Thermal decomposition of calcium carbonate polymorphs precipitated in the presence of ammonia and alkylamines

• Vaterite–calcite mixtures were obtained in presence of ammonia and alkylamines.
• The spherical shape of precipitated vaterite is maintained in the calcined product.
• Spherical vaterite may be a good precursor for CaO catalyst in biodiesel synthesis.

Precipitated calcium carbonate was obtained by CO2 bubbling in CaCl2 solution. Ammonia and alkylamines were used to enhance CO2 absorption and control the polymorphic phases. Vaterite and calcite mixtures were obtained, mainly vaterite in ammonia and mono-methylamine and mostly calcite in tri-methylamine environment. The thermal decomposition of precipitated calcium carbonate leads to high purity CaO. During the thermal decomposition the vaterite to calcite transformation was noticed but the final spherical shape of vaterite was maintained. As the use of CaO as catalyst in biodiesel synthesis may recommend a spherical shape and high contact surface, a precipitated calcium carbonate, rich in vaterite phase, may be a good precursor for CaO catalyst preparation.

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