Lead
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 is bluish white when freshly cut but tarnishes to dull gray when exposed to air. Lead is used in building construction,
lead-acid batteries,
bullets and 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.)
Lead has a dull 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
antimony or other metals to it. Lead is the only metal in which there is zero
Thomson effect. Lead is also
poisonous.
*Lead is a major constituent of the
lead-acid battery used extensively in car batteries.
*Lead is used as a coloring element in
ceramic glazes, notably in the colors red and yellow.
*Lead is used as
projectiles for
firearms and fishing
sinkers because of its density, low cost compared to alternative products and ease of use due to relatively low melting point. For health concerns see [
1]
*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. [
2]
*Lead is used as shielding from
radiation.
*Molten lead is used as a
coolant, eg. for
lead cooled fast reactors.
*
Lead glass is composed of 12-28% lead. It changes the optical characteristics of the glass and reduces the transmission of radiation.
*Lead is the traditional base metal of
organ pipes, mixed with varying amounts of
tin to control the tone of the pipe.
*Lead is used as
electrodes in the process of
electrolysis.
*Lead is used in
solder for electronics.
*Lead is used in high voltage power cables as sheathing material to prevent water diffusion into insulation.
*Lead is used for the
ballast keel of sailboats. Its high weight-to-volume ratio allows it to counterbalance the heeling effect of wind on the sails while at the same time occupying a small volume and thus offering the least underwater resistance.
*Lead is added to
brass to reduce
machine tool wear.
*Lead sheets are used as roofing material.
Former applications
* Lead was used as a pigment in
lead paint for white as well as yellow and red colors. It was discontinued because of the dangers of lead poisoning.
* Lead was used for
plumbing in
Ancient Rome and water mains and service pipes up until the early 1970's.
*
Tetraethyl lead was used in
leaded fuels to reduce
engine knocking; however, this is no longer common practice in the
Western world due to health concerns [
3].
* Lead was used to make bullets for
slings.
* Lead was formerly used as a component of toys, though due to many toy safety regulations, this has been stopped.
Lead has been used by humans for at least 7000 years, because it is widespread, easy to extract and easy to work with. It is highly malleable and ductile as well as easy to smelt. In the early
bronze age lead was used with
antimony and
arsenic. Lead was mentioned in the
Book of Exodus.
Alchemists think 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.
However, it is also toxic, and
lead poisoning was recognised even by the ancients. Similarly, in the Twentieth Century, the use of lead in paint pigments was ended because of the danger of lead poisoning, especially to children [
4] [
5] [
6]. 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.
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 (PbCO
3) and
anglesite (PbSO
4). But more than half of the lead used currently comes from recycling.
In mining, the ore is extracted by drilling or blasting and then is crushed and ground. The ore is then treated using
extractive metallurgy. The
Froth flotation process 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
sintered before 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 mineralsMain article:
Isotopes of leadLead has four stable, naturally occurring
isotopes:
204Pb (1.4%),
206Pb (24.1%),
207Pb (22.1%), and
208Pb (52.4%).
206Pb,
207Pb and
208Pb are all
radiogenic, and are the end products of complex
decay chains that begin at
238U,
235U and
232Th, respectively. The corresponding
half-lives of these decay schemes vary markedly: 4.47
× 10
9, 7.04 × 10
8 and 1.4 × 10
10 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
206Pb/
204Pb, 15.0 - 17.0 for
207Pb/
204Pb, and 35.0 - 50.0 for
208Pb/
204Pb, although numerous examples outside these ranges are reported in the literature.
Because lead is radiogenic and formed from the decay of most of the heavier elements that formed billions of years ago, it is much more common and much cheaper than most heavy elements. The cost has been further lowered in recent years with the phasing out of lead in many processes, including gasoline and paint.
* see
isotope geochemistryLead 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 PbO
2) can cause
nephropathy, and
colic-like abdominal pains. The historical use of
lead acetate (also known as
sugar of lead) by the
Roman Empire as a sweetener for wine is considered by some to be the cause of the
dementia which 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 scandal involving lead-laced Mexican candy being eaten by children in California.
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 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
pencils actually used lead, though '
pencil leads' have been made for the last couple of centuries from
graphite, a naturally occurring form (
allotrope) of
carbon.
Lead as a
soil contaminant is a widespread issue, since lead may enter soil through (leaded) gasoline leaks from
underground storage tanks or through a wastestream of lead paint or lead grindings from certain industrial operations.
*
Lead compounds*
Derbyshire lead mining history*
Plumbosolvency* 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 Through 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.
*
A Small Dose of Toxicology:Lead *
Los Alamos National Laboratory - Lead*
NIST's X-Ray Mass Attenuation Coefficients - Lead*http://www.ocregister.com/investigations/2004/lead/part1_printable.html - Scandal involving lead-laced Mexican candy being eaten by children in California]
*
Case Studies in Environmental Medicine - Lead Toxicity*
ToxFAQs™: Lead*
National Pollutant Inventory - Lead and compounds fact sheet*
WebElements.com - Lead*
The Lead Education and Abatement Design Group (Australia)*
International Lead & Zinc Study Group*
International Lead Management Center*
Lead Development Association International*
Do lead fishing sinkers threaten the environment? (from
The Straight Dope)
