Dissolution kinetics of calcium vanadates in sulfuric 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 degrees C. Under the conditions with solid/liquid ratio of 1:150 g mL(-1), temperature range of 30 to 70 degrees 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 center dot 0.5H(2)O, 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. (c) 2020 Society of Chemical Industry