Specific Features of the Oxidizing Roasting of Vanadium Slags with a CaCO3 Additive for the Transformation of Vanadium into Soluble Forms

The results of studying the oxidizing roasting of vanadium slags involving CaO for the transformation of vanadium into soluble forms are discussed. Three samples of the vanadium slag are tested using CaCO 3 as a reactive sample. The sequence of processes that occur during slag oxidation and the temperature range of the intense interaction of CaCO 3 and vanadium oxides with the formation of calcium vanadates are determined. The effect of the roasting temperature in a range of 775–975°C and the lime module (weight ratio CaO tot /V 2 O 5 ) of the charge on the completeness of access to vanadium and parameters of vanadium recovery during the sulfuric acid leaching of the cinder at pH 2.5 followed by cake washing on a filter with a solution of 3% H 2 SO 4 is studied in detail. The selective interaction of CaCO 3 with vanadium oxides is found to occur in a temperature range of 800–875°C to form calcium vanadates highly soluble in weakly acidic solutions. The degree of recovery of vanadium from a slag reaches 90–95% at the lime module of the charge of about 0.35. In the indicated temperature range, an increase in the amount of the CaCO 3 additive exerts a very weak effect on the results of vanadium recovery. A further increase in the temperature leads to the violation of the selectivity of formation of calcium vanadates due to the interaction of CaCO 3 with free SiO 2 and other slag components. This exerts a negative effect on the results of vanadium recovery during the sulfuric acid leaching of the cinder.