Chet Voss, age 14, of Dodge City, Kan., for his question:
WHERE DO WE GET ALUMINUM?
Aluminum is the most common metallic element in the Earth's crust. Yet aluminum does not occur as a metal in nature. It is never found in the free or pure state but only in combination with other elements. In its most concentrated form, however, it is found in an ore called bauxite.
A Danish physicist named Hans Oersted produced aluminum for the first time in 1825. But it wasn't until 1886 that an American chemist named Charles Hall found a way to extract pure aluminum. A French chemist named Paul Heroult worked out the same process just a few weeks later.
They found aluminum oxide in melted cryolite, a compound of aluminum, sodium and fluorine. They placed the cryolite in a carbon vessel and passed an electric current through it. Small drops of metallic aluminum formed in the bottom of the smelting pot.
The Hall Heroult method, with only a few minor modifications, is still used in the world's yearly aluminum production of about 10 million tons.
After aluminum is drawn from the smelting pots, it is usually put into 14 foot ingots. It is then processed by a number of different methods, depending on the product desired. Aluminum can be cast, extruded, forged, drawn, turned or rolled.
The United States produces most of its aluminum from bauxite mined fn Jamaica and Surinam. Arkansas furnishes about 90 percent of the bauxite that is mined in the U.S.
To be considered bauxite, the ore must have more than 32 percent alumina, which is aluminum oxide, that can be recovered. Most aluminum comes from bauxite that has 55 percent alumina.
It takes four tons of bauxite to make two tons of alumina, which will make about one ton of aluminum metal. About half a ton of carbon is used in producing one ton of aluminum. From 16,000 to 20,000 kilowatt hours of electric power must be used to turn out one tor. of metal.
Bauxite isn't too expensive. However, the electrochemical treatment that is necessary to make aluminum is very expensive, since it takes a great deal of electric power to do the job. Hydroelectric power is the cheapest source of electrical energy, so aluminum plants are usually built near rivers that can provide lots of power.
Molten aluminum is siphoned out of a processing cell and is poured into molds called pigs or sows. A pig is a 50 pound piece of untreated, impure aluminum. A sow is a 1,000 pound piece.
The Hall Heroult process is a continuous one. Once started, a cell operates 24 hours a day, seven days a week with aluminum being removed on a regular schedule. A large cell will turn out about 900 pounds of aluminum every 24 hours.
Sows or pigs are placed in furnaces and other metals are added such as copper, magnesium, silicon and zinc to form aluminum alloys. When the alloy is melted and of the proper composition, it is cast into ingots.