The scientific principles underpinning the recycling of some common materials are explored by a roving 'trouble shooter'. The presenter visits an aluminium recycling plant, and the recycling techniques are compared with the original extraction process. These techniques are found to be simpler and much cheaper partly as a result of the low melting point of the metal.

The presenter moves on to a factory that recycles cast iron. It is explained how iron waste is changed into a product that has some advantages over mild steel.

Problems associated with the re-use of various plastics are then tackled from an operational perspective and in terms of the molecular structures of thermoplastic and thermosetting materials.

Finally, the recycling of paper is examined and contrasted with the procedures previously seen. 00.00 - 00.47 Introduction

• The growth of the recycling industry in recent years.

• The simple molecular structure of solid aluminium gives it a low density and a relatively low melting point.
• A detailed look at a recycling plant which transforms scrap metal into ingots.
• When aluminium is extracted from its ore, bauxite, the process is much more complex and energy-consuming.

• Cast iron waste is recycled by melting; but iron's melting point is higher than that of aluminium.
• The electromagnetic induction furnace: an alloy of magnesium is used in the process to improve the quality of the product.
• A comparison of cast iron and steel.
• The products of casting.

• The processes involved in recycling paper, such as the addition of water, and shredding, are illustrated.
• The effect of the mechanical stress on the fibre length.
• Removing the water efficiently, and making the new paper, produces a humid environment.
• A method used to remove printer's ink is demonstrated.

• Much plastic waste is produced, but little of it can be recycled.
• The molecular structures of thermoplastics and thermosets are compared and contrasted.
• Attempts to melt, and to recycle, thermosets, fail.
• Some useful products made from recycled plastic.

• The need to sort waste into separate materials before processing.