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Sources of calcium are generally widespread and quite extensive. These sources are limestone, dolomite, marl, chalk, and oyster shell. Cement plants account for nearly half of the demand, while two hundred lime plants in the United States and Puerto Rico consume about twenty five percent. Since the chemical composition of the limestone and other sources of calcium is critical in the cement and lime industry, particularly for the deleterious compounds such as sodium oxide, Na2O, magnesium oxide, MgO, phosphorus pentoxide, P2O5, and potassium oxide, K2O, accurate determinations are critical. Due to the tonnage per hour, these determinations must be made rapidly and accurately. X-ray fluorescence can thereby satisfy this need for accuracy and also precision. Production of lime is performed by calcining limestone or dolomite in which the industry is generally located and concentrated in the States of Michigan, Pennsylvania, and Michigan. The resulting product is quicklime, CaO, and hydrated lime, Ca(OH)2 Substantial amounts of quicklime is further processed into calcium carbide in order to produce acetylene gas. In this case, the determination of P2O5 is critical since minor quantities of phosphorus in acetylene gas can cause premature explosions. Other uses for lime are well known in the treatment of water, the paper and pulp industry, and in the steel industry for the production of slag to remove impurities. Dolomitic lime is heavily utilized in the manufacture of magnesite refractories by reacting dolomitic lime with brines from the Michigan Basin to produce magnesium oxide, MgO, and calcium chloride, CaCl2. Sample preparation for these materials usually is performed by grinding and pelletizing or fusion with lithium-tetra-borate, Li2B4O7.
Limestone, dolomite, sample preparation, mineralogy, matrix corrections, X-ray fluorescence, α coefficients
Principal Scientist (Retired), Rigaku/USA, Danvers, MA