People have been recycling（反復(fù)使用）metals for hundreds of years. Today, re-using metal waste or scrap（廢料）provides work for many people, especially in developing countries. Three kinds of metals are recycled. They are ferrous metals（黑色金屬）, non-ferrous metals（有色金屬）and precious metals（貴金屬）.

Ferrous metals contain iron. They are low in cost and recycled in huge amounts. Metallic iron（精練鐵）called pig iron（生鐵）is produced when iron is heated in a hot industrial stove. This kind of stove is called a blast furnace（鼓風爐）. Pig iron also contains another element, carbon（炭）. 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 and melted. Tin cans are mostly steel. If the scrap is heated before the temperature gets to the melting point（熔點）, 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（銅）and aluminum（鋁）. 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 an old black-and-white camera. 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.

You can learn more about recycling metals from Volunteers in Technical Assistance, or VITA. VITA is on the Internet at vita.org.

This VOA Special English Development Report was written by Gary Garriott.