5.4 Recycling

Recycling requirements and limitations

Recycling, regardless of the material involved, has some basic requirements to succeed. The public and/or industries must be willing to contribute appropriate materials to the recycling process, which may involve some cleaning and sorting. A system must exist for collecting recyclable waste and conveying it to recycling facilities. Economically reasonable methods of recycling must exist. Finally, a market must exist for the recycled materials.

A significant barrier to recycling of some materials is that creation of new materials (fresh wood, newly mined and smelted metals, freshly produced glass, etc.) may be cheaper than production of recycled materials, particularly if externalities are permitted to occur in the production of new materials, for example through unsustainable timber and mining activities. Recycling often involves chemicals, equipment, and energy – it can be expensive in multiple ways. Just sorting out the components of a refrigerator, a truck, a railway engine, or a cellphone may require considerable time and labor, or sophisticated machinery. Energy requirements for recycling may be high, potentially leading to high greenhouse gas production, and where energy requirements are high, water requirements are also often high.

Contamination is also an issue in all recycling streams. Pizza cheese on cardboard, or oils on metal or glass can degrade an entire load of recyclable material, reducing its value. Sorting to remove contaminated materials increases the cost of the process. The “feel-good” aspect of recycling can lead to what has been called “aspirational recycling,” which increases contamination and can significantly reduce the economic viability of the recycling industry. You can read more [click] here.

The present limits of recycling are apparent in the record of US recycling of municipal waste (Fig 1). Paper dominates throughout, comprising more than 60% of the recycling tonnage in 2018, despite comprising less than 25% of total municipal waste (Fig 2). The second largest recycled material, metals, reaches less than a quarter of paper’s tonnage, in 2018. Overall, the total recycling was on the order of 70 million tons in 2018, but total municipal waste production approached 300 million tons in that year.

Recycling specifics

Paper

Paper users and the paper industry have improved sustainability of the industry even before recycling, with reduction in use. Some paper products are lighter than in the past. Newspapers have reduced page size and margins, to use less paper. Not all reductions in use improve sustainability: in some cases, paper use has been reduced by strengthening the paper with coatings of wax or plastic. Although this reduces paper use, the resulting product is typically not recyclable. Shredded paper tends to tangle in machinery used in paper recycling; as a result, many facilities will not accept shredded paper.

Watch a quick, simple [click here to watch the] video on the paper recycling process. Breaking paper down into pulp often uses fairly strong, caustic chemicals; de-inking and brightening use solvents and bleaching agents.

Each successive recycling shortens the fibers in the paper, and this reduces the kinds of uses for which the recycled product is suitable. As a result, the market for the recycled product is reduced.

Despite drawbacks in paper recycling, this is the waste stream with the highest rate of recycling among municipal wastes.

Metal

Worldwide, mining of metal ores increased almost four-fold from 1970 to 2022. About 70% of this activity is related to international supply chains.^[1] Mining may pollute air, water, and soil, cause habitat loss and reduce biodiversity, and consume also needed for other uses. Recycling of metals is an obvious way to limit these harms.

Whereas the paper stream comprises, well, paper (also, often, paperboard, but not cardboard), the metal stream comprises many different metals, with different recycling processes and markets. Metals are infinitely recyclable; they do not degrade in the recycling process. Different metals have widely varying recycling rates; here, we look at some of the most recycled metals.

Steel is the most recycled material by weight, overall, in the world. Steel is about 97% iron, with much smaller amounts of carbon and other additives, including other metals. In the US, a 2021 report from an industry trade association estimated that approximately 70% of steel was recycled. ^[2] A 2019 (approximately) report indicates over 90% of end-of-life steel products are recycled in the EU. ^[3] Globally, scrap accounted for about 30% of the metals used to make steel in 2022.^[4]

Smelting new steel still uses coal for production, resulting in high greenhouse gas emissions. Recycling uses only about 28% of the energy of smelting and saves 1.67 tonnes of CO₂ per ton of steel. Use of scrap steel needs to rise by perhaps 50% to meet climate-change targets. But recycled steel is a potentially limiting resource, due to the lifespan of steel products. Scrap steel is a subject of international trade as well as trade barriers, resulting in an uneven availability of the metal for recycling. ^[5]

You can watch here to see how scrap metal is recovered from items such as car bodies and sorted to produce useful recycling streams.

Aluminum is the second most recycled metal, by weight, in the US. ^[6] Aluminum is largely used as alloys with small amounts of other metals. It is used in transportation, construction and other industries, packaging, household items, and in electrical lines. Recycling information for aluminum is uneven among sectors, with good reporting on recycling of aluminum cans but indifferent reporting elsewhere. For 2018, the US EPA estimated overall aluminum recycling at 35%, with aluminum cans at 50%. ^[7] For the same year, the EU recovered 90% of aluminum from construction and transportation (65% of aluminum by use).

A 2022 analysis of the slower US recycling rates pinpointed issues with aluminum-can recycling involving consumers unwilling or unable to separate waste for recycling (accounting for 80% of aluminum lost to recycling), municipal recycling facilities that landfill the can they collect to save money, and problems with older sorting facilities that misidentify cans. With larger scrap, scrap yards tend to prioritize higher-value components, so that aluminum is often not well separated from the rest of the waste. The mix of low-value material is exported to developing nations where low-cost labor is available to sort the material, rather than being recycled domestically in the US.  The EU uses a deposit on cans, which creates an incentive to recycle. Incentives could also motivate scrap yards to do a more thorough sorting of waste so that higher-quality aluminum scrap would become available. ^[8]

Emissions from aluminum scrap are 92% lower than emissions from smelting aluminum from bauxite ore. Globally, production using recycled aluminum is twice the volume of production of aluminum from bauxite. It’s not surprising, then, that demand for scrap is expected to increase by 50% by 2050 in the EU over demand in 2019. ^[9]

Lead is used most commonly in car batteries (approximately 86% of lead used in the US is in car batteries); in the US these are considered hazardous waste, not only for the heavy metal toxicity of the lead, but also because of the corrosive nature of the acid. As a result of the care required to dispose of car batteries, lead recycling rates are quite high and new car batteries are largely made of recycled material. Overall, 76% of US lead is recycled. ^[10]

However, despite the high recycling rate, aspects of lead recycling are less sustainable. Because of the market for recycled lead, and the low melting point of the metal, informal, and often illegal recycling of lead is common, for example, in China. ^[11] Because of lead’s toxicity, poor recycling practices create public health risks. ^[12]

Copper, globally, is used most in electricity generation and distribution, as well as in construction, appliances, and transportation. Between 2009 and 2018, 32% of the copper used came from recycled sources, worldwide. In the EU, which has low copper reserves, 44% of copper comes from recycled metal, and 70% of end-of-life copper is recycled.

Because copper stays in service for long periods, lots of the already-smelted copper is bound up in use and is not available for recycling, driving demand for new metal. ^[13] In addition, copper is often used in complex electronics applications that do not lend themselves well to material recovery. However, copper ores are declining in quality, and new mines are only opening slowly, increasing the pressure to improve recycling rates. ^[14]

As with lead, informal recovery of copper, particularly from copper cable used in electrical cables or in electronics causes health hazards. Open burning is a common approach to removing the plastic insulation on such cables, releasing dioxins, mercury, and other hazardous chemicals into the air, where they can be absorbed through the lungs and skin and can be adsorbed onto soil and washed into ground water and surface water. ^[15]

Glass

Glass, like plastic, is a forever substance, able to survive for millennia without breaking down. At its simplest, glass is simply sand (SiO₂) that has been heated until it is molten and then cooled. It is infinitely recyclable because it does not degrade during recycling, which remelts the glass and reforms it. However, most glass recycling is limited to fairly basic forms of glass. Other kinds of glass – coated and laminated glass, for example – can be recycled, but at higher expense and potentially lower recovery rates. ^[16] In 2019, the US glass recycling rate was 33%, compared to 90% for some European nations. ^[17] The recycling stream in the US is often a single stream of co-mingled material because this is cheaper for municipalities to handle. Often, that thoroughly mixed set of recyclable materials is contaminated with trash and food wastes, which further complicates recycling of all the components, not only glass. US transport distances are often farther than in Europe, and the US does not have Europe’s high landfill costs, which encourage reducing trash output and favor recycling. The US states in which consumers pay a deposit on bottles have rates of bottle recycling on a par with Europe’s.

Use of recycled glass reduces energy costs of glass production. And for every 6 tons of recycled glass, one fewer ton of CO₂ emissions is produced. The heat needed to melt glass limits recycling to industrial facilities, so glass recycling is not connected to the health hazards of metal recycling. However, glass is heavy, relative to plastic and even metal, which increases transportation costs both to get used glass to recyclers and to put recycled glass back into the hands of consumers. And sand is in increasingly short supply. It is used in many other applications, especially road building and cement manufacture; mining it causes the same kind of habitat destruction as most forms of mining, in addition to creating dust that causes the respiratory disease silicosis.

Plastic

We saw, in section 5.2, the never-ending environmental problems associated with plastics. Some plastics can be recycled. However, no reasonable level of recycling could keep up with the volume of plastics being produced, let alone the volume anticipated in the future.

Begin with this “How Simple Things Work” video about the plastic recycling process and some of its limitations.

Then read or listen here for a discussion of how the vast plastic recycling business came to be, in the face of an abject failure to accomplish recycling.

Critical minerals

We have seen some examples of real progress in recycling, some halting progress in recycling, and an example of almost mythical recycling. Critical minerals recycling is both a young and an old field that shares some of the problems associated with copper recycling because critical minerals co-occur with copper in many examples of modern technology and electronics. It’s not surprising, then, that recycling rates for other critical minerals rise no higher than copper (Fig 3).

Critical minerals are minerals that one or more nations consider to be important for key industrial and national security applications that are also rare or associated with potential supply-chain problems. The US Geological Survey provides this extended definition.

The Energy Act of 2020 defined critical minerals as those that are essential to the economic or national security of the United States; have a supply chain that is vulnerable to disruption; and serve an essential function in the manufacturing of a product, the absence of which would have significant consequences for the economic or national security of the U.S. The act further specified that critical minerals do not include fuel minerals; water, ice, or snow; or common varieties of sand, gravel, stone, pumice, cinders, and clay.

Mineral criticality is not static, but changes over time as supply and demand dynamics evolve, import reliance changes, and new technologies are developed.

Critical mineral recycling is as old as hoary (and also quite new) tales of grave robbers digging in graveyards to steal gold fillings and jewelry. Gold is a critical mineral. It conducts electricity very well and resists corrosion, making it a common component, in small quantities, in electronics. We will discuss other aspects of critical minerals in Section 6.3 in the Energy chapter, because of the importance of critical minerals in renewable energy components such as wind turbines and solar panels. Our attention here is on recycling.

Recycling of critical minerals is not only important for economic and environmental sustainability but also, given their nature, for national security and such peace as the world can manage. Lithium-ion batteries, which power electric vehicles, computers, cell phones, and home appliances are a clear target for improved recycling, given the lithium recycling rates in evidence in Figure 3. The more commonplace lead-acid batteries used in automobiles have a 99% recycling rate in the US, where recycling is required by law. Many fewer lithium mines will be needed if the same rate can be achieved with this newer battery type, despite the sometimes more difficult process of accessing them. Traditional means of recycling copper can be scaled up to improve rates of recycling of this more common but still critical mineral. For rarer minerals, a considerable improvement in recycling of e-waste will be important. EV motors and wind turbines are related technologies that account for rare-earth minerals ^[18] as well as copper. Each wind turbine contains several tons of copper, depending on its rating. As we saw in section 5.2, not only will recycling rates need to increase, but regulation and oversight of disposal and recovery will also need to improve, to reduce health risks presently associated with the processes.

Knowledge Check

Take a moment to complete the short quiz below to assess your understanding of this section. Read each question carefully and refer to the section content as needed. This quiz is not graded – it’s simply an opportunity for you to reflect on what you’ve learned and reinforce key concepts.