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= Zinc =
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Introduction
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Zinc is a chemical element; it has symbol Zn and atomic number 30. It
is a slightly brittle metal at room temperature and has a
shiny-greyish appearance when oxidation is removed. It is the first
element in group 12 (IIB) of the periodic table. In some respects,
zinc is chemically similar to magnesium: both elements exhibit only
one normal oxidation state (+2), and the Zn2+ and Mg2+ ions are of
similar size. Zinc is the 24th most abundant element in Earth's crust
and has five stable isotopes. The most common zinc ore is sphalerite
(zinc blende), a zinc sulfide mineral. The largest workable lodes are
in Australia, Asia, and the United States. Zinc is refined by froth
flotation of the ore, roasting, and final extraction using electricity
(electrowinning).
Zinc is an essential trace element for humans, animals, plants and for
microorganisms and is necessary for prenatal and postnatal
development. It is the second most abundant trace metal in humans
after iron, an important cofactor for many enzymes, and the only metal
which appears in all enzyme classes. Zinc is also an essential
nutrient element for coral growth.
Zinc deficiency affects about two billion people in the developing
world and is associated with many diseases. In children, deficiency
causes growth retardation, delayed sexual maturation, infection
susceptibility, and diarrhea. Enzymes with a zinc atom in the reactive
center are widespread in biochemistry, such as alcohol dehydrogenase
in humans.
Consumption of excess zinc may cause ataxia, lethargy, and copper
deficiency. In marine biomes, notably within polar regions, a deficit
of zinc can compromise the vitality of primary algal communities,
potentially destabilizing the intricate marine trophic structures and
consequently impacting biodiversity.
Brass, an alloy of copper and zinc in various proportions, was used as
early as the third millennium BC in the Aegean area and the region
which currently includes Iraq, the United Arab Emirates, Kalmykia,
Turkmenistan and Georgia. In the second millennium BC it was used in
the regions currently including West India, Uzbekistan, Iran, Syria,
Iraq, and Israel. Zinc metal was not produced on a large scale until
the 12th century in India, though it was known to the ancient Romans
and Greeks. The mines of Rajasthan have given definite evidence of
zinc production going back to the 6th century BC. The oldest evidence
of pure zinc comes from Zawar, in Rajasthan, as early as the 9th
century AD when a distillation process was employed to make pure zinc.
Alchemists burned zinc in air to form what they called "philosopher's
wool" or "white snow".
The element was probably named by the alchemist Paracelsus after the
German word 'Zinke' (prong, tooth). German chemist Andreas Sigismund
Marggraf is credited with discovering pure metallic zinc in 1746. Work
by Luigi Galvani and Alessandro Volta uncovered the electrochemical
properties of zinc by 1800.
Corrosion-resistant zinc plating of iron (hot-dip galvanizing) is the
major application for zinc. Other applications are in electrical
batteries, small non-structural castings, and alloys such as brass. A
variety of zinc compounds are commonly used, such as zinc carbonate
and zinc gluconate (as dietary supplements), zinc chloride (in
deodorants), zinc pyrithione (anti-dandruff shampoos), zinc sulfide
(in luminescent paints), and dimethylzinc or diethylzinc in the
organic laboratory.
Physical properties
=====================
Zinc is a bluish-white, lustrous, diamagnetic metal, though most
common commercial grades of the metal have a dull finish. It is
somewhat less dense than iron and has a hexagonal crystal structure,
with a distorted form of hexagonal close packing, in which each atom
has six nearest neighbors (at 265.9 pm) in its own plane and six
others at a greater distance of 290.6 pm. The metal is hard and
brittle at most temperatures but becomes malleable between 100 and 150
°C. Above 210 °C, the metal becomes brittle again and can be
pulverized by beating. Zinc is a fair conductor of electricity. For a
metal, zinc has relatively low melting (419.5 °C) and boiling point
(907 °C). The melting point is the lowest of all the d-block metals
aside from mercury and cadmium; for this reason among others, zinc,
cadmium, and mercury are often not considered to be transition metals
like the rest of the d-block metals.
Many alloys contain zinc, including brass. Other metals long known to
form binary alloys with zinc are aluminium, antimony, bismuth, gold,
iron, lead, mercury, silver, tin, magnesium, cobalt, nickel,
tellurium, and sodium. Although neither zinc nor zirconium is
ferromagnetic, their alloy, , exhibits ferromagnetism below 35 K.
Occurrence
============
Zinc makes up about 75 ppm (0.0075%) of Earth's crust, making it the
22nd-most abundant element. It also makes up 312 ppm of the Solar
System, where it is the 22nd most abundant element. Typical background
concentrations of zinc do not exceed 1 μg/m3 in the atmosphere; 300
mg/kg in soil; 100 mg/kg in vegetation; 20 μg/L in freshwater and 5
μg/L in seawater. The element is normally found in association with
other base metals such as copper and lead in ores. Zinc is a
chalcophile, meaning the element is more likely to be found in
minerals together with sulfur and other heavy chalcogens, rather than
with the light chalcogen oxygen or with non-chalcogen electronegative
elements such as the halogens. Sulfides formed as the crust solidified
under the reducing conditions of the early Earth's atmosphere.
Sphalerite, which is a form of zinc sulfide, is the most heavily mined
zinc-containing ore because its concentrate contains 60-62% zinc.
Other source minerals for zinc include smithsonite (zinc carbonate),
hemimorphite (zinc silicate), wurtzite (another zinc sulfide), and
sometimes hydrozincite (basic zinc carbonate). With the exception of
wurtzite, all these other minerals were formed by weathering of the
primordial zinc sulfides.
Identified world zinc resources total about 1.9-2.8 billion tonnes.
Large deposits are in Australia, Canada and the United States, with
the largest reserves in Iran. The most recent estimate of reserve base
for zinc (meets specified minimum physical criteria related to current
mining and production practices) was made in 2009 and calculated to be
roughly 480 Mt. Zinc reserves, on the other hand, are geologically
identified ore bodies whose suitability for recovery is economically
based (location, grade, quality, and quantity) at the time of
determination. Since exploration and mine development is an ongoing
process, the amount of zinc reserves is not a fixed number and
sustainability of zinc ore supplies cannot be judged by simply
extrapolating the combined mine life of today's zinc mines. This
concept is well supported by data from the United States Geological
Survey (USGS), which illustrates that although refined zinc production
increased 80% between 1990 and 2010, the reserve lifetime for zinc has
remained unchanged. About 346 million tonnes have been extracted
throughout history to 2002, and scholars have estimated that about
109-305 million tonnes are in use.
Isotopes
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Five stable isotopes of zinc occur in nature, with 64Zn being the most
abundant isotope (49.17% natural abundance). The other isotopes found
in nature are (27.73%), (4.04%), (18.45%), and (0.61%).
Several dozen radioisotopes have been characterized. , which has a
half-life of 243.66 days, is the least active radioisotope, followed
by with a half-life of 46.5 hours. Zinc has 10 nuclear isomers, of
which 69mZn has the longest half-life, 13.76 h. The superscript 'm'
indicates a metastable isotope. The nucleus of a metastable isotope is
in an excited state and will return to the ground state by emitting a
photon in the form of a gamma ray. has three excited metastable
states and has two. The isotopes , , and each have only one excited
metastable state.
The most common decay mode of a radioisotope of zinc with a mass
number lower than 66 is electron capture. The decay product resulting
from electron capture is an isotope of copper.
: + → +
The most common decay mode of a radioisotope of zinc with mass number
higher than 66 is beta decay (β−), which produces an isotope of
gallium.
: → + +
Reactivity
============
Zinc has an electron configuration of [Ar]4s23d10 and is a member of
the group 12 of the periodic table. It is a moderately reactive metal
and strong reducing agent; in the reactivity series it is comparable
to manganese. The surface of the pure metal tarnishes quickly,
eventually forming a protective passivating layer of the basic zinc
carbonate, , by reaction with atmospheric carbon dioxide.
Zinc burns in air with a bright bluish-green flame, giving off fumes
of zinc oxide. Zinc reacts readily with acids, alkalis and other
non-metals. Extremely pure zinc reacts only slowly at room temperature
with acids. Strong acids, such as hydrochloric or sulfuric acid, can
remove the passivating layer and the subsequent reaction with the acid
releases hydrogen gas.
Zinc chemistry resembles that of the late first-row transition metals,
nickel and copper, as well as certain main group elements. Almost all
zinc compounds have the element in the +2 oxidation state. When Zn2+
compounds form, the outer shell 's' electrons are lost, yielding a
bare zinc ion with the electronic configuration [Ar]3d10. The filled
interior 'd' shell generally does not participate in bonding,
producing diamagnetic and mostly colorless compounds. In aqueous
solution an octahedral complex, is the predominant species.
The ionic radii of zinc and magnesium happen to be nearly identical.
Consequently some of the equivalent salts have the same crystal
structure, and in other circumstances where ionic radius is a
determining factor, the chemistry of zinc has much in common with that
of magnesium. Compared to the transition metals, zinc tends to form
bonds with a greater degree of covalency. Complexes with N- and S-
donors are much more stable. Complexes of zinc are mostly 4- or 6-
coordinate, although 5-coordinate complexes are known.
Other oxidation states require unusual physical conditions, and the
only positive oxidation states demonstrated are +1 or +2. The
volatilization of zinc in combination with zinc chloride at
temperatures above 285 °C indicates the formation of , a zinc compound
with a +1 oxidation state. Calculations indicate that a zinc compound
with the oxidation state of +4 is unlikely to exist. Zn(III) is
predicted to exist in the presence of strongly electronegative
trianions; however, there exists some doubt around this possibility.
Zinc(I) compounds
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Zinc(I) compounds are very rare. The [Zn2]2+ ion is implicated by the
formation of a yellow diamagnetic glass by dissolving metallic zinc in
molten ZnCl2. The [Zn2]2+ core would be analogous to the [Hg2]2+
cation present in mercury(I) compounds. The diamagnetic nature of the
ion confirms its dimeric structure. The first zinc(I) compound
containing the Zn-Zn bond, (η5-C5Me5)2Zn2 has been reported in 2004.
Zinc(II) compounds
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Binary compounds of zinc are known for most of the metalloids and all
the nonmetals except the noble gases. The oxide ZnO is a white powder
that is nearly insoluble in neutral aqueous solutions, but is
amphoteric, dissolving in both strong basic and acidic solutions. The
other chalcogenides (ZnS, ZnSe, and ZnTe) have varied applications in
electronics and optics. Pnictogenides (Zinc nitride, zinc phosphide,
zinc arsenide and zinc antimonide), the peroxide (zinc peroxide), the
hydride (zinc hydride), and the carbide () are also known. Of the four
halides, zinc fluoride has the most ionic character, while the others
(zinc chloride, zinc bromide, and zinc iodide) have relatively low
melting points and are considered to have more covalent character.
In weak basic solutions containing ions, the hydroxide Zinc hydroxide
forms as a white precipitate. In stronger alkaline solutions, this
hydroxide is dissolved to form zincates (zincate). The nitrate Zinc
nitrate, chlorate Zinc chlorate, sulfate Zinc sulfate, phosphate Zinc
phosphate, molybdate Zinc molybdate, cyanide Zinc cyanide, arsenite ,
arsenate and the chromate Zinc chromate (one of the few colored zinc
compounds) are a few examples of other common inorganic compounds of
zinc.
Organozinc compounds are those that contain zinc-carbon covalent
bonds. Diethylzinc (Diethylzinc) is a reagent in synthetic chemistry.
It was first reported in 1848 from the reaction of zinc and ethyl
iodide, and was the first compound known to contain a metal-carbon
sigma bond.
Test for zinc
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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.
Ancient use
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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 BC
contains 23% zinc.
Knowledge of how to produce brass spread to Ancient Greece by the 7th
century BC, but few varieties were made. Ornaments made of alloys
containing 80-90% zinc, with lead, iron, antimony, and other metals
making up the remainder, have been found that are 2,500 years old. A
possibly prehistoric statuette containing 87.5% zinc was found in a
Dacian archaeological site.
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. Zinc in such remnants in smelting ovens was usually discarded as
it was thought to be worthless.
The manufacture of brass was known to the Romans by about 30 BC. They
made brass by heating powdered 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.
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 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
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 ( and 187 BCE). 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.
Early studies and naming
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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.
Alchemists burned zinc metal in air and collected the resulting zinc
oxide on a condenser. Some alchemists called this zinc oxide '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 , 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 'zinn' meaning tin. Yet another possibility is
that the word is derived from the Persian word '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 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.
Isolation
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Metallic zinc was isolated in India by 1300 AD. Before it was isolated
in Europe, it was imported from India in about 1600 CE. 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 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 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 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. This procedure
became commercially practical by 1752.
Later work
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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 "animal electricity". The galvanic cell and the
process of galvanization were both named for Luigi Galvani, and his
discoveries paved the way for 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 cells, 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 electrons 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.
The digestive enzyme carboxypeptidase became the second known
zinc-containing enzyme in 1955.
Mining and processing
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Top zinc mine production output (by countries) 2023
Rank !!Country !!Tonnes
| **1**||**China** ||align="right"| **4,000,000**
| **2**||**Peru** ||align="right"| **1,400,000**
| **3**||**Australia** ||align="right"| **1,100,000**
| **4**||**India**|| align="right" | **860,000**
| **5**||**United States**|| align="right" | **750,000**
| **6**||**Mexico** ||align="right"| **690,000**
Zinc is the fourth most common metal in use, trailing only iron,
aluminium, and copper with an annual production of about 13 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 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%
.
Roasting converts the zinc sulfide concentrate to zinc oxide:
:2ZnS + 3O2 ->[t^o] 2ZnO + 2SO2
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 Deposit in Namibia)
are used for zinc production, the roasting can be omitted.
For further processing two basic methods are used: pyrometallurgy or
electrowinning. Pyrometallurgy reduces zinc oxide with carbon or
carbon monoxide at 950 C 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:
: ZnO + C ->[950^oC] Zn + CO
: ZnO + CO ->[950^oC] Zn + CO2
In electrowinning, zinc is leached from the ore concentrate by
sulfuric acid and impurities are precipitated:
:ZnO + H2SO4 -> ZnSO4 + H2O
Finally, the zinc is reduced by electrolysis.
:2ZnSO4 + 2H2O -> 2Zn + O2 + 2H2SO4
The sulfuric acid is regenerated and recycled to the leaching step.
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).
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 million tonnes of metallic
zinc and 130 thousand tonnes of lead were mined and smelted in the
Belgian towns of 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 million tonnes per year in the
1980s and declined to 2.7 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 to 1.
Zinc in rivers flowing through industrial and mining areas can be as
high as 20 ppm. Effective sewage treatment greatly reduces this;
treatment along the Rhine, for example, has decreased zinc levels to
50 ppb. Concentrations of zinc as low as 2 ppm adversely affects the
amount of oxygen that fish can carry in their blood.
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 ppm in soil
interfere with the ability of plants to absorb other essential metals,
such as iron and manganese. Zinc levels of 2000 ppm to 180,000 ppm
(18%) have been recorded in some soil samples.
Applications
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Major applications of zinc include, with percentages given for the US
# Galvanizing (55%)
# Brass and bronze (16%)
# Other alloys (21%)
# Miscellaneous (8%)
Anti-corrosion and batteries
==============================
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 ( 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 volts, zinc is used
as an anode material for batteries. (More reactive lithium (SEP −3.04
V) is used for anodes in lithium batteries ). Powdered zinc is used in
this way in alkaline batteries and the case (which also serves as the
anode) of 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 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.
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 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, 33200 t of zinc were used to
produce 13.6 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, 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 concerns, zinc appears in
weights for various applications ranging from fishing to tire balances
and flywheels.
Cadmium zinc telluride (CZT) is a 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
=======================
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 varistors and photocopying products. The zinc zinc-oxide
cycle is a two step thermochemical process based on zinc and zinc
oxide for hydrogen production.
Zinc chloride is often added to lumber as a fire retardant and
sometimes as a wood preservative. It is used in the manufacture of
other chemicals. Zinc methyl () is used in a number of organic
syntheses. Zinc sulfide (ZnS) is used in luminescent pigments such as
on the hands of clocks, X-ray and television screens, and luminous
paints. Crystals of ZnS are used in lasers that operate in the
mid-infrared part of the spectrum. Zinc sulfate is a chemical in dyes
and pigments. Zinc pyrithione is used in antifouling paints.
Zinc powder is sometimes used as a propellant in model rockets. 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 bistros and oyster bars, and is
known for the rustic look imparted by its surface oxidation in use to
a blue-gray patina and susceptibility to scratching.
, the most abundant isotope of zinc, is very susceptible to neutron
activation, being transmuted into the highly radioactive , which has a
half-life of 244 days and produces intense gamma radiation. Because of
this, zinc oxide used in nuclear reactors as an anti-corrosion agent
is depleted of before use, this is called depleted zinc oxide. For
the same reason, zinc has been proposed as a salting material for
nuclear weapons (cobalt is another, better-known salting material). A
jacket of isotopically enriched would be irradiated by the intense
high-energy neutron flux from an exploding thermonuclear weapon,
forming a large amount of significantly increasing the radioactivity
of the weapon's fallout. Such a weapon is not known to have ever been
built, tested, or used.
is used as a 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 fungicides;
these include Zineb, Metiram, Propineb and Ziram. Zinc naphthenate is
used as wood preservative. Zinc in the form of ZDDP, is used as an
anti-wear additive for metal parts in engine oil.
Organic chemistry
===================
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 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 alcohols.
Commercially available diorganozinc compounds include dimethylzinc,
diethylzinc and diphenylzinc. Like Grignard reagents, organozincs are
commonly produced from organobromine precursors.
Zinc has found many uses in catalysis in organic synthesis including
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.
Dietary supplement
====================
In most single-tablet, over-the-counter, daily vitamin and mineral
supplements, zinc is included in such forms as zinc oxide, zinc
acetate, zinc gluconate, or zinc amino acid chelate.
Generally, zinc supplement is recommended where there is high risk of
zinc deficiency (such as low and middle income countries) as a
preventive measure. Although zinc sulfate is a commonly used zinc
form, zinc citrate, gluconate and picolinate may be valid options as
well. These forms are better absorbed than zinc oxide.
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 granulocytes secrete zinc), or both.
Weight gain
=============
Zinc deficiency may lead to loss of appetite. The use of zinc in the
treatment of anorexia has been advocated since 1979. At least 15
clinical trials have shown that zinc improved weight gain in anorexia.
A 1994 trial showed that zinc doubled the rate of body mass increase
in the treatment of anorexia nervosa. Deficiency of other nutrients
such as tyrosine, tryptophan and thiamine could contribute to this
phenomenon of "malnutrition-induced malnutrition".
A meta-analysis of 33 prospective intervention trials regarding zinc
supplementation and its effects on the growth of children in many
countries showed that zinc supplementation alone had a statistically
significant effect on linear growth and body weight gain, indicating
that other deficiencies that may have been present were not
responsible for growth retardation.
Other
=======
People taking zinc supplements may slow down the 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.
Topical use
=============
Topical preparations of zinc include those used on the skin, often in
the form of zinc oxide. Zinc oxide is generally recognized 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 bad
breath; zinc citrate helps reduce the build-up of 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
======================================================================
Zinc is an essential trace element for humans. and other animals, for
plants and for microorganisms. Zinc is required for the function of
over 300 enzymes and 1000 transcription factors, and is stored and
transferred in metallothioneins. It is the second most abundant trace
metal in humans after iron and it is the only metal which appears in
all 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 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, 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 ligands", 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 neurons 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 zinc transporter involved in
cerebral zinc homeostasis.
Enzymes
=========
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 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
() regulation and digestion of proteins, respectively.
In vertebrate blood, carbonic anhydrase converts into bicarbonate and
the same enzyme transforms the bicarbonate back into 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 acetic
acid (auxin) and alcoholic fermentation.
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.
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 ZIP transporters.
Other proteins
================
Zinc serves a purely structural role in zinc fingers, twists and
clusters. Zinc fingers form parts of some transcription factors, which
are proteins that recognize DNA base sequences during the replication
and transcription of DNA. Each of the nine or ten ions in a zinc
finger helps maintain the finger's structure by coordinately binding
to four amino acids 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 zinc signaling to communicate with other cells.
Zinc may be held in metallothionein reserves within microorganisms or
in the intestines or liver of animals. Metallothionein in intestinal
cells is capable of adjusting absorption of zinc by 15-40%. 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 high affinity extracellular
zinc binding site which, upon zinc binding, inhibits dopamine reuptake
and amplifies amphetamine-induced dopamine efflux 'in vitro'. The
human serotonin transporter and norepinephrine transporter do not
contain zinc binding sites. Some EF-hand calcium binding proteins such
as S100 or NCS-1 are also able to bind zinc ions.
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 mg/day, respectively. The RDAs are 8 and 11 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 mg/day.
RDA for lactation is 12 mg/day. For infants up to 12 months the RDA is
3 mg/day. For children ages 1-13 years the RDA increases with age from
3 to 8 mg/day. As for safety, the IOM sets Tolerable upper intake
levels (ULs) for vitamins and minerals when evidence is sufficient. In
the case of zinc the adult UL is 40 mg/day including both food and
supplements combined (lower for children). Collectively the EARs,
RDAs, AIs and ULs are referred to as Dietary Reference Intakes (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 mg/day as phytate
intake increases from 300 to 1200 mg/day; for men the range is 9.4 to
16.3 mg/day. These PRIs are higher than the U.S. RDAs. The EFSA
reviewed the same safety question and set its UL at 25 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 mg, but on May 27,
2016, it was revised to 11 mg. A table of the old and new adult daily
values is provided at Reference Daily Intake.
Dietary intake
================
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. Zinc is
also found in beans, nuts, almonds, whole grains, pumpkin seeds,
sunflower seeds, and blackcurrant.
Other sources include fortified food and dietary supplements 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.
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 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 mg/day - again with intake decreasing
with age.
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. Zinc deficiency depresses immunity, 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 chelator
phytate, found in seeds and cereal bran, can contribute to zinc
malabsorption. Some evidence suggests that more than the US RDA (8
mg/day for adult women; 11 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 biomarkers, and the most widely used
indicator, plasma zinc, has poor sensitivity and specificity.
Soil remediation
==================
Species of 'Calluna', 'Erica' and 'Vaccinium' can grow in
zinc-metalliferous soils, because translocation of toxic ions is
prevented by the action of ericoid mycorrhizal fungi.
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 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.
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
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 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 mg of zinc daily may suffer
induced copper deficiency. A 2007 trial observed that elderly men
taking 80 mg daily were hospitalized for urinary complications more
often than those taking a placebo. Levels of 100-300 mg may interfere
with the use of copper and iron or adversely affect cholesterol. Zinc
in excess of 500 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 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 PARP-dependent energy crisis in
cultured human keratinocytes and melanocytes.
Poisoning
===========
In 1982, the US Mint began minting 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 kg of zinc) resulted in death due to gastrointestinal
bacterial and fungal sepsis. Another patient who ingested 12 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.
See also
======================================================================
* List of countries by zinc production
* Spelter
* Wet storage stain
* Zinc alloy electroplating
* Metal fume fever
* Piotr Steinkeller
External links
======================================================================
* [
http://ods.od.nih.gov/factsheets/zinc/ Zinc Fact Sheet] from the
U.S. National Institutes of Health
* [
http://elements.vanderkrogt.net/element.php?sym=Zn History &
Etymology of Zinc]
* [
http://minerals.usgs.gov/minerals/pubs/commodity/zinc/index.html
Statistics and Information from the U.S. Geological Survey]
* [
https://www.organic-chemistry.org/chemicals/reductions/zinc-zn.shtm
Reducing Agents > Zinc]
* [
http://www.zinc.org American Zinc Association] Information about
the uses and properties of zinc.
* [
http://www.iszb.org ISZB] International Society for Zinc Biology,
founded in 2008. An international, nonprofit organization bringing
together scientists working on the biological actions of zinc.
* [
http://zinc-uk.org Zinc-UK] Founded in 2010 to bring together
scientists in the United Kingdom working on zinc.
* [
http://www.periodicvideos.com/videos/030.htm Zinc] at 'The Periodic
Table of Videos' (University of Nottingham)
* [
https://zincbind.net ZincBind] - a database of biological zinc
binding sites.
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=========
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Original Article:
http://en.wikipedia.org/wiki/Zinc
