Abstract:A novel process of vanadium extraction from vanadium slag in its molten state was conducted at the laboratory scale by oxidation with pure oxygen in the presence of CaO. The effect of mass ratio of CaO to V₂O₅ on the recovery of vanadium was studied. The sintered samples were leached by H₂SO₄ solution and characterized by XRD, XPS, SEM and EDS techniques. Compared with the roasting process, the energy saving effect of the proposed process was also discussed. The results showed that vanadium-rich phases were formed and vanadium mainly existed in the forms of CaV₂O₅ and Ca₂V₂O₇. The formation mechanism of calcium vanadates in the molten vanadium bearing slag was explained. The XRD and XPS results implied that there was a limit to the oxidation reaction of V(IV) to V(V) under the high temperatures even though oxygen-supply was sufficient. An increase in the CaO content led to an increase in the formation of Ca₂V₂O₇. About 90% of the vanadium recovery was obtained under optimal experiment conditions (mass ratio of CaO to V₂O₅ of 0.6, particle size 120 to 150 μm, leaching temperature 90 °C, leaching time 2 h, H₂SO₄ concentration 20%, liquid to solid ratio 5:1 mL/g, stirring speed 500 r/min). The energy of 1.85×10⁶ kJ could be saved in every 1000 kg of vanadium bearing slag using the proposed process from the theoretical calculation results. Recovery of vanadium from the molten vanadium bearing slag and utilisation of its heat energy are important not only for saving metal resources, but also for energy saving and emission reduction.

Key words: molten vanadium bearing slag; CaO; oxidation; acid leaching; vanadium recovery; energy saving effect