Recycling metals and life-cycle assessments

Melting and reshaping scrap metal generally requires less energy than extracting metal from its ore. Where the energy comes from fossil fuels, lower energy demand can reduce fuel use and the emissions that contribute to climate change. Recycling has environmental impacts of its own, but these can be smaller than those of mining and extraction.

Lower energy demand can also mean lower production costs. Recycling is particularly economically valuable for metals that are expensive to extract, such as aluminium. Collecting and processing scrap metal also creates employment.

These benefits must be weighed against costs. Scrap needs to be collected and transported, which requires vehicles, fuel and workers. It must often be sorted to keep different materials separate: unwanted materials can affect the quality of the recycled product. Sorting and operating recycling facilities require energy and labour. Recycling is therefore not free or impact-free; its advantages depend on the savings compared with obtaining new metal.

Looking at the whole life of a product

Recycling concerns what happens to materials after use, but a product can affect the environment long before it becomes waste. A life-cycle assessment, or LCA, considers environmental effects throughout a product’s life. It helps compare products and identify where their main impacts occur.

The four stages are obtaining raw materials, manufacturing, use and final disposal. Transport between stages also uses energy and may produce emissions.

Obtaining raw materials: consider where the materials come from and the effects of obtaining them. Mining metal ores uses resources and disturbs land. A product made using recycled metal may reduce the amount of new ore needed.

Manufacturing: consider energy use, emissions, waste and land used for factories. Fuel-powered machinery and transport can contribute to pollution.

Using the product: the impact depends on the product. A wooden desk has relatively little environmental impact during use, whereas a fuel-powered car uses fuel and produces air pollution. How long the product lasts and whether it is reused also matter.

Disposing of the product: consider what happens when it is no longer useful. Landfill occupies space, while recycling can recover useful materials. Whether the product breaks down and whether its parts can be recycled affect its environmental impact.

Evaluating evidence: plastic and paper shopping bags

An LCA can reveal a trade-off: one product may have an advantage at one stage but a disadvantage at another. Consider these qualitative comparisons for plastic and paper shopping bags.

Paper’s biodegradability is an advantage at disposal, but it does not remove the impacts of obtaining its raw materials or manufacturing it. Similarly, plastic’s potential for reuse is only an advantage if it is actually reused.

A justified conclusion is therefore conditional. A plastic bag used many times may be preferable to repeatedly obtaining replacement paper bags. If the plastic bag is used only once, its reuse advantage disappears. Recycling the paper bag can make the paper option more favourable. These comparisons do not establish that one material is always better.

Turning LCA data into a judgement

Start by comparing products that provide the same service. Comparing one long-lasting bag with one bag used once can be misleading if they carry different amounts of shopping over their lifetimes. Check the assumptions about lifetime, number of uses and disposal.

Then identify the advantages and disadvantages at each stage. If numerical data are given, check the units and compare like with like. Energy values in the same unit can be added across stages, but an energy value cannot simply be added to a mass of waste to create a meaningful total.

Finally, explain which evidence supports your decision and what could change it. Different impacts are not always easy to measure or weigh against one another, so choices about assessment criteria can influence the conclusion. An LCA informs a decision rather than guaranteeing a single perfect answer; environmental benefits may also need to be balanced against economic costs.

• Process: collect → sort → melt → recast.
• Raw materials: reduces demand for finite ores; conserves valuable supplies.
• Environment: less mining and habitat damage, less landfill waste, generally lower energy demand and fossil-fuel emissions.
• Economy: can reduce production costs, especially for costly-to-extract metals such as aluminium; creates employment.
• Limitations: collection, transport, sorting and processing require fuel, energy and labour. Contamination can affect quality.

Four LCA stages

1. Obtain raw materials: resource depletion, energy use and damage to land.
2. Manufacture: energy, emissions, waste and factory land use.
3. Use: fuel or energy demand, pollution, lifetime and reuse.
4. Dispose: landfill, biodegradability and recycling.

Include transport impacts between stages.

Evaluate an LCA

• Compare the same service and check units, lifetime and reuse assumptions.
• Weigh evidence across stages, not just disposal.
• Give a supported conclusion and explain when it might change.
• Plastic–paper bag comparisons depend on actual reuse and recycling; neither is automatically best.
• Assessment criteria and difficult-to-measure impacts can influence conclusions.