29 September 2020
Calcium carbonate is one of the most useful and versatile materials known to man. One simple example of calcium carbonate is chalk that has been used as a writing tool for over 10,000 years. As limestone, calcium carbonate is a biogenic rock, and is more compacted than chalk. As marble, calcium carbonate is a coarse-crystalline, metamorphic rock, which is formed when chalk or limestone is recrystallised under conditions of high temperature and pressure. Large deposits of marble are found in North America and in Europe; e.g., in Carrara, Italy, the home of the pure white "statuario" from which Michelangelo created his sculptures.
Iceland crystal or Iceland spar is a transparent variety of crystallized calcium carbonate found as large readily cleavable crystals, easily divisible into rhombuses, and is remarkable for its birefringence, meaning that the index of refraction of the crystal is different for light of different polarization (***Many thanks to Dr. Alan Rawle from Malvern Panalytical for his contribution to this post).
Calcium carbonate is extracted by mining or quarrying for industrial purposes. Pure calcium carbonate can be obtained from (GCC) or (PCC), both are same in terms of chemical formula, CaCO3, but they differ in their manufacturing process, properties and end uses.
Ground Calcium Carbonate GCC is produced by mechanical grinding of limestone and classified to required size. No chemical change is involved in the process. Manufacture of Precipitated Calcium Carbonate PCC is made by hydrating high-calcium quicklime and then reacting the resulting slurry with carbon dioxide. The resulting product is extremely white and typically has a uniform narrow particle size distribution. PCC is available in numerous crystal morphologies and sizes, which can be tailored to optimize performance in a specific application. The PCC process allows products to be made with very small sizes, with high surface areas, high oil absorptions, and/or with different powder bulk densities— from ultra-low to super-high powder densities. The different shapes allow PCC to act as a functional additive in sealants, adhesives, plastics, rubber, inks, paper, pharmaceuticals, as well as nutritional supplements.
As mentioned previously, PCC and GCC have the same chemical composition but differ in particle size and shape. The distribution of particle sizes in a GCC is much broader than in a PCC, d90 particle size being much higher for a GCC. The PCC allows the generation of high oil absorptions, useful in certain applications.
Ground Calcium Carbonate or limestone is used in paper and plastic fillers, coatings and paints. It is also used in cement, converted to quick-lime (calcium oxide) and slaked lime (calcium hydroxide). Calcium carbonate is the active ingredient in agricultural lime, and is used as a fertilizer to neutralize acidic conditions in soil and provide additional calcium for plants that require it.
PCC also finds many industrial uses due to its ability to achieve small particle sizes, narrow particle size distribution and special particle shapes. In rigid polyvinyl chloride (PVC), PCC increases impact strength with some of the smaller particles able to replace expensive impact modifiers. Nano PCCs (less than 0.1 micron in size) control viscosity and sag in automotive and construction sealants, such as PVC plastisols, polysulfides, urethanes, and silicones. In paint, PCC's unique particle shapes improve hiding and allow reductions in titanium dioxide levels. PCC enhances optical properties and print characteristics of paper products, improves paper machine productivity, and can reduce papermaking costs through the replacement of more expensive pulp fiber and optical brightening agents.
Calcium carbonate is used widely as an effective dietary calcium supplement, antacid, phosphate binder, or base material for medicinal tablets. Being high in calcium content, PCC enables the formulation of high dosage calcium supplements and multi-vitamin/mineral tablets. The small particle sizes and special particle shapes contribute to the development of good tasting calcium fortified foods and beverages.
In Alfatestlab we are experts of particle characterization and benefit of a long lasting experience in calcium carbonate analysis, our lab is equipped with the state of the art techniques to determine particle size and shape, surface area, porosity and density, flow properties, thermal properties, crystal structure, etc. Contact us to discuss your analytical needs.