A Study on Vanadium Extraction from Fe-V-P Melts Derived from Primary and Secondary Sources

Sammanfattning: Vanadium extraction methods were developed for iron-vanadium-phosphorus (Fe-V-P) melts derived from processing of V-bearing titanomagnetites and steel slags. Studies on phase relationships of V slags were carried out to provide important understanding of the extraction processes. Phase relationship in vanadiferous slag was investigated experimentally at 1573K, 1673K and 1773K, for the compositional range of 0-6mass% Al2O3, 1-5mass% CaO, 10-17mass% SiO2, with MnO and V2O3 fixed at 5.5mass% and 30mass%, balanced with FeO. The slags were found to be solid-liquid mixtures, of liquid, spinel and in some cases free silica. Alumina was identified as the preferred additive to prohibit precipitation of free silica. A method for V extraction to vanadiferous slag was developed based on Fe-V(2mass%)-P(0.1mass%) melts at 1677K using a semi-industrial scale BOF. Oxidation was carried out with an oxygen enriched air jet and iron ore pellets. The complete dissolution of pellets was achieved by deliberately creating good stirring conditions utilising high momentary decarburisation rates. The P distribution to the slag was low when good stirring conditions was obtained. Phase relationship in Al2O3-CaO(25-35mass%)-SiO2-VOx slag was investigated experimentally at an oxygen partial pressure of 9.37•10-11atm and 1873K. The maximum solubility of V-oxide in the slag was 9-10mass% V2O3. Two solid phases were found, a solid solution of Al2O3 in V2O3 (karelianite) and hibonite with fractionation of V into the crystal structure. V extraction experiments to Al2O3-CaO-SiO2 based slags were carried out in 150kg scale by blowing CO2 gas into the metal bath consisting mainly of 1-10mass% V and 1mass% P. At these conditions, oxidation of V was favoured over Fe. Up to 10-13mass% V2O3 could be dissolved in the slag before a viscous slag saturated in V-oxide was observed. The phosphate capacity in the slag was low and as a result this slag could at once be subjected to a final reduction step for production of ferrovanadium with 40-50mass% V.