Photovoltaic cutting waste (PCW) is a promising pre-reductant for the enrichment of vanadium and the removal of iron from vanadium slag. However, the dissolution of SiO2 contained in PCW affects the kinetic conditions and composition of vanadium slag during silicothermic reduction. In the present work, the dissolution behavior of SiO2 was investigated from 1823 K to 1873 K under FeO concentrations of 37.0 to 11.8 wt pct in FeO–SiO2–V2O3–CaO–MnO–Cr2O3–TiO2 system, that is, the pre-reduction process of vanadium slag. The results show that SiO2 dissolution in vanadium slag with different FeO contents is a pure dissolution and diffusion process and that no compact product or residual layer is generated. The rate-controlling step of SiO2 dissolution is the diffusion process, and the main driving force of SiO2 dissolution is the concentration difference between the slag and the interface of spherical SiO2 particles. The chemical reaction rate constant and diffusion coefficient of SiO2 at 1873 K range from 1.60 × 10−5 to 6.78 × 10−6 m/s and 3.49 × 10−8 to 1.52 × 10−8 m2/s, respectively. The dissolution activation energy of SiO2 increases from approximately 270.82 to 341.26 kJ/mol.
