Aluminium is the most abundant metal in the earth’s crust, where it is found in the form of hydrated oxides like bauxite.
Important ores of Aluminium:
• Bauxite: Chemial formula is: Al2O3.2H20
• Bauxite is the principal ore of aluminium. Bauxite is chemically known as hydrated aluminium oxide.
• Corundum: Chemial formula is: Al2O3. Corundum is the aluminium oxide.
• Cryolite: Chemial formula is: Na3AlF6. Cryolite is sodium aluminium fluoride
The extraction of aluminium from bauxite involves three steps:
• The purification of bauxite using Bayer’s process.
• The electrolytic reduction of anhydrous Al2O3 by Hall and Herault’s process.
• The last step is the purification of impure aluminium by Hoope’s process
In Baeyer’s process, impure bauxite is converted into pure alumina. The conversion process involves mainly three reactions:
Bauxite is also concentrated through Hall’s process, in which sodium aluminate is prepared by adding sodium carbonate to bauxite. When excess carbon dioxide is passed through sodium aluminate in the presence of water, it forms aluminium hydroxide along with sodium carbonate. When dried aluminium hydroxide is ignited, alumina is formed.
Alumina is a very stable oxide and aluminium shows a strong affinity to combine with oxygen. Therefore, reducing it with reducing agents is practically difficult. Hence, it is reduced by electrolytic reduction through Hall-Heroult’s process.
Hall-Heroult’s Process:
The molten aluminium obtained after electrolysis is more than 99 per cent pure, and is refined further by Hoope’s process to make it 99.9 per cent pure.
When current is passed, aluminium ions from the electrolyte move towards the cathode, where they gain electrons to form pure aluminium. More aluminium ions from the impure aluminium in the bottom layer enter the middle layer to get electrons and get collected at the cathode. The bottom layer is replenished with impure aluminium at frequent intervals.
Impure aluminium is refined by Hoope’s process to produce 99.9 per cent pure aluminium.
Aluminium is used in:
• Manufacture of automobile components
• Construction process
• Manufacture of electric wires
• Packing medicines and pharmaceutical products
• Manufacture of soft drink cans and espresso coffee makers
• Manufacture of utensils
Aluminium is the most abundant metal in the earth’s crust, where it is found in the form of hydrated oxides like bauxite.
Important ores of Aluminium:
• Bauxite: Chemial formula is: Al2O3.2H20
• Bauxite is the principal ore of aluminium. Bauxite is chemically known as hydrated aluminium oxide.
• Corundum: Chemial formula is: Al2O3. Corundum is the aluminium oxide.
• Cryolite: Chemial formula is: Na3AlF6. Cryolite is sodium aluminium fluoride
The extraction of aluminium from bauxite involves three steps:
• The purification of bauxite using Bayer’s process.
• The electrolytic reduction of anhydrous Al2O3 by Hall and Herault’s process.
• The last step is the purification of impure aluminium by Hoope’s process
In Baeyer’s process, impure bauxite is converted into pure alumina. The conversion process involves mainly three reactions:
Bauxite is also concentrated through Hall’s process, in which sodium aluminate is prepared by adding sodium carbonate to bauxite. When excess carbon dioxide is passed through sodium aluminate in the presence of water, it forms aluminium hydroxide along with sodium carbonate. When dried aluminium hydroxide is ignited, alumina is formed.
Alumina is a very stable oxide and aluminium shows a strong affinity to combine with oxygen. Therefore, reducing it with reducing agents is practically difficult. Hence, it is reduced by electrolytic reduction through Hall-Heroult’s process.
Hall-Heroult’s Process:
The molten aluminium obtained after electrolysis is more than 99 per cent pure, and is refined further by Hoope’s process to make it 99.9 per cent pure.
When current is passed, aluminium ions from the electrolyte move towards the cathode, where they gain electrons to form pure aluminium. More aluminium ions from the impure aluminium in the bottom layer enter the middle layer to get electrons and get collected at the cathode. The bottom layer is replenished with impure aluminium at frequent intervals.
Impure aluminium is refined by Hoope’s process to produce 99.9 per cent pure aluminium.
Aluminium is used in:
• Manufacture of automobile components
• Construction process
• Manufacture of electric wires
• Packing medicines and pharmaceutical products
• Manufacture of soft drink cans and espresso coffee makers
• Manufacture of utensils