Lead

 

Lead

Chemical formula	Pb
Atomic Number	82
OTP appearance	grey solid
Molar Mass(g/mol)	207.2
Density(g/cc)	11.3
Melting Point(°C)	327.46
Boiling Point(°C)	1749
Coefficient of Thermal Expansion(×10-6 °C-1)	29.3
NFPA 704	0 2 0

Lead is one of the seven metals of antiquity.

Uses

Primary

• Frequently used in chamber process chambers for the production of sulfuric acid
• Key component in lead-acid batteries
• Sealant

Secondary

• Component in solder
• Ballast

Natural Occurence

• Elemental lead does not occur naturally.
• -sulfide occurs as the mineral galena
• -carbonate occurs as the mineral cerussite

Hazards

While lead is not toxic itself, many of its compounds are, and lead is fairly reactive. Take special care when disposing of lead-bearing waste, and around lead fumes.

Character

Density as a liquid

• The density of liquid lead is 10·678 g/cm3 at its melting point (600·6°K), and 8·803 g/cm3 at its boiling point (2024°K).
• It can be expressed by the equation: D=10·678 − 13·174×10^-4(T − 600·6°) where T is in °K.

Production

Extraction

cf. smelting

From galena

with calcium oxide

Including 20% by weight of calcium oxide provides several thermodynamically favored paths to pure lead. It is important that this reaction be maintained between 750°C and 825°C. Lower and lead will not form, higher and lead will boil away.

1. Combine 4 ubw of galena with 1 ubm calcium oxide
2. Heat (in open air) to 800°C for an hour

   PbS + 3 O

   {

   →

   535°C}

   PbO + SO₂ΔH=-99

   PbO + SO₂ + O

   {

   →

   535°C}

   PbSO₄ΔH=-96

   CaO + SO₂ + O

   {

   →

   550°C}

   CaSO₄ΔH=-117

   PbS + PbSO₄

   {

   →

   735°C}

   2 Pb + 2 SO₂ΔH=+98 // lead forming, endothermic

   PbS + 2 PbO

   {

   →

   800°C}

   3 Pb + SO₂ΔH=+52.8 // lead forming, endothermic

3. The resulting mixture is ready for carbothermic reduction

From cerussite

1. Roast cerussite at approximately 315°C, releasing carbon dioxide

   PbCO₃

   {

   →

   315°C}

   PbO + CO₂

2. Reduce lead (II) oxide using charcoal (carbothermic reduction) usually over 805°C to facilitate carbon monoxide production. If you have room-temperature carbon monoxide, no heating is necessary.

   PbO + CO → Pb + CO₂

Purification

Lead ores usually have many metallic impurities. Each is removed by the addition and vigorous mixing of some other substance followed by skimming the slag off the molten lead. The slags can usually be processed to separate the various components.

• Silver and gold are removed by zinc via the Parkes process.
• Zinc, copper, arsenic, antimony, and cadmium are removed by sodium hydroxide.
• Bismuth is removed by adding a mixture of calcium and magnesium.

See Also

• Lead smelting and refining: with some notes on lead mining
  by Walter Renton Ingalls