Aluminum Production
Historical Production of Aluminum: Uses processes that were developed in the 1880s. Bayer developed the sodium aluminate leaching process to produce pure alumina (Al2O3). Hall and Heroult developed an electrolytic process for reducing the alumina to pure aluminum.
Process: The production of aluminum follows the following process:
1. The mining of the aluminum ore, bauxite.
2. Crushing of the bauxite, which is then washed, to remove clay and silica materials, and kiln dried afterwards.
3. Mixing the crushed bauxite with soda ash and lime and passed through a digester, pressure reducer, and settling tank to produce a concentrated solution of sodium aluminate. (This removes silica, iron oxide, and other impurities).
4. Seeding of the solution with hydrated alumina crystals in precipitator towers. The seeds attract other alumina crystals and form groups that settle out of solution.
5. The resulting alumina is reduced with the Hall-Heroult process and melted in a cryolite bath (a molten salt of sodium-aluminum-fluoride).
6. A current is passed between anodes and cathodes of carbon, which separates the aluminum from the oxygen and the molten aluminum is collected at the cathode at the bottom of the bath.
The final molten aluminum is either shipped to a foundry for casting into final products or is cast into ingots. The ingots are formed by a direct chill process that produces sheets for rolling mills, or square billets for production of wire, rod and bar stock.
Final products are made by either casting or deforming solid aluminum stock. Casting is the oldest method, and can be done in three ways:
1. Die Casting – Forcing molten aluminum into mold under high pressure.
2. Permanent Mold Casting – Pouring aluminum into reusable metal mold.
3. Sand Casting – Sand with a binder packed around a pattern, aluminum poured into pattern, reproducing the shape.
The deformation processes are:
1. Forging
2. Impact Extrusion
3. Stamping
4. Drawing
5. Drawing Plus Ironing
Recycling Aluminum: Scrap stock is melted in a furnace. The molten aluminum is purified and alloys are added.
Historical Production of Aluminum: Uses processes that were developed in the 1880s. Bayer developed the sodium aluminate leaching process to produce pure alumina (Al2O3). Hall and Heroult developed an electrolytic process for reducing the alumina to pure aluminum.
Process: The production of aluminum follows the following process:
1. The mining of the aluminum ore, bauxite.
2. Crushing of the bauxite, which is then washed, to remove clay and silica materials, and kiln dried afterwards.
3. Mixing the crushed bauxite with soda ash and lime and passed through a digester, pressure reducer, and settling tank to produce a concentrated solution of sodium aluminate. (This removes silica, iron oxide, and other impurities).
4. Seeding of the solution with hydrated alumina crystals in precipitator towers. The seeds attract other alumina crystals and form groups that settle out of solution.
5. The resulting alumina is reduced with the Hall-Heroult process and melted in a cryolite bath (a molten salt of sodium-aluminum-fluoride).
6. A current is passed between anodes and cathodes of carbon, which separates the aluminum from the oxygen and the molten aluminum is collected at the cathode at the bottom of the bath.
The final molten aluminum is either shipped to a foundry for casting into final products or is cast into ingots. The ingots are formed by a direct chill process that produces sheets for rolling mills, or square billets for production of wire, rod and bar stock.
Final products are made by either casting or deforming solid aluminum stock. Casting is the oldest method, and can be done in three ways:
1. Die Casting – Forcing molten aluminum into mold under high pressure.
2. Permanent Mold Casting – Pouring aluminum into reusable metal mold.
3. Sand Casting – Sand with a binder packed around a pattern, aluminum poured into pattern, reproducing the shape.
The deformation processes are:
1. Forging
2. Impact Extrusion
3. Stamping
4. Drawing
5. Drawing Plus Ironing
Recycling Aluminum: Scrap stock is melted in a furnace. The molten aluminum is purified and alloys are added.
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