The proportioning scheme of fly ash desulfurization gypsum filling material suitable for coal mine filling

In order to effectively treat the two major industrial wastes of power plants, fly ash and desulfurized gypsum, and realize the resource utilization of solid wastes of thermal power plants, fly ash and desulfurized gypsum are mixed with quicklime and cement in an appropriate proportion. Through tests such as bleeding rate, fluidity, uniaxial compressive strength, X-ray diffraction and scanning electron microscopy, the flow performance and mechanical performance are comprehensively considered, The proportioning scheme of fly ash desulfurization gypsum filling material suitable for coal mine filling is obtained. The results show that when the proportion of fly ash, desulfurized gypsum, quicklime and cement is 3 ∶ 1 ∶ 1 ∶ 1, the slurry fluidity of the mineral admixture can reach more than 300 mm, and the bleeding rate is 4.71%. The 7d compressive strength of the filling body is greater than 3MPa, and the 28d compressive strength is greater than 4MPa; With the increase of the proportion of fly ash and desulfurized gypsum, the 3d and 7d strength gradually increased, and the 14d and 28d strength increased first and then decreased. The hydration products of fly ash desulfurization gypsum filling materials mainly include ettringite, hydrated calcium silicate, hydrated calcium aluminum carbonate, and dihydrate gypsum. The hydration products will fill the pore structure inside the filling body, and the macroscopic performance is to improve the strength of the filling body.

Fly ash (FA) and desulfurized gypsum (FGD) are two major industrial wastes of coal-fired power plants, which will pollute the environment if stacked on the ground in large quantities. In recent years, the filling mining technology with power plant fly ash, aeolian sand, coal gangue as the main filling materials has been rapidly developed and applied in the central and eastern mining areas of China. In cementation filling, fly ash can partially replace cement as cementitious material in alkaline environment. Fly ash and desulfurized gypsum are combined in a suitable proportion and a small amount of cement clinker is added to make a filling body with fly ash desulfurized gypsum as the main component. The sulfate activation effect of desulfurized gypsum on fly ash is fully utilized to realize the resource utilization of solid wastes in thermal power plants and reduce the filling cost of mines.

Domestic and foreign scholars have carried out a series of studies on the preparation of filling materials for the fly ash desulfurization gypsum system. BOONSERM et al. found that desulfurization gypsum can increase the leaching amount of A13+in cement-based materials and improve the strength of cementitious materials. Lu Qianming et al. studied the influence of desulfurization gypsum content on the strength of sludge ash cement composite cementitious material at each age. The results showed that with the increase of desulfurization gypsum content, the strength of composite cementitious system at each curing age showed a trend of first increasing and then decreasing. Gao Shujie and other researchers have shown that when the content of desulfurized gypsum is 19%, the strength of the filling block is the largest. Wang Yongding et al. developed a new type of cementitious material by using fly ash, desulfurization gypsum and slag consolidation powder. The proportion is 40% ～ 45% of fly ash, 10% ～ 12% of cement clinker, 10% ～ 12% of desulfurization gypsum and 33% ～ 38% of slag micro powder. Wei Jianqiang et al. studied the modification of desulfurization gypsum fly ash mineral powder composite cementation material. The results showed that m (desulfurization gypsum): m (fly ash): m (mineral powder)=40 ∶ 20 ∶ 40, which can improve the compressive strength of the cement. Wu Yonghua and other researchers have shown that the desulfurization gypsum fly ash cement cementitious system has compressive strength. Dongyue uses fly ash, slag, etc. to prepare consolidated powder filling materials. Gao Yingli et al. showed that when the ratio of desulfurized gypsum to fly ash was 1 ∶ 2 and 30% cement was replaced, the later compressive strength could be similar to that of the reference cement. It can be seen from the current research that the fly ash desulfurization gypsum cementitious system can effectively improve the compressive strength at an appropriate proportion. Therefore, the research on the composite material of fly ash desulfurization gypsum can effectively treat industrial solid waste materials such as fly ash and desulfurization gypsum. However, at present, the research on the composite mineral of fly ash and desulfurized gypsum is all in the construction and metal mining industry, and has not been studied and utilized in the coal mine. Considering the performance requirements and practical application of coal mine filling, it is of great signif icance to design the feasibility test of different proportions of fly ash and desulfurized gypsum.