copper processing

copper processing, the extraction of copper from its ores and the preparation of copper metal or chemical compounds for use in various products.

In its pure form or as an alloy, copper (Cu) is one of the most important metals in society. The pure metal has a face-centred cubic crystal structure, and there is no critical temperature at which this crystal structure changes. Consequently, it is ductile and possesses a high level of electrical and thermal conductivity, making it attractive for a wide range of ornamental and practical applications. With cold-working, copper becomes harder, but it can be made soft again with the heat treating process known as annealing.

History

Copper was discovered and first used during the Neolithic Period, or New Stone Age. Though the exact time of this discovery will probably never be known, it is believed to have been about 8000 bce. Copper is found in the free metallic state in nature; this native copper is the material that humans employed as a substitute for stone. From it they fashioned crude hammers and knives and, later, other utensils. The malleability of the material made it relatively simple to shape implements by beating the metal. Pounding hardened the copper so that more durable edges resulted; the bright reddish colour of the metal and its durability made it highly prized.

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The search for copper during this early period led to the discovery and working of deposits of native copper. Sometime after 6000 bce the discovery was made that the metal could be melted in the campfire and cast into the desired shape. Then followed the discovery of the relation of metallic copper to copper-bearing rock and the possibility of reducing ores to the metal by the use of fire and charcoal. This was the dawn of the metallic age and the birth of metallurgy.

The early development of copper probably was most advanced in Egypt. As early as 5000 bce, copper weapons and implements were left in graves for the use of the dead. Definite records have been found of the working of copper mines on the Sinai Peninsula about 3800 bce, and the discovery of crucibles at these mines indicates that the art of extracting the metal included some refining. Copper was hammered into thin sheets, and the sheets were formed into pipes and other objects. During this period bronze first appeared. The oldest known piece of this material is a bronze rod found in the pyramid at Maydūm (Medum), near Memphis in Egypt, the date of origin being generally accepted as about 3700 bce.

Bronze, an alloy of copper and tin, is both harder and tougher than either; it was widely employed to fashion weapons and objects of art. The period of its extensive and characteristic use has been designated the Bronze Age. From Egypt the use of bronze rapidly spread over the Mediterranean area: to Crete in 3000 bce, to Sicily in 2500 bce, to France and other parts of Europe in 2000 bce, and to Britain and the Scandinavian area in 1800 bce.

About 3000 bce copper was produced extensively on the island of Cyprus. The copper deposits there were highly prized by the successive masters of the island—Egyptians, Assyrians, Phoenicians, Greeks, Persians, and Romans. Cyprus was almost the sole source of copper to the Romans, who called it aes cyprium (“ore of Cyprus”), which was shortened to cyprium and later corrupted to cuprum, from which comes the English name copper. The first two letters of the Latin name constitute the chemical symbol Cu.

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When copper and bronze were first used in Asia is not known. The epics of the Shujing mention the use of copper in China as early as 2500 bce, but nothing is known of the state of the art at that time or of the use of the metal prior to that time. Bronze vessels of great beauty made during the Shang dynasty, 1766–1122 bce, have been found, indicating an advanced art. The source of the metals, however, is unknown.

The Copper Age in the Americas probably dawned between 100 and 200 ce. Native copper was mined and used extensively and, though some bronze appeared in South America, its use developed slowly until after the arrival of Columbus and other European explorers. Both North and South America passed more or less directly from the Copper Age into the Iron Age.

As man learned to fashion weapons from iron and steel, copper began to assume another role. Being a durable metal and possessed of great beauty, it was used extensively for household utensils and water pipes and for marine uses and other purposes that required resistance to corrosion. The unusual ability of this metal to conduct electric current accounts for its greatest use today.