About Gypsum in Cement
The cement manufacturing industry is the major consumer of gypsum, which is added to the clinker in a percentage of 3–5 wt% , , . As it is well known, the workability property of cement solutions depends on reaction rate of C3A with water and to justify this, retarder raw materials are used. In cement industry, natural gypsum (CaSO4·2H2O) is the most effective raw material for this purpose.
Gypsum helps soil better absorb water and reduces erosion. It also cuts down on phosphorus movement from soils to lakes and streams and improves the quality of various fruits and vegetables, among other benefits. The chemical formula of Gypsum is CaSO4. 2H2O. It contains two moles of water in it. It can also be said as Calcium Sulphate dihydrate.
Dissolving gypsum in water or soil results in the following reaction: CaSO4·2H2O = Ca2+ + SO42- + 2H2O. It adds calcium ions (Ca2+) and sulfate ions (SO42-), but does not add or take away hydrogen ions (H+). Therefore, it does not act as a liming or acidifying material. The hydroxamic acid and the named salts thereof have the ability to dissolve gypsum, and also the ability to convert gypsum not actually dissolved into a water dispersible sludge.