Mercury (element)

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Mercury is a chemical element with the symbol Hg and atomic number 80. In ancient literature it was commonly referred to as liquid silver and also as quicksilver or hydrargyrium. Silvery-looking element, heavy metal belonging to block D of the periodic table, mercury is the only metallic element that is liquid under standard laboratory conditions; the only other element that is liquid under these conditions is bromine (a nonmetal), although other metals such as cesium, gallium, and rubidium melt at slightly higher temperatures.

Mercury appears in deposits around the world, primarily as cinnabar (mercury sulfide). The red pigment called vermilion is obtained by crushing natural cinnabar or mercury sulfide obtained by synthesis.

Mercury is used in thermometers, barometers, manometers, sphygmomanometers, some types of valves such as vacuum pumps, mercury switches, fluorescent lamps, and other devices, although concerns about the element's toxicity have led to mercury thermometers and sphygmomanometers being largely phased out in clinical settings in favor of other alternatives, such as glass thermometers that use alcohol or gallinstan, thermistors, or electronic instruments based on the measurement of infrared radiation. Similarly, mechanical manometers and electronic strain gauge sensors have replaced mercury sphygmomanometers. Mercury remains in use in scientific research applications and in dental amalgams, still used in some countries. It is also used in fluorescent lighting, where electricity passing through a lamp containing low-pressure mercury vapor produces short-wavelength ultraviolet radiation, which in turn causes the phosphor coating the tube to fluoresce, producing visible light.

Mercury poisoning can result from exposure to water-soluble forms of mercury (such as mercuric chloride or methylmercury), by inhaling mercury vapor, or by ingesting any of its forms.

General characteristics

A glass amp with a sample of liquid mercury.

Mercury drops spread over a surface.

Mercury is a silvery heavy metal that is an odorless liquid at room temperature. It is not a good conductor of heat compared to other metals, although it is a good conductor of electricity. It is easily alloyed with many other metals such as gold or silver, producing amalgams, but not with iron. It is insoluble in water and soluble in nitric acid. When its temperature increases -above 40 °C-, it produces toxic and corrosive vapors, heavier than air, which is why it evaporates, creating thousands of particles in the vapor that, when cooled, are deposited again. It is harmful by inhalation, ingestion and contact: it is a very irritating product for the skin, eyes and respiratory tract. It is incompatible with concentrated nitric acid, acetylene, ammonia, chlorine and metals.

Mercury is an anomalous element in several of its properties. It is a noble metal, since its redox potential Hg²⁺/Hg is positive (+0.85 V), compared to the negative of cadmium Cd (-0.40 V), its immediate neighbor of group. It is a unique metal with some resemblance to cadmium, but more like gold and thallium. It is the only transition metal with such a high density, 13.53 g/cm³; a 76 cm column defines an atmosphere, while with water a 10 m high column is needed. Its liquid state under standard conditions indicates that its metallic bond is weak and is justified by the low participation of the 6s² electrons in electronic delocalization in the metallic system (relativistic effects).

It has the highest first ionization energy of all metals (10.4375 eV) for the same reason as above. In addition, Hg²⁺ has a very low hydration enthalpy compared to zinc Zn²⁺ and cadmium Cd²⁺, preferably by coordination two in Hg(II) complexes, as isoelectronic Au(I) gold. This brings as a consequence that the redox potentials of those are negative and that of mercury is noble (positive).

The low reactivity of mercury in oxidative processes is justified by the relativistic effects on the 6s² electrons very contracted towards the nucleus and by the strength of its electronic structure of noble pseudogas.

It is also the only element of the group that presents the +1 state, in the form of a dinuclear species Hg₂²⁺, although the general tendency to stabilize the states of Low oxidation is the opposite in transition groups: formation of Hg(I) compounds with clusters of Hg-Hg pairs. This rich covalency can also be seen in Hg(II) compounds, where many of these Hg(II) compounds are seen to be volatile like HgCl₂, a molecular solid with Cl-Hg- entities Cl in solid, vapor and even in aqueous solution. The resistance of mercury amides, imides and organometallics to hydrolysis and oxygen from the environment is also noteworthy, indicating the great strength of the bond with the Hg-C carbon. Also sulfur S and phosphorus P are suitable donor atoms: effective soft ligands for soft acids like Hg in oxidation states zero, I and II.

The highest oxidation state of mercury is II due to its outer electronic configuration d¹⁰s², and because the sum of its first three ionization energies are too high for oxidation states III or higher to be generated under standard conditions. However, in 2007 it was discovered that at very low temperatures, of the order of -260 °C (that is, the average temperature of space), it exists in oxidation state IV, being able to associate with four fluorine atoms and thus obtaining that additional degree of oxidation. This form is called mercury tetrafluoride (HgF₄); the structure is planar-square, the most stable for a d⁸ species > from a metal ''5d''. This behavior is to be expected, given that mercury has a greater relativistic expansion of its 5d orbitals in relation to its group 12 homologues, which means that in extreme conditions, compared to fluorine, the most oxidizing element in the periodic table, it can generate covalent bonds. The possibility of synthesizing this mercuric fluoride, HgF₄, was predicted theoretically in 1994 according to models indicated above. For the same reason, the possibility of oxidation state III for this metal can be considered, and indeed a complex species has been isolated, in a special medium and by electrochemical oxidation, where the complex cation appears, [Hg cyclam]^{3 +}; cyclam is a chelate ligand that stabilizes mercury in this rare oxidation state (1,4,8,11-Tetraazacyclotetradecane = cyclam). With all this, it must be concluded that mercury should be reconsidered to be included as a transition metal, since it generates species with internal d orbitals that are empty, therefore that there is a favorable energy of stabilization by the field of ligands (EECL).

Properties

Physical properties

A coin of one pound (density of ~7.6 g/cm3) floats in mercury thanks to the combination of floating force and surface tension.

Mercury is a heavy, silvery-white metal. Compared to other metals, it is a poor conductor of heat, but a good conductor of electricity. It has a freezing point of -38.83 °C and a boiling point of 356.73 °C, both exceptionally low for a metal. Furthermore, mercury's boiling point of 629.88 Kelvin (356.7 °C) is the lowest of any metal. A full explanation of this fact goes deep into the realm of quantum physics, but can be summarized as follows: mercury has a unique electronic configuration, in which the electrons cover all available levels 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s, 5p, 5d and 6s. Because this configuration greatly resists the release of an electron, mercury behaves similarly to the noble gases, which form weak bonds and therefore melt at low temperatures. After freezing, the volume of mercury decreases by 3.59% and its density changes from 13.69 g/cm³ in the liquid state to 14.184 g/cm³ when it solidifies. The volumetric expansion coefficient is 181.59x10⁻⁶ at 0 °C, 181.71x10⁻⁶ at 20 °C and 182.50x10⁻⁶ at 100 °C (for every °C).

The stability of the 6s orbital is due to the presence of the replete 4f level. The f shell weakly shields the effective nuclear charge, which increases the attraction due to the Coulomb force between the 6s layer and the nucleus (see lanthanide contraction). The absence of a filled interior f level is the reason for the somewhat higher melting point of cadmium and zinc, although these two metals also melt easily and also have unusually low boiling points.

On the other hand, gold, which occupies a space to the left of mercury in the periodic table, has atoms with one fewer electron in the 6s shell than mercury. Those electrons are more easily released and shared between the gold atoms, which form a relatively strong metallic bond.

Chemical Properties

Mercury does not react with most acids, such as dilute sulfuric acid, although oxidizing acids such as concentrated sulfuric acid and nitric acid or aqua regia dissolve it to give sulfate, nitrate, and chloride. Like silver, mercury reacts with atmospheric hydrogen sulfide. It also reacts with solid sulfur flakes, which are used in equipment to absorb mercury in the event of a spill (activated carbon and powdered zinc are also used for this purpose).

Amalgams

Mercury discharge lamp to calibrate spectrometers.

Mercury dissolves many other metals such as gold and silver to form amalgams. Iron is an exception, so iron containers have traditionally been used for mercury trade. Several other elements of the first rank of the transition metals (with the exception of manganese, copper, and zinc) are reluctant to form amalgams. Another element that does not easily amalgamate with mercury is platinum. Sodium amalgam is a common reducing agent in organic synthesis and is also used in high-pressure sodium-vapor lamps. Pressure.

Mercury readily combines with aluminum to form an aluminum amalgam when the two pure metals come into contact. This amalgam destroys the aluminum oxide layer that protects metallic aluminum from oxidizing in depth (as happens to iron in water). Even small amounts of mercury can severely corrode aluminum. For this reason, mercury is not allowed on board an aircraft under most circumstances, due to the risk of amalgam formation with exposed aluminum parts on the aircraft.

Mercury attack on aluminum is one of the most common types of embrittlement by liquid metal.

Isotopes

Main article: Isotopes of mercury

There are seven stable isotopes of mercury, with 202
Hg being the most abundant (29.86%). The longest-lived radioisotopes are 194
Hg with a half-life of 444 years, and 203
Hg with a half-life of 46,612 days. Most of the remaining radioisotopes have half-lives that are less than one day. 199
Hg and 201
Hg are the active nuclei most often studied by nuclear magnetic resonance, having spins of ¹⁄₂ and ³⁄₂ respectively.

Etymology

Hg is the modern chemical symbol for mercury for short. It comes from hydrargyrum, a Latinized form of the Greek term ὑδράργυρος (hydrargyros), which is a compound word meaning "water-silver" (from ὑδρ- hydr- , the root of ὕδωρ, "water", and ἄργυρος argyros "silver"), since it is liquid like water and shiny like silver. It shares the name with the Roman god Mercury, known for his speed and mobility. For the same reason, it is also associated with the planet Mercury. The astrological symbol for the planet is also the alchemical symbol for metal; the Sanskrit word for alchemy is Rasavātam, which literally means "the path of mercury". Mercury is the only metal for which its alchemical planetary name became its name. common.

History

The symbol of the planet mercury (.) was used for many years to represent the chemical element.

Mercury is found in Ancient Egyptian tombs dating back to 1500 B.C. C.

In China and Tibet the use of mercury was recommended to prolong life, heal fractures and maintain general good health, although exposure to mercury vapors is now known to lead to serious adverse health effects. China's first emperor, Qin Shi Huang (supposedly buried in the so-called 'Qin Shi Huang Mausoleum', which contained flowing rivers of mercury reproducing a model of the ruled earth in which rivers were depicted of China) died from drinking a mixture of mercury and powdered jade prescribed by Qin Dynasty alchemists (causing liver failure, mercury poisoning and brain death) that was intended to give him eternal life. Khumarawayh ibn Ahmad ibn Tulun, the second Tulunid ruler of Egypt (r. 884-896), known for his extravagance and waste according to contemporary chronicles, built a container filled with mercury, in which he stretched out on top of cushions filled with air and he rocked to sleep.

In November 2014, "large numbers" of mercury in a 60-foot chamber beneath an 1,800-year-old temple known as the "Pyramid of the Feathered Serpent," "the third largest pyramid at Teotihuacan", Mexico, along with "jade statues, watchful jaguars, a box full of carved shells and rubber balls".

In Ancient Greece, mercury was used in ointments; in Egypt and Rome they used it in cosmetics. At Lamanai (in present-day Belize), an important city of the Mayan civilization, a raft of mercury was found under a marker in a ballcourt. By the year 500 mercury was used to make amalgams (from the Latin medieval amalgamation, "mercury alloy") with other metals.

Alchemists thought of mercury as the raw material, from which all metals were formed. They believed that different metals could be produced by varying the quality and quantity of sulfur contained within the mercury. The purest of these was gold, and mercury was used in attempts to transmute base (or impure) metals into gold, which was the goal of many alchemists.

The mines of Almadén (Spain), Monte Amiata (Italy) and Idrija (Slovenia) dominated mercury production from the opening of the Almadén mine 2,500 years ago, until new deposits appeared at the end of the 19th century..

Distribution

See also: Category:Mine of mercury and Mercury minerals.

Mercury Producers in 2005.

Mercury is an extremely rare element in the Earth's crust, having a weight-average abundance of just 0.08 parts per million. Because it does not mix geochemically with those elements that make up the majority of the mass In the earth's crust, mercury minerals are extraordinarily concentrated considering the abundance of the element in ordinary rock. The richest mercury ores contain up to 2.5% mercury by weight, and even the poorest concentrate deposits contain at least 0.1% mercury (12,000 times the mean abundance in the Earth's crust). It occurs either as a native (rare) metal or in the form of cinnabar, lamborite, livingstonite, and other minerals, with cinnabar (HgS) being the most abundant ore. Mercury deposits are generally found in orogenic zones. recent, where high-density rocks are forced to rise to the Earth's crust, driven by hot springs or by the activity of certain volcanic regions.

Neighbor glass with its characteristic dark red, Almaden mines, Ciudad Real, Spain.

Native Mercury with Neighborhood, Socrates Mine, Sonoma County, California. Native mercury is sometimes altered in the oxidation zones of deposits.

Starting in 1558, with the invention of the patio process to extract silver from its ores using mercury, this metal became an essential resource in the economy of Spain and its American colonies. The mercury was used to extract silver in the lucrative mines of New Spain and Peru. Initially, the Spanish Crown mines in Almadén (located in south central Spain) supplied all the mercury needed in the colonies, until new deposits were discovered in the New World, and more than 100,000 tons of mercury were mined from the Huancavelica region of Peru (especially from the Santa Bárbara mine) over the three centuries after the discovery of its deposits in 1563. First the patio process and later the pan amalgamation process created a great demand for mercury for the treatment of silver ores until the end of the XIX century.

Old mines in Italy, the United States and Mexico, which once produced a large proportion of the world's supply, have been completely depleted or, in the case of Slovenia (Idrija) and Spain (Almadén), had to close due to the fall in the price of mercury. The McDermitt mine in Nevada, the last mercury mine in the United States, closed in 1992. The price of mercury has been highly volatile in recent years, and in 2006 was $650 per 76-pound container (34.46 kg).

Mercury is extracted by heating cinnabar in a stream of air and condensing the vapor. The equation for this extraction is:

HgS + O₂ → Hg + SO₂

In 2005, China was the leading producer of mercury, with nearly two-thirds of the world's share, followed by Kyrgyzstan. Other countries are believed to maintain unrecorded mercury production from copper electrowinning processes and from recovery of the effluents.

Due to the high toxicity of mercury, both cinnabar mining and mercury refining are dangerous and historical causes of poisoning. In China, prison labor was used by a private mining company as recently as the 1990s. of 1950, to exploit new cinnabar mines. Thousands of prisoners were used by the Luo Xi mining company to dig new galleries. The health of miners in operating mines is at high risk.

The European Union directive making compact fluorescent lamps mandatory from 2012 has encouraged China to reopen its cinnabar mines to obtain the mercury needed to manufacture compact fluorescent lamps. Environmental hazards have been a concern, particularly in the southern cities of Foshan and Guangdong, and in the southwestern Guizhou province.

Abandoned mercury mine processing plants often contain very dangerous waste accumulations of calcined cinnabar. Runoff water at these locations is a recognized source of ecological damage. Former mercury mines may be suitable for constructive reuse. For example, in 1976 Santa Clara County (California) purchased the historic Almaden Quicksilver Mine and created a County park, after conducting a comprehensive safety survey and environmental analysis of the property.

World production

Annual global mercury production
N.o	Country	(Tm)
1	China	1600
2	Kyrgyzstan	100
3	Chile	50
4	Russia	50
5	Peru	45
6	Tajikistan	45
7	Morocco	32
(Year 2013. Source:IndexMundi)

World mercury production has historically experienced continued growth (at first linked primarily to gold and silver mining in the New World, and from the turn of the century XX also related to the industrial production of chlorine), with a progressive decrease from the 1980s, when the environmental risks involved in its indiscriminate use began to become apparent. For example, in the 1970s it was estimated that the Almadén mines had produced some 200,000 mt of mercury throughout their entire useful life, and that they still housed another 200,000 mt inside. From the end of World War II until the 1970s, annual world production rose from 3,200 mt in 1948 to 8,650 mt in 1965, stabilizing for a decade at 9,000-10,000 mt per year.

Starting in the 1990s, both for economic reasons (the drop in metal prices forced the closure of many of the main mines in Western countries, which were no longer profitable), and environmental reasons (production was concentrated in countries with fewer legal restrictions in relation to the environment), China has dominated the world market, with more than 80% of total production in the first years of the century XXI.

World production in 2013 was of the order of 1,900 tons (practically a fifth of its historical maximum, recorded as already noted in the 1970s), with China in prominent first place (see figure attached table), with Kyrgyzstan and Chile being second and third producers, with much lower percentages.

World production in 2019, in tons per year
1.	ChinaChina	3.600
2.	Tajikistan	100
3.	Mexico Mexico	63
4.	Argentina	50
5.	Peru Peru	40
6.	Norway Norway	20
7.	Kyrgyzstan Kyrgyzstan	15

Source: USGS. NOTE: Unpublished data for the United States.

Chemistry

Mercury(I) Compounds

Unlike its lighter neighbors, cadmium and zinc, mercury usually forms stable compounds with simple metal-metal bonds. Most mercury(I) compounds are diamagnetic and contain the dimeric cation, Hg2+
2. Stable derivatives include the chloride and the nitrate. Treatment of complex Hg(I) compounds with strong ligands such as sulfur or cyanide induces a disproportionation to Hg2+
and the formation of elemental mercury. Mercury(I) chloride, a colorless solid also known as calomel, is actually the compound with the formula Hg₂Cl₂, with the structure Cl-Hg-Hg-Cl, a standard in electrochemistry that reacts with chlorine to give mercuric chloride HgCl₂, which is opposed to further oxidation. Mercury(I) hydride, a colorless gas, has the formula HgH, which does not contain any Hg-Hg bonds.

Indicative of their tendency to stick to themselves are the forms of mercury polycations, which consist of linear chains with mercury centers, capped with a positive charge. An example is the Hg2+
3(AsF−
6)
2.

Mercury(II) Compounds

Mercury (II) is the most common oxidation state and therefore the most frequent in nature. All four mercury halides are known, which form tetrahedral complexes with other ligands, but the halides adopt linear coordination geometry, somewhat like Ag⁺. The best known is mercury(II) chloride, a white solid substance that easily sublimates. HgCl₂ forms complexes that are typically tetrahedral, for example the HgCl2−
4.

Mercury(II) oxide, the main oxide of mercury, forms when the metal is exposed to air for long periods of time at elevated temperatures. The elements separate again if the oxide is heated to near 400 °C, as demonstrated by Joseph Priestley in one of the first synthesis of pure oxygen. Hydroxides of mercury are poorly characterized, as are their neighboring elements gold and silver..

Being a soft metal for pH purposes, mercury derivatives form very stable combinations with the heavier chalcogens. The most abundant form is mercury(II) sulfide, HgS, which occurs naturally as the mineral cinnabar, used as a bright red pigment under the name vermilion. Like ZnS, HgS crystallizes in two forms, the reddish cubic form and the black one with a spire-like configuration. Mercury(II) selenide (HgSe) and mercury(II) telluride (HgTe) They are also known, as well as various derivatives, such as mercury cadmium telluride and mercury zinc telluride, which are useful semiconductors as infrared detector materials.

Mercury(II) salts form a variety of compounds derived from ammonia. These include Millon's base (Hg₂N⁺), a one-dimensional polymer (salts of (HgNH+
2)
n), and a "fusible white precipitate" (the [Hg(NH₃)₂]Cl₂). Known as Nessler's reagent, potassium tetraiodomercurate(II) (HgI2−
4) remains sometimes used for testing for ammonia, due to its tendency to form the intensely colored iodide salt of Millon's base.

Mercury(II) fulminate is a detonator widely used in explosives.

Higher oxidation states

Oxidation states greater than 2 in an uncharged species are extremely rare, although a cyclic mercury(IV) cation, with three substituents, may be an intermediate in oxymercuration reactions. In 2007 a report was published in which reported the synthesis of a mercury(IV) compound, mercury(IV) fluoride. In the 1970s there was a claim to the synthesis of a mercury(III) compound, but it is now believed which is false.

Organomercury compounds

Main article: Organomercurial compounds

Organic mercury compounds are historically important in the development of chemistry, but in the Western world they are of little industrial value. Mercury(II) salts are a rare example of simple metal complexes that react directly with aromatic rings. Organomercuric compounds are always divalent and usually two-dimensional and linear in geometry. Unlike organocadmic and organozinc compounds, organomercurial compounds do not react with water. They usually have the formula HgR₂, which are often volatile, or HgRX, which are often solid, where R is aryl or alkyl and X is usually halide or acetate. Methylmercury, a generic term for compounds with the formula CH₃HgX, forms a family of hazardous compounds often found in contaminated water. They arise by a process known as biomethylation.

Mercury(II) forms complexes with nitrogen, phosphorus, and sulfur donor ligands, but resists complexing with oxygen donors; it also generates very stable complexes with bromine, iodine and chlorine as befits a soft cation. The stability of mercury (II) complexes is greater than that of the other two elements of their group, zinc and cadmium, because in addition to σ bonds with adequate hybridizations of the metal, π bonds will be involved. by the further expansion of the 5d of mercury (relativistic effects), which inject charge into the empty d orbitals of the ligands: a resonant system will be created that is compatible with the quantum association of the filled subshell 5d¹⁰, while reinforcing M-L back-donation links. This is unusual, since the smallest ions usually form the best complexes. Complexes with π ligands, such as CO, NO or alkenes, are not known. Zinc complexes are colorless, but mercury complexes, and to a lesser extent cadmium complexes, are colored due to charge transfer from the metal to the ligand (charge transfer absorptions), and from the ligand to the metal, which is more evident in the mercury as indicated above (5d>4d expansion).

Most Hg(II) complexes are distorted octahedral, with two short bonds and four long bonds. The extreme case of this distortion is the formation of only 2 bonds, an example of this are the compounds Hg(CN)₂ and Hg(SCN)2, and the complex [Hg(NH₃)₂]Cl₂; the latter contains the linear ion [H₃N-Hg-NH₃]²⁺. Mercury(II) also forms tetrahedral complexes such as [Hg(SCN)₄]^2- and K₂[HgI₄]. The latter is the so-called Nessler reagent for the determination of ammonia in solution; concentrations as low as 1ppm are detected and a yellow or brown precipitate, [Hg₂NI.H₂O] ({Hg₂ units) is formed. >N}⁺ giving Hg tetrahedral environment for N and linear for Hg (II), polymeric cation with cuprite-like 3D structure, Cu₂O, or fine anti-β-cristobalite.

Other examples of mercury(II) complexes where different coordination environments can be seen are:

Lineal: [Hg (py)₂]²⁺, the ligand, py, is the piridine
Planotriangular: [HgX₃]^-, being X = Cl, Br, I
Tetraédrico: [HgI₄]^2-[Hg (en)₂]²⁺; in, it is ethylenediamine-leading quelate, and each connects two sites to mercury.
8: [Hg (en)₃]²⁺

Applications

Bulb of a mercury thermometer.

Mercury is used primarily for the manufacture of industrial chemicals or for electrical applications and is used in some thermometers, especially those used to measure elevated temperatures. An increasing amount is used as gaseous mercury in fluorescent lamps, while most other applications are slowly being phased out due to health and safety regulations, being replaced in some applications by less toxic, but considerably more expensive materials, as the Galinstanne alloy.

Medicine

Dental filling with mercury amalgam.

Chlorine and caustic soda production

Chlorine is produced from sodium chloride (common salt, NaCl) using electrolysis to separate metallic sodium from chlorine gas. Usually, salt is dissolved in water to produce a brine. The by-products of this chlor-alkali process are hydrogen (H₂) and sodium hydroxide (NaOH), commonly known as caustic soda. By far the largest use of mercury at the end of the 20th century was in the process of mercury cells (also called Castner-Kellner process), in which metallic sodium is formed as an amalgam on a cathode made of mercury. This sodium is reacted with water to produce sodium hydroxide. Many of the industrial mercury emissions of the 20th century come of this process, although modern plants claimed to be safe in this regard. After around 1985, all new chlor-alkali production facilities that were built in the United States use reverse osmosis technologies to produce chlorine.

Use in laboratory equipment

Some thermometers, especially high-temperature ones, contain mercury; although they are gradually disappearing. In the United States, the over-the-counter sale of mercury thermometers has been prohibited since 2003.

Mercury is also used in liquid mirror telescopes.

Some transit telescopes use a container of mercury to form a flat and absolutely horizontal mirror, useful in determining an absolute vertical or perpendicular reference. Concave horizontal parabolic mirrors can be formed by rotating liquid mercury in a cylindrical container: the liquid thus assumes a parabolic shape, allowing the reflection and focus of the incident light. These telescopes are cheaper than conventional large mirror telescopes by up to a factor of 100, but the liquid mercury mirror cannot be tilted and must always point vertically to the spot.

Liquid mercury is a part of the popular secondary reference electrode (called the calomel electrode) in electrochemistry, as an alternative to the standard hydrogen electrode. The calomel electrode is used to calculate the electrode potential of the half cells. Last but not least, the triple point of mercury, -38.8344 °C, is a fixed point used as a temperature standard for the International Scale of Temperature (ITS-90).

The electrodes used in polarography use elemental mercury. This use allows a new, uncontaminated electrode to be available for each measurement or for each new experiment.

Lighting and electronics

Gas mercury is used in mercury vapor lamps, and fluorescent lamps and in some "neon sign" type advertising. These low pressure lamps emit light with very narrow spectral lines, which are traditionally used in spectroscopy for the calibration of spectral positions. Commercial calibration lamps are sold for this purpose; Analyzing light from a ceiling fluorescent in a spectrometer is a common calibration practice. Gaseous mercury is also found in some electronic tubes, including ignitrons, thyratrons, and mercury arc rectifiers. It is also used in lamps. specialized medical care for skin tanning and disinfection. Gaseous mercury is added to cold cathode lamps containing argon to increase ionization and electrical conductivity. A mercury-free argon-filled lamp will show dull spots and will no longer illuminate properly. Lighting systems containing mercury can only be heat treated once. When mercury vapor is added to neon-filled tubes, the light produced will present inconsistent red/blue flecks, until the initial thermal process is complete; eventually, a single color will light up, eventually displaying a coherent muted blue color.

The dark violet gloss of a mercury vapor discharge in a germid lamp, whose spectrum is rich in invisible ultraviolet radiation.
Skin tanning device containing a low-pressure mercury steam lamp and two infrared lamps, which act both as a light source and as an electric ballast.
Various types of fluorescent lamps.

Cosmetics

Mercury, in the form of thiomersal, is widely used in the manufacture of mascara. In 2008, Minnesota became the first state in the United States to ban intentionally added mercury in cosmetics, setting a tougher standard than the federal government.

A study of the geometric mean concentration of mercury in urine identified a previously unrecognized source of inorganic mercury exposure among New York residents: skin care products. Studies based on population biomonitoring also showed that mercury concentration levels are higher among fish and shellfish consumers.

Firearms

A mercury compound called "mercury fulminate" It was mainly used in percussion caps as a detonator for the powder charge of the cartridges that serve as ammunition for firearms.

Historical uses

Type mercury switch (SPST).

Mercury column gauge.

Many historical applications make use of the peculiar physical properties of mercury, especially as a dense liquid and as a liquid metal:

Amounts of liquid mercury between 90 and 600 g have been recovered from the graves of the elites of Mayan civilization (between 100 and 700) or in ritual vessels in six places. This mercury may have been used in bowls as a mirror for divinatory purposes. Five of them date from the classical period of Mayan civilization (c. 250-900), but one of the six examples is earlier.
It was used as a bermell-shaped dye (powder-cooling), forming an extensive part of red paints for centuries, until replaced by cadmium red (not toxic).
In Islamic Spain it was used to fill decorative pools. Centuries later, American artist Alexander Calder built a mercury source for the Spanish Pavilion of the 1937 Paris International Exhibition. The source is now on display at Fundació Joan Miró in Barcelona.
Mercury was used within fishing lures oscillating. Its heavy form, with the very instability of liquid mercury inside it, makes the irregular movement of these lures very attractive to fish. Its use was prohibited for environmental reasons, but there has been the subsequent reopening of this illegal fishing art.
Fresnel lenses of ancient lighthouses used a mercury bath on which they floated and rotated, acting like a bearing.

Mercury turbine switch. The engine spins the denate wheel that passes through a projected mercury flow through the teeth path. Adjusting the position of the wheel up or down the cycle induced in the current of the primary circuit can be modified.

In the early years of broadcasting at the beginning of the centuryXX., to generate black waves with kilocycle frequencies, electromechanical switches were used consisting of a metal dented wheel that intercepted a continuous flow of mercury in which electricity was circulated (see Mercury connectors).

Sphygmomanometers (blood pressure meters), barometers, diffusion pumps, coulombimetres, and many other laboratory instruments use mercury. As opaque liquid with high density and almost linear thermal expansion, it is ideal for this use.
As a electricity-driven liquid, it was used in mercury switches (including some types of domestic light switches installed before 1970), tilting switches used in antique fire detectors, and inclining switches of some types of domestic thermostats.
Due to its acoustic properties, mercury was used as a means of propagation in devices with line-up memory used in the first half-century digital computersXX..
Experimental mercury steam turbines were installed to increase the efficiency of the power of fossil fuel plants. The South Meadow energy plant in Hartford (Connecticut), used mercury as a workflow (in a binary setting with a secondary water circuit) for a number of years from the end of the 1920s, in an attempt to improve plant efficiency. Several other plants were built with this turbine design, including the Schiller station in Portsmouth, New Hampshire, which was launched in 1950. The idea was not successful throughout the industry due to the weight and toxicity of mercury, as well as the emergence of supercritical steam plants in the following years.
Similarly, liquid mercury was used as a refrigerant for some nuclear reactors; however, sodium has been imposed for liquid metal-coated reactors, because the high density of mercury requires much more energy to circulate through the cooling circuits.
Mercury was an ionic engine thruster at the beginning of electrical space retropropulsion systems. Its advantages were its high molecular weight, low ionization energy, low dual ionization energy, high liquid density and metal storage capacity at room temperature. Their disadvantages were the problems related to both environmental impacts associated with testing, as well as the eventual cooling and condensation of some of the propellants on the spacecraft in long-term operations on land. The first space flight that used electric propulsion with a mercury ion propulsor as fuel (developed by NASA Lewis research center) was NASA's "SERT-1" spacecraft in 1964. The SERT-1 flight was followed by SERT-2 in 1970. Mercury and cesium were the thrusters used in the first ion engines, until the Hughes Research Laboratory found that xenon gas is a more appropriate substitute. The xenon is now the propellant used in ion engines, as it has a high molecular weight, little or no reactivity due to its noble gas nature, and presents a high density when stored as a low temperature liquid.

Other applications make use of the chemical properties of mercury:

The mercury battery is a type of non-rechargeable electric accumulator, a very common primary cell in the mid-centuryXX.. It was used in a wide variety of applications and was available in several sizes, particularly for small ones batteries button. His constant voltage output and long service life gave him a specific use in light meters the cameras and the hearing aids. Mercury batteries were effectively banned in most countries in the 1990s owing to concerns about soil mercury contamination.
Mercury is used for the conservation of wood, the creation of daguerrotypes, the silver mirrors, in naval paints to avoid attaching different organisms to the hull of the ships (used abandoned in 1990), herbicides (bandonado in 1995), small toys in the form of pocket labyrinths in which a drop of mercury, some cleaning products, and in the sensors of some automotive suspension devices should be guided. As medicines, mercury compounds have been used in antiseptics, laxatives, antidepressants, and syphilis treatments.
It was supposedly used by Allied spies in sabotage actions against Luftwaffe, through a mercury paste that caused the rapid corrosion of the aircraft's aluminium, causing serious structural failures.
Chloroalcali Process: The main industrial use of mercury during the centuryXX. was in the electrolysis to separate the chlorine and sodium from the brine; serving mercury as an anode of the Castner-Kellner process. The chlorine is used for paper laundering (so the location of many of these plants was near paper factories), while the sodium is used to manufacture sodium hydroxide used in soaps and other cleaning products. This use has been largely abandoned, replaced by other technologies that use osmotic membranes.
As electrodes in some types of electrolysis, catalysts and insecticides.
Mercury was also used as a cleaner inside the guns.
From the mid-centuryXVIII until the middle of the centuryXIX, a process called "carroting" was used in the manufacture of felt hats. Animal skins were washed in a metric nitrate solution (Hg (NO)₃2H₂O₂) orange (the term "carroting", of carrot in English, came from this color). This process separates the skin from the coated, although this dissolution and the vapors it produces are highly toxic. The United States Public Health Service banned the use of mercury in the felt industry in December 1941. Psychological symptoms associated with mercury poisoning inspired English expression "mother a hatter" (loco as a hat). The character of The Hatter by Lewis Carroll in his book The Adventures of Alice in Wonderland It was a word game based on the old sentence, but the character's very character has no symptoms of mercury poisoning.
Gold and silver mining. Historically, mercury was widely used in hydraulic mining in order to separate gold (which sinks into mercury) from the mixture of gravel and water that accompany it. Fine gold particles can also form a mercury-gold amalgam and therefore increase the percentages of gold recovery. The large-scale use of mercury stopped in the 1960s. However, it is still used on a small scale, often clandestine, in the exploration of gold. It is estimated that 45,000 metric tons of mercury that were used in California in the exploitation of ourfer pleasures have not been recovered. Mercury was also used in silver mining.

Historical medicinal use

Mercury(I) chloride (also known as calomel or mercury chloride) has been used in traditional medicine as a diuretic, topical disinfectant, and laxative. Mercury(II) chloride (also known as mercuric chloride or corrosive sublimate) was once used to treat syphilis (along with other mercury compounds), although it is so toxic that symptoms of its toxicity are sometimes confused with those of syphilis that it was believed to treat. It is also used as a disinfectant. "Blue mass", a pill or syrup in which mercury is the main ingredient, was prescribed throughout the century 19th century for numerous ailments, including constipation, depression, infertility, and headaches. Early 19th century XX, mercury was administered to young children as a laxative and vermifuge, and used in dental powder for infants. Merbromin, a mercury-containing organohalide (sometimes sold as mercurochrome) is still widely used, but has been banned in some countries such as the United States.

Toxicity and safety

See also: Mercury poisoning and Cycle of mercury.

Mercury and most of its compounds are extremely toxic and must be handled with care; In cases of mercury-related spills (for example, in the case of broken thermometers or fluorescent tubes containing the metal or its vapors), there are specific cleanup procedures to avoid exposure and prevent its dispersion. Protocols for physically fusing smaller droplets onto hard surfaces so they can be picked up with an eyedropper, or gently nudged the spill into a disposable container. Vacuum cleaners and brooms cause further dispersion of mercury and should not be used. Flakes of sulfur, zinc, or some other powdered material that easily forms an amalgam (alloy) with mercury at ordinary temperatures are then scattered over the area affected by the spill, before being collected and properly deposited. Cleaning porous surfaces and clothing is not effective in removing all traces of mercury and therefore it is advised to discard these types of items when they have been exposed to a mercury spill.

Mercury can be absorbed through the skin and mucous membranes, and mercury vapors can be accidentally inhaled, so mercury containers must be tightly sealed to prevent spillage or evaporation. Heating of mercury or its compounds, which can release it when heated, should be done with adequate ventilation to minimize exposure to mercury vapor. The most toxic forms of mercury are its organic compounds, such as dimethylmercury and methylmercury. Mercury can cause both chronic and acute poisoning, including mercury poisoning.

Chronic exposure primarily affects the central nervous system and kidneys. Nephrotoxicity is due to the high affinity between mercuric ions and reduced sulfhydryl (-SH) groups, mercuric conjugates with albumin, L-cysteine, homocysteine, and glutathione are the biologically important forms of Hg²⁺ in circulation.

Both the organic and inorganic forms of mercury are captured and accumulate in the renal cortex, outside the external medulla, mainly along the three segments of the proximal tubule, thus expressing their toxicity at the renal level. The inorganic species being the ones with the greatest nephrotoxic relevance, on the contrary, in the case of organic species, high doses and multiple exposures are needed to produce renal failure.

The most sensitive part of the nephron to the toxic effects caused by these compounds is the proximal tubule, specifically the S3 segment.

The nephrotoxicity caused by this metal depends on the exposure time, if the exposure is brief, acute tubular necrosis occurs, however, if the exposure is long-term, glomerulonephritis occurs.

Release into the environment

Amount of atmospheric mercury deposited in Fremont (Wyoming) superior glacier between 1720 and 1990.

Pre-industrial deposition rates of mercury from the atmosphere may be about 4 ng/(1 l of ice deposition). Although it can be considered a natural level of exposure, regional or global sources have significant effects. Volcanic eruptions can increase the atmospheric level between 4 and 6 times.

Natural sources, such as volcanoes, are responsible for about half of mercury emissions into the atmosphere. Pollution caused by human activity can be divided into the following estimated percentages:

65 % of thermal power plants, with coal plants being the largest aggregate source (40 per cent of United States mercury emissions in 1999). This includes gas power plants where mercury has not been eliminated. The emissions from coal combustion are between one and two orders of magnitude greater than emissions from oil combustion, depending on each country.
11 % of gold production. The three largest sources of mercury emissions in the US. The United States is the three largest gold mines. The hydrogeochemical release of mercury from the excavation of gold mines has been recognized as a significant source of mercury emission to the atmosphere in eastern Canada.
6.8 % of non-ferrous metal production, typically in casts.
6.4 % of cement production.
3 % from landfills, including domestic trash and hazardous waste, crematory furnaces, and incineration of depuration fanges.
3 % of sosa caustic production.
1.4% of the production of root and steel.
1.1 % of mercury production, especially for batteries.
2 % of other sources.

The above percentages are estimates of global human-induced mercury emissions in the year 2000, excluding biomass burning, a significant source in some regions.

Recent air pollution by mercury in outdoor urban environments was measured with values between 0.01-0.02 mg/m³. In 2001, mercury levels were measured and studied at 12 indoor residential locations chosen to represent a cross section of building classes, locations, and ages in the New York area. This study found elevated mercury concentrations inside homes significantly higher than those registered outdoors, in a range between 0.0065 and 0.523 mg/m³. The average was 0.069 g/m³.

Mercury also enters the environment through improper disposal (for example, in landfills and incinerators) from certain mercury-containing products, such as: auto parts, batteries, fluorescent light bulbs, products medical devices, thermometers and thermostats. Due to health concerns (see below), mercury in these products is being phased out or phased out. For example, the amount of mercury contained in thermostats sold in the United States dropped from 14.5 tons in 2004 to 3.9 tons in 2007.

Most thermometers now use tinted alcohol instead of mercury, and galinstan alloy thermometers are also an available option. Mercury thermometers are still used from time to time in the medical field, as they are more accurate than alcohol thermometers, although both are frequently being replaced by electronic thermometers and less commonly by the aforementioned gallinstan thermometers.. Mercury thermometers are still widely used for certain scientific applications due to their higher accuracy and working range.

Historically, one of the largest releases occurred at the Colex Industrial Plant, a lithium isotope separation facility located in Oak Ridge, Tennessee. The plant operated in the 1950s and 1960s. Records are sketchy and unclear, but government commissions have estimated that about nine hundred tons of mercury are unaccounted for.

A major industrial disaster was the spill of mercury compounds into Minamata Bay in Japan. It is estimated that more than 3,000 people suffered various severe deformities, symptoms of mercury poisoning, or death, in what is known as Minamata disease due to mercury poisoning.

More recently, in various communities in the state of Querétaro, Mexico, the presence of mercury has been discovered in foods of animal and plant origin and in water, and levels of contamination by this element "exceed by up to thousand percent the maximum allowed, which implies serious health risks".

Global Pollution

Mercury measured in the ice of Mount Logan and in the glacier Fremont and Hg emitted from anthropogenic origin. Figure redibujada from the original published by Beal et al. (2015).

Emissions of mercury into the atmosphere are globally distributed and contaminate all ecosystems. As already noted, mercury comes from human activities (coal combustion, direct mining of mercury, silver and gold) and natural activities (volcanism, for example). Emissions produce mostly Hg⁰, with less Hg²⁺. The deposited mercury can be re-emitted to the atmosphere through its exchange between the ocean and the air or the combustion of biomass.

Mercury stored in the ice on Mount Logan (5,340 meters above sea level; Yukon, Canada) from the year 1400 to 1998 has been precisely measured. Most of the mercury accumulation of anthropogenic origin during 600 years occurred on Mount Logan during the 20th century and especially between 1940 and 1975. The increase between 1993 and 1998 (final sampling) may reflect the increase in air emissions from coal burning in Asia and small-scale mining in developing countries, which has been estimated to continue to the present day. The collection and study of new samples of ice is urgent due to the accelerated disappearance of the glaciers.

Work exposure

Because of the health effects of mercury exposure, its industrial and commercial uses are regulated in many countries. The World Health Organization, OSHA, and NIOSH treat mercury as an occupational hazard, and specific occupational exposure limits have been established. Emissions and disposal of environmental mercury are regulated in the US primarily by the Environmental Protection Agency.

Epidemiological studies have confirmed numerous harmful effects of mercury, such as tremors, impaired cognitive abilities, and sleep disturbances in workers with chronic exposure to mercury vapor, even at low concentrations (in the range of 0.7 to 42 mg /m³. A study has shown that point exposure (4-8 hours) to elemental mercury levels estimated to be between 1.1 and 44 mg/m³ resulted in chest pain, dyspnea, cough, hemoptysis, impaired lung function, and evidence of pneumonitis. Acute interstitial exposure to mercury vapor has been shown to produce profound effects on the central nervous system, including psychotic reactions characterized by delusions, hallucinations, and suicidality. Occupational exposure has been embodied in a wide range of functional disturbances, including erethism, irritability, nervousness, excessive shyness, and insomnia.With continued exposure, a slight tem blor, which can turn into violent muscle spasms. The tremor initially involves the hands, later spreading to the eyelids, lips, and tongue. Long-term, low-level exposure has been associated with more subtle symptoms of erethism, including fatigue, irritability, memory loss, vivid dreams, and depression.

Fetal damage

The harmful effects of mercury can be transmitted from mother to fetus, including brain damage, mental retardation, incoordination, blindness, seizures, and the inability to speak. Children with mercury poisoning can develop problems with their nervous and digestive systems and kidney damage.

Treatment

Research on the treatment of mercury intoxication and poisoning is limited. Currently available drugs to treat acute mercury poisoning include N-acetyl-D chelators, L-penicillamine (PAN), Dimercaprol, 2,3-dimercapto-1-propanesulfonic acid (DMPS), and dimercaptosuccinic acid (DMSA).. In a small study including 11 construction workers exposed to elemental mercury, patients were treated with DMSA and NAP. Chelation therapy with both drugs resulted in the mobilization of a small fraction of the estimated total body mercury. DMSA was able to increase mercury excretion to a greater degree than NAP.

Fish and shellfish

Main article: Presence of mercury in fish

Fish and shellfish have a natural tendency to concentrate mercury in their bodies, often in the form of methylmercury, a highly toxic organic compound. Fish species that are part of the higher levels of the food chain, such as sharks, swordfish, mackerel, tuna or albacore, contain higher concentrations of mercury than others. Because mercury and methylmercury are fat soluble, they accumulate primarily in the gut, although they are also deposited throughout muscle tissue. When a fish is eaten by a predator, the mercury level builds up. Since fish are inefficient at clearing methylmercury buildup, concentrations in their tissues increase with time. Therefore, species higher up the food chain accumulate a body burden of mercury that can be ten times higher than that of the species they consume. This process is called biomagnification. This type of mercury poisoning occurred in this way in Minamata, Japan, giving rise to the so-called Minamata disease.

Precautions

Transportation

It is transported in a liquid state, in accordance with the European code of the ADR Agreement: [2809-80-8-8,Â66° c)]. The containers must be hermetically closed. Steel, stainless steel, iron, plastic, glass or porcelain containers can be used. Lead, aluminum, copper, tin and zinc containers should be avoided.

Store in cool, dry, well-ventilated areas, away from solar radiation and sources of heat and/or ignition, since at temperatures above 40 °C it produces steam. It should be away from concentrated nitric acid, acetylene and chlorine. It should be stored in unbreakable containers made of corrosion resistant and compatible materials.

Stains

Mercury can accidentally amalgamate with noble metals such as gold, producing stains on its surface. Since mercury evaporates at around 360 °C (in fact, it must be stored at a temperature that does not exceed 40 °C to avoid the emanation of vapors), it is possible to remove a stain (for example, from some jewelry) by placing it in the flame of a lighter and then polishing it. If the stain is very large, the jewel can be immersed in concentrated nitric acid or concentrated sulfuric acid (the jewel must be made of gold or platinum, otherwise it will dissolve). Acids react with mercury, so it should be noted that these reactions are exothermic and release toxic vapors.

Tagging

In accordance with European Union legislation, the labeling must include the R phrases: R 23 ("Toxic by inhalation") and R 33 ("Danger of cumulative effects"). The S phrases should also be incorporated: S 1/2 ("Keep locked up and out of the reach of children"), S 7 ("Keep container tightly closed") and S 45 ("In case of accident or if you feel unwell, seek medical advice immediately (show the label if possible)").

Rules

International

A total of 140 countries agreed at the Minamata Convention on Mercury to the United Nations Environment Program (UNEP) in order to avoid dangerous emissions. The agreement was signed on October 10, 2013.

European Union

In the European Union, the directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment (see RoHS) prohibits mercury from certain electrical and electronic products, and limits the amount of mercury in other products to less than 1000 ppm. Restrictions have also been imposed for the concentration of mercury in packaging (the limit is 100 ppm for the sum of mercury, lead, hexavalent chromium and cadmium) and in batteries (the limit is 5 ppm). In July 2007, the European Union also banned mercury in non-electric measuring devices, such as thermometers and barometers. The ban only applies to new devices, and contains exceptions for the healthcare sector and a two-year grace period for barometer manufacturers.

Norway

Norway enacted a complete ban on the use of mercury in the manufacture and import/export of mercury products on 1 January 2008. In 2002, several lakes in Norway were found to be in poor condition due to pollution by mercury, with an excess of 1 µg/g of mercury in their sediments. In 2008, Norway's Minister of Development for the Environment, Erik Solheim, stated that: "Mercury is one of the most dangerous environmental toxins. Satisfactory alternatives to mercury in products are already available, so it is appropriate to introduce a ban".

Sweden

Mercury-containing products were banned in Sweden in 2009.

Denmark

In 2008, Denmark also banned dental mercury amalgam, except for filling the chewing surface of permanent teeth, such as adult molars.

United States

In the United States, the Environmental Protection Agency (EPA) is responsible for regulating and managing mercury pollution. Various laws give EPA this authority. In addition, in the regulations contained in the "Mercury-Containing and Rechargeable Battery Management Act", approved in 1996, the use of mercury in batteries is gradually withdrawn, and the efficient and cost-effective disposal of the many types of used batteries. North American countries contributed approximately 11% of total global anthropogenic mercury emissions in 1995.

The "Clean Air Act" (1990), passed in 1990, put mercury on a list of toxic pollutants that need to be controlled to the greatest extent possible. Therefore, industries that release high concentrations of mercury into the environment have agreed to install Maximum Achievable Control Technologies (MACT). In March 2005, the EPA enacted a regulation that added power plants to the list of sources that must be controlled and instituted a national Emissions Trading system. Tighter controls were given until November 2006, but after legal challenge from several states, the regulations were struck down by a federal appeals court on February 8, 2008. The rule is not considered sufficient to protect health of people living near coal-fired power plants, given the negative effects documented in the 1998 EPA Study Report to Congress. However, new data published in 2015 showed that after the introduction of stricter controls on mercury, mercury dropped dramatically, indicating that the Clean Air Act had its intended effect.

The EPA announced new rules for coal-fired power plants on December 22, 2011. Cement kilns that burn hazardous waste are held to a less stringent level of control than standard hazardous waste incinerators, so they constitute a disproportionate source of mercury contamination.

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