MATSE 81
Materials in Today's World

Recycling of Metals

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As mentioned in the e-book, aluminum is the most commonly recycled nonferrous metal. (Ferrous is Latin for iron, so a nonferrous metal is a metal which does not contain iron.) Aluminum is recycled because it takes a lot less energy to recycle aluminum than it takes to extract aluminum from bauxite ore, which requires heating and electrolysis. In addition, aluminum readily forms an oxide that forms a protective surface. This protective surface protects the bulk of the aluminum from oxidizing further. This results in most of the aluminum being recovered every time it goes to the recycling phase, in contrast to iron.

In the case of iron, oxidation, i.e., rust, does not protect iron from oxygen and water, and significant amounts of iron are not recyclable because the iron has been converted to rust. Please watch the following video (5:04) which summarizes the points about recycling of metals emphasized in your e-book and this website.

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Click for transcript Recycling Metals.

Certain metals can be extracted from their ores. For example, iron is extracted from hematite in a blast furnace and copper can be extracted from malachite. The process of extracting metals from their ores can be time-consuming, costly, and harmful to the environment. Other less reactive metals such as gold and platinum can be found naturally as native metal. The issue here is that there is a finite or limited supply of these metals on earth. In this lesson we will learn about recycling metals and the advantages and disadvantages to these industrial processes.

Aluminum is the most commonly recycled metal. Aluminum is used to make soft drink cans, aluminum foil, certain food cans, and even certain packaging materials. Aluminum is also used to make the outer bodies of some cars and airplanes due to the fact that it is less dense than steel. The extraction of aluminum from its ore is done by electrolysis. It may not seem like a lot of electrical energy is needed, but keep in mind that this is done on an industrial scale worldwide. The recycling of aluminum uses only 5% of the energy used in its extraction from its ore which uses a small voltage but a large current. In fact some countries really encourage recycling by having separate sections in their public waste containers. One for waste, one for cans and other metal products, and another for paper products. Some countries also have mandatory household recycling in a sense that if aluminum cans are found in regular waste bins for pickup the fine can be issued. In fact recycling aluminum is so common that any aluminum material that you encounter today has some if not more than 50% recycled aluminum content.

Steel can be recycled and most steel mills primarily use recycled scrap steel instead of caste or pig iron from blast furnaces. Copper is also recycled. Once again this is a more energy efficient process than the extraction from its ore as well the copper ore supply on earth is being depleted at a very fast rate. As a result other methods for the extraction of copper such as phytomining and bioleaching are being used instead.

Silver and gold from jewelry are also recycled. As these metals are found as native metals the issue here is not the energy cost but rather the rarity of these metals. The main source of gold is recycled electronic goods such as computers which have their electrical contacts plated with gold so there is no corrosion and a perfect electrical connection. The main issue with recycling metals is the separation process in the waste containers. Most often not all metal products are clearly labeled as recyclable. As well, many metal products are alloys. Can you remember what an alloy is? Please pause the lesson and continue when you are ready.

An alloy is a mixture of two or more elements with at least one of the elements in the mixture as a metal. Many metal products are made into alloys for increased strength and other desirable properties, but not all alloys can be recycled such as manganese aluminum alloys. Some alloys which can be recycled need to be molten and separated into their constituent metals thereby making it a more energy costly process. As well, we have to take into consideration the fact that these metal products must first be collected and then transported to recycling facilities. All depending on the distances covered this could involve quite a bit of fuel usage, and therefore increasing CO2 and noxious gas emissions.

In summary, aluminum steel and copper are the most commonly recycled metals and the recycling process usually uses significantly less energy than extraction from their ores.

In the next section, we will discuss recycling of ceramics, in particular, the recycling of glass which is the most common commercial ceramic.