Carbothermal reduction of Si-Al-Fe-Ca quaternary system in a high-silica coal

During coal pyrolysis and gasification, the minerals in coal undergo various transformations, which affects coal conversion and characteristics of coal ash obviously. Carbothermal reduction of Si-Al-Fe-Ca quaternary system in high-silica coal under different temperature was investigated. Composition of products obtained was analyzed by X-ray diffraction (XRD) and field emission scanning electron microscope-energy dispersive spectrometer (FESEM-EDS) technology. The results show that Fe₂O₃ plays a positive role in carbothermal reaction of silicon-bearing minerals, which could effectively improve activity of Si. On the contrary, CaO reacts with Al₂O₃ and SiO₂ to form dense Ca-Al-Si eutectic, mainly CaAl₂Si₂O₈, at lower temperature, covering surface of the reactant, which hinders the carbothermal reaction of silicon-containing minerals. With increasing temperature, CaAl₂Si₂O₈ reacts with graphite to generate SiC, CaAl₄O₇ and CaSiO₃. The related thermodynamic calculations are in accordance with the experiment results.