Calcium sulfate

Raw materials

1. Gypsum

2. Anhydrite

Process

The main sources of calcium sulfate are naturally occurring gypsum and anhydrite which occur at many locations worldwide as evaporites. These may be extracted by open-cast quarrying or by deep mining.

In addition to natural sources, calcium sulfate is produced as a by-product in a number of processes:

• In flue gas desulfurization, exhaust gases from fossil-fuel burning power stations and other processes (e.g. cement manufacture) are scrubbed to reduce their sulfur oxide content, by injecting finely ground limestione or lime. This produces an impure calcium sulfite, which oxidizes on storage to calcium sulfate.
• In the production of phosphoric acid from phosphate rock, calcium phosphate is treated with sulfuric acid and calcium sulfate precipitates.
• In the production of hydrogen fluoride, calcium fluoride is treated with sulfuric acid, precipitating calcium sulfate.
• In the refining of zinc, solutions of zinc sulfate are treated with lime to co-precipitate heavy metals such as barium.
• Calcium sulfate can also be recovered and re-used from scrap drywall at construction sites.

Product
Calcium sulphate, also known as Plaster of Paris

Used as
Coagulant (in products like tofu)

Production facility
Kalannie, WA

Export
Praia, Cape Verde