The formation and transformation mechanism of calcium carbonate in water

Journal Article · Thu Oct 01 00:00:00 EDT 1987 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(87)90155-4· OSTI ID:7000745

Ogino, Takeshi; Suzuki, Toshio; Sawada, Kiyoshi ^[1]

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1. Nigata Univ. (Japan)

High supersaturated solutions of Ca{sup 2+} and CO{sub 3}{sup 2{minus}} ions rapidly precipitate amorphous calcium carbonate, ACC, the logarithmic thermodynamic solubility product of which is about {minus}6.0 at 25{degree}C. The ACC initially formed is transformed to a mixture of several crystalline calcium carbonate polymorphs within several minutes. The transformed polymorphs are vaterite and calcite at low temperature (14 to 30{degree}C), and aragonite and calcite at high temperature (60 to 80{degree}C). At intermediate temperatures (40 to 50{degree}C) the formation of all three polymorphs was observed. Metastable polymorphs are gradually transformed to the stable form, calcite. It takes about 200 min at 25{degree}C and 370 min at 30{degree}C for the complete transformation of vaterite to calcite, and 100-1300 min for that of aragonite to calcite at 60-80{degree}C. At 50{degree}C, vaterite is predominantly transformed at first to aragonite within 60 min, and then the aragonite is transformed to calcite in about 900 min. The results of the change in the ion activity product of the solution and the abundances of the polymorphs strongly suggest that the polymorphic transformation of vaterite and aragonite to calcite takes place through dissolution of the metastable phase and growth of the stable phase, calcite. The rate-determining step of the transformation is the growth of calcite. The relative abundance of vaterite becomes higher at 25{degree}C with increasing concentrations of calcium and carbonate ions in the supersaturated solution. When the ion activity product of the initial supersaturated solution is lower than the solubility product of ACC at 25{degree}c, only vaterite directly precipitates after some induction period. The vaterite crystals formed are free of calcite seeds and the vaterite saturated solutions are stable for several days.

• OSTI ID: 7000745
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 51:10; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ARAGONITE
DISSOLUTION
PRECIPITATION
CALCITE
CALCIUM CARBONATES
SOLUBILITY
SOLUTIONS
THERMODYNAMIC PROPERTIES
AMORPHOUS STATE
CHEMICAL REACTION KINETICS
GEOCHEMISTRY
IONIC COMPOSITION
PHASE TRANSFORMATIONS
SUPERSATURATION
TEMPERATURE EFFECTS
WATER
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CHEMISTRY
DISPERSIONS
HYDROGEN COMPOUNDS
KINETICS
MINERALS
MIXTURES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
REACTION KINETICS
SATURATION
SEPARATION PROCESSES
580000* - Geosciences