Industrial preparation
1. Calcium sulfate is obtained by removing impurities from natural gypsum ore and heating the soil to 300°C in an electric furnace to calcine and grind it.
2. Sodium sulfate is added in the by-product calcium chloride of ammonia-alkali method, by calcium chloride-sodium sulfate precipitation method, product is obtained through refining, reaction equation:
CaCl2+Na2SO4=CaSO4↓+NaCl.
3. By-products in the production of organic acids. For example, calcium oxalate obtained when producing oxalic acid is decomposed with sulfuric acid and purified. Reaction equation:
CaC2O4+2H2SO4=CaSO4+2CO2↑+2H2O+SO2↑
4. Using calcium sulfate dihydrate as raw material, the suspension formed by dissolving in water is continuously stirred in a closed reaction kettle, heated to a certain temperature, and after reaching a certain pressure, calcium sulfate whiskers are obtained. Or at a certain temperature, a high concentration of calcium sulfate dihydrate is transformed into needle-like or fibrous whiskers in an acidic solution.
Laboratory method
Calcium sulfate is usually prepared in the laboratory by soluble calcium salts and sulfates, such as:
Ca(H2PO4)2+Fe2SO4=CaSO4+ 2FePO4+2H2SO4.
