engleski

Precipitation of amorphous and metastable CaCO3 phases in the systems with different chemical complexity

Calcium carbonate is among the most widely occurring natural minerals. Biogenic calcium carbonate minerals occur in e.g. soils and calcifying marine plankton and are a key component of the global carbon cycle. Abiotic calcium carbonate (synthetic) has a wide range of uses: as a component of pharmaceuticals and foodstuffs, in water treatment, and as a filler in ceramics, plastics, coatings, and paper. Calcium carbonate with desired chemical and structural composition, size and morphology could be tuned by a strict control of precipitation conditions. Amorphous calcium carbonate (ACC), biogenic or synthetic, is an important (meta)stable phase or transient precursor to crystalline calcium carbonate minerals. Depending on the preparation method or its biogenic source, ACC varies in composition, stability and structure. It was found that organisms use organic macromolecules, magnesium, phosphate and structural water to induce ACC formation and to determine its stability. Three model systems with broad range of relative supersaturations, have been investigated previously: (a) Simple system containing only constituent ions: calcium and carbonate, (b) Complex system including constituent ions and their co-ions, sodium and chloride, and (c) Physiological system with the addition of inorganic cation, Mg2+, and at increased ionic strength, 0.15 M NaCl (mimicking the simplified inorganic environment in selected living organisms). In this work, the investigations of ACC stability and transformation were performed for all three model systems. The analyses of precipitation in model systems of different chemical complexity gave the insight into precipitation boundaries and supersaturation domains for formation of different CaCO3 phases. The results have shown that besides the increased initial supersaturation, the complexity of precipitation domain (increased ionic strength, the presence of common inorganic ions, in particular magnesium) has an important role on the formation and properties of the amorphous, metastable and stable CaCO3 phases. The amorphous phases isolated in simple and complex systems have similar properties and transformed to vaterite and cacite. Those formed in physiological system are more stable and transform to monohydrocalcite/aragonite, or remain stable.

kalcijev karbonat ; amorfna faza ; biomineralizacija

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