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Principles of Extraction of Aluminium

This article explains the principles of extraction of aluminium with the help of elaborated notes. Aside from this, it also focuses on discussing the other aspects of aluminium.

Being one of the most abundant metals, aluminium has many compounds. These do not come as naturally as we might think; aluminium is a very reactive metal; nevertheless, it is distributed widely. Ores have aluminium in the form of oxides. Bauxite (a combination of hydrated aluminium oxide) is the principal and exclusive ore that gives plenty of aluminium when extraction begins for the overall benefits. Some other crucial ores of aluminium are – corundum, feldspar, cryolite, alunite, and kaolin. In addition, the gemstones like garnet, chrysoberyl, topaz, etc., have aluminium. It comes about in the state of mica, mainly in India.

Uses of Aluminium

Aluminium is used for a variety of purposes based on its properties. The most common uses of aluminium include the following.

  • Aluminium is utilised as utensils, surgical instruments, aeroplane spares, and other things because it is light and tensile. 

  • Alumina is used for manufacturing bricks and ultramarine.

  • You can use it for steaming metal objects when combined with oil.

  • For packaging purposes, aluminium is utilised.

  • Metals like chromium, iron, manganese can be manufactured with the help of aluminium when applied as an agent for the reduction.

  • Aluminium is also used to create wires as it is a better conductor and less expensive.

  • The dyes and paints have mordants made of alums.

Metallurgy of Aluminium

The primary ore for the extraction of aluminium is bauxite made of a material same as clay and red, which is referred to as laterite soil—various components like silica, aluminium oxide compounds (Alumina), titanium dioxide, and iron oxides. The electrolysis of alumina produces aluminium. Bauxite is generally discovered in tropical and subtropical areas.

Extraction of Aluminium

During the extraction of aluminium, three steps take place-

  • Purification of the main ore-Bauxite

  • Electrolytic diminution of Alumina

  • Purification of the Aluminium

Purification of Main Ore-Bauxite

Concentrated sodium carbonate is treated with crushed bauxite to begin the extraction process of aluminium. The phenomenon is known as leaching, where alumina forms sodium aluminate. The process of removing a chemical from a solid material that has come into contact with a liquid is known as leaching. The temperature, pressure, and concentration are controlled by the origin of the bauxite and the kind of state of aluminium oxide it contains. 

Al2O3.2H2O + Na2CO3 + heat 2NaAlO2 +2H2O +CO2

 The leftovers or the contamination in the bauxite continue to stay as solids. These solid impurities are removed from the purifying solution (sodium tetrahydroxoaluminate) by the process of filtration. These impurities create a kind of “red mud” collected in large lagoons. This whole process is also known as the Baeyer’s process.

Precipitation of aluminium hydroxide

The purifying solution of sodium tetrahydroxoaluminate is chilled and then sowed with already produced aluminium hydroxide. This combination creates a brand-new aluminium hydroxide precipitate.

2NaAlO2 +3H2O +CO2 Na2CO3 + 2Al(OH)3

Formation of Pure Aluminium Oxide

Aluminium hydroxide is heated to around 1100 to 1200 degrees Celsius to produce aluminium oxide, also called alumina.

2Al(OH)3 → Al2O3 + 3H2O

Electrolytic diminution of Alumina

The alumina is melted into a molten solution called cryolite. This cryolite electrolysed the alumina inside an iron tank, acting as a cathode. This molten solution of cryolite decreased the melting point and enhanced the conductivity of the electrolyte. 

Anodes are the rods released from the top into the electrolyte solution. This procedure of electrolysis of aluminium is also known as Hall Heroult Process. 

At Anode –

O-2 O+2e

2O O2

C(coke) + O CO

2CO + (air)O2 2CO2

The aluminium is released, accumulated, and taken out regularly at the bottom of the iron tank, called a cathode. 

At Cathode –

2Al+3 + 3e → Al

Purification of the Aluminium

Although the aluminium collected at the bottom of the iron tank is in a pure state, it is still not in the purest form. Therefore, the hoope’s electrolytic method is applied for further refinement. This procedure is also done in an iron tank with a carbon lining. The tank also has three coatings of molten solutions with varied densities. Among them, the topmost has the aluminium in its pure form with carbon electrode acting as cathode sinking-in. The second coating combines sodium, barium, and aluminium fluorides in a molten solution. It behaves as an electrolyte. The last coating has contaminated aluminium, and this, together with the carbon lining, is the anode. 

Bypassing the electric current, the aluminium ions of the second coating are released in the cathode as unpolluted aluminium. This clean aluminium is separated from the tapping hole. The same quantity of aluminium from the last coating moves up to the second coating, separating itself from the impurities. And hence, with the help of this procedure, aluminium is in its purest form.

Other ways could refine the aluminium and could eliminate its impurities. For example, chlorine could be applied in practice to further refine the aluminium by bubbling it into aluminium’s molten solution. The molten solution of aluminium is melted again and then could be heated to do away with impurities, oxides, contaminates, and other responsive metals. 

Conclusion

Aluminium is one of the lightest and easiest to handle and is being used increasingly for various purposes in daily life and industrial businesses. Though aluminium has multiple uses, it still takes some time to extract aluminium from its ore. This aluminium extraction process takes place in various steps, and it is necessary to extract aluminium from its ore and purify this extracted aluminium. Using various methods like – Bayer’s process and Hall Heroult’s process to extract aluminium could explain how the extraction comes together.