Experimental study on the magnetic characteristics of coal fly ash at different combustion temperatures

Two different coals containing iron minerals were combusted in a drop tube furnace at different temperatures. The ash samples collected were analyzed in detail to investigate the transformation behaviors of iron-bearing minerals and the magnetic characteristics of coal fly ash (FA). The vibrating sample magnetometer (VSM) was used to analyze the magnetic characteristics of the ash samples and Mössbauer spectroscopy was used to analyze the iron-bearing components in FA. The results indicate that combustion temperature does not significantly affect the crystals phases formed in FA, but does change the relative content of crystals. With an increase in temperature, the relative content of maghemite (γ-Fe₂O₃) and magnetite (Fe₃O₄) decreases, while the relative content of hematite (α-Fe₂O₃) increases. The rising combustion temperature also results in a decreasing trend on saturation magnetization of FA. Furthermore, there is a significant positive correlation between the equivalent content of iron-bearing minerals and the saturation magnetization of FA, which can be applied to remove the particulates from flue gas more efficiently.