Lead is an acute and a chronic toxicant. Acute effects are ataxia, headache, vomiting, stupor, hallucination, tremors and convulsions. Chronic symptoms from occupational exposure include weight loss, anemia, kidney damage and memory loss. (Patnaik, P. 1999. A Comprehensive Guide to the Hazardous Properties of Chemical Substances, 2nd ed. New York: John Wiley & Sons.) Permanent brain damage has been noted among children. Lead bioaccumulates in bones and teeth. The metal is classified as an environmental priority pollutant by the US EPA.
The action level for lead in drinking water is 15μg/L. Its content in food and house paints is regulated in the USA by the Food and Drug Administration.
Lead is produced commercially from its principal ore, galena (PbS). The ore is associated with sulfides of several metals including iron, copper, zinc, silver, bismuth, arsenic, antimony and tin. The ore is crushed and ground. It then is selectively separated from gangue and other valuable minerals by one or more processes that include gravity separation and flotation. Selective flotation processes are most commonly employed to remove significant quantities of most metal sulfides, silica, and other impurities. This yields relatively pure galena concentrate containing 50 to 80% lead.
In the presence of carbon, the combination of chlorine trifluoride with aluminum, copper, Lead, magnesium, silver, tin, or zinc results in a violent reaction [Mellor 2, Supp. 1: 1956]. A solution of sodium azide in copper pipe with Lead joints formed copper and Lead azide, both are detonating compounds [Klotz 1973]. Sodium acetylide becomes pyrophoric when mixed with metals like Lead. Mixtures of trioxane with 60% hydrogen peroxide in contact with metallic Lead when heated detonated. Lead containing rubber ignited in a nitric acid atmosphere. Lead is incompatible with strong oxidants such as: ammonium nitrate, chlorine trifluoride, hydrogen peroxide, etc.
History, Occurrence, and Uses
Lead is one of the oldest metals known to civilization. The uses of some of its alloys and salts have been documented early in history. The element derived its symbol Pb from the Latin word plumbium. The metal is rarely found in nature in its native form; however, it is found in several minerals, such as galena (PbS), anglesite (PbSO4), minium (Pb3O4) and cerussite (PbCO3). Its concentration in the earth’s crust is 12.5 mg/kg and in sea water 0.03mg/L.
Lead has numerous applications as metal, alloys and compounds. The major applications of the metal and its alloys such as solder are as materials of construction for pipe lines, plumbing fixtures, wires, ammunition, containers for corrosive acids and shield against short-wavelength radiation. Another major application is in storage batteries in which both the metal and its dioxide are used. Several lead compounds, such as lead chromate (chrome yellow), lead sulfate (white lead), lead tetroxide (red lead), and the basic carbonate are used in paints.
The metal is not attacked by hot water. But in the presence of free oxygen, lead(II) hydroxide is formed. The overall reaction is:
2Pb + 2H2O + O2 → 2Pb(OH)2
In hard water, however, the presence of small amounts of carbonate, sulfate, or silicate ions form a protective film on the metal surface, and prevent the occurrence of the above reaction and thus, corrosion of the metal.
Lead does not evolve hydrogen readily with acids. Nitric acid attacks the metal readily, forming lead nitrate and oxides of nitrogen:
3Pb + 8HNO3 → 3Pb(NO3)2 + 2NO + 4H2O
This reaction is faster in dilute nitric acid than strong acid. Hydrochloric acid has little effect on the metal. At ordinary temperatures, lead dissolves slowly in hydrochloric acid, forming a coating of lead(II) chloride, PbCl2 over the metal, which prevents further attack.
At ordinary temperatures, lead is not readily attacked by sulfuric acid. A coating of insoluble lead sulfate formed on the metal surface prevents any further reaction of the metal with the acid. The acid is, therefore, stored in specially designed lead containers. Also, the action of hot concentrated sulfuric acid is very low up to about 200°C. However, at temperatures near 260°C, both the concentrated sulfuric and hydrochloric acids dissolve lead completely. At ordinary temperatures, hydrofluoric acid also has little action on the metal. Formation of insoluble PbF2 prevents dissolution of lead in the acid.
Organic acids in the presence of oxygen react slowly with lead, forming their soluble salts. Thus, acetic acid in the presence of oxygen forms lead(II) acetate:
2Pb + 4CH3COOH + O2 → 2Pb(CH3COO)2 + 2H2O
Lead dissolves in alkalies forming plumbite ion, Pb(OH)42¯ with the evolution of hydrogen:
Pb + 2OH¯ + 2H2O → Pb(OH)42¯ + H2
Lead combines with fluorine, chlorine, and bromine, forming bivalent lead halides:
Pb + Cl2 → PbCl2
Fusion with sulfur at elevated temperatures yields lead sulfide, PbS.
The metal is oxidized to PbO when heated with sodium nitrate at elevated temperatures.
Pb + NaNO3 → PbO + NaNO2
Lead is widely used in storage batteries. Each cell consists of a spongy lead plate as cathode and lead dioxide as anode immersed in the electrolyte sulfuric acid. The overall chemical reaction in the cell during discharge is as follows: PbO2 + Pb + 2H2SO4 → 2PbSO4 + 2H2O
Soft silver-bluish white to gray metal.
Air & Water Reactions
Insoluble in water.
Lead in Body
The main body compartments that store lead are the blood, soft tissues, and bone; the half-life of lead in these tissues is measured in weeks for blood, months for soft tissues, and years for bone. Lead in the bones, teeth, hair, and nails is bound tightly and not available to other tissues and is generally thought not to be harmful. In adults, 94% of absorbed lead is deposited in the bones and teeth, but children only store 70% in this manner, a fact which may partially account for the more serious health effects on children. The estimated half-life of lead in bone is 20 30 years, and bone can introduce lead into the bloodstream long after the initial exposure is gone. The half-life of lead in the blood in men is about 40 days, but it may be longer in children and pregnant women, whose bones are undergoing remodelling, which allows the lead to be continuously reintroduced into the bloodstream. Also, if lead exposure takes place over years, clearance is much slower, partly due to the rerelease of lead from bone. Many other tissues store lead, but those with the highest concentrations (other than blood, bone, and teeth) are the brain, spleen, kidneys, liver, and lungs. It is removed from the body very slowly, mainly through urine. Smaller amounts of lead are also eliminated through the faeces and very small amounts in hair, nails, and sweat.
Flash point data for Lead are not available, however, Lead is probably non-combustible.
Construction material for tank linings, piping, and other equipment handling corrosive gases and liqs used in the manufacture of sulfuric acid, petroleum refining, halogenation, sulfonation, extraction, condensation; for x-ray and atomic radiation protection; manufacture of tetraethyllead, pigments for paints, and other organic and inorganic lead Compounds; bearing metal and alloys; storage batteries; in ceramics, plastics, and electronic devices; in building construction; in solder and other lead alloys; in the metallurgy of steel and other metals.
Silvery grey metal with bright luster; face-centered cubic crystals; very soft, malleable and ductile; easily cast, rolled and extruded; density 11.3 g/cm3; Moh’s hardness 1, Brinell hardness 4.0 (high purity metal); easily melted, melts at 327.46°C; vaporizes at 1,749°C; vapor pressure 1 torr at 970°C and 10 torr at 1160°C; poor conductor of electricity; electrical resistivity 20.65 microhm–cm at 20°C and of liquid melt 94.6 microhm–cm at its melting point; viscosity of molten metal 3.2 centipoise at its melting point and 2.32 centipoise at 400°C; surface tension 442 dynes/cm at 350°C; tensile strength 2,000 psi; thermal neutron absorption cross section 0.17 barn; standard electrode potential, Pb2+ + 2e– Pb –0.13V; very resistant to corrosion.
grey metal granules, shot, foil, sheet or powder