Understanding the influence of iron on fluidity and crystallization characteristics of synthetic coal slags

Iron was an important component in coal ash slag and had a significant influence on the gasification reactivity and slag discharge in industrial gasification process. In this study, five synthetic slags with different iron contents (Fe2O3 ratios: 0%, 5%, 10%, 15%, 20%) were prepared to investigate the effect of iron on fluidity and crystallization characteristics of synthetic slag. The results showed that the fusion temperatures of synthetic slags decreased with the increase of iron content, which was mainly resulted from the neutralization between iron and high-melting-temperature lime and the formation of lower-melting-temperature srebrodolskite during fusion process of synthetic slag. At high temperatures, slag viscosity decreased with the increase of iron content. But as the temperature further decreased, the viscosity changes of coal ash diverged without following the simple monotonous trend. Viscosity transformation after crystallization was affected by multi-factors such as interfacial crystallization, temperature and atmosphere. The sudden viscosity changes of synthetic slags showed close relationship with the formation of gehlenite and anorthite, which was mainly owing to the position replacement and polymerization degree decrease of Al3+, Si2+ and Ca2+ in melt network by iron as an amphoteric substance.