Precipitated calcium carbonate (PCC) is produced by adding carbon dioxide to lime milk. This causes finely divided calcium carbonate to be formed, generally with a particle size of less than 5 microns. Ideally this process is carried out at a lime producing plant where both raw materials – quicklime and waste gases with a high CO2-content – are available from one source, the lime kiln.
Quicklime with a high content of available lime, i.e. a low content of residual CO2 and other impurities, is desirable. Whilst unburnt CaCO3 can be removed by filtering the lime milk, some other impurities, such as MgO, SiO2, Al2O3 and especially Fe2O3, because of their small particle size, can remain in the PCC, adversely effecting its properties, e.g. brightness and opacity. Depending on the PCC producers, lime with different levels of reactivity is asked for; however optimum consistency is always stipulated.
PCC is used in many different industrial sectors, as pigment, coating and filler. The main fields of application are paper, paints and coatings, plastics, rubber, pharmaceutical products and cosmetics.
Single shaft kilns, such as the annular shaft kiln and the Maerz HPS single shaft kiln are suitable for producing the required lime quality, whilst continuously delivering offgases with a high CO2 content.