Influence of impurities on hydration, hardening and morphology of flue gas desulphurization gypsum plaster

The influence of soluble sodium, magnesium and chlorine ions on hydration process, hardening and morphology of FGD plaster were studied by external addition. The results showed that these impurities short the setting time of FGD gypsum, therein, the sodium has an obvious effect on the shortening the setting time. Under the low concentrations for sodium and chlorine, the morphology of FGD gypsum hydration product and the strength of FGD plaster remained unchanged, the resulting crystals showed predominantly a mixture of needle shaped, radiated sticklike crystals, and the crystals have interlocking appearance and exhibit uniform distribution. Whereas, under high concentrations, the strength of FGD plaster was reduced. The fall in strength is attributed to the formation of crystals of small ratio of length to diameter and poor stacking of the crystals of irregular boundaries. Magnesium had slight influence on the strength of FGD plaster and the morphology of FGD gypsum hydration product.