Scrap metal, used metals that are an important source of industrial metals and alloys, particularly in the production of steel, copper, lead, aluminum, and zinc. Smaller amounts of tin, nickel, magnesium, and precious metals are also recovered from scrap.

Impurities consisting of such organic materials as wood, plastic, paint, and fabric can be burned off. Metallic impurities may be desirable, inert, or undesirable. Undesirable ones may be diluted to tolerable proportions by the addition of pure metal, or they may be removed by refining. Scrap is usually blended and remelted to produce alloys similar to or more complex than those from which the scrap was derived.