Where Found (Encyclopedia of Global Resources)
Primary Uses (Encyclopedia of Global Resources)
Mercury is used in the industrial production of chlorine and caustic soda. It is also used in dry cell batteries, paints, dental amalgams, gold mining, scientific measuring instruments, and mercury vapor lamps. Several of these uses are now banned in the United States.
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Technical Definition (Encyclopedia of Global Resources)
Mercury (chemical symbol Hg) is a silvery white metal that belongs to Group IIB (the zinc group) of the periodic table. It has an atomic number of 80 and an atomic weight of 200.5. It has seven stable isotopes and a density of 13.6 grams per cubic centimeter. Also known as quicksilver, mercury has a melting point of -38.87° Celsius, making it the only metal that is liquid at normal room temperature. It boils at a temperature of 356.9° Celsius and has a constant rate of expansion throughout the entire range of temperature of the liquid. Mercury alloys with most metals and is a good conductor of electricity.
(The entire section is 104 words.)
Description, Distribution, and Forms (Encyclopedia of Global Resources)
Mercury is a relatively scarce element on Earth, accounting for only 3 parts per billion in crustal rocks. It is found both as free liquid metal and, more commonly, as the sulfide mineral cinnabar (HgS). It is generally found in areas of past volcanic activity. Mercury compounds are formed from mercury with either a +1 or +2 oxidation state. The most common mercury (I) compound is mercury chloride (Hg2Cl2), and the most common mercury (II) compounds are mercury oxide (HgO), mercury bichloride (HgCl2), and mercury sulfide (HgS). (The Roman numerals refer to the valence state of the mercury.)
Mercury forms compounds that are used in agriculture, industry, and medicine. Some organic mercury compounds, such as phenylmercury acetate, are used in agriculture as fungicides to control seed rot, for spraying trees, and for controlling weeds. Because of their highly toxic nature, care must be used when applying or using such mercury compounds.
Mercury is a rare crustal element that is found both as liquid elemental mercury and combined with other elements in more than twenty-five minerals. Cinnabar is the primary ore mineral of mercury, and it is generally found in volcanic rocks and occasionally in associated sedimentary rocks. The volcanic rocks were generally formed as volcanic island arc systems near subduction zones. Since the deposits are concentrated in faulted and fractured rocks that were formed at...
(The entire section is 469 words.)
History (Encyclopedia of Global Resources)
Mercury has been known since at least the second century b.c.e. Chinese alchemists used mercury in futile attempts to transform the base metals into gold. Mercury was also used in ancient Egypt. Cinnabar, the red ore mineral of mercury, has long been used by aboriginal peoples as an important pigment. By Roman times the distillation of mercury was known, and a mercury trade between Rome and the rich Spanish cinnabar mines was well established. Beginning with the Renaissance and the scientific revolution in the sixteenth and seventeenth centuries, mercury became important for use in measuring devices such as thermometers and barometers. The major modern industrial, medicinal, and agricultural uses of mercury were developed in the nineteenth and twentieth centuries.
The toxicity of mercury compounds has been known since the early poisoning of cinnabar miners. Later, in the early nineteenth century, the mental effects that mercury had on felt makers gave birth to the phrase “mad as a hatter.” The tragic effects of mercury poisoning were felt in Japan during the 1950’s and Iraq in 1972, when hundreds died from ingesting organic mercury compounds.
In the United States, the Energy Independence and Security Act of 2007 will phase out the use of incandescent bulbs in federal buildings, to be replaced by mercury-containing compact fluorescent bulbs. Disposal of the new, energy-saving bulbs will therefore require special handling....
(The entire section is 249 words.)
Obtaining Mercury (Encyclopedia of Global Resources)
The primary mercury deposits of the world are found in Spain, China, central Europe, and Algeria. Spain is estimated to have the greatest reserves, almost 60 percent of the world’s total. In 2008, world production of mercury was approximately 950 metric tons. Mercury is also recovered through the recycling of batteries, dental amalgams, thermostats, fluorescent lamp tubes, and certain industrial sludges and solutions.
(The entire section is 61 words.)
Uses of Mercury (Encyclopedia of Global Resources)
In the past, the primary use of mercury in the world was in the industrial production of chlorine and caustic soda. However, beginning in the twenty-first century this usage was curtailed significantly, reflecting a general movement away from mercury usage. The United States has exported refined mercury for the production of chlorine and caustic soda, fluorescent lights, and dental amalgam. Mercuric sulfate and mercuric chloride have been used industrially to produce vinyl chloride, vinyl acetate, and acetaldehyde. Pharmacological uses of mercury compounds include mercury bichloride and mercurochrome as skin antiseptics, and mercurous chloride (calomel) as a diuretic. Many of these uses have been curtailed, and a ban on U.S. exports was passed by Congress in 2008.
(The entire section is 116 words.)
Further Reading (Encyclopedia of Global Resources)
Adriano, Domy C. “Mercury.” In Trace Elements in Terrestrial Environments: Biogeochemistry, Bioavailability, and Risks of Metals. 2d ed. New York: Springer, 2001.
Eisler, Ronald. Mercury Hazards to Living Organisms. Boca Raton, Fla.: CRC/Taylor & Francis, 2006.
Greenwood, N. N., and A. Earnshaw. “Zinc, Cadmium, and Mercury.” In Chemistry of the Elements. 2d ed. Boston: Butterworth-Heinemann, 1997.
Harte, John, et al. Toxics A to Z: A Guide to Everyday Pollution Hazards. Berkeley: University of California Press, 1991.
Hightower, Jane M. Diagnosis Mercury: Money, Politics, and Poison. Washington, D.C.: Island Press/Shearwater Books, 2009.
Massey, A. G. “Group 12: Zinc, Cadmium, and Mercury.” In Main Group Chemistry. 2d ed. New York: Wiley, 2000.
Risher, J. F. Elemental Mercury and Inorganic Mercury Compounds: Human Health Aspects. Geneva, Switzerland: World Health Organization, 2003.
Natural Resources Canada. Canadian Minerals Yearbook, Mineral and Metal Commodity Reviews. http://www.nrcan-rncan.gc.ca/mms-smm/busi-indu/cmy-amc/com-eng.htm
U.S. Geological Survey. Mercury: Statistics and Information. http://minerals.usgs.gov/minerals/pubs/commodity/mercury
U.S. Geological Survey. Mercury Contamination of Aquatic Ecosystems....
(The entire section is 194 words.)
Overview (The Solar System)
Mercury completes one Revolution about the Sun in only 87.97 days. Mercury’s orbit has a mean distance from the Sun of only 0.387 astronomical unit (1 AU is the mean Earth-Sun distance), an Eccentricity of 0.206, and an inclination of 7° with respect to the ecliptic plane. Mercury rotates about an axis with no obliquity and has a period of 58.65 days. The ratio of Mercury’s rotational period to its revolution period is almost precisely two to three (2:3). Mercury’s mass is 3.30 1023 kilograms, and its mean radius is 2,439 kilometers; therefore, Mercury’s mean density is 5,420 kilograms per cubic meter. Mercury’s most prevalent features are craters, scarps, and deformed terrain. Degradation of original craters has resulted from secondary impact and ballistic infilling, Seismic activity resulting from impacts, lava flows, and isostatic readjustment.
Mercury’s surface appears remarkably similar to that of Earth’s moon, although Mercury’s radius is about 50 percent larger than the Moon’s. Both bodies are heavily pockmarked with impact craters. Closer examination, however, reveals many important differences between the surfaces of Mercury and the Moon. The Moon has greater color variations across its surface than does Mercury. Mercury’s albedo, or reflectivity, is 0.12, a brightness similar to that of the lunar highlands seen on the Moon’s Earth-facing side. Although there are 20 percent Albedo contrasts...
(The entire section is 1283 words.)
Methods of Study (The Solar System)
Mercury is a planet known to the ancients. However, Mercury reveals few of its secrets to visual observation from Earth. Because it is so close to the Sun, it is often hidden by solar glare and can be seen only briefly, visually or telescopically, at twilight or daybreak. The Hubble Space telescope could not be used to obtain high-resolution images of Mercury’s surface because of the tremendous brightness of the Sun, which would overpower and damage that orbiting observatory’s sensitive instruments. Nevertheless, Mercury studies have advanced greatly since the first days of visual observations of this innermost planet in our solar system. Astronomers once incorrectly assumed that Mercury did not Rotate as it revolved around the Sun. Few surface features were known before the Mariner 10 encounters. Indeed, for all intents and purposes, almost all that was known about Mercury prior to 2008 was obtained through scientific investigations performed by the Mariner 10 Spacecraft on its three brief flybys in the mid-1970’s. That probe was equipped with seven primary experiments; they involved high-resolution television imaging, infrared radiometry, radio wave propagation, extreme ultraviolet spectroscopy, magnetometry, plasma detection, and charged particle flux measurements.
Mercury’s atmosphere was studied during a solar Occultation using Mariner 10’s ultraviolet experiment. The instrument measured the drop in the...
(The entire section is 1602 words.)
Context (The Solar System)
Mercury is the Roman name for the Greek god Hermes, patron of trade, travel, and thieves. Timocharis is considered to have registered the first recorded observation of Mercury, in 265 b.c.e. Very little more was learned about the planet until the invention of the telescope. Observation of the phases of Mercury was first reported in 1639 c.e. by Italian astronomer Giovanni Battista Zupus. Telescope technology improved, and evidence of surface features was found in the early 1800’s, when astronomers Karl Ludwig Harding and Johann Schröter measured albedo variations.
It was not until the early 1960’s that Mercury’s rotation rate was precisely measured using radar observations. Then came the launch of Mariner 10, the final spacecraft in the historic Mariner series, on November 3, 1973, at 12:45 a.m. eastern time atop an Atlas-Centaur launch vehicle from Launch Complex 36B at Cape Canaveral. Photographs obtained during this flyby mission began the geologic analysis of Mercury. This spacecraft became the first to use gravity assists from large Solar system bodies to redirect its trajectory to multiple photographic targets. It was recognized that the alignment of Earth, Venus, and Mercury was such that a single spacecraft could be launched between 1970 and 1973 from Earth toward Venus and then reach Mercury. Giuseppe Colombo of the Institute of Applied Mechanics in Padua, Italy, noted during an early 1970 Jet Propulsion Laboratory...
(The entire section is 877 words.)
Further Reading (The Solar System)
Balogh, André, Leonid Ksanfomality, and Rudolf von Steiger, eds. Mercury. New York: Springer, 2008. This work provides background information and reviews changes in humanity’s understanding about Mercury since the Mariner 10 flybys.
Beatty, J. Kelly, Carolyn Collins Petersen, and Andrew Chaikin, eds. The New Solar System. 4th ed. Cambridge, Mass.: Sky, 1999. Amply illustrated with color images, diagrams, and informative tables, this book is aimed at a popular audience but can also be useful to specialists. Contains an appendix with planetary data tables, a bibliography for each chapter, planetary maps, and an index.
Clark, Pamela. Dynamic Planet: Mercury in the Context of Its Environment. New York: Springer, 2007. Written by a NASA space scientist who edits the Mercury Messenger newsletter, this book covers the search for understanding of the solar system’s closest planet to the Sun.
Davies, Merton E., Stephen E. Dwornik, Donald E. Gault, and Robert G. Strom. Atlas of Mercury. NASA SP-423. Washington, D.C.: National Aeronautics and Space Administration, Scientific and Technical Information Office, 1978. Provides an excellent contemporary description of Mariner 10 and its mission. Includes a full atlas of spacecraft photography of Mercury. An essential reference for the planetary science enthusiast or researcher; also accessible to general audiences....
(The entire section is 589 words.)
Mercury (Encyclopedia of Environmental Issues, Revised Edition)
Mercury, often called quicksilver, is a relatively rare element, making up only about 3 parts per billion of the earth’s crust. Mercury occurs in its elemental form as a liquid, but it is more commonly found combined with other elements to form various minerals. The most common mercury-containing mineral is cinnabar (mercury sulfide), which is found mainly in Spain, Algeria, and China.
Mercury and its inorganic compounds have been used in producing caustic soda, dry-cell batteries, scientific measuring devices, dental amalgams, and mercury vapor lamps. Workers in factories making such products may be exposed to relatively high levels of mercury vapors and compounds. Dental assistants may also be exposed to relatively high levels of mercury vapor. Mercury is also released into the environment by the waste incineration of these products and may eventually accumulate in food sources such as grains and fish. For a long time, mercury was used as an additive to latex paints to inhibit the growth of bacteria and fungi, but this use was eliminated in the United States in 1991. Mercury compounds have also been used in agriculture as fungicides; workers who handle these compounds may experience negative health effects. Other sources of mercury in the environment are mercury mines and smelters, which may release considerable amounts of mercury into surrounding regions.
Some bacteria can convert inorganic mercury into organic compounds, such...
(The entire section is 760 words.)
Further Reading (Encyclopedia of Environmental Issues, Revised Edition)
Bakir, F., et al. “Methylmercury Poisoning in Iraq.” Science 181 (July, 1973): 230-241.
Eisler, Ronald. Mercury Hazards to Living Organisms. Boca Raton, Fla.: CRC Press, 2006.
Montgomery, Carla W. “Water Pollution.” In Environmental Geology. 9th ed. New York: McGraw-Hill, 2010.
Timbrell, John. “Environmental Pollutants.” In Introduction to Toxicology. 3d ed. New York: Taylor & Francis, 2002.
(The entire section is 51 words.)
Mercury (Forensic Science)
The discovery of mercury in an Egyptian tomb built some thirty-five hundred years ago proves that humanity’s fascination with the element is of long standing. Because metallic mercury almost seems alive as it flows, it became a key ingredient in the experiments of alchemists who thought gold was a compound that could be made from mercury and other metals. During the early eighteenth century, the distinguished scientist Sir Isaac Newton suffered periods of extreme depression that were probably caused by mercury poisoning acquired during his own alchemical experiments. In modern times, various uses of mercury—for example, as part of a process for mining gold and as an element in dental amalgam—have become controversial.
When mercury metal is released into the environment, microorganisms convert it into methylmercury by adding a methyl group (three hydrogen atoms and one carbon atom). Methylmercury has a strong affinity for the amino acid cysteine, and with cysteine attached, the body treats the combined molecule as a protein and allows it to cross both the placenta and the blood-brain barrier, making it particularly dangerous.
The worst case of widespread mercury poisoning in modern times occurred in Iraq during the late 1960’s and early 1970’s. After several years of poor harvest, the Iraqi government decided to import a special type of wheat from Mexico. When the grain arrived too late in the year for planting, the Iraqi...
(The entire section is 526 words.)
Further Reading (Forensic Science)
Casdorph, H. Richard, and Morton Walker. Toxic Metal Syndrome. Garden City Park, N.Y.: Avery, 1995.
Eisler, Ronald. Mercury Hazards to Living Organisms. Boca Raton, Fla.: CRC Press, 2006.
Sadiq, Muhammad. Toxic Metal Chemistry in Marine Environments. New York: Marcel Dekker, 1992.
(The entire section is 39 words.)
Mercury (Chemical Elements)
Mercury is a transition metal. A transition metal is one of the elements found between Groups 2 (IIA) and 13 (IIIA) on the periodic table. The periodic table is a chart that shows how chemical elements are related to one another. Mercury has long been known as quicksilver, because it is a silver liquid. The chemical symbol also reflects this property. The symbol, Hg, comes from the Latin term hydrargyrum, meaning "watery silver."
Mercury has been known for thousands of years. In many cultures, people learned to make mercury metal from its most important ore, cinnabar. When heated cinnabar releases mercury as a vapor (gas). The vapor is cooled and captured as liquid mercury.
Some mercury compounds are known to be poisonous. For example, mercuric chloride (corrosive sublimate) was often used to kill pests and, sometimes, people. On the other hand,...
(The entire section is 2575 words.)
Mercury (Encyclopedia of Public Health)
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 usesncluding its use in the extraction of gold from oresnd 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.
MARGARET H. WHITAKER
BRUCE A. FOWLER
(SEE ALSO: Environmental Determinants of Health; Foods and Diets; Heavy Metals; Minamata Disease; Occupational Safety and Health)
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): A6469.
U.S. Environmental Protection Agency (1997). Report to Congress on Mercury. Available at .
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.
Mercury (How Products are Made)
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.
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.
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.
- 1 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.
Because cinnabar ore is relatively concentrated, it can be processed directly without any intermediate steps to remove waste material.
- 2 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.
- 3 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.
- 4 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.
- 5 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.
- 6 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.
- 7 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
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.
- 8 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.
- 9 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.
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.
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
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.
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.
[This website contains a summary of the history, sources, properties, and uses of mercury.]