Intermediate Topic 638 of 1102 Inorganic Chemistry
Extraction of Aluminium
Bauxite is refined to alumina and electrolyzed in molten cryolite.
In-depth explanation of Extraction of Aluminium
Aluminium is extracted from bauxite in two stages. The Bayer process dissolves alumina in hot concentrated sodium hydroxide, separating it from iron oxide and silica, and then precipitates aluminium hydroxide, which is calcined to pure Al2O3. The Hall-Heroult process dissolves the alumina in molten cryolite, Na3AlF6, which lowers the melting point to about 950 degrees C, and electrolyses the melt with carbon electrodes. Aluminium forms at the cathode, while the carbon anode is consumed as it forms carbon dioxide. The process needs roughly 13 to 15 kWh per kilogram of aluminium, so recycling saves most of that energy.
Going deeper: Extraction of Aluminium
Key ideas: Bauxite Al2O3.2H2O is purified by the Bayer process: digestion in hot concentrated NaOH gives soluble aluminate, Fe2O3 remains as red mud, then seeding precipitates Al(OH)3, which is calcined to pure Al2O3. The Hall-Heroult process electrolyzes it dissolved in molten cryolite Na3AlF6 at 950 C with CaF2, using carbon electrodes. Cathode: Al3+ + 3e- gives Al; anode carbon burns to CO2. About 14 kWh per kg is needed.
Common mistakes and connections: Students suggest carbon reduction or electrolysis of aqueous solution; Al is too reactive for both. Cryolite lowers the melting point (from 2072 C) and improves conductivity; it is not an ore here. Anodes must be replaced, since they are consumed. Links to electrometallurgy, Ellingham diagrams and recycling that needs only 5 percent of the energy.
Visualization of Extraction of Aluminium
Hall-Heroult cell: alumina dissolved in molten cryolite near 950 C is electrolysed, depositing aluminium at the cathode while the carbon anode burns away. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Recycling aluminium cans uses only about 5 percent of the energy needed to make new aluminium from ore.
Frequently asked questions about Extraction of Aluminium
What is Extraction of Aluminium?
Bauxite is refined to alumina and electrolyzed in molten cryolite.
Is Extraction of Aluminium a beginner, intermediate or advanced topic?
Extraction of Aluminium is a intermediate topic in Inorganic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Extraction of Aluminium?
Study these earlier topics in Inorganic Chemistry first: Boranes, Aluminium Chemistry, Alums.
What comes after Extraction of Aluminium?
The next topics in Inorganic Chemistry are Carbon Family and Silicon Chemistry.
Can I practise Extraction of Aluminium with quizzes?
Yes. The interactive lesson includes a self-check question on Extraction of Aluminium, and the Inorganic Chemistry quiz draws on every topic in this area.
Where Extraction of Aluminium fits in Inorganic Chemistry
Extraction of Aluminium is topic 23 of 113 in Inorganic Chemistry.