Lead

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

Uses

Primary

Secondary

  • Feedstock for pewters
  • 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).[1]
  • It can be expressed by the equation: D=10·678 − 13·174×10-4(T − 600·6°) where T is in °K.[1]

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.

Testing

Storage

Disposal

See Also

References

  1. 1.0 1.1  (1961) "The density of liquid lead from the melting"
    Journal of Inorganic and Nuclear Chemistry 33(1-2); pp33-38. 
    DOI:10.1016/0022-1902(61)80226-1
    link courtesy ResearchGate.