The manufacture of cement is a two-phase process.
Clinker is first produced in a kiln system from calcareous (limestone, chalk or marl) and argillaceous (clay or shale) materials, with addition, in some cases, of small amounts of corrective materials (sand, waste bauxite, iron ore). Various fossil fuels and waste fuels are used in this process to reach the reaction temperature of 1450 °C.
Secondly, the clinker is ground with calcium sulphates and with industrial processes wastes such as blast furnace slag, limestone, natural pozzolana and industrial pozzolanic materials, e.g. fly ash, silica fume and burnt shale. 90-150 kWh/t cement are used in the process
(1) Limestone: Contains predominantly calcium carbonate (CaCO3) and to use in cement manufacture, it should have 42-43% lime (CaO) minimum. In cement manufacture it is prime raw material and its usage would be 90-93%.
(2) Clay: It contains more of silica (SiO2) and its usage should be 2 to 3% in cement manufacture.
(3) Bauxite: It contains alumina(Al2O3) and it's usage should be 2 to 3% in cement manufacture.
(4) Iron Ore: It contains mainly iron oxide (Fe2O3) and it's usage should be 1 to 2% in cement manufacture