Lead Compounds

Julie M. Schoenung

Abstract Lead compounds include over forty naturally occurring minerals from which five lead oxides can be derived. The lead oxides, as well as some lead silicates, are used as raw materials in lead-containing glasses and crystalline electronic ceramics. The presence of lead in glass increases the refractive index, decreases the viscosity, increases the electrical resistivity, and increases the X-ray absorption capability of the glass. The lead in electronic ceramics increases the Curie temperature and modifies various electrical and optical properties. The refinement of metallic lead from minerals and recycled goods such as lead acid batteries and cathode ray tubes is a multistep process, supplemented by oxidation steps to produce lead oxides. Lead compounds are known to be toxic and are therefore highly regulated.

1 Introduction

Lead and lead compounds have been used in a multitude of products for centuries. Lead (metal) is occasionally used as a “pure” material, but this is relatively rare when compared with the extent of its use in alloys and in ceramic compounds and glasses.

Lead is the 82nd element in the periodic table. It is present in the IVA column below carbon, silicon, germanium, and tin, and in the sixth row between thallium and bismuth. It is metallic in its pure state and crystallizes into the face-centered – cubic crystal structure. Lead has a low bond energy, as is evidenced by its low melting point (327°C). Lead and its alloys exhibit low elastic moduli, yield strength, and tensile strength when compared with other metals, glasses, and technical ceramics (see Table 1). The fracture toughness is also low when compared with other metals. The lead atom is large (atomic radius = 0.175 nm) and exhibits two possible oxidation states: +2 and +4. Lead is one of the commonly used heaviest metals with an atomic weight of 207.2 amu and a density of bulk material 11.35 g cm-3 at 20°C. These fundamental, chemical, and physical attributes define the foundation for the reason why lead is used in most of its applications. The most common and important applications of lead and lead compounds in ceramics and glasses are described in Sect. 2.

J. F. Shackelford and R. H. Doremus (eds.), Ceramic and Glass Materials: Structure, Properties and Processing.

© Springer 2008

Table 1 Selected mechanical properties of various materials [1]

Material

Elastic modulus (GPa)

Yield strength (MPa)

Tensile strength (MPa)

Fracture toughness (MPa m1’2)

Lead alloys

12.5-15.0

8-14

12-20

5-15

Aluminum alloys

68-82

30-500

58-550

22-35

Copper alloys

112-148

30-500

100-550

30-90

Iron alloys

165-217

170-1,155

345-2,240

12-280

Glasses

61-110

264-2,129a

22-177

0.5-1.7

Technical ceramics

140-720

524-6,833a

160-800

0.8-6.0

Leather

0.1-0.5

5-10

20-26

3-5

Polyethylene

0.6-0.9

18-29

21-45

1.4-1.7

Polypropylene

0.9-1.6

21-37

28-41

3.0-4.5

Polyvinylchloride

2.1-4.1

35-52

41-65

1.5-5.1

a Yield strength for glasses and ceramics is measured in compression; all other materials are measured in tension

Lead is found in a wide variety of naturally occurring minerals (see Table 2). These minerals range from rather simple substances, such as pure lead, PbTe, PbSe, and PbS, to complex hydroxides, such as Pb2Cu(AsO4)(SO4)OH and Pb26Cu24Ag10Cl62(OH)48 3H2O. As shown in Table 3, these minerals represent a wide range of crystal systems, of which the most common are monoclinic, orthorhombic, and tetragonal. Low hard­ness values (typically between 2 and 3 Mohs with extreme values of 1.5 for pure lead and 5.5 for plattnerite) and high theoretical densities (typically greater than 5 and as high as 11.3 g cm-3) are characteristic of these lead-containing minerals.

As described in Sect. 3, these minerals can be refined to produce metallic lead, or they can be processed to produce lead oxides. Because of lead’s two oxidation states, four lead oxide compositions are possible: PbO, PbO2, Pb2O3, and Pb3O4. The PbO composition can form into two different crystal structures: orthorhombic (called massicot) and tetragonal (called litharge). Thus, five possible lead-containing oxides are available for glass and ceramic fabrication. The JCPDS cards that describe the crystallographic characteristics for these oxides are as follows: 05-0561 for litharge (PbO), 38-1477 for massicot (PbO), 41-1492 for platnerite (PbO2), and 41-1494 for minium (Pb3O4). Litharge is the most commonly used oxide for glass and ceramic fabrication. Alternatively, lead silicates can also be used. These include (2PbO-SiO2), (PbO-SiO2), and (4PbO-SiO2). Selected physical, thermal, and mechanical properties of the lead oxides are listed in Table 4. It can be seen that for all of these oxides, the lead content is very high (85-93 wt%), the density is high (8.9-10.1 gcm-3), and the hardness values are low (2-2.5 Mohs). The melting point values show more variability, ranging from 290 to 888°C. Thermodynamic data for the lead oxides, lead silicates, and selected lead-containing minerals are presented in Table 5.

Many lead-containing products, including leaded glass, can be recycled and provide another source of material to supplement the naturally occurring minerals. The processing required to produce metallic lead and lead oxides are outlined in Sect. 3. Descriptions of the most important sources of lead and statistics on lead production and consumption are also presented.

The use of lead and lead compounds, although ubiquitous at present, is expected to decrease in the future because of health concerns. It is commonly known that lead is toxic to humans, especially children. As a consequence, legislative bodies have

Table 2 Various lead-containing minerals [2]

Mineral

Chemical name

Chemical formula

Altaite

Lead telluride

PbTe

Anglesite

Lead sulfate

PbSO4

Arsentsumebite

Lead copper arsenate sulfate hydroxide

Pb2Cu(AsO4)(SO4)OH

Baumhauerite

Lead arsenic sulfide

Pb3As4S9

Bayldonite

Hydrated copper lead arsenate hydroxide

Cu3Pb(AsO4)2 • H2O

Beudantite

Lead iron arsenate sulfate hydrox­ide

PbFe3AsO4SO4(OH)6

Bideauxite

Lead silver chloride fluoride hydroxide

Pb2AgCl3(F, OH)2

Bindheimite

Lead antimony oxide hydroxide

Pb2Sb2 6(O, OH)

Boleite

Hydrated lead copper silver chlo­ride hydroxide

Pb26Cu24Ag10Cl62(OH)48 • 3H2O

Boulangerite

Lead antimony sulfide

Pb5Sb4S11

Caledonite

Copper lead carbonate sulfate hydroxide

Cu2Pb5CO3(SO4)3(OH)6

Cerussite

Lead carbonate

PbCO3

Clausthalite

Lead selenide

PbSe

Crocoite

Lead chromate

PbCrO4

Cumengite

Lead copper chloride hydroxide

Pb21Cu20Cl42(OH)40

Diaboleite

Copper lead chloride hydroxide

CuPb2Cl2(OH)4

Dundasite

Hydrated lead aluminum carbonate hydroxide

Pb2Al4(CO3)4(OH)8 • 3H2O

Fiedlerite

Lead chloride fluoride hydroxide

Pb3Cl4F(OH)2

Galena

Lead sulfide

PbS

Gratonite

Lead arsenic sulfide

Pb9As4S15

Hedyphane

Lead calcium arsenate chloride

Pb3Ca2(AsO4)3Cl

Jordanite

Lead arsenic antimony sulfide

Laurionite

Lead chloride hydroxide

PbClOH

Leadhillite

Lead sulfate carbonate hydroxide

Pb4SO4(CO3)2(OH)2

Massicot

Lead oxide

PbO

Meneghinite

Lead antimony sulfide

Pb13Sb7S23

Mimetite

Lead chloroarsenate

Pb5(AsO4)3Cl

Minium

Lead oxide

Pb3O4

Native lead

Elemental lead

Pb

Nealite

Lead iron arsenate chloride

Pb4Fe(AsO4)2Cl4

Phosgenite

Lead carbonate chloride

Pb2CO3Cl2

Plattnerite

Lead oxide

PbO2

Pseudoboleite

Hydrated lead copper chloride hydroxide

Pb5Cu4Cl10(OH)8 • 2H2O

Pyromorphite

Lead chlorophosphate

Pb5(PO4)3Cl

Semseyite

Lead antimony sulfide

Pb9Sb8S21

Susannite

Lead sulfate carbonate hydroxide

Pb4SO4(CO3)2(OH)2

Vanadinite

Lead chlorovanadinate

Pb5(VO4)3Cl

Wulfenite

Lead molybdenate

PbMoO4

targeted the use of lead in numerous products, mandating labeling, recycling, and/or complete termination of use. The known health risks and existing legislative initiatives dealing with lead and lead compounds are summarized in Sect. 4.

Table 3 Crystal structure, hardness, and density for various lead-containing minerals [2]

Mineral

Crystal system

Hardness (Mohs)

Density (g cm 3)

Altaite

Isometric

2.5-3

8.2-8.3

Anglesite

Orthorhombic

2.5-3.0

6.3+

Arsentsumebite

Monoclinic

3

6.4

Baumhauerite

Triclinic

3

5.3

Bayldonite

Monoclinic

4.5

5.5

Beudantite

Rhombohedrons,

pseudocubic

4

4.3-4.5

Bideauxite

Isometric

3

6.3

Bindheimite

Isometric

4-4.5

7.3-7.5

Boleite

Tetragonal

3-3.5

5+

Boulangerite

Monoclinic

2.5

5.8-6.2

Caledonite

Orthorhombic

2.5-3

5.6-5.8

Cerussite

Orthorhombic

3.0-3.5

6.5+

Clausthalite

Isometric

2.5

8.1-8.3

Crocoite

Monoclinic

2.5-3

6.0+

Cumengite

Tetragonal

2.5

4.6

Diaboleite

Tetragonal

2.5

5.4-5.5

Dundasite

Orthorhombic

2

3.5

Fiedlerite

Monoclinic

3.5

5.88

Galena

Cubic and octahedron

2.5+

7.5+

Gratonite

Trigonal

2.5

6.2

Hedyphane

Hexagonal

4.5

5.8-5.9

Jordanite

Monoclinic

3

5.5-6.4

Laurionite

Orthorhombic

3-3.5

6.1-6.2+

Leadhillite

Monoclinic

2.5-3

6.3-6.6

Massicot

Orthorhombic

2

9.6-9.7

Meneghinite

Orthorhombic

2.5

6.3-6.4

Mimetite

Hexagonal

3.5-4

7.1+

Minium

Tetragonal

2.5-3

8.9-9.2

Native lead

Isometric

1.5

11.3+

Nealite

Trigonal

4

5.88

Phosgenite

Tetragonal

2.0-3.0

6.0+

Plattnerite

Tetragonal

5-5.5

6.4+

Pseudoboleite

Tetragonal

2.5

4.9-5.0

Pyromorphite

Hexagonal

3.5-4

7.0+

Semseyite

Monoclinic

2.5

5.8-6.1

Susannite

Trigonal

2.5-3

6.5

Vanadinite

Hexagonal

3

6.6+

Wulfenite

Tetragonal

3

6.8

Table 4 Selected physical, thermal, and mechanical properties of

various lead oxides

Oxide

Formula weight (g mol-1)

Lead content (wt%)

Crystal system

Density (g cm-3)

Melting point (°C)

Hardness

(Mohs)

PbO (massicot)

223.2

92.8

Orthorhombic

9.64

489

2

PbO (litharge)

223.2

92.8

Tetragonal

9.35

888

2

PbO2

239.2

86.6

Tetragonal

9.64

290

5.5

Pb2O3

462.4

89.6

Monoclinic

10.05

530a

Pb3O4

685.6

90.1

Tetragonal

8.92

830

2.5

a Decomposition temperature

Table 5 Thermodynamic properties of various lead-containing minerals, lead silicates, and lead oxides [3]

Chemical formula

Afl° (kJ mol-1)

AfG° (kJ mol-1)

So (J (mol K)-1)

Cp (J (mol K)-1)

PbTe

-70.7

-69.5

110.0

50.5

PbS

-100.4

-98.7

91.2

49.5

PbSe

-102.9

-101.7

102.5

50.2

PbCO3

-699.1

-625.5

131.0

87.4

PbSO4

-920.0

-813.0

148.5

103.2

PbCrO4

-930.9

PbMoO4

-1,051.9

-951.4

166.1

119.7

PbSiO3

-1,145.7

-1,062.1

109.6

90.0

Pb2SiO4

-1,363.1

-1,252.6

186.6

137.2

PbO (Massicot)

-217.3

-187.9

68.7

45.8

PbO (Litharge)

-219.0

-188.9

66.5

45.8

PbO2

-277.4

-217.3

68.6

64.6

Pb3O4

-718.4

-601.2

211.3

146.9

AfHo standard molar enthalpy (heat) of formation at 298.15 K in kJ mol-1; AfG° standard molar Gibbs free energy of formation at 298.15 K in kJ mol-1; So standard molar entropy at 298.15 K in J (mol K)-1; Cp molar heat capacity at constant pressure at 298.15 K in J (mol K)-1