FactSage simulation, X-ray diffraction (XRD), and scanning electron microscopy (SEM) coupled to energy-dispersive spectroscopy (EDS) analyses were performed to explore the combined influence of SiO₂ and O₂ on the crystallization behavior of modified Ti-bearing blast furnace slag. The results of FactSage simulation showed that an increase in the added amount of SiO₂ was beneficial to the conversion of Ti-bearing minerals into simple titanium oxides. An increase in oxidation time was conducive to the transformation of low-valent titanium oxides to tetravalent titanium oxide. Therefore, Ti components were precipitated only in the form of rutile under the optimal added amount of SiO₂ (40 g) and the optimum oxidation time (126 s). The results of XRD and SEM analyses were well in agreement with the results of FactSage simulation. Moreover, the mechanism of formation of rutile and glassy phases was discussed.

The isothermal precipitation kinetics of rutile crystals was studied to clarify the mechanism for the influence of TiO₂ content on the shape transformation of rutile crystals. The results indicate that the growth index n values were about 2, 3, and 4 when the TiO₂ contents of the raw materials were 27, 37, and 47%, indicating that the precipitation of the rutile crystal had a one-dimensional, two-dimensional, and three-dimensional growth. Thus, the shapes of the rutile crystals were a cuboid, a cube, and a sphere when the TiO₂ contents of the raw materials were 27, 37, and 47%. An increase in the TiO₂ content of raw materials can encourage the transformation of rutile crystals into spheres, which is beneficial to the settling of rutile crystals in molten slag. It realizes the conversion of rutile from a lean ore to a rich ore and avoids subsequent beneficiation processes.

The effects of SiO ₂ and CO ₂ on the crystallization action of Ti-containing mixed molten slag (molten Ti-containing blast furnace slag and molten Ti slag) were discussed by thermodynamic calculation and specific experiments. The results of thermodynamic calculation indicated that the increase of SiO ₂ addition mass and CO ₂ oxidation time can promote the transformation of anosovite and sphene to rutile. The experiment results showed that the phase composition of modification slag was only rutile under the SiO ₂ addition mass of 110 g and the CO ₂ oxidation time of 180 s. Moreover, the formation theory of rutile was investigated. Using CO ₂ as an oxidizing gas can not only prepare rutile but also achieve carbon neutrality, which is a clean preparation method.