Review of leaching, separation and recovery of vanadium from roasted products of vanadium slag

Vanadium is a strategic metal with extensive applications in steel production and emerging energy technologies. In vanadium metallurgy, the pivotal steps encompass the roasting of vanadium slag, leaching, and precipitation of vanadium. The roasting process, which involves elements such as sodium, calcium, manganese, and magnesium, facilitates the phase transformation and extraction of vanadium. Considering the phase separation behavior of vanadium-enriched phases (MV2O6, MV2O7, or MV2O8) in various leaching media, including acid, alkali, and water, the wet decomposition of these phases can be classified into two categories: (i) those yielding insoluble M and soluble V and (ii) those resulting in both soluble M and V. Thermodynamically, the reaction equilibrium constants and temperature profiles of the vanadium-rich phases in various acid and alkaline decomposition processes were calculated and juxtaposed. This review also reports the limiting factors of leaching kinetics of vanadium-rich phases in acid and alkaline decomposition processes, particularly the separation and transformation of vanadium-rich phases in calcified vanadium slag. The vanadium precipitation process encompasses a detailed elaboration of the mechanisms behind the precipitation of hydrolyzed vanadium product and ammonium‑vanadium product. Finally, the vanadium slag roasting-leaching‑vanadium precipitation process was evaluated from four aspects: principle, laboratory and plant practice, resource and environment, and cost and benefit.