Abstract
In this paper, the brightness of fly ash is improved by carbon removal by heating and iron-containing oxides removal by acid treatment using a two-step method to realize the application of fly ash as filler or coating in the future, which not only increases the range of resource utilization of fly ash, but also reduces dust pollution. The modification results show that the brightness of fly ash reaches the maximum value of 38.27% ISO (Brightness unit) after decarburization by heating at 600 °C. On this basis, the Box–Benhnken design scheme is adopted to optimize the brightening process for removing iron-containing oxides in fly ash. Finally, when the concentration of hydrochloric acid is 15%, the acid leaching time is 0.75 h, the reaction temperature is 74 °C, and the brightness of fly ash can eventually increase to 43.92% ISO.
Highlights
Fly ash (FA) is a finely dispersed solid waste mainly composed of glass phase, which is produced by high-temperature combustion of pulverized coal through a series of physical and chemical changes in a coal-fired boiler [1]
It is difficult to find the presence of magnetite in fly ash, probably due to the fact that such fly ash does not contain magnetite or a small amount
The brightness of the fly ash retained on the mesh screen reached a maximum value, with which is close to the theoretical prediction value of 43.93% ISO
Summary
Fly ash (FA) is a finely dispersed solid waste mainly composed of glass phase, which is produced by high-temperature combustion of pulverized coal through a series of physical and chemical changes in a coal-fired boiler [1]. With the development of the power industry, the output of fly ash from coal-fired power plants has increased year by year [3,4]. The global average utilization rate of fly ash is estimated to be nearly. It is clear that a significant proportion of coal fly ash is left untreated. Once it is discharged into the environment, it will cause different degrees of pollution such as significant damage to water, air and soil, and cause great harm to living beings. The improvement of the utilization of fly ash and the development of its applications are extremely urgent [10]
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