The main raw materials used in the cement manufacturing process are limestone, clay, sand, shale and iron ore. Limestone is usually mined on site while the other minor materials may be mined either on site or in nearby quarries. Another source of raw materials is industrial by-products. The use of by-product materials to replace natural raw materials is a key element in achieving sustainable development.
Cement Clinker's Wet Process:
In the wet process, each raw material is proportioned to meet a desired chemical composition and fed to a rotating ball mill with water. The raw materials are ground to a size where the majority of the materials are less than 75 microns. Materials exiting the mill are called "slurry" and have flowability characteristics. This slurry is pumped to blending tanks and homogenized to insure the chemical composition of the slurry is correct. Following the homogenization process, the slurry is stored in tanks until required.
Cement Clinker's Dry Process:
In the dry process, each raw material is proportioned to meet a desired chemical composition and fed to either a rotating ball mill or vertical roller mill. The raw materials are dried with waste process gases and ground to a size where the majority of the materials are less than 75 microns. The dry materials exiting either type of mill are called "kiln feed". The kiln feed is pneumatically blended to insure the chemical composition of the kiln feed is well homogenized and then stored in silos until required.