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mercury processing
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What is mercury?
Mercury (Hg) is a liquid metal element in group 12 of the periodic table. It has a low melting point (-38.83 °C) and a high boiling point (356.62 °C). Mercury's properties, such as uniform volume expansion and high electrical conductivity, make it useful in thermometers, barometers, sealed electrical switches, and lamps.
Mercury processing involves preparing mercury ore for various applications. Methods of extraction rely on the metal's volatility. Cinnabar is decomposed by air or lime to yield free metal. Mercury is extracted from cinnabar by roasting it in air, followed by condensation of the mercury vapor.
Because mercury is highly toxic, care must be taken when handling and transporting it. Exposure to mercury can lead to mercury poisoning, with symptoms varying depending on the type of compound and mode of contact.
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Where is mercury found in nature?
Mercury is found globally in the earth's crust at an average concentration of about 0.08 grams per ton of rock. While there are over 25 known minerals containing mercury, the most important one is cinnabar, a mercury sulfide mineral. Mercury deposits are typically small and irregular, sometimes occurring as disseminated deposits but usually as veinlets, which means large-scale mining is not viable.
Cinnabar is found on every continent except Antarctica. Major historical deposits have been mined in Almadén, Spain; Idrija, Slovenia; and New Almaden, California, U.S. China is currently the world's leading mercury producer, often as a byproduct of gold mining. Mercury also enters the environment through events such as volcanic eruptions or rock breakdown.
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How is mercury extracted from its ores?
Mercury is extracted from its ores, mainly cinnabar, through a process called pyrometallurgical extraction, which is essentially distillation. The sulfide ore is heated in the presence of air, causing oxygen to combine with the sulfur, forming sulfur dioxide and liberating the mercury as a vapor at a temperature above its boiling point. The gases are then passed through a series of U-shaped tubes to condense the mercury vapor into liquid form.
Various furnaces, like the Cermak-Spirek shaft furnace, retorts, and multiple-hearth furnaces, are used, each with its own advantages. The furnaces heat the ore with charcoal or coke, and the liberated mercury vapor is condensed. Retorts are cheaper to install but more costly to operate, while rotary and multiple-hearth furnaces offer higher capacity and continuous operation.
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What are the main steps involved in processing mercury?
Mercury processing involves several key steps, beginning with mining the ore, often underground due to the small and irregular nature of mercury deposits.
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Concentration Various methods like jigging, shaking, screening, elutriation, and flotation are employed to concentrate the ore because most cinnabar contains less than 1% mercury as mined.
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Extraction The pyrometallurgical extraction of mercury from its ore is essentially a distillation process. Applying heat to the sulfide ore in the presence of air causes oxygen to combine with the sulfur, forming sulfur dioxide, and the metal is liberated as a vapor. This vapor is then condensed into liquid mercury. Furnaces and retorts are used for this process, with the choice depending on the scale of the operation.
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Refining The metal produced through furnacing, known as prime virgin mercury, typically has a purity exceeding 99.9%. Impurities can be removed through multiple distillations for applications requiring higher purity.
Because mercury is highly toxic, care must be taken in its handling and transport.
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What are some common uses of processed mercury?
Processed mercury has various applications because of its unique physical and chemical properties. However, due to its high toxicity, its use has declined in favor of safer alternatives.
Common uses include:
* Electrical Components Mercury's high electrical conductivity makes it useful in sealed electric switches and relays, industrial power rectifiers, fluorescent and mercury-vapor lamps, and mercury cell batteries.
* Chlor-alkali Industry Mercury is used as a moving cathode in the large-scale production of chlorine and caustic soda, but this application is declining due to mercury losses and environmental concerns.
* Measurement Devices Mercury's uniform volume expansion makes it suitable for use in thermometers, barometers, and manometers.
* Gold and Silver Recovery Mercury dissolves gold and silver to form an amalgam, which is then heated to distill off the mercury, leaving the precious metals behind.
* Chemical Industry Mercury compounds are utilized in pharmacology, chemical processes, and agriculture. For example, mercuric chloride is a catalyst in the production of vinyl chloride.5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What environmental or health concerns are related to mercury processing?
Mercury processing can lead to significant environmental and health concerns due to mercury's highly toxic nature. Exposure to mercury, its vapors, and its compounds can result in mercury poisoning. Industrial processes, including chemical manufacturing, mining, and the use of mercury in various products, contribute to environmental contamination through air emissions and effluent wastes.
Once released into aquatic environments, mercury is converted into methylmercury, a highly toxic form that bioaccumulates in fish, posing a risk to humans who consume them. Symptoms of mercury poisoning vary depending on the type of compound and mode of contact, ranging from inflammation of the digestive tract and kidney damage in acute cases to neurological and psychological changes in chronic exposure. Historical incidents, such as the Minamata disease outbreak in Japan, highlight the devastating consequences of mercury contamination from industrial sources, emphasizing the importance of preventive measures like proper ventilation, plant cleanliness, and personal hygiene to mitigate the dangers of mercury poisoning.
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mercury processing, preparation of the ore for use in various products.
Mercury (Hg) has a unique combination of physical properties. Its low melting point (−38.87 °C [−38 °F]) and boiling point (356.9 °C [674 °F]), high specific gravity (13.5 grams per cubic centimetre), uniform volume expansion over the entire range of temperatures in its liquid state, and high surface tension (so that it does not wet glass) make it useful for the measurement of temperature in thermometers and of pressure in barometers and manometers. In addition, the high electrical conductivity of liquid mercury has led to its use in sealed electric switches and relays, industrial power rectifiers, fluorescent and mercury-vapour lamps, mercury cell batteries, and as moving cathodes in the large-scale production of chlorine and caustic soda.
Because mercury is highly toxic, care must be exercised in its handling and transport. By limiting exposure to mercury metal, vapours, and compounds through such preventive measures as proper ventilation, plant cleanliness and personal hygiene, industrial plants can be made relatively safe from the dangers of mercury poisoning.
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History
The recovery and uses of mercury, also known as quicksilver, have been described since antiquity. Its use in the early 2nd millennium bce in Egypt has been implied but not authenticated, as the use of synonyms in ancient writings obscures the meaning of some writers, but the mining and concentrating of cinnabar, the most common ore of mercury, were certainly described in the 4th century bce. Alchemists in China were believed to have used mercury in trying to convert base metals to gold as early as the 2nd century bce, and the Roman writer Pliny the Elder wrote in the 1st century about the recovery of quicksilver by distillation and condensation, the forerunner of modern methods of metallurgical treatment. Pliny also described the trade in mercury and cinnabar between Spain and Rome.
Because mercury was credited in folklore with the power to ward off evil spirits and cure various ailments, it acquired various therapeutic and agricultural uses. By the 16th century, crude furnaces for treating cinnabar by distillation and condensation were meeting the growing demand for quicksilver in medicine and in the amalgamation of gold and silver ores. Beginning in the 17th century, advancing science and technology brought a continuous increase in demand for mercury for use in thermometers, barometers, and electrical and chemical applications.
In the early mining and furnacing of cinnabar and mercury, workers showed the symptoms of mercury poisoning, but little was known of the cause and treatment. As operators learned to reduce the escape of gases by improving furnaces and condensers and to promote personal hygiene, the incidence of poisoning declined. Throughout history, cinnabar has been used as a pigment or colouring because of its attractive red colour, and in the 19th century some American Indians in California complained of illness that was diagnosed as mercury poisoning caused by cinnabar in war paint. Little was known about the release of mercury into the environment by the chemical, electrical, and battery industries until the 20th century, when the medical profession and government agencies began to evaluate plants and operations. Thereafter, regulations reducing plant emissions improved the environment in and around these operations.
Ores
There are more than 25 known minerals containing mercury, but the principal ore mineral is cinnabar, a soft, red to reddish brown mercury sulfide. Some cinnabar deposits may also contain elemental mercury. The mineral has been found in all continents except Antarctica. It occurs in all types and ages of rock, usually alone but sometimes in association with antimony, gold, iron, and zinc.
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Large commercial deposits of mercury have been mined at Almadén, Spain; Idrija, Slovenia; Monte Amiata, Italy; Santa Barbara, Peru; and New Almaden, California, U.S. The world’s leading producers of mercury are China, Kyrgyzstan, and Chile.
Mining and concentrating
Mercury deposits are small and irregular, occurring sometimes as disseminated deposits but usually as veinlets. This precludes large-scale, highly mechanized mining methods. The most common method of ore recovery is underground mining, with conventional drilling and blasting followed by scraping or mechanical loading into ore cars.
Because most cinnabar as mined contains less than 1 percent mercury, various mineral-processing methods, such as jigging, shaking, screening, elutriation, and flotation, have been practiced to concentrate the ore. Flotation separation by the usual procedures for sulfide ores has had some success in the United States, but, because cinnabar is soft and friable, crushing and grinding the ore to reduce it to a size small enough to liberate the mineral may cause significant losses as slimes in the flotation tank. Although various methods are effective in producing higher-grade concentrates of cinnabar for furnacing, they cannot compete economically with the direct furnacing of the ore either as mined or after preliminary sorting by hand. A growing source of mercury in the United States is as a by-product of large, low-grade gold mining operations.