Magnetic forces play a significant role in the modern recycling process, serving as a fundamental technology within material recovery facilities (MRFs). This technique, known as magnetic separation, is a high-speed, automated sorting method that improves the efficiency and purity of recovered materials. By automatically extracting metals from mixed waste streams, magnetic equipment ensures that valuable resources are captured and contaminant levels are minimized.
Separating Iron and Steel (Ferrous Metals)
The most straightforward application of magnets involves the recovery of ferrous metals, which are materials containing iron, such as steel and cast iron. These metals are ferromagnetic, meaning they are directly attracted to a magnetic field, allowing for simple extraction from other waste. This separation is typically the first step in a material recovery facility’s sorting line, removing magnetic scrap before it interferes with later equipment.
Two primary types of magnetic separators are deployed to recover these metals. Overhead belt magnets are suspended above a conveyor belt carrying the mixed waste stream. As the waste passes underneath, the magnet lifts the ferrous items out of the flow and onto a separate, self-cleaning belt, which deposits the recovered metals into a collection bin.
Magnetic drum separators offer an alternative mechanism for ferrous metal recovery, often used for finer materials or higher purity requirements. In this system, the material is fed onto a non-magnetic shell that rotates around a fixed internal magnetic assembly. Ferrous materials are held against the rotating drum’s surface by the magnet until they are carried out of the magnetic field’s range, where they drop into a dedicated chute.
Recovering Aluminum and Non-Ferrous Metals
The separation of non-ferrous metals, such as aluminum, copper, and brass, requires a more complex application of magnetic principles since they are not directly attracted to standard magnets. This is accomplished using Eddy Current Separation (ECS), which relies on a dynamic physical principle. ECS equipment features a high-speed rotating magnetic rotor, spinning up to 3,000 revolutions per minute, creating a rapidly changing magnetic field.
As a piece of conductive non-ferrous metal passes over the rotor, the changing magnetic field induces a circulating electrical current within the metal itself; these are the eddy currents. This induced current creates its own temporary magnetic field that opposes the original field from the rotor. Because like poles repel, this opposing magnetic field generates a strong repulsive force on the non-ferrous metal piece.
This repulsion effectively “throws” the aluminum or copper particle forward and away from the main material stream, over a splitter plate. Non-metallic materials like plastic and paper simply fall off the end of the conveyor belt. Eddy current separators are typically placed later in the sorting process, after all ferrous metals have been removed, to maximize the efficiency and purity of the recovered non-ferrous metals.
Integration Across Recycling Streams
The use of magnetic separation extends far beyond municipal curbside recyclables, integrating into various specialized waste management streams. In the processing of shredded scrap, such as from retired automobiles, large-scale drum magnets recover structural steel and iron from the residual material. This step is important for producing high-purity scrap metal ready for steel mills.
Construction and demolition (C&D) waste also relies heavily on magnetic separation to reclaim valuable metals from concrete, wood, and rubble. Overhead electromagnets with deep magnetic fields are often deployed to pull rebar, nails, and other structural ferrous components out of the debris. These processes ensure that a greater volume of the C&D waste can be diverted from landfills.
Electronics recycling, or E-waste, utilizes both ferrous and eddy current separators to recover a complex mix of materials. While standard magnets pull out the steel casings and components, ECS technology separates conductive non-ferrous metals like copper and aluminum from shredded circuit boards and plastics. The efficient nature of these sorting systems maximizes the recovery of these high-value metals for reuse.