Dictionary:

mercury

  (mûr'kyə-rē)

1. (Symbol Hg) A silvery-white poisonous metallic element, liquid at room temperature and used in thermometers, barometers, vapor lamps, and batteries and in the preparation of chemical pesticides. Atomic number 80; atomic weight 200.59; melting point −38.87°C; boiling point 356.58°C; specific gravity 13.546 (at 20°C); valence 1, 2. Also called quicksilver.
2. Temperature: The mercury had fallen rapidly by morning.
3. Any of several weedy plants of the genera Mercurialis or Acalypha.

[Middle English mercurie, from Medieval Latin mercurius, from Latin Mercurius, Mercury.]

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Background

Mercury is one of the basic chemical elements. It is a heavy, silvery metal that is liquid at normal temperatures. Mercury readily forms alloys with other metals, and this makes it useful in processing gold and silver. Much of the impetus to develop mercury ore deposits in the United States came after the discovery of gold and silver in California and other western states in the 1800s. Unfortunately, mercury is also a highly toxic material, and as a result, its use has severely declined over the past 20 years. Its principal applications are in the production of chlorine and caustic soda, and as a component of many electrical devices, including fluorescent and mercury-vapor lamps.

Mercury has been found in Egyptian tombs dating to about 1500 B.C., and it was probably used for cosmetic and medicinal purposes even earlier. In about 350 B.C., the Greek philosopher and scientist Aristotle described how cinnabar ore was heated to extract mercury for religious ceremonies. The Romans used mercury for a variety of purposes and gave it the name hydrargyrum, meaning liquid silver, from which the chemical symbol for mercury, Hg, is derived.

Demand for mercury greatly increased in 1557 with the development of a process that used mercury to extract silver from its ore. The mercury barometer was invented by Torricelli in 1643, followed by the invention of the mercury thermometer by Fahrenheit in 1714. The first use of a mercury alloy, or amalgam, as a tooth filling in dentistry was in 1828, although concerns over the toxic nature of mercury prevented the widespread use of this new technique. It wasn't until 1895 that experimental work by G.V. Black showed that amalgam fillings were safe, although 100 years later scientists were still debating that point.

Mercury found its way into many products and industrial applications after 1900. It was commonly used in batteries, paints, explosives, light bulbs, light switches, pharmaceuticals, fungicides, and pesticides. Mercury was also used as part of the processes to produce paper, felt, glass, and many plastics.

In the 1980s, increasing understanding and awareness of the harmful health and environmental effects of mercury started to greatly outweigh its benefits, and usage began to drop sharply. By 1992, its use in batteries had dropped to less than 5% of its level in 1988, and overall use in electrical devices and light bulbs had dropped 50% in the same period. The use of mercury in paints, fungicides, and pesticides has been banned in the United States, and its use in the paper, felt, and glass-manufacturing processes has been voluntarily discontinued.

Worldwide, production of mercury is limited to only a few countries with relaxed environmental laws. Mercury mining has ceased altogether in Spain, which until 1989 was the world's largest producer. In the United States, mercury mining has also stopped, although small quantities of mercury are recovered as part of the gold refining process to avoid environmental contamination. China, Russia (formerly the USSR), Mexico, and Algeria were the largest producers of mercury in 1992.

Raw Materials

Mercury is rarely found by itself in nature. Most mercury is chemically bound to other materials in the form of ores. The most common ore is red mercury sulfide (HgS), also known as cinnabar. Other mercury ores include corderoite (Hg₃S₂Cl₂), livingstonite (HgSb₄S₈), montroydite (HgO), and calomel (HgCl). There are several others. Mercury ores are formed underground when warm mineral solutions rise towards the earth's surface under the influence of volcanic action. They are usually found in faulted and fractured rocks at relatively shallow depths of 3-3000 ft (1-1000 m).

Other sources of mercury include the dumps and tailing piles of earlier, less-efficient mining and processing operations.

The Manufacturing
Process

The process for extracting mercury from its ores has not changed much since Aristotle first described it over 2,300 years ago. Cinnabar ore is crushed and heated to release the mercury as a vapor. The mercury vapor is then cooled, condensed, and collected. Almost 95% of the mercury content of cinnabar ore can be recovered using this process.

Here is a typical sequence of operations used for the modern extraction and refining of mercury.

Mining

Cinnabar ore occurs in concentrated deposits located at or near the surface. About 90% of these deposits are deep enough to require underground mining with tunnels. The remaining 10% can be excavated from open pits.

• Cinnabar is dislodged from the surrounding rocks by drilling and blasting with explosives or by the use of power equipment. The ore is brought out of the mine on conveyor belts or in trucks or trains.

Roasting

Because cinnabar ore is relatively concentrated, it can be processed directly without any intermediate steps to remove waste material.

• The ore is first crushed in one or more cone crushers. A cone crusher consists of an interior grinding cone that rotates on an eccentric vertical axis inside a fixed outer cone. As the ore is fed into the top of the crusher, it is squeezed between the two cones and broken into smaller pieces.
• The crushed ore is then ground even smaller by a series of mills. Each mill consists of a large cylindrical container laying on its side and rotating on its horizontal axis. The mill may be filled with short lengths of steel rods or with steel balls to provide the grinding action.
• The finely powdered ore is fed into a furnace or kiln to be heated. Some operations use a multiple-hearth furnace, in which the ore is mechanically moved down a vertical shaft from one ledge, or hearth, to the next by slowly rotating rakes. Other operations use a rotary kiln, in which the ore is tumbled down the length of a long, rotating cylinder that is inclined a few degrees off horizontal. In either case, heat is provided by combusting natural gas or some other fuel in the lower portion of the furnace or kiln. The heated cinnabar (HgS) reacts with the oxygen (02) in the air to produce sulfur dioxide (SO₂), allowing the mercury to rise as a vapor. This process is called roasting.

Condensing

• The mercury vapor rises up and out of the furnace or kiln along with the sulfur dioxide, water vapor, and other products of combustion. A considerable amount of fine dust from the powdered ore is also carried along and must be separated and captured.
• The hot furnace exhaust passes through a water-cooled condenser. As the exhaust cools, the mercury, which has a boiling point of 675° F (357° C), is the first to condense into a liquid, leaving the other gases and vapors to be vented or to be processed further to reduce air pollution.
• The liquid mercury is collected. Because mercury has a very high specific gravity, any impurities tend to rise to the surface and form a dark film or scum. These impurities are removed by filtration, leaving a liquid mercury that is about 99.9% pure. The impurities are treated with lime to separate and capture any mercury, which may have formed compounds.

Refining

Most commercial-grade mercury is 99.9% pure and can be used directly from the roasting and condensing process. Higher purity mercury is needed for some limited applications and must be refined further. This ultrapure mercury commands a premium price.

• Higher purity can be obtained through several refining methods. The mercury may be mechanically filtered again, and certain impurities may be removed through oxidation with chemicals or air. In some cases the mercury is refined through an electrolytic process, in which an electric current is passed through a tank of liquid mercury to remove the impurities. The most common refining method is triple distillation, in which the temperature of the liquid mercury is carefully raised until the impurities either evaporate or the mercury itself evaporates, leaving the impurities behind. This distillation process is performed three times, with the purity increasing each time.

Shipping

• Commercial-grade mercury is poured into wrought-iron or steel flasks and sealed. Each flask contains 76 lb (34.5 kg) of mercury. Higher purity mercury is usually sealed in smaller glass or plastic containers for shipment.

Quality Control

Commercial-grade mercury with 99.9% purity is called prime virgin-grade mercury. Ultrapure mercury is usually produced by the triple-distillation method and is called triple-distilled mercury.

Quality control inspections of the roasting and condensing process consist of spot checking the condensed liquid mercury for the presence of foreign metals, since those are the most common contaminants. The presence of gold, silver, and base metals is detected using various chemical-testing methods.

Triple-distilled mercury is tested by evaporation or spectrographic analysis. In the evaporation method, a sample of mercury is evaporated, and the residue is weighed. In the spectrographic analysis method, a sample of mercury is evaporated, and the residue is mixed with graphite. Light coming from the resulting mixture is viewed with a spectrometer, which separates the light into different color bands depending on the chemical elements present.

Health and Environmental Effects

Mercury is highly toxic to humans. Exposure may come from inhalation, ingestion, or absorption through the skin. Of the three, inhalation of mercury vapor is the most dangerous. Short-term exposure to mercury vapor can produce weakness, chills, nausea, vomiting, diarrhea, and other symptoms within a few hours. Recovery is usually complete once the victim is removed from the source. Long-term exposure to mercury vapor produces shaking, irritability, insomnia, confusion, excessive salivation, and other debilitating effects.

In normal situations, most exposure to mercury comes from the ingestion of certain foods, such as fish, in which the mercury has accumulated at high levels. Although mercury is not absorbed in great quantities when passing through the human digestive system, ingestion over a long period of time has been shown to have cumulative effects.

In industrial situations, mercury exposure is a far more serious hazard. Mining and processing mercury ore can expose workers to mercury vapor as well as to direct contact with the skin. The production of chlorine and caustic soda can also cause significant mercury exposure hazards. Dentists and dental assistants can be exposed to mercury while preparing and placing mercury amalgam fillings.

Because mercury poses a serious health hazard, its use and release to the environment has come under increasingly tight restrictions. In 1988, it was estimated that 24 million lb/yr (11 million kglyr) of mercury were released into the air, land, and water worldwide as the result of human activities. This included mercury released by mercury mining and refining, various manufacturing operations, the combustion of coal, the discarding of municipal refuse and sewage sludge, and other sources.

In the United States, the Environmental Protection Agency (EPA) has banned the use of mercury for many applications. The EPA has set a goal of reducing the level of mercury found in municipal refuse from 1.4 million Ib/yr (0.64 million kg/yr) in 1989 to 0.35 million lb/yr (0.16 million kg/yr) by 2000. This is to be accomplished by decreasing the use of mercury in products and increasing the diversion of mercury from municipal refuse through recycling.

The Future

Mercury is still an important component in many products and processes, although its use is expected to continue to decline. Improved handling and recycling of mercury are expected to significantly reduce its release to the environment and thereby reduce its health hazard.

Where to Learn More

Books

Brady, George S., Henry R. Clauser, and John A. Vaccari. Materials Handbook, 14th Edition. McGraw-Hill, 1997.

Heiserman, David L. Exploring Chemical Elements and Their Compounds. TAB Books, 1992.

Kroschwitz, Jacqueline I., executive editor, and Mary Howe-Grant, editor. Encyclopedia of Chemical Technology, 4th edition. John Wiley and Sons, Inc., 1993.

Stwertka, Albert. A Guide to the Elements. Oxford University Press, 1996.

Periodicals

Raloff, J. "Mercurial Airs: Tallying Who's to Blame." Science News (February 19, 1994): 119.

Spencer, Peter, and G. Murdoch. "Mercury in Paint." Consumers' Research Magazine (January 1991): 2.

Stone, R. "Mercurial Debate." Science (March 13, 1992): 1356-1357.

Other

http://www.intercorr.com/periodic/80.htm [This website contains a summary of the history, sources, properties, and uses of mercury.]

[Article by: Chris Cavette]

A chemical element, Hg, atomic number 80 and atomic weight 200.59. Mercury is a silver-white liquid at room temperature (melting point −38.89°C or −37.46°F); it boils at 357.25°C (675.05°F) under atmospheric pressure. It is a noble metal that is soluble only in oxidizing solutions. Solid mercury is as soft as lead. The metal and its compounds are very toxic. With some metals (gold, silver, platinum, uranium, copper, lead, sodium, and potassium, for example) mercury forms solutions called amalgams. See also Transition elements.

In its compounds, mercury is found in the 2+, 1+, and lower oxidation states, for example, HgCl₂, Hg₂Cl₂, or Hg₃(AsF₆)₂. Often the mercury atoms are doubly covalently bonded, for example, ClHgCl or ClHgHgCl. Some mercury(II) salts, for example, Hg(NO₃)₂ or Hg(ClO₄)₂, are quite soluble in water and dissociate normally. The aqueous solutions of these salts react as strong acids because of hydrolysis. Other mercury(II) salts, for example, HgCl₂ or Hg(CN)₂, also dissolve in water, but exist in solution as only slightly dissociated molecules. There are compounds in which mercury atoms are bound directly to carbon or nitrogen atoms, for example, H₃CHgCH₃ or H₃CCONHHgNHCOCH₃. In complex compounds, for example, K₂(HgI₄), mercury often has three or four bonds.

Metallic mercury is used as a liquid contact material for electrical switches, in vacuum technology as the working fluid of diffusion pumps, for the manufacture of mercury-vapor rectifiers, thermometers, barometers, tachometers, and thermostats, and for the manufacture of mercury-vapor lamps. It finds application for the manufacture of silver amalgams for tooth fillings in dentistry. Of importance in electrochemistry are the standard calomel electrode, used as the reference electrode for the measurement of potentials and for potentiometric titrations, and the Weston standard cell.

Mercury is commonly found as the sulfide, HgS, frequently as the red cinnabar and less often as the black metacinnabar. A less common ore is the mercury(I) chloride. Occasionally the mercury ore contains small drops of metallic mercury.

The surface tension of liquid mercury is 484 dynes/cm, six times greater than that of water in contact with air. Hence, mercury does not wet surfaces with which it is in contact. In dry air metallic mercury is not oxidized. After long standing in moist air, however, the metal becomes coated with a thin layer of oxide. In air-free hydrochloric acid or in dilute sulfuric acid, the metal does not dissolve. Conversely, it is dissolved by oxidizing acids (nitric acid, concentrated sulfuric acid, and aqua regia).

Mercury (Hg) is a naturally occurring silvery metal that has been associated with adverse health effects throughout history. Elemental mercury is a liquid at room temperature, and, because of this, Aristotle named mercury "quicksilver." There are three forms of mercury: elemental mercury (Hg⁰), organic mercury (e.g., methylmercury), and inorganic mercury (e.g., Hg⁺, Hg²⁺). Many different organic and inorganic mercury compounds are found in nature because of mercury's ability to form covalent or ionic bonds with other chemicals. Mercury has numerous commercial uses—including its use in the extraction of gold from ores—and is an ingredient in alkaline batteries (approximately 0.025% of battery content), mercury vapor lamps, thermostats, and mercury amalgam fillings (in the United States, 50% of a dental filling is made of mercury). Humans can be exposed to mercury compounds via the oral, inhalation, and dermal routes. The primary source of exposure to mercury compounds is attributed to the ingestion of fish and other seafood (marine mammals, crustaceans) that have bioaccumulated mercury compounds. Dental amalgams, which leach mercury, are another source.

Adverse health effects from elemental and inorganic mercury compounds have been observed, particularly in occupational settings. Health consequences commonly observed from exposure to compounds such as elemental mercury vapor and mercuric chloride include tremors, bleeding gums, abdominal pain, vomiting, and kidney damage.

Health effects from organic mercury compounds have also been well-documented, primarily because of the tragic mass poisonings from organic mercurials in locations such as Minamata, Japan, and in Iraq. These mass poisonings were primarily associated with central nervous system toxicity and death. Adverse health effects observed in poisoned individuals and their offspring included ataxia, dysarthria, impaired vision and hearing, and death. Methylmercury is particularly toxic because 95 percent of an ingested dose is absorbed into the bloodstream and can cross the blood-brain and placental barriers, causing adult and fetal neurotoxicity. One of the reasons that offspring are particularly susceptible is that methylmercury can accumulate at 30 percent higher levels in fetal red blood cells than in maternal red blood cells. Besides damaging the brain and peripheral nervous system, methylmercury may also adversely affect the adult and fetal cardiovascular systems.

Research continues to be performed on the potential neurodevelopment effects of ingesting low levels of mercury in seafood. Three particularly important, ongoing studies involve residents of New Zealand and the Seychelles and Faroe Islands who consume significant portions of seafood as part of their normal diets. Analyses performed to date on mother-offspring pairs from the Seychelles identified adverse neurodevelopmental impact in offspring attributable to maternal methylmercury exposure from seafood. Mild developmental effects were also reported among offspring of New Zealand and Faroe Island residents who ingested seafood containing relatively high levels of methylmercury. These studies are particularly pertinent to assessing potential health effects among Native Arctic populations who consume marine mammals (beluga whales, ringed seals) as part of their normal diet. An increased level of mercury has been noted in the Arctic environment since the 1970s, possibly due to anthropogenic sources such as fossil fuel combustion, or possibly from increased natural releases of mercury from geologic sources. It is hypothesized that the cold Arctic climate acts as a sink for mercury; a particularly troublesome prospect for Native Arctic populations who continue to consume mercury-laden mammals and seafood.

(SEE ALSO: Environmental Determinants of Health; Foods and Diets; Heavy Metals; Minamata Disease; Occupational Safety and Health)

Bibliography

Agency for Toxic Substances and Disease Registry (1999). Toxicological Profile for Mercury (Update). Washington, DC: U.S. Department of Health and Human Services.

Arctic Monitoring and Assessment Programme (1999). Arctic Pollution Issues: A State of the Arctic Environment Report. Available at http://www.amap.no.

National Research Council (2000). Toxicological Effects of Methyl Mercury. Washington, DC: Committee on the Toxicological Effects of Mercury. Board on Environmental Studies and Toxicology. Commission on Life Sciences.

Tenenbaum, D. J. (1998). "Northern Overexposure." Environmental Health Perspective 106(2): A64–A69.

U.S. Environmental Protection Agency (1997). Report to Congress on Mercury. Available at http://www.epa.gov/oar/mercury.html.

World Health Organization (1990). Methyl Mercury, Vol. 101. Geneva: International Programme on Chemical Safety, WHO.

—— (1990). Inorganic Mercury, Vol. 118. Geneva: International Programme on Chemical Safety, WHO.

— MARGARET H. WHITAKER; BRUCE A. FOWLER

For more information on mercury, visit Britannica.com.

Possible carcinogen. May cause brain, kidney, or fetal damage. Highest concentration is in fish. Grains and meat account for half of the dietary intake.

Also popularly known as quicksilver. Known for many centuries, the metal has played an important part in the history of alchemy. In its refined state it forms a coherent, very mobile liquid that at ordinary room temparature was a well-known unique substance. The early alchemists believed that nature formed all metals from mercury, and that it was a living and feminine principle. It went through many processes, and the metal that evolved was pure or impure according to the locality of its production.

The mercury of the philosophers' stone needed to be a purified and revivified form of the ordinary metal; as the Arabian alchemist Geber stated in his Summa perfectionis: "Mercury, taken as Nature produces it, is not our material or our physic, but it must be added to."

Mercury seems to have been an entirely different substance than any ordinary metal or chemical element. Depending upon one's interprepation of alchemy as a system of spiritual growth, mercury could be one of several substances or states of consciousness.

In chemistry, a heavy, silvery metallic element, a liquid at normal temperatures. Mercury expands or contracts rapidly in response to changes in temperature and therefore was once widely used in thermometers.

Environment

Often in or close to volcanic regions, in low-temperature veins.

Mercury is the only metal that is liquid at normal temperatures. It does not become solid until the temperature falls to -40°F (which equals -40°C). Hence, we find it in nature only in the form of liquid metallic drops or as thin metallic films on small cavities and surfaces of rocks.

Silvery white. Luster metallic; specific gravity 13.6. Liquid, whence the name "quicksilver."

Mercury, sometimes with a little silver. Poisonous and instantly amalgamates with gold, so caution is recommended in any utilization or testing. Avoid breathing any fumes.

Volatilizes (disappears as fumes) under a blowpipe; dissolves in nitric acid.

The liquid droplets cannot be confused with anything else. The silvery films are more confusing but can easily be burned off with a blowpipe. The usual association with cinnabar (HgS) helps in identification.

Native mercury is almost invariably associated with the red sulfide of mercury, cinnabar. It is often found in cavities and cracks in cinnabar-impregnated rocks and sometimes forms as a result of the weathering of cinnabar, which leaves little holes lined with drops and films of mercury. Mercury and cinnabar will be found in rocks of regions where there has been some volcanic or hot-spring activity, though the deposits may lie some distance from any obvious source.

Found in the U.S. in California, Oregon, Texas, and Arkansas. The most notable occurrences are the Almadén (Spain) and the Idrija, in the former Yugoslavia, cinnabar mines. It is never an ore alone, but often enriches the mercury sulfide ores.

A chemical element, atomic number 80, atomic weight 200.59, symbol Hg.
Mercury forms two sets or classes of compounds: mercurous, in which a single atom of mercury combines with a monovalent radical, and mercuric, in which a single atom of mercury combines with a bivalent radical. Mercury and its salts have been employed therapeutically as purgatives; as alternatives in chronic inflammations; and as intestinal antiseptics, disinfectants and astringents. They are absorbed by the skin and mucous membranes, causing chronic mercurial poisoning, or hydrargyria. The mercuric salts are more soluble and irritant than the mercurous. See also mercurous, mercuric.

• ammoniated m. — used as an antiseptic skin and ophthalmic ointment.
• organic m. — includes the fungistats phenylmercurials, ethyl and methyl mercurials, e.g. methoxyethylmercury silicate; poisonous to animals and cause unacceptable residues in animal products.
• m. plant — mercurialis annua.
• m. poisoning — by inorganic compounds causes gastritis and kidney damage manifested by diarrhea and terminal uremia. Organic mercury compounds were until recently extensively used as fungistatic agents in stored grain. They cause poisoning manifested by nervous signs, including incoordination, blindness and recumbency. With larger doses there are convulsions.