The materials placed in a recycling bin begin their journey at a specialized facility called a Materials Recovery Facility (MRF). This facility transforms a mixed stream of paper, plastics, glass, and metals into clean commodities ready for manufacturing new products. The modern MRF uses human labor and sophisticated machinery to sort materials based on size, shape, density, and chemical composition, achieving the high purity standards required by end-user markets.
Receiving and Pre-Sorting
The recycling process begins when collection trucks deliver loads to the tipping floor. Mechanical shovels push the commingled material onto conveyor belts, ensuring a steady, controlled flow into the automated sorting system.
At the start of the conveyor line, human workers perform an initial quality control check, known as pre-sorting. Their primary role is to manually remove large contaminants and hazardous items that could damage the machinery. Common items removed include bulky non-recyclables, plastic bags that wrap around equipment, and hazardous materials like batteries. This manual step safeguards the automated processes and prevents costly downtime.
Mechanical Separation of Fiber and Glass
After contaminants are removed, the material moves into mechanical separation, which uses size and shape to divide recyclables. The first step targets Old Corrugated Cardboard (OCC) using large, angled disk screens. These rotating disks allow smaller, three-dimensional items like cans and bottles to fall through, while the flat cardboard rides across the top for separate collection.
The remaining materials pass over a series of screens, often vibrating or rotating trommels, which separate flat paper from heavier containers. Flat, light paper tends to travel across the screens, while denser items like plastic bottles and metal cans fall through the openings. Glass, often broken during collection and transport, drops through the screens early in the process as small fragments (cullet) to be collected separately.
Technology for Identifying Metals and Plastics
The container stream, now free of paper, proceeds to advanced sorting technologies that separate materials by their intrinsic properties. Ferrous metals, such as steel cans, are easily removed using powerful overhead magnets positioned above the conveyor belt. The magnetic field attracts the steel, lifting it out of the material flow and diverting it into a collection chute.
Non-ferrous metals, primarily aluminum cans, are separated using an Eddy Current Separator (ECS). This device uses a rapidly spinning magnetic rotor to create a fluctuating magnetic field on the conveyor belt. When an aluminum can passes over the field, the changing magnetism induces an electric current, temporarily turning the can into an electromagnet with a polarity opposite to the rotor. This repulsion forcefully ejects the aluminum from the material stream.
The remaining materials, mostly different types of plastic, are sorted using highly precise optical sorters. These machines use Near-Infrared (NIR) light sensors to scan the materials passing underneath. Each plastic polymer, such as Polyethylene Terephthalate (PET) or High-Density Polyethylene (HDPE), reflects the NIR light with a unique chemical signature. Once the sensor identifies the polymer, high-speed air jets fire a burst of compressed air to push the item off the conveyor belt into the correct collection bin.
Preparing Materials for Market
After sorting separates the mixed recyclables into individual material streams, the final step is preparing these recovered commodities for sale. Materials segregated by type—such as PET plastic, aluminum cans, or mixed paper—are transferred to a baling machine. Balers compress the loose material into dense, uniform cubes secured with wire or strapping.
This densification maximizes storage efficiency and reduces transportation costs to manufacturers. Before the bales are shipped, a final quality control check is performed to ensure the material meets the purity specifications demanded by the end-user market. High-quality bales, free of contaminants, command better prices, confirming the sorting process successfully created a valuable, market-ready resource for use in new product manufacturing.