Copper (Cu)

Where Found

Copper deposits are found in several types of geologic environments. Most common are the copper deposits that formed in magmatic arcs associated with subduction zones. These types of ores are found in Canada, the western United States, Mexico, Peru, and Chile. Other important copper deposits were formed by different processes and are found in central Europe, southern Africa, Cyprus, Indonesia, and Japan.

Primary Uses

The major uses of copper are in the electrical industry because of the substance’s ability to conduct electricity efficiently. Copper is also utilized extensively in the construction industry especially for plumbing. Most of the remaining copper is alloyed with other metals to make bronze (with tin), brass (with zinc), and nickel silver (with zinc and nickel, not silver).

Technical Definition

Copper (chemical symbol Cu) is a reddish mineral that belongs to Group IB of the periodic table. Copper has an atomic number of 29 and an atomic weight of 63.546, and it is composed of two stable isotopes, copper 63 (69.17 percent) and copper 65 (30.83 percent). Pure copper has a face-centered cubic crystalline structure with a of 8.96 grams per cubic centimeter at 20° Celsius. The melting point of copper is 1,083° Celsius, and the boiling point is 2,567° Celsius.

Description, Distribution, and Forms

Copper is a ductile metal and a good conductor of heat and electricity. It is not especially hard or strong, but these properties can be increased by cold working of the metal.

Copper is a relatively rare element, making up only 50 parts per billion in the Earth’s crustal rocks. It occurs in nature both in elemental form and incorporated into many different minerals. The primary minerals are the sulfides (chalcopyrite, bornite, covellite, and others), oxides (cuprite and others), and carbonates (malachite and azurite). Copper has two valences (degrees of combining power), +1 and +2, and important industrial compounds have been synthesized using both states. The most useful industrial +1 (cuprous, or Cu I) compounds are cuprous (Cu₂O), cuprous sulfide (Cu₂S), and cuprous chloride (Cu₂Cl₂). Important +2 (cupric, or Cu II) compounds used by industry are cupric oxide (CuO), cupric sulfate (CuSO₄), and cupric chloride (CuCl₂).

Although copper is relatively rare in the crust of the Earth, it has been concentrated into ore deposits by geologic processes. There are four major types of copper ore deposits, each formed by a different set of geologic events.

Most of the copper mined is taken from porphyry copper deposits. These deposits are composed of copper minerals disseminated fairly evenly throughout porphyritic granitic rocks and associated veins. The primary ore mineral is chalcopyrite, a copper/iron sulfide. Porphyry copper ore deposits are generally located in rocks that have been formed near convergent plate boundaries where the granites have been produced from generated during the subduction of an oceanic plate beneath a continental plate. This tectonic regime has existed along the western coasts of North America and South America for more than 200 million years; consequently, giant porphyry copper deposits are found in western Canada, the western United States, Mexico, Peru, and Chile. The world’s two largest producers of copper are Chile and the United States, and the largest copper ore deposit in the world is located in Chile. Other porphyry copper deposits are found in Australia, New Guinea, Serbia, the Philippines, and Mongolia.

A second kind of copper ore deposit is commonly called a Kupferschiefer type because of the large quantity of copper found in the Kupferschiefer shale of central Europe. The copper occurs in a marine shale that is associated with evaporites and nonmarine rocks. The origin of the copper in these ores is still debated. The Zambian-Democratic Republic of the Congo copper belt of southern Africa contains more than 10 percent of the world’s copper reserves.

Copper is also found in massive sulfide deposits in volcanic rocks, ophiolites, greenstone belts, and fumarolic deposits. Copper-bearing massive sulfide ores are found in Canada, Cyprus, and Japan.

A fourth type of copper deposit is found on the deep-ocean floors, where manganese nodules have formed very slowly in areas of unusually slow sedimentation. These nodules contain not only manganese but also copper, cobalt, and nickel in economically important concentrations. Since these nodules generally form in water depths of 900 to 2,000 meters, they are difficult to mine. They do, however, represent an important potential source of copper for the future.

Copper is an essential trace of life and is found in various concentrations within plants and animals. For example, copper is found in many blue-blooded mollusks and crustaceans because it is the central element in hemocyanin, a molecule that transports oxygen in the organisms. It is found in lesser concentrations in many other organisms, such as seaweeds, corals, and arthropods.

Copper can be found in most soils, and its absence or unavailability to plants will cause the soil to be relatively infertile. For example, many muck soils that are very rich in organic material cannot sustain plant life because the copper is bound to the organic matter and is therefore not available to plants.

Some soils have suffered from copper pollution attributable to the excess of copper-bearing fertilizers and the application of copper-rich fungicides or sewage wastes to the land. Research has shown that the accumulations of copper in these soils will not be effectively leached from the land for decades or even centuries because the copper has an affinity for soil colloids that can tightly bind the copper.

Copper is distributed throughout the Earth’s lithosphere, hydrosphere, atmosphere, and pedosphere in various concentrations. About 5 percent of the copper content of the is found in sedimentary rocks, particularly shale, and only about 0.00004 percent in soils. Only about 0.001 percent of the copper of the lithosphere is in exploitable concentrations, and some of these deposits have been mined for centuries. The total production of copper by mining is approximately 300 million metric tons, of which about 80 percent was mined in the twentieth century. Almost 30 percent of the entire world’s historic production of copper was mined in the 1980’s. The total copper mined amounts to about twice the total copper in the upper 2 centimeters of soil worldwide and nearly ten times the total copper found in all living organisms. Much of the copper produced has been used and then disposed of on land or wasted in water or the atmosphere. The impact of the transfer of this much copper from the deposits of the crust to the surface of the Earth is not yet well understood.

The total amount of copper released into the atmosphere has been estimated to be almost three times the amount of carbon in the today. The residence time of copper in the atmosphere is quite short, and there probably has not been a significant buildup of copper over time, but the atmosphere does act as a medium for transferring copper around the globe. Copper pollution of many local ecosystems has been well documented in areas near smelters and copper mines. Although it is clear that copper concentrates in the soils and waters near the areas, the impact of copper pollution is often hard to separate from the environmental effects resulting from increased levels of other heavy metals and from sulfur dioxides and other gases released from smelters.

Research has also shown that urban areas generally have much higher levels of copper in the soils and air than are found in rural areas. In many cases the copper concentration in urban soils is more than ten times that of nearby rural areas. In addition, it is well established that the dumping of sewage into rivers, lakes, and the ocean can raise the concentrations of copper in the sediments by factors of two to one hundred times the background levels in unpolluted areas. However, distinguishing the environmental impact of copper from the effects of the associated metals found in sewage effluent is difficult.

Copper is an essential element in the human diet. It is found in several oxidative enzymes, such as cytochromes a and a3, ferroxidase, and dopamine hydroxylase. The copper is used by enzymes in the oxidation and absorption of iron and vitamin C. The level of copper in the body is primarily controlled by the excretion of the element in bile. Absorbed copper is probably stored internally by some intracellular proteins.

Generally, copper deficiencies in humans are rare. There are two known genetic diseases, Wilson’s disease and Menkes disease, that disrupt copper metabolism. In Wilson’s disease, an unknown mechanism restricts the excretion of copper in bile, and as a result copper builds up in various tissues in the body. Once diagnosed, Wilson’s disease can be treated by giving the patient a chelating agent to remove the accumulated copper. Menkes disease, commonly called steely or kinky hair syndrome, causes inefficient utilization of copper in the body. This lack of copper affects the normal formation of connective tissue and the loss of some widespread enzymatic activity. Death generally occurs within the first three years.

History

Copper was one of the first metals mined and used by humans. It, along with gold and silver, occurs naturally as a free elemental metal and thus can be extracted and used without or refining. Neolithic humans probably learned that this unusual metal could be shaped by hammering with tools and that the copper tools could be hardened by continued cold working. The first use of copper probably predated 8000 B.C.E. By 6000 B.C.E. it was known that copper could be melted in crude furnaces and poured into casts to elaborate weapons and ornaments.

Egyptian copper artifacts are dated as far back as 5000 B.C.E., and ancient Egyptians appear to have been the first to copper with tin to make bronze. The earliest record of a bronze artifact dates to about 3700 B.C.E. Bronze makes better weapons and ornaments because it is much harder and tougher than pure copper. As a result, the bronze technology spread throughout the Middle East and into Asia. Bronze items at least as old as 2500 B.C.E. have been found in China, but the alloy may have been used earlier.

Bronze was superseded by iron as the metal of choice for weapons and for structural uses. This technological advance occurred after furnaces were developed that could obtain temperatures high enough to smelt iron from its ores. After the introduction of iron and later steel into common use, copper and its alloys were used primarily for ornaments, utensils, pipes for plumbing, and coinage. Because of its natural resistance to most corrosion caused by air and seawater, copper was commonly utilized for purposes requiring such protection. The discovery of electricity and the invention of the incandescent lightbulb and electric motors led to the extensive use of copper for the transmission of electricity. This became the most common and most important use of copper.

Obtaining Copper

Copper is mined in fifty to sixty countries worldwide, with Chile accounting for about 35 percent of the production in 2008. The primary ore minerals of copper are chalcopyrite (copper-iron sulfide), chalcocite (copper sulfide), covellite (copper sulfide), azurite (copper carbonate), and malachite (copper carbonate). Other ore minerals of lesser importance are native copper, bornite, enargite, tetrahedrite, cuprite, tenorite, chalcanthite, and chrysocolla.

The copper sulfide minerals are found in porphyry, massive sulfide, and Kupferschiefer type deposits, and the copper carbonates and copper oxides are commonly found in the upper zones of such deposits that have been exposed to and action.

Much of the copper of the world is extracted from open-pit mines that expose the ore deposits. The of surrounding or soil covering the ore is physically removed, and the ore extracted by drilling and detonating explosives to loosen the ore. Underground mining is done using standard techniques of tunneling and blasting. The ore from either underground mines or open-pit mines is then gathered and hauled to ore processing plants, where the ore is crushed and the copper and other metals are concentrated. The concentrated ore usually measures 20 to 30 percent copper, and it is then either smelted or leached to produce a relatively high concentration of copper, which still contains some impurities. This smelted copper is then electrolytically refined to a purity of more than 99 percent.

Uses of Copper

Copper was one of the first metals used by humans because it can be found in nature as pure metal and can be worked easily by hand. Pure copper was probably first mined and used by humans around 8000 B.C.E. Through the ensuing ages, copper has remained an important metal and a component of such important materials as pewter, brass, and other bronzes. After the Industrial Revolution, copper became the second most used metal in the industrial world behind only iron. However, the discovery of aluminum, its properties, and its general availability made aluminum more useful in modern society.

Copper is one of the most commonly used metals in the world, and, because of its special qualities of high and electrical conductivity, it is used extensively in the electrical industries. Copper that has been refined electrolytically is up to 99.62 percent pure; the primary remaining material is oxygen. The oxygen helps to increase the density and conductivity of copper wire. The wire can be produced in large quantities by rolling the copper into rods, which are then drawn through tungsten carbide or diamond dies to form the wire.

Copper is also produced in sheets or smaller strips by initially rolling hot copper, with later rollings done with cold copper. The resultant strips or sheets are generally of even thickness and uniform surface appearance. This strip copper can be cut or pressed to be used in the electrical or construction industries.

One of the earliest uses of copper was in the production of bronze. The early bronzes were copper/arsenic alloys; later, tin was added at various concentrations. Modern bronzes are alloys of copper and tin, and they are used primarily for ornaments, bells, and musical instruments. The bronze used in making bells and musical instruments usually contains up to 20 percent tin to impart the proper tonal qualities to the sounds produced from these instruments. Another traditional use for copper is in the production of pewter, which is an alloy of copper and lead. Since lead is highly toxic, the use of pewter has been restricted in recent times and is generally reserved for ornamental pieces.

Brass is a widely used alloy of copper and zinc. Although the copper content of brass can range from less than 5 percent to more than 95 percent, only brasses of at least 55 percent copper can be worked and used industrially. White brasses contain more than 45 percent zinc and are not at all malleable and thus are not useful for industrial purposes. The various relative concentrations of copper and zinc produce brasses of widely varying physical properties of hardness, ductility, and malleability. Many brasses can be drawn into wire, rolled into sheets, or formed into rods.

Copper and nickel are completely and therefore can be mixed in any relative concentration. The various mixtures produce alloys with various physical properties and different industrial uses. The alloys using 2 percent to 45 percent nickel produce a material with a much higher than pure copper, and the mixture of about 20 percent nickel produces an extremely ductile alloy that can be cold worked without annealing. This makes this mixture useful for drop forging, cold stamping, and pressing. Industrially this alloy is commonly used for fittings in the automobile industry and for bullet sheathing. Copper and nickel occur together in some ores and can be smelted to produce a natural alloy called Monel metal. The natural ores usually also contain some manganese, which, with other impurities, is incorporated in the alloy. It is also produced artificially by mixing the appropriate levels of nickel, copper, and manganese. Monel metal is extremely strong at normal and high temperatures and thus has many engineering applications.

Copper can also be alloyed with various metals to form other types of bronzes. It can be mixed with 9 percent aluminum to form aluminum bronzes, which are corrosion-resistant metals. Manganese bronzes, which are high-strength alloys, usually contain copper, zinc, aluminum, and 2 to 5 percent manganese. The addition of 1 to 3 percent silicon and 1 percent manganese to copper produces the silicon bronzes, which have good welding and casting qualities. A very strong alloy of copper and about 2 percent beryllium can be strengthened by heat working and will produce a metal with a hardness equal to that of many of the harder steels.

Many copper-containing compounds are used for industrial purposes. Cuprous oxide is used as an antifouling agent in some paints and to give some glass a red color. A green color can be imparted to glass by cupric oxide, and cupric chloride is used in the manufacture of some pigments. Copper sulfate is commonly used as a desiccant and in the production of electrolytically refined copper. Like many other copper compounds, copper carbonates impart strong blue or green colors to solutions and are used in the production of many pigments. Copper can also be combined with arsenic; these compounds are used as insecticides.

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