Steel slag is a by-product of the steelmaking process, and its yield are about 15% of steel production. The recycling of steel slag is one of the key issues that steel companies need to solve. With its composition characteristics, a small amount of steel slag has been used in metallurgy, engineering backfilling, road construction, sewage treatment and preparation of glass-ceramics. Besides, the incorporation of steel slag into cement to prepare steel slag cement is an effective and efficient way to use. However, the existence of wustite phase, which is difficult to separate in steel slag, limits its application in the field of building materials. The oxidative modification can transform the wustite in the steel slag to the ferromagnetic magnetite, and there is no greenhouse gas emission during the upgrading process. The oxidative upgrading process of CaO-SiO2-FeO system steel slag has been studied in the past, but the CaO-SiO2-FeO-MgO system which is closer to the actual steel slag composition has relatively less research. In addition, the nucleation and growth mechanism of the magnesioferrite spinel in the oxidation process still needs further exploration. This work refers to the actual composition of the converter steel slag of a steel plant, and the solidification of the steel slag is carried out by calcination under an oxidizing atmosphere (Synthetic air). X-ray diffraction (XRD) analysis, backscattered scanning electron microscopy (BEI-SEM) and X-ray energy dispersive spectroscopy (EDS) were used to analyze the mineral phase products of CaO-SiO2-FeO-MgO system synthesis slag, combined with thermodynamics. The calculation software (FactSage 7.0) was used to study the thermodynamic trends of the main product phase formation. In addition, simultaneous thermal analyzer (TG-DSC) was carried out to study the kinetic mechanism of the formation of magnesioferrite spinel, and the corresponding kinetic model was also established. The results show that with the solid phase reforming temperature rising from 1 000℃ to 1 150℃, the yield of magnesioferrite spinel increases first and then decreases, and reaches a maximum value when the upgrading temperature is 1 100℃. The magnesioferrite spinel changes in the (311) crystal plane corresponding to the diffraction angle as follows: 2θ=35.44° (1 000℃)→2θ=35.49° (1 050℃)→2θ=35.49° (1 100℃)→2θ=35.43°(1 150℃). With the oxidation temperature increa-sing from 1 000℃ to 1 150℃, the weight gain of the 600 s oxidation system increases from 351.273×10-3 mg to 499.077×10-3 mg, and the weight gain of the 1 800 s oxidation system increases from 364.390×10-3 mg to 535.341×10-3 mg. According to the kinetic mechanism, the solid phase modification process of CaO-SiO2-FeO-MgO quaternary system can be divided into three stages: initial stage, chemical reaction phase and diffusion phase. The theoretically calculated kinetic model is well consistent with the thermogravimetric change trend of the TG experimental results. The kine-tic model can accurately describe the nucleation and growth process of the magnesium iron spinel during the solid phase reforming of steel slag. © 2019, Materials Review Magazine. All right reserved.
