User Contributed Dictionary
References
- Charlton T. Lewis (1891) An Elementary Latin Dictionary, 1st edition. (Oxford University Press)
Extensive Definition
Lead () is a transitional element with a symbol Pb
(lang-la plumbum). Lead
has the atomic
number 82. Lead is a soft, malleable poor metal,
also considered to be one of the heavy
metals. Lead has a bluish white color when freshly cut, but
tarnishes to a dull grayish color when it is exposed to air and is
a shiny chrome silver when melted into a liquid. Lead is used in
building construction, lead-acid
batteries, bullets
and shot, weights,
and is part of solder,
pewter, and fusible
alloys. Lead has the
highest atomic
number of all stable
elements, although the next element, bismuth, has a half-life so long
(longer than the estimated age of the universe) it can be
considered stable. Like mercury,
another heavy metal, lead is a potent neurotoxin that accumulates
in soft tissues and bone over time.
Notable characteristics
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, and because of this property, it is used to contain corrosive liquids (e.g. sulfuric acid). Because lead is very malleable and resistant to corrosion it is extensively used in building construction e.g. external coverings of roofing joints. Lead can be toughened by adding a small amount of antimony or other metals to it. It is a common misconception that lead has a zero Thomson effect. All lead, except 204Pb, is the end product of a complex radioactive decay (see isotopes of lead below). Lead is also poisonous.History
Lead has been commonly used for thousands of 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 (15:10). The principal ores of lead are galena (PbS), anglesite () and cerussite (PbCO3). Most ores contain less than 10% lead, and ores containing as little as 3% lead can be economically exploited. Ores are crushed and concentrated by froth flotation typically to 70% or more. Sulfide ores are roasted, producing primarily lead oxide and a mixture of sulfates and silicates of lead and other metals contained in the ore.Lead oxide from the roasting process is reduced
in a coke-fired blast furnace. This converts most of the lead to
its metallic form. Three additional layers separate in the process
and float to the top of the metallic lead. These are slag (silicates containing 1.5%
lead), matte
(sulfides containing 15% lead), and speiss (arsenides of iron and
copper). These wastes contain concentrations of copper, zinc,
cadmium, and bismuth that can be recovered economically, as can
their content of unreduced lead.
Most lead ores contain significant concentrations
of silver, resulting in
the smelted metal also containing silver as a contaminant. Metallic
silver as well as gold is removed and recovered economically by
means of the Parkes
process.
- Annual Metal Production (2006): 7918 Thousand tonnes
- Annual Mine Production (2006): 3442 Thousand tonnes (lead content)
At current use rates, the supply of lead is
estimated to run out in 42 years. Environmental analyst, Lester
Brown, however, has suggested lead could run out within 18
years based on an extrapolation of 2% growth per year. This may
need to be reviewed to take account of renewed interest in recycling, and rapid progress
in fuel
cell technology.
Isotopes
Lead has seven isotopes in total (3 stable, 3 unstable 1 radiogenic). The 3 stable isotopes are 206Pb, 207Pb, & 208Pb, and the 3 unstable isotopes are 204Pb, 205Pb, & 210Pb, along with one common radiogenic isotope 202Pb with a half-life of ~53,000 years.Health effects
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. The concern about lead's role in cognitive deficits in children has brought about widespread reduction in its use (lead exposure has been linked to schizophrenia). Most cases of adult elevated blood lead levels are workplace-related. High blood levels are associated with delayed puberty in girls.Older houses may still contain substantial
amounts of lead paint.
White lead paint has been withdrawn from sale in industrialized
countries, but the yellow lead
chromate is still in use; for example, Holland
Colours Holcolan Yellow. Old paint should not be stripped by
sanding, as this produces 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. Lead acetate
(also known as sugar of lead) was used by the Roman Empire
as a sweetener for wine, and some consider this to be the cause of
the dementia that
affected many of the Roman Emperors.
Lead as a soil
contaminant is a widespread issue, since lead is present in
natural deposits and may also enter soil through (leaded) gasoline
leaks from underground
storage tanks or through a wastestream of lead paint or lead
grindings from certain industrial operations.