A green and efficient route for simultaneous recovery of low valence of vanadium and chromium, titanium and iron from vanadium slag

Traditional methods to recover vanadium from vanadium slag by oxidizing V(III) in slag to V(V) at above 800 °C, result in discharge of significant amount of residue containing Cr, Ti, Fe, and wastewater containing highly toxic V(V) and Cr(VI). Then V2O5 was reduced to low valence vanadium (LVV) for applications, such as vanadium flow battery, vanadium alloy. It is necessary to effectively utilize vanadium slag for the sustainable development of vanadium metallurgy industry. In present work, a clean method was developed to directly recover LVV from vanadium slag and valuable elements such as Cr, Ti, Fe were retrieved simultaneously, without producing V(V) and Cr(VI) bearing hazardous wastewater and residue. Vanadium slag was roasted with sulfuric acid under low temperature and then leached with water, while the volatile roasting tail gas was stripped with water. During the roasting, metal ions, V(III), Cr(III), Fe(II), Ti(IV) converted to their corresponding sulfates subsequently leached out into the leachate. Almost all of vanadium and chromium retained in the form of low valence during the process. By optimizing the roasting-leaching conditions, the best recovery of V, Cr, Ti, Fe reached 96.20%, 94.39%, 90.60%, 90.13%, respectively. This low temperature roasting process provides a new route to recover useful elements from vanadium slag without discharging wastes, it is an environmentally benign and clean technology.