Vanadium Extraction from Molten Vanadium Slag with High Ca and P Contents by Direct Oxidation-acid Leaching Method

Abstract

A novel method of extracting vanadium from molten vanadium slag was developed to process vanadium slag with high Ca and P contents. The mineral phases of the clinker obtained after oxidizing the molten vanadium slag with high Ca and P contents (10.71 wt. % V2O3, 19.20 wt. % CaO, 1.03 wt. % P2O5) were analyzed by X-ray diffraction (XRD) to fully comprehend the compositions of the clinker. The leaching conditions of extracting vanadium from the clinker and the kinetics during the leaching process were also investigated in this paper in order to obtain a better leaching rate of vanadium. The results indicate that most of V in the clinker exists in the form of calcium orthovanadate (Ca3V2O8), and the rest turns into the vanadate with low valence state of V. Silicates mainly include pyroxene (Ca(Mg/Fe/Ca)Si2O6), calcium silicoaluminate (CaAl2Si2O8) and calcium orthosilicate (Ca2SiO4). P exists in the form of calcium phosphate (Ca3(PO4)2). The leaching rate of vanadium can reach 95% under the conditions: sulfuric acid concentration of 15%, liquid to solid ratio of 5:1 mL/g, leaching temperature of 90℃, leaching time of 40 min, stirring rate of 240 r/min. Kinetic analysis results show that the acid leaching process of the clinker can be well interpreted by the unreacted shrinking core model under internal diffusion control, and the apparent activation energy is 8.36 kJ/mol. KEYWORD: Molten vanadium slag with high Ca and P contents; vanadium extraction; phase; leaching; kinetics