Alexei Volkov
The process of recycling involves breaking down items made of specific materials and reusing them. While some materials can be recycled, they must first be separated before they can be useful. For instance, you cannot recycle broken bottles into bike frames, cardboard into cans, or plastics into paper. Many local authorities in the UK collect recyclable waste mixed together in the same bin. However, modern recycling facilities use advanced technology to separate paper, metal, and plastic. This involves identification techniques such as x-ray fluorescence and rapid-scanning near-infrared spectroscopy, which work in conjunction with computer-controlled mechanisms to physically separate each item.
| Characteristics | Values |
|---|---|
| Sorting methods | Single-stream, double-stream, manual, automated |
| Sorting techniques | X-ray fluorescence (XRF), near-infrared (NIR) spectroscopy, magnets, star screens, eddy current separators |
| Materials separated | Paper, metal, plastic, glass, cardboard, food scraps, wood scraps |
| Further processing | Melting, crushing, baling, composting, grinding |
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What You'll Learn
Sorting paper, metal, plastic and glass
Sorting paper, metal, plastic, and glass is an important step in the recycling process. These materials are commonly used in packaging and products, and proper sorting ensures they can be recycled and reused effectively. While some local authorities collect recyclable waste mixed together in the same bin, others require separation into different containers. Here is how these materials can be sorted and recycled:
Sorting Paper
Paper and cardboard are versatile and can be transformed into a variety of new paper and cardboard products. Technology has advanced to separate newspapers from other types of paper. There are several methods to separate paper and cardboard from mixed waste. One method is using trommel screens, which allow other materials to fall through while retaining sheets of paper and cardboard. Another method involves using jets of air or an overhead vacuum to remove paper and cardboard due to their low densities and high surface area.
Sorting Metal
Metal, including steel and aluminium cans, can be recycled endlessly. Magnets are an essential part of recycling machines and are used to separate different types of metal cans. The sorted metal is then melted down with other scrap metal and used in various applications.
Sorting Plastic
Plastic bottles are typically recycled rather than reused due to their low softening point, which makes them challenging to sterilise. Plastics need to be clean when sorted for recycling. There are several types of plastics, and the recycling process depends on the facilities available in a particular area. Most plastic items, such as bottles, jars, and containers, can be recycled in many places if they are cleaned before disposal.
Sorting Glass
Glass, like metal, can be recycled infinitely. However, sorting glass by colour can be expensive. Advanced Material Recovery Facilities (MRFs) use cameras or Near-Infrared (NIR) spectroscopy to distinguish between glass colours, directing each piece to the appropriate collection bin. Scrap glass is often used in road building as aggregate.
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Identification techniques: XRF and NIR spectroscopy
XRF (X-Ray Fluorescence) analyzers are commonly used in scrap metal recycling to provide a fast, accurate, and automated way to identify and sort different types of metals. Sorting scrap metal is necessary to maintain product quality and meet customer specifications. The scrap often contains a mix of metals from various sources, such as automobiles, appliances, and electronic waste, and the value of the scrap depends on the type and quality of the metals present.
XRF analyzers work by providing incident X-rays that generate excitation in the atoms of the sample material. The atoms then emit energy, producing an X-ray signature that the XRF equipment captures and analyzes. This allows for the identification of the elements present in the sample and their percentages, as well as grade identification. XRF technology can be used to separate metals in shredded scrap, such as separating ferrous items that also contain other wanted or unwanted metals. It can also be used to detect metals in coloured glass, such as cobalt in blue glass or iron in green glass, allowing for the separation of different colours of glass.
In addition to XRF, LIBS (Laser-Induced Breakdown Spectroscopy) technology is also used in recycling facilities. Handheld LIBS analyzers use a laser to ablate the surface of a sample, forming a plasma that atomizes and excites the sample. The emitted light is transmitted through fibre optics to a spectrometer, where it is split into its component wavelengths, producing a spectrum that can be analyzed to determine the concentration of each element.
NIR (Near-Infrared) Spectroscopy has become a standard in the recycling industry, especially for the identification and classification of plastics. Plastics are one of the most difficult materials to classify in recycling waste streams due to the time-consuming and error-prone nature of traditional identification methods. NIR spectroscopy enables the rapid and automatic identification of different plastics by utilizing reflection measurements to detect the distinctive fingerprint spectra of various polymers. This allows for the identification of recyclable plastics and the elimination of contaminants, enhancing the efficiency and accuracy of polymer analysis.
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Physical separation: magnets and conveyor belts
The process of recycling often begins with a manual step, where trained human pickers remove items that are non-recyclable, large, badly contaminated, or unsuitable for the recycling process. This includes items such as wood, pots, and pans. This step is crucial to minimise identification problems and potential damage to the machinery used in the subsequent automated stages of the recycling process.
After this initial manual stage, the mixed waste is fed into a specialised materials recovery facility (MRF) to separate the different materials. The first stage of the mechanical sorting procedure involves using identification techniques such as x-ray fluorescence (XRF) and rapid-scanning near-infrared (NIR) spectroscopy, which rely on reflected and/or transmitted light to differentiate between materials.
Once the materials are identified, computer-controlled mechanisms, including magnets and conveyor belts, physically separate each item. For example, magnets can attract and separate ferromagnetic materials, such as iron and steel, from other recyclables. Conveyor belts, on the other hand, can separate materials based on their shape, size, or density. By adjusting the speed and angle of the conveyor belts, certain materials may be diverted or allowed to continue on the belt, thus achieving separation.
While magnets and conveyor belts are essential tools in the physical separation stage, more advanced MRFs may employ additional techniques. These facilities can differentiate between various types of paper, metal, plastic, and glass, ensuring an efficient and comprehensive recycling process.
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Eddy current separator: magnetising aluminium
Eddy current separators are devices that use a rotating drum with permanent magnets or an electromagnet to separate non-ferrous metals, such as aluminium, from other materials like paper and plastic during recycling. The process involves feeding the material onto a conveyor belt that moves it across a magnetic rotor, which is the key component of the separator. This rotor has a series of permanent rare earth magnets mounted on a support plate attached to a shaft.
As the material passes over the separator, the magnets inside the rotor rotate at a high speed, generating eddy currents in the aluminium or other non-ferrous metals present. These eddy currents create a magnetic field around the aluminium, with a polarity that matches the rotating magnet. As a result, the aluminium is repelled by the magnet, causing it to be separated from the other materials.
The Eddy Current Separator is specifically designed for industrial applications and is effective in dirty, dusty environments often found at job sites. Its deeper magnetic fields compared to conventional designs enhance the rate of non-ferrous metal separation and recovery, leading to increased profitability. Additionally, its durable construction, ease of maintenance, and low operating costs make it a reliable solution for separating aluminium and other non-ferrous metals from various streams.
The Eddy Current Separator's ability to separate aluminium and other non-ferrous metals is crucial for recycling applications. It can effectively separate aluminium cans, stainless steel, copper, and brass from municipal solid waste, scrap residue, and other recyclables. This separation process ensures that valuable materials like aluminium are recovered and can be recycled into new products, reducing waste and promoting sustainability.
Furthermore, the Eddy Current Separator's design features, such as its multiple shell layers made of durable materials like fiberglass, stainless steel, and ceramic tile, provide maximum protection for the critical magnetic rotor assembly. This robust construction extends the equipment's lifespan and simplifies maintenance procedures, resulting in reduced maintenance and repair costs over time.
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Steel baling and melting for new goods
The steel bales are then transported to melt mills, also known as steel mills or steel plants, where they play a vital role in the stainless steel supply chain. In these mills, recycled steel is combined with virgin steel and melted together to create new stainless steel products. The makeup of the steel is typically around 90% recycled steel and 10% virgin steel. This process is not limited to stainless steel but is also applicable to carbon steel.
Before melting, the scrap steel is purchased, checked, and sorted by scrap vendors to ensure purity and consistency in the final product. This "precision scrap" is carefully sorted by alloy type to avoid impurities. The sorted scrap is then sold back to the melt mills for processing.
Melt mills use various furnaces, such as electric arc furnaces (EAFs), to melt the steel and create different steel grades. The eco-friendly EAFs are preferred over traditional blast furnaces due to their lower energy consumption and carbon emissions. The steel chemistry is carefully adjusted by introducing or reducing alloy elements to achieve optimal purity.
The melted and refined steel is then cast into usable forms, such as strips, bars, plates, or wires. From the melt mill, the steel may be sent to service centers or re-rollers, depending on its intended application and thickness. Re-rollers play a crucial role in creating steel varieties with specific features for specialized sectors, such as the medical and aerospace industries. The steel then continues its journey through the supply chain until it reaches the end user, completing the cycle of steel recycling and manufacturing.
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Frequently asked questions
Materials Recovery Facilities (MRFs) use a combination of manual and automated processes to separate materials. The first stage of the sorting procedure at an MRF is a manual process where trained human pickers remove items that the sorting equipment won't be able to handle. The automated processes include the use of conveyor belts, screens, magnets, and lasers to separate materials.
Metal is separated from other materials through the use of magnets. A cross-belt magnet is placed over a conveyor belt to draw steel recyclables from the belt. A magnetic field can also be used to induce electrons in aluminium to create a magnetic field of their own, known as an eddy field, which pushes the aluminium off the main conveyor onto another one.
Paper is separated from heavier items like jars and cans using air. Air is blown from below rotary screens, causing paper items to keep moving up the separators to a new conveyor belt.
