Effect and Mechanism of Retarders on Hydration and Hardening Process of Flue Gas Desulphurization Gypsum

Due to a wide variety of retarders, this paper studies the influence of different retarders on the retarding effect and hardening strength of Flue Gas Desulphurization (FGD) Gypsum. The mechanism of influence of retarders on crystallization process of FGD gypsum is studied through ionic analysis and image analysis of gypsum micro-morphology. The results indicate that the retarders play the same role for FGD gypsum as they do for natural gypsum and the impurities of retarders doesn't have any harmful effects on retarding effect. The researches show that retarders can decrease the crystallization speed of dihydrate gypsum, and influence the development of FGD crystals, thus causing the strength-reduction and coarsening of the hardened crystal particles. Under the condition that all the retarders achieve the same retarding effect, citric acid has the slightest effect on the strength-reduction of FGD gypsum among all the retarders. Borax is unsuitable for engineering application because of its lower solubility under normal temperature.