The basic steps
Recycling is the process of turning used materials into raw material for new products instead of throwing them away. Whatever the material, the process usually has four stages.
- Collection. Materials are gathered from households, businesses and public sites. Systems differ a lot: some places collect everything mixed in one bin, others ask people to separate paper, glass and containers, and some use deposit schemes in which a small refundable fee is paid on bottles or cans.
- Sorting. At a sorting facility, materials are separated by type. Machines use screens to separate flat paper from containers, magnets to pull out steel, eddy-current devices to push aluminum away from other materials, and optical sensors that identify different plastics. Workers remove items that do not belong.
- Reprocessing. Each material is cleaned and converted into a form that manufacturers can use, such as paper pulp, metal ingots, crushed glass called cullet or plastic flakes and pellets.
- Manufacturing and sale. The recycled material is sold and made into new products. This last step matters because recycling only works if someone wants to buy the output.
How different materials are handled
Metals. Steel and aluminum are among the easiest materials to recycle because they can be melted and reformed many times without losing their basic properties. Making aluminum from recycled scrap is widely reported to take a small fraction of the energy needed to make it from raw ore, which is one of the strongest cases for recycling. The properties of metals come down to their atomic structure, but the key point here is that melting does not destroy them.
Glass. Glass can be crushed, melted and formed into new containers without a loss of quality, and adding cullet to a furnace generally lowers the energy needed. Problems arise when glass is mixed with other materials, broken into tiny fragments or contaminated with ceramics, which do not melt in the same way. The basics of glass making explain why: pure, sorted glass is a valuable feedstock, and mixed glass is much less so.
Paper and cardboard. Paper is mixed with water and broken down into a pulp, and ink and other contaminants are removed. Each time paper is recycled, the cellulose fibers get shorter and weaker, so they can usually go through only a limited number of cycles, often cited as roughly five to seven. Fresh fibers are needed to keep the supply going.
Plastics. Plastics are the hardest case. There are many types, which generally cannot be mixed, because even small amounts of a different plastic can ruin the quality of a batch. Many items combine layers or colors. Some common types, particularly clear drink bottles and certain rigid containers, are recycled routinely. Others, such as thin films and many food packaging items, rarely are. Recycling often produces a lower-grade material than the original, so a bottle may become fiber for clothing or a bench rather than another bottle. Part of the problem comes from the way plastic polymers are made and how durable they are.
What recycling can achieve
When it works well, recycling offers real benefits. It can reduce the amount of waste sent to landfills or incinerators. It can reduce the need to mine, quarry or harvest new raw materials. And for some materials, especially metals, it can save a large proportion of the energy needed to make new products, which can in turn reduce greenhouse gas emissions. How large these savings are depends on the material, the distance it must be transported and the energy sources used.
Recycling also creates jobs in collection, sorting and processing, and it can supply local industries with material.
Honest limits
Recycling is not a cure-all, and several practical problems keep reducing its effect.
- Contamination. Food residue, the wrong items in the bin and mixed materials can make a load unsaleable. When this happens, material that people hoped was recycled may be landfilled or burned instead.
- Markets. Recycled materials compete with newly made ones. When the price of new plastic or metal falls, recycled material may become hard to sell, and collection programs can lose money.
- Quality loss. Some materials degrade each time they are processed, so recycling delays their disposal rather than ending it.
- Energy and transport. Collection, trucks, washing and reprocessing all use energy and water. In some cases the net benefit is small.
- Different local rules. What is accepted varies from place to place, which causes confusion and mistakes. It is worth checking what your local service takes.
The recycling rates quoted by different countries are also not always comparable, since some count what is collected and others count what is actually turned into new material.
Where recycling fits
Many waste experts describe a priority order, often called the waste hierarchy: first reduce what is used, then reuse items, then recycle, and only then recover energy or dispose. Recycling is in the middle, valuable but not the first option. For materials such as paper, metal and glass that are well suited to it, recycling is generally a sound choice. For items that are hard to recycle, using less in the first place often makes a bigger difference.
Recycling is also only one part of a wider picture. The energy sources used in industry, such as a shift toward renewable energy, how products are designed and how long they last all affect environmental impact. Outcomes differ between places and materials, so general claims, whether positive or negative, should be treated with some caution.