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How Does Aluminum Get Made?

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If you’re like most manufacturers and builders, you don’t put a lot of thought into where your raw materials come from. You source your materials from a supplier like Clinton Aluminum, who delivers your metal in a form that’s as close to ready to work with as possible, to your specifications. But the truth is that understanding how the metal and other components you need get into that form can actually have a positive effect on the way you select and process your key materials.

If you have questions about how your aluminum and stainless steel get processed, feel free to contact one of the trained technical professionals at Clinton Aluminum. We’ll be happy to discuss our methodologies with you and can advise customers on how to get the most out of their production activities.

Raw Aluminum: Extremely Common Yet Strangely Elusive

Aluminum is one of the chemical elements on the periodic table, found in the boron group. It is referred to with its symbol Al and has the atomic number of 13. Although it is one of the most common elements on Earth, it is actually very rarely found in its native form. It makes up approximately 8% of the Earth’s crust, making it the third most abundant element, and the most abundant metal, following oxygen and silicon.

Pure aluminum, which is silvery-white, soft, ductile, and non-magnetic, is known to be very chemically reactive, which is why it is so rarely encountered on its own, even in the laboratory. Instead, there are more than 270 known minerals that are made up of some combination of aluminum and other elements. The most common and economically important of these ores is bauxite.

For these reasons, aluminum was discovered much later than most of the other common metals used commercially today. The origin of its name, and the impetus for its discovery, stems from alum, a hydrated sulfate that contains aluminum that has been known about and used commercially since antiquity. It wasn’t until the 1700’s, however, that scientists began to suspect that alum was made up of an as yet undiscovered element.

Starting in the 1760’s, researchers began attempting to extract aluminum, unsuccessfully, until the German scientist Friedrich Wöhler was able to isolate pure aluminum in 1845 and began to identify some of its properties. Although his method was not commercially viable, Wöhler has been recognized as the discoverer of aluminum.

How Does Aluminum Get Processed For Commercial Use?

After Wöhler’s discovery, it was another half-century of experimentation before an effective method of extracting aluminum was developed. It was actually discovered independently by two different scientists, French engineer Paul Héroult and American engineer Charles Martin Hall. The method is now collectively known as the Hall–Héroult process. The technique involves converting the mineral alumina into aluminum. A few years later, Austrian chemist Carl Joseph Bayer came up with a separate method for purifying bauxite in order to yield alumina. Together, these two methods made large-scale commercialization of aluminum possible.

It can be instructive to take a closer look at how these two processes work so that we have a better understanding of where aluminum comes from.

How Does The Bayer Process Work?

The first problem that needed to be solved in order to get aluminum was the fact that one of the most prevalent aluminum ores, bauxite, was not very useful by itself. But it does provide a relatively easy and abundant source of alumina, thanks to the Bayer Process.

First, the bauxite ore needs to be mechanically crushed. It can then be mixed with caustic soda and run through a grinding mill, creating a slurry. Next, the slurry gets pumped into a pressure cooker and heated to extremely high temperatures (as high as 270°C) for several hours. This forms a sodium aluminate solution that then gets passed through a series of flash tanks and into a settling tank.

This allows the impurities to be separated from the caustic soda, while the aluminum remains in dissolved form. The residue, known as red mud, can then be removed. The remaining liquid is pumped through cloth filters to remove the extremely fine impurities that have yet to be filtered out. The liquid next moves through precipitation tanks, to which alumina hydrate crystals are added, in order to extract the alumina from the liquid.

As the crystals grow, they settle at the bottom of the tank and are removed. They are then heated again in a kiln. This removes any water molecules that have bonded with the crystals, and the final result is pure alumina. After cooling, the alumina is ready for further processing.

How Does The Hall–Héroult Process Work?

In order to get pure aluminum, the alumina must be smelted. This occurs in a reduction pot that has been lined with carbon. This acts as an electrode, which is opposed by carbon rods suspended above the pot. Inside the reduction pot, the alumina crystals get dissolved into molten cryolite, which requires a temperature of at least 960° C.  This results in an electrolyte solution that is able to conduct electricity. When a direct current is passed through the solution, it breaks the bonds between the aluminum and oxygen atoms. The oxygen combines with the carbon to form carbon dioxide, leaving behind pure aluminum.

As more alumina is added, more aluminum is processed, which should be about 99.8% pure. The molten metal gets transferred to a holding furnace, where it is shaped into ingots and hardened.

This of course is not the end of the process. Pure aluminum is not durable enough to have many commercial uses. Instead, the aluminum ingots will be used to create aluminum alloys. As every manufacturer knows, it is these aluminum alloys that have transformed nearly every type of industry over the last century. That is because aluminum alloys possess many desirable properties, such as superior strength, tremendous corrosion resistance, and extreme formability, not to mention an extremely attractive appearance.

The more you know about the process of creating aluminum, the better choices you can make about which material is best for your particular application. To learn more about which alloy is right for you, please contact one of the friendly and knowledgeable representatives from Clinton Aluminum today.

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