Aluminum scrap is often categorized as “new scrap” from production processes and “old scrap” from post consumer use. The second most abundant metallic element in the Earth’s crust after silicon, aluminum is a comparatively new industrial metal, which has been produced for commercial uses for just over 100 years. The metal weighs about 1/3rd as much as copper or steel, is malleable, ductile, has excellent corrosion resistance and durability and can be easily machined and cast. Measured either in value or quantity, the use of aluminum exceeds that of any other metal except iron, and it has proved to be important in virtually all the segments of the global economy. Some of the important uses of aluminum metal include transportation (airplanes, trucks, rail cars, marine vessels, etc.), packaging (cans, foil, etc.), consumer durables (appliances, cooking utensils, etc.), construction (windows, doors, siding, etc), electrical transmission lines, machinery, and several other applications.
New scrap arises during the manufacturing of aluminum semi-fabricated and final products. Old scrap refers to those products collected after disposal by consumers. Old scrap is often more contaminated than new scrap. End-of-life vehicles, demolished buildings and constructions, discarded packaging material, home and office appliances, as well as machinery equipment are all potential sources of old aluminum scrap.
The collection and sorting of aluminum scrap, especially old scrap, is often a complex scheme involving millions of households, local and regional authorities, small and medium collectors and metal merchants. Waste and environmental policies can also have strong influences on the effectiveness of collection schemes.
Sorted aluminum scrap may need to be separated further and pre-treated before the metal can be recovered in melting furnaces. Separation of aluminum at this stage can be done by various mechanical operations, such as magnetic, gravity, eddy current, or color sensor. Further separation of different aluminum alloys can also be achieved through x-ray methods. Often wrought alloys and casting alloys are, whenever possible, separated before the mechanical processes.
Other input materials are also required to transform valuable aluminum scrap into aluminum metal. Alloying elements are crucial to the wide range of functionalities and characteristics of aluminum products. In refining aluminum scrap, impurities that cannot be removed by mechanical separation will be eliminated through the addition of salt flux in the melting furnaces.