Preparation of α-calcium sulfate hemihydrate from FGD gypsum in K, Mg-containing concentrated CaCl2 solution under mild conditions

• Published in: Fuel (Guildford) Vol. 88; no. 7; pp. 1286 - 1293
• Main Authors: Guan, Baohong, Yang, Liuchun, Wu, Zhongbiao, Shen, Zhuoxian, Ma, Xianfa, Ye, Qingqing
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier 01-07-2009
• Subjects: Air pollution caused by fuel industries; Applied sciences; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Pollution reduction; Combustion gas desulfurization; Air pollution control; Calcium sulfate hemihydrate; K+ ions; Water content; Gypsum; Magnesium chloride; Dehydration; Under pressure; FGD gypsum; Calcium sulfate; Calcium chloride
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2009.01.004

To prepare alpha-calcium sulfate hemihydrate (alpha-HH) from flue gas desulfurization (FGD) byproduct under atmospheric pressure, the dehydration of FGD gypsum in a concentrated Ca and Mg chlorides solution medium at 95 deg C was investigated, and the effects of K+ ions were focused on. The crystal water content variation, material phases, and morphological characteristics of the dehydration products were examined and compared. The solubilities of alpha-HH in the mixed salt solutions with different K+ ion concentrations were also determined. It was found that with low concentration of K+ ions in the mixed salt solution (i.e. 0.001-0.035 M), the dehydration rate was enhanced, while with higher K+ ion concentration (i.e. 0.087-0.263 M), this process was retarded. alpha-HH was the dehydration product when K+ ion concentration was at appropriate level, while anhydrite (AH) occurred when K+ ion concentration was above 0.173 M. K+ ions were assumed to behave as a capping agent to control the morphology of the alpha-HH, resulting in crystals of lower aspect ratio. FGD gypsum can be successfully transformed into alpha-HH in concentrated Ca and Mg chloride solution under mild conditions, and K+ ions play an important role in the process.