Effects of dry grinding on the structure and granularity of calcite and its polymorphic transformation into aragonite

• An aggregation of ultrafine calcite particles took place after 20 min of grinding.
• The crystalline degree of calcite had a tendency to decrease gradually with grinding treatment until 60 min.
• A polymorphic transformation of partial calcite into aragonite took place after 360 min of grinding.

The structure and granularity of calcite were measured during dry grinding in a ball mill by X-ray diffraction, Fourier transform infrared spectroscopy and laser diffraction, and its morphology was observed by a scanning electron microscope. During the early stage of grinding (0–10 min), the median particle size and X-ray diffraction intensity of the calcite decreased, while the full width at half maximum increased as grinding progressed. During the middle grinding stage (20–300 min), the grain size and crystalline degree of ultrafine calcite particles no longer changed with time; this was attributed to aggregation, which hindered the breakage of particles. During the final grinding stage (360–720 min), a polymorphic transformation of calcite into aragonite took place.

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