Cement kiln have temperature 1450°C → 70° to 110°C: Free water is evaporate → 400 to 600°C: Clay like mineral are decomposed into their constituent oxides principally SiO2and Al2O3 . Dolomite (CaHg(CO3)2) decomposes to calcium carbonats CaCO3 , HgO and CO2 , → 650°C to 900°C: CaCO3 reacts with SiO2 to form belite (Ca2SiO4 ) (also known as C2S) → 900°C to 1050°C: Remaining CaCO3 decomposes to CaO and CO2 →1300°C to 1450°C: Partial (20 - 30%) melting takes place, and belite reacts with CaO to form Alite (Ca3O.SiO4 ) (C3S)