Research On Application Of Fume Gas Desulfurization Gypsum In Self-leveling Material

Wet flue gas desulfurization technology is always used to control SO₂ emission in coal-fired power plants.Flue gas is introduced to an aqueous lime/limestone solution and by-product called FGD gypsum which consists mostly of CaSO₄·2H₂O is produced. In China,the annual output of FGD gypsum is expected to be 20-30 million tons.So large scale utilization is needed to reuse or recycle the huge amount of FGD gypsum.In this paper,self-leveling screed material(SLSM) was evaluated as a potential way for FGD gypsum utilization.The pastes were prepared by blending cement and or bauxite with different proportions of FGD gypsum and water.The feasibility of SLSM preparation from FGD gypsum was investigated firstly by plaster apparent properties;focus on the mixture of FGD gypsum,cement and or bauxite.Secondly,the strength of SLSM with different percentage of FGD gypsum was tested to confirm composition of SLSM,which met the standard value.Finally,the hydrating and hardening of SLSM were observed carefully. The relation among minerals,structure and performance of SLSM originated from FGD gypsum and cemnt was illuminated.According to the standard,the direction for SLSM was crudely ascertained from flowability,setting time and sweatings.The flowability depended on the ratio of water to gypsum and cement,and the water-reducing agent had little effect on the plaster. FGD gypsum no more than 60%was necessary in order to get higher strength for SLSM of gypsum.Cement could be partial replaced with bauxite powder to decrease the cost of SLSM.Even the SLSM met the standard,its unhydrated surface led to a lower strength for the skin layer.This could be remedied by impregnating no more than 40% fine sand into the SLSM.For the purpose of lowing cost,Portland cement could substitute partial for calcium aluminum cement(CAC) in SLSM.But the substitution was limited by the mount of FGD gypsum in the SLSM.When the FGD decreased from 60%to 10%,the ratio of CAC(andbauxite) to Portland cement could be reduced from 5.0 to 0.5.It was also found that latex powder could enhance the bending strength, while compressive strength fell.The hydrates of the pastes were detected with X-ray diffraction(XRD) and differential scanning calorimetry(DSC) and the microstructures of pastes were observed by scanning electron microscopy(SEM).The results showed that the quick formation of ettringite accelerates the hydrations of the pastes and contributes to lower volume shrinkage and higher strength,especially in the paste with 30%-40%FGD gypsum.The experiments showed that SLSM prepared from FGD gypsum and CAC appeared satisfied physical and mechanical characteristics.Above all,FGD gypsum, CAC and bauxite mixture attributed the fast hydrating,short setting time and higher early strength SLSM.SLSM which is preferably hydraulic binder with large proportion of FGD gypsum would be one of the potentially optimum utilizations of FGD gypsum.