This is the VOA Special English Development Report.

People have been recycling metals for hundreds of years. Today, re-using metal waste or scrap provides work for many people, especially in developing countries. Three kinds of metals are recycled. They areferrous metals, non-ferrous metals andprecious metals.

Ferrous metals contain iron. They are low in cost and recycled in large amounts. Metallic iron called pig iron is produced when iron is heated in a hot industrial stove. This kind of stove is called ablast furnace.Pig iron  contains another element, carbon. Pig iron is useful because it can be formed into solid, heavy objects or objects with unusual shapes.

Another kind of iron is steel, which is iron without the carbon. Making steel is simply removing the carbon by burning it away. This makes the steel stronger and easier to cut than iron. Both pig iron and steel waste or scrap are useful because they can be melted to make new products.

In countries where there is a shortage of steel scrap, old tin cans are sometimes used. Tin cans are mostly steel. They can be melted. If the scrap is heated before the temperature gets to the melting point, the blast furnace can be more simply designed and less costly. These simpler furnaces are called foundries. Products are made in foundries all over the world, but especially in Asia.

Non-ferrous metals include copper and aluminum. Copper is the perfect material for recycling. It is valuable, easy to identify and easy to clean. People who operate foundries around the world buy copper wire and cable to recycle.

Aluminum is another very popular non-ferrous scrap metal. It is cheap to produce and very easy to work with. In developing countries, small foundries produce aluminum bars, sheets and wire.

Precious metals like silver also are recycled. Silver can be found in pictures made with old cameras. And it can be found in X-rays after they have been developed. X-ray film is very valuable for recycling silver, because both sides of the film are usually developed.

And that's the VOA Special English Development Report. You can learn more about recycling metals through VITA, Volunteers in Technical Assistance. VITA is on the Web at enterpriseworks.org. And Internet users can find transcripts and archives of all of our reports at voaspecialenglish.com. This is Shep O'Neal.

ferrous metal :黑色金属

precious metal :贵金属

blast furnace :鼓风炉

pig iron :生铁