About Aluminum

About Aluminum

Aluminum is the most abundant metallic element, making up 8% of the earth’s crust by weight. It reacts with water and air to form powdery oxides and hydroxides so it is never found in nature in the metallic state. Many minerals (including feldspars) contain aluminum but extracting the metal from most minerals is very expensive.

Bauxite

The main ore of aluminum is bauxite (the source of over 99% of metallic aluminum).
Bauxite is a mixture of minerals that contain hydrated aluminum oxides and is therefore a rock and not a mineral. Soil-like in appearance, bauxite forms when silica in aluminum-bearing rocks (rocks with high feldspar content) is washed away (leached). This weathering process occurs in tropical and subtropical climates such as Africa, western India, South America and Australia.
 

Alumina

Most bauxite is first processed to make alumina, or aluminum oxide. Alumina is lighter than bauxite because the water has been removed and it flows readily in processing plants, unlike bauxite, which has a sticky consistency. Aluminum metal is refined from alumina. In the refining process, called the Hall-Heroult process, alumina (aluminum oxide) is dissolved in molten cryolite. The alumina is then separated into its elements by electrolysis. Because this process requires so much energy, it is usually done in countries with large supplies of cheap hydroelectric power.
 

Aluminum Processing

Aluminum ingots can be processed in three ways:
Casting – pouring melted aluminum into steel molds of various designs.
Rolling – processing aluminum using large presses. The raw material is processed into flat aluminum plates of different thickness.
Extrusion – forcing aluminum that has been melted to flow through a shaped opening in a die.