Bismuth

Bismuth (pronounced /ˈbɪzməth/) 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.

Bismuth compounds are used in cosmetics 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.

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Notable characteristics

Bismuth is a brittle metal with a pinkish 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, thallium, and antimony.

No other metal is more naturally diamagnetic (as opposed to superdiamagnetic) than bismuth, and it has a high electrical resistance. Of any metal, it has the second lowest thermal conductivity and the highest Hall coefficient. When deposited in sufficiently thin layers on a substrate, bismuth is a semiconductor, rather than a poor metal.^[1]

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.

While bismuth was traditionally regarded as the element with the heaviest stable isotope, 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,^[2] 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. Basilius Valentinus described some of its uses in 1450. Claude François Geoffroy showed in 1753 that this metal is distinct from lead.

Artificial bismuth was commonly used in place of the actual mineral. 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.^[3]

Bismuth was also known to the Incas and used (along with the usual copper and tin) in a special bronze alloy for knives.^[4]

Occurrence

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, but also tungsten or other metal alloys.

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.

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 (BAN), the price (NY Dealer) for bismuth metal from year-end 2000 to September 2005 was stuck in a range from lows of $2.70-$3.10 per lb. in late November 2002 and $2.60-$2.90 per lb. in December 2003 to highs of $3.85-$4.15 per lb. at year-end 2000 and $3.65-$4.00 per lb. in mid June 2004. BAN shows the range pressing to $4.20-$4.60 per lb. in September 2005 and then $4.50-$4.75 per pound in mid September 2006, before bursting upwards steeply to $6.00-$6.50 per lb in mid November 2006, $7.30-$7.80 in late December 2006, $9.25-$9.75 per lb in early March 2007, $10.50-$11.00 per lb in late March 2007, $13.00-$14.50 per lb. in mid April 2007, to an all-time high of $18.00-$19.00 per lb in mid June 2007, and then backed off to $13.50-$15.00 per lb in mid November 2007. This unprecedented event reflects an extreme scarcity of bismuth, perhaps temporary.  

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 273 °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) is used as an antidiarrheal and to treat some other gastro-intestinal diseases. 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 stool (poop).

Some other current uses:

• 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.

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 paint
• Ingredient in free-machining brasses for plumbing applications
• Ingredient in free-cutting 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.^{[citation needed]} 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

See also: Category:Bismuth compounds

Precautions

Bismuth is not known to be toxic, compared to its periodic table neighbours (lead, antimony, and polonium), although some compounds (including bismuth chloride) are toxic and should be handled with care.

See also

• Bismuth minerals

References

• Taylor, Harold A. Jr., "Bismuth", Financial Times Executive Commodity Reports (London: Mining Journal Books Ltd.) 2000 ISBN 1-84083 326 2