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what is gypsum and different types of gypsum

From : clirik    Date : 2019-01-11 13:14

         What is  Gypsum?

        Raw gypsum (Ca[SO4]•2H2O) has a Mohs hardness of 2 and a density of 2.3 g/cm3. Anhydrite is anhydrous calcium sulfate (Ca[SO4]), usually in the form of dense blocks or granules, white and off-white, with a Mohs hardness of 3 to 3.5 and a density of 2.8 to 3.0 g/cm3.
 
         Dihydrate gypsum: raw gypsum and desulfurized gypsum in natural gypsum.
 
         Natural gypsum:

        gypsum stone in nature, mainly dihydrate gypsum and anhydrite (anhydrous gypsum). The mineral layer of natural anhydrite is below the dihydrate gypsum.
Desulfurization gypsum: A technique in which limestone recovers sulfur dioxide from flue gas from coal or oil. The technique is to grind lime into a slurry, and the dust-removed SO2-containing flue gas is passed through a slurry scrubber to remove SO2. The lime slurry reacts with SO2 to form calcium sulfate and calcium sulfite, and the calcium sulfite is converted into calcium sulfate by oxidation to obtain industrial by-product gypsum, which is called desulfurization gypsum.
 
Β-type hemihydrate gypsum (CaSO4•0.5H2O), that is, building gypsum, also known as plaster, stucco, burned out in a rotary kiln, 107-170 degrees.
 
Alpha-type hemihydrate gypsum (CaSO4•0.5H2O) is usually made by steaming in a saturated steam medium, also known as high-strength gypsum.
 
Soluble anhydrite: CaSO4 easily re-absorbs the moisture in the air and returns to the hemihydrate gypsum.
 
Dead burnt gypsum: Also known as floor plaster, the temperature will reach 600 degrees or more and will not change back to semi-hydrated plaster. Its coagulation and hardening are slower, but the strength, wear resistance and water resistance after hardening are better than ordinary building gypsum, and it can be used as a cement retarder.

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