Aluminum Flow-Sheet
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The Production of Aluminum
The figure shown below schematically describes Aluminum Production. Aluminum
is produced from alumina by an electrolytic process that uses large quantities
of electrical energy to separate aluminum from oxygen in the alumina. For
this process, a modern smelter requires about 13,500 (DC) kilowatt-hours
of electricity to produce one tonne of aluminum.
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In nature, aluminum is never found in its metallic state but is a common constituent of many minerals where it is normally combined with silicon and oxygen. Bauxite is the only ore from which aluminum can be economically retrieved.
1. Aluminum Chemical Process
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Al Chemical Process
The first step in Aluminum Production is to mix crushed bauxite in a solution of hot caustic soda in digesters. This allows the alumina hydrate to be dissolved from the ore. After the red mud residue is removed by decantation and filtration, the caustic solution is piped into huge tanks, called precipitators, where the alumina hydrate crystallizes. The hydrate is then filtered and sent to calciners to dry and, under very high temperature, is transformed into the fine, white powder known as alumina. The alumina is transferred to the Electrolytic Process for aluminum reduction.
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2. Aluminum Electrolytic Process
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Al Electrolytic Process
Alumina is a compound of aluminum and oxygen. To obtain metal from the alumina, these elements must be separated by electricity in the smelting process. This reaction takes place in large, carbon-lined steel cells, or pots, through which a direct electrical current is passed.
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Molten Aluminum |
The bottom of each pot acts as a cathode, or negative electrode. Carbon blocks are suspended in the pot to serve as an anode, or positive electrode. Inside the pot, alumina is dissolved in a molten electrolyte, composed mainly of the mineral cryolite. The electrical current passing from the anode to the cathode causes the oxygen in the mixture to react with the carbon anode to form carbon dioxide, while the aluminum settles to the bottom of the pot to be siphoned off to Casting and Fabricating.
3. Aluminum Casting & Fabrication
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Al
Casting & Fabricating
Before casting into ingot for fabricating, the molten aluminum is treated
to ensure cleanliness and purity. Alloying ingredients are usually added
to increase strength or provide special properties. Traditionally, the
metal is then cast into ingots of various shapes, sizes and compositions
for a number of uses.
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Aluminum Ignot |
Ingots are converted by Alcan or its customers into sheet, plate or foil
products, as well as extruded shapes for engineering and architectural
applications. Value-added foundry alloy ingots for shape castings and
unalloyed ingots for remelting are sold mainly to third parties.
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