10
vii.
Combine the captured carbon dioxide with the slaked lime. Calcium carbonate reforms, and since it is insoluble in water, precipitates out.
CaOH
2
+ CO
2
CaCO
3
+ H
2
O
viii.
Separate additional impurities and grit from the PCC slurry.
ix.
If the PCC is to be used in a paper mill or shipped to a latex paint plant, the lower solids slurry may be used as is, or processed to bring up the solids
level, then tested before transfer or shipment.
x.
If the PCC is to be used as a dry product, the slurry is dewatered, dried, milled, packaged and tested.
While the process is simple on a laboratory scale, making precipitated calcium carbonates commercially on a large scale requires a great deal of process control and
process technology to assure the right size, uniformity, shape, surface area and surface chemistry. This body of PCC technology developed by Specialty Minerals
Research is what makes SMI PCCs outstanding in quality and consistency. Freeman, et al., 2002
2.4 Manufacturing Process for Nano Precipitated Calcium Carbonate
Precipitated calcium carbonate is produced using the most economic process existing today. Limestone is converted into calcium oxide and carbon dioxide by means of
calcination at temperatures in excess of 900°C. To ensure a high level of purity, the calcination process is carried out using natural gas. After the calcined lime has been
slaked with water, the resulting milk of lime is purified and carbonated with the carbon dioxide obtained from the calcination process See reactions bellow
Figure 2.1: Reaction of Calcination Process
11 Following total carbonation, a suspension of CaCO3 results. A cake comprising 40
- 60 solid matter depending on particle diameter is then obtained by filtration. This filter cake is then dried and subsequently deagglomerated in grinders. Ultrafine
PCC grades are reacted with fatty acids prior to filtration i.e. when still in the suspension stage Freeman, et al., 2002.
The fineness of the grain, as well as the crystal form aragonite, calcite, is controlled by
temperature, concentration of reactants and time.
Depending on the chemical composition of the milk of lime used and on the purifying stages during production, both technical as well as foodstuff and
pharmaceutical grades can be produced Freeman, et al., 2002.
Figure 2.2: Manufacturing Process for Nano Precipitated Calcium Carbonate
2.5 Filler
Fillers are particles added to material plastics, Composite material, Concrete to lower the consumption of more expensive binder material or to better some
properties of the mixtured material. Worldwide more than 50 million tons of fillers with a total sum of ca. 25 billion Euro for different application areas, such as paper,
plastics, rubber, paints and adhesives, are consumed annually. As such, fillers,
