneous material and composes of one or

more aluminum hydroxide minerals, principally gibbsite [Al(OH)3], boehmite [γ-AlO(OH)] and diaspore [α-AlO(OH)]4. In addition, other compounds are also found in bauxite such as hematite [Fe2O3], goethite [FeO(OH)], quartz [SiO2], rutile/anatase [TiO2], kaolinite [Al2Si2O5(OH)4] with impurities in traces, as shows Table 1. Most commercial bauxite has a minimum Al2O3 content of 50–55% [5]. Based on mode of occurrence and parent rock, bauxite deposits can be subdivided

• Alumina-rich or lateritic bauxite, resulting from the weathering of rocks

• Terra rossa, occurring as a weathered residue on, or closely associated, with limestone and dolomite. The relatively mobile ions, including alkalis, alkali earths and silica, are leached out leaving a residue of aluminum and iron

hydroxides, titania and other insoluble materials

thermal stability, in combination with their lower CO2 footprint [1].

cycle and transport factors [2].

Geopolymers and Other Geosynthetics

mina to aluminum metal.

into two major groups.

74

containing alumina.

2.1 Nature and occurrence

2. Bauxite potential and outlook

Several concepts are used to define the content of a geological deposit: resource, reserve, potential, etc. No matter definitions used, taking into account its identified bauxite deposits both in tonnage and grade, it appears from all studies that Guinea is the country the most endowed with bauxite in the world [6]. The country account for more than one-third of the world's known reserves.

As shows Table 2 its potential is about 40 billion tons. Its production of bauxite, sourced from three mines located at Sangarédi, Kindia and Fria, is among the largest in the world. At present, crude bauxite and alumina constitute about 60% of Guinea's exports and generate a quarter of its tax revenues [8].

However, Guinea has not realized the full potential of its mineral resources. Annual production of bauxite is very low considering the proven reserves. A comparison of the country's bauxite reserves and production pattern with other major world producers shows that whereas Guinea has the largest known bauxite reserves in the world it has the lowest alumina to bauxite production ratio of all the major bauxite and alumina producing countries. The country has only one alumina refinery plant which has a production capacity of about 0.6 million tons, hence, more than 95% of the bauxite is exported raw. Among others a reason for the poor performance of the sector is insufficient emphasis on local transformation. Power supply constraints and a generally weak investment climate are other possible reasons for low growth in the sector [8]. Power supply, which is vital to production of alumina and aluminum, is a major constraint in Guinea. Poor transport infrastructure and lack of human capital and organizational capacity are also serious concerns. Figure 1 shows a train transporting bauxite from Débélé (Kindia) on a distance of 130 km to the Port of Conakry.

