Zinc/ja: Difference between revisions

亜鉛の[[Binary compound/ja|二元化合物]]は、ほとんどの[[metalloid/ja|メタロイド]]と[[noble gas/ja|希ガス]]を除くすべての[[Nonmetal (chemistry)/ja|非金属]]で知られている。酸化物[[zinc oxide/ja|ZnO]]は白色の粉末で、中性の水溶液にはほとんど溶けないが、[[amphoteric/ja|両性]]であり、強い塩基性溶液にも酸性溶液にも溶ける。他の[[chalcogen/ja|カルコゲン]]化物（[[zinc sulfide/ja|ZnS]]、[[zinc selenide/ja|ZnSe]]、[[zinc telluride/ja|ZnTe]]）は電子工学や光学で様々な用途がある。また、[[Zinc nitride/ja|{{chem|Zn|3|N|2}}]、[[zinc phosphide/ja|{{chem|Zn|3|P|2}}]、[[zinc arsenide/ja|{chem|Zn|3|As|2}}]などの[[Pnictogenide/ja|ニクトゲン化物]]材料もある、また、[[zinc antimonide/ja|{chem|Zn|3|Sb|2}}]、過酸化物（[[zinc peroxide/ja|{{Chem|ZnO|2}}]）、水素化物（[[zinc hydride/ja|{Chem|ZnH|2}}]）、炭化物（{{Chem|ZnC|2}}）も知られている。4つの[[halide/ja|ハロゲン化物]]のうち、[[zinc fluoride/ja|{{化学式|ZnF|2}}]は最もイオン的な性質を持ち、他のもの（[[zinc chloride/ja|{{化学式|ZnCl|2}}]、[[zinc bromide/ja|{{化学式|ZnBr|2}}]、[[zinc iodide/ja|{{化学式|ZnI|2}}]）は比較的融点が低く、共有結合的な性質が強いと考えられている。

Cobalticyanide paper (Rinnmann's test for Zn) can be used as a chemical indicator for zinc. 4 g of K₃Co(CN)₆ and 1 g of KClO₃ is dissolved on 100 ml of water. Paper is dipped in the solution and dried at 100 °C. One drop of the sample is dropped onto the dry paper and heated. A green disc indicates the presence of zinc.

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==History==

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===Ancient use===

Various isolated examples of the use of impure zinc in ancient times have been discovered. Zinc ores were used to make the zinc–copper alloy [[brass]] thousands of years prior to the discovery of zinc as a separate element. Judean brass from the 14th to 10th centuries&nbsp;BC contains 23% zinc.

Knowledge of how to produce brass spread to [[Ancient Greece]] by the 7th&nbsp;century&nbsp;BC, but few varieties were made. Ornaments made of [[alloy]]s containing 80–90% zinc, with lead, iron, [[antimony]], and other metals making up the remainder, have been found that are 2,500 years old.

[[Strabo]] writing in the 1st century BC (but quoting a now lost work of the 4th century BC historian [[Theopompus]]) mentions "drops of false silver" which when mixed with copper make brass. This may refer to small quantities of zinc that is a by-product of smelting [[sulfide]] ores.

The manufacture of brass was known to the [[Ancient Rome|Romans]] by about 30&nbsp;BC. They made brass by heating powdered [[Calamine (mineral)|calamine]] (zinc [[silicate]] or carbonate), charcoal and copper together in a crucible. The resulting [[calamine brass]] was then either cast or hammered into shape for use in weaponry. Some coins struck by Romans in the Christian era are made of what is probably calamine brass.

[[File:Hemmoorer Eimer.jpg|upright|thumb|Late Roman brass bucket – the [[Hemmoor]]er Eimer from Warstade, Germany, second to third century AD|alt=Large black bowl-shaped bucket on a stand. The bucket has incrustation around its top.]]

The oldest known pills were made of the zinc carbonates hydrozincite and smithsonite. The pills were used for sore eyes and were found aboard the Roman ship [[Relitto del Pozzino]], wrecked in 140&nbsp;BC.

The [[Berne zinc tablet]] is a votive plaque dating to [[Roman Gaul]] made of an alloy that is mostly zinc.

The [[Charaka Samhita]], thought to have been written between 300 and 500&nbsp;AD, mentions a metal which, when oxidized, produces ''pushpanjan'', thought to be zinc oxide. Zinc mines at Zawar, near [[Udaipur]] in India, have been active since the [[Mauryan period]] ({{circa| 322}} and 187&nbsp;BC). The smelting of metallic zinc here, however, appears to have begun around the 12th century AD. One estimate is that this location produced an estimated million tonnes of metallic zinc and zinc oxide from the 12th to 16th centuries. Another estimate gives a total production of 60,000 tonnes of metallic zinc over this period. The [[Rasaratna Samuccaya]], written in approximately the 13th century AD, mentions two types of zinc-containing ores: one used for metal extraction and another used for medicinal purposes.

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===Early studies and naming===

Zinc was distinctly recognized as a metal under the designation of ''Yasada'' or Jasada in the medical Lexicon ascribed to the Hindu king Madanapala (of Taka dynasty) and written about the year 1374. Smelting and extraction of impure zinc by reducing calamine with wool and other organic substances was accomplished in the 13th century in India. The Chinese did not learn of the technique until the 17th century.

[[File:Zinc symbol (fixed width).svg|thumb|left|[[Alchemical symbol]] for the element zinc]]

[[Alchemy|Alchemists]] burned zinc metal in air and collected the resulting zinc oxide on a [[Condenser (heat transfer)|condenser]]. Some alchemists called this zinc oxide {{lang|la|lana philosophica}}, Latin for "philosopher's wool", because it collected in wooly tufts, whereas others thought it looked like white snow and named it ''nix album''.

The name of the metal was probably first documented by [[Paracelsus]], a Swiss-born German alchemist, who referred to the metal as "zincum" or "zinken" in his book ''Liber Mineralium II'', in the 16th century. The word is probably derived from the German {{lang|de|zinke}}, and supposedly meant "tooth-like, pointed or jagged" (metallic zinc crystals have a needle-like appearance). ''Zink'' could also imply "tin-like" because of its relation to German {{lang|de|zinn}} meaning tin. Yet another possibility is that the word is derived from the [[Persian language|Persian]] word {{lang|fa|سنگ}} ''seng'' meaning stone. The metal was also called ''Indian tin'', ''tutanego'', ''calamine'', and ''spinter''.

German metallurgist [[Andreas Libavius]] received a quantity of what he called "calay" (from the Malay or Hindi word for tin) originating from [[Malabar Coast|Malabar]] off a cargo ship captured from the Portuguese in the year 1596. Libavius described the properties of the sample, which may have been zinc. Zinc was regularly imported to Europe from the Orient in the 17th and early 18th centuries, but was at times very expensive.

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===Isolation===

[[File:Andreas Sigismund Marggraf-flip.jpg|thumb|upright|[[Andreas Sigismund Marggraf]] is given credit for first isolating pure zinc.|alt=Picture of an old man head (profile). The man has a long face, short hair and tall forehead.]]

Metallic zinc was isolated in India by 1300&nbsp;AD. Before it was isolated in Europe, it was imported from India in about 1600&nbsp;AD. [[Postlewayt]]'s ''Universal Dictionary'', a contemporary source giving technological information in Europe, did not mention zinc before 1751 but the element was studied before then.

Flemish [[metallurgist]] and [[alchemist]] [[P. M. de Respour]] reported that he had extracted metallic zinc from zinc oxide in 1668. By the start of the 18th century, [[Étienne François Geoffroy]] described how zinc oxide condenses as yellow crystals on bars of iron placed above zinc ore that is being smelted. In Britain, [[John Lane (metallurgist)|John Lane]] is said to have carried out experiments to smelt zinc, probably at [[Landore]], prior to his bankruptcy in 1726.

In 1738 in Great Britain, [[William Champion (metallurgist)|William Champion]] patented a process to extract zinc from calamine in a vertical [[retort]]-style smelter. His technique resembled that used at Zawar zinc mines in [[Rajasthan]], but no evidence suggests he visited the Orient. Champion's process was used through 1851.

German chemist [[Andreas Sigismund Marggraf|Andreas Marggraf]] normally gets credit for isolating pure metallic zinc in the West, even though Swedish chemist Anton von Swab had distilled zinc from calamine four years previously. In his 1746 experiment, Marggraf heated a mixture of calamine and charcoal in a closed vessel without copper to obtain a metal.

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===Later work===

[[File:Luigi Galvani, oil-painting.jpg|thumb|upright|left|[[Galvanization]] was named after [[Luigi Galvani]].|alt=Painting of a middle-aged man sitting by the table, wearing a wig, black jacket, white shirt and white scarf.]]

William Champion's brother, John, patented a process in 1758 for [[calcining]] zinc sulfide into an oxide usable in the retort process. Prior to this, only calamine could be used to produce zinc. In 1798, [[Johann Christian Ruberg]] improved on the smelting process by building the first horizontal retort smelter. [[Jean-Jacques Daniel Dony]] built a different kind of horizontal zinc smelter in Belgium that processed even more zinc.

Italian doctor [[Luigi Galvani]] discovered in 1780 that connecting the [[spinal cord]] of a freshly dissected frog to an iron rail attached by a brass hook caused the frog's leg to twitch. He incorrectly thought he had discovered an ability of nerves and muscles to create [[electricity]] and called the effect "[[bioelectricity|animal electricity]]". The galvanic cell and the process of galvanization were both named for Luigi Galvani, and his discoveries paved the way for [[Battery (electricity)|electrical batteries]], galvanization, and [[cathodic protection]].

Galvani's friend, [[Alessandro Volta]], continued researching the effect and invented the [[Voltaic pile]] in 1800. Volta's pile consisted of a stack of simplified [[galvanic cell]]s, each being one plate of copper and one of zinc connected by an [[electrolyte]]. By stacking these units in series, the Voltaic pile (or "battery") as a whole had a higher voltage, which could be used more easily than single cells. Electricity is produced because the [[Volta potential]] between the two metal plates makes [[electron]]s flow from the zinc to the copper and corrode the zinc.

The non-magnetic character of zinc and its lack of color in solution delayed discovery of its importance to biochemistry and nutrition. This changed in 1940 when [[carbonic anhydrase]], an enzyme that scrubs carbon dioxide from blood, was shown to have zinc in its [[active site]].

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==Production==

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===Mining and processing===

|+ Top zinc mine production output (by countries) 2019

! [[Ranking|Rank]] !![[Country]] !![[Tonne]]s

| '''1'''||'''[[China]]''' ||align="right"| '''4,210,000'''

| '''2'''||'''[[Peru]]''' ||align="right"| '''1,400,000'''

| '''3'''||'''[[Australia]]''' ||align="right"| '''1,330,000'''

| '''4'''||'''[[United States]]'''|| align="right" | '''753,000'''

| '''5'''||'''[[India]]'''|| align="right" | '''720,000'''

| '''6'''||'''[[Mexico]]''' ||align="right"| '''677,000'''

{{Main|Zinc mining|Zinc smelting}}

{{See also|List of countries by zinc production}}

[[File:Price of Zinc.webp|thumb|325px|right|Price of Zinc]]

[[File:World Zinc Production 2006.svg|thumb|upright=1.6|Percentage of zinc output in 2006 by countries|alt=World map revealing that about 40% of zinc is produced in China, 20% in Australia, 20% in Peru, and 5% in US, Canada and Kazakhstan each.]]

[[File:Zinc world production.svg|thumb|lang=en|World production trend]]

[[File:Zink Mine Rosh Pinah.jpg|thumb|Zinc Mine Rosh Pinah, [[Namibia]]<br />{{coord|27|57|17|S|016|46|00|E|region:NA_type:landmark|name=Rosh Pinah}}]]

[[File:Skorpion Zink Mine.jpg|thumb|Zinc Mine Skorpion, [[Namibia]]<br />{{coord|27|49|09|S|016|36|28|E|region:NA_type:landmark|name=Skorpion}}]]

Zinc is the fourth most common metal in use, trailing only [[iron]], [[aluminium]], and [[copper]] with an annual production of about 13&nbsp;million tonnes. The world's largest zinc producer is [[Nyrstar]], a merger of the Australian [[OZ Minerals]] and the Belgian [[Umicore]]. About 70% of the world's zinc originates from mining, while the remaining 30% comes from recycling secondary zinc.

Commercially pure zinc is known as Special High Grade, often abbreviated ''SHG'', and is 99.995% pure.

Worldwide, 95% of new zinc is mined from [[sulfide|sulfidic]] ore deposits, in which sphalerite (ZnS) is nearly always mixed with the sulfides of copper, lead and iron. Zinc mines are scattered throughout the world, with the main areas being China, Australia, and Peru. China produced 38% of the global zinc output in 2014.

Zinc metal is produced using [[extractive metallurgy]]. The ore is finely ground, then put through [[froth flotation]] to separate minerals from [[gangue]] (on the property of [[hydrophobicity]]), to get a zinc sulfide ore concentrate consisting of about 50% zinc, 32% sulfur, 13% iron, and 5% {{chem|SiO|2}}.

[[Roasting (metallurgy)|Roasting]] converts the zinc sulfide concentrate to zinc oxide:

The sulfur dioxide is used for the production of sulfuric acid, which is necessary for the leaching process. If deposits of [[zinc carbonate]], [[zinc silicate]], or [[zinc-spinel]] (like the [[Skorpion Zinc|Skorpion Deposit]] in [[Namibia]]) are used for zinc production, the roasting can be omitted.

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For further processing two basic methods are used: [[pyrometallurgy]] or [[electrowinning]]. Pyrometallurgy reduces zinc oxide with [[carbon]] or [[carbon monoxide]] at {{convert|950|C|F|abbr=on}} into the metal, which is distilled as zinc vapor to separate it from other metals, which are not volatile at those temperatures. The zinc vapor is collected in a condenser. The equations below describe this process:

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In [[electrowinning]], zinc is leached from the ore concentrate by [[sulfuric acid]] and impurities are precipitated:

Finally, the zinc is reduced by [[electrolysis]].

When galvanised feedstock is fed to an [[electric arc furnace]], the zinc is recovered from the dust by a number of processes, predominantly the [[Waelz process]] (90% as of 2014).

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===Environmental impact===

Refinement of sulfidic zinc ores produces large volumes of sulfur dioxide and [[cadmium]] vapor. Smelter [[slag]] and other residues contain significant quantities of metals. About 1.1&nbsp;million tonnes of metallic zinc and 130 thousand tonnes of lead were mined and smelted in the Belgian towns of [[Kelmis|La Calamine]] and [[Plombières]] between 1806 and 1882. The dumps of the past mining operations leach zinc and cadmium, and the sediments of the [[Geul River]] contain non-trivial amounts of metals. About two thousand years ago, emissions of zinc from mining and smelting totaled 10 thousand tonnes a year. After increasing 10-fold from 1850, zinc emissions peaked at 3.4&nbsp;million tonnes per year in the 1980s and declined to 2.7&nbsp;million tonnes in the 1990s, although a 2005 study of the Arctic troposphere found that the concentrations there did not reflect the decline. Man-made and natural emissions occur at a ratio of 20&nbsp;to&nbsp;1.

Zinc in rivers flowing through industrial and mining areas can be as high as 20&nbsp;ppm. Effective [[sewage treatment]] greatly reduces this; treatment along the [[Rhine]], for example, has decreased zinc levels to 50&nbsp;ppb. Concentrations of zinc as low as 2&nbsp;ppm adversely affects the amount of oxygen that fish can carry in their blood.

{{wide image|The Zinc Works and Incat.jpg|1150px|Historically responsible for high metal levels in the [[Derwent River (Tasmania)|Derwent River]], the zinc works at [[Lutana]] is the largest exporter in Tasmania, generating 2.5% of the state's [[Gross domestic product|GDP]], and producing more than 250,000 tonnes of zinc per year.|alt=A panorama featuring a large industrial plant on a sea side, in front of mountains.}}

[[soil contamination|Soils contaminated]] with zinc from mining, refining, or fertilizing with zinc-bearing sludge can contain several grams of zinc per kilogram of dry soil. Levels of zinc in excess of 500&nbsp;ppm in soil interfere with the ability of plants to absorb other [[Dietary mineral|essential metals]], such as iron and [[manganese]]. Zinc levels of 2000&nbsp;ppm to 180,000&nbsp;ppm (18%) have been recorded in some soil samples. The European Soil Observatory has published the first high resolution spatial assessment of topsoil Zinc (Zn) concentrations in Europe. The mean concentration of Zn in topsoils is 47 mg/kg while 1% of the measured 22,000 samples had concentrations higher than 167 mg/kg.

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==Applications==

# [[Galvanization|Galvanizing]] (55%)

# [[Brass]] and [[bronze]] (16%)

# Other alloys (21%)

# Miscellaneous (8%)

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===Anti-corrosion and batteries===

[[File:Feuerverzinkte Oberfläche.jpg|thumb|Hot-dip handrail [[galvanization|galvanized]] crystalline surface|alt=Merged elongated crystals of various shades of gray.]]

[[File:Zinkanode neu.jpg|thumb|Zinc [[sacrificial anode]]]]

Zinc is most commonly used as an anti-[[corrosion]] agent, and galvanization (coating of [[iron]] or [[steel]]) is the most familiar form. In 2009 in the United States, 55% or 893,000 tons of the zinc metal was used for galvanization.

Zinc is more reactive than iron or steel and thus will attract almost all local oxidation until it completely corrodes away. A protective surface layer of oxide and carbonate ({{chem|Zn|5|(OH)|6|(CO|3|)|2|)}} forms as the zinc corrodes. This protection lasts even after the zinc layer is scratched but degrades through time as the zinc corrodes away. The zinc is applied electrochemically or as molten zinc by [[hot-dip galvanizing]] or spraying. Galvanization is used on chain-link fencing, guard rails, suspension bridges, lightposts, metal roofs, heat exchangers, and car bodies.

The relative reactivity of zinc and its ability to attract oxidation to itself makes it an efficient [[sacrificial anode]] in [[cathodic protection]] (CP). For example, cathodic protection of a buried pipeline can be achieved by connecting anodes made from zinc to the pipe. Zinc acts as the [[anode]] (negative terminus) by slowly corroding away as it passes electric current to the steel pipeline. Zinc is also used to cathodically protect metals that are exposed to sea water. A zinc disc attached to a ship's iron rudder will slowly corrode while the rudder stays intact. Similarly, a zinc plug attached to a propeller or the metal protective guard for the keel of the ship provides temporary protection.

With a [[standard electrode potential]] (SEP) of −0.76 [[volt]]s, zinc is used as an anode material for batteries. (More reactive lithium (SEP −3.04 V) is used for anodes in [[Lithium battery|lithium batteries]] ). Powdered zinc is used in this way in [[alkaline battery|alkaline batteries]] and the case (which also serves as the anode) of [[Zinc–carbon battery|zinc–carbon batteries]] is formed from sheet zinc. Zinc is used as the anode or fuel of the [[zinc–air battery]]/fuel cell. The [[Zinc–cerium battery|zinc-cerium]] [[redox flow battery]] also relies on a zinc-based negative half-cell.

===Alloys===

A widely used zinc alloy is brass, in which copper is alloyed with anywhere from 3% to 45% zinc, depending upon the type of brass. Brass is generally more [[ductile]] and stronger than copper, and has superior [[corrosion resistance]]. These properties make it useful in communication equipment, hardware, musical instruments, and water valves.

[[File:Microstructure of rolled and annealed brass; magnification 400X.jpg|thumb|left|Cast brass microstructure at magnification 400x|alt=A mosaica pattern composed of components having various shapes and shades of brown.]]

Other widely used zinc alloys include [[nickel silver]], typewriter metal, soft and aluminium [[solder]], and commercial [[bronze]]. Zinc is also used in contemporary pipe organs as a substitute for the traditional lead/tin alloy in pipes. Alloys of 85–88% zinc, 4–10% copper, and 2–8% aluminium find limited use in certain types of machine bearings. Zinc has been the primary metal in [[Lincoln cent|American one cent coins]] (pennies) since 1982. The zinc core is coated with a thin layer of copper to give the appearance of a copper coin. In 1994, {{convert|33200|t|ST}} of zinc were used to produce 13.6&nbsp;billion pennies in the United States.

Alloys of zinc with small amounts of copper, aluminium, and magnesium are useful in [[die casting]] as well as [[spin casting]], especially in the automotive, electrical, and hardware industries. These alloys are marketed under the name [[Zamak]]. An example of this is [[zinc aluminium]]. The low melting point together with the low [[viscosity]] of the alloy makes possible the production of small and intricate shapes. The low working temperature leads to rapid cooling of the cast products and fast production for assembly. Another alloy, marketed under the brand name Prestal, contains 78% zinc and 22% aluminium, and is reported to be nearly as strong as steel but as malleable as plastic. This [[superplasticity]] of the alloy allows it to be molded using die casts made of ceramics and cement.

Similar alloys with the addition of a small amount of lead can be cold-rolled into sheets. An alloy of 96% zinc and 4% aluminium is used to make stamping dies for low production run applications for which ferrous metal dies would be too expensive. For building facades, roofing, and other applications for [[sheet metal]] formed by [[deep drawing]], [[roll forming]], or [[bending (metalworking)|bending]], zinc alloys with [[titanium]] and copper are used. Unalloyed zinc is too brittle for these manufacturing processes.

As a dense, inexpensive, easily worked material, zinc is used as a [[lead]] replacement. In the wake of [[Lead poisoning|lead concerns]], zinc appears in weights for various applications ranging from fishing to [[tire balance]]s and flywheels.

[[Cadmium zinc telluride]] (CZT) is a [[semiconductor|semiconductive]] alloy that can be divided into an array of small sensing devices. These devices are similar to an [[integrated circuit]] and can detect the energy of incoming [[gamma ray]] photons. When behind an absorbing mask, the CZT sensor array can determine the direction of the rays.

===Other industrial uses===

[[File:Zinc oxide.jpg|thumb|Zinc oxide is used as a white [[pigment]] in [[paint]]s.|alt=White powder on a glass plate]]

Roughly one quarter of all zinc output in the United States in 2009 was consumed in zinc compounds; a variety of which are used industrially. Zinc oxide is widely used as a white pigment in paints and as a [[catalyst]] in the manufacture of rubber to disperse heat. Zinc oxide is used to protect rubber polymers and plastics from [[ultraviolet radiation]] (UV). The [[semiconductor]] properties of zinc oxide make it useful in [[varistor]]s and photocopying products. The [[zinc zinc-oxide cycle]] is a two step [[Thermochemistry|thermochemical]] process based on zinc and zinc oxide for [[hydrogen production]].

[[Zinc chloride]] is often added to lumber as a [[fire retardant]] It is used in the manufacture of other chemicals. [[Zinc methyl]] ({{chem|Zn(CH₃)|2}}) is used in a number of organic [[organic synthesis|syntheses]]. [[Zinc sulfide]] (ZnS) is used in [[luminescence|luminescent]] pigments such as on the hands of clocks, [[X-ray]] and television screens, and [[luminous paint]]s. Crystals of ZnS are used in [[laser]]s that operate in the mid-[[infrared]] part of the spectrum. [[Zinc sulfate]] is a chemical in [[dye]]s and pigments. [[Zinc pyrithione]] is used in [[antifouling]] paints.

Zinc powder is sometimes used as a [[propellant]] in [[model rocket]]s. When a compressed mixture of 70% zinc and 30% [[sulfur]] powder is ignited there is a violent chemical reaction. This produces zinc sulfide, together with large amounts of hot gas, heat, and light.

Zinc sheet metal is used as a durable covering for roofs, walls, and countertops, the last often seen in [[bistro]]s and [[oyster bar]]s, and is known for the rustic look imparted by its surface [[oxidation]] in use to a blue-gray [[patina]] and susceptibility to scratching.

{{chem|64|Zn}}, the most abundant isotope of zinc, is very susceptible to [[neutron activation]], being [[Nuclear transmutation|transmuted]] into the highly radioactive {{chem|65|Zn}}, which has a half-life of 244 days and produces intense [[gamma ray|gamma radiation]]. Because of this, zinc oxide used in nuclear reactors as an anti-corrosion agent is depleted of {{chem|64|Zn}} before use, this is called [[depleted zinc oxide]]. For the same reason, zinc has been proposed as a [[Salted bomb|salting]] material for [[nuclear weapon]]s ([[cobalt]] is another, better-known salting material). A jacket of [[Isotope separation|isotopically enriched]] {{chem|64|Zn}} would be irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, forming a large amount of {{chem|65|Zn}} significantly increasing the radioactivity of the weapon's [[Nuclear fallout|fallout]].

{{chem|65|Zn}} is used as a [[isotopic tracer|tracer]] to study how alloys that contain zinc wear out, or the path and the role of zinc in organisms.

Zinc dithiocarbamate complexes are used as agricultural [[fungicide]]s; these include [[Zineb]], Metiram, Propineb and Ziram. Zinc in the form of [[Zinc dithiophosphate|ZDDP]], is used as an anti-wear additive for metal parts in engine oil.

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===Organic chemistry===

[[File:DiphenylzincCarbonylAddition.png|thumb|upright=1.6|Enantioselective addition of diphenylzinc to an aldehyde]]

[[Organozinc compound|Organozinc]] chemistry is the science of compounds that contain carbon-zinc bonds, describing the physical properties, synthesis, and chemical reactions. Many organozinc compounds are commercially important. Among important applications are:

* The Frankland-Duppa Reaction in which an [[oxalate]] [[ester]] (ROCOCOOR) reacts with an [[alkyl halide]] R'X, zinc and [[hydrochloric acid]] to form α-hydroxycarboxylic esters RR'COHCOOR

* Organozincs have similar reactivity to [[Grignard reagent|Grignard reagents]] but are much less nucleophilic, and they are expensive and difficult to handle. Organozincs typically perform nucleophilic addition on electrophiles such as [[aldehydes]], which are then reduced to [[Alcohol (chemistry)|alcohols]]. Commercially available diorganozinc compounds include [[dimethylzinc]], [[diethylzinc]] and diphenylzinc. Like Grignard reagents, organozincs are commonly produced from [[organobromine compound|organobromine]] precursors.

Zinc has found many uses in catalysis in organic synthesis including [[asymmetric reaction|enantioselective synthesis]], being a cheap and readily available alternative to precious metal complexes. Quantitative results (yield and [[enantiomeric excess]]) obtained with chiral zinc catalysts can be comparable to those achieved with palladium, ruthenium, iridium and others.

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===Dietary supplement===

[[File:Zinc pills.jpg|thumb|[[Zinc gluconate]] supplement pills]]

[[File:Zinc gluconate structure.svg|thumb|upright=1.35|[[Zinc gluconate]] is one compound used for the delivery of zinc as a [[dietary supplement]].|alt=Skeletal chemical formula of a planar compound featuring a Zn atom in the center, symmetrically bonded to four oxygens. Those oxygens are further connected to linear COH chains.]]

{{see also|Zinc sulfate (medical use)|Zinc gluconate}}

In most single-tablet, over-the-counter, daily [[vitamin]] and [[Dietary mineral|mineral]] supplements, zinc is included in such forms as [[zinc oxide]], [[zinc acetate]], [[zinc gluconate]], or zinc amino acid chelate.

====Gastroenteritis====

Zinc is an inexpensive and effective part of treatment of [[diarrhea]] among children in the developing world. Zinc becomes depleted in the body during diarrhea and replenishing zinc with a 10- to 14-day course of treatment can reduce the duration and severity of diarrheal episodes and may also prevent future episodes for as long as three months. [[Gastroenteritis]] is strongly attenuated by ingestion of zinc, possibly by direct antimicrobial action of the ions in the [[gastrointestinal tract]], or by the absorption of the zinc and re-release from immune cells (all [[granulocyte]]s secrete zinc), or both.

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====Common cold{{anchor|Common cold}}====

{{Excerpt|Zinc and the common cold}}

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====Weight gain====

{{See also|Zinc deficiency#Appetite}}

====Other====

A 2023 Cochrane review stated that people taking zinc supplements may be less likely to progress to [[age-related macular degeneration]]. Zinc supplement is an effective treatment for [[acrodermatitis enteropathica]], a genetic disorder affecting zinc absorption that was previously fatal to affected infants. Zinc deficiency has been associated with [[major depressive disorder]] (MDD), and zinc supplements may be an effective treatment. Zinc may help individuals sleep more.

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===Topical use===

{{further|Zinc oxide#Medicine}}

[[Topical administration|Topical preparations]] of zinc include those used on the skin, often in the form of [[zinc oxide]]. Zinc oxide is generally recognised by the FDA as safe and effective and is considered a very photo-stable. Zinc oxide is one of the most common active ingredients formulated into a sunscreen to mitigate [[sunburn]]. Applied thinly to a baby's diaper area ([[perineum]]) with each diaper change, it can protect against [[diaper rash]].

Chelated zinc is used in toothpastes and mouthwashes to prevent [[halitosis|bad breath]]; zinc citrate helps reduce the build-up of [[Calculus (dental)|calculus]] (tartar).

[[Zinc pyrithione]] is widely included in shampoos to prevent dandruff.

Topical zinc has also been shown to effectively treat, as well as prolong remission in [[genital herpes]].

==Biological role==

{{Main|Zinc in biology}}

Zinc is an essential [[trace element]] for humans and other animals, for plants and for [[microorganism]]s. Zinc is required for the function of over 300 [[enzyme]]s and 1000 [[transcription factor]]s, and is stored and transferred in [[metallothionein]]s. It is the second most abundant trace metal in humans after iron and it is the only metal which appears in all [[Enzyme#Naming conventions|enzyme classes]].

In proteins, zinc ions are often coordinated to the amino acid side chains of [[aspartic acid]], [[glutamic acid]], [[cysteine]] and [[histidine]]. The theoretical and computational description of this zinc binding in proteins (as well as that of other transition metals) is difficult.

Roughly {{nowrap|2–4}}&nbsp;grams of zinc are distributed throughout the human body. Most zinc is in the brain, muscle, bones, kidney, and liver, with the highest concentrations in the prostate and parts of the eye. [[Semen]] is particularly rich in zinc, a key factor in [[prostate gland]] function and [[reproductive organ]] growth.

Zinc homeostasis of the body is mainly controlled by the intestine. Here, [[SLC39A4|ZIP4]] and especially [[TRPM7]] were linked to intestinal zinc uptake essential for postnatal survival.

In humans, the biological roles of zinc are ubiquitous. It interacts with "a wide range of organic [[ligand]]s", and has roles in the metabolism of RNA and DNA, [[signal transduction]], and [[gene expression]]. It also regulates [[apoptosis]]. A review from 2015 indicated that about 10% of human proteins (~3000) bind zinc, in addition to hundreds more that transport and traffic zinc; a similar ''[[in silico]]'' study in the plant ''[[Arabidopsis thaliana]]'' found 2367 zinc-related proteins.

In the [[brain]], zinc is stored in specific [[synaptic vesicles]] by [[glutamatergic]] [[neuron]]s and can modulate neuronal excitability. It plays a key role in [[synaptic plasticity]] and so in learning. Zinc [[homeostasis]] also plays a critical role in the functional regulation of the [[central nervous system]]. Dysregulation of zinc homeostasis in the central nervous system that results in excessive synaptic zinc concentrations is believed to induce [[neurotoxicity]] through mitochondrial oxidative stress (e.g., by disrupting certain enzymes involved in the [[electron transport chain]], including [[complex I]], [[complex III]], and [[α-ketoglutarate dehydrogenase]]), the dysregulation of calcium homeostasis, glutamatergic neuronal [[excitotoxicity]], and interference with intraneuronal [[signal transduction]]. L- and D-histidine facilitate brain zinc uptake. [[SLC30A3]] is the primary [[Solute carrier family#Solute carrier family 30|zinc transporter]] involved in cerebral zinc homeostasis.

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===Enzymes===

[[File:Carbonic anhydrase.png|thumb|[[Ribbon diagram]] of human [[carbonic anhydrase]] II, with zinc atom visible in the center|alt=Interconnected stripes, mostly of yellow and blue color with a few red segments.]]

[[File:Zinc finger rendered.png|thumb|[[Zinc fingers]] help read DNA sequences.|alt=A twisted band, with one side painted blue and another gray. Its two ends are connected through some chemical species to a green atom (zinc).]]

Zinc is an efficient [[Lewis acid]], making it a useful catalytic agent in [[hydroxylation]] and other enzymatic reactions. The metal also has a flexible [[coordination geometry]], which allows proteins using it to rapidly shift [[protein structure|conformations]] to perform biological reactions. Two examples of zinc-containing enzymes are [[carbonic anhydrase]] and [[carboxypeptidase]], which are vital to the processes of [[carbon dioxide]] ({{chem|CO|2}}) regulation and digestion of proteins, respectively.

In vertebrate blood, carbonic anhydrase converts {{chem|CO|2}} into bicarbonate and the same enzyme transforms the bicarbonate back into {{chem|CO|2}} for exhalation through the lungs. Without this enzyme, this conversion would occur about one million times slower at the normal blood [[pH]] of 7 or would require a pH of 10 or more. The non-related β-carbonic anhydrase is required in plants for leaf formation, the synthesis of [[indole-3-acetic acid|indole acetic acid]] (auxin) and [[alcoholic fermentation]].

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Carboxypeptidase cleaves peptide linkages during digestion of proteins. A [[coordinate covalent bond]] is formed between the terminal peptide and a C=O group attached to zinc, which gives the carbon a positive charge. This helps to create a [[hydrophobic]] pocket on the enzyme near the zinc, which attracts the non-polar part of the protein being digested.

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===Signalling===

Zinc has been recognized as a messenger, able to activate signalling pathways. Many of these pathways provide the driving force in aberrant cancer growth. They can be targeted through [[Zinc transporter protein|ZIP transporters]].

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===Other proteins===

Zinc serves a purely structural role in [[zinc finger]]s, twists and clusters. Zinc fingers form parts of some [[transcription factor]]s, which are proteins that recognize [[DNA sequence|DNA base sequences]] during the replication and transcription of [[DNA]]. Each of the nine or ten {{chem|Zn|2+}} ions in a zinc finger helps maintain the finger's structure by coordinately binding to four [[amino acid]]s in the transcription factor.

In [[blood plasma]], zinc is bound to and transported by [[albumin]] (60%, low-affinity) and [[transferrin]] (10%). Because transferrin also transports iron, excessive iron reduces zinc absorption, and vice versa. A similar antagonism exists with copper. The concentration of zinc in blood plasma stays relatively constant regardless of zinc intake. Cells in the salivary gland, prostate, immune system, and intestine use [[Cell signaling|zinc signaling]] to communicate with other cells.

Zinc may be held in [[metallothionein]] reserves within microorganisms or in the intestines or liver of animals. However, inadequate or excessive zinc intake can be harmful; excess zinc particularly impairs copper absorption because metallothionein absorbs both metals.

The human [[dopamine transporter]] contains a [[affinity (pharmacology)|high affinity]] extracellular zinc [[binding site]] which, upon zinc binding, inhibits dopamine [[reuptake]] and amplifies [[amphetamine]]-induced [[neurotransmitter efflux|dopamine efflux]] ''[[in vitro]]''. The human [[serotonin transporter]] and [[norepinephrine transporter]] do not contain zinc binding sites. Some [[EF hand|EF-hand]] [[Calcium-binding protein|calcium binding proteins]] such as [[S100 protein|S100]] or [[Neuronal calcium sensor-1|NCS-1]] are also able to bind zinc ions.

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=== Nutrition ===

====Dietary recommendations====

The [[U.S. Institute of Medicine]] (IOM) updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for zinc in 2001. The current EARs for zinc for women and men ages 14 and up is 6.8 and 9.4&nbsp;mg/day, respectively. The RDAs are 8 and 11&nbsp;mg/day. RDAs are higher than EARs so as to identify amounts that will cover people with higher than average requirements. RDA for pregnancy is 11&nbsp;mg/day. RDA for lactation is 12&nbsp;mg/day. For infants up to 12 months the RDA is 3&nbsp;mg/day. For children ages 1–13 years the RDA increases with age from 3 to 8&nbsp;mg/day. As for safety, the IOM sets [[Tolerable upper intake level]]s (ULs) for vitamins and minerals when evidence is sufficient. In the case of zinc the adult UL is 40&nbsp;mg/day including both food and supplements combined (lower for children). Collectively the EARs, RDAs, AIs and ULs are referred to as [[Dietary Reference Intake]]s (DRIs).

The [[European 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 people ages 18 and older the PRI calculations are complex, as the EFSA has set higher and higher values as the [[phytate]] content of the diet increases. For women, PRIs increase from 7.5 to 12.7&nbsp;mg/day as phytate intake increases from 300 to 1200&nbsp;mg/day; for men the range is 9.4 to 16.3&nbsp;mg/day. These PRIs are higher than the U.S. RDAs. The EFSA reviewed the same safety question and set its UL at 25&nbsp;mg/day, which is much lower than the U.S. value.

For U.S. food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value (%DV). For zinc labeling purposes 100% of the Daily Value was 15&nbsp;mg, but on May 27, 2016, it was revised to 11&nbsp;mg. A table of the old and new adult daily values is provided at [[Reference Daily Intake]].

====Dietary intake====

[[File:Foodstuff-containing-Zinc.jpg|thumb|upright|[[Recommended Dietary Allowance|Foods and seasonings]] containing zinc|alt=Several plates full of various cereals, fruits and vegetables on a table.]]

Animal products such as meat, fish, shellfish, fowl, eggs, and dairy contain zinc. The concentration of zinc in plants varies with the level in the soil. With adequate zinc in the soil, the food plants that contain the most zinc are wheat (germ and bran) and various seeds, including [[sesame]], [[poppy]], [[alfalfa]], [[celery]], and [[Mustard (condiment)|mustard]]. Zinc is also found in [[bean]]s, [[nut (fruit)|nuts]], [[almond]]s, [[whole grain]]s, [[pumpkin seed]]s, [[sunflower seed]]s, and [[blackcurrant]].

Other sources include [[food fortification|fortified food]] and [[dietary supplement]]s in various forms. A 1998 review concluded that zinc oxide, one of the most common supplements in the United States, and zinc carbonate are nearly insoluble and poorly absorbed in the body. This review cited studies that found lower plasma zinc concentrations in the subjects who consumed zinc oxide and zinc carbonate than in those who took zinc acetate and sulfate salts. For fortification, however, a 2003 review recommended cereals (containing zinc oxide) as a cheap, stable source that is as easily absorbed as the more expensive forms. A 2005 study found that various compounds of zinc, including oxide and sulfate, did not show statistically significant differences in absorption when added as fortificants to maize tortillas.

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===Deficiency===

{{Main|Zinc deficiency}}

Nearly two billion people in the developing world are deficient in zinc. Groups at risk include children in developing countries and elderly with chronic illnesses. In children, it causes an increase in infection and diarrhea and contributes to the death of about 800,000 children worldwide per year. The World Health Organization advocates zinc supplementation for severe malnutrition and diarrhea. Zinc supplements help prevent disease and reduce mortality, especially among children with low birth weight or stunted growth. However, zinc supplements should not be administered alone, because many in the developing world have several deficiencies, and zinc interacts with other micronutrients. While zinc deficiency is usually due to insufficient dietary intake, it can be associated with [[malabsorption]], [[acrodermatitis enteropathica]], chronic liver disease, chronic renal disease, [[sickle cell disease]], [[diabetes]], [[malignancy]], and other chronic illnesses.

In the United States, a federal survey of food consumption determined that for women and men over the age of 19, average consumption was 9.7 and 14.2&nbsp;mg/day, respectively. For women, 17% consumed less than the EAR, for men 11%. The percentages below EAR increased with age. The most recent published update of the survey (NHANES 2013–2014) reported lower averages – 9.3 and 13.2&nbsp;mg/day – again with intake decreasing with age.

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Symptoms of mild zinc deficiency are diverse. Clinical outcomes include depressed growth, diarrhea, impotence and delayed sexual maturation, [[alopecia]], eye and skin lesions, impaired appetite, altered cognition, impaired immune functions, defects in carbohydrate use, and reproductive [[teratogenesis]]. but excessive zinc does also.

Despite some concerns, western vegetarians and vegans do not suffer any more from overt zinc deficiency than meat-eaters. Major plant sources of zinc include cooked dried beans, sea vegetables, fortified cereals, soy foods, nuts, peas, and seeds. However, [[phytates]] in many whole-grains and fibers may interfere with zinc absorption and marginal zinc intake has poorly understood effects. The zinc [[chelation|chelator]] [[phytic acid|phytate]], found in seeds and [[cereal]] [[bran]], can contribute to zinc malabsorption. Some evidence suggests that more than the US RDA (8&nbsp;mg/day for adult women; 11&nbsp;mg/day for adult men) may be needed in those whose diet is high in phytates, such as some vegetarians. The [[European Food Safety Authority]] (EFSA) guidelines attempt to compensate for this by recommending higher zinc intake when dietary phytate intake is greater. These considerations must be balanced against the paucity of adequate zinc [[biomarker]]s, and the most widely used indicator, plasma zinc, has poor [[sensitivity and specificity]].

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===Soil remediation===

Species of ''[[Calluna]]'', ''[[Erica (plant)|Erica]]'' and ''[[Vaccinium]]'' can grow in zinc-metalliferous soils, because translocation of toxic ions is prevented by the action of [[Ericoid mycorrhiza|ericoid mycorrhizal fungi]].

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===Agriculture===

Zinc deficiency appears to be the most common micronutrient deficiency in crop plants; it is particularly common in high-pH soils. Zinc-deficient [[soil]] is [[Tillage|cultivated]] in the cropland of about half of Turkey and India, a third of China, and most of Western Australia. Substantial responses to zinc fertilization have been reported in these areas. Plants that grow in soils that are zinc-deficient are more susceptible to disease. Zinc is added to the soil primarily through the weathering of rocks, but humans have added zinc through fossil fuel combustion, mine waste, phosphate fertilizers, pesticide ([[zinc phosphide]]), limestone, manure, sewage sludge, and particles from galvanized surfaces. Excess zinc is toxic to plants, although zinc toxicity is far less widespread.

==Precautions==

{{main|Zinc toxicity}}

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===Toxicity===

Although zinc is an essential requirement for good health, excess zinc can be harmful. Excessive absorption of zinc suppresses copper and iron absorption. The free zinc ion in solution is highly toxic to plants, invertebrates, and even vertebrate fish. The Free Ion Activity Model is well-established in the literature, and shows that just [[mole (unit)|micromolar]] amounts of the free ion kills some organisms. A recent example showed 6 micromolar killing 93% of all ''[[Daphnia]]'' in water.

The free zinc ion is a powerful [[Lewis acid]] up to the point of being [[corrosive]]. Stomach acid contains [[hydrochloric acid]], in which metallic zinc dissolves readily to give corrosive zinc chloride. Swallowing a post-1982 American one [[Cent (United States coin)|cent]] piece (97.5% zinc) can cause damage to the stomach lining through the high solubility of the zinc ion in the acidic stomach.

Evidence shows that people taking 100–300&nbsp;mg of zinc daily may suffer induced [[copper deficiency]]. A 2007 trial observed that elderly men taking 80&nbsp;mg daily were hospitalized for urinary complications more often than those taking a placebo. Levels of 100–300&nbsp;mg may interfere with the use of copper and iron or adversely affect cholesterol. Zinc in excess of 500&nbsp;ppm in soil interferes with the plant absorption of other essential metals, such as iron and manganese. A condition called the [[zinc shakes]] or "zinc chills" can be induced by inhalation of zinc fumes while [[brazing]] or welding galvanized materials. Zinc is a common ingredient of [[denture]] cream which may contain between 17 and 38&nbsp;mg of zinc per gram. Disability and even deaths from excessive use of these products have been claimed.

The U.S. [[Food and Drug Administration]] (FDA) states that zinc damages nerve receptors in the nose, causing [[anosmia]]. Reports of anosmia were also observed in the 1930s when zinc preparations were used in a failed attempt to prevent [[polio]] infections. On June 16, 2009, the FDA ordered removal of zinc-based intranasal cold products from store shelves. The FDA said the loss of smell can be life-threatening because people with impaired smell cannot detect leaking gas or smoke, and cannot tell if food has spoiled before they eat it.

Recent research suggests that the topical antimicrobial zinc pyrithione is a potent [[heat shock]] response inducer that may impair genomic integrity with induction of [[Poly ADP ribose polymerase|PARP]]-dependent energy crisis in cultured human [[keratinocyte]]s and [[melanocyte]]s.

===Poisoning===

In 1982, the [[United States Mint|US Mint]] began minting [[Cent (United States coin)|pennies]] coated in copper but containing primarily zinc. Zinc pennies pose a risk of zinc toxicosis, which can be fatal. One reported case of chronic ingestion of 425 pennies (over 1&nbsp;kg of zinc) resulted in death due to gastrointestinal bacterial and fungal [[sepsis]]. Another patient who ingested 12&nbsp;grams of zinc showed only [[lethargy]] and [[ataxia]] (gross lack of coordination of muscle movements). Several other cases have been reported of humans suffering zinc intoxication by the ingestion of zinc coins.

Pennies and other small coins are sometimes ingested by dogs, requiring veterinary removal of the foreign objects. The zinc content of some coins can cause zinc toxicity, commonly fatal in dogs through severe [[hemolytic anemia]] and liver or kidney damage; vomiting and diarrhea are possible symptoms. Zinc is highly toxic in [[parrots]] and poisoning can often be fatal. The consumption of fruit juices stored in galvanized cans has resulted in mass parrot poisonings with zinc.

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==See also==

* [[List of countries by zinc production]]

* [[Spelter]]

* [[Wet storage stain]]

* [[Zinc alloy electroplating]]

* [[Metal fume fever]]

* [[Piotr Steinkeller]]

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== Bibliography ==

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==External links==

{{Zinc compounds}}

{{Ionotropic glutamate receptor modulators}}