Formation of CaCO3 hollow microspheres in carbonated distiller waste from Solvay soda ash plants.

For decades, distiller waste and CO₂ were not the first choice for production of high valued products. Here, CaCO₃ hollow microspheres, a high-value product was synthesized from such a reaction system. The synthetic methods, the formation mechanism and operational cost were discussed. When 2.5 L·min⁻¹·L⁻¹ CO₂ was flowed into distiller waste (pH = 11.4), spheres with 4–13 diameters and about 2 shell thickness were obtained. It is found that there is a transformation of CaCO₃ particles from solid-cubic nuclei to hollow spheres. Firstly, the Ca(OH)₂ in the distiller waste stimulated the nucleation of calcite with a non-template effect and further maintained the calcite form and prevented the formation of vaterite. Therefore, in absence of auxiliaries, the formation of hollow structures mainly depended on the growth and aging of CaCO₃. Studies on the crystal morphology and its changes during the growth process point to the inside-out Ostwald effect in the formation of hollow spheres. Change in chemical properties of the bulk solution caused changes in interfacial tension and interfacial energy, which promoted the morphological transformation of CaCO₃ particles from cubic calcite to spherical clusters. Finally, the flow process for absorption of CO₂ by distiller waste was designed and found profitable. [ABSTRACT FROM AUTHOR]