Synthesis of α-CaSO₄·0.5H₂O from flue gas desulfurization gypsum regulated by C₄H₄O₄Na₂·6H₂O and NaCl in glycerol-water solution
2017
Guan, Qing-Jun | Sun, Wei | Hu, Yue-Hua | Yin, Zhi-Gang | Guan, Chang-Ping
A brand new method to transform flue gas desulfurization gypsum (FGD gypsum) into α-calcium sulfate hemihydrate (α-HH) with short hexagonal prisms mediated by succinic acid disodium salt hexahydrate (C₄H₄O₄Na₂·6H₂O) and NaCl in glycerol-water solution is studied, in which the appropriate reaction temperature is 90 °C. The addition of NaCl facilitates the dissolution of calcium sulfate dihydrate (DH) and creates much higher supersaturation which is a greater driving force for the phase transformation from DH to α-HH. C₄H₄O₄Na₂·6H₂O as the crystal modifier effectively suppresses the α-HH crystal growth along the c axis, and the products generally change from needle-like particles to fat and short hexagonal prisms, which is attributed to the preferential adsorption of C₄H₄O₄²⁻ on the top facets of the crystals by chelating Ca²⁺.
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