Transformation of Vanadium-Bearing Titanomagnetite Concentrate in Additive-Free Roasting and Alkaline-Pressure Leaching for Extracting Vanadium (V)

With a view to satisfying the requirements of environmental protest and efficient usage of resources, a novel process for efficiently extracting vanadium (V), titanium (Ti), and iron (Fe) from vanadium-bearing titanomagnetite concentrate was developed. In the new process, vanadium is pre-extracted by additive-free roasting under the air atmosphere and alkaline leaching technologies. In this paper, transformation of vanadium-bearing titanomagnetite concentrate in the roasting is investigated based on thermodynamic analyses and experimental discussion. Thermodynamic analyses show that oxidation of V(III) into V(V) would happen in the roasting experiment over the range of 327–1327 °C and vanadium-iron spinel phase (FeV2O4) can be oxidized more easily than magnetite (Fe3O4) when the temperature is higher than 861 °C. Experimental results show that some compounds (V2O5, Fe2Al4Si5O18, and Fe2SiO4) with low melting temperature were obtained by solid reactions at low temperature and melted as a binding phase at elevated temperature. Liquids were generated due to some chemical reactions or phase transformation reaction (Fe2V2O4(s) → Fe2O3(s) + liquid) at elevated temperature. Main phases of Fe2O3 and Fe2TiO5 are connected and sintered with the binding phases of the compounds with low melting temperature or the mixtures with low liquidus temperature. In addition, higher roasting temperature leads to higher vanadium leaching efficiency over the range of 800–1200 °C. However, over-burning would happen at 1250 °C, some of vanadium oxide was wrapped by silicate network, and the conversion of V(III) into V(V) was prevented from occurring. Therefore, the vanadium leaching efficiency decreased from 59.1% (Troa. = 1200 °C) to 57% (Troa. = 1250 °C).