Characteristics Occurrence Applications Former Applications Processing Methods Descriptive Chemisty

Compounds Isotopes Precautions Trivia Lead Data Interactive Periodic Table

Alchemical Symbol for Lead

Characteristics

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 - although the next element, Bismuth, has a half life so long it can be considered stable.  Like Mercury, another heavy metal, Lead is a potent neurotoxin which accumulates in soft tissues and bone over time.

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.  All Lead, except ²⁰⁴Pb, is the end product of a complex radioactive decay.

Known to the ancients, lead takes its name from the Anglo-Saxon word for the metal and its symbol comes from the Latin (from which we get the modern word "plumber" since old plumbing was done with lead pipes).

Additional Representations of Alchemical Symbols of Lead

Although lead is not very common in the earth's crust, what is there is readily available and easy to refine. Its chief use today is in lead-acid storage batteries such as those used in automobiles. In pure form it is too soft to be used for much else. Lead has a blue-white color when first cut but quickly dulls on exposure to air, forming Pb₂O, one of the few lead (I) compounds.  Most stable lead compounds contain lead in oxidation states of +2 or +4.

Various isotopes of lead come at the end of the natural decay series of elements like uranium, thorium and actinium. These are Pb-206, Pb-207 and Pb-208

Occurrence

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).   The largest source of raw Lead, however, is recycling, primarily of automobile batteries.

In mining, the ore is extracted by drilling or blasting and then is crushed and ground.   The ore is then treated using extraction 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.

Applications

• 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.
• 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.
• 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 Oxide.  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, although this usage is being phased out to reduce the amount of environmentally unfriendly waste.
• 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.
• Lead is frequently used in scuba diving weight belts to counteract the natural buoyancy of neoprene wetsuits.

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.  However, Lead Chromate is still in use.
• Lead was used for plumbing in Ancient Rome. 
• Lead was used for joining cast iron water pipes and used as a material for small diameter water pipes until the early 1970s.
• 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.
• 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 was used in car body filler, which was used in many custom cars in the 1940s-60's.   Hence the term Leadsled.
• Lead is a superconductor at 7.2^oK and IBM tried to make a Josephson Computer out of lead-alloy.

Contrary to popular belief, pencil 'leads' have never been made from lead.  The term comes from the Roman stylus, called the penicillus, which was made of lead.   When the pencil originated as a wrapped graphite writing tool, the particular type of graphite being used was named plumbago (lit. acts like lead).

Processing Methods

The principle ores of lead are Galena (PbS), Anglesite (PbSO₄), 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.

Metallic Lead that results from the roasting and blast furnace processes still contains significant contaminants of Arsenic, Antimony, Bismuth, Zinc, Copper, Silver, and Gold.   The melt is treated in a reverberatory furnace with air, steam, and Sulfur, which oxidizes the contaminants except Silver, Gold, and Bismuth.  The oxidized contaminants are removed by drossing, where they float to the top and are skimmed off.

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.

Desilvered Lead is freed of Bismuth according to the Betterton-Kroll Process by treating it with metallic Calcium and Magnesium, which forms a Bismuth dross that can be skimmed off.

Very pure Lead can be obtained by processing smelted lead electolytically by means of the Betts Process.  The process uses anodes of impure Lead and cathodes of pure Lead in an electrolyte of Silica Fluoride.

Descriptive Chemistry

Various oxidized forms of lead are easily reduced to the metal. An example is heating PbO with mild organic reducing agents such as glucose. A mixture of the oxide and the sulfide heated together without any reducing agent will also form the metal.

2PbO + PbS     3 Pb + SO₂

Metallic lead is attacked only superficially by air, forming a thin layer of oxide that protects it from further oxidation.  The metal is not attacked by Sulfuric or Hydrochloric Acids.  It does, however, dissolve in Nitric Acid with the evolution of Nitric Oxide gas gas to form dissolved Pb(NO₃)₂.

3 Pb + 8 H⁺ + 8 NO₃^–     3 Pb²⁺ + 6 NO₃^– + 2 NO + 4H₂O

When heated with Nitrates of alkali metals, metallic lead oxidizes to form Litharge, PbO, leaving the corresponding Alkali Nitrate.  PbO is representative of lead's II oxidation state.  It is soluble in Nitric and Acetic Acids, from which solutions it is possible to precipitate Halide, Sulfate, Chromate, Carbonate (PbCO₃), and basic carbonate (Pb₃(OH)₂(CO₃)₂) salts of lead. The Sulfide can also be precipitated from Acetate solutions . These salts are all poorly soluble in water.  Among the Halides, the Iodide is less soluble than the Bromide, which, in turn, is less soluble than the Chloride.

The II oxide is also soluble in Alkali Hydroxide solutions to form the corresponding plumbite salt.

PbO + 2OH^– + H₂O     Pb(OH)₄^2–

Chlorination of plumbite solutions causes the formation of lead's IV oxidation state.

Pb(OH)₄^2– + Cl₂     PbO₂ + 2 Cl^– + 2 H₂O

Lead Dioxide is representative of the IV state, and is a powerful oxidizing agent.   The Chloride of this oxidation state is formed only with difficulty and decomposes readily into the II Chloride and Chlorine gas.  The Bromide and Iodide of IV Lead are not known to exist.  Lead Dioxide dissolves in Alkali Hydroxide solutions to form the corresponding plumbates.

PbO₂ + 2 OH^– + 2 H₂O     Pb(OH)₆^2–

Lead also has an oxide that is a hybrid between the II and IV oxidation states.  Red Lead (also called minium) is Pb₃O₄.

Lead readily forms an equimolar alloy with sodium metal that reacts with Alkyl Halides to form organometallic compounds of Lead such as Tetraethyl Lead.

Compounds

Isotopes

Lead 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 ²³¹Th, respectively.  The corresponding half-lives of these decay schemes vary markedly: 4.47 x 10⁹, 7.04 x 10⁸ and 1.4 x 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 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.

Precautions

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 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 2004 scandal involving Lead-laced Mexican candy being eaten by children in California.  Even in these cases however, it should be noted that the Lead is not an additive but merely a contaminant that enters incidentally via for instance, metal particles accumulated during grinding processes.

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 schizophrena).   Lead-white paint has been withdrawn from sale in industralised countries.  The yellow Lead Chromate is still in use; for example, Holland Colours Holcolan Yellow.  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.

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.

There has been an e-mail circulating about the lead content of various consumer products, such as shampoo and most notably lipstick, since 2003.  Though there are trace amounts of lead in some products, these levels are monitored by the FDA in the US and pose no real danger to health.

Trivia

A "Lead Pipe Cinch" is something that is absolutely certain.   In the 19th century a horse saddle that was safe when it was well "cinched".  The "lead pipe" qualifier is an obscure "intensifier".

(Anglo-Saxon lead; L. plumbum) Long known, mentioned in Exodus. the alchemists believed lead to be the oldest metal and associated with the planet Saturn. Native lead occurs in nature, but it is rare. Lead is obtained chiefly from galena (PbS) by a roasting process. Anglesite, cerussite, and minim are other common lead minerals. Lead is a bluish-white metal of bright luster, is very soft, highly malleable, ductile, and a poor conductor of electricity. It is very resistant to corrosion; lead pipes bearing the insignia of Roman emperors, used as drains from the baths, are still in service. It is used in containers for corrosive liquids (such as sulfuric acid) and may be toughened by the addition of a small percentage of antimony or other metals. Natural lead is a mixture of four stable isotopes: 204Pb (1.48%), 206Pb (23.6%), 207Pb (22.6%), and 208Pb (52.3%). Lead isotopes are the end products of each of the three series of naturally occurring radioactive elements: 206Pb for the uranium series, 207Pb for the actinium series, and 208Pb for the thorium series. Twenty seven other isotopes of lead, all of which are radioactive, are recognized. Its alloys include solder, type metal, and various antifriction metals. Great quantities of lead, both as the metal and as the dioxide, are used in storage batteries. Much metal also goes into calbe covering, plumbing, ammunition, and in the manufacture of lead tetraethyl. The metal is very effective as a sound absorber, is used as a radiation shield around X-ray equipment and nuclear reactors, and is used to absorb vibration. White lead, the basic carbonate, sublimed white lead, chrome yellow, and other lead compounds are used extensively in paints, although in recent years the use of lead in paints has been drastically curtailed to eliminate or reduce health hazards. Lead oxide is used in producing fine "crystal glass" and "flint glass" of a high index of refraction for achromatic lenses. The nitrate and the acetate are soluble salts. Lead salts such as lead arsenate have been used as insecticides, but their use in recent years has been practically eliminated in favor of less harmful organic compounds. Care must be used in handling lead as it is a cumulative poison. Environmental concerns with lead poisoning has resulted in a national program to eliminate the lead in gasoline.

Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond

Lead has been known since ancient times. It is sometimes found free in nature, but is usually obtained from the ores galena (PbS), anglesite (PbSO₄), cerussite (PbCO₃) and minum (Pb₃O₄). Although lead makes up only about 0.0013% of the earth's crust, it is not considered to be a rare element since it is easily mined and refined. Most lead is obtained by roasting galena in hot air, although nearly one third of the lead used in the United States is obtained through recycling efforts.

Lead is a soft, malleable and corrosion resistant material. The ancient Romans used lead to make water pipes, some of which are still in use today. Unfortunately for the ancient Romans, lead is a cumulative poison and the decline of the Roman empire has been blamed, in part, on lead in the water supply. Lead is used to line tanks that store corrosive liquids, such as sulfuric acid (H₂SO₄). Lead's high density makes it useful as a shield against X-ray and gamma-ray radiation and is used in X-ray machines and nuclear reactors. Lead is also used as a covering on some wires and cables to protect them from corrosion, as a material to absorb vibrations and sounds and in the manufacture of ammunition. Most of the lead used today is used in the production on lead-acid storage batteries, such as the batteries found in automobiles.

Several lead alloys are widely used. Solder, an alloy that is nearly half lead and half Tin, is a material with a relatively low melting point that is used to join electrical components, pipes and other metallic items. Type metal, an alloy of Lead, Tin and Antimony, is a material used to make the type used in printing presses and plates. Babbit metal, another lead alloy, is used to reduce friction in bearings.

Lead forms many useful compounds. Lead Monoxide (PbO), also known as litharge, is a yellow solid that is used to make some types of glass, such as lead crystal and flint glass, in the vulcanizing of rubber and as a paint pigment. Lead Dioxide (PbO₂) is a brown material that is used in lead-acid storage batteries.  Trilead Tetraoxide (Pb₃O₄), also known as red lead, is used to make a reddish-brown paint that prevents rust on outdoor steel structures.  Lead Arsenate (Pb₃(AsO₄)₂) has been used as an insecticide although other, less harmful, substances have now largely replaced it.  Lead Carbonate (PbCO₃), also known as cerussite, is a white, poisonous substance that was once widely used as a pigment for white paint.  Use of Lead Carbonate in paints has largely been stopped in favor of Titanium Oxide (TiO₂).   Lead Sulfate (PbSO₄), also known as anglesite, is used in a paint pigment known as sublimed white lead.  Lead Chromate (PbCrO₄), also known as crocoite, is used to produce chrome yellow paint.   Lead Nitrate (Pb(NO₃)₂) is used to make fireworks and other pyrotechnics.  Lead Silicate (PbSiO₃) is used to make some types of glass and in the production of rubber and paints.