Formation of calcium carbonates from Ca(OH)₂-H₂O-supercritical CO₂ using a rapid spraying method

Particle formation techniques using supercritical fluid are simple processes that can control particle size and morphology, although high-pressure is required. The purpose of this study was to investigate how the experimental conditions affect the extent and rate of CaCO₃ conversion and the size and morphology of the precipitated CaCO₃ from the carbonation tests with rapid spraying of reactants causing rapid depressurization of supercritical fluid. The relatively low temperature and pressure conditions (35 °C and 7.5MPa) resulted in low CaCO₃ conversion efficiency (41.4–51.9%), high vaterite content (70–78%) of CaCO₃, and smaller-sized particles. The relatively high temperature and pressure conditions (80 °C and 12.0MPa) resulted in high CaCO₃ conversion efficiency (66.8–73.2%), high calcite content (50–80%) of CaCO₃, and larger-sized particles. The particle size of solid products ranged between 20 and 180nm with approximately a peak of 100 nm in the particle size distribution (PSD) curve, irrespective of the test conditions; however, shorter reaction times led to smaller particles. The optimal conditions under which the extent of CaCO₃ conversion and calcite content were maximum were 50 °C, 9.0MPa, and 1 h of reaction time (CaCO₃ conversion: 92.9%; calcite content of CaCO₃: 87%).