Primary aluminum production consists of three basic steps: Bauxite mining and
processing, alumina refining, and smelting.
Bauxite is mined using open pit methods and transported to a beneficiation plant. The ore is crushed, washed, kiln dried and shipped to a refinery.
At the refinery, the Bayer process can be employed to digest the bauxite in hot caustic. Insoluble impurities are removed from the solution, and the alumina is then precipitated and calcined to anhydrous alumina.
At the smelter, purified alumina is dissolved in molten cryolite in an electrolytic cell with carbon electrodes. Oxygen in the alumina collects at the anode and combines with carbon to release carbon dioxide. The free molten aluminum collects on the carbon lining (cathode) at the bottom of the cell and is siphoned off. The molten aluminum is then moved in insulated ladles to users, cast into ingots and cooled, undergoes strand casting, or is alloyed with other metals and cast into shapes.
Over 90% of the bauxite and about 50% of the alumina feedstock used in the United States is imported.
