Vanadium Extraction Mechanism in the Sodium Sulfate Roasting Process

Vanadium redox-flow batteries (VRFBs) have recently gained attention because they resolve the intermittent and uncontrollable characteristics of renewable energy sources. Consequently, the increasing demand for VRFBs will increase the demand for V. This study investigated a roasting process for V extraction from Korean vanadiferous titanomagnetite ores. The optimum roasting conditions and mechanisms were studied for the combination of Na₂SO₄ roasting and water-leaching processes. The effects of roasting temperature and mixing ratio of Na₂SO₄ were investigated, revealing the more prominent effect of roasting temperature compared with that Na₂SO₄ mixing ratio. The leaching efficiencies for other impurities were investigated by varying the Na₂SO₄ mixing ratio and roasting temperature. The X-ray-diffraction-analysis results indicated no notable phase change during the roasting process. Moreover, the hot-stage-microscope-analysis results demonstrated that the roasting temperature was higher than the softening temperature, implying no reaction between the liquidus and solid ore. The formation of sulfuric gas was verified by thermodynamic calculations, differential scanning calorimetry, and evolved gas analysis. The reaction of V₂O₅, SO₃, and SO₄ was expected to form a water-soluble VOSO₄ phase. The gas–solid reaction in the Na₂SO₄ roasting process resulted in high selectivity and high leaching efficiency for V.