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Primary and Secondary Aluminum


Aluminum is one of the most prevalent and widely used metals in the industrial world, but most people don’t think about where it comes from.  It may come as a surprise to realize that aluminum is the most abundant metal in the Earth’s crust, and the third most abundant element of any kind following oxygen and silicon.   Today, aluminum can be found in almost every industry for a wide variety of products and uses.

It wasn’t always this way.  Despite its popularity in the 21st century, it was discovered relatively recently, and most people don’t take much time to consider where aluminum comes from or how it gets processed.  For manufacturers, however, it is essential that they have a working understanding of the aluminum supply chain, from raw material to finished product.  One of the most important distinctions is between primary and secondary aluminum.

One of the best decisions a manufacturer can make is to partner with an experienced and reliable aluminum supplier, so there’s no doubt that the aluminum they are using is of the highest quality.

What is aluminum ingot?

When manufacturers purchase aluminum, it can come in many forms.  At Clinton Aluminum, some of the standard aluminum products we offer include cast and wrought plate, flat, square and round bar, sheet, extrusions, pipe and tube.

So, what is ingot?  Simply speaking, an ingot of metal is a solid mass of high purity material that can be further processed as needed into the aforementioned products.  The term is sometimes used interchangeably (and incorrectly) with billet and slab, though there are distinctions between the three in different industries.  Other metals including stainless steel begin production in ingot or billet form.  Some products, like flashlights or engine valve covers, are advertised as being machined from aircraft quality aluminum billet, but they are fabricated from cold finished bar or rolled plate.  The process of extracting and refining aluminum from the earth and turning it into ingot, slab or billet is known as primary production.

Where does primary aluminum come from?

So how does aluminum end up as ingot? The answer helps to explain why aluminum, despite being such a prevalent metal, has only become a commercially viable material in the last century or so. The process to create aluminum is generally a two-step process.

First, aluminum must be extracted from the ground, which is not an easy endeavor. This is because natural occurring aluminum is extremely rare, as the element is highly reactive and bonds easily to other materials.  The most common form of aluminum is in an ore known as bauxite.

The Bayer process involves blending bauxite until it has a uniform composition and then the material is ground into a slurry.  Sodium hydroxide is added, and the mixture goes through a digester vessel at high pressure, so that the aluminum hydroxide is dissolved, and the other impurities are converted into insoluble compounds.

The material is then cooled, the bauxite residue removed, and more aluminum hydroxide crystals are added, prompting the decomposition of the original material and isolating the original aluminum hydroxide.  The result is that the aluminum has been extracted from the bauxite in the form of alumina (also known as aluminum oxide).

Step 2 of the conversion process is known as the Hall–Héroult process.  This converts the aluminum oxide into pure aluminum.  Alumina is added to a molten mixture of cryolite. At extremely hot temperatures, the material is electrolyzed, so that the liquid aluminum sinks to the bottom of the solution.  It will eventually harden into aluminum.

The Hall–Heroult process results in aluminum that is more than 99% pure.  It should be noted the aluminum can be further purified with a third step, known as the Hoopes process, which will result in a purity level of 99.99%.

Primary aluminum versus secondary aluminum

The above processes are extremely energy intensive.  The extraction, processing and refining of primary aluminum is a costly undertaking.  That is why one of the chief attributes of aluminum is so important: it’s recyclability.  Much of the aluminum in use today has been recycled and reprocessed for further use.  This recycled aluminum product is known as secondary aluminum.

The secondary production of aluminum involves collecting and recycling aluminum scrap back into a usable state.  Studies have shown that recycled aluminum is 92 percent more energy efficient when compared to primary production.  In fact, almost 40 percent of the aluminum being sold in North America today is from secondary processing, and this number continues to grow.

The process starts with the collection of used aluminum instead of allowing it to end up in waste streams.  Since aluminum is easy to recycle and more energy efficient, used aluminum is a valuable commodity.  Prime scrap that has been segregated by grade is more valuable than mixed scrap composed of different alloys.  New advanced technologies like laser spectroscopy have been employed to expedite chemical analysis and more accurately segregate scrap aluminum.

The scrap is then melted in a furnace by temperatures of 1300-1400°F.  Additional elements, such as magnesium, zinc, copper, silicon and manganese can be added to produce a heat to a specific alloy chemistry.  The molten aluminum is then cast into ingots, slabs or billets that can be rolled to plate or sheet or extruded into bar or other solid/hollow profiles.  Aluminum doesn’t lose any performance or strength during this process, so it can be recycled indefinitely.

Your Technical Services Professional

Whether to use primary or secondary aluminum is an important decision that depends on several factors.  That’s why working with a seasoned aluminum supplier can help ensure that your manufacturing process runs smoothly.

To learn more about the differences between primary or secondary aluminum, contact a friendly customer service representative at Clinton Aluminum, the Midwest’s leading supplier of aluminum and stainless steel.


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