Synthesis of Calcium Carbonate Hollow Microspheres and the Pelletization Mechanism by Electrostatic Attraction of PEG–SDS

Calcium carbonate is a common natural mineral with a wide range of applications. In this study, hollow calcite microspheres were successfully synthesized by using calcium chloride and sodium carbonate as raw materials in an SDS–PEG system. The results suggested that the appropriate concentration of SDS is necessary during the spherical crystallization of calcium carbonate. It was found that the crystals started to aggregate under the effect of SDS, and aggregation was enhanced with an increase in SDS concentration, leading to the transformation from hollow to solid microspheres. However, high temperatures will lead to the transformation from calcite to aragonite, resulting in the collapse of the formed spherical structure. Infrared spectroscopy and conductivity analysis suggested that when the concentration of SDS reached 0.3 g/L in the PEG–SDS system, SDS and PEG formed a spherical supramolecular structure. This structure could act as a template, leading to the aggregation of calcite through electrostatic attraction and finally to the formation of a hollow spherical structure.