S. Kabasci et al., BATCH-PRECIPITATION OF CALCIUM-CARBONATE FROM HIGHLY SUPERSATURATED SOLUTIONS, Chemical engineering research & design, 74(A7), 1996, pp. 765-772
The formation of different polymorphs in the batch-precipitation of ca
lcium carbonate from aqueous sodium carbonate and calcium nitrate solu
tions was investigated. In most of the experiments vaterite was found
to be the predominant polymorph. The vaterite crystals are composed of
densely packed needle-like units with a thickness of 0.1 to 0.2 mu m
in a spherulitic-type arrangement. Depending on the concentration and
the temperature of the feed solutions as well as on the type of mixing
device used, some precipitations led to calcite formation with an int
ermediate occurrence of vaterite. The transformation of vaterite to ca
lcite is believed to be based on a mechanism of dissolution of the met
astable vaterite and growth of the stable calcite crystals. A process
of parallel nucleation of the different polymorphs is supposed to be r
esponsible for the course of the generation of intermediate phases in
the precipitation of calcium carbonate.