Vanadium : leaching and solvent extraction

The fundamental understanding of vanadium hydrometallurgy was developed in three phases: vanadium (V) leaching, vanadium (III) oxidative leaching, and solvent extraction of vanadium (V&IV). In the first section, V₂O₅ leaching was studied in three steps. First, vanadium leaching and solubility of VO₂⁺ at different pH’s and temperatures were investigated in sulfuric acid. Secondly, the kinetics of vanadium leaching in pH 5 and pH 8 solutions, and the reductive leaching of vanadium pentoxide using sodium sulfite were studied. It was shown that the kinetics of acid leaching is rapid but suffers from low solubility of VO₂⁺ in solution. Thirdly, the shrinking sphere model was employed to analyze the kinetics of reductive leaching. In the second step, V₂O₃ oxidative leaching was studied from 30°C to 90°C in sulfuric acid. This study has also been done in three different sections. First, the kinetics of oxidative leaching using oxygen was investigated. It was shown that this oxidative leaching is chemical reaction rate controlled with an activation energy of 69 kJ/mol. In the next step, it was shown that the presence of ferric enhanced kinetics significantly. Finally, oxidative leaching using a constant ferric-ferrous ratio from 1 to 300 was studied. The addition of KMnO₄ solution to the leach reactor was found to be a suitable oxidant for controlling solution potential. The oxidation rate using the constant ferric-ferrous ratio was very sensitive to temperature, with a large activation energy (38 kJ/mol) and the rate was proportional to the Fe(III)/Fe(II) concentration to the power of 0.47. In the third part, purification of synthetic vanadium-containing solutions using the solvent extraction technique was investigated. Various solvent extractants have been tested for vanadium recovery from acid leachates. One of the biggest problems for purification of the vanadium solution is iron separation. Therefore, this research assesses selectivity of vanadium over iron. The extraction of vanadium (V&IV), iron (III&II) with phosphinic acid (CYANEX 272), phosphonic acid (IONQUEST 801), phosphoric acid (D2EHPA) and phosphine oxide (CYANEX 923) extractants is reported. In addition, the extraction reactions for vanadium (V) and (IV) extraction using CYANEX 923 and D2EHPA were also studied.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat