Fly ash is the fine ash collected from the flue gas after coal combustion. Fly ash is the main solid waste discharged from coal-fired power plants. Most of the combustibles in coal can be burned out in the furnace, while the non-combustibles (mainly ash) in pulverized coal are mixed in large quantities in high temperature flue gas. These noncombustibles are partially melted due to high temperature and form a large number of fine spherical particles due to surface tension. Under the suction action of the draught fan at the tail end of the boiler, the flue gas containing a large amount of ash flows to the furnace tail. As the flue gas temperature decreases, some of the melted particles become vitreous due to quenching to a certain extent, and thus have high potential activity. These fine spherical particles are separated and collected by the dust collector before the exhaust gas is discharged into the atmosphere by the induced draft fan. The main oxides of fly ash in China's thermal power plants are SiO₂, Al₂O₃, FeO, Fe₂O₃, CaO, TiO₂ and so on. Fly ash is one of the industrial waste slags with large discharge in China. With the development of electric power industry, the amount of fly ash emission from coal-fired power plants increases year by year. A large amount of fly ash without treatment will produce dust, polluting the atmosphere; if discharged into the river system will cause siltation, and the toxic chemicals will also cause harm to human beings and organisms.