Research On The Properties Of Flue Gas Desulphurization Gypsum

The Flue gas desulfurization (FGD) gypsum is a kind of by-produced in the power stations, which is mainly composed of CaSO4·2H2O. The FGD gypsum has more excellent performance than that of natural gypsum. It is one of the best alternatives instead of natural gypsum. Therefore, the research on the comprehensive utilization of the FGD gypsum has become a hot issue.In this paper, the influence of thermal treatment system on FGD gypsum has been studied, which determines the effective and efficient thermal treatment routines for the FGD gypsum. A systematic study on the water-resistance factors of hemihydrate gypsum generated from the FGD gypsum and the influences on the efflorescence of the FGD gypsum have been made.Firstly, the strength and conversion of calcium sulfate hemihydrates prepared from different thermal treatment of FGD gypsum has been studied and has got the fitting curve, at the same time, the main components analysis of the FGD gypsum after thermal treatment have also been analyzed using the XRD technology. The research results show that the thermal treatment temperature and time both have great impacts on the conversion ratio and the strength of calcium sulfate hemihydrates. The results show that the reasonable calcined temperature is 180℃and the benefitial calcined time is about 1.5h. Under these conditions, conversion ratio and the strength of the FGD gypsum can reach its maximum value and after the thermal treatment the main components are mainly composed of hemihydrate gypsum products.Secondly, the effects of hemihydrate gypsum by separately adding with the slag the cement and their compounds on the water resistance of hemihydrates gypsum mixture have been studied. The results show that: the hemihydrates gypsum mixed with compounds has shown well-defined effects on improving the water resistance of gypsum. From SEM photos and X-ray diffraction patterns of the cementitious materials, it can be seen that the hydration products of cementitious materials are mainly calcium sulfate dihydrate crystals, C-S-H gel and AFt etal. The best ratio of hemihydrates gypsum, slag and cement is 70:28:2. The softening coefficient of the gypsum by curing 28 days is 0.85 and the water absorption is 0.14. Adding slag separately is the second available selection and the best ratio between hemihydrates gypsum and slag is 7:3.Finally, the efflorescence theories of the FGD gypsum are studied. It is found that main components of efflorescence are MgSO4·4H2O and a tiny amount of Na2SO4 by XRD analysis. By comparing with the influences of water-gypsum ratios, the curing conditions and additives, it is found that the mechanism and incentives of the efflorescence include soluble salt, water, porous system and the curing temperature. There is a good effect to suppress the efflorescence by adding rubber powder.