Utilization of flue gas desulfurization gypsum for producing calcium sulfoaluminate cement

With the rapid development of industries, flue gas desulfurization (FGD) gypsum has become one of the bulk industrial solid wastes which trigger many local environmental problems in China. Due to the high purity of calcium sulfate dehydrate, FGD gypsum has a high potential for eco-friendly calcium sulfoaluminate (CSA) cement manufacture. This would reduce nature resource and energy consumption in cement industry, and bring economic and ecological benefits for waste management. Given the high sensitivity of hydrates to the temperature, the hydration features of FGD gypsum blended CSA cement under usual climate temperature (0, 10, 20 and 40 °C) were identified by using calorimetry, XRD and DSC-TGA analysis in this work. Meanwhile, the compressive strengths and dimensional stability of prepared pastes were measured in an effort to correlate the overall performance with microstructure development. Results demonstrate that the hydration of CSA cement is highly dependent on the variations of FGD gypsum dosage and curing temperature. The addition of FGD gypsum contributes to more ettringite and alumina hydroxide generated under all curing regimes, and restrains the formation of monosulfate and strätlingite at 40 °C. Therefore, it favors the strengths development of those pastes cured at 40 °C. Additionally, moderate dosage of FGD gypsum leads to the lowest shrinkage. As a by-product generated from industry, utilizing the FGD gypsum in CSA cement production is a promising and value-added way for waste management, especially when the products applied under high temperature climate region.