The Story of Aluminum – Part 1: What is Aluminum and How Do We Produce It?

Similar to the birth of iron, it is thought that aluminum is produced in stars at the time of their death. When stars explode, as a result of their rapid collapse and eventual violent explosion, as depicted in Figure 1, aluminum is spread throughout the blast. Some of this aluminum is deposited on the planet which we call Earth.

Figure 1 Depiction of an Exploding Star.

Aluminum, in the form of its oxides, is the most abundant metal element in the earth's crust as it is a very light metal, floating to the surface of the Earth on cooling and becoming part of its crust. This is unlike like iron and nickel which are denser and tend to sink further into the Earth’s mantle and core. 

The ore source for aluminum is a weathered rock called bauxite with an aluminum oxide content in the range of 45%–60% that also contains an appreciable number of other oxides. Bauxite is commonly found in subtropical to tropical climates and the largest resources occur in, Guinea, Australia, Brazil, Vietnam andJamaica

However, the world’s biggest Aluminum producers in order of total production in 2022 were: 

• China, 40 million metric tonnes (MT)

• Russia, 4 million MT

• India, 3.7 million MT

• Canada, 3 million MT

• UAE 2.7 million MT

The naturally occurring impurities in bauxite are iron oxide, silicon oxide and titanium oxide. Since bauxite deposits are close to the earth surface it can be mined by open pit mining using draglines or shovels. 

Light, strong, flexible, non-corrosive and infinitely recyclable, aluminum is one of the most widely used and recycled metals in the world.

Important facts for aluminum production in Canada

• Canada produced an estimated 3.1 million tonnes of primary aluminum in 2021. 

• As per above, Canada is the world's fourth-largest primary aluminum producer following China, India and Russia.

• By using mostly hydroelectricity and the latest generation of technologies, Canadian aluminum producers have the lowest carbon footprint in the world when compared to other large producers. This is a very important fact as we move forward into the “green economy”

• There are 10 primary aluminum smelters in Canada: one is located in Kitimat, British Columbia, and the other nine are in Quebec. The Quebec locations are in the Sept-Isles, Baie Corneau, Saguenay-Lac Saint-Jean, and Becancour. 

• There is also one alumina refinery, located in Jonquiere, Quebec.

• No bauxite is mined in Canada.

Since the mined rock contains about 50 percent alumina, it first has to undergo a preliminary treatment to remove the bulk of the impurities. The preliminary refining of bauxite is conducted in the Bayer process, which was developed for the aluminum industry in 1888. In the Bayer process bauxite is crushed, mixed in a solution of sodium hydroxide, and seeded with crystals to precipitate aluminum hydroxide. The hydroxide is washed and dried to produce aluminum oxide which is a very stable compound and, to reduce this oxide to metal requires a considerable amount of energy.

The reduction of aluminum oxide to aluminum is conducted in a smelter cell. The reduction process is called the Hall-Heroult process and a schematic is shown in Figure 2. The alumina is fed into a molten fluoride salt (cryolite) that floats between a carbon anode and graphite-lined cell walls that act as a cathode. With the current flow of 50,000– 150,000 amps between the electrodes, the alumina is reduced to metallic aluminum and gaseous oxygen.

Figure 2. The Hall-Heroult Process - The electrolytic process of separating the Alumina atom into molten Aluminium

The aluminum is heavier than the cryolite and settles to the bottom while the  electric current through the cell keeps the aluminum and the electrolyte molten. There are several hundred cells at a smelter, and on a daily basis transfer crucibles are brought to the cells and the metal is siphoned out and into these “transfer crucibles.” 

As previously stated, Canada’s aluminum production can be considered “green” as it uses hydro electricity to power it. Another significant way to reduce the any carbon footprint is to recycle aluminum. Aluminum can be re-melted many times and thus can be recycled and used time and time again. This is very attractive with respect to energy conservation and a ‘green footprint’ because recycling consumes only 5% of the energy required for producing primary aluminum from the original bauxite ore. 

The main source of feedstock for the recycling plants in North America is the beverage can and there are large recycling plants that de-coat and re-melt the can scrap. The beverage cans are re-melted, cast into ingots and rolled into sheet. Similarly, there are re-melt facilities in the extrusion industry, where process scrap and scrap recovered from other sources are re-melted, alloyed if necessary, and cast into extrusion ingots. The product of the recycling process stream is called secondary aluminum, as opposed to primary aluminum produced from the smelter. 

During the recycling of aluminum, there is some deterioration of metal purity due to the pick-up of elements such as titanium and silicon from coating pigments, some iron from the molten metal handling equipment, zinc from clad aluminum scrap and other metals that may contaminate the feedstock to the recycling plant. 

The recycled metal composition, thus, may be outside the specified limits of a specific alloy. In such cases, pure aluminum is added to the melt to reduce the impurities to an acceptable level. 

Aluminium and its alloys are extremely versatile metals with a number of very positive advantages and we will expand on these advantages, and its weldability, in future notes on “The Story of Aluminum.”