PCC, Precipitated Calcium

PCC (Precipitated Calcium Carbonate) is by definition a very fine, high purity processed calcium carbonate with controlled morphology, particle size and particle size distribution. PCC is often used in the production of paper [1], but can also be used in different fields of applications, mainly as fillers (in paints, polymers...). There is therefore a need for Lhoist to further improve its expertise in the field of synthetic carbonates and to develop innovative synthetic carbonates with new properties and especially new morphologies. For this purpose, an area in which Lhoist does not have much experience has been explored, that is the production of synthetic carbonates starting from a natural dolomite (CaC03.MgC03) instead of limestone (CaCOs). 

Calcium carbonate is a common inorganic compound known as limestone. Calcium carbonate has many applications in industries such as medicine, agriculture, paint plastic and surface coatings etc. The vast majority of calcium carbonate used in industry is extracted by mining process. Pure calcium carbonate (e.g. for food or pharmaceutical use), is synthesized by passing carbon dioxide into a solution of calcium hydroxide slurry. In this process calcium carbonate precipitates out, and this grade of product is referred to as precipitate calcium carbonate (abbreviated as PCC). The common reaction is as follows ... 

PCC [Partial combustion cracking] Not to be confused with precipitated calcium carbonate. A process for cracking crude petroleum or heavy oil to a mixture of olefins and aromatic hydrocarbons. The heat carrier is steam, produced by the partial combustion of the feed. Developed by Dow Chemical Company. It was piloted in 1979 and a larger plant was built in Freeport, TX, in 1984. 

There are two sources of calcium carbonate, ground calcium carbonate (GCC) and precipitated calcium carbonate (PCC). 

Calcium carbide is used to produce acetylene. Some of the other chemicals made with lime include calcium hypochlorite, citric acid, and sodium alkalis. Lime is used to produce precipitated calcium carbonate (PCC), which is a fine-grained form of calcium carbonate. To produce PCC, lime is hydrated to produce slaked lime and the slaked lime is combined with water to produce limewater. Carbon dioxide is added to the limewater, causing calcium carbonate to precipitate as PCC. PCC is used widely in plastics production, papermaking, pharmaceuticals, and the petrochemical industry. 

Figure 14.1 The precipitated calcium carbonate (PCC) production process A schematic representation, according to the acetic acid route [21, 51].

The primary particle size of Winnofil stearate coated precipitated calcium carbonate from Zeneca Resins is in the region of 0.075 micron. When compounded into natural and synthetic elastomers, the hydrophobic surface coating assists wetting and aids dispersion. When compounded into plasticised PVC for cable sheathing, the PCC allows for formulations with minimal potential for acid gas release in combustion conditions. In rigid PVC, stearate coated PCC has been used in compounding as an alternative to conventional acrylic processing aids and as a means to reduce impact modifier levels. 

The principal components of ash are calcium carbonate— in the form of precipitated calcium carbonate (PCC) or ground calcium carbonate (GCC)—that typically constitutes 20% and up to 75% of dry sludge content, and clay. These two minerals are typically loaded into paper as a coating and filler to improve the mechanical characteristics as well as the appearance of paper. The resulting papermaking sludge, particularly mixed office paper sludge, consists primarily of two major components, that is, fiber and minerals finely mixed with each other. 

The production of precipitated calcium carbonate (PCC) is categorised as a use of slaked lime and is described in section 31.2. However, PCC is clearly a limestone in terms of its chemical analysis and competes with whiting in a number of applications (the applications of both whiting and PCC are outlined in section 12.9). 

Precipitated calcium carbonate is made as a by-product of causticisation (see section 31.20). While it has been shown that commercial grades of PCC can be made by this route, it has not yet been exploited on the full scale [31.2]. 

In most processes, the precipitated calcium carbonate is a waste product. It does not meet the stringent requirements for PCC. At least one company calcines the precipitate and re-uses the resulting quicklime [31.23]. 

S. Hansen, Limestone for Precipitated Calcium Carbonate (PCC) , Proc. International Lime Congress, Berlin, 1994. 

Precipitated calcium carbonate is produced by the controlled carbonation of milk of lime (see section 31.2). The use of PCC as a pigment is mentioned in section 12.9. 

Precipitated calcium carbonate (PCC) is produced by blowing carbon dioxide into milk of lime, thereby precipitating finely divided calcium carbonate, generally with a mean particle size of less than 5 pm. 

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