VanadiumVanadium is widely used in metallurgy, energy, aerospace, and other fields due to its positive effect on the properties of materials. Roasting of vanadium-bearing slags involves the destruction of iron-vanadium spinelsIron-vanadium spinels and the formation of soluble vanadate, while the presence of minor elementsMinor elements affects the stability of iron-vanadium spinels upon roasting. In this study, the phase evolution of iron-vanadium spinels and the roles of minor elementsMinor elements upon calcium roastingCalcium roasting were investigated systematically by thermodynamic calculations. The results showed that the iron-vanadium spinel underwent a phase transitionPhase transition to form two main distinct phases, namely, a Ca2V2O7 and a M2O3 solid solution, with an extremely small amount of Ca3V2O8 formed. Meanwhile, the formation of vanadate followed a two-step reaction, i.e., the first reaction between CaO and V2O5 to form CaV2O6, and the second reaction between residual CaO and CaV2O6 to form Ca2V2O7. A higher roasting temperature over 850 °C effectively inhibited the formation of CaCrO4 in the presence of Cr2O3. Conversely, a lower roasting temperature less than 850 °C prevented the formations of slag-liquid phase and CaTiO3 in the presence of TiO2. These findings provided a theoretical guidance for destroying iron-vanadium spinels’Iron-vanadium spinels structures for vanadiumVanadium extractionExtraction from vanadium-bearing slags.