Different metals have different values and uses and need to be separated when recycling. Magnets stick to metals that contain iron and will not stick to metals that do not contain iron. Magnets are used to separate metals that contain iron, such as tin cans, as part of the recycling process.
Magnets are also combined with electricity to create electromagnetic currents that can separate metals that do not contain iron, such as aluminium soda cans, from other materials.
Magnetism causes objects to be attracted to or repelled from each other. It is caused by the arrangement of electrical charges on the very small particles, called atoms, that make up the objects. When the charges are opposite, with one material having a positive charge, and the other having a negative charge, the objects will attract and stick to each other. When the charges are the same, the objects will push apart and separate.
Ferrous and Nonferrous Metals
Metals that contain iron are called ferrous or ferromagnetic. This is because the Latin word for iron is ferrum. Ferrous metals can be wrought iron, or an alloy containing iron such as carbon or stainless steel. Ferrous metals are found in cars, appliances, food cans and paper clips, and are the most common material recycled in North America.
Examples of nonferrous metals, which do not contain iron, are aluminium, copper, lead, nickel, gold, silver, tin, titanium and zinc.
Separating Ferrous Metals
Many recycling containers combine all types of metals in one bin. Because ferrous metals are magnetic, and nonferrous metals are not, magnets are used to separate out the ferrous from the nonferrous metals. The metals collected in the recycling bins are passed along a conveyor through a tunnel or chute that is lined with powerful magnets. The ferrous metals stick to the magnets, and the nonferrous metals continue on through the chute.
Separating Nonferrous Metals
Some communities use single-stream recycling, where all recyclable materials are combined in one bin, making recycling easier for the consumer. Various methods are used to separate plastics, glass and metals at the recycling plant. Magnets are used to pull the ferrous metals out of the mixed materials. Nonferrous metals, such as aluminium, can also be separated from the stream by using an electromagnetic current. Electricity and magnets are combined in an electromagnetic field that repels nonferrous metals, pushing them out of the mixed materials into a separate container.