Role of Minor Elements on Phase and Composition Evolutions of Iron–Vanadium Spinels Upon Calcium Roasting

Vanadium, an extremely important metal element, is dominantly produced from the roasting–leaching process of vanadium–bearing slags, with the roasting process involving a conversion of vanadium–containing phases including iron–vanadium spinels and liquid phase into soluble vanadate. It is difficult to extract vanadium from iron–vanadium spinels due to their ultrastabilities and complex compositions. The presence of minor elements affects the stability of iron–vanadium spinels upon roasting as well as the further leaching process. In this study, the roles of various minor elements on phase and composition evolutions of iron–vanadium spinels upon calcium roasting were investigated by both advanced experimental characterizations (EPMA, XRD and XPS) and thermodynamic calculation using FactSage 8.3. The results first showed that the iron–vanadium spinel underwent a phase transition to form two distinct phases, namely a V-enriched phase and a Fe 2 O 3 solid solution. The presence of Cr 2 O 3 , MnO and MgO did not produce a new phase, but affected the compositions of the two phases formed. However, new phases were generated in the presence of TiO 2 and Al 2 O 3 , namely a Fe 2 TiO 5 phase and an Al-enriched phase, respectively. Moreover, a higher roasting temperature enhanced the partitioning of TiO 2 , Al 2 O 3 and Cr 2 O 3 from the V-enriched phase to the Fe 2 O 3 solid solution, which promoted the enrichment of V 2 O 5 into the V-enriched phase. A lower roasting temperature promoted the formation of manganese vanadate and magnesium vanadate for further leaching process. These findings offer a guidance for optimizing the roasting conditions for maximum vanadium extraction from iron–vanadium spinels.