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Bismuth
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Bismuth is a chemical element that has the symbol Bi and atomic number 83. This heavy, brittle, white crystalline trivalent poor metal has a pink tinge and chemically resembles arsenic and antimony. Of all the metals, it is the most naturally diamagnetic, and only mercury has a lower thermal conductivity. It is generally considered to be the last naturally occurring stable, non-radioactive element on the periodic table, although it is actually slightly radioactive, with an extremely long half-life.
Bismuth compounds are used in cosmetics, medicines, and in medical procedures.
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Encyclopedia
Bismuth is a chemical element that has the symbol Bi and atomic number 83. This heavy, brittle, white crystalline trivalent poor metal has a pink tinge and chemically resembles arsenic and antimony. Of all the metals, it is the most naturally diamagnetic, and only mercury has a lower thermal conductivity. It is generally considered to be the last naturally occurring stable, non-radioactive element on the periodic table, although it is actually slightly radioactive, with an extremely long half-life.
Bismuth compounds are used in cosmetics, medicines, and in medical procedures. As the toxicity of lead has become more apparent in recent years, alloy uses for bismuth metal as a replacement for lead have become an increasing part of bismuth's commercial importance.
Characteristics
Bismuth is a brittle metal with a white, silver-pink hue, often occurring in its native form with an iridescent oxide tarnish showing many refractive colors from yellow to blue. When combusted with oxygen, bismuth burns with a blue flame and its oxide forms yellow fumes. Its toxicity is much lower than that of its neighbors in the periodic table such as lead, tin, tellurium, antimony, and polonium.
Although ununpentium is theoretically more diamagnetic, no other metal is verified to be more naturally diamagnetic than bismuth. (Superdiamagnetism is a different physical phenomenon.) Of any metal, it has the second lowest thermal conductivity (after mercury) and the highest Hall coefficient. It has a high electrical resistance. When deposited in sufficiently thin layers on a substrate, bismuth is a semiconductor, rather than a poor metal.
Elemental bismuth is one of very few substances of which the liquid phase is denser than its solid phase (water being the best-known example). Because bismuth expands on freezing, it was long an important component of low-melting typesetting alloys, which needed to expand to fill printing molds.
Isotopes
While bismuth was traditionally regarded as the element with the heaviest stable isotope, bismuth-209, it had long been suspected to be unstable on theoretical grounds. This was finally demonstrated in 2003 when researchers at the Institut d'Astrophysique Spatiale in Orsay, France, measured the alpha emission half-life of 209Bi to be 1.9 x 1019 years, over a billion times longer than the current estimated age of the universe. Owing to its extraordinarily long half-life, for nearly all applications bismuth can be treated as if it is stable and non-radioactive. The radioactivity is of academic interest, however, because bismuth is one of few elements whose radioactivity was suspected, and indeed theoretically predicted, before being detected in the laboratory.
History
Bismuth (New Latin bisemutum from German Wismuth, perhaps from weiße Masse, "white mass") was confused in early times with tin and lead because of its resemblance to those elements. Bismuth has been known since ancient times, and so no one person is credited with its discovery. However, Claude François Geoffroy demonstrated in 1753 that this metal is distinct from lead and tin.
"Artificial bismuth" was commonly used in place of the actual metal. It was made by hammering tin into thin plates, and cementing them by a mixture of white tartar, saltpeter, and arsenic, stratified in a crucible over an open fire.
Bismuth was also known to the Incas and used (along with the usual copper and tin) in a special bronze alloy for knives.
Occurrence and production
In the Earth's crust, bismuth is about twice as abundant as gold. It is not usually economical to mine it as a primary product. Rather, it is usually produced as a byproduct of the processing of other metal ores, especially lead, tungsten (China), tin, copper, and also silver (indirectly) or other metallic elements.
The most important ores of bismuth are bismuthinite and bismite. In 2005, China was the top producer of bismuth with at least 40% of the world share followed by Mexico and Peru, reports the British Geological Survey. Native bismuth is known from Australia, Bolivia, and China.
New York prices | Time | Price (USD/lb.) |
|---|
| Dec 2000 | $3.85-$4.15 | | Nov 2002 | $2.70-$3.10 | | Dec 2003 | $2.60-$2.90 | | Jun 2004 | $3.65-$4.00 | | Sep 2005 | $4.20-$4.60 | | Sep 2006 | $4.50-$4.75 | | Nov 2006 | $6.00-$6.50 | | Dec 2006 | $7.30-$7.80 | | Mar 2007 | $9.25-$9.75 | | Apr 2007 | $10.50-$11.00 | | Jun 2007 | $18.00-$19.00 | | Nov 2007 | $13.50-$15.00 | |
According to the USGS, world 2006 bismuth mine production was 5,700 tonnes, of which China produced 3,000 tonnes, Mexico 1,180 tonnes, Peru 950 tonnes, and the balance Canada, Kazakhstan and other nations. World 2006 bismuth refinery production was 12,000 tonnes, of which China produced 8,500 tonnes, Mexico 1,180 tonnes, Belgium 800 tonnes, Peru 600 tonnes, Japan 510 tonnes, and the balance Canada and other nations.
The difference between world bismuth mine production and refinery production reflects bismuth's status as a byproduct metal. Bismuth travels in crude lead bullion (which can contain up to 10% bismuth) through several stages of refining, until it is removed by the Kroll-Betterton process or the Betts process. The Kroll-Betterton process uses a pyrometallurgical separation from molten lead of calcium-magnesium-bismuth drosses containing associated metals (silver, gold, zinc, some lead, copper, tellurium, and arsenic), which are removed by various fluxes and treatments to give high-purity bismuth metal (over 99% Bi). The Betts process takes cast anodes of lead bullion and electrolyzes them in a lead fluosilicate-hydrofluosilicic acid electrolyte to yield a pure lead cathode and an anode slime containing bismuth. Bismuth will behave similarly with another of its major metals, copper. Thus world bismuth production from refineries is a more complete and reliable statistic.
According to the Bismuth Advocate News, the price for bismuth metal from year-end 2000 to September 2005 was stuck in a range from $2.60 to $4.15 per lb., but after this period the price started rising rapidly as global bismuth demand as a lead replacement and other uses grew rapidly. New mines in Canada and Vietnam may relieve the shortages, but prices are likely to remain above their previous level for the foreseeable future. The Customer-Input price for bismuth is more oriented to the ultimate consumer; it started January 2008 at US$39.40 per kilogram ($17.90 per pound) in January 2008 and reached US$35.55 per kg (US$16.15 per lb.) in September 2008.
Sustainability and Life-Cycle Assessment
While bismuth is most available today as a byproduct, its sustainability is more dependent on recycling. Bismuth is mostly a byproduct of lead smelting, along with silver, zinc, antimony, and other metals, and also of tungsten production, along with molybdenum and tin, and also of copper and tin production. Recycling bismuth is difficult in many of its end uses, primarily because of scattering. Probably the easiest to recycle would be bismuth-containing fusible alloys in the form of larger objects, then larger soldered objects. Half of the world solder consumption is in electronics (i.e., circuit boards). As the soldered objects get smaller or contain little solder or little bismuth, the recovery gets progressively more difficult and less economic, although solder with a sizable silver content will be more worth recovering. Next in recycling feasibility would be sizeable catalysts with a fair bismuth content, perhaps as bismuth phosphomolybdate, and then bismuth used in galvanizing and as a free-machining metallurgical additive. Finally, the bismuth in the uses where it gets scattered the most, in stomach medicines (bismuth subsalicylate), paints (bismuth vanadate) on a dry surface, pearlescent cosmetics (bismuth oxychloride), and bismuth-containing bullets. The bismuth is so scattered in these uses as to be unrecoverable with present technology. Bismuth can also be available sustainably from greater efficiency of use or substitution, most likely stimulated by a rising price. For the stomach medicine, another active ingredient could be substituted for some or all of the bismuth compound. It would be more difficult to find an alternative to bismuth oxychloride in cosmetics to give the pearlescent effect. However, there are many alloying formulas for solders and therefore many alternatives.
The life-cycle assessment of bismuth will focus on solders, one of the major uses of bismuth, and the one with the most complete information. The average primary energy use for solders is around 200 MJ per kg, with the high-bismuth solder (58% Bi) only 20% of that value, and three low-bismuth solders (2% to 5% Bi) running very close to the average. The global warming potential averaged 10 to 14 kg carbon dioxide, with the high-bismuth solder about two-thirds of that and the low-bismuth solders about average. The acidification potential for the solders is around 0.9 to 1.1 kg sulfur dioxide equivalent, with the high-bismuth solder and one low-bismuth solder only one-tenth of the average and the other low-bismuth solders about average. There is very little life-cycle information on other bismuth alloys or compounds.
Crystals
Though virtually unseen in nature, high-purity bismuth can form distinctive hopper crystals. These colorful laboratory creations are typically sold to collectors. Bismuth is relatively nontoxic and has a low melting point just above 271 °C, so crystals may be grown using a household stove, although the resulting crystals will tend to be lower quality than lab-grown crystals.
Applications
Bismuth oxychloride is sometimes used in cosmetics. Bismuth subnitrate and bismuth subcarbonate are used in medicine. Bismuth subsalicylate (the active ingredient in Pepto-Bismol and (modern) Kaopectate) is used as an antidiarrheal and to treat some other gastro-intestinal diseases (oligodynamic effect). Also, the product Bibrocathol is an organic molecule containing Bismuth and is used to treat eye infections. Bismuth subgallate (the active ingredient in Devrom) is used as an internal deodorant to treat malodor from flatulence (or gas) and faeces.
Some other current uses:
- New research by physicists has found a potential role of bismuth as an ingredient in electronic circuits and in manufacturing next-generation solar cells which would have a greater efficiency. Bismuth allows for the creation of new diodes that can reverse their direction of current flow. Ordinary semiconductor diodes are fixed in their direction.
- Many bismuth alloys have low melting points and are widely used for fire detection and suppression system safety devices.
- Bismuth is used as an alloying agent in production of malleable irons.
- A carrier for U-235 or U-233 fuel in nuclear reactors
- Bismuth has also been used in solders. The fact that bismuth and many of its alloys expand slightly when they solidify make them ideal for this purpose.
- Bismuth subnitrate is a component of glazes that produces an iridescent luster finish.
- Bismuth telluride is an excellent thermoelectric material; it is widely used.
- A replacement propellant for xenon in Hall effect thrusters
- In 1997 an antibody conjugate with Bi-213, which has a 45 minute half-life, and decays with the emission of an alpha-particle, was used to treat patients with leukemia.
- In 2001, Professor Barry Allen and Dr. Graeme Melville at St. George Hospital in Sydney successfully produced Bi-213 in linac experiments which involved bombarding radium with bremsstrahlung photons. This cancer research team used Bi-213 in its Targeted Alpha Therapy (TAT) program.
- The delta form of bismuth oxide when it exists at room temperature is a solid electrolyte for oxygen. This form normally only exists above and breaks down below a high temperature threshold, but can be electrodeposited well below this temperature in a highly alkaline solution.
In the early 1990s, research began to evaluate bismuth as a nontoxic replacement for lead in various applications:
- As noted above, bismuth has been used in solders; its low toxicity will be especially important for solders to be used in food processing equipment and copper water pipes.
- A pigment in artists' oil and acrylic paint (Bismuth Vanadate)
- Ingredient in free-machining brasses for plumbing applications
- Ingredient in free-machining steels for precision machining properties
- A catalyst for making acrylic fibres
- In low-melting alloys used in fire detection and extinguishing systems
- Ingredient in lubricating greases
- Dense material for fishing sinkers
- In crackling microstars (dragon's eggs) in pyrotechnics, as the oxide, subcarbonate, or subnitrate
- Replacement for lead in shot and bullets. The UK, U.S., and many other countries now prohibit the use of lead shot for the hunting of wetland birds, as many birds are prone to lead poisoning due to mistaken ingestion of lead (instead of small stones and grit) to aid digestion. Bismuth-tin alloy shot is one alternative that provides similar ballistic performance to lead. (Another less expensive but also more poorly performing alternative is "steel" shot, which is actually soft iron.)
- Bismuth core bullets are also starting to appear for use in indoor shooting ranges, where fine particles of lead from bullets impacting the backstop can be a chronic toxic inhalant problem. Owing to bismuth's crystalline nature, the bismuth bullets shatter into a non-toxic powder on impact, making recovery and recycling easy. The lack of malleability does, however, make bismuth unsuitable for use in expanding hunting bullets.
- Fabrique Nationale de Herstal uses bismuth in the projectiles for its FN 303 less-lethal riot gun.
According to the USGS, U.S. bismuth consumption in 2006 totaled 2,050 tonnes, of which chemicals (including pharmaceuticals, pigments, and cosmetics) were 510 tonnes, bismuth alloys 591 tonnes, metallurgical additives 923 tonnes, and the balance other uses.
Compounds
Bismuth subcitrate, metronidazole, and tetracycline are combined and together with omeprazole use for treating Helicobacter pylori bacteria cause stomach infection or ulcer
Precautions
Bismuth is not known to be toxic, compared to its periodic table neighbours (lead, antimony, and polonium), although some compounds (including bismuth chloride due to its corrosive acidity) are toxic and should be handled with care. As with lead, overexposure to bismuth can result in the formation of a black deposit on the gingiva, known as a bismuth line.
Fine bismuth powder can be pyrophoric.
See also
Bismuth minerals
External links
- - United States Geological Survey minerals information for bismuth
- by Jan Kihle Crystal Pulling Laboratories, Norway
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