Commonly encountered compounds are copper(II) salts, which often impart blue or green colors to such minerals asazurite,malachite, andturquoise, and have been used widely and historically as pigments.
Copper is essential to all living organisms as a tracedietary mineral because it is a key constituent of the respiratory enzyme complexcytochrome c oxidase. Inmolluscs andcrustaceans, copper is a constituent of the blood pigmenthemocyanin, replaced by the iron-complexedhemoglobin in fish and othervertebrates. In humans, copper is found mainly in the liver, muscle, and bone.[12] The adult body contains between 1.4 and 2.1 mg of copper per kilogram of body weight.[13]
Etymology
In theRoman era, copper was mined principally onCyprus, the origin of the name of the metal, fromaes cyprium (metal of Cyprus), which later evolved intocuprum in popular Latin.Coper (Old English) andcopper were derived from this, the later spelling first used around 1530.[14]
Characteristics
Physical
A copper disc (99.95% pure) made bycontinuous casting;etched to revealcrystallitesCopper just above its melting point keeps its pink luster color when enough light outshines the orangeincandescence color.
Copper,silver, andgold are ingroup 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 highductility, and electrical and thermal conductivity. The filled d-shells in these elements contribute little to interatomic interactions, which are dominated by the s-electrons throughmetallic bonds. Unlike metals with incomplete d-shells, metallic bonds in copper are lacking acovalent character and are relatively weak. This observation explains the lowhardness and high ductility ofsingle crystals of copper.[15] At the macroscopic scale, introduction of extended defects to thecrystal 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-grainedpolycrystalline form, which has greater strength than monocrystalline forms.[16]
The softness of copper partly explains its high electrical conductivity (59.6×106S/m) and high thermal conductivity, second highest (second only to silver) among pure metals at room temperature.[17] 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.[15] The maximum possible current density of copper in open air is approximately3.1×106 A/m2, above which it begins to heat excessively.[18]
Copper is one of a few metallic elements with a natural color other than gray or silver.[19] Pure copper is orange-red and acquires a reddishtarnish when exposed to air. This is due to the lowplasma 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.[20]
As with other metals, if copper is put in contact with another metal in the presence of anelectrolyte,galvanic corrosion will occur.[21]
Chemical
Unoxidized copper wire (left) and oxidized copper wire (right)The East Tower of theRoyal Observatory, Edinburgh, showing the contrast between the refurbished copper installed in 2010 and the green color of the original 1894 copper
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 therust that forms on iron in moist air, protects the underlying metal from further corrosion (passivation). A green layer ofverdigris (copper carbonate) can often be seen on old copper structures, such as the roofing of many older buildings[22] and theStatue of Liberty.[23] Coppertarnishes when exposed to somesulfur compounds, with which it reacts to form variouscopper sulfides.[24]
There are 29isotopes of copper.63 Cu and65 Cu are stable, with63 Cu comprising approximately 69% of naturally occurring copper; both have aspin of3⁄2.[25] The other isotopes areradioactive, with the most stable being67 Cu with ahalf-life of 61.83 hours.[25] Sevenmetastable isomers have been characterized;68m Cu is the longest-lived with a half-life of 3.8 minutes. Isotopes with amass number above 64 decay byβ−, whereas those with a mass number below 64 decay byβ+.64 Cu , which has a half-life of 12.7 hours, decays both ways.[26]
Typical background concentrations of copper do not exceed1 ng/m3 in the atmosphere;150 mg/kg in soil;30 mg/kg in vegetation; 2 μg/L in freshwater and0.5 μg/L in seawater.[32]
Most copper is mined orextracted as copper sulfides from largeopen pit mines inporphyry copper deposits that contain 0.4 to 1.0% copper. Sites includeChuquicamata, in Chile,Bingham Canyon Mine, in Utah, United States, andEl Chino Mine, in New Mexico, United States. According to theBritish 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.[17] Copper can also be recovered through thein-situ leach process. Several sites in the state of Arizona are considered prime candidates for this method.[33] 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.[34] An alternative source of copper forcollection currently being researched arepolymetallic nodules, which are located at the depths of thePacific Ocean approximately 3000–6500 meters below sea level. These nodules contain other valuable metals such ascobalt andnickel.[35]
Reserves and prices
Copper has been in use for at least 10,000 years, but more than 95% of all copper ever mined andsmelted has been extracted since 1900.[36] 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.[37] Recycling is a major source of copper in the modern world.[36]
Price of Copper 1959–2022
The price of copper isvolatile.[38] After a peak in 2022 the price unexpectedly fell.[39]
The great majority of copper ores are sulfides. Common ores are the sulfides chalcopyrite (CuFeS2), bornite (Cu5FeS4) and, to a lesser extent, covellite (CuS) and chalcocite (Cu2S).[41] These ores occur at the level of <1% Cu. Concentration of the ore is required, which begins withcomminution followed byfroth flotation. The remaining concentrate is smelted, which can be described with two simplified equations:[42]
Cuprous sulfide is oxidized to cuprous oxide:
2 Cu2S + 3 O2 → 2 Cu2O + 2 SO2
Cuprous oxide reacts with cuprous sulfide to convert toblister copper upon heating:
2 Cu2O + Cu2S → 6 Cu + 2 SO2
This roasting gives matte copper, roughly 50% Cu by weight, which is purified by electrolysis. Depending on the ore, sometimes other metals are obtained during the electrolysis including platinum and gold.
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 frommine tailings and heaps. A variety of methods are used including leaching with sulfuric acid, ammonia, ferric chloride. Biological methods are also used.[42][43]
A potential source of copper is polymetallic nodules, which have an estimated concentration 1.3%.[44][45]
Flowchart of copper refining (Anode casting plant of Uralelektromed)
According to theInternational Resource Panel'sMetal Stocks in Society report, the global per capita stock of copper in use in society is 35–55 kg. Much of this is in more-developed countries (140–300 kg per capita) rather than less-developed countries (30–40 kg per capita). In 2001, a typical automobile contained 20–30 kg of copper.[42]
Likealuminium, copper is recyclable without any loss of quality, both from raw state and from manufactured products.[46] An estimated 80% of all copper ever mined is still in use today.[47] In volume, copper is the third most recycled metal after iron and aluminium.[48] As of 2023[update], recycled copper supplies about one-third of global demand.[49]
The process of recycling copper is roughly the same as is used to extract copper but requires fewer steps. High-purity scrap copper is melted in afurnace and thenreduced and cast intobillets andingots.[50] Lower-purity scrap is melted to formblack copper (70–90% pure, containing impurities such as iron, zinc, tin, and nickel), followed by oxidation of impurities in aconverter to form blister copper (96–98% pure), which is thenrefined as before.[51]: 202
Environmental impacts
The environmental cost of copper mining was estimated at 3.7 kgCO2-eq per kg of copper in 2019.[52]Codelco, a major producer in Chile, reported that in 2020 the company emitted 2.8 t CO2-eq per ton (2.8 kg CO2-eq per kg) of fine copper.[53]Greenhouse gas emissions primarily arise from electricity consumed by the company, especially when sourced from fossil fuels, and from engines required for copper extraction and refinement. Companies that mine land often mismanage waste, rendering the area sterile for life. Additionally, nearby rivers and forests are also negatively impacted. ThePhilippines is an example of a region where land is overexploited by mining companies.[54]
Copper mining waste in Valea Şesei, Romania, has significantly altered nearby water properties. The water in the affected areas is highly acidic, with a pH range of 2.1–4.9, and shows elevated electrical conductivity levels between 280 and 1561 mS/cm.[55] These changes in water chemistry make the environment inhospitable for fish, essentially rendering the water uninhabitable for aquatic life.
Alloys
Copper alloys are widely used in the production of coinage; seen here are two examples – post-1964 Americandimes, which are composed of the alloycupronickel[56] and a pre-1968Canadian dime, which is composed of an alloy of 80 percent silver and 20 percent copper.[57]
Numerous copperalloys have been formulated, many with important uses.Brass is an alloy of copper andzinc.Bronze usually refers to copper-tin alloys, but can refer to any alloy of copper such asaluminium bronze. Copper is one of the most important constituents of silver andkarat gold solders used in the jewelry industry, modifying the color, hardness and melting point of the resulting alloys.[58] Some lead-freesolders consist of tin alloyed with a small proportion of copper and other metals.[59]
The alloy of copper andnickel, calledcupronickel, is used in low-denomination coins, often for the outer cladding. The US five-cent coin (currently called anickel) consists of 75% copper and 25% nickel in homogeneous composition. Prior to the introduction of cupronickel, which was widely adopted by countries in the latter half of the 20th century,[60] alloys of copper andsilver were also used, with the United States using an alloy of 90% silver and 10% copper until 1965, when circulating silver was removed from all coins with the exception of the half dollar—these were debased to an alloy of 40% silver and 60% copper between 1965 and 1970.[61] The alloy of 90% copper and 10% nickel, remarkable for its resistance to corrosion, is used for various objects exposed to seawater, though it is vulnerable to the sulfides sometimes found in polluted harbors and estuaries.[62] Alloys of copper with aluminium (about 7%) have a golden color and are used in decorations.[29]Shakudō is a Japanese decorative alloy of copper containing a low percentage of gold, typically 4–10%, that can bepatinated to a dark blue or black color.[63]
Copper forms a rich variety of compounds, usually withoxidation states +1 and +2, which are often calledcuprous andcupric, respectively.[64] Copper compounds promote or catalyse numerous chemical and biological processes.[65]
Binary compounds
As with other elements, the simplest compounds of copper are binary compounds, i.e. those containing only two elements, the principal examples being oxides, sulfides, andhalides. Bothcuprous andcupric oxides are known. Among the numerouscopper sulfides,[66] important examples includecopper(I) sulfide (Cu2S) andcopper monosulfide (CuS).[67]
Copper(II) gives a deep blue coloration in the presence of ammonia ligands. The one used here istetraamminecopper(II) sulfate.
Copper formscoordination complexes withligands. In aqueous solution, copper(II) exists as[Cu(H 2O) 6]2+ . This complex exhibits the fastest water exchange rate (speed of water ligands attaching and detaching) for any transitionmetal aquo complex. Adding aqueoussodium hydroxide causes the precipitation of light blue solidcopper(II) hydroxide. A simplified equation is:
Pourbaix diagram for copper in uncomplexed media (anions other than OH- not considered). Ion concentration 0.001 m (mol/kg water). Temperature 25 °C.
Copper(III) is most often found in oxides. A simple example is potassiumcuprate, KCuO2, a blue-black solid.[81] The most extensively studied copper(III) compounds are thecuprate superconductors.Yttrium barium copper oxide (YBa2Cu3O7) consists of both Cu(II) and Cu(III) centres. Like oxide,fluoride is a highlybasicanion[82] and is known to stabilize metal ions in high oxidation states. Both copper(III) and even copper(IV) fluorides are known,K3CuF6 andCs2CuF6, respectively.[64]
Some copper proteins formoxo complexes, which, in extensively studied synthetic analog systems, feature copper(III).[83][84] Withtetrapeptides, purple-colored copper(III) complexes are stabilized by the deprotonatedamide ligands.[85]
Copper occurs naturally asnative metallic copper and was known to some of the oldest civilizations on record. The history of copper use dates to 9000 BC in the Middle East;[90] a copper pendant was found in northern Iraq that dates to 8700 BC.[91] Evidence suggests that gold andmeteoric iron (but not smelted iron) were the only metals used by humans before copper.[92] The history of copper metallurgy is thought to follow this sequence: first,cold working of native copper, thenannealing,smelting, and, finally,lost-wax casting. In southeasternAnatolia, all four of these techniques appear more or less simultaneously at the beginning of theNeolithicc. 7500 BC.[93]
Copper smelting was independently invented in different places. The earliest evidence oflost-wax casting copper comes from an amulet found inMehrgarh, Pakistan, and is dated to 4000 BC.[94]Investment casting was invented in 4500–4000 BC in Southeast Asia[90] Smelting was probably discovered in China before 2800 BC, in Central America around 600 AD, and in West Africa about the 9th or 10th century AD.[95]Carbon dating has established mining atAlderley Edge inCheshire, UK, at 2280 to 1890 BC.[96]
While scholars have long believed that major changes in supra-regional networks occurred with the onset of theBronze Age (due to the need for bronze), it is now clear that even the early copper in Europe was associated with intensified networks. The copper that reached the Alps, central and northern Europe in the fourth millennium BC was mined in Bulgaria and Serbia.[97]
Ötzi the Iceman, a male dated from 3300 to 3200 BC, was found with an axe with a copper head 99.7% pure; high levels ofarsenic in his hair suggest an involvement in copper smelting.[98] Experience with copper has assisted the development of other metals; in particular, copper smelting likely led to the discovery ofiron smelting.[98]
Copper artifacts from theOld Copper Complex of North America, which may have existed from approximately 9500–5400 years before present
Production in theOld Copper Complex in Michigan and Wisconsin is dated between 6500 and 3000 BC.[99][100][101] A copper spearpoint found in Wisconsin has been dated to 6500 BC.[99] Copper usage by the indigenous peoples of the Old Copper Complex from theGreat Lakes region of North America has been radiometrically dated to as far back as 7500 BC.[99][102][103] Indigenous peoples of North America around theGreat Lakes may have also been mining copper during this time, making it one of the oldest known examples ofcopper extraction in the world.[104] There is evidence from prehistoric lead pollution from lakes in Michigan that people in the region began mining copperc. 6000 BC.[104][99] Evidence suggests that utilitarian copper objects fell increasingly out of use in the Old Copper Complex of North America during the Bronze Age and a shift towards an increased production of ornamental copper objects occurred.[105]
Natural bronze, a type of copper made from ores rich in silicon, arsenic, and (rarely) tin, came into general use in the Balkans around 5500 BC.[106] Alloying copper with tin to make bronze was first practiced about 4000 years after the discovery of copper smelting, and about 2000 years after "natural bronze" had come into general use.[107] Bronze artifacts from theVinča culture date to 4500 BC.[108]Sumerian andEgyptian artifacts of copper and bronze alloys date to 3000 BC.[109]Egyptian Blue, or cuprorivaite (calcium copper silicate) is a synthetic pigment that contains copper and started being used inancient Egypt around 3250 BC.[110] The manufacturing process of Egyptian blue was known to the Romans, but by the fourth century AD the pigment fell out of use and the secret to its manufacturing process became lost. The Romans said the blue pigment was made from copper, silica, lime andnatron and was known to them ascaeruleum.
TheBronze Age began in Southeastern Europe around 3700–3300 BC, in Northwestern Europe about 2500 BC. It ended with the beginning of the Iron Age, 2000–1000 BC in the Near East, and 600 BC in Northern Europe. The transition between theNeolithic period and the Bronze Age was formerly termed theChalcolithic period (copper-stone), when copper tools were used with stone tools. The term has gradually fallen out of favor because in some parts of the world, the Chalcolithic and Neolithic are coterminous at both ends. Brass, an alloy of copper and zinc, is of much more recent origin. It was known to the Greeks, but became a significant supplement to bronze during the Roman Empire.[109]
In Greece, copper was known by the namechalkos (χαλκός). It was an important resource for the Romans, Greeks and other ancient peoples. In Roman times, it was known asaes Cyprium,aes being the generic Latin term for copper alloys andCyprium fromCyprus, where much copper was mined. The phrase was simplified tocuprum, hence the Englishcopper.Aphrodite (Venus in Rome) represented copper in mythology and alchemy because of its lustrous beauty and its ancient use in producing mirrors; Cyprus, the source of copper, was sacred to the goddess. The seven heavenly bodies known to the ancients were associated with the seven metals known in antiquity, and Venus was assigned to copper, both because of the connection to the goddess and because Venus was the brightest heavenly body after the Sun and Moon and so corresponded to the most lustrous and desirable metal after gold and silver.[111]
Copper was first mined in ancient Britain as early as 2100 BC. Mining at the largest of these mines, theGreat Orme, continued into the late Bronze Age. Mining seems to have been largely restricted tosupergene ores, which were easier to smelt. The rich copper deposits ofCornwall seem to have been largely untouched, in spite of extensivetin mining in the region, for reasons likely social and political rather than technological.[112]
In North America, native copper is known to have been extracted from sites onIsle Royale with primitive stone tools between 800 and 1600 AD.[113] Copper annealing was being performed in the North American city ofCahokia around 1000–1300 AD.[114] There are several exquisite copper plates, known as theMississippian copper plates that have been found in North America in the area around Cahokia dating from this time period (1000–1300 AD).[114] The copper plates were thought to have been manufactured at Cahokia before ending up elsewhere in the Midwest and southeastern United States like theWulfing cache andEtowah plates.
In South America a copper mask dated to 1000 BC found in the Argentinian Andes is the oldest known copper artifact discovered in the Andes.[115] Peru has been considered the origin for early coppermetallurgy in pre-Columbian America, but the copper mask from Argentina suggests that theCajón del Maipo of the southern Andes was another important center for early copper workings in South America.[115] Copper metallurgy was flourishing in South America, particularly in Peru around 1000 AD. Copper burial ornamentals from the 15th century have been uncovered, but the metal's commercial production did not start until the early 20th century.[citation needed]
The cultural role of copper has been important, particularly in currency. Romans in the 6th through 3rd centuries BC used copper lumps as money. At first, the copper itself was valued, but gradually the shape and look of the copper became more important.Julius Caesar had his own coins made from brass, whileOctavianus Augustus Caesar's coins were made from Cu-Pb-Sn alloys. With an estimated annual output of around 15,000 t,Roman copper mining and smelting activities reached a scale unsurpassed until the time of theIndustrial Revolution; theprovinces most intensely mined were those ofHispania, Cyprus and in Central Europe.[116][117]
Acid mine drainage affecting the stream running from the disusedParys Mountain copper mines 18th-century copperkettle from Norway made from Swedish copper
TheGreat Copper Mountain was a mine in Falun, Sweden, that operated from the 10th century to 1992. It satisfied two-thirds of Europe's copper consumption in the 17th century and helped fund many of Sweden's wars during that time.[119] It was referred to as the nation's treasury; Sweden had acopper backed currency.[120]
Chalcography of the city ofVyborg at the turn of the 17th and 18th centuries. The year 1709 carved on the printing plate.
Copper is used in roofing,[22] currency, and for photographic technology known as thedaguerreotype. Copper was used inRenaissance sculpture, and was used to construct theStatue of Liberty; copper continues to be used in construction of various types.Copper plating andcopper sheathing were widely used to protect the under-water hulls of ships, a technique pioneered by the British Admiralty in the 18th century.[121] TheNorddeutsche Affinerie in Hamburg was the first modernelectroplating plant, starting its production in 1876.[122] The German scientistGottfried Osann inventedpowder metallurgy in 1830 while determining the metal's atomic mass; around then it was discovered that the amount and type of alloying element (e.g., tin) to copper would affect bell tones.[citation needed]
During the rise in demand for copper for the Age of Electricity, from the 1880s until the Great Depression of the 1930s, the United States produced one third to half the world's newly mined copper.[123] Major districts included the Keweenaw district of northern Michigan, primarily native copper deposits, which was eclipsed by the vast sulphide deposits ofButte, Montana, in the late 1880s, which itself was eclipsed by porphyry deposits of the Southwest United States, especially atBingham Canyon, Utah, andMorenci, Arizona. Introduction of open pit steam shovel mining and innovations in smelting, refining, flotation concentration and other processing steps led to mass production. Early in the twentieth century,Arizona ranked first, followed byMontana, thenUtah andMichigan.[124]
Flash smelting was developed byOutokumpu in Finland and first applied atHarjavalta in 1949; the energy-efficient process accounts for 50% of the world's primary copper production.[125]
TheIntergovernmental Council of Copper Exporting Countries, formed in 1967 by Chile, Peru, Zaire and Zambia, operated in the copper market asOPEC does in oil, though it never achieved the same influence, particularly because the second-largest producer, the United States, was never a member; it was dissolved in 1988.[126]
In 2008, China became the world's largest importer of copper and has continued to be as of at least 2023.[127]: 187
For some purposes, other metals can substitute,aluminium wire was substituted in many applications, but improper design resulted in fire hazards.[131] The safety issues have since been solved by use of larger sizes of aluminium wire (#8AWG and up), and properly designed aluminium wiring is still being installed in place of copper. For example, theAirbus A380 uses aluminum wire in place of copper wire for electrical power transmission.[132]
Speculative investing
Copper may be used as a speculative investment due to the predicted increase in use from worldwide infrastructure growth, and the important role it has in producingwind turbines,solar panels, and otherrenewable energy sources.[133][134] Another reason predicted demand increases is the fact thatelectric cars contain an average of 3.6 times as much copper as conventional cars, although the effect ofelectric cars on copper demand is debated.[135][136] Some people invest in copper through copper mining stocks,ETFs, andfutures. Others store physical copper in the form of copper bars or rounds although these tend to carry a higher premium in comparison to precious metals.[137] Those who want to avoid the premiums of copperbullion alternatively store oldcopper wire,copper tubing or Americanpennies made before 1982.[138]
Copper fittings for soldered plumbing jointsA very large copper seal end cap
The major applications of copper are electrical wire (60%), roofing and plumbing (20%), and industrial machinery (15%). Copper is used mostly as a pure metal, but when greater hardness is required, it is put into such alloys asbrass andbronze (5% of total use).[29] For more than two centuries, copper paint has been used on boat hulls to control the growth of plants and shellfish.[139] A small part of the copper supply is used for nutritional supplements and fungicides in agriculture.[68][140]Machining of copper is possible, although alloys are preferred for goodmachinability in creating intricate parts.
For a short period from the late 1960s to the late 1970s, copper wiring was replaced byaluminium wiring in many housing construction projects in America. The new wiring was implicated in a number of house fires and the industry returned to copper.[146]
Electronics and related devices
Copper electricalbusbars distributing power to a large building
Copper's superiorconductivity enhances the efficiency of electricalmotors.[148] This is important because motors and motor-driven systems account for 43–46% of all global electricity consumption and 69% of all electricity used by industry.[149] Increasing the mass and cross section of copper in acoil increases the efficiency of the motor.Copper motor rotors, a new technology designed for motor applications where energy savings are prime design objectives,[150][151] are enabling general-purposeinduction motors to meet and exceedNational Electrical Manufacturers Association (NEMA)premium efficiency standards.[152]
Copper plays an important role in these renewable energy systems,[155][156][157][158][159] mainly for cables and pipes. Copper usage averages up to five times more in renewable energy systems than in traditional power generation, such as fossil fuel andnuclear power plants.[160] Since copper is an excellentthermal andelectrical conductor among engineering metals (second only to silver),[161] electrical systems that utilize copper generate and transmit energy with high efficiency and with minimum environmental impacts.
When choosing electrical conductors, facility planners and engineers factor capital investment costs of materials against operational savings due to their electrical energy efficiencies over their useful lives, plus maintenance costs. Copper often fares well in these calculations. A factor called "copper usage intensity," is a measure of the quantity of copper necessary to install one megawatt of new power-generating capacity.
Copper wires for recycling
When planning for a new renewable power facility, engineers and product specifiers seek to avoid supply shortages of selected materials. According to theUnited States Geological Survey, in-ground copperreserves have increased more than 700% since 1950, from almost 100 million tonnes to 720 million tonnes in 2017, despite the fact that world refined usage has more than tripled in the last 50 years.[162] Copper resources are estimated to exceed 5,000 million tonnes.[163][164]
Bolstering the supply fromcopper extraction is the more than 30 percent of copper installed from 2007 to 2017 that came from recycled sources.[165] Itsrecycling rate is higher than any other metal.[166]
The metal's distinctive natural greenpatina has long been coveted by architects and designers. The final patina is a particularly durable layer that is highly resistant to atmospheric corrosion, thereby protecting the underlying metal against further weathering.[171][172][173] It can be a mixture of carbonate and sulfate compounds in various amounts, depending upon environmental conditions such as sulfur-containing acid rain.[174][175][176][177] Architectural copper and its alloys can also be'finished' to take on a particular look, feel, or color. Finishes include mechanical surface treatments, chemical coloring, and coatings.[178]
Copper isbiostatic, meaning bacteria and many other forms of life will not grow on it. For this reason it has long been used to line parts of ships to protect againstbarnacles andmussels. It was originally used pure, but has since been superseded byMuntz metal and copper-based paint. Similarly, as discussed incopper alloys in aquaculture, copper alloys have become important netting materials in theaquaculture industry because they areantimicrobial and preventbiofouling, even in extreme conditions[180] and have strong structural andcorrosion-resistant[181] properties in marine environments.
Copper-alloy touch surfaces have natural properties that destroy a wide range ofmicroorganisms (e.g.,E. coli O157:H7,methicillin-resistantStaphylococcus aureus (MRSA),Staphylococcus,Clostridium difficile,influenza A virus,adenovirus,SARS-CoV-2, andfungi).[182][183] Indians have been using copper vessels since ancient times for storing water, even before modern science realized its antimicrobial properties.[184] Some copper alloys were proven to kill more than 99.9% of disease-causing bacteria within just two hours when cleaned regularly.[185] TheUnited States Environmental Protection Agency (EPA) has approved the registrations of these copper alloys as "antimicrobial materials with public health benefits";[185] that approval allows manufacturers to make legal claims to the public health benefits of products made of registered alloys. In addition, the EPA has approved a long list of antimicrobial copper products made from these alloys, such as bedrails,handrails, over-bed tables,sinks,faucets,door knobs,toilet hardware,computer keyboards,health club equipment, andshopping cart handles. Copper doorknobs are used by hospitals to reduce the transfer of disease, andLegionnaires' disease is suppressed by copper tubing in plumbing systems.[186] Antimicrobial copper alloy products are now being installed in healthcare facilities in the U.K., Ireland, Japan, Korea, France, Denmark, and Brazil, as well as being called for in the US,[187] and in the subway transit system in Santiago, Chile, where copper–zinc alloy handrails were installed in some 30 stations between 2011 and 2014.[188][189][190]Textile fibers can be blended with copper to create antimicrobial protective fabrics.[191][unreliable source?]
Folk medicine
Copper is commonly used in jewelry, and according to some folklore, copper bracelets relievearthritis symptoms.[192] In one trial for osteoarthritis and one trial for rheumatoid arthritis, no differences were found between copper bracelet and control (non-copper) bracelet.[193][194] No evidence shows that copper can be absorbed through the skin. If it were, it might lead tocopper poisoning.[195]
Degradation
Chromobacterium violaceum andPseudomonas fluorescens can both mobilize solid copper as a cyanide compound.[196] The ericoid mycorrhizal fungi associated withCalluna,Erica andVaccinium can grow in metalliferous soils containing copper.[196] The ectomycorrhizal fungusSuillus luteus protects young pine trees from copper toxicity. A sample of the fungusAspergillus niger was found growing from gold mining solution and was found to contain cyano complexes of such metals as gold, silver, copper, iron, and zinc. The fungus also plays a role in the solubilization of heavy metal sulfides.[197]
Rich sources of copper include oysters, beef and lamb liver, Brazil nuts, blackstrap molasses, cocoa, and black pepper. Good sources include lobster, nuts and sunflower seeds, green olives, avocados, and wheat bran.
Biochemistry
Copper proteins have diverse roles in biological electron transport and oxygen transportation, processes that exploit the easy interconversion of Cu(I) and Cu(II).[198] Copper is essential in the aerobicrespiration of alleukaryotes. Inmitochondria, it is found incytochrome c oxidase, which is the last protein inoxidative phosphorylation. Cytochrome c oxidase is the protein that binds the O2 between a copper and an iron; the protein transfers 4 electrons to the O2 molecule to reduce it to two molecules of water. Copper is also found in manysuperoxide dismutases, proteins that catalyze the decomposition ofsuperoxides by converting it (bydisproportionation) to oxygen andhydrogen peroxide:
Cu2+-SOD + O2− → Cu+-SOD + O2 (reduction of copper; oxidation of superoxide)
Cu+-SOD + O2− + 2H+ → Cu2+-SOD + H2O2 (oxidation of copper; reduction of superoxide)
The proteinhemocyanin is the oxygen carrier in mostmollusks and somearthropods such as thehorseshoe crab (Limulus polyphemus).[199] Because hemocyanin is blue, these organisms have blue blood rather than the red blood of iron-basedhemoglobin. Structurally related to hemocyanin are thelaccases andtyrosinases. Instead of reversibly binding oxygen, these proteins hydroxylate substrates, illustrated by their role in the formation oflacquers.[200] The biological role for copper commenced with the appearance of oxygen in Earth's atmosphere.[201] Several copper proteins, such as the "blue copper proteins", do not interact directly with substrates; hence they are not enzymes. These proteins relay electrons by the process calledelectron transfer.[200]
Photosynthesis functions by an elaborate electron transport chain within thethylakoid membrane. A central link in this chain isplastocyanin, a blue copper protein.
Chemical compounds which were developed for treatment of Wilson's disease have been investigated for use in cancer therapy.[203]
Nutrition
Copper is an essentialtrace element in plants and animals, but not all microorganisms. The human body contains copper at a level of about 1.4 to 2.1 mg per kg of body mass.[204]
Absorption
Copper is absorbed in the gut, then transported to the liver bound toalbumin.[205] After processing in the liver, copper is distributed to other tissues in a second phase, which involves the proteinceruloplasmin, carrying the majority of copper in blood. Ceruloplasmin also carries the copper that is excreted in milk, and is particularly well-absorbed as a copper source.[206] Copper in the body normally undergoesenterohepatic circulation (about 5 mg a day, vs. about 1 mg per day absorbed in the diet and excreted from the body), and the body is able to excrete some excess copper, if needed, viabile, which carries some copper out of the liver that is not then reabsorbed by the intestine.[207][208]
Dietary recommendations
TheU.S. Institute of Medicine (IOM) updated the estimated average requirements (EARs) and recommended dietary allowances (RDAs) for copper in 2001. If there is not sufficient information to establish EARs and RDAs, an estimate designatedAdequate Intake (AI) is used instead. The AIs for copper are: 200 μg of copper for 0–6-month-old males and females, and 220 μg of copper for 7–12-month-old males and females. For both sexes, the RDAs for copper are: 340 μg of copper for 1–3 years old, 440 μg of copper for 4–8 years old, 700 μg of copper for 9–13 years old, 890 μg of copper for 14–18 years old and 900 μg of copper for ages 19 years and older. For pregnancy, 1,000 μg. For lactation, 1,300 μg.[209] As for safety, the IOM also setstolerable upper intake levels (ULs) for vitamins and minerals when evidence is sufficient. In the case of copper, the UL is set at 10 mg/day. Collectively the EARs, RDAs, AIs and ULs are referred to asDietary Reference Intakes.[210]
TheEuropean Food Safety Authority (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR. AI and UL are defined the same as in the United States. For women and men ages 18 and older, the AIs are set at 1.3 and 1.6 mg/day, respectively. AIs for pregnancy and lactation is 1.5 mg/day. For children ages 1–17 years, the AIs increase with age from 0.7 to 1.3 mg/day. These AIs are higher than the U.S. RDAs.[211] The European Food Safety Authority reviewed the same safety question and set its UL at 5 mg/day, which is half the U.S. value.[212]
For U.S. food and dietary supplement labeling purposes, the amount in a serving is expressed as a percent of Daily Value (%DV). For copper labeling purposes, 100% of the Daily Value was 2.0 mg, but as of May 27, 2016[update], it was revised to 0.9 mg to bring it into agreement with the RDA.[213][214] A table of the old and new adult daily values is provided atReference Daily Intake.
Deficiency
Because of its role in facilitating iron uptake,copper deficiency can produceanemia-like symptoms,neutropenia, bone abnormalities, hypopigmentation, impaired growth, increased incidence of infections, osteoporosis, hyperthyroidism, and abnormalities in glucose and cholesterol metabolism. Conversely,Wilson's disease causes an accumulation of copper in body tissues.
Severe deficiency can be found by testing for low plasma or serum copper levels, low ceruloplasmin, and low red blood cell superoxide dismutase levels; these are not sensitive to marginal copper status. The "cytochrome c oxidase activity of leucocytes and platelets" has been stated as another factor in deficiency, but the results have not been confirmed by replication.[215]
Gram quantities of various copper salts have been taken in suicide attempts and produced acute copper toxicity in humans, possibly due to redox cycling and the generation ofreactive oxygen species that damageDNA.[216][217] Corresponding amounts of copper salts (30 mg/kg) are toxic in animals.[218] A minimum dietary value for healthy growth in rabbits has been reported to be at least 3 ppm in the diet.[219] However, higher concentrations of copper (100 ppm, 200 ppm, or 500 ppm) in the diet of rabbits may favorably influencefeed conversion efficiency, growth rates, and carcass dressing percentages.[220]
Chronic copper toxicity does not normally occur in humans because of transport systems that regulate absorption and excretion. Autosomal recessive mutations in copper transport proteins can disable these systems, leading toWilson's disease with copper accumulation andcirrhosis of the liver in persons who have inherited two defective genes.[204]
Copper is a constituent oftobacco smoke.[225][226] Thetobacco plant readily absorbs and accumulatesheavy metals, such as copper from the surrounding soil into its leaves. These are readily absorbed into the user's body following smoke inhalation.[227] The health implications are not clear.[228]
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Copper.org – official website of the Copper Development Association, a North American industry association with an extensive site of properties and uses of copper
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