The differences between Ground Calcium Carbonate (GCC) and Precipitated Calcium Carbonate (PCC).

The difference between Ground Calcium Carbonate (GCC) and Precipitated Calcium Carbonate (PCC).

Both are same in terms of chemical formula, CaCO3. But they differ in their manufacturing process, properties and end uses.

Production:

GCC is produced by mechanical grinding of the raw material, limestone. Then it is classified to required size. No chemical change is involved in the process.

Manufacture of PCC involves following chemical changes.

• Calcination: Limestone is heated at about 1000 degree centigrade temperature in a Kiln to produce quick lime.

CaCO3 Heat → CaO(Lime/quick lime) + CO2

• Hydration/slacking: The quick lime pebbles are mixed with water in a calculated ratio to form hydrated lime slurry, called milk of lime.

2CaO + 2H2O → 2Ca(OH)2

• Carbonation: Milk of lime slurry is then treated with CO2 evolved during calcination process and convert back to CaCO3.

Ca(OH)2 + CO2 → CaCO3 + H2O

• Filtration and Drying: The CaCO3 formed is in slurry form (some application uses as slurry) which is then filtered and dried to powder form.

The size and shape of PCC is controlled and other impurities are removed during the process. Hence PCC has more advanced applications as compared to GCC.

• What Is Unique About A Precipitated Calcium Carbonate?

The different shapes allow PCC to act as a functional additive in sealants, adhesives, plastics, rubber, inks, paper, pharmaceuticals, nutritional supplements and many other demanding applications. A formulator can choose a shape, and the physical properties that result from that shape, that gives the best performance in the end use.

In the PCC process, products can 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.

How Does Precipitated Calcium Carbonate (PCC) Differ From Ground Calcium Carbonate (GCC)?

In chemical composition, they are the same. PCC is purer than the limestone from which it is made, and is lower in silica and lead.

PCC’s shape and size are different from that of ground calcium carbonate (GCC). Under high magnification, GCC is seen to be irregularly rhombohedral in shape. The PCC crystal shape depends on the product, and the particles are more uniform and regular.

The distribution of particle sizes in a GCC is much broader than for a PCC of the same size-that is, there are many more large particles and many more small particles than in a PCC, and the size of the largest of the particles (the "top size") is much greater for a GCC than for a PCC. The lower top size of a PCC gives better impact resistance in plastics than with a GCC. The narrower particle size distribution allows the generation of high oil absorptions, useful in certain applications.

These differences can be quickly seen in these photos of a PCC and a GCC of the same median particle size, 0.7 microns.