<p>Vanadium-bearing slags are one of the most important secondary resources for vanadium extraction and the dominant method is roasting-assisted leaching. The composition, phase, and subsequent roasting conditions of vanadium-bearing slags all affect the overall vanadium extraction efficiency. In this study, the chemical composition and phase formations of the vanadium-bearing slags were regulated by adding CaO and changing the cooling rate during the cooling step. Four different samples, namely LC-WQ, LC-SC, HC-WQ, and HC-SC, obtained after cooling were used for further roasting at different roasting conditions. The samples from cooling to roasting were investigated by both advanced experimental characterizations including SEM-EPMA, XPS, XRD, and thermodynamic analysis. The results of the chemical composition and phase formations regulation during cooling step showed that the V-enriched spinels with a higher stability in the LC-WQ and HC-WQ were (Fe,Mn)V₂O₄, while that with a lower stability in the LC-SC and HC-SC were MnV₂O₄. The roasting results showed that the cooling rate of the hot vanadium-bearing slags affected the roasting effect, where slow cooling obviously enhanced the roasting effect with a relatively higher concentration of V₂O₅ and a relatively lower concentration of impurities in the V-enriched phase due to the lower stability of MnV₂O₄ during roasting. Additionally, a shorter roasting time could maintain a lower concentration of impurities. These findings offer a significant guidance for the optimization of cooling and roasting conditions to enhance the directional transformation of vanadium during the roasting of the vanadium-bearing slags.</p>