Phase transformations during the oxidation of calcium-containing titanium-vanadium slags and their influence on the formation of calcium vanadates

The processes of oxidation of titanium-vanadium slags with the participation of CaO are studied in the temperature range 800–1250°C, and the effect of these processes on the formation of calcium vanadates, which are easily dissolved in weakly acid media, is analyzed. The temperature ranges of the processes related to the oxidation of vanadium-containing phases and the release of vanadium oxides are found. It is shown that anosovite oxides in the temperature range 800–950°C, spinelides oxidize in the range 900–1050°C, and vanadium from the slag phase of calcium aluminotitanate oxidizes at 1050–1250°C. Vanadium-containing perovskite is the most stable phase: it undergoes insignificant structural changes upon roasting. The degree of vanadium extraction from slags reaches 88–92.5% under favorable conditions. The effect of the CaO and FeO contents in a slag on the oxidation of vanadium-containing phases is investigated. A decrease in the FeO content in a slag to 8% or below is shown to negatively affect the oxidation of vanadium in slag phases. At 8.3 or 5.0% FeO in a slag, the maximum degree of vanadium extraction from the slag is 81 or 59%, respectively.