Copper
Copper is a chemical element; it has symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, and constantan used in strain gauges and thermocouples for temperature measurement.
Copper is one of the few native metals, meaning metals that occur naturally in a directly usable, unalloyed metallic form. This led to very early human use in several regions, from. Thousands of years later, it was the first metal to be smelted from sulfide ores, ; the first metal to be cast into a shape in a mold, ; and the first metal to be purposely alloyed with another metal, tin, to create bronze,.
Commonly encountered compounds are copper salts, which often impart blue or green colors to such minerals as azurite, malachite, and turquoise, and have been used widely and historically as pigments.
Copper used in buildings, usually for roofing, oxidizes to form a green patina of compounds called verdigris. Copper is sometimes used in decorative art, both in its elemental metal form and in compounds as pigments. Copper compounds are used as bacteriostatic agents, fungicides, and wood preservatives.
Copper is essential to all aerobic organisms. It is particularly associated with oxygen metabolism. For example, it is found in the respiratory enzyme complex cytochrome c oxidase, in the oxygen carrying hemocyanin, and in several hydroxylases. Adult humans contain between 1.4 and 2.1 mg of copper per kilogram of body weight.
Etymology
The name of the metal derives from aes cyprium meaning "metal of Cyprus" in Latin. In Late Latin this became cuprum. Old English adopted this as Coper and copper, first used in the 12th century, derives from that word.Characteristics
Physical
Copper, silver, and gold are in group 11 of the periodic table; these three metals have one s-orbital electron on top of a filled d-electron shell and are characterized by high ductility and electrical and thermal conductivity. The filled d-shells in these elements contribute little to interatomic interactions, which are dominated by the s-electrons through metallic bonds. Unlike metals with incomplete d-shells, metallic bonds in copper are lacking a covalent character and are relatively weak. This observation explains the low hardness and high ductility of single crystals of copper. At the macroscopic scale, introduction of extended defects to the crystal lattice, such as grain boundaries, hinders flow of the material under applied stress, thereby increasing its hardness. For this reason, copper is usually supplied in a fine-grained polycrystalline form, which has greater strength than monocrystalline forms.The softness of copper partly explains its high electrical conductivity and high thermal conductivity, second highest among pure metals at room temperature. This is because the resistivity to electron transport in metals at room temperature originates primarily from scattering of electrons on thermal vibrations of the lattice, which are relatively weak in a soft metal. The maximum possible current density of copper in open air is approximately, above which it begins to heat excessively.
Copper is one of a few metallic elements with a natural color other than gray or silver. Pure copper is orange-red and acquires a reddish tarnish when exposed to air. This is due to the low plasma frequency of the metal, which lies in the red part of the visible spectrum, causing it to absorb the higher-frequency green and blue colors.
As with other metals, if copper is put in contact with another metal in the presence of an electrolyte, galvanic corrosion will occur.
Chemical
Copper does not react with water, but it does slowly react with atmospheric oxygen to form a layer of brown-black copper oxide which, unlike the rust that forms on iron in moist air, protects the underlying metal from further corrosion. A green layer of verdigris can often be seen on old copper structures, such as the roofing of many older buildings and the Statue of Liberty. Copper tarnishes when exposed to some sulfur compounds, with which it reacts to form various copper sulfides.Isotopes
There are 29 isotopes of copper. and are stable, with comprising approximately 69% of naturally occurring copper; both have a spin of. The other isotopes are radioactive, with the most stable being with a half-life of 61.83 hours. Ten metastable isomers have been characterized; is the longest-lived with a half-life of 3.8 minutes. Isotopes with a mass number above 64 decay by β−, whereas those with a mass number below 64 decay by β+. Copper-64|, which has a half-life of 12.7 hours, decays both ways.and have significant applications. is used in -PTSM as a radioactive tracer for positron emission tomography.
Occurrence
Copper is produced in massive stars and is present in the Earth's crust in a proportion of about 50 parts per million. In nature, copper occurs in a variety of minerals, including native copper, copper sulfides such as chalcopyrite, bornite, digenite, covellite, and chalcocite, copper sulfosalts such as tetrahedite-tennantite, and enargite, copper carbonates such as azurite and malachite, and as copper or copper oxides such as cuprite and tenorite, respectively. The largest mass of elemental copper yet discovered weighed 420 tonnes and was found in 1857 on the Keweenaw Peninsula in Michigan, US. Native copper is a polycrystal, with the largest single crystal ever described measuring. Copper is the 26th most abundant element in Earth's crust, representing 50 ppm compared with 75 ppm for zinc, and 14 ppm for lead.Typical background concentrations of copper do not exceed in the atmosphere; in soil; in vegetation; 2 μg/L in freshwater and in seawater.
Production
Most copper is mined or extracted as copper sulfides from large open pit mines in porphyry copper deposits that contain 0.4 to 1.0% copper. Sites include Chuquicamata, in Chile, Bingham Canyon Mine, in Utah, United States, and El Chino Mine, in New Mexico, United States. According to the British Geological Survey, in 2005, Chile was the top producer of copper with at least one-third of the world share followed by the United States, Indonesia and Peru. Chile, the world's largest copper producer, supplies the US with 70% of refined copper and alloy imports through 2024. Together with Canada and Peru, they account for 94% of U.S. copper imports. Copper can also be recovered through the in-situ leach process. Several sites in the state of Arizona are considered prime candidates for this method. The amount of copper in use is increasing and the quantity available is barely sufficient to allow all countries to reach developed world levels of usage. An alternative source of copper for collection currently being researched are polymetallic nodules, which are located at the depths of the Pacific Ocean approximately 3000–6500 meters below sea level. These nodules contain other valuable metals such as cobalt and nickel.Reserves and prices
Copper has been in use for at least 10,000 years, but more than 95% of all copper ever mined and smelted has been extracted since 1900. As with many natural resources, the total amount of copper on Earth is vast, with around 1014 tons in the top kilometer of Earth's crust, which is about 5 million years' worth at the current rate of extraction. However, only a tiny fraction of these reserves is economically viable with present-day prices and technologies. Estimates of copper reserves available for mining vary from 25 to 60 years, depending on core assumptions such as the growth rate. Recycling is a major source of copper in the modern world.The price of copper is volatile. After a peak in 2022 the price unexpectedly fell. And by May 2024, the price on the London Metal Exchange has reached an all-time high above $11,000 per ton.
The global market for copper is one of the most commodified and financialized of the commodity markets, and has been so for decades. The top exporters of raw copper were Zambia and Chile, followed by Democratic Republic of the Congo. Raw copper's top importers were China, Switzerland, and India.
Copper demand
In 2024, global copper production was estimated at roughly 22.8–22.9 million metric tons. Copper demand is increasing due to the ongoing energy transition to electricity. China accounts for over half the demand.Extraction
The great majority of copper ores are sulfides. Common ores are the sulfides chalcopyrite, bornite and, to a lesser extent, covellite and chalcocite. These ores occur at the level of <1% Cu. Concentration of the ore is required, which begins with comminution followed by froth flotation. The remaining concentrate is smelted, which can be described with two simplified equations:- Cuprous sulfide is oxidized to cuprous oxide:
- Cuprous oxide reacts with cuprous sulfide to convert to blister copper upon heating:
Aside from sulfides, another family of ores are oxides. Approximately 15% of the world's copper supply derives from these oxides. The beneficiation process for oxides involves extraction with sulfuric acid solutions followed by electrolysis. In parallel with the above method for "concentrated" sulfide and oxide ores, copper is recovered from mine tailings and heaps. A variety of methods are used including leaching with sulfuric acid, ammonia, ferric chloride. Biological methods are also used.
A potential source of copper is polymetallic nodules, which have an estimated concentration 1.3%.