Overview

Recycling of metals from secondary sources is a growing industry. There are a large number of secondary sources, collectively called "scrap", which is defined in the dictionary as "discarded metal in the form of machinery, auto parts, etc., suitable only for reprocessing". As the primary sources of metal, natural ores are steadily getting depleted, there is an obvious recognition that the total supply of any metal on Earth is finite. It is evident, the metals have to be recycled from "scrap" to maintain a steady supply to met the demands of industry and wherever else metals are used. In this context, the word "discarded" should be eliminated from the dictionary definition. This is even truer in the case of metals, which do not occur in abundant concentration and their extraction from the scarce primary resources is often expensive, which, in most but not all case may be justified by the price of the metals produced. This is the case for precious metals like gold and platinum group metals (platinum, palladium, rhodium). In such cases, precious metal content as low as 0.001% to 0.03% can justify reprocessing of the scrap to recover the metals in it. As an example, scrap containing only 0.003% rhodium has a value of $2,500 per ton, even if all other metal values of the scrap are ignored (Hoffmann, 1992a).

Metals are a renewable resource. Most metals are used in industry in a fairly massive elemental form, which greatly facilitates recycling. The properties of metals that...