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Calcium carbonate is an insoluble white powder that occurs naturally in many minerals including limestone, chalk and marble. It is also a naturally occurring substance in plants and animals including shells, bones, coral and teeth. It is an odorless, tasteless and non-toxic compound. It is used to neutralize acidity, enrich soil and water, and treat waste gases such as sulfur dioxide and nitrogen oxides. It is also used to manufacture plastics, paper and pharmaceuticals and in a wide variety of demanding applications.
The melting point of calcium carbonate is a function of temperature and pressure, but is not as high at 2000 K as some have reported. At lower temperatures, the melt is fluid-like and accurate viscosities can be calculated up to 32.6 GPa. At higher temperatures, however, the liquid reaches a non-ideal state and shows a slow relaxation toward calcite deposition.
This behavior has been predicted by theoretical calculations and the results closely match experimental observations. The rhombohedral crystal structure of the calcites is less stable than the acicular aragonite form, and this difference contributes to the nonideal liquid behavior. The chemistry of the melt can be controlled by setting cooling water indices such as the Langelier and Ryznar Index to avoid scaling or corrosive conditions, respectively.
PCC is manufactured on a large scale by passing carbon dioxide gas through calcium hydroxide (otherwise known as slaked lime). When the resulting precipitated calcium carbonate has been sized to the desired particle shape, it is dried and milled, packaged and shipped for use in latex paint, pulp and paper, sealants and many other demanding applications. This process requires a lot of fine tuning to assure that the right size, uniformity, shape and surface chemistry are achieved. This body of technology is what makes SMI’s PCC outstanding in quality and performance.