Mercury Price, Occurrence, Extraction and Uses

Mercury (ancient Greek ὑδράργυρος Hydrargyros, liquid silver ', derived from Latin hydrargyrum (Hg), so named by Dioscurides; Latin argentum vivum and mercurius; English mercury and quicksilver) is a chemical element with the symbol Hg and the atomic number 80. Although it has a closed d-shell, it is often counted among the transition metals. In the periodic table it is in the 2nd subgroup or the 12th IUPAC group, which is also called the zinc group. It is the only metal and, besides bromine, the only element that is liquid under standard conditions. Due to its high surface tension, mercury does not wet its inert base, but rather forms lenticular drops because of its strong cohesion. Like any other metal, it is electrically conductive.

etymologie

Mercury originally means "perky silver", ie fast - see English quick - or moving or living silver (from ahd. Quëcsilabar, quëchsilper, mhd. Quëcsilber, këcsilber to Germanic kwikw, [quick] lively ') as a translation of synonymous Latin argentum vivum, "living silver", e.g. B. Pliny

Sulfur alcohols are called mercaptans ("mercury scavengers") because they can react with mercury to form mercury sulfides.

History

Mercury has been known at least since ancient times. It is already mentioned in the works of Aristotle, Theophrastus of Eresus, Pliny the Elder and other writers of antiquity. From ancient times to the 20th century it was used as a medicinal product (due to its toxicity, which was first reported by the doctor and empiricist Herakleides of Taranto, but with corresponding negative consequences).

In ancient times, mercury was obtained by rubbing cinnabar with vinegar or by heating cinnabar using a sublimation process. Vitruvius was already familiar with the alloy of mercury with gold. This was used for fire gilding objects, whereby the mercury evaporated. In the 5th century AD, the sublimate (mercury (II) chloride) was known as a mercury compound. Paracelsus was the first doctor who made precipitates and basic mercury salts and used them as remedies. From the 16th century onwards, mercury became economically important because it was needed to extract silver from silver ores through amalgam formation.

At the end of the 19th century, mercury was considered a suitable drug for gynecological problems, which is why it was sometimes administered in toxic quantities.

From the end of the 15th to the beginning of the 20th century, mercury preparations such as the gray mercury ointment or asurol were widely used to treat syphilis (most recently also in combination with arsenic compounds such as arsphenamine; see also organic biometallic chemistry). For a mercury cure, the mercury was usually applied to the skin, injected or occasionally even inhaled, which in many cases resulted in symptoms of poisoning. Syphilis was considered a popular disease and allusions to the symptoms of syphilis and the associated mercury poisoning can be found in many literary works of the time.

During the same period, metallic mercury was used to treat obstructions in the intestine. The patient ingested several kilograms of metallic mercury orally in order to overcome the obstacle in the intestine. If he survived treatment, the metal would naturally leave his body with no further symptoms of intoxication.

In the past, mercury (I) chloride was used externally, for example against corneal spots or genital warts, and often internally and until the 1990s as a spermicide in the form of vaginal suppositories for contraception. In the past, almost all Merfen preparations, including lozenges, had the organic mercury compound phenyl mercury borate, which was discovered to be effective around 1951, as an active ingredient, whereas today these are all mercury-free. Merbromin also had an antiseptic effect in Mercurochrome, which was only approved until 2003.

The Dutch physicist Heike Kamerlingh Onnes discovered the phenomenon of superconductivity in mercury for the first time in 1911. The electrical resistance disappears completely below 4,183 Kelvin (−268,967 ° C). The proximity to the boiling point of helium contributed to the discovery, but it is purely coincidental.

In ancient Greece, mercury symbolized both the god Hermes and the planet that belonged to it. This was later adopted by the Romans and alchemists for the equated god Mercurius. Therefore, in Latin mercurius and in English mercury, both the name for mercury and for the planet and god. In English, however, quicksilver is also used as an alternative term for the metal.

Mercury was used in alchemy to refine metals. For example, the addition of mercury should turn copper into silver. The aim was also to solidify the mercury, the fixatio mercurii, for example (described in the 15th century by Hans Kluge) by physico-chemical treatment of a mixture of mercury with vitriol to which other additives such as tartar, saltpeter and glass powder were added.

occurrence

Mercury occurs naturally in its pure form and is the only liquid substance that has traditionally been recognized as a mineral by the IMA. Mercury is also a companion mineral in hard coal.

There are mercury deposits in Serbia, Italy, China, Algeria, Russia and Spain, among others. It is mostly found as a mineral in the form of cinnabar (HgS) in areas with former volcanic activity. Mercury is also less common than normal. The largest cinnabar deposits on earth are located near the Spanish town of Almadén. Production ended in 2003 and the Almadén mine was converted into a visitor mine. Much rarer mercury minerals are montroydite (HgO), paraschachnerite, schachnerite, eugenite, luanheit and moschellandsbergite (all AgHg). Another mineral is Belendorffit (CuHg).

Large amounts of mercury are also bound in the frozen biomass of the permafrost soils of the northern hemisphere. About twice as much mercury is stored in these as in all other soils, the atmosphere and the oceans combined. If the permafrost is thawed more intensely, as is expected from man-made global warming, biological degradation processes would set in, through which the mercury is possibly released into the environment, where it could harm the arctic ecosystems, aquatic life in the oceans and human health, among other things .

Mercury is traditionally traded in metal barrels (English "flask") of 76 pounds (34,473 kg) and quoted on the commodities exchange in the unit "FL" = flask.

Due to the long atmospheric lifespan of elemental mercury of several months to a year, emissions into the air lead to a median air concentration of 1,2 to 1,8 ng / m3 in the northern hemisphere and around 1,0, which is relatively constant over the entire earth's atmosphere .3 ng / mXNUMX in the southern hemisphere.

Extraction and presentation

Pure mercury is obtained by allowing the mercury ore cinnabar (HgS) to react with oxygen (roasting process). The reaction products are elemental mercury and sulfur dioxide:

Around one million tons of metallic mercury has been extracted from cinnabar and other ores worldwide over the past five centuries. About half of this occurred before 1925 (as of 2000).

Features

Mercury is a silver-white, liquid heavy metal. It is sometimes still counted among the precious metals, but is much more reactive than the classic precious metals (for example platinum, gold), which are in the same period. It forms alloys with many metals, the so-called amalgams. Mercury is a poor conductor of electricity compared to other metals. Apart from the noble gases, it is the only element that is monatomic in the gas phase at room temperature.

With a density of 13,5 g / cm3, mercury is around 13,5 times as dense as water, so that, according to Archimedes' principle, its carrying capacity is also 13,5 times as high; thus an iron cube (density 7,9 g / cm3) also floats in mercury. Recently performed Monte Carlo simulations show that the density of mercury is also subject to relativistic effects. Non-relativistic calculations would suggest a density of 16,1 g / cm3.
conductivity

The metal bond in mercury is created by delocalized electrons. These electrons occupy certain, discrete energy levels in bands that are created by the broadening of atomic states through interaction. There is no periodic structure in liquid metals like mercury. Therefore, the quasi-pulse is not a good quantum number and the electronic band configuration cannot be represented in the Brillouin zone, as is usual for solid metals. Due to the Pauli principle, the electrons gradually fill up the energy states, only the conduction band remains incompletely occupied. The electrons in this band are delocalized and form the electron gas. The electrical conductivity can also be explained classically by these electrons.

Physical state

The answer to the question of why mercury is liquid at room temperature can be found in the consideration of the bond between the mercury atoms. First of all, mercury has a very special electron configuration. As an element of the 12th group of the PSE, mercury atoms have completely filled s and d atom orbitals, which means a very stable and energetically favorable constellation. The conduction band is thereby empty. In the case of the lighter homologues zinc and cadmium, which are in the same group of PSE as mercury, but are solid at room temperature, the energetic difference between the valence band and the conduction band is so small that electrons can easily jump from the valence band to the conduction band, creating a metal bond comes about.

The peculiarity of mercury lies in the 14f orbital which is completely filled with 4 electrons. Due to the lanthanide contraction and the relativistic effect, there is an increase in mass and a less efficient shielding of the nuclear charge. Only recently was it possible to demonstrate using a Monte Carlo simulation that the melting point anomaly of mercury is actually due to relativistic effects. Without relativistic effects, a melting point would be expected that would be 105 K higher than that observed experimentally.

Occupied orbitals are thereby drawn closer to the nucleus, as is the valence band of mercury. However, unoccupied orbitals such as the conduction band are not shifted towards the core, which leads to a particularly large energy difference between the valence and conduction band, which is significantly lower for zinc and cadmium. Hardly any electrons can leave the valence band and reach the conduction band, which makes the metal bond unusually weak. This also explains the volatility and the atypical poor conductivity of mercury for metals.

isotope

A total of 34 isotopes and 9 nuclear isomers with mass numbers from 175 to 208 are known of mercury. Seven of these isotopes are stable (with mass numbers 196, 198, 199, 200, 201, 202 and 204). Of the radioactive isotopes, only 194Hg has a relatively long half-life of 444 years (520 years according to more recent data). The other isotopes and core isomers only have half-lives between 1,1 milliseconds and 46,612 days.

Usage

The thermal expansion of mercury is almost an order of magnitude lower compared to other liquids, but shows only about 0 percent linearity errors in the range between 180 ° C and 2 ° C:

In addition, mercury does not wet glass and is easy to detect visually. It is therefore suitable for use in liquid thermometers and contact thermometers. As an outdoor thermometer in very cold regions, however, it can only be used to a limited extent due to its melting point (−38,83 ° C).

Due to its high toxicity, its use is nowadays limited to the scientific field; Depending on the temperature range, mercury can be partially replaced by colored fillings made of alcohol, petroleum, propylene carbonate, pentane, toluene, creosote, isosamyl benzoate, hydrogenated mineral oil or Galinstan as well as electronic thermometers.

The first usable mercury thermometer was developed by Daniel Gabriel Fahrenheit around 1720. A thermometer contains an average of 150 mg of mercury. In a clinical thermometer, the amount can be up to 1 g. This corresponds roughly to a bead with a diameter of 5,2 mm.

Since April 3, 2009, the placing on the market of new mercury-containing clinical thermometers, barometers and blood pressure monitors has been prohibited within the EU; This does not apply to measuring devices for scientific or medical use as well as old and used devices.

Manometer / barometer

The classic design of a manometer (“differential pressure meter”) is a U-tube, the ends of which are connected to the two pressure atmospheres via lines. To this day, mercury is widely used as a pressure gauge liquid. The advantages of mercury are: high density, the non-wetting of glass and the negligible vapor pressure. Mercury is colorless but opaque.

The simplest and oldest design of the barometer is a stable, one-sided closed glass tube with an inner diameter of about 4–6 mm, which is filled to the brim with mercury with the closed end facing down, then closed with the thumb, uprighted upside down and with the thumb under the mercury level in a wide, half-full cup is dipped before the thumb reveals the opening below.

The mercury column in the pipe only sinks until the force of the air pressure outside the pipe and the weight of the mercury in the pipe are in equilibrium. At normal pressure (1 atmosphere) this is 760 mm "mercury column". The old specification in the Torr unit of measurement for air pressure corresponds to the height of the mercury column in millimeters, 1 mm of mercury column corresponds to 133,21 Pascal.

Switch

Due to its electrical conductivity and the very high surface tension (0,476 N / m at 20 ° C), mercury is ideal for use as a contact material in the mercury switches previously used. Because of the problem with the disposal of electronic scrap, the use of mercury in switches has been prohibited in most areas of application in the EU (“RoHS” directive) since 2005. In special applications, contacts wetted with mercury are still used today in order to achieve particularly low contact resistances or to prevent the contacts from bouncing (e.g. Hg relays).

Thanks to gravity, mercury tilt switches work similarly to the spirit level on a spirit level; A movable drop of mercury in a curved or straight glass tube opens and closes the electrical contact between two metal pins melted into the glass, depending on the inclination. Such inclination switches are sometimes found in old staircase light time switches, in thermostats of boilers, in pressure switches of domestic water pumps and as rumble protection in washing machines. In the previously used turbo inverters, a mercury beam was used as a circling "switch finger".

Mercury vapor lamps

Visible part of the mercury spectrum. The purple line is barely visible to the eye. Particularly strong lines are in the (left) subsequent invisible UV.

Hg gas discharge tube

Mercury is used in discharge vessels (mercury vapor lamps) of gas discharge lamps (fluorescent lamps, "energy-saving lamps", cold cathode tubes, high and ultra-high pressure mercury vapor lamps, sunlamps, quartz lamps, so-called "black light lamps").

Amalgam

Mercury spontaneously forms alloys with many other metals called amalgams. Amalgams are z. B. used as a dental filler. A mixture of mercury and powder of metals such as silver can be pressed into a drilled opening in the tooth for a period of time and soon hardens to form amalgam. While tooth material shrinks over the years as a result of bacterial-chemical attack, amalgam has a tendency to expand plastically as a result of high chewing pressure as a metal and has the side effect of inhibiting the growth of bacteria. If a piece of aluminum foil is pressed firmly onto an amalgam filling while chewing - possibly accidentally, as is typical of chocolate packaging - a galvanic element is formed and an electrical direct current flows accordingly, which is perceived as an unpleasant metallic stimulus in the tooth nerve.

In March 2017, a regulation was passed in the European Parliament that significantly restricts the use of amalgam. From July 2018, young people under the age of 15 as well as pregnant and breastfeeding women will no longer be allowed to receive dental fillings made from amalgam. Basically, from then on, premixed mixtures must also be used in order to keep the mercury content optimal. Amalgam separators are then also required in the ordination waste water line. A study should clarify by 2020 whether amalgam should be completely banned from dentistry by 2030. Restrictions have also been imposed on the industrial use of mercury.

Since mercury destroys the protective oxide skin of the aluminum through aluminum amalgam formation, carrying mercury-containing devices (e.g. clinical thermometers) on airplanes is not prohibited, but limited according to the IATA Dangerous Goods Regulations (1 piece / passenger and mandatory in a protective cover - DGR 2.3 ). Mercury is assigned to dangerous goods class 8 - corrosive materials. There is a corrosive effect in connection with almost all metals, including zinc, magnesium and aluminum, which are used in aircraft construction.

Disinfectants and pickling agents

In the wound disinfectant mercurochrome, the active ingredient was an organic mercury salt. The mercuchrome iodine solution available today is a povidone iodine solution. Merfen, another disinfectant, used to contain phenyl mercury borate. HgCl2 (sublimate) was previously used as a disinfectant in hospitals. Thimerosal is an organic mercury compound that is used in very low concentrations as a bactericide to preserve vaccines.

Conventional agriculture uses mercury compounds as a dressing agent for seeds. This has been banned in Germany since 1984. In Iraq there was mass poisoning from 1971–1972 as a result of the consumption of seeds.

Mercury (II) chloride was previously used as a disinfectant and pickling agent as well as for wood preservation and corpse preservation.

electrolysis

In terms of quantity, mercury played a major role in the production of caustic soda and chlorine by chlor-alkali electrolysis using the amalgam process. During the electrolysis, the reduced sodium metal is transferred as an amalgam, a sodium-mercury alloy, into a separate cell, the decomposer, in order to prevent the formation of the explosive chlorine gas and the undesired sodium monooxochlorate (sodium hypochlorite) in the electrolysis cell. Currently, a large part of the German and European facilities working with the amalgam process are being converted to alternative, mercury-free processes (membrane processes) in order to reduce mercury emissions.

Gold washing

One process of gold mining uses mercury to loosen the fine gold dust, creating gold amalgam (see amalgamation). Since mercury becomes liquid at low temperatures, it forms alloys that melt particularly easily. During washing and subsequent annealing to recover pure gold, the mercury is released into the environment. This is the main reason for the high level of environmental pollution caused by this type of gold mining (see also environmental emissions, below). Alternatives to the amalgam process should be promoted. The gold for the German river gold ducats minted between the 17th and 19th centuries was also extracted or purified by amalgamation in order to melt it.

Art

It is said that there were rivers of mercury in the tomb of the first Chinese emperor Qin Shihuangdi. The soil in the area has been scientifically examined and an unnaturally high mercury content has been found. But this alone is no proof of the correctness of the legend.

Mexican archaeologists have found liquid mercury beneath the Mayan temple pyramid of the Quetzalcoatl. The researchers suspect that it is the ritual representation of the Maya underworld river - comparable to the ancient Greek Styx.

The American artist Alexander Calder built a mercury fountain in 1937 to commemorate the victims of mercury mining. Around the year 1000 there were pools filled with mercury in the palaces of the caliphs of Córdoba (Medina az-Zahra), Cairo and Baghdad, which were used to play with the effects of light, as well as mercury ponds set in large porphyry shells (for Cairo, 50 cubits are in Square, i.e. approx. 26 m × 26 m).

Fire gilding was in use for a long time in handicrafts. As in gold mining, the easy amalgam formation and thermal separation of gold and mercury were used here. This method can also be used to gild copper sheets, which was used, for example, for the domes of St. Isaac's Cathedral in St. Petersburg in the 19th century.

Other uses

• The metal is used in button cells and batteries. In the meantime, however, there is only one producer in Taiwan; import into the EU is no longer permitted.
• Mercury vapor rectifier emits light during operation
• In the past it was also used in some electronic tubes such as mercury vapor rectifiers, ignitrons, excitrons, and thyratrons.
• In astronomy, mercury is used to build relatively inexpensive telescopes with a large mirror surface (see liquid mirror): Mercury is filled into a plate-shaped, air-bearing mirror carrier, which is then set in rotation. As a result of the rotation, the mercury is distributed over the entire surface of the mirror support in a thin layer and forms an almost perfect parabolic mirror. A disadvantage of these telescopes is that they can only look vertically upwards (zenith), since only then does a suitable paraboloid of rotation arise as a result of gravity. Without rotation of the mirror, mercury mirrors were used in metrology as a flatness standard.
• The property of mercury to behave like a non-wetting liquid (exceptions: amalgam formers such as copper, silver, gold, aluminum) is the basis for mercury porosimetry. Here, mercury is pressed under pressure (0 to 4000 bar) into pores of different sizes. Statements can be made about the nature, shape, distribution and size of pores and cavities via the pressure applied and the amount of mercury required. This method is used, among other things, in mineralogy, pharmacy and the ceramic sciences.
• In the past, mercury salts were used by hat makers, especially to make castor hats made of beaver fur, which were very fashionable in the 18th century. The English expression "mad as a hatter" ("crazy like a hatter") (see also hat maker syndrome) probably goes back to the application. He was also popularized by the Mad Hatter character in Lewis Carroll's Alice in Wonderland.
• In the past, mercury was used alongside water as a working medium in steam power plants. The vapor of the metal reached a temperature of 500 ° C at a pressure of 10 bar. Despite its thermodynamic advantages, the process did not gain acceptance because of the toxicity of the metal.
• The first nuclear reactors of the fast breeder type were cooled with mercury (e.g. Clementine reactor in Los Alamos / USA 1946–1952 and similar reactors in the Soviet Union). However, due to major corrosion problems and the difficult handling of the poisonous mercury, the company soon switched to liquid sodium. While the Clementine reactor was dismantled by 1970, this is still pending for the Russian mercury-cooled reactors, which were decommissioned more than 50 years ago.
• It has been known for several years that, from around 1955, boiling mercury was used in the military HERMEX project to separate weapons-grade plutonium from spent reactor fuel elements. More than 1000 tons of plutonium-containing mercury from this decommissioned HERMEX project are still stored in the Oak Ridge National Laboratory.
• Also in the Oak Ridge National Laboratory, an extensive project for the extraction of tritium for hydrogen bombs using approx. 1950 tons of mercury was carried out from 1963 to 11.000. About 3% of the mercury was released into the environment.
• Mercury is (or was mainly used in the past) as a working medium in diffusion pumps to generate an oil-free high vacuum.
• Mercury vapor was used to develop the image in the daguerreotype, the first practicable photography process. The resulting photo consisted of a mercury precipitate on a silver-plated copper plate.
• At the end of the 17th century, the physician Anton Nuck introduced the injection of mercury into anatomical specimens.
• Mercury is used in high-power spallation sources as a target for generating neutrons, e.g. B. SNS / USA or JSNS / Japan. Approx. 20 tons of mercury are bombarded with a proton beam with a particle energy of approx. 1 GeV. Mercury atomic nuclei are shattered and around 20 neutrons are released for each irradiated proton. The European Spallation Source ESS planned in Lund (Sweden) is not expected to use any mercury.

Pushing back the application and extraction

The Aarhus Heavy Metals Protocol to the 1979 UNECE Convention on Long-Range Transboundary Air Pollution came into force in 2003 and aims to reduce emissions of the heavy metals lead, cadmium and mercury.

From 9th (the day of the pharmacy) to 25th October 2007 in a campaign by the Ministry of Life and the Chamber of Pharmacists in Austria, one million mercury thermometers were collected from private households via pharmacies and brought to an underground warehouse in Germany via pharmaceutical wholesalers and the waste disposal company Saubermacher. This amount corresponds to one tonne of mercury. As an incentive, there was a digital clinical thermometer (worth approx. € 1) for every returned item. The initiators only expected 50.000 thermometers and had to deliver 200.000 digital thermometers.

In 2009 Sweden decided to ban the use of mercury in general. The ban means that the use of amalgam in dental fillings will cease and that mercury-containing products will no longer be allowed to be marketed in Sweden. According to the Swedish Ministry of the Environment, the ban is "a strong signal for other countries and Sweden's contribution to the EU and UN goals to reduce the use and emissions of mercury." This was preceded by a 2008 ban on the use of mercury in Norway. A UN conference was held in Stockholm in 2010 on this subject. In Switzerland, the quantities of mercury imported fell sharply after 2008 from over 3000 kg to around 600 kg per year in the period 2009–2013 and further to 70 kg in 2016. Mercury intended for dental products makes up the majority of this.

The EU's “Community Strategy for Mercury” of January 28, 2005 aims to reduce emissions, supply and demand for mercury. Existing quantities should be managed, people protected from exposure, understanding created and measures promoted. According to the EU directive of September 2006, the mercury content of batteries and accumulators was limited to 0,0005 percent by weight (button cells, however, 2%).

The EC regulation on the prohibition of the export of mercury and certain compounds as well as the safe storage of mercury of October 22, 2008 has banned the export of mercury and mercury-containing - with exceptions - from the EU since March 15, 2011. On the same date, mercury, which is being put out of function in the chlor-alkali industry in particular by changing processes, is to be treated as hazardous waste and stored and monitored in high-security areas underground, such as abandoned salt mines. So far, Europe has been the main producer of mercury in the world. The inventory of mercury, especially in the chlor-alkali electrolysis concentrated in Germany, is around 1000 t.

The world production of mercury has decreased from its maximum in 1970 with 10.000 t / a until 1992 by 3.000 t / a.

In its United Nations Environmental Program Governing Council, the United Nations has placed mercury on the list of regulated substances of global pollution since 2001.

Ten years after the impetus from Switzerland and Norway, 140 states signed the Minamata Convention on January 19, 2013 in Geneva after lengthy negotiations, the first binding agreement to restrict the extraction and containment of mercury emissions. The convention regulates the production, use and storage of mercury and the handling of waste containing mercury; compliance is monitored by an advisory commission. New mines are not allowed to be built, existing ones have to be closed within 15 years, so that mercury is then only available for recycling. Humans have doubled the mercury concentration in the top 100 m of the oceans over the past 100 years, according to a UN report.

disposal

Spilled mercury can be picked up with special mercury tongs or by shoveling two suitably troughed sheets of paper against each other. Small residues can be amalgamated with a zinc plate or zinc powder or converted to sulphide with sulfur and then swept together solidified. Mercury waste must be collected as hazardous waste and specially disposed of.

In laboratory practice, it should be avoided that mercury flows into cracks in the floor, from where it would be released into the environment through evaporation over the years.

Connections

Either mercury (I) (also diquecury (I)) or mercury (II) compounds are important here:

• Dimethyl mercury
• Mercury (II) acetate
• Mercury (II) amide chloride (D0602Z)
• Mercury (I) chloride (mineral calomel)
• Mercury (II) chloride (sublimate)
• Mercury (II) fulminate (fiery mercury)
• Mercury (II) iodide (Neßler reaction)
• Mercury (II) nitrate
• Mercury (II) oxide
• Mercury (II) sulfide (mineral cinnabarite, cinnabar)

Analytics

• Classic, inorganic detection reactions
• Amalgam sample
• Amalgam sample

Mercury salts can be detected with the help of the amalgam sample. The hydrochloric acid solution is poured onto a copper sheet and a solid, silvery amalgam stain remains. Silver ions can interfere with the detection and are therefore precipitated as AgCl.

Glow tube sample

Another proof of mercury is the glow tube sample. The substance to be analyzed is mixed with approximately the same amount of sodium carbonate (soda) and ignited in the fume cupboard. Elemental mercury is deposited as a metallic mirror on the test tube wall.

Qualitative proof in the separation process

In the qualitative separation process, mercury can be detected in both the HCl group and the H2S group. After adding HCl, calomel, Hg2Cl2, is formed, which reacts to finely divided mercury and mercury (II) amido chloride after adding ammonia solution. After the introduction of H2S, divalent mercury precipitates in the form of black cinnabar, HgS, and can be detected with the help of the amalgam sample.

Instrumental analysis of mercury

A number of methods are available for trace analysis of mercury and its organic derivatives. However, new or improved methods are constantly being presented in the literature. Sample preparation is a problem that should not be underestimated.

Atomic absorption spectrometry (AAS)

Of the various AAS techniques, the quartz tube and graphite tube techniques provide the best results for inorganic and organometallic mercury compounds. A quartz cuvette is heated electrically to over 900 ° C and the sample is atomized. The absorption is then measured at 253,7 nm. An example is a detection limit for CH3HgCl of 100 µg / L. Another popular technique for the detection of elemental mercury or mercury organylene is the generation of cold steam in connection with the AAS. At very low concentrations, the volatile analyte species are initially enriched with the formation of amalgams on gold or silver surfaces that have been placed in a graphite cuvette. It is then atomized at 1400 ° C and the absorption measured. A detection limit of 0,03 ng was achieved in this way.

Atomic Emission Spectrometry (AES)

In AES, microwave-induced plasma (MIP) and inductively coupled plasma (ICP) have proven their worth for atomization. With this method, too, detection takes place at 253,65 nm and 247,85 nm. With the help of the MIP-AES, absolute detection limits of 4,4 ng / g sample were found. The ICP-AES has a detection limit of 20 to 50 ng / mL.

Mass spectrometry (MS)

Mercury has a total of seven stable isotopes of different abundance. For mass spectrometry, however, often only 201Hg (13,22%) and 202Hg (29,80%) are relevant. With the help of ICP-MS, inorganic mercury compounds and mercury organyls such as methyl mercury, CH3Hg, can be determined with detection limits of up to 2,6 ng / g.

Neutron Activation Analysis (NAA)

The NAA is based on the nuclear reaction AHg (n, γ) A + 1Hg (irradiation of mercury with neutrons). This creates radioactive mercury nuclides. The intensity of the resulting characteristic gamma radiation is determined with a high-purity germanium detector. It is proportional to the number of activated cores present and quantitative statements can be made through internal calibration. Often 197mHg is detected with a half-life of 2,7 days at 77,3 keV.

voltammetry

Anodic stripping voltammetry (ASV) is best suited for the electrochemical determination of Hg traces. The voltammetric measurement is preceded by a reductive enrichment period on the gold measuring electrode. The actual determination then follows by measuring the oxidation current when scanning a voltage window from 0 V to 600 mV. The height of the oxidation peak at 500 mV correlates with the amount of mercury present. Detection limits of 12 pM (2,4 ng / l) mercury were achieved in seawater after an enrichment time of 2 minutes. In addition, inverse voltammetry on gold, platinum or carbon electrodes can be used.

Automated analytics

There are now automated analyzers for the routine analysis of mercury. They are usually based on the principle of thermal decomposition, followed by amalgamation and subsequent measurement of the atomic absorption (see AAS). With such analysis devices, solid and liquid samples can be examined for their mercury content within a few minutes. These commercially available devices are very sensitive and meet the requirements of national quality assurance standards such as US EPA method 7473 and ASTM method D-6722-01.

Environmental emissions

Mercury is released in large quantities through human activities. It is estimated that around 2200 tons of mercury are released into the atmosphere as gaseous mercury every year, as well as significant amounts in the soil and water. The total emissions to the environment from human activities from the dawn of civilization to 2010 have been estimated at 1,1–2,8 million tons.

Significant sources of emissions are:

• the (small-scale) gold mining (Artisanal Small Scale Mining). According to estimates, 20 to 30 percent of the gold mined worldwide is obtained through non-industrial prospecting, i.e. by gold prospectors. If all gold miners in the world were to use the environmentally friendly borax process, the emission of around 1.000 tons of mercury, around 30% of global mercury emissions, could be avoided.
• The energy industry, especially coal-fired power plants: The mercury emissions from the energy industry for 2010 are estimated at around 859 tons worldwide, of which around 86% come from the burning of coal. The ongoing expansion of coal-fired power plants in China will mean that coal combustion will become the largest emitter in the future. Mercury only occurs in traces in hard coal and lignite, but the large amount of coal burned worldwide leads to considerable release rates. In Germany, the energy industry has been emitting around 1995 tons of mercury at a constant rate since 7.
• Cement works (due to mercury in limestone and when using waste / sewage sludge as fuel),
• Non-ferrous metal smelters (due to mercury in ores, especially in gold, copper, zinc and lead extraction),
• Steel production (especially when using scrap),
• Production of chlorine, hydrogen and caustic soda (chlor-alkali electrolysis with amalgam process).

In the airside mercury emissions from Germany (10257 kg in 2013), the energy industry had a share of 68% (6961 kg) due to the coal-fired power plants, metal smelting 11% (1080 kg) and the cement and mineral industry 6% (609 kg). With around 10 tons of mercury emissions, Germany, together with Poland and Greece, is the front runner in Europe.

In January 2016, a study commissioned by the Greens showed that the mercury limit values ​​that have been in force in the USA for 2015 coal-fired power plants since April 1100 are not complied with by any coal-fired power plant in Germany, as there are no correspondingly strict legal requirements. If the same limit values ​​for mercury emissions were to apply as in the USA (in the monthly mean converted about 1,5 µg / m³ for hard coal power plants and 4,4 µg / m³ for lignite power plants), of the 53 reportable coal power plants in Germany, only the power plant that has since been shut down could be used Dates (block 1–3) stay on the net. For several years now, the Federal Environment Agency has recommended lowering the limit value in the exhaust gas from coal-fired power plants to 3 µg / m³ as a daily average and 1 µg / m³ as an annual average. When implementing the European Industrial Emissions Directive, the federal government and the majority of the Bundestag decided at the end of October 2012 for coal-fired power plants to have limit values ​​of 30 µg / m³ as a daily average and (for existing power plants from 2019) 10 µg / m³ as an annual average. At the expert hearing in the Environment Committee of the Bundestag on October 15, 2012, an adjustment to the US limit values ​​was recommended. In June 2015, a working group headed by the European Commission with representatives from member states, industrial and environmental associations determined that annual mean mercury emission values ​​below 1 µg / m³ can be achieved in coal-fired power plants with mercury-specific technologies. Low mercury emissions can be achieved by adding activated carbon, using a precipitant in the flue gas scrubber or special filter modules. Catalysts and the addition of bromine salts can improve mercury discharge because they convert elemental mercury into ionic mercury. The increase in electricity generation costs associated with these processes is estimated to be less than 1 percent.

For example, the hard coal power plant in Lünen-Stummhafen, the hard coal power plant in Wilhelmshaven, the hard coal power plant in Werne, the hard coal power plant in Hamm-Uentrop, the hard coal power plant in Hamm-Uentrop, Power plant in Großkrotzenburg near Hanau and the lignite power plant in Oak Grove (Texas / USA).

Products containing mercury have been banned in Norway since 2008 and in Sweden since 2009.

Due to the known dangers of released mercury, the UN Environment Program (UNEP) drew up an international agreement ("Minamata Agreement"), which was signed by 2013 countries in October 140. The aim is to reduce mercury emissions from mining, production processes, products and waste worldwide. The agreement became binding with the ratification of the 50th signatory state on May 18, 2017 and entered into force on August 16, 2017.

The American Blacksmith Institute has determined the top 2006 most heavily contaminated places on earth since 10. Here, mercury is often one of the pollutants in the “nominated” locations.

The export of mercury or mercury-containing substances with a concentration of over 95% mercury from the EU to non-EU countries is prohibited.

Damage to health from mercury

Mercury is a poisonous heavy metal that gives off vapors even at room temperature. Pure metallic mercury is comparatively harmless when absorbed through the digestive tract, but inhaled vapors are highly toxic.

However, organic mercury compounds are extremely toxic because, unlike elemental mercury, they are fat-soluble. They can be ingested with food, but also through the skin. They easily penetrate most protective gloves. They are almost completely absorbed and incorporated into fatty tissue. They arise in the food chain through biomethylation of mercury (or mercury salts) to methyl mercury. The main source of human exposure to methylmercury is through consumption of marine fish. Organic mercury compound poisoning became known worldwide in the mid-1950s through reports of Minamata disease. When it comes to exposure to inorganic mercury, the main sources are ingestion through food and through dental amalgam.

Depending on the intake, both acute and chronic poisoning are possible. The fall of the English ship Triumph in 1810, on which more than 200 people poisoned themselves when a barrel of mercury leaked, can serve as an example. In 2007 and 2015, Ayurvedic remedies with high levels of mercury attracted attention.

 

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