Calcium sulfate

 

Calcium sulfate

Chemical formula	{{#Chem: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	0 1 0

Uses

Primary

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

Secondary

• Carbon sequestration and source of sulfate by converstion to calcium carbonate

Natural occurrence

• -dihydrate occurs naturally as gypsum

Production

WARNING Like barium sulfate, this is a "terminal chemical". Producing this compound at scale for any purpose might be a bad idea. Every mol of sulfate ions trapped in this compound is one mol of sulfuric acid lost.

Extraction

from gypsum

• Heat gypsum to over 180°C producing anhydrite

Synthesis

as a byproduct

• During the production of phosphoric acid:

  {{#Chem: Ca3(PO4)2 + 3 H2SO4 = 2 H3PO4 + 3 CaSO4 }}

from chalk

• Combine sulfuric acid and calcium carbonate

  {{#Chem: CaCO3 + H2SO4 = CaSO4 + H2O + CO2 }}

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:

{{#Chem: CaSO4(s) + 2NaOH(aq) { = ≤ 18°C strong mixing } Ca(OH)2(aq) + Na2SO4}}

{{#Chem: CaSO4(s) + Na2CO3(aq) { = cold, strong mixing } CaCO3(aq) + Na2SO4 // may also work with bicarbonate, producing bisulfate}}

See Also

• Gypsum