Primary aluminum production

Primary aluminum ingot production includes the following steps:

  • mining of bauxite;
  • extraction of alumina (aluminum oxide) from bauxite;
  • electrolysis of aluminum from alumina;
  • treatment of aluminum melt and casting it into ingots.

Primary aluminum production from bauxite [2]

Bauxite mining and alumina production

Initial ore for the production of aluminum - bauxite - is quite common throughout the world and is mined by open method. Bauxite is a mixture of aluminum compounds – aluminum hydroxides, and also iron oxide and silicon. from bauxites, mainly by Bayer, are alumina. Alumina is a technical aluminum oxide (Al2O3), white powder.

Alumina production by the Bayer method [1]

Primary Aluminum Electrolysis

Metallic (primary) aluminum is smelted from alumina by electrolysis by the Hall-Heroult method. It takes place in electrolytic cells, which is a bath of molten cryolite. This molten cryolite electrolyte is in this electrochemical process. A typical electrolytic cell has a length of approximately 5-10 m. Cathode in the electrolytic process is the bottom of the electrolytic bath, which is lined with carbon blocks.

Anodes are massive carbon blocks, which gradually immersed in the cryolite as their combustion. Therefore, the carbon anodes require constant replacement, and it is a significant part of the work and costs. Cryolite (Na3AlF6) in the electrolysis process is practically not consumed.

Alumina is gradually added to the electrolytic cell from the top of the melt, where it is melted. The temperature in the electrolytic bath is 950-970 ° C. Drops of liquid aluminum formed and accumulates on the tub bottom. This is the primary aluminum. Molten aluminum goes out of the cell at a temperature of about 900 ° C.

Direct electric current, which is supplied to the cell, generally has voltage 4-5 volts and current about 150000 A.

manufacturing 1 kg of aluminum requires about 2 kg of alumina, 0,5 kg coal and 15 kWh of electric energy.

One electrolysis plant may comprise 600-700 electrolyzers and have a length of up to 1 km.

Electrolyzer [1]

Treatment of primary aluminum

On the territory of an electrolysis plant is usually a casting department, in which at minimum liquid flow paths coming from primary aluminum housings electrolyzers. The foundry houses large, electrically heated reverberatory furnaces (mixers).

Typically, to improve the quality of products set sequentially paired two reverberatory furnaces. One oven - “sump” - is designed to receive, upholding, averaging the temperature and chemical composition of the metal. Another oven - “filling” or “distributing” - designed for casting various types of products. Typically, these kilns are stationary, that unlike the tilting furnace allows continuous casting process.

The liquid aluminum is kept in the oven for 30-45 minutes at a temperature of 690-730 ° C for floating and precipitation of non-metallic inclusions, and the evolution of gases from a metal.

Impurities are removed from molten aluminum by refining. To do this, it is usually flushed with chlorine. The resulting gaseous aluminum chloride, passing through the melt, envelops the particles of impurities, that float to the surface of the metal in slag, which is mechanically removed. aluminum Chlorination also removes the Na, That, Mg and gases, dissolved in aluminum. After refining purity primary aluminum reaches 99,5-99,85 %.

Casting primary aluminum in the mold

Casting ingots - small bullions - usually produced in the mold at the filling machine conveyor type. casting metal in the mold are short flat jet. After filling the mold with the surface of the metal oxide film is removed. These machines are equipped with a mechanism for mechanically stamping ingots and air or water cooling system of the molds.

Economic geography primary aluminum

The main consumables and resources in the production of primary aluminum are:

  • bauxite;
  • hard coal (coke) and
  • Electric Energy.

Unfortunately, These three components are never in the world in the same place. Therefore, usually selected for primary aluminum production location near hydroelectric plants with cheap electric energy. These plants may be several thousand kilometers away from the source of alumina and aluminum ingots markets.

A source:

  1. The Metal Aluminium – Materials Aluminum Association of Germany
  2. TALAT 1100.01

Encyclopedia of Aluminum and Its Alloys, Two-Volume Set (2019)