Most students will tell you that recycling is a good thing, but is it always as efficient as it could be? In the case of low-value, high-bulk materials, such as glass or paper, the economic benefit is marginal.
However, the common ring-pull aluminium can represents a special case. Just like people, ring-pull cans have their own life-cycle, but theirs involves the realistic possibility of continuous reincarnation. The estimated life, death and rebirth of an aluminium can is just 95 days, and it goes something like this:
* the can is bought and its contents are drunk;
* it is then discarded into a recycling bin;
* from there, it is transported to a recycling plant;
* at the plant, it is crushed, shredded and moved past a magnet to remove any steel;
* its coating is stripped off (the lacquer coating prevents any chemical reaction between the can and its contents);
* the can is melted, the impurities removed, and a new metal ingot cast;
* this is rolled into a strip and formed into new cans;
* the new cans are filled and distributed to retailers.
But are there any weak points in this virtuous green circle? Could anything be done to increase the numbers of cans being recycled? Students could consider issues such as:
* the location of recycling bins (fast-food outlets, for example, have a trail of debris around each store);
* financial incentives, such as vouchers in exchange for cans (in Scandinavia, supermarkets have recycling machines where bottles and cans are exchanged for credit notes);
* fines or other penalties for failing to recycle.
The last point seems like a doomed idea. In 2001, when some UK retailers began to charge a recycling fee for the removal of old fridges, owners reacted in a predictable way. Fly-tipping became a growth industry and hedgerows became decorated with redundant household fridges.
These issues are common to most recycling initiatives, but not in the reprocessing of ring-pull cans. The two key ideas for students to examine are energy use and cash value. The two are closely linked.
There is no shortage of aluminium. It is the most common metal in the planet's crust. When you trudge across a muddy clay field, you are walking on aluminium. The cost of extracting it from clay is prohibitive. But we are never going to run out of this metal, unlike some other raw materials, such as oil.
It is the way in which aluminium is produced that makes recycling cans such an attractive option. It was first isolated in 1808 by Sir Humphry Davy. In the early days, the methods used to extract it bordered on the suicidal.
Dangerously reactive materials such as potassium were employed in a pyrotechnical display that produced only small amounts of metal.
The element was so rare and expensive that the French Emperor Napoleon III reserved the aluminium cutlery for honoured guests. The hoi polloi had to eat with gold knives and forks.
Aluminium is now produced in an energy-intensive way, using vast amounts of electricity, much of which is derived from burning fossil fuels. The energy required to make one kilogram of new metal from raw materials is sufficient to produce 20kg of recycled metal from old cans. The quality of recycled aluminium is virtually identical to the new metal. Only hi-tech industries, such as aerospace, avoid using recycled metal. It would be unnerving to think the plane in which you were travelling had wings made from 20,000 recycled cans.
However, recycling has resulted in a major reduction in air pollution and the need for new sources of raw materials, both metal ores and fuels.
Ask students to research the prices of metals in the financial press or on the internet. Get them to identify the top five bulk metals in terms of selling price. Clearly, the prices of metals used in jewellery, such as platinum and gold, will be significantly higher than the prices of metals produced in bulk. Which metal or metals are the best candidates for recycling in terms of their prices?
Within the European Union, it will soon be necessary for car manufacturers to take back old wrecks and recycle all the materials. This will change the way designers work. If you have to recycle an old car, you need to separate the materials and identify them. Can students spot the difference between PVC, polyurethane and polystyrene? This is not as straightforward as throwing glass bottles into the green, brown or clear bins.
Recycling is not a simple issue. Ask students to summarise the case for and against its use. After all, more recycling means fewer jobs in quarrying, mining and manufacturing. Is recycling worth doing?
Ray Oliver teaches science at St Albans' Girls Schoool, Hertfordshire