The transformation process of amorphous CaCO
3 obtained from the reaction between aqueous solution of Ca (OH)
2 and CO
2 at 10, 15, 20 and 25°C was traced continuously by measuring the electrical conductivity of the reaction solution and the influences of reaction temperature, electrical conductivity value of the reaction solution, stirring rate and additives on the products after transformation were examined by X-ray powder diffraction, thermoanalysis and electron microscopy.
The results obtained were summarized as follows :
(1) Amorphous CaCO
3 was hydrous and contained a small amount of Ca (OH)
2.
(2) The induction period was observed for each transformation and was influenced by reaction temperature, electrical conductivity value of the reaction solution and stirring rate. The apparent activation energy for the nucleation of calcite associated with the reciprocal induction period was 87. 6 kJ/mol.
(3) In the aqueous solution of Ca (OH)
2 at an electrical conductivity of 1 mS/cm, the morphology of the products after transformation was rohmbohedral type at higher temperatures or at lower stirring rates and was spindle type at lower temperatures or at higher stirring rates.
(4) In the aqueous solntions of Ca (OH)
2 at 2 to 8 mS/cm, the morphology after transformation was chain-like CaCO
3·OH
- ions would be mainly responsible for the formation of chain-like CaCO
3.
(5) In the aqueous solutions of Ca (OH)
2 at more than 9 mS/cm, the products after transformation were basic CaCO
3 and chain-like CaCO
3. The yieled of basic CaCO
3 of them incresed in the aqueous solutions of Ca (OH)
2 at higher electrical conductivities or at higher stirring rates.
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