Study on the carbothermal reduction process of SiO2-Fe2O3-Al2O3-CaO system in coal gasification fine slag

Abstract

The Si-Fe-Al-Ca alloy preparation from coal gasification fine slag (CGFS) by high-temperature carbothermal reduction provides an effective way to realize the high-value utilization of solid waste, solve environmental problems caused by waste accumulation, and reduce the production cost of ferrosilicon alloys. However, the carbothermal reduction mechanism of the complex quaternary SiO₂-Fe₂O₃-Al₂O₃-CaO system in CGFS is still unclear, which is difficult to explain by existing theories. In this study, CGFS was used with petroleum coke as an additional reducing agent to prepare Si-Fe-Al-Ca alloys by high-temperature carbothermal reduction, and the intermediate state of the smelting process was observed by slice analysis of the rapidly cooled product. The carbothermal reduction process and mechanism of the SiO₂-Fe₂O₃-Al₂O₃-CaO quaternary oxide system were discussed in depth in conjunction with thermodynamic calculations by FactSage software. The results show that the carbothermal reduction process of the SiO₂-Fe₂O₃-Al₂O₃-CaO system can be divided into three stages, the first stage of rapid generation FeSi and SiC; the second stage of the reaction of a small amount of Al₄C₃ and CaC₂ with SiO₂; the third stage of the reaction of CaO, Al₂O₃ with SiC. In the third stage, the reaction of SiC with CaO and Al₂O₃ is the main reaction to generate Ca and Al. The mass-generated SiC whiskers block the C particles from oxides causing the difficulty of smelting CGFS. The complexity of the phase composition of the alloy is due to the generation of Fe-Si alloy and Si-Al-Ca alloy at different stages of the reaction, which alternately fell into the alloy melt pool with gravity.