Antimony
Antimony is a chemical element with symbol Sb (from Latin:
stibium) and atomic number 51.
A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral
stibnite
(Sb2S3). Antimony compounds have been known since ancient
times and were used for cosmetics; metallic antimony was also known, but it was
erroneously identified as lead upon its discovery. It was first isolated by Vannoccio Biringuccio and described in 1540.
For
some time, China has been the largest producer of antimony and its compounds,
with most production coming from the Xikuangshan Mine in Hunan. The industrial methods to produce antimony are roasting
and subsequent carbothermal reduction or direct reduction of stibnite with
iron.
The
largest applications for metallic antimony are as alloying material for lead
and tin and for lead antimony plates in lead–acid batteries. Alloying lead and tin with antimony improves the
properties of the alloys which are used in solders,
bullets
and plain bearings. Antimony compounds are prominent additives for chlorine
and bromine-containing fire retardants
found in many commercial and domestic products. An emerging application is the
use of antimony in microelectronics.
Occurrences and Uses
The
abundance of antimony in the Earth's crust is estimated at 0.2 to 0.5 parts per
million, comparable to thallium at 0.5 parts per million and silver at 0.07
ppm. Even though this element is not abundant, it is found in over 100 mineral
species. Antimony is sometimes found natively (e.g. on Antimony Peak), but more
frequently it is found in the sulfide stibnite (Sb2S3) which is the predominant
ore mineral.
Cobalt
Cobalt is a chemical
element with symbol Co and atomic number 27. Like nickel, cobalt in the Earth's
crust is found only in chemically combined form, save for small deposits found
in alloys of natural meteoric iron. The free element, produced by reductive
smelting, is a hard, lustrous, silver-gray metal.
Cobalt-based blue
pigments (cobalt blue) have been used since ancient times for jewelry and
paints, and to impart a distinctive blue tint to glass, but the color was later
thought by alchemists to be due to the known metal bismuth. Miners had long
used the name kobold ore (German for goblin ore) for some of the blue-pigment
producing minerals; they were so named because they were poor in known metals,
and gave poisonous arsenic-containing fumes upon smelting. In 1735, such ores
were found to be reducible to a new metal (the first discovered since ancient
times), and this was ultimately named for the kobold.
Today, some cobalt is
produced specifically from various metallic-lustered ores, for example
cobaltite (CoAsS), but the main source of the element is as a by-product of
copper and nickel mining. The copper belt in the Democratic Republic of the
Congo, Central African Republic and Zambia yields most of the cobalt mined
worldwide.
Cobalt is primarily
used as the metal, in the preparation of magnetic, wear-resistant and
high-strength alloys. Its compounds cobalt silicate and cobalt(II) aluminate
(CoAl2O4, cobalt blue) give a distinctive deep blue color to glass, ceramics,
inks, paints and varnishes. Cobalt occurs naturally as only one stable isotope,
cobalt-59. Cobalt-60 is a commercially important radioisotope, used as a
radioactive tracer and for the production of high energy gamma rays.
Cobalt is the active
center of coenzymes called cobalamins, the most common example of which is
vitamin B12. As such it is an essential trace dietary mineral for all animals.
Cobalt in inorganic form is also an active nutrient for bacteria, algae and
fungi.
Occurrence
and Uses
The stable form of
cobalt is created in supernovas via the r-process. It comprises 0.0029% of the
Earth's crust and is one of the first transition metals.
Free cobalt (the native
metal) is not found in on Earth due to the amount of oxygen in the atmosphere
and chlorine in the ocean. Oxygen and chlorine are abundant enough in the upper
layers of the Earth's crust so as to make native metal cobalt formation
extremely rare. Except as recently delivered in meteoric iron, pure cobalt in
native metal form is unknown on Earth (see below). Though the element is of
medium abundance, natural compounds of cobalt are numerous. Small amounts of cobalt
compounds are found in most rocks, soil, plants, and animals.
In nature, cobalt is
frequently associated with nickel, and both are characteristic components of
meteoric iron, though cobalt is much less abundant in iron meteorites than
nickel. As with nickel, cobalt in meteoric iron alloys may have been well
enough protected from oxygen and moisture to occur as the free metal, a state
which otherwise is not seen with either element in the ancient terrestrial
crust.
Cobalt in compound form
occurs as a minor component of copper and nickel minerals. It is the major
metallic component in combination with sulfur and arsenic in the sulfidic
cobaltite (CoAsS), safflorite (CoAs2), glaucodot ((Co,Fe)AsS), and skutterudite
(CoAs3) minerals.[9] The mineral cattierite is similar to pyrite and occurs
together with vaesite in the copper deposits of the Katanga Province.[39] Upon
contact with the atmosphere, weathering occurs and the sulfide minerals oxidize
to form pink erythrite ("cobalt glance": Co3(AsO4)2·8H2O) and spherocobaltite
(CoCO3).
Copper
Copper is a chemical
element with symbol Cu (from Latin: cuprum) and atomic number 29. It is a soft,
malleable and ductile metal with very high thermal and electrical conductivity.
A freshly exposed surface of pure copper has a reddish-orange color. It is used
as a conductor of heat and electricity, as a building material, and as a
constituent of various metal alloys.
Copper is found as a
pure metal in nature, and this was the source of the first metal to be used by
humans, ca. 8,000 BC; it was the first metal to be smelted from its ore, ca.
5,000 BC; it was the first metal to be cast into a shape in a mold, ca. 4,000
BC; and it was the first metal to be purposefully alloyed with another metal,
tin, to create bronze, ca. 3,500.
In the Roman era,
copper was principally mined on Cyprus, the origin of the name of the metal
from aes сyprium (metal of Cyprus), later corrupted to сuprum, from which the
words copper (English), cuivre (French), Koper (Dutch) and Kupfer (German) are
all derived.[4] Its compounds are commonly encountered as copper(II) salts,
which often impart blue or green colors to minerals such as azurite, malachite
and turquoise and have been widely used historically as pigments. Architectural
structures built with copper corrode to give green verdigris (or patina).
Decorative art prominently features copper, both by itself and in the form of
pigments.
Copper is essential to
all living organisms as a trace dietary mineral because it is a key constituent
of the respiratory enzyme complex cytochrome c oxidase. In molluscs and
crustacea copper is a constituent of the blood pigment hemocyanin, which is
replaced by the iron-complexed hemoglobin in fish and other vertebrates. The
main areas where copper is found in humans are liver, muscle and bone.[5]
Copper compounds are used as bacteriostatic substances, fungicides, and wood
preservatives.
Occurrence
and Uses
Native copper from the Keweenaw
Peninsula Michigan about 2.5 inches (6.4 cm) long.
Copper
is synthesized in massive stars and is present in the Earth's crust at a
concentration of about 50 parts per million (ppm), where it occurs as native copper
or in minerals such as the copper sulfides chalcopyrite
and chalcocite,
the copper carbonates azurite and malachite, and the copper(I) oxide
mineral cuprite.
The largest mass of elemental copper discovered weighed 420 tonnes and was
found in 1857 on the Keweenaw Peninsula in Michigan, US. Native copper is a polycrystal,
with the largest described single crystal measuring 4.4×3.2×3.2 cm.
Gallium
Gallium
is a chemical element with symbol Ga and atomic number 31. Elemental gallium
does not occur in free form in nature, but as the gallium(III) compounds that
are in trace amounts in zinc ores and in bauxite. Gallium is a soft, silvery
metal, and elemental gallium is a brittle solid at low temperatures, and melts
at 29.76 °C (85.57 °F) (slightly above room temperature). The melting point of
gallium is used as a temperature reference point. The alloy galinstan (68.5%
gallium, 21.5% indium, and 10% tin) has an even lower melting point of −19 °C
(−2 °F), well below the freezing point of water. Since its discovery in 1875,
gallium has been used as an agent to make alloys that melt at low temperatures.
It has also been useful in semiconductors, including as a dopant.
Gallium
is predominantly used in electronics. Gallium arsenide, the primary chemical
compound of gallium in electronics, is used in microwave circuits, high-speed
switching circuits, and infrared circuits. Semiconductive gallium nitride and
indium gallium nitride produce blue and violet light-emitting diodes (LEDs) and
diode lasers. Gallium is also used in the production of artificial gadolinium
gallium garnet for jewelry.
Gallium
has no known natural role in biology. Gallium(III) behaves in a similar manner
to ferric salts in biological systems and has been used in some medical
applications, including pharmaceuticals and radiopharmaceuticals. Gallium
thermometers are manufactured as an eco-friendly alternative to mercury
thermometers.
Occurrence
and Uses
Gallium does not exist
in free form in nature, and the few high-gallium minerals such as gallite
(CuGaS2) are too rare to serve as a primary source of the element or its
compounds. Its abundance in the Earth's crust is approximately 16.9 ppm. Gallium
is found and extracted as a trace component in bauxite and to a small extent
from sphalerite. The amount extracted from coal, diaspore and germanite in
which gallium is also present is negligible. The United States Geological
Survey (USGS) estimates gallium reserves to exceed 1 million tonnes, based on
50 ppm by weight concentration in known reserves of bauxite and zinc ores. Some
flue dusts from burning coal have been shown to contain small quantities of
gallium, typically less than 1% by weight.
Gold
Gold is a chemical
element with symbol Au (from Latin: aurum) and atomic number 79. In its purest
form, it is a bright, slightly reddish yellow, dense, soft, malleable and
ductile metal. Chemically, gold is a transition metal and a group 11 element.
It is one of the least reactive chemical elements, and is solid under standard
conditions. The metal therefore occurs often in free elemental (native) form,
as nuggets or grains, in rocks, in veins and in alluvial deposits. It occurs in
a solid solution series with the native element silver (as electrum) and also
naturally alloyed with copper and palladium. Less commonly, it occurs in
minerals as gold compounds, often with tellurium (gold tellurides).
Gold's atomic number of
79 makes it one of the higher atomic number elements that occur naturally in
the universe. It is thought to have been produced in supernova nucleosynthesis
from the collision of two neutron stars and to have been present in the dust
from which the Solar System formed. Because the Earth was molten when it was
just formed, almost all of the gold present in the early Earth probably sank
into the planetary core. Therefore, most of the gold that is present today in
the Earth's crust and mantle is thought to have been delivered to Earth later,
by asteroid impacts during the late heavy bombardment, about 4 billion years
ago.
Gold resists attacks by
individual acids, but it can be dissolved by aqua regia (nitro-hydrochloric
acid, literally "royal water"). The acid mixture causes the formation
of a soluble gold tetrachloride anion. Gold metal also dissolves in alkaline
solutions of cyanide, which are used in mining and electroplating. It is
insoluble in nitric acid, which dissolves silver and base metals, a property
that has long been used to refine gold and to confirm the presence of gold in
items, giving rise to the term acid test; it dissolves in mercury, though,
forming amalgam alloys, but this is not a chemical reaction.
This metal has been a
valuable and highly sought-after precious metal for coinage, jewelry, and other
arts since long before the beginning of recorded history. In the past, a gold
standard was often implemented as a monetary policy within and between nations,
but gold coins ceased to be minted as a circulating currency in the 1930s, and
the world gold standard was finally abandoned for a fiat currency system after
1976. The historical value of gold was rooted in its medium rarity, easy
handling and minting, easy smelting, corrosion resistance, distinct color, and
non-reactivity to other elements.
A total of 183,600
tonnes of gold is in existence above ground, as of 2014. This is equivalent to
9513 m3 of gold. The world consumption of new gold produced is about 50% in
jewelry, 40% in investments, and 10% in industry. Gold’s high malleability,
ductility, resistance to corrosion and most other chemical reactions, and
conductivity of electricity have led to its continued use in corrosion
resistant electrical connectors in all types of computerized devices (its chief
industrial use). Gold is also used in infrared shielding, colored-glass
production, gold leafing, and tooth restoration. Certain gold salts are still
used as anti-inflammatories in medicine.
Occurrence
and Uses
This 156-troy-ounce
(4.9 kg) nugget, known as the Mojave Nugget, was found by an individual
prospector in the Southern California Desert using a metal detector.
Gold's atomic number of
79 makes it one of the higher atomic number elements that occur naturally.
Traditionally, gold is thought to have formed by the R-process in supernova
nucleosynthesis, but a relatively recent paper suggests that gold and other
elements heavier than iron may also be produced in quantity by the collision of
neutron stars.[80] In both cases, satellite spectrometers only indirectly
detect the resulting gold: "we have no spectroscopic evidence that [such]
elements have truly been produced."
These gold
nucleogenesis theories hold that the resulting explosions scattered
metal-containing dusts (including heavy elements such as gold) into the region
of space in which they later condensed into our solar system and the Earth.
Because the Earth was molten when it was just formed, almost all of the gold
present on Earth sank into the core. Most of the gold that is present today in
the Earth's crust and mantle is thought to have been delivered to Earth later,
by asteroid impacts during the Late Heavy Bombardment.
Iron
Iron is a chemical
element with symbol Fe (from Latin: ferrum) and atomic number 26. It is a metal
in the first transition series. It is by mass the most common element on Earth,
forming much of Earth's outer and inner core. It is the fourth most common
element in the Earth's crust. Its abundance in rocky planets like Earth is due
to its abundant production by fusion in high-mass stars, where the production
of nickel-56 (which decays to the most common isotope of iron) is the last
nuclear fusion reaction that is exothermic. Consequently, radioactive nickel is
the last element to be produced before the violent collapse of a supernova
scatters precursor radionuclide of iron into space.
Like other group 8
elements, iron exists in a wide range of oxidation states, −2 to +6, although
+2 and +3 are the most common. Elemental iron occurs in meteoroids and other
low oxygen environments, but is reactive to oxygen and water. Fresh iron
surfaces appear lustrous silvery-gray, but oxidize in normal air to give
hydrated iron oxides, commonly known as rust. Unlike many other metals which
form passivating oxide layers, iron oxides occupy more volume than the metal
and thus flake off, exposing fresh surfaces for corrosion.
Iron metal has been
used since ancient times, although copper alloys, which have lower melting
temperatures, were used even earlier in human history. Pure iron is relatively
soft, but is unobtainable by smelting. The material is significantly hardened
and strengthened by impurities, in particular carbon, from the smelting
process. A certain proportion of carbon (between 0.002% and 2.1%) produces
steel, which may be up to 1000 times harder than pure iron. Crude iron metal is
produced in blast furnaces, where ore is reduced by coke to pig iron, which has
a high carbon content. Further refinement with oxygen reduces the carbon
content to the correct proportion to make steel. Steels and low carbon iron
alloys along with other metals (alloy steels) are by far the most common metals
in industrial use, due to their great range of desirable properties and the
widespread abundance of iron-bearing rock.
Iron chemical compounds
have many uses. Iron oxide mixed with aluminium powder can be ignited to create
a thermite reaction, used in welding and purifying ores. Iron forms binary
compounds with the halogens and the chalcogens. Among its organometallic
compounds is ferrocene, the first sandwich compound discovered.
Iron plays an important
role in biology, forming complexes with molecular oxygen in hemoglobin and
myoglobin; these two compounds are common oxygen transport proteins in
vertebrates. Iron is also the metal at the active site of many important redox
enzymes dealing with cellular respiration and oxidation and reduction in plants
and animals.
Lithium
Lithium (from Greek:
λίθος lithos, "stone") is a chemical element with the symbol Li and
atomic number 3. It is a soft, silver-white metal belonging to the alkali metal
group of chemical elements. Under standard conditions it is the lightest metal
and the least dense solid element. Like all alkali metals, lithium is highly
reactive and flammable. For this reason, it is typically stored in mineral oil.
When cut open, it exhibits a metallic luster, but contact with moist air
corrodes the surface quickly to a dull silvery gray, then black tarnish.
Because of its high reactivity, lithium never occurs freely in nature, and
instead, only appears in compounds, which are usually ionic. Lithium occurs in
a number of pegmatitic minerals, but due to its solubility as an ion, is
present in ocean water and is commonly obtained from brines and clays. On a
commercial scale, lithium is isolated electrolytically from a mixture of
lithium chloride and potassium chloride.
The nuclei of lithium
verge on instability, since the two stable lithium isotopes found in nature
have among the lowest binding energies per nucleon of all stable nuclides.
Because of its relative nuclear instability, lithium is less common in the
solar system than 25 of the first 32 chemical elements even though the nuclei
are very light in atomic weight.[3] For related reasons, lithium has important
links to nuclear physics. The transmutation of lithium atoms to helium in 1932
was the first fully man-made nuclear reaction, and lithium-6 deuteride serves
as a fusion fuel in staged thermonuclear weapons.
Lithium and its
compounds have several industrial applications, including heat-resistant glass
and ceramics, lithium grease lubricants, flux additives for iron, steel and
aluminium production, lithium batteries and lithium-ion batteries. These uses
consume more than three quarters of lithium production.
Trace amounts of
lithium are present in all organisms. The element serves no apparent vital
biological function, since animals and plants survive in good health without
it. Non-vital functions have not been ruled out. The lithium ion Li+
administered as any of several lithium salts has proved to be useful as a
mood-stabilizing drug in the treatment of bipolar disorder, due to neurological
effects of the ion in the human body.
Occurrence
and Uses
Lithium is about as
common as chlorine in the Earth's upper continental crust, on a per-atom basis.
Astronomical
According to modern
cosmological theory, lithium—as both of its stable isotopes lithium-6 and
lithium-7—was among the 3 elements synthesized in the Big Bang.[34] Though the
amount of lithium generated in Big Bang nucleosynthesis is dependent upon the
number of photons per baryon, for accepted values the lithium abundance can be
calculated, and there is a "cosmological lithium discrepancy" in the
Universe: older stars seem to have less lithium than they should, and some
younger stars have far more. The lack of lithium in older stars is apparently
caused by the "mixing" of lithium into the interior of stars, where
it is destroyed.Furthermore, lithium is produced in younger stars. Though it
transmutes into two atoms of helium due to collision with a proton at
temperatures above 2.4 million degrees Celsius (most stars easily attain this
temperature in their interiors), lithium is more abundant than predicted in
later-generation stars, for causes not yet completely understood.
Nova Centauri 2013 is
the first in which evidence of lithium has been found.
Though it was one of
the three first elements (together with helium and hydrogen) to be synthesized
in the Big Bang, lithium, together with beryllium and boron are markedly less
abundant than other nearby elements. This is a result of the low temperature
necessary to destroy lithium, and a lack of common processes to produce it.
Lithium is also found
in brown dwarf substellar objects and certain anomalous orange stars. Because
lithium is present in cooler, less-massive brown dwarfs, but is destroyed in
hotter red dwarf stars, its presence in the stars' spectra can be used in the
"lithium test" to differentiate the two, as both are smaller than the
Sun. Certain orange stars can also contain a high concentration of lithium.
Those orange stars found to have a higher than usual concentration of lithium
(such as Centaurus X-4) orbit massive objects—neutron stars or black
holes—whose gravity evidently pulls heavier lithium to the surface of a
hydrogen-helium star, causing more lithium to be observed.
Terrestrial
Although lithium is
widely distributed on Earth, it does not naturally occur in elemental form due
to its high reactivity. The total lithium content of seawater is very large and
is estimated as 230 billion tonnes, where the element exists at a relatively
constant concentration of 0.14 to 0.25 parts per million (ppm), or 25
micromolar; higher concentrations approaching 7 ppm are found near hydrothermal
vents.
Estimates for the
Earth's crustal content range from 20 to 70 ppm by weight. In keeping with its
name, lithium forms a minor part of igneous rocks, with the largest
concentrations in granites. Granitic pegmatites also provide the greatest
abundance of lithium-containing minerals, with spodumene and petalite being the
most commercially viable sources. Another significant mineral of lithium is
lepidolite. A newer source for lithium is hectorite clay, the only active
development of which is through the Western Lithium Corporation in the United
States.[45] At 20 mg lithium per kg of Earth's crust, lithium is the 25th most
abundant element.
According to the
Handbook of Lithium and Natural Calcium, "Lithium is a comparatively rare
element, although it is found in many rocks and some brines, but always in very
low concentrations. There are a fairly large number of both lithium mineral and
brine deposits but only comparatively few of them are of actual or potential commercial
value. Many are very small, others are too low in grade."
The US Geological
Survey estimates that in 2010 Chile had the largest reserves by far (7.5
million tonnes) and the highest annual production (8,800 tonnes). One of the
largest reserve bases [note 1] of lithium is in the Salar de Uyuni area of
Bolivia, which has 5.4 million tonnes. Other major suppliers include Australia,
Argentina and China.
In June 2010, the New
York Times reported that American geologists were conducting ground surveys on dry
salt lakes in western Afghanistan believing that large deposits of lithium are
located there. "Pentagon officials said that their initial analysis at one
location in Ghazni Province showed the potential for lithium deposits as large
as those of Bolivia, which now has the world's largest known lithium
reserves."These estimates are "based principally on old data, which
was gathered mainly by the Soviets during their occupation of Afghanistan from
1979–1989" and "Stephen Peters, the head of the USGS's Afghanistan
Minerals Project, said that he was unaware of USGS involvement in any new
surveying for minerals in Afghanistan in the past two years. 'We are not aware
of any discoveries of lithium,' he said."
Biological
Lithium is found in
trace amount in numerous plants, plankton, and invertebrates, at concentrations
of 69 to 5,760 parts per billion (ppb). In vertebrates the concentration is
slightly lower, and nearly all vertebrate tissue and body fluids have been found
to contain lithium ranging from 21 to 763 ppb. Marine organisms tend to
bioaccumulate lithium more than terrestrial ones. It is not known whether
lithium has a physiological role in any of these organisms, but nutritional
studies in mammals have indicated its importance to health, leading to a
suggestion that it be classed as an essential trace element with an RDA of 1
mg/day. Observational studies in Japan, reported in 2011, suggested that
naturally occurring lithium in drinking water may increase human lifespan.
Manganese
Manganese is a chemical
element with symbol Mn and atomic number 25. It is not found as a free element
in nature; it is often found in combination with iron, and in many minerals.
Manganese is a metal with important industrial metal alloy uses, particularly
in stainless steels.
Historically, manganese
is named for various black minerals (such as pyrolusite) from the same region
of Magnesia in Greece which gave names to similar-sounding magnesium, Mg, and
magnetite, an ore of the element iron, Fe. By the mid-18th century, Swedish
chemist Carl Wilhelm Scheele had used pyrolusite to produce chlorine. Scheele
and others were aware that pyrolusite (now known to be manganese dioxide)
contained a new element, but they were unable to isolate it. Johan Gottlieb
Gahn was the first to isolate an impure sample of manganese metal in 1774, by
reducing the dioxide with carbon.
Manganese phosphating
is used as a treatment for rust and corrosion prevention on steel. Depending on
their oxidation state, manganese ions have various colors and are used
industrially as pigments. The permanganates of alkali and alkaline earth metals
are powerful oxidizers. Manganese dioxide is used as the cathode (electron
acceptor) material in zinc-carbon and alkaline batteries.
In biology, manganese (II)
ions function as cofactors for a large variety of enzymes with many functions.
Manganese enzymes are particularly essential in detoxification of superoxide
free radicals in organisms that must deal with elemental oxygen. Manganese also
functions in the oxygen-evolving complex of photosynthetic plants. The element
is a required trace mineral for all known living organisms but is a neurotoxin.
In larger amounts, and apparently with far greater effectiveness through
inhalation, it can cause a poisoning syndrome in mammals, with neurological
damage which is sometimes irreversible.
Occurrence
and production
Manganese makes up
about 1000 ppm (0.1%) of the Earth's crust, making it the 12th most abundant
element there. Soil contains 7–9000 ppm of manganese with an average of 440
ppm. Seawater has only 10 ppm manganese and the atmosphere contains 0.01 µg/m3.
Manganese occurs principally as pyrolusite (MnO2), braunite,
(Mn2+Mn3+6)(SiO12), psilomelane (Ba,H2O)2Mn5O10, and to a lesser extent as
rhodochrosite (MnCO3).
The most important
manganese ore is pyrolusite (MnO2). Other economically important manganese ores
usually show a close spatial relation to the iron ores. Land-based resources
are large but irregularly distributed. About 80% of the known world manganese
resources are found in South Africa; other important manganese deposits are in
Ukraine, Australia, India, China, Gabon and Brazil. In 1978, 500 billion tons
of manganese nodules were estimated to exist on the ocean floor. Attempts to
find economically viable methods of harvesting manganese nodules were abandoned
in the 1970s.
Mercury
Mercury is a chemical
element with symbol Hg and atomic number 80. It is commonly known as
quicksilver and was formerly named hydrargyrum (/haɪˈdrɑːrdʒərəm/). A heavy,
silvery d-block element, mercury is the only metallic element that is liquid at
standard conditions for temperature and pressure; the only other element that
is liquid under these conditions is bromine, though metals such as caesium,
gallium, and rubidium melt just above room temperature.
Mercury occurs in
deposits throughout the world mostly as cinnabar (mercuric sulfide). The red
pigment vermilion is obtained by grinding natural cinnabar or synthetic
mercuric sulfide.
Mercury is used in
thermometers, barometers, manometers, sphygmomanometers, float valves, mercury
switches, mercury relays, fluorescent lamps and other devices, though concerns
about the element's toxicity have led to mercury thermometers and
sphygmomanometers being largely phased out in clinical environments in favor of
alternatives such as alcohol- or galinstan-filled glass thermometers and
thermistor- or infrared-based electronic instruments. Likewise, mechanical
pressure gauges and electronic strain gauge sensors have replaced mercury
sphygmomanometers. Mercury remains in use in scientific research applications
and in amalgam for dental restoration in some locales. It is used in
fluorescent lighting. Electricity passed through mercury vapor in a fluorescent
lamp produces short-wave ultraviolet light which then causes the phosphor in
the tube to fluoresce, making visible light.
Mercury poisoning can
result from exposure to water-soluble forms of mercury (such as mercuric
chloride or methylmercury), by inhalation of mercury vapor, or by eating food
contaminated with mercury.
Occurrence
and Uses
Mercury is an extremely
rare element in Earth's crust, having an average crustal abundance by mass of
only 0.08 parts per million (ppm). Because it does not blend geochemically with
those elements that constitute the majority of the crustal mass, mercury ores
can be extraordinarily concentrated considering the element's abundance in
ordinary rock. The richest mercury ores contain up to 2.5% mercury by mass, and
even the leanest concentrated deposits are at least 0.1% mercury (12,000 times
average crustal abundance). It is found either as a native metal (rare) or in
cinnabar, corderoite, livingstonite and other minerals, with cinnabar (HgS) being
the most common ore. Mercury ores usually occur in very young orogenic belts
where rocks of high density are forced to the crust of Earth, often in hot
springs or other volcanic regions.
Beginning in 1558, with
the invention of the patio process to extract silver from ore using mercury,
mercury became an essential resource in the economy of Spain and its American
colonies. Mercury was used to extract silver from the lucrative mines in New
Spain and Peru. Initially, the Spanish Crown's mines in Almadén in Southern
Spain supplied all the mercury for the colonies. Mercury deposits were
discovered in the New World, and more than 100,000 tons of mercury were mined
from the region of Huancavelica, Peru, over the course of three centuries
following the discovery of deposits there in 1563. The patio process and later
pan amalgamation process continued to create great demand for mercury to treat
silver ores until the late 19th century.
Molybdenum
Molybdenum is a
chemical element with symbol Mo and atomic number 42. The name is from
Neo-Latin molybdaenum, from Ancient Greek Μόλυβδος molybdos, meaning lead,
since its ores were confused with lead ores. Molybdenum minerals have been
known throughout history, but the element was discovered (in the sense of
differentiating it as a new entity from the mineral salts of other metals) in
1778 by Carl Wilhelm Scheele. The metal was first isolated in 1781 by Peter
Jacob Hjelm.
Molybdenum does not
occur naturally as a free metal on Earth, but rather in various oxidation states
in minerals. The free element, which is a silvery metal with a gray cast, has
the sixth-highest melting point of any element. It readily forms hard, stable
carbides in alloys, and for this reason most of world production of the element
(about 80%) is in making many types of steel alloys, including high strength
alloys and superalloys.
Most molybdenum
compounds have low solubility in water, but the molybdate ion MoO2−4 is soluble
and forms when molybdenum-containing minerals are in contact with oxygen and water.
Industrially, molybdenum compounds (about 14% of world production of the
element) are used in high-pressure and high-temperature applications, as
pigments, and as catalysts.
Molybdenum-containing
enzymes are by far the most common catalysts used by some bacteria to break the
chemical bond in atmospheric molecular nitrogen, allowing biological nitrogen
fixation. At least 50 molybdenum-containing enzymes are now known in bacteria
and animals, although only bacterial and cyanobacterial enzymes are involved in
nitrogen fixation. These nitrogenases contain molybdenum in a different form
from the other molybdenum-containing enzymes, which all contain fully oxidized
molybdenum incorporated into a molybdenum cofactor. Owing to the diverse
functions of the various molybdenum cofactor enzymes, molybdenum is a required
element for life in all higher eukaryote organisms, though it is not required
by all bacteria.
Occurrence
and production
Lustrous, silvery,
flat, hexagonal crystals in roughly parallel layers sit flowerlike on a rough,
translucent crystalline piece of quartz.
Molybdenum is the 54th
most abundant element in the Earth's crust and the 25th most abundant element
in its oceans, with an average of 10 parts per billion; it is the 42nd most
abundant element in the Universe. The Russian Luna 24 mission discovered a
molybdenum-bearing grain (1 × 0.6 µm) in a pyroxene fragment taken from Mare
Crisium on the Moon. The comparative rarity of molybdenum in the Earth's crust
is offset by its concentration in a number of water-insoluble ores, often
combined with sulfur, in the same way as copper, with which it is often found.
Though molybdenum is found in such minerals as wulfenite (PbMoO4) and powellite
(CaMoO4), the main commercial source is molybdenite (MoS2). Molybdenum is mined
as a principal ore and is also recovered as a byproduct of copper and tungsten
mining.
The world's production
of molybdenum was 250,000 tonnes in 2011, the largest producers being China
(94,000 t), United States (64,000 t), Chile (38,000 t), Peru (18,000 t) and
Mexico (12,000 t). The total reserves are estimated at 10 million tonnes, and
are mostly concentrated in China (4.3 Mt), US (2.7 Mt) and Chile (1.2 Mt). By
continent, 93% of world molybdenum production is about evenly split between North
America, South America (mainly in Chile), and China. Europe and the rest of
Asia (mostly Armenia, Russia, Iran and Mongolia) produce the remainder.
Nickel
Nickel is a chemical
element with symbol Ni and atomic number 28. It is a silvery-white lustrous
metal with a slight golden tinge. Nickel belongs to the transition metals and
is hard and ductile. Pure nickel shows a significant chemical activity that can
be observed when nickel is powdered to maximize the exposed surface area on
which reactions can occur, but larger pieces of the metal are slow to react
with air at ambient conditions due to the formation of a protective oxide
surface. Even then, nickel is reactive enough with oxygen that native nickel is
rarely found on Earth's surface, being mostly confined to the interiors of
larger nickel–iron meteorites that were protected from oxidation during their
time in space. On Earth, such native nickel is found in combination with iron,
a reflection of those elements' origin as major end products of supernova
nucleosynthesis. An iron–nickel mixture is thought to compose Earth's inner
core.
The use of nickel (as a
natural meteoric nickel–iron alloy) has been traced as far back as 3500 BCE.
Nickel was first isolated and classified as a chemical element in 1751 by Axel
Fredrik Cronstedt, who initially mistook its ore for a copper mineral. The element's
name comes from a mischievous sprite of German miner mythology, Nickel (similar
to Old Nick), that personified the fact that copper-nickel ores resisted
refinement into copper. An economically important source of nickel is the iron
ore limonite, which often contains 1-2% nickel. Nickel's other important ore
minerals include garnierite, and pentlandite. Major production sites include
the Sudbury region in Canada (which is thought to be of meteoric origin), New
Caledonia in the Pacific, and Norilsk in Russia.
Because of nickel's
slow rate of oxidation at room temperature, it is considered
corrosion-resistant. Historically, this has led to its use for plating metals
such as iron and brass, coating chemistry equipment, and manufacturing certain
alloys that retain a high silvery polish, such as German silver. About 6% of
world nickel production is still used for corrosion-resistant pure-nickel
plating. Nickel-plated items are noted for provoking nickel allergy. Nickel has
been widely used in coins, though its rising price has led to some replacement
with cheaper metals in recent years.
Nickel is one of four
elements that are ferromagnetic around room temperature. Alnico permanent
magnets based partly on nickel are of intermediate strength between iron-based
permanent magnets and rare-earth magnets. The metal is chiefly valuable in the
modern world for the alloys it forms; about 60% of world production is used in
nickel-steels (particularly stainless steel). Other common alloys, as well as
some new superalloys, make up most of the remainder of world nickel use, with
chemical uses for nickel compounds consuming less than 3% of production.[5] As
a compound, nickel has a number of niche chemical manufacturing uses, such as a
catalyst for hydrogenation. Enzymes of some microorganisms and plants contain
nickel as an active site, which makes the metal an essential nutrient for them.
Occurrence
and Uses
On Earth, nickel occurs
most often in combination with sulfur and iron in pentlandite, with sulfur in
millerite, with arsenic in the mineral nickeline, and with arsenic and sulfur
in nickel galena. Nickel is commonly found in iron meteorites as the alloys
kamacite and taenite.
The bulk of the nickel
mined comes from two types of ore deposits. The first are laterites, where the
principal ore minerals are nickeliferous limonite: (Fe, Ni)O(OH) and garnierite
(a hydrous nickel silicate): (Ni, Mg) 3Si2O5(OH)
4. The second are
magmatic sulfide deposits, where the principal ore mineral is pentlandite: (Ni,
Fe) 9S8. Australia and New Caledonia have the biggest estimate reserves (45%
all together).
In terms of World
Resources, identified land-based resources averaging 1% nickel or greater
contain at least 130 million tons of nickel (about the double of known
reserves). About 60% is in laterites and 40% is in sulfide deposits.
Based on geophysical
evidence, most of the nickel on Earth is postulated to be concentrated in the
Earth's outer and inner cores. Kamacite and taenite are naturally occurring
alloys of iron and nickel. For kamacite, the alloy is usually in the proportion
of 90:10 to 95:5, although impurities (such as cobalt or carbon) may be
present, while for taenite the nickel content is between 20% and 65%. Kamacite
and taenite occur in nickel iron meteorites.
Niobium
Niobium, formerly
columbium, is a chemical element with symbol Nb (formerly Cb) and atomic number
41. It is a soft, grey, ductile transition metal, which is often found in the
pyrochlore mineral, the main commercial source for niobium, and columbite. The
name comes from Greek mythology: Niobe, daughter of Tantalus since it is so
similar to tantalum.
Niobium has physical
and chemical properties similar to those of the element tantalum, and the two
are therefore difficult to distinguish. The English chemist Charles Hatchett
reported a new element similar to tantalum in 1801 and named it columbium. In
1809, the English chemist William Hyde Wollaston wrongly concluded that
tantalum and columbium were identical. The German chemist Heinrich Rose
determined in 1846 that tantalum ores contain a second element, which he named
niobium. In 1864 and 1865, a series of scientific findings clarified that
niobium and columbium were the same element (as distinguished from tantalum),
and for a century both names were used interchangeably. Niobium was officially
adopted as the name of the element in 1949, but the name columbium remains in
current use in metallurgy in the United States.
It was not until the
early 20th century that niobium was first used commercially. Brazil is the leading
producer of niobium and ferroniobium, an alloy of niobium and iron. Niobium is
used mostly in alloys, the largest part in special steel such as that used in
gas pipelines. Although these alloys contain a maximum of 0.1%, the small
percentage of niobium enhances the strength of the steel. The temperature
stability of niobium-containing superalloys is important for its use in jet and
rocket engines. Niobium is used in various superconducting materials. These
superconducting alloys, also containing titanium and tin, are widely used in
the superconducting magnets of MRI scanners. Other applications of niobium
include its use in welding, nuclear industries, electronics, optics,
numismatics, and jewelry. In the last two applications, niobium's low toxicity
and ability to be colored by anodization are particular advantages.
Occurrence
and Uses
Niobium is estimated to
be the 34th most common element in the Earth’s crust, with 20 ppm. Some think
that the abundance on Earth is much greater, but that the "missing"
niobium may be located in the Earth’s core due to the metal's high density. The
free element is not found in nature, but niobium occurs in combination with
other elements in minerals.[28] Minerals that contain niobium often also
contain tantalum. Examples include columbite ((Fe,Mn)(Nb,Ta)2O6) and
columbite–tantalite (or coltan, (Fe,Mn)(Ta,Nb)2O6). Columbite–tantalite minerals are most usually
found as accessory minerals in pegmatite intrusions, and in alkaline intrusive
rocks. Less common are the niobates of calcium, uranium, thorium and the rare
earth elements. Examples of such niobates are pyrochlore ((Na,Ca)2Nb2O6(OH,F))
and euxenite ((Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6). These large deposits of niobium
have been found associated with carbonatites (carbonate-silicate igneous rocks)
and as a constituent of pyrochlore.
The two largest
deposits of pyrochlore were found in the 1950s in Brazil and Canada, and both
countries are still the major producers of niobium mineral concentrates. The
largest deposit is hosted within a carbonatite intrusion at Araxá, Minas Gerais
Brazil, owned by CBMM (Companhia Brasileira de Metalurgia e Mineração); the
other deposit is located in Goiás and owned by Anglo American plc (through its
subsidiary Mineração Catalão), also hosted within a carbonatite intrusion. Altogether
these two Brazilian mines produce around 75% of world supply. The third largest
producer of niobium is the carbonatite-hosted Niobec Mine, Saint-Honoré near
Chicoutimi, Quebec owned by Iamgold Corporation Ltd, which produces around 7%
of world supply.
Rare
Earth
A rare earth element
(REE) or rare earth metal (REM), as defined by IUPAC, is one of a set of
seventeen chemical elements in the periodic table, specifically the fifteen
lanthanides, as well as scandium and yttrium. Scandium and yttrium are
considered rare earth elements because they tend to occur in the same ore
deposits as the lanthanides and exhibit similar chemical properties.
Despite their name,
rare earth elements are – with the exception of the radioactive promethium –
relatively plentiful in Earth's crust, with cerium being the 25th most abundant
element at 68 parts per million, or as abundant as copper. However, because of
their geochemical properties, rare earth elements are typically dispersed and
not often found concentrated as rare earth minerals in economically exploitable
ore deposits.[3] It was the very scarcity of these minerals (previously called
"earths") that led to the term "rare earth". The first such
mineral discovered was gadolinite, a mineral composed of cerium, yttrium, iron,
silicon and other elements. This mineral was extracted from a mine in the
village of Ytterby in Sweden; four of the rare earth elements bear names
derived from this single location.
Occurrence
Rare earth elements
became known to the world with the discovery of the black mineral
"Ytterbite" (renamed to Gadolinite in 1800) by Lieutenant Carl Axel
Arrhenius in 1787, at a quarry in the village of Ytterby, Sweden.[8]
Arrhenius's
"ytterbite" reached Johan Gadolin, a Royal Academy of Turku
professor, and his analysis yielded an unknown oxide (earth) that he called
yttria. Anders Gustav Ekeberg isolated beryllium from the gadolinite but failed
to recognize other elements that the ore contained. After this discovery in
1794 a mineral from Bastnäs near Riddarhyttan, Sweden, which was believed to be
an iron–tungsten mineral, was re-examined by Jöns Jacob Berzelius and Wilhelm
Hisinger. In 1803 they obtained a white oxide and called it ceria. Martin
Heinrich Klaproth independently discovered the same oxide and called it
ochroia.
Silver
Silver is a chemical
element with symbol Ag (Greek: άργυρος árguros, Latin: argentum, both from the
Indo-European root *h₂erǵ-
for "grey" or "shining") and atomic number 47. A soft,
white, lustrous transition metal, it possesses the highest electrical
conductivity, thermal conductivity and reflectivity of any metal. The metal
occurs naturally in its pure, free form (native silver), as an alloy with gold
and other metals, and in minerals such as argentite and chlorargyrite. Most
silver is produced as a byproduct of copper, gold, lead, and zinc refining.
Silver has long been
valued as a precious metal. More abundant than gold, silver metal has in many
premodern monetary systems functioned as coinable specie, sometimes even
alongside gold. In addition, silver has numerous applications beyond currency,
such as in solar panels, water filtration, jewelry and ornaments, high-value
tableware and utensils (hence the term silverware), and also as an investment in
the forms of coins and bullion. Silver is used industrially in electrical
contacts and conductors, in specialized mirrors, window coatings and in
catalysis of chemical reactions. Its compounds are used in photographic film
and X-rays. Dilute silver nitrate solutions and other silver compounds are used
as disinfectants and microbiocides (oligodynamic effect), added to bandages and
wound-dressings, catheters and other medical instruments.
Occurrence
and Uses
Silver is found in
native form, as an alloy with gold (electrum), and in ores containing sulfur,
arsenic, antimony or chlorine. Ores include argentite (Ag2S), chlorargyrite
(AgCl), which includes horn silver, and pyrargyrite (Ag3SbS3). The principal
sources of silver are the ores of copper, copper-nickel, lead, and lead-zinc
obtained from Peru, Bolivia, Mexico, China, Australia, Chile, Poland and
Serbia. Peru, Bolivia and Mexico have been mining silver since 1546, and are
still major world producers. Top silver-producing mines are Cannington
(Australia), Fresnillo (Mexico), San Cristobal (Bolivia), Antamina (Peru),
Rudna (Poland), and Penasquito (Mexico). Top near-term mine development
projects through 2015 are Pascua Lama (Chile), Navidad (Argentina), Jaunicipio
(Mexico), Malku Khota (Bolivia), and Hackett River (Canada). In Central Asia,
Tajikistan is known to have some of the largest silver deposits in the world.
The metal is primarily
produced as a byproduct of electrolytic copper refining, gold, nickel, and zinc
refining, and by application of the Parkes process on lead metal obtained from
lead ores that contain small amounts of silver. Commercial-grade fine silver is
at least 99.9% pure, and purities greater than 99.999% are available. In 2012,
Mexico was the top producer of silver (5,360 tonnes or 21% of the world's
total), closely followed by China (3,900 t) and Peru (3,480 t).
Strontium
Strontium is a chemical
element with symbol Sr and atomic number 38. An alkaline earth metal, strontium
is a soft silver-white or yellowish metallic element that is highly reactive
chemically. The metal turns yellow when it is exposed to air. Strontium has
physical and chemical properties similar to those of its two vertical neighbors
calcium and barium. It occurs naturally in the minerals celestine, putnisite
and strontianite. While natural strontium is stable, the synthetic 90Sr isotope
is present in radioactive fallout and has a half-life of 28.90 years.
Both strontium and
strontianite are named after Strontian, a village in Scotland near which the
mineral was discovered in 1790 by Adair Crawford and William Cruickshank. The
production of sugar from sugar beet was in the 19th century its largest
application (see strontian process). At the peak of production of television
cathode ray tubes, up to 75 percent of U.S. strontium consumption was used to
make the faceplate glass. With the displacement of cathode ray tubes by other display
methods in television sets, consumption of strontium has dramatically declined.
Occurrence
and Uses
Strontium commonly
occurs in nature, the 15th most abundant element on Earth, estimated to average
approximately 360 parts per million in the Earth's crust and is found chiefly
as the form of the sulfate mineral celestite (SrSO4) and the carbonate
strontianite (SrCO3). Of the two, celestite occurs much more frequently in
sedimentary deposits of sufficient size to make development of mining
facilities attractive. Because strontium is used most often in the carbonate
form, strontianite would be the more useful of the two common minerals, but few
deposits have been discovered that are suitable for development.
In groundwater
strontium behaves chemically much like calcium. At intermediate to acidic pH
Sr2+ is the dominant strontium species. In the presence of calcium ions
strontium commonly forms coprecipitates with calcium minerals such as calcite
and anhydrite at an increased pH. At intermediate to acidic pH dissolved
strontium is bound to soil particles by cation exchange.
The mean strontium
content of ocean water is 8 mg/l. At a concentration between 82 and 90 µmol/l
of strontium the concentration is considerably lower than the calcium
concentration which is normally between 9.6 and 11.6 mmol/l.
Tantalum
Tantalum is a chemical
element with symbol Ta and atomic number 73. Previously known as tantalium, its
name comes from Tantalus, an antihero from Greek mythology. Tantalum is a rare,
hard, blue-gray, lustrous transition metal that is highly corrosion-resistant.
It is part of the refractory metals group, which are widely used as minor
components in alloys. The chemical inertness of tantalum makes it a valuable
substance for laboratory equipment and a substitute for platinum. Tantalum is
also used for medical implants and bone repair. Its main use today is in
tantalum capacitors in electronic equipment such as mobile phones, DVD players,
video game systems and computers. Tantalum, always together with the chemically
similar niobium, occurs in the minerals tantalite, columbite and coltan (a mix
of columbite and tantalite). Tantalum is a rare metal, comprising 8×10−9% of
the universe, making it one-fifteenth as abundant in the universe as gold
(which makes up 6×10−8%).[6] Tantalum also comprises 1.5×10−4% of the earth's
crust, making it more abundant than other metals in the sixth period, such as
rhenium (abundance 2.6×10−7%), osmium (abundance 1.8×10−7%), and iridium
(abundance 4×10−8%), but not as abundant as barium (abundance 3.4×10−2%)
Occurrence
and Uses
Tantalum is estimated
to make up about 1 ppm or 2 ppm of the Earth's crust by weight. There are many
species of tantalum minerals, only some of which are so far being used by
industry as raw materials: tantalite, microlite, wodginite, euxenite,
polycrase. Tantalite (Fe, Mn) Ta2O6 is the most important mineral for tantalum
extraction. Tantalite has the same mineral structure as columbite (Fe, Mn) (Ta,
Nb)2O6; when there is more tantalum than niobium it is called tantalite and
when there is more niobium than tantalum is it called columbite (or niobite).
The high density of tantalite and other tantalum containing minerals makes the
use of gravitational separation the best method. Other minerals include samarskite
and fergusonite.
The primary mining of
tantalum is in Australia, where the largest producer, Global Advanced Metals,
formerly known as Talison Minerals, operates two mines in Western Australia,
Greenbushes in the Southwest and Wodgina in the Pilbara region. The Wodgina
mine was reopened in January 2011 after mining at the site was suspended in
late-2008 due to the global financial crisis.[34] Less than a year after it
reopened, Global Advanced Metals announced that due to again "...
softening tantalum demand ...", and other factors, tantalum mining
operations were to cease at the end of February 2012. Wodgina produces a
primary tantalum concentrate which is further upgraded at the Greenbushes
operation before being sold to customers. Whereas the large-scale producers of
niobium are in Brazil and Canada, the ore there also yields a small percentage
of tantalum. Some other countries such as China, Ethiopia, and Mozambique mine
ores with a higher percentage of tantalum, and they produce a significant
percentage of the world's output of it. Tantalum is also produced in Thailand
and Malaysia as a by-product of the tin mining there. During gravitational
separation of the ores from placer deposits, not only is Cassiterite (SnO2)
found, but a small percentage of tantalite also included. The slag from the tin
smelters then contains economically useful amounts of tantalum, which is
leached from the slag.[13][37] Future sources of supply of tantalum, in order
of estimated size, are being explored in Saudi Arabia, Egypt, Greenland, China,
Mozambique, Canada, Australia, the United States, Finland, and Brazil.
Thorium
Thorium is a chemical
element with symbol Th and atomic number 90. A radioactive actinide metal,
thorium is one of only two significantly radioactive elements that still occur
naturally in large quantities as a primordial element (the other being
uranium).[a] It was discovered in 1828 by the Norwegian Reverend and amateur
mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns
Jakob Berzelius, who named it after Thor, the Norse god of thunder.
A thorium atom has 90
protons and therefore 90 electrons, of which four are valence electrons.
Thorium metal is silvery and tarnishes black when exposed to air. Thorium is
weakly radioactive: all its known isotopes are unstable, with the seven
naturally occurring ones (thorium-227, 228, 229, 230, 231, 232, and 234) having
half-lives between 25.52 hours and 14.05 billion years. Thorium-232, which has
142 neutrons, is the most stable isotope of thorium and accounts for nearly all
natural thorium, with the other five natural isotopes occurring only in traces:
it decays very slowly through alpha decay to radium-228, starting a decay chain
named the thorium series that ends at lead-208. Thorium is estimated to be
about three to four times more abundant than uranium in the Earth's crust, and
is chiefly refined from monazite sands as a by-product of extracting rare earth
metals.
Thorium was once
commonly used as the light source in gas mantles and as an alloying material,
but these applications have declined due to concerns about its radioactivity.
Thorium is still widely used as an alloying element in TIG welding electrodes
(at a rate of 1%-2% mix with tungsten). It remains popular as a material in
high-end optics and scientific instrumentation; thorium and uranium are the
only significantly radioactive elements with major commercial applications that
do not rely on their radioactivity. Thorium is predicted to be able to replace
uranium as nuclear fuel in nuclear reactors, but only a few thorium reactors
have yet been completed.
Occurrence
and Uses
Thorium-232 is a
primordial nuclide, having existed in its current form for over 4.5 billion
years, predating the formation of the Earth; it was forged in the cores of
dying stars through the r-process and scattered across the galaxy by
supernovae. Its radioactive decay produces a significant amount of the Earth's
internal heat.
Natural thorium is
essentially isotopically pure 232Th, which is the longest-lived and most stable
isotope of thorium, having a half-life comparable to the age of the universe.
If the source contains no uranium, the only other thorium isotope present would
be 228Th, which occurs in the decay chain of thorium-232 (the thorium series):
the ratio of 228Th to 232Th would be under 10−10. However, if uranium is
present, tiny traces of several other isotopes will be present: 231Th and 227Th
from the decay chain of uranium-235 (the actinium series), and slightly larger
but still tiny traces of 234Th and 230Th from the decay chain of uranium-238
(the uranium series). 229Th is also been produced in the decay chain of 237Np
(the neptunium series): while all primordial 237Np is extinct, it is still
produced today as a result of nuclear reactions in uranium ores. 229Th is
mostly produced as a daughter of artificial uranium-233, itself produced from
neutron irradiation of 232Th, due to its extreme rarity in nature.
Titanium
Titanium is a chemical
element with symbol Ti and atomic number 22. It is a lustrous transition metal
with a silver color, low density and high strength. It is highly resistant to
corrosion in sea water, aqua regia and chlorine.
Titanium was discovered
in Cornwall, Great Britain, by William Gregor in 1791 and named by Martin
Heinrich Klaproth for the Titans of Greek mythology. The element occurs within
a number of mineral deposits, principally rutile and ilmenite, which are widely
distributed in the Earth's crust and lithosphere, and it is found in almost all
living things, rocks, water bodies, and soils. The metal is extracted from its
principal mineral ores via the Kroll process or the Hunter process. Its most
common compound, titanium dioxide, is a popular photocatalyst and is used in
the manufacture of white pigments. Other compounds include titanium
tetrachloride (TiCl4), a component of smoke screens and catalysts; and titanium
trichloride (TiCl3), which is used as a catalyst in the production of
polypropylene.
Titanium can be alloyed
with iron, aluminum, vanadium, and molybdenum, among other elements, to produce
strong, lightweight alloys for aerospace (jet engines, missiles, and
spacecraft), military, industrial process (chemicals and petro-chemicals,
desalination plants, pulp, and paper), automotive, agri-food, medical
prostheses, orthopedic implants, dental and endodontic instruments and files,
dental implants, sporting goods, jewelry, mobile phones, and other
applications.
The two most useful
properties of the metal are corrosion resistance and the highest
strength-to-density ratio of any metallic element. In its unalloyed condition,
titanium is as strong as some steels, but less dense. There are two allotropic
forms and five naturally occurring isotopes of this element, 46Ti through 50Ti,
with 48Ti being the most abundant (73.8%). Although they have the same number
of valence electrons and are in the same group in the periodic table, titanium
and zirconium differ in many chemical and physical properties.
Occurrence
and Uses
Titanium is always
bonded to other elements in nature. It is the ninth-most abundant element in
Earth's crust (0.63% by mass) and the seventh-most abundant metal. It is
present in most igneous rocks and in sediments derived from them (as well as in
living things and natural bodies of water). Of the 801 types of igneous rocks
analyzed by the United States Geological Survey, 784 contained titanium. Its
proportion in soils is approximately 0.5 to 1.5%.
It is widely
distributed and occurs primarily in the minerals anatase, brookite, ilmenite,
perovskite, rutile and titanite (sphene). Of these minerals, only rutile and
ilmenite have economic importance, yet even they are difficult to find in high
concentrations. About 6.0 and 0.7 million tonnes of these minerals have been
mined in 2011, respectively. Significant titanium-bearing ilmenite deposits
exist in western Australia, Canada, China, India, Mozambique, New Zealand,
Norway, Ukraine and South Africa.[15] About 186,000 tonnes of titanium metal
sponge were produced in 2011, mostly in China (60,000 t), Japan (56,000 t), Russia
(40,000 t), United States (32,000 t) and Kazakhstan (20,700 t). Total reserves
of titanium are estimated to exceed 600 million tonnes.
The concentration of Ti
is about 4 picomolar in the ocean. At 100 °C, the concentration of titanium in
water is estimated to be less than 10−7 M at pH 7. The identity of titanium
species in aqueous solution remains unknown because of its low solubility and
the lack of sensitive spectroscopic methods, although only the 4+ oxidation
state is stable in air. No evidence exists for a biological role for titanium,
although rare organisms are known to accumulate high concentrations.
Titanium is contained
in meteorites and has been detected in the Sun and in M-type stars,[4] which
are the coolest type of star, with a surface temperature of 3,200 °C (5,790
°F).[21] Rocks brought back from the Moon during the Apollo 17 mission are
composed of 12.1% TiO2.[4] It is also found in coal ash, plants, and even the human
body.
Uranium
Uranium is a chemical
element with symbol U and atomic number 92. It is a silvery-white metal in the
actinide series of the periodic table. A uranium atom has 92 protons and 92
electrons, of which 6 are valence electrons. Uranium is weakly radioactive
because all its isotopes are unstable (with half-lives of the 6 naturally known
isotopes, uranium-233 to uranium-238, varying between 69 years and 4.5 billion
years). The most common isotopes of uranium are uranium-238 (which has 146
neutrons and accounts for almost 99.3% of the uranium found in nature) and
uranium-235 (which has 143 neutrons, accounting for 0.7% of the element found
naturally). Uranium has the second highest atomic weight of the primordially
occurring elements, lighter only than plutonium. Its density is about 70%
higher than that of lead, but slightly lower than that of gold or tungsten. It
occurs naturally in low concentrations of a few parts per million in soil, rock
and water, and is commercially extracted from uranium-bearing minerals such as
uraninite.
In nature, uranium is
found as uranium-238 (99.2739–99.2752%), uranium-235 (0.7198–0.7202%), and a
very small amount of uranium-234 (0.0050–0.0059%). Uranium decays slowly by
emitting an alpha particle. The half-life of uranium-238 is about 4.47 billion
years and that of uranium-235 is 704 million years, making them useful in
dating the age of the Earth.
Many contemporary uses
of uranium exploit its unique nuclear properties. Uranium-235 has the
distinction of being the only naturally occurring fissile isotope. Uranium-238
is fissionable by fast neutrons, and is fertile, meaning it can be transmuted
to fissile plutonium-239 in a nuclear reactor. Another fissile isotope,
uranium-233, can be produced from natural thorium and is also important in
nuclear technology. While uranium-238 has a small probability for spontaneous
fission or even induced fission with fast neutrons, uranium-235 and to a lesser
degree uranium-233 have a much higher fission cross-section for slow neutrons. In
sufficient concentration, these isotopes maintain a sustained nuclear chain
reaction. This generates the heat in nuclear power reactors, and produces the
fissile material for nuclear weapons. Depleted uranium (238U) is used in
kinetic energy penetrators and armor plating.
Uranium is used as a
colorant in uranium glass producing orange-red to lemon yellow hues. It was
also used for tinting and shading in early photography. The 1789 discovery of
uranium in the mineral pitchblende is credited to Martin Heinrich Klaproth, who
named the new element after the planet Uranus. Eugène-Melchior Péligot was the
first person to isolate the metal and its radioactive properties were
discovered in 1896 by Henri Becquerel. Research by Otto Hahn, Lise Meitner,
Enrico Fermi and others, such as J. Robert Oppenheimer starting in 1934 led to
its use as a fuel in the nuclear power industry and in Little Boy, the first
nuclear weapon used in war. An ensuing arms race during the Cold War between
the United States and the Soviet Union produced tens of thousands of nuclear
weapons that used uranium metal and uranium-derived plutonium-239. The security
of those weapons and their fissile material following the breakup of the Soviet
Union in 1991 is an ongoing concern for public health and safety.[8] See
Nuclear proliferation.
Occurrence
and Uses
Uranium is a naturally
occurring element that can be found in low levels within all rock, soil, and
water. Uranium is the 51st element in order of abundance in the Earth's crust.
Uranium is also the highest-numbered element to be found naturally in
significant quantities on Earth and is almost always found combined with other
elements. Along with all elements having atomic weights higher than that of
iron, it is only naturally formed in supernovae. The decay of uranium, thorium,
and potassium-40 in the Earth's mantle is thought to be the main source of heat
that keeps the outer core liquid and drives mantle convection, which in turn
drives plate tectonics.
Uranium's average
concentration in the Earth's crust is (depending on the reference) 2 to 4 parts
per million, or about 40 times as abundant as silver.The Earth's crust from the
surface to 25 km (15 mi) down is calculated to contain 1017 kg (2×1017 lb) of
uranium while the oceans may contain 1013 kg (2×1013 lb). The concentration of
uranium in soil ranges from 0.7 to 11 parts per million (up to 15 parts per
million in farmland soil due to use of phosphate fertilizers), and its
concentration in sea water is 3 parts per billion.
Uranium is more plentiful
than antimony, tin, cadmium, mercury, or silver, and it is about as abundant as
arsenic or molybdenum. Uranium is found in hundreds of minerals, including
uraninite (the most common uranium ore), carnotite, autunite, uranophane,
torbernite, and coffinite. Significant concentrations of uranium occur in some
substances such as phosphate rock deposits, and minerals such as lignite, and
monazite sands in uranium-rich ores (it is recovered commercially from sources
with as little as 0.1% uranium).
Five cylinder-like
bodies on a flat surface: four in a group and one separate.
Citrobacter species can
have concentrations of uranium in their bodies 300 times the level of the
surrounding environment
Some bacteria, such as
Shewanella putrefaciens, Geobacter metallireducens and some strains of
Burkholderia fungorum, use uranium for their growth and convert U(VI) to U(IV).
Zinc/Lead
Zinc, in commerce also
spelter, is a chemical element with symbol Zn and atomic number 30. It is the
first element of group 12 of the periodic table. In some respects zinc is
chemically similar to magnesium: its ion is of similar size and its only common
oxidation state is +2. 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 mineable amounts are found in
Australia, Asia, and the United States. Zinc production includes froth
flotation of the ore, roasting, and final extraction using electricity
(electrowinning).
Brass, which is an
alloy of copper and zinc, has been used since at least the 10th century BC in
Judea and by the 7th century BC in Ancient Greece.[3] Zinc metal was not
produced on a large scale until the 12th century in India and was unknown to
Europe until the end of the 16th century. The mines of Rajasthan have given
definite evidence of zinc production going back to the 6th century BC. To date,
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. 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 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
zinc methyl or zinc diethyl in the organic laboratory.
Zinc is an essential
mineral perceived by the public today as being of "exceptional biologic
and public health importance", especially regarding prenatal and postnatal
development.[6] Zinc deficiency affects about two billion people in the
developing world and is associated with many diseases. In children it 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 can cause ataxia, lethargy and copper deficiency.
Occurrence
and Uses
Zinc makes up about 75
ppm (0.0075%) of Earth's crust, making it the 24th most abundant element. Soil
contains 5–770 ppm of zinc with an average of 64 ppm. Seawater has only 30 ppb
zinc and the atmosphere contains 0.1–4 µg/m3.
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 has a low affinity for oxides and
prefers to bond with sulfides. Chalcophiles 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 minerals from
which zinc is extracted include smithsonite (zinc carbonate), hemimorphite
(zinc silicate), wurtzite (another zinc sulfide), and sometimes hydrozincite
(basic zinc carbonate).[18] With the exception of wurtzite, all these other
minerals were formed as a result of weathering processes on the primordial zinc
sulfides.
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