Dissolution kinetics of calcium vanadates in sulphuric acid: A fundamental study for the vanadium extraction process

BACKGROUND: The dissolution behavior of calcium vanadates is vital for the vanadium extraction process, as well as the utilization of calcium vanadates based function materials. Therefore, the dissolution kinetics study of calcium vanadates (CaV₂O₆, Ca₂V₂O₇, and Ca₃V₂O₈) in sulfuric acid are presented. The effects of stirring speed, solid/liquid ratio, pH, and temperature on the dissolution rate of calcium vanadates were determined. The mineralogical and microstructure of the residue after dissolution are also performed. RESULTS: The results showed that the dissolution rate of calcium vanadates significantly increased with the increase of temperature from 30 to 70 °C. Under the conditions with solid/liquid ratio of 1:150 g mL⁻¹, temperature range of 30 to 70 °C, and pH of 4, the rate of Ca₃V₂O₈ dissolution is the fastest, followed by Ca₂V₂O₇ and CaV₂O₆, especially at low temperature. CONCLUSION: The mineralogical analyses results showed that the main products for the dissolution of Ca₂V₂O₇ and Ca₃V₂O₈ are needle‐like CaSO₄·0.5H₂O, whereas for CaV₂O₆ are undissolved CaV₂O₆ and hydrolyzed V₂O₅. The dissolution kinetics indicate that the dissolution of CaV₂O₆ follows second‐order pseudo‐homogeneous model, whilst Ca₂V₂O₇ and Ca₃V₂O₈ follow the diffusion through the product or ash layer model. The apparent activation energies for the dissolution of CaV₂O₆, Ca₂V₂O₇, and Ca₃V₂O₈ were determined as 46.44, 38.72, and 23.50 kJ mol⁻¹, respectively. © 2020 Society of Chemical Industry