Bauxite: Formula, Types & Uses

Ans: Bauxite is a sedimentary rock that occurs naturally and is heterogeneous in nature. It is composed primarily of one or more aluminium hydroxide minerals and various mixtures of silica, iron oxide, titania, aluminosilicate, and other impurities in traces. 

• Bauxite deposits are primarily produced by aluminous rock weathering. 
• Some have been transported to their present sites, but most are residual accumulations from which most other components of the parent rock are leached besides alumina.

Ans: Bauxite, on the Mohs scale, is usually a mild mineral with a hardness of just 1 to 3. With a pisolitic shape, earthy lustre, and low specific gravity between 2.0 and 2.5, it is white to grey to sepia. Bauxite is formed when aluminosilicates break down into different types of hydrated aluminium oxide.

Ans: In the metallurgy of aluminium, purified Al₂O₃ is mixed with Na₃AlF₆ or CaF₂, which lowers the melting point of the mix and brings conductivity. The fused matrix is electrolyzed. A steel vessel with carbon lining acts as a cathode, and a graphite anode is employed. The overall reaction may be written as:

2Al₂O₃ + 3C → 4Al + 3CO₂ (6.44)

This process of electrolysis is widely referred to as the Hall-Heroult process. Thus, electrolysis of the molten mass is administered in an electrolytic cell using carbon electrodes. 

• The oxygen liberated at the anode reacts with the carbon of the anode, producing CO and CO₂. 
• This way, about 0.5 kg of carbon anode is burnt away for every kg of aluminium produced. 
• The electrolytic reactions are:

Cathode: Al₃ + (melt) + 3e– → Al(l) (6.45)

Anode: C(s) + O^_2– (melt) → CO(g) + 2e^– (6.46)

C(s) + 2O₂^– (melt) → CO₂ (g) + 4e^– (6.47)

Ans: Aluminium Oxide is the name of a chemical compound, but “Bauxite” is a naturally occurring mineral. Like most minerals, bauxite is a mixture of several compounds; it has to be refined by solvent fractionation to remove the acidic SiO₂ and amphoteric Al₂O₃ from the basic Fe₃O₄ and TiO₂. 

• The process uses 30% NaOH in the Bayer process. 
• The iron and titanium compounds are removed as “red mud”, and silicates crystallize out as Na₂Si(OH)₆. 
• Successive acidifications and neutralization precipitate out the aluminates (Al (OH)₄^-), which are converted into Al₂O₃ by very gentle acidification with carbon dioxide.
• The aluminium oxide at this point is pure enough to be used for conversion to pure aluminium in an electrolytic cell.

Ans: Bauxite is a residual deposit formed by the weathering of rocks containing Al; under tropical conditions, it contains hydrated Alumina, oxides of iron and titanium, and small amounts of silica. The raw materials for High Alumina cement are limestone and bauxite. HA Cement contains 40% Al and lime each and 15 % oxides of iron. Hence, bauxite is used.

Ans: There are many minerals and rocks containing aluminium; however, only a few can be used for extracting aluminium. Bauxites are the foremost widely used raw materials for aluminium. Initially, a semi-finished product, Alumina (Al₂O₃₎, is extracted from the ores, and the metallic aluminium is produced electrolytically from the alumina. 

• Nepheline-syenites, as well as nepheline-apatites, are used as aluminium ores. 
• These minerals are simultaneously used as a source of phosphates. 
• Other minerals which can be used as a source of aluminium include alunite, leucitic lavas (the mineral leucite), labradorites, anorthosites, and high-alumina clays and kaolins, also as cyanotic, sillimanite, and andalusite schists. 
• Aluminium also occurs in beryl, cryolite, garnet, spinel, and turquoise minerals.

Ans: Bauxite is the ore of aluminium. The main constituent is alumina (aluminium oxide). As a mineral that occurs in the earth, bauxite will contain stones, sand, silica, iron, and many other impurities alongside alumina. These impurities can be removed using physical and chemical methods to recover alumina from bauxite. Purified alumina is electrolyzed to obtain aluminium metal.

Ans: We forget that Aluminium is a very reactive metal. In the air, it forms a protective barrier of Aluminium Oxide by reacting with the air, so Aluminium objects are impervious to corrosion. Also, many of our Aluminium objects are alloys to both resist chemical attacks and increase their strength.

• After the creation of the earth, all the abundant aluminium atoms are found as compounds, bauxite being one of them. 
• There wouldn’t need to be free oxygen where bauxite was created. 
• Free Aluminium atoms can pull Oxygen atoms away from other compounds, particularly in the high-temperature conditions around as the earth was being formed. 
• Iron oxide and aluminium powders are mixed and used in the thermite process. 
• Here, the Aluminium strips the iron oxide of its oxygen, forming molten iron in the process. 
• This reaction gives off a lot of heat, hence the molten iron.

Ans: The different types of bauxite are as follows:

• Lateritic Bauxites: Lateritic Bauxite is a type of bauxite were formed due to the lateralization of various silicate rocks such as granite, gneiss, basalt, and shale. It is is also known as silicate bauxite. 
• Karst Bauxites: Karst Bauxite is a type of bauxite were formed by lateritic weathering and residual accumulation of intercalated clay layers. It is is also known as carbonate bauxite.

Ans:

• Bauxite ore is easily attacked by atmospheric oxygen, heat and microorganisms.
• It turns the rainwater acidic in nature.
• Due to industrial waste, Bauxite gets dissolved in both groundwater and surface water bodies.
• It can lead to gastrointestinal symptoms, hepatic disease, cardiomyopathies, diabetes, and hyperpigmentation.

Ans: The bauxite is purified by Bayer Process. In the purification process, ore is first washed along with hot sodium hydroxide solution. With the condensation of compound, insoluble compounds like aluminium and silicon oxides are obtained.

• It will completely dissolve the oxide of aluminium and silicon compound.
• The impurities of iron are removed by the process of filtration.
• Next, aluminium hydroxide is obtained by precipitation of aluminium.
• Lastly, aluminium hydroxide is calcined to produce alumina, Al₂O₃.

Ans: The different types of bauxite mineral are as follows:

• Gibbsite: Its formual is Al₂O₃.3H₃O Or Al(OH)_3. The properties of Gibbsite includes water evaporation at the lowest temperature level of around 143 to 150 degrees Celsius, obtaining alumina. 
• Boehmite: Its formual is Al₂O₃.H₂O. The properties of boehmite includes water evaporation at more than 240 degrees Celsius because it has one water molecule attached to the alumina, and the bonds are stronger compared to that of the gibbsite.
• Diaspore:  Its formual is α – AlO (OH). The properties of diaspore includes the bond of water and Al2O3 breaks at more than 260 degrees Celsius, as it has a very dense chemical structure.