Gypsum Stone

Gypsum Specifications
Chemical Analysis:
Pure Gypsum:
97%
Calcium:
23%
Sulphur:
18%
Si02:
2.5%
CaC03:
0.2%
Fe2O3:
0.1%
NaCl:
0.2%
Cadmium:
<1.25ppm
Mercury:
1.175ppm
Lead:
<2.5ppm
The silica (SiO2) and sodium chloride (NaCl), should not be more than 6% and 0.01% respectively, and it should be free from clayey meterial. As the gypsum directly enters into chemical reaction, the higher the percentage of CaSO4.2H2O content in gypsum the better is the plant performance and the greater is the production of ammonium sulphate. Ammonium sulphate is manufactured by reacting ammonium carbonate and powdered gypsum and the calcium carbonate sludge thus recovered as a by-product is utilized in the manufacture of cement. This is one of the greatest advantages in utilizing gypsum for fertilizer manufacture. Although gypsum of 75% to 85% purity is used in the manufacture of cement, yet a minimum of 82% CaSO4.2H2O is preferred. Nearly 0.04 to 0.05 tonne of gypsum is required per tonne of cement produced. It is mixed with the clinker in the end and then crushed to form cement. It acts as retarder in quick setting of cement. For the manufacture of Plaster of Paris, selenite crystals of purity varying from 97 to 80% are preferred. Three grades of Plaster of Paris are generally known and manufactured: Surgical Technical Commercial
For surgical grade the selenite should be of the highest purity. Other grades are used for making dolls and castings in pottery industry. Sometimes pure white lumpy gypsum of alabaster type is used for the Plaster of Paris manufacture. For the manufacture of distemper also pure white lumpy gypsum of high purity is required. Gypsum of 75% purity and below is used as manure or as sweet-lime.