Lead is a chemical element in the periodic table that has the symbol Pb (L. Plumbum) and atomic number 82. A soft, heavy, toxic and malleable poor metal, lead has a dull gray appearance and is bluish white when freshly cut but tarnishes to dull gray when exposed to air. Lead is used in building construction, lead-acid accumulators, bullets and shot, and is part of solder, pewter, and fusible alloys. Lead has the highest atomic number of all stable elements.*
Lead has a bright luster and is a 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 antimony or other metals to it.
Early uses of lead included building materials, pigments for glazing ceramics, and pipes for transporting water. The castles and cathedrals of Europe contain considerable quantities of lead in decorative fixtures, roofs, pipes, and windows. Lead is the fifth most widely used metal (in its elemental state) after iron, aluminium, copper and zinc. Common uses include:
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. Lead was mentioned in the Book of Exodus. Alchemists thought 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 history and in the history of the industry in other English centres. Lead's symbol Pb is an abbreviation of its Latin name 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.
Native lead does occur in nature, but it is rare. Currently lead is usually found in ore with zinc, silver and (most abundantly) copper, and is extracted together with these metals. The main lead mineral is 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 taken through a process developed in the 19th century at Broken Hill, Australia. A flotation process separates the lead and other minerals from the waste rock (tailings) to form a concentrate by passing the ore, water and certain chemicals through a series of tanks in which the slurry is constantly mixed. Air is blown through the tanks and lead sulfides attach to the bubbles and rise to form a foam which can be removed. The foam (which is around 50% lead) is dried and then sintered before being smelted 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.
Lead has four stable, naturally occurring isotopes: Pb-204 (1.4%), Pb-206 (24.1%), Pb-207 (22.1%) and Pb-208 (52.4%). Pb-206, Pb-207 and Pb-208 are all radiogenic, and are the end products of complex decay chains that begin at U-238, U-235 and Th-232 respectively. The corresponding half-lives of these decay schemes vary markedly: 4.47 × 109, 7.04 × 108 and 1.4 × 1010 years, respectively. Each is reported relative to 204Pb, the only non-radiogenic stable isotope. The ranges of isotopic ratios for most natural materials are 14.0-30.0 for Pb-206/Pb-204, 15.0-17.0 for Pb-207/Pb-204 and 35.0-50.0 for Pb-208/Pb-204, although numerous examples outside these ranges are reported in the literature.
Lead is a poisonous metal 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. Its historical use by the Roman Empire for water piping (and its salt, lead acetate, also known as sugar of lead, as a sweetener for wine) is considered by some to be the cause for the dementia that affected many of the emperors.
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 apple juice in the manufacture of cider. Lead is considered to have particularly nasty consequences for mothers in spe, i.e. girls and young women. For that reason many universities do not hand out lead containing samples to girls for instructional laboratory analyses.
See also: lead poisoning
The Latin plumbum has given birth to a number of terms in the English language:
The origin of the name of the fruit called a plum is not related.
*Bismuth-209 has a half-life of the order of a billion times the believed age of the universe and is sometimes considered stable, thus sometimes bismuth is considered to have the highest atomic number of all stable elements.
ca:Plom de:Blei eo:Plumbo es:Plomo et:Plii fr:Plomb it:Piombo ja:鉛 nl:Lood (element) pl:Ołów pt:Chumbo ru:Свинец sl:Svinec sv:Bly