Calcium sulfate

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Calcium sulfate
Chemical formula CaSO4
OTP appearance white solid 
Molar Mass(g/mol) 136.14 
Density(g/cc) 2.96 
Melting Point(°C) 1460 
Solubility in water(g/L) 2.1
NFPA 704
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Uses

Primary

  • The γ-anhydrite form (1-5 molar percent water) is the primary component of gypsum plaster

Secondary

Natural occurrence

  • -dihydrate occurs naturally as gypsum

Hazards

Production

Extraction

from gypsum

  • Heat gypsum to over 180°C producing anhydrite

Synthesis

as a byproduct

  • During the production of phosphoric acid:
    Ca3(PO4)2 + 3 H2SO4 2 H3PO4 + 3 CaSO4

from chalk

Testing

Storage

Disposal

Calcium sulfate in any degree of hydration is a naturally occurring minearl and may be disposed of directly into the environment.

Calcium sulfate is not a terminal state for sulfate or calcium. Calcium sulfate may be converted to sodium sulfate and either calcium hydroxide or calcium carbonate by combining it with sodium salts while maintaining low temperatures, large amounts of water, and strong intermixing:

CaSO4(s) + 2 NaOH(aq)
{
≤ 18°C strong mixing}
Ca(OH)2(aq) + Na2SO4
[1]
CaSO4(s) + Na2CO3(aq)
{
cold, strong mixing}
CaCO3(aq) + Na2SO4 // may also work with bicarbonate, producing bisulfate

References

  1. US patent 3170815 "Removal of calcium sulfate deposits"
    Link courtesy Google

See Also