The influence of some naturally occurring minerals on the precipitation of calcium carbonate polymorphs

In this work precipitation of calcium carbonates, influenced by the addition of suspended mineral particles (quartz, kaolinite or montmorillonite) is reported. In the investigated systems the initial concentrations of calcium and carbonate species, as well as the concentration of NaCl, were similar to those in seawater. In the reference system, to which no mineral particles were added, vaterite was the only solid phase precipitating. Quartz and kaolinite had no influence on precipitation, while the addition of calcium montmorillonite caused an instantaneous precipitation of calcite. This was taken as an indication that montmorillonite is a suitable substrate for the overgrowth of this polymorph. The progress of precipitation was followed by measuring the pH value of the solution, while the solid phases were analyzed by means of X-ray diffraction and FT-IR spectroscopy. The samples of calcite were additionally characterized by means of the electron spin resonance spectroscopy, which revealed distortions of the crystal lattice of the calcite epitaxially grown on montmorillonite.