Industrial Bases by Chemical Routes

The dominant source of calcium carbonate is lime-stone, the most widely used of all rocks, but this occurs in nature with at least traces of clay, silica, and other minerals which may interfere with some applications. However, high calcium limestone consists of about 95% or better calcium carbonate. White marble, a metamorphosed form of pure limestone with a closely packed crystal structure, is chemically suitable. But marble is usually of higher value for other applications than as a chemical feedstock. Dolomitic limestones consist of calcium and magnesium carbonates present in a near one to one molar basis, though this ratio can vary widely in ordinary dolomites. For some applications at least, the presence of the magnesium carbonate is not a handicap to the use of this calcium base component of the dolomite. The remaining principal natural sources of calcium carbonate more closely reflect their biogenetic origin in the forms of chalk, which comprises the shells of microscopic marine organisms, bivalve shells, which for example are accessible in sufficient quantities on shores of the Gulf of Mexico to be employed as an industrial feedstock, and coral, which consists of the massive, sub-marine fused skeletons of multiple stationary organisms.