Primary vs Secondary Aluminum

What are the differences between primary vs secondary aluminum?

1. Sources
2. Process
3. Energy Consumption
4. Waste and Pollution
5. Uses

Aluminum is one of the most widely used metals in the modern world, but most people don’t think about how it’s made. Today, aluminum is used in almost every industry and can be found in a variety of products thanks to its manufacturing processes. For those interested in taking on an aluminum project, you must have a thorough knowledge of the aluminum supply chain, from raw material to finished product. One of the most important distinctions you should be aware of is between primary vs secondary aluminum.

Sources

Primary aluminum is labeled as ‘primary’ because it is made from new aluminum. Aluminum is derived from bauxite, a common ore found in topsoil in tropical and subtropical regions. Bauxite ore is chemically treated in a method called the Bayer process, which produces alumina, an aluminum oxide compound. The alumina is then smelted into new, pure aluminum ingots in a method called Hall–Héroult process.

Secondary aluminum gets its name from its source. It’s ‘secondary’ because it is made from recycled aluminum scrap. This scrap can come from all sorts of aluminum products and profiles, such as aluminum turnings, aluminum sheets, aluminum shreds, aluminum radiators, cast aluminum, extrusions, painted sidings, aluminum dross, and more. Generally, secondary aluminum has a higher tolerance for alloying elements, such as iron, magnesium, and silicon (which are commonly added in the recycling process).

Process

Primary aluminum goes is made using a method called the Hall–Héroult process. In this process, alumina is dissolved in a carbon-lined steel pot using a molten cryolite bath. Carbon anodes are placed in the bath and pass an electric current through the mixture. This separates oxygen atoms from the alumina, leaving pure molten aluminum at the bottom of the pot. The liquid aluminum is periodically removed from the pot to be placed in a holding furnace. From the holding furnace, it is cast into an ingot.

Manufacturing of secondary aluminum begins with extracting used aluminum products from waste streams to ready them for recycling. The aluminum scraps are then segregated according to their chemical composition, or alloy. New techniques, like Laser-Induced Breakdown Spectroscopy, can efficiently separate aluminum alloys while removing contaminants — greatly improving the quality of the scrap. This recycling process allows aluminum scraps to be recycled multiple times in a closed-loop process.

Once the scrap is gathered and sorted, it is put into a furnace and turned into molten aluminum. This molten aluminum is either kept liquid or cast into ingots for further processing. For some applications, alloying elements are retained or added into the molten aluminum to produce a specific profile for the desired products.

Energy Consumption

The Hall–Héroult process and smelting in primary aluminum production requires significant amounts of electricity to perform. The production of primary aluminum only became economically viable when large-scale electricity was available. As a result, most primary aluminum smelters are often found in areas with lower-cost electricity. In the 110 year history of aluminum production, many efforts have been made to reduce the amount of electricity needed. However, there are still no viable alternatives to the Hall–Héroult process, which hampers efforts to become more energy efficient.

On the other hand, secondary aluminum production uses less energy. The most labor-intensive aspect of creating secondary aluminum is cleaning and separating aluminum scrap from other materials. Once processed, it is melted down, usually by natural gas. Thus, the energy requirements of secondary production are much less energy-intensive. Statistics support this — increasing aluminum recycling rates by only 10% can decrease aluminum processing gas emissions by up to 15%.

Waste and Pollution

In primary aluminum production, there are several sources of waste and pollution. Air emissions are made from grinding bauxite ore or the Hall–Héroult process. These particulates can be metal-rich, or volatile gases such as hydrogen fluoride and carbon monoxide. These emissions are serious health hazards to workers. Air emissions equipment is used to capture these particulates in manufacturing areas.

There is not much liquid waste made from primary aluminum manufacturing. Wastewater is produced in the clarification and precipitation in the Hall–Héroult process. However, much of the wastewater is directly reused.

Solid waste is made up of bauxite refining waste (called red mud) and reduced waste from the carbon-lined steel pots. Red mud is typically managed on-site and is not hazardous. The refraction waste can be a concern, as it can produce RCRA K088 hazardous waste.

In secondary aluminum production, there are not many sources of waste or pollution. Scrap aluminum is the primary component of secondary aluminum, it uses plenty of wasted materials. Scraps are melted down, and impurities are removed using chlorine or other fluxes until the molten metal reaches the desired purity. Some secondary aluminum manufacturers use dross with their aluminum scraps. Dross is one of the by-products of primary aluminum. This allows for further reduction of pollution from primary aluminum manufacturing.

Uses

Primary aluminum has many uses in several industries, such as transportation, commercial, technological, medical, and more. This is because primary aluminum has many different alloys, and can be easily formed into different shapes. Primary aluminum ingots can be made into sheets, pipes, flats, and other products. Primary aluminum can also be smelted into billets, which can be extruded into a shaped product, such as window frames or electronics cases.

For secondary aluminum, the uses are pretty much the same. Additional metals can be added during the smelting process to produce certain alloys for a specific product. Even high-performing products such as building materials or automotive parts can be made from this process.

As aluminum never loses its performance or strength during the recycling process, the same piece of aluminum can enter the secondary manufacturing process time and time again, and be reformed for different products and purposes each time.

Key Takeaway

When weighing primary vs secondary aluminum for your project, you must consider their differences. While this article explains some of the bigger contrasts between the two, there are many niches that only experts can understand. This is why working with a knowledgeable and credible aluminum supplier can help ensure that your project runs smoothly. To learn more about the different types of aluminum profiles, contact the AMC Aluminum team today!