Crystallization behavior and kinetics of calcium carbonate in highly alkaline and supersaturated system

• Crystallization kinetics of CaCO3 in causticization was investigated.
• Formation of calcite is quite fast in causticization system.
• Large Ca(OH)2 concentration affects the crystallization behavior of CaCO3.
• OH− may prohibit the nucleation and growth of CaCO3.
• Kinetic parameters are greatly different with those in liquid–liquid systems.

In causticization process of Na2CO3–Ca(OH)2, which is a liquid–solid system with high alkalinity and supersaturation, agglomeration and morphology instability of CaCO3 crystal have greatly limited its application. To deeply investigate the internal relations between crystallization process and condition control in this system, crystallization kinetics was conducted in a continuously operated crystallizer. The kinetic equations of growth rate, nucleation rate and agglomeration kernel were correlated in terms of power law kinetic expressions based on the agglomeration population balance equation. Magma density and mean residence time exert a considerable effect on crystal growth, nucleation, and agglomeration. Crystal growth and nucleation are surface-integration-limited and size-limited, respectively. Agglomeration increases with increasing mean residence time, but the increase in magma density break down the agglomerates by frequent and energetic collisions. Through the study, crystallization behavior of CaCO3 in causticization system was revealed, and the particle size and morphology were efficiently predicted and controlled. These results can provide a basis for understanding the design of the reactor.