Foundry Sand in Portland Cement Manufacturing

There are eight types of Portland cements, each with special use and chemical requirement. Their manufacturing process, however, is essentially the same. Portland cement is a product of a kiln operation. The kiln is where ground raw materials undergo chemical transformation. Raw materials used in Portland cement manufacturing must contain the appropriate proportion of calcium oxide, silica, alumina, and iron oxide. Most of these necessary ingredients are usually contained in shale, dolomite, and limestone. When deficiencies in these ingredients are encountered in the rock normally used in cement production, additional silica and alumina are added. Since sand is a good source of silica, alumina, and iron oxides, it is often used in the production of Portland cement. Specifications for suitable sands include a minimum silica content of 80% (Leidel et al. 1994). Foundry by-products can also be used as a source of minerals. For example, slag is a source of aluminum oxide and magnesia and foundry sand is a source of silica. Also, the clay fraction of foundry sand is a source of iron and aluminum oxides.

According to the Portland cement industry, foundry sand can be beneficially reused in the manufacturing of Portland cement when it possesses the following properties: (1) silica content 80%, (2) Low alkali level, and (3) uniform particle size. In addition, large quantities of foundry sands must be available for it to be used by Portland cement manufacturers.

Foundry sand used in Portland cement manufacturing should be separated from other foundry by-products. Most Portland cement plants also require that core butts be ground to a uniform grain size.