Removing Metal in Plastic Waste – Magnetic Separators and Metal Detection

As the years go on, the global focus on managing plastic waste continues to intensify. Currently, there is a great emphasis placed on improving waste collection in order to prevent plastic from entering the ecosystem. After waste has been collected, the next issue is determining how to deal with that plastic waste. This can be done by either re-introducing waste material into the plastics process so it can be used as a new, raw material, or by using plastic waste in another product, such as furniture and clothing made from recycled plastic material. There are many ways to repurpose plastic waste into a useful material. However, this process can be hindered if the plastic material is contaminated with metal. Bunting magnetic separators and metal detection equipment is designed for the specific needs of customers in the recycling and plastics industries.

Technology has advanced significantly, but the main problems of plastic recycling persist. Today, complex recycling plants are able to separate different types of plastic by type and color, but the process has not yet been perfected. Further complicating the problem is the fact that non-related materials, such as metal and even building materials like concrete and brick, contaminate a great deal of waste plastic packaging.

Contaminated Pre-Sorted Waste

To use one scenario as an example, plastic packaging often enters the recycling process as pre-sorted household waste. However, the degree to which material has been “sorted” varies wildly between different countries, different states, and even from town to town. For example, one town may require residents to separate different types of recyclable material from each other (plastic, glass, aluminum cans, etc.), but another town may only require residents to differentiate recyclable materials from waste materials.

Regardless of how material was sorted originally, once recyclable material arrives at a recycling facility, it will be separated out into metal, plastic, cardboard, and other groupings based on the parameters set by that recycling facility. Materials are separated from each other using technology in combination with human pickers, as technology has not yet advanced enough to be able to complete this type of separation task on its own yet.

It is difficult to successfully separate materials in a recycling facility because of the ongoing presence of other waste. Whether due to negligence, ignorance, or another reason, non-recyclable materials often become mixed up in recycling bags and impede the recycling process. Materials can include paint cans, food waste, used diapers, and other items that belong in waste facilities, not recycling facilities.

At a recycling facility, there are several different ways to separate materials like metal out from other materials like plastics. If ferrous metals are present, they can be recovered using crossbelt magnets positioned over the main feed conveyor. For other materials, though, separation must be done by hand. Up until recently, mixed recycled plastic material can be sent to a specialist plastic recycling plant or overseas to countries such as China.

Contaminated Plastic Waste

For years, countries such as the United States and the United Kingdom have been exporting waste material to China. Since 2012, for example, British companies have shipped over 2.7 million tons of plastic scrap to mainland China and Hong Kong. Still, this number represents only two-thirds of all plastic waste exported from the United Kingdom.

When plastic waste is sent to China, it is hand-sorted into individual plastic types when possible. This is miserable, low-paid, and time-consuming work that can involve such menial tasks as manually unscrewing plastic caps from bottles. Laborers also must remove any contamination present by hand. Because of differences in labor law, it would not be possible to establish manual recycling operations in European countries and the United States because such operations would be prohibitively costly with unacceptable working conditions.

In December 2017, China announced that starting in 2018 it would no longer import foreign garbage, as such waste material was often contaminated with filthy, hazardous substances. Countries such as the United Kingdom have gone on to try and start domestic recycling plants, but due to being “financially unviable,” many have been forced to shutter.

Plastics Recycling Operations

In any typical plastics recycling operation, it is necessary to have a complex system of separation equipment. Additionally, a plastics plant must be able to adapt to huge variations in the nature of waste plastic being delivered. There are also many strict regulations regarding proper storage and handling of waste plastic that must be adhered to. Because of all these factors, plastics recycling plants are very expensive to install and operate.

Early on in the process, magnetic separators and eddy current separators remove ferrous and non-ferrous metal contamination from waste plastic. Initially, after plastic is freed from the compacted bale, it will be fed into a primary shredder. To protect the shredder from damage, a crossbelt magnetic separators should be suspended above the feed conveyor to remove large ferrous metal. Additionally, a metal detector should be installed at this step in the process so that shredders downstream are protected from the damages metal contamination can cause.

During this stage in the process, the ferrous metal contamination found trapped in the plastic is diverse and can often be surprising. Examples of metal contamination can be incorrectly sorted metal packaging, heavy lumps of iron that increase the plastic bale’s weight, and metal picked up during transportation. In some cases, even items like car engine blocks have been found.

If metal contamination is able to enter the shredder, it can cause significant, costly damage. When key equipment such as shredders is damaged, it can also result in the plant being forced to close entirely until repairs have been completed.

Following the primary shredder, waste plastic will have been reduced in size and many of the contaminants will have been liberated. Then, this shredded waste plastic will be fed onto another magnetic separator, such as a drum magnetic separators or pulley magnet, that will further remove smaller ferrous metals.

At this stage, the type of ferrous metal separated can include nuts, bolts, steel spanners, screws, fine metal wires, iron shards, springs, fine ferrous dust, and chunks of work-hardened stainless steel. Most of this ferrous metal contamination was not originally part of the plastic being recycled but was introduced at some point between disposal and processing.

Next, cleansed plastic waste will pass over an eddy current separator to remove non-ferrous metals. Examples of commonly separated metals here include aluminum beverage cans, tubes, foils, and even window frames.

Once the metal contamination has been removed, the plastic waste progresses to the next stage of recycling in the plant. This next stage could involve further separation of contamination or sorting by color or plastic type.

Future Challenges

The high levels of metal contamination found in plastic recycling plants are one of the biggest challenges currently facing waste plastic processors. Metal contamination often is not a part of the original plastic product being recycled, but still must be removed at a plastic recycling plant.

As countries continue to push for increased plastics recycling, the practicalities and difficulties involved with processing plastic waste material must be taken into consideration. While reducing contamination will make it easier to recycle waste plastic, there will always be some degree of contamination present.

For more information on magnetic separators and metal detectors for plastics recycling plants, contact Bunting today.