Introduction to Copper

Copper, a reddish metallic element. It was one of the first metals to be made into tools. After iron, it is the most useful of all metals. Copper can be drawn into wire that has great strength. It is one of the best conductors of electricity. It does not rust, but forms a greenish coating called patina when exposed to moist air. Copper mixes with zinc to form brass and with tin to make bronze, and forms other useful alloys with such metals as gold, silver, nickel, aluminum, and iron.

Copper is used in the manufacture of electrical conductors, especially in the form of wire. It is used in building construction as a roofing material and for flashings, gutters, and downspouts. Large quantities are used in making water pipes, coils, and tanks. Copper is also used as a catalyst in many chemical processes. It is made into coins, utensils, jewelry, and craft articles. Copper also has important uses in a wide range of industrial products.

The bodies of many animals, including humans, require tiny amounts of copper for proper nutrition. Nearly all ordinary foods contain some copper. The tissues of the human liver are about 0.00003 per cent copper. Physiologists do not fully understand the part copper plays in body functions.

In some animals, including arthropods and mollusks, the oxygen in the blood is not carried by hemoglobin (an iron compound), but by a copper compound called hemocyanin. The blood of these animals is bluish-green.

Copper Compounds

There are two series of copper compounds, the cupric and the cuprous. Cupric compounds are most common.

The most important copper compound is cupric sulfate, more commonly called copper sulfate or blue vitriol. It is used in making fungicides, in electroplating, and in the manufacture of other copper compounds.

Cupric oxide (black oxide of copper) is found in the ores called melaconite and tenorite. The compound is used as an oxidizing agent and to rectify (change) alternating current to direct current. Cuprous oxide (red oxide of copper) is found in a crystallized form in several copper ores.

Cupric arsenite, or Scheele's green, is used in paint pigments and as an insecticide. Paris green (cupric acetoarsenite) is a useful insecticide and wood preservative. Cupric acetate has a similar use, and is also a textile dye.

Alloys of Copper

Among the many alloys of copper are the following:

Brass

5 to 40 per cent zinc, with or without small amounts of other metals such as tin.

Bronze

An alloy of copper that often contains tin and that may also contain phosphorus, lead, nickel, aluminum, iron, or manganese.

Gun Metal

88 per cent copper, 8 per cent tin, and 4 per cent zinc.

Bell Metal

60 to 85 per cent copper, with the remainder tin.

Nickel Coinage

75 per cent copper and 25 per cent nickel.

Nickel Silver,

formerly called German Silver 55 to 65 per cent copper, with the remainder nickel and zinc in various proportions.

Monel Metal

25 to 35 per cent copper, 60 to 70 per cent nickel, and 1 to 6 per cent iron.

Sterling Silver

7.5 per cent copper and 92.5 per cent silver.

Copper Ores

Copper is one of the few metallic elements that occur in nature uncombined with other elements. Such copper, called native copper, occurs in lumps of various sizes. One of the most important ores of copper is chalcocite, a dark gray mineral containing copper sulfide. Chalcopyrite is a sulfide of copper and iron, having a yellowish appearance.

Malachite is a green basic carbonate of copper, sometimes polished and used in inlaid work. Azurite has a similar composition, but its color is bright to deep blue. Cuprite, red copper oxide, and melaconite and tenorite, black copper oxide, are copper ores of less importance.

Mining and Refining of Copper

Copper ore is mined both underground and on the surface. Large excavations formed by surface mining are called open-pit mines. Most of the copper ores mined today are oxide or sulfide ores.

From the mines, copper ore is taken to mills, where it is crushed and finely ground in preparation for refining. The method of refining varies with the type of ore.

In the case of copper-oxide ores, the copper is usually leached (dissolved) from the ore with a solution of sulfuric acid.

The copper can be recovered from the leaching solution through electrolysis. In this process, a direct electric current is set up between positive and negative electrodes placed in the solution. The negative electrodes, called cathodes, are usually made of thin sheets of pure copper and the positive electrodes, called anodes, are usually made of lead. The electric current causes the copper in the solution to be deposited on the cathodes as a coating of pure copper.

Another method is to pass the solution over scrap iron; a chemical reaction causes the copper to be deposited on the iron. The copper is separated from the iron by methods used to refine copper-sulfide ores (many of which also contain iron).

Copper-sulfide ores are first treated by a process called flotation. In this process, bubbles are produced in a mixture of ground copper ore, water, and chemical reagents. The particles of copper-bearing minerals in the ore stick to the bubbles and float to the top of the mixture, where they can be skimmed off.

The copper-bearing minerals are roasted to drive off a part of the sulfur. The resulting product is smelted, yielding a molten combination of copper sulfate and iron sulfide called matte. Some light impurities in the matte combine to form slag, which is removed. The matte is then poured into a converter, where air is forced through it to burn out the remaining sulfur and to oxidize the iron. At this stage, most of the remaining impurities, including the oxidized iron, float to the top of the matte to form more slag, which is poured off.

The metallic copper that is left at the bottom of the converter is known as blister copper. It is very pure, but further refining is necessary to remove impurities consisting of small amounts of gold, silver, and other precious metals.

This refining is done electrochemically, using a process similar to the one used with oxide ores. In this case, however, the anode is molded from blister copper and decomposes during electrolysis. The direct electric current that flows between the electrodes placed in an electrolytic tank transfers the copper of the blister copper anode onto the cathode. The precious-metal impurities collect at the bottom of the tank.

A significant portion of the copper produced today is refined from copper scrap. Copper produced from scrap is called secondary copper.

History

Native copper was used by prehistoric humans as early as 6000 B.C. for beads and tools. It was shaped by being hammered while unheated until it was discovered that heated metal is easier to work. Some early peoples melted copper into molds to get a variety of shapes. Around 4500 B.C. the peoples of Mesopotamia became the first to extract copper from ores by smelting (a heating process), marking the beginning of the art of metallurgy. About 3000 B.C. the Mesopotamians began combining copper with tin to make bronze, which is stronger and easier to cast than copper. The name copper comes from Kupras, Greek for Cyprus, a major source of copper in ancient times.

The Romans worked copper mines in central Europe, Spain, and Britain. The Indians of North and South America knew and used copper at a very early date. Small shipments of copper ore were sent from America to Europe in the 18th century, but it was not until the middle of the 19th century that copper became important in the mineral production of the United States.

For the world's leading producers, see graph. In the United States, Arizona is by far the leading producer.

Symbol: Cu. Atomic number: 29. Atomic weight: 63.546. Melting point: 1,981.4 F. (1,083 C.). Boiling point: 4,653 F. (2,567 C.). Specific gravity: 8.96. Copper belongs to Group I-B of the Periodic Table and has a valence of +1 or +2.