Naslov
Factors influencing the precipitation of calcium carbonate

Autori
Kontrec, Jasminka ; Kralj, Damir ; Brečević, Ljerka

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
XVIII. hrvatski skup kemičara i kemijskih inženjera - sažetci, abstracts / Zrnčević, Stanka - Zagreb : Hrvatsko društvo kemijskih inženjera i tehnologa (HDKI) ; Hrvatsko kemijsko društvo, 2003

Skup
XVIII. hrvatski skup kemičara i kemijskih inženjera

Mjesto i datum
Zagreb, Hrvatska, 16.02.2003. - 19.02.2003

Vrsta sudjelovanja
Poster

Vrsta recenzije
Domaća recenzija

Ključne riječi
Precipitation; calcium carbonate; Mg^2+; sulphate

Sažetak
Calcium carbonate is a versatile filler and pigment that is utilized in paper, plastics, rubber, paint, textiles, pharmaceuticals and food. Although the Earst's crust contains > 4% calcium carbonate and the deposits are plentiful, only a limited number of deposits contain raw material having the properties that satisfy the industrial needs. The principal physical chemical properties (shape and size of particles, mineral and chemical purity, colour...) of a synthetic product, precipitated calcium carbonate (PCC), can be controlled by modulating the process. The mostly used technological process of PCC production is the recarbonation of milk of lime. In such a production, the presence and the properties of suspended materials are the principal parameters that dictate the modification of calcium carbonate. In order to overcome the limitations in controlling the properties of PCC, imposed by the presence of suspended lime, in this work calcium carbonate polymorphs were precipitated from a homogeneous system using low-cost reactants, i.e. carbonic acid and calcium hydroxide. The effect of hydrodynamics (magnetic stirring and mechanical agitation with a flat-bladed stirrer) and additives (MgSO4, Mg(NO3)2 and Na2SO4) on the mineralogical composition and crystal morphology were studied in a glass thermostated batch crystalliser at 25 °C. Within the investigated range of initial supersaturations, 15<(S-1)<35, calcite was found to be the predominant polymorphic modification present in the system 20 min after mixing the reactants. Only at the highest initial supersaturations, (S-1)>30, and when the mechanical stirring was applied, a mixture of calcite and vaterite was observed. The average size and the specific surface area of the precipitated particles increased with increasing the initial supersaturation. Agitation of the system by means of the Teflon-coated magnetic stirring bar caused the appearance of calcite as the only precipitate. The addition of inorganic additives (Mg2+ and SO42-), the possible impurities in a real technological process, did not influence the mineralogical composition of the precipitate. Changes in the morphology of calcite, originally rhombohedral, were more pronounced with the increase of additive concentration, both Mg2+ and SO42-. A shift and broadening of the IR absorption band at 712 cm-1 and a shift of the band at 875 cm-1, both typical for calcite, as well as the appearance of the band at 1084 cm-1, characteristic for magnesium calcite, indicate the incorporation of Mg2+ ions into the crystal lattice of calcite. The addition of SO42- to the precipitation system caused a broadening of the absorption band at 712 cm-1 and a shift of the band at 875 cm-1 to 872 cm-1. The appearance of a broad band at approximately 1150 cm-1 indicates also the incorporation of SO42- in the calcite lattice.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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