How Aluminum Is Made

In many ways, aluminum is the perfect metal. It is strong, light, resistant to heat and corrosion and a good conductor of electricity. On top of that it is plentiful and inexpensive.

Aluminum is also the most abundant metal in the Earth’s crust, and the third most abundant element after oxygen and silicon. However, it was not until 1809 that English chemist Sir Humphry Davy formally identified and named it.

Today, aluminum is the most commonly used metal in the world after iron and steel. Aluminum is a vital component of almost every part of our lives, from the vehicles we drive to the packaging of our food.

Aluminum is at its most versatile when it’s combined with other metals to form aluminum alloys. The alloying process gives aluminum improved properties to suit a range of applications.

How Aluminum Is Made

Aluminum is made in the following stages:

• Finding the Aluminum Ore
• Mining Aluminum
• Refining the Bauxite
• Aluminum Smelting

Finding the Aluminum Ore

Aluminum tends to combine with other elements and rarely exists in nature in its pure metallic form. Aluminum compounds are found in most common rock types including clay, slate, shale, granite and anorthosite.

The most important aluminum ore is bauxite, a rock containing about 52% aluminum oxide with impurities of iron oxide, silica, and titania. Bauxite is commonly found in deposits on or close to the Earth’s surface throughout many parts of the world, including Europe, Asia, Australia and South America.

Mining Aluminum

Geologists locate bauxite deposits by taking samples and conducting investigatory drilling. When deposits are found, they are mined in open pits. The earth is blasted loose and the bauxite is extracted using power shovels or draglines.

90% of all mined bauxite is made into alumina to be smelted into aluminum. The remaining 10% is used for other purposes including the manufacture of abrasives, furnace linings, and proppants for the oil industry. It takes 4 tons of high-quality bauxite to produce 2 tons of alumina, from which 1 ton of aluminum can be made.

Refining the Bauxite

The bauxite is refined using the Bayer process which was first developed by Karl Joseph Bayer in 1888. The Bayer process has four steps: digestion, clarification, precipitation and calcination.

Digestion

The bauxite is ground, mixed with caustic soda and pumped into pressure tanks where steam heat and pressure is applied. This causes the caustic soda to react with the aluminum compounds in the bauxite to form a solution of sodium aluminate. The unwanted impurities are left behind in what is known as red mud.

Clarification

Next, the sodium aluminate solution is passed through blow-off tanks where the pressure is reduced to atmospheric pressure. The red mud is removed with the use of clarifying agents and cloth filters. The clarified solution is then cooled in heat exchangers and pumped into tall silos.

Precipitation

Aluminum hydroxide seed crystals are added to the sodium aluminate solution to cause precipitation. During this process, the aluminum becomes solid. This results in large aluminum crystals which are filtered and washed to remove water and other impurities.

Calcination

Now the aluminum hydroxide crystals are subjected to calcination, a thermal treatment process where the supply of air is controlled. Rotary kilns are used to heat the crystals to temperatures over 960° C which removes any remaining impurities, leaving a fine white powder known as alumina, or aluminum oxide.

Aluminum Smelting

Smelting is the process during which aluminum is extracted from the alumina. This is carried out by the Hall-Héroult process, which was invented in 1886 by Charles Martin Hall and Paul Héroult.

The smelting takes place in steel reduction pots filled with molten electrolyte, where carbon anodes are used to pass an electric current through the electrolyte. Alumina is then added to the molten surface. The electric current deposits molten aluminum which can be collected and siphoned off.

The molten aluminum is then poured into molds to form foundry ingot. At this stage it’s 99.8% pure. Now it can be further refined to produce superpure aluminum or used for alloying with other metals.

Superpure Aluminum

Superpure aluminum of high purity (99.99%) is soft and lacks tensile strength. However, it is corrosion-resistant and an excellent conductor of electricity. Superpure aluminum is used in chemical equipment, electronic components, and to make gasoline.

Aluminum Alloys

Most aluminum is alloyed with other elements. By alloying the aluminum, its hardness and strength can be significantly improved. Common aluminum alloys are aluminum-manganese (used in beverage containers), aluminum-magnesium (used in appliances and utensils), aluminum-magnesium-silicon (used in buildings and vehicles), and aluminum-copper (used in aircraft).

Recycling Aluminum

Aluminum can be endlessly recycled without losing its quality. This makes it one of the most environmentally friendly metals on the planet. Incredibly, most of the aluminum ever produced is still being used today.