Background

Lead has been around since the times of Exodus. Alchemists believed that lead was the oldest metal and associated it with the planet Saturn.

Native lead does occur in nature however, it is rare. It is mainly obtained from galena (PbS) by a roasting process. Leads common minerals are anglesite (PbSO4), cerussite (PbCO3) and minim (Pb3O4).

Lead is a bluish-white metal of brighter lustre, it is very soft, highly malleable, ductile and a poor conductor of electricity. Lead has a face-centred cubic crystal structure, leading to its malleability, but does become hard and brittle on repeated melting because of the formation of oxides. Its surface oxidises easily however, and it is then very resistant to corrosion. Lead is soluble in nitric acid, but is not in sulphuric or hydrochloric, and is considered one of the most stable of metals.

Natural lead is a mix of four stable isotopes: 204Pb (1.48%), 206Pb (23.6%), 207Pb% (22.6%) and 208Pb (52.3%). Isotopes of lead are end products of each three series of naturally occurring radioactive elements. Those being 206Pb for the uranium series, 207Pb for the actinium series and 208Pb for the thorium series. Twenty-seven (27) other radioactive isotopes of lead are recognised.

Lead has a high capacity for the capture of neutrons and gamma rays and is often implemented as radiation shielding.

Lead is highly toxic and therefore poses a health hazard. Inhalation of dust and fumes should be avoided. It should not be used in contact with food, foodstuffs, or drinking products.
Applications

Lead as the metal is used in:

· Storage batteries.

· Solders and bearing metals.

· Cable coverings for telephone line and power lines to prevent mechanical injury.

· Plumbing as pipes, fittings, roofing, storage tanks, gutters, flashing.

· Collapsible piping.

· Ammunition.

· Automotive fuel tanks for the protection against corrosion (Terneplate).

· Machine bearings (Hoyt metal), railway car bearings (lining metal) and locomotive crosshead linings (Dandelion metal).

· Lead tetraethyl manufacturing.

· As a sound and vibration absorber.

· Radiation shielding, implemented around X-ray equipment and nuclear reactors – in the form of shielding cements, neoprene-lead fabric, ceramic mortars, paints (Chemtree 82) and other plastic composite structures.

· Toys, small castable articles.

· As an alloying element to improve specific mechanical properties such as tensile strength, elongation, hardness.

Lead compounds are used for:

· Pigments for paints e.g. 2PbCO3.Pb(OH)2 or white lead, PbCrO4 or yellow chrome, Pb3O4 or red lead, PbWO4 or lead tungstate (a yellow pigment).

· Lead meta-silicate (PbSiO3) a white crystal used for glazing ceramics and fireproofing textiles.

· Lead oxide is used in the production of fine crystal glass and flint glass, for achromatic lenses, it is also used as a filler in rubbers.

· Lead sulphide (PbS), may be used as a filler in missiles, due to its sensitivity to heat rays.

· Lead dioxide or lead peroxide (PbO2), a brown powder, is used in matches, dyes, and pyrotechnics, as a mordant and as an oxidising agent.