Study on Preparation of High-strength Gypsum by FGD Gypsum

With the enlarging of industrial desulfurization, the amount of FGD gypsum is increasing rapidly. The preparation of alpha-calcium sulfate hemihydrate (α-HH) is one of the biggest concerns for FGD gypsum reclamation. The influence of mixed chlorate solution of Mg-Ca-Na concentrations (5-30 wt%) and FGD gypsum concentrations(5-30 wt%) by hydrothermal salt solution method at atmospheric were investigated at temperatures (75-99C) within a reaction time of 4h and a pH value of neutral. The results showed that 20 wt%, 20 wt% and 97C was respectively optimal parameter of salt media concentration, FGD gypsum concentration and temperature. Products obtained from the dehydration process of optional experimental conditions with mixed crystal modifier were characterized based on relevant standards in this study. The results showed that α-HH had integrity crystal structure, 2h flexural strength and oven dry compressive strength were 5.34MPa and 30.21MPa, which had meet the industry standards of α30 grade. Introduction In China, the characteristic of energy resources structure means that the coal is the main energy. Actually, the fuel has been surveyed with a high sulfur content and its massive application has contributed to heavy emissions of sulfur dioxide (SO2). To meet Clean Air standards, the local government stipulates that coal-fired flue gas disposed with desulfurization can only be emitted into the atmosphere. Currently, the wet limestone-gypsum method has become a leading technology in the field of pollution prevention of flue gas, which results that the amount of flue gas desulfurization (FGD) gypsum has been increasing rapidly[1-2]. Viewed from the resource recovery, it is desiderated to seek new technologies of FGD gypsum utilization. It is proved that FGD gypsum can be used to produce the high-strength gypsum which is treated as a green building material[3-4]. The highstrength gypsum, consisted of α-calcium sulfate hemihydrates (α-HH), is known as its better workability and high strength values and widely used in precise molding, arts and crafts, ceramic mould and dental materials and so on. This research area has strong theoretic significance and practice value in the construction industry. Generally, the production of α-HH contains two ways, such as the autoclave method and hydrothermal method[5-6], and the latter is proved to be more economic and easily controlled. Based on this point, this research, providing theoretical basis for actual industrial applications, is aimed at exploring technological conditions of hydrothermal salt solution method at atmospheric pressure by single factor experiment.