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 1
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.
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.
Figure 2
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