Recycling materials

Waste materials such as polymers and metals are often disposed of in landfill sites. Waste polymers may be incinerated. However, these disposal methods waste valuable resources, including these raw materials:

  • crude oil for making most polymers
  • metal ores for making most metals

These are finite resources - they form extremely slowly or are no longer being made. Recycling reduces the problems of disposal, and also conserves raw materials.

Recycling polymers and metals

Recycling involves collecting used items and producing new materials from them. The first steps usually needed are:

  • collecting used items
  • transporting the used items to a recycling centre
  • breaking up the items and sorting the different materials

Polymers

Recycling polymers also involves:

  • sorting the different polymers from one another
  • melting the waste polymer
  • forming the polymer into a new product
Separating items at a recycling centre is just the first stage in sorting polymers

Metals

Recycling metals also involves:

  • sorting the different metals from one another
  • melting the metal and removing impurities from the molten metal
  • solidifying the metal in ingots

The ingots can then be used to manufacture new metal items.

Question

Describe a simple way to separate aluminium from iron.

A magnet or electromagnet will attract iron but not aluminium.

Advantages of recycling

The advantages of recycling include:

  • fewer oil wells, quarries or mines are needed
  • less noise, dust and heavy traffic are produced
  • smaller areas of natural habitats are damaged

In addition, less energy is usually needed to produce a material by recycling than is needed to produce it from its raw materials.

Question

This table shows the percentage of energy saved by recycling two metals compared to extraction from their ores:

MetalEnergy saved (%)
Iron70
Aluminium92

Suggest an explanation for the difference.

Aluminium is extracted from its ore using electrolysis but iron is extracted by heating with carbon. Electrolysis uses more energy, so more energy is used to extract aluminium in the first place. Aluminium has a lower melting point than iron, so less energy is needed to melt it during recycling.

Disadvantages of recycling

Disadvantages of recycling arise from the recycling process itself:

  • the collection and transport of used items needs organisation, workers, vehicles and fuel
  • it can be difficult to sort different materials from one another
  • the sorted materials may need to be transported to where they can be processed