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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 Fua,*, Caiyun Jiab, Qiaoshan Chenb, Xueting Caoa, Xiaomin Zhanga

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    • Effect of particle size on transformation kinetics of FGD gypsum to α-HH was investigated. • Particle size exerted significant effect on induction time but little effect on growth time of α-HH. • Gypsum of smaller size provided more nucleation sites but can hardly enhance the driving force. • The activation enthalpy decreased and activation entropy increased with decreasing particle size. • The proportion of smaller α-HH crystals in products increased with decreasing parent crystal size.


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


Particle size; Gypsum; Phase transformation; Crystallization