Elemental Distribution Modification Toward Target Calcium Roasting of Vanadium-Bearing Slags

The elemental distributions among various phases in vanadium-bearing slags have been quantified toward high-efficiency separation and extraction by calcium roasting using electron probe X-ray microanalysis. The roles of the roasting conditions were clarified, including roasting temperature, roasting time, and calcium amount. It was found that, with increasing roasting temperature, the V₂O₅ concentration in the target vanadium-enriched phase, predominantly in a form of 2(Ca,Mn)O·V₂O₅, decreased along with more SiO₂ and Fe₂O₃ in this phase; while, with increasing roasting time, the V₂O₅ concentration in the vanadium-enriched phase increased due to a more complete reaction. However, a higher calcium addition induced a lower V₂O₅ concentration in the vanadium-enriched phase and, therefore, a CaO/V₂O₅ weight ratio of 0.6 was employed. In addition to the vanadium-enriched phase, the solubilities, especially V₂O₅ in the SiO₂ and Fe₂O₃ solid solutions under varying roasting conditions, were also identified for a reduction of vanadium loss. Based on those quantitative results, the main principles to target to adjust the elemental distributions among various phases during the calcium roasting of vanadium-bearing slags are discussed toward a low-cost and high-efficiency vanadium extraction.