24
Lead [Pb, 82]
24.1 INTRODUCTION
Lead (Pb), a metal of the group 14 in the periodic table of elements, occurs in the Earth’s
crust at the mean content of 15 mg/kg. It is concentrated in acidic magmatic rocks
(up to 25  mg/kg, in granites) and in argillaceous sediments (up to 40 mg/kg).
In sandstones and limestones, its contents do not exceed 10 mg/kg. Lead contents of
coal vary within the broad range from 10 to 1900 mg/kg, and may be concentrated
in fly ash up to about 50 mg/kg.
In the terrestrial environment, two kinds of Pb are present: primary and secondary. Primary Pb is of geogenic origin and is present in various minerals, whereas
secondary Pb is of radiogenic origin from the decay of U and Th. The ratio of Pb
isotopes, especially 210 Pb, with a half-life of 22.3 years, is used for dating the host
materials, and for the identification of its anthropogenic pollution sources.
Lead occurs mainly at +2 oxidation state, and sometimes +4. It has high chalcophilic properties, and thus its most common, primary mineral is galena, PbS. Other
common minerals are anglesite, PbSO 4 ; minium, Pb 3 O 4 ; pyromorphite, Pb 3 (PO 4 ) 3 Cl;
and minetesite, Pb 5 (AsO 4 ) 3 Cl. Goethite reveals a strong affinity for the Pb sorption,
which is controlled by organic acids (Perelomov et al. 2011).
World mine Pb production (rounded) in 2010 was 4100 kt, of which China produced
1750; Australia produced 620; the United States produced 400; Peru produced 280;
Bolivia produced 90; and Russia produced 90 (USGS 2011). The largest worldwide use
of Pb is for lead–acid batteries. It is also utilized for buildings constructions, in alloys
(pewters, Sn–Pb and fusibles), for solders, and anticorrosion paint (red lead, Pb 3 O 4 ).
Lead content in crude oil is low, at about 4 mg/kg. For many years (since the
beginning of the 1920s to the mid-1970s, in the United States), Pb was added to
petrol, at amounts around 650 mg/kg, as an antiknock element, in the form of tetraethyllead. It is still used as an additive in some gasoline for some aviation and
automotive racing. The major sources of Pb emissions have historically been from
fuels in motor vehicles (mainly cars and trucks), and industrial sources. Although
the use of tetraethyl and tetramethyl Pb has been forbidden in the most countries,
there are still some markets for these gasoline additives, especially in the aviation
gasoline.
Lead environmental pollution is presently of a great concern. Data from the
ice cores from Greenland indicate that the large-scale Pb pollution started about
2500 years ago, from the smelting and mining of Pb and Ag, during the Greek and
Roman eras. Lead concentrations in the ice cores decreased after the decline of the
Roman Empire, and did not surpass Roman levels, until the start of the Industrial
Revolution. In the twentieth century, Pb concentrations increase to 200 times its
levels, of the pre-Greek and Roman times. Since the passing of the Clean Air Act in
1970 (U.S. EPA), Pb concentrations have begun to fall. However, there are also data
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