Lead

Pb redirects here. For PB or pb as an abbreviation, go to PB.

Lead is a chemical elementin the periodic tablethat has the symbol Pb (L.plumbum) and atomic number82. A soft, heavy, toxicand malleablepoor metal, lead is bluish white when freshly cut but tarnishes to dull gray when exposed to air. Lead is used in building construction, lead-acid batteries, bulletsand shot, and is part of solder, pewter, and fusible alloys. Lead has the highest atomic number of all stable elements. (But see the article on Bismuth, which has a half life so long it can be considered stable.)

Notable characteristics

Lead has a bright luster and is a dense, ductile, very soft, highly malleable, bluish-white metal that has poor electrical conductivity. This true metal is highly resistant to corrosion. Because of this property, it is used to contain corrosive liquids (e.g. sulfuric acid). Lead can be toughened by adding a small amount of antimonyor other metals to it. Lead is the only metal in which there is zero Thomson effect.

Applications

• Lead is a major constituent of the Lead-acid batteryused extensively in car batteries.
• Lead was used as a pigment in Lead paintfor white as well as yellow and red colors.
• Lead is used as a coloring element in ceramicglazes, notably in the colors red and yellow.
• Lead was used for plumbingin Ancient Romeand water mains and service pipes up until the early 1970's.
• Lead sticks were used as pencilsbut has been replaced by graphitefor the last 450 years.
• Lead is used as projectilesfor firearmsand fishing sinkersbecause of its density, low cost verse alternative products and ease of use due to relatively low melting point.
• Lead is used in some candles to treat the wick to ensure a longer, more even burn. Because of the dangers, European and North American manufacturers use more expensive alternatives such as zinc. [1]
• Lead is used as shielding from radiation.
• Molten lead is used as a coolant, eg. for lead cooled fast reactors.
• Lead glassis comprised of 12-28% lead. It changes the optical characteristics of the glass and reduces the transmission of radiation.
• Tetraethyl leadhas been used in leaded fuelsto reduce engine knocking; however, this is no longer common practice in the Western Worlddue to health concerns.
• Lead is used as electrodesin the process of electrolysis.

History

Lead has been used by humans for at least 7000 years, because it was (and continues to be) widespread and easy to extract, as well as easy to work with, being both highly malleable and ductile as well as easy to smelt. In the early bronze agelead was used with antimonyand arsenic. Lead was mentioned in the Book of Exodus. Alchemiststhought that lead was the oldest metal and associated it with the planet Saturn. Lead pipes that bear the insignia of Roman emperors are still in service and many Roman "pigs" (ingots) of lead figure in Derbyshire lead mining historyand in the history of the industry in other English centres. Lead's symbol Pb is an abbreviation of its Latinname plumbum. The English word "plumbing" also derives from this Latin root.

By the mid-1980s, a significant shift in lead end-use patterns had taken place. Much of this shift was a result of the U.S. lead consumers' compliance with environmental regulations that significantly reduced or eliminated the use of lead in nonbattery products, including gasoline, paints, solders, and water systems. Recently, lead use is being further curtailed by the RoHS directive.

Occurrence

Image:LeadOreUSGOV.jpg Native lead does occur in nature, but it is rare. Currently lead is usually found in ore with zinc, silverand (most abundantly) copper, and is extracted together with these metals. The main lead mineralis galena(PbS), which contains 86.6% lead. Other common varieties are cerussite(PbCO₃) and anglesite(PbSO₄). But more than half of the lead used currently comes from recycling.

In mining, the ore is extracted by drilling or blasting and then crushed and ground. The ore is then treated using extractive metallurgy. The Froth flotationprocess separates the lead and other minerals from the waste rock (tailings) to form a concentrate. The concentrate, which can range from 50% to 60% lead, is dried and then treated using pyrometallurgy. The concentrate is sinteredbefore being smelted in to produce a 97% lead concentrate. The lead is then cooled in stages which causes the lighter impurites (dross) to rise to the surface where they can be removed. The molten lead bullion is then refined by additional smelting with air being passed over the lead to form a slag layer containing any remaining impurities and producing 99.9% pure lead.

• See Category:Lead minerals

Isotopes

Main Article: Isotopes of lead

Lead has four stable, naturally occurring isotopes:
Pb²⁰⁴ (1.4%)
Pb²⁰⁶(24.1%)
Pb²⁰⁷(22.1%)
and Pb²⁰⁸ (52.4%).
Pb²⁰⁶, Pb²⁰⁷ Pb²⁰⁸ are all radiogenic, and are the end products of complex decay chainsthat begin at U²³⁸, U²³⁵ and Th²³² respectively. The corresponding half-livesof these decay schemes vary markedly: 4.47 ×10⁹, 7.04 × 10⁸ and 1.4 × 10¹⁰ years, respectively. Each is reported relative to Pb²⁰⁴, the only non-radiogenic stable isotope. The ranges of isotopic ratios for most natural materials are 14.0-30.0 for Pb²⁰⁶/Pb²⁰⁴, 15.0-17.0 for Pb²⁰⁷/Pb²⁰⁴, and 35.0-50.0 for Pb²⁰⁸/Pb²⁰⁴, although numerous examples outside these ranges are reported in the literature.

• see isotope geochemistry

Precautions

Lead is a poisonousmetal that can damage nervous connections (especially in young children) and cause blood and brain disorders. Long term exposure to lead or its salts (especially soluble salts or the strong oxidant PbO₂) can cause nephropathy, and colic-like abdominal pains. The historical use of lead acetate(also known as sugar of lead) by the Roman Empireas a sweetener for wine is considered by some to be the cause of the dementiawhich affected many of the Roman Emperors. At one point in time, some lead compounds, because of their sweetness, were used by candy makers. Although this has been banned in industrialized nations, there was a recent scandal involving lead-laced Mexican candy being eaten by children in California (http://www.ocregister.com/investigations/2004/lead/part1_printable.html).

Health effects

Main article: lead poisoning

The concern about lead's role in mental retardation in children has brought about widespread reduction in its use (lead exposure has been linked to schizophrenia). Paint containing lead has been withdrawn from sale in industralised countries, though many older houses may still contain substantial lead in their old paint: it is generally recommended that old paint should not be stripped by sanding, as this generates inhalable dust.

Lead salts used in pottery glazes have on occasion caused poisoning, when acid drinks, such as fruit juices, have leached lead ions out of the glaze. It has been suggested that what was known as "Devon colic" arose from the use of lead-lined presses to extract applejuice in the manufacture of cider. Lead is considered to be particularly harmful for women's ability to reproduce. For that reason many universities do not hand out lead-containing samples to women for instructional laboratory analyses.

The earliest pencilsactually used lead, though 'pencil leads' have been made for the last couple of centuries from graphite, a naturally occurring form (allotrope) of carbon.

Language derivations

The Latin plumbum has given birth to a number of terms in the English language:

• Plumbing, or system of piping, derives from the fact that pipes were once made of lead.
• Plumb bob or plummet, a small, pointed body of metal the weight of which is used to draw a string vertical under tension, refers to the fact that they were originally made from lead.
• Plumb wall is so-said because a plumb bob is used to find the vertical.
• Plumbing the depths derives from the use of the lead weight to draw the sounding line down to the bottom of the water body (or to the end of the line if the water's really deep!).
• Plumb crazy may derive from the fact that lead poisoning can cause insanity; or, according to the Oxford English Dictionary, from a U.S. sense of plum (derived from plumb) meaning 'completely'.
• Plumbism is the medical term for lead poisoning.
• Aplomb comes from the French à plomb, meaning plumb vertical, and therefore confident and cool.

The plum, however, does not get its name from this root. Rather, plum is derived from the Old Englishword plume.

Literature

• Keisch, B., Feller, R. L., Levine, A. S., and Edwards, R. R.: Dating and Authenticating Works of Art by Measurement of Natural Alpha Emitters. In: Science, 155, No. 3767, p. 1238-1242, 1967.
• Keisch, B: Dating Works of Art Trough their Natural Radioactivity: Improvements and Applications. In: Science, 160, p. 413-415, 1968.
• Keisch, B: Discriminating Radioactivity Measurements of Lead: New Tool for Authentication. In: Curator, 11, No. 1., p. 41-52, 1968.

References

• A Small Dose of Toxicology:Lead
• Los Alamos National Laboratory - Lead

External links

• Case Studies in Environmental Medicine - Lead Toxicity
• National Pollutant Inventory - Lead and compounds fact sheet
• WebElements.com - Lead
• Do lead fishing sinkers threaten the environment?(from The Straight Dope)

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It uses material from the http://en.wikipedia.org/wiki/Lead Wikipedia article Lead.