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Extraction of Aluminium

  • Last Updated : 13 Jan, 2022

Aluminium has a lower density than other common metals, about one-third that of steel. When exposed to air, it forms a protective layer of oxide on the surface due to its high affinity for oxygen. Aluminium resembles silver in appearance, both in colour and in its ability to reflect light. It is pliable, nonmagnetic, and ductile. Aluminium is the twelfth most abundant element in the universe.

Aluminium is a chemical element with the symbol Al and atomic number 13. Aluminium is a chemically weak metal in the boron group; as is typical for the group, it forms compounds primarily in the +3 oxidation state. Because the aluminium cation is small and highly charged, it is polarising, and the bonds formed by aluminium tend to be covalent. 

Because of its strong affinity for oxygen, aluminium is commonly found in nature in the form of oxides; as a result, aluminium is found on Earth primarily in rocks in the crust, where it is the third most abundant element after oxygen and silicon, rather than in the mantle, and almost never as a free metal.

Properties of Aluminium

  • The element is extremely reactive. It is approximately one-third the stiffness and density of steel.
  • Aluminium is resistant to corrosion.
  • It has the ability to superconduct.
  • There are many unknown hydrogen isotopes with mass numbers ranging from twenty-one to forty-one.
  • Reaction with HCl: Aluminium reacts with dilute hydrochloric acid at room temperature. When the metal aluminium dissolves in hydrochloric acid, it produces aluminium chloride and colourless hydrogen gas. Aluminium and hydrochloric acid have an irreversible reaction.

2Al + 6HCl → 2Al­Cl₃ + 3H₂↑

  • Reaction with Sodium hydroxide: Sodium aluminate is also formed when sodium hydroxide reacts with elemental aluminium, which is an amphoteric metal. Once established, the reaction becomes highly exothermic and is accompanied by the rapid evolution of hydrogen gas.

2NaOH + 2H2O → 2NaAlO2 + 3H2

  • Reaction with water: Aluminium metal rapidly forms a thin layer of aluminium oxide a few millimetres thick, which prevents it from reacting with water. According to the equation, aluminium reacts with water to produce hydrogen gas.

2Al + 3H2O → 3H2 + Al2O3

Uses of Aluminium

  1. Aluminium is commonly used in the packaging industry to make coils, cans, foils, and other wrapping materials.
  2. It is also found in many everyday items such as utensils and watches.
  3. Aluminium is used in the construction industry to make doors, windows, wires, and roofing.
  4. It is used in the transportation industry to make bicycles, spacecraft, car bodies, aircraft, and marine parts.
  5. Many coins are made of alloys containing aluminium.
  6. Aluminium is also used in the manufacture of paints, reflective surfaces, and wires.

Ores of Aluminium

In 1821, near Les Baux in southern France, the most important aluminium ore, an iron-containing rock containing approximately 52 % aluminium oxide, was discovered. The substance was later dubbed bauxite. 

Bauxite is best defined as an aluminium ore of varying purity in which aluminium, in the form of aluminium hydroxide or aluminium oxide, is the most abundant single constituent. Iron oxide, silica, and titania are the most common impurities.

The physical appearance of bauxite varies greatly depending on its composition and impurities. If the iron oxide content is high, the colour ranges from yellowish-white to grey, or from pink to dark red or brown. It could be earthy, or it could take the form of clay or rock. Except for Antarctica, bauxite has been discovered on all seven continents. The richest deposits are typically found in areas that were in tropical or subtropical climates at the time of formation, providing optimal conditions of heavy rainfall, constant warm temperatures, and good drainage.

Properties of Bauxite 

  • Bauxite is a soft material with a hardness range of 1 to 3 on the Mohs scale.
  • It ranges in colour from white to grey to reddish-brown, has a pisolitic structure, an earthy lustre, and low specific gravity of 2.0 to 2.5.
  • These properties are useful for identifying bauxite, but they have nothing to do with the value or utility of bauxite. This is because bauxite is almost always processed into a material with distinctly different physical properties than bauxite.

Uses of Bauxite

  • Metallurgy
    • Bauxite is the only and best material for producing aluminium.
    • The extraction of aluminium from bauxite involves several processes, including the Bayer Process and the Hall-Heroult Process.
    • Once extracted, aluminium and alloys based on aluminium are widely used in electronics, construction, vehicles, and even utensils.
  • Industries
    • Bauxite is used in a variety of industries, including the chemical, refractory, abrasive, cement, steel, and petroleum industries.
    • Bauxite, along with alumina, is used in the production of aluminium chemicals.
    • It is used as a raw material in the manufacture of several refractory products.
    • Bauxite is a critical component in the aerospace, electric, machinery, and civil tool-making industries.
    • It’s also used as a desiccant, adsorbent, a catalyst, and in the production of dental cement.It is also used as a desiccating agent, adsorbent, catalyst and in the manufacture of dental cement.
  • Building Material and Road Aggregates
    • When no other materials are available, lateritic bauxite is frequently used as a building material.
    • Construction companies use calcined bauxite as an anti-skid road aggregate in certain areas to prevent accidents.
  • Other Uses
    • Bauxite has a limited number of applications, but it is widely used in paper manufacturing, water purification, and petroleum refining.
    • Bauxite is also used in other industries such as rubber, plastic, paint, and cosmetics.

Sample Questions

Question 1: Why is aluminium expensive than steel?

Answer:

Aluminium is significantly more expensive than carbon steel. Aluminium repair is also more expensive than steel repair. When stressed, steel’s carbon content makes it harder, more dent resistant, and more durable. Steel is a strong material that is less likely to warp, deform, or bend when subjected to weight, force, or heat.

Question 2: What is the main useful property of Aluminium alloys?

Answer:

Aluminium is a soft, ductile, corrosion-resistant metal with a high electrical conductivity. It is widely used for foil and conductor cables, but it must be alloyed with other elements to provide the higher strengths required for other applications.

Question 3: What are the two classifications of aluminium alloys?

Answer:

Casting alloys and wrought alloys, which are further classified into heat-treatable and non-heat-treatable alloys, are the two basic classes.

Question 4: Who discovered aluminium?

Answer:

Hans Christian Orsted discovered aluminium

Question 5: How does aluminium react with water?

Answer:

Aluminium metal rapidly forms a thin layer of aluminium oxide a few millimetres thick, which prevents it from reacting with water..

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