Partic. vol. 40 pp. 98-104 (October 2018)
doi: 10.1016/j.partic.2017.10.004

Effect of particle size on the transformation kinetics of flue gas desulfurization gypsum to α-calcium sulfate hemihydrate under hydrothermal conditions

Hailu Fu^a,*, Caiyun Jia^b, Qiaoshan Chen^b, Xueting Cao^a, Xiaomin Zhang^a

hlfu@cjlu.edu.cn

Abstract

The effect of particle size on the transformation kinetics of flue gas desulfurization (FGD) gypsum to α-calcium sulfate hemihydrate (α-HH) in calcium chloride (CaCl₂) solutions was investigated to better guide value-added FGD gypsum use. Gypsum samples from different sources were sieved into several size groups, and their transformation rates were compared. The results showed that using FGD gypsum with a smaller particle size accelerated the transformation to α-HH. The size effect accelerated nucleation kinetics of α-HH rather than its crystal growth rate (that is, the thermodynamic driving force for the transformation changed little with particle size variation). Analysis using a kinetics model revealed that a smaller gypsum particle size lowered the overall activation energy barrier for the transformation. This is because the smaller gypsum particles had a larger relative specific surface area and thus provided more nucleation sites and crystalline defects to promote α-HH nucleation. A smaller particle size of FGD gypsum also gave a higher yield of fine α-HH particles because of the increased incidence of primary and secondary nucleation coupled with attrition. This paper indicates the transformation of FGD gypsum into α-HH could be effectively promoted by regulating FGD gypsum particle size.

Graphical abstract

Keywords

Particle size; Gypsum; Phase transformation; Crystallization