Leaching kinetics of vanadium from calcification roasting converter vanadium slag in acidic medium

Acid leaching technology was introduced to leach out vanadium from calcification roasting converter vanadium slag. The effects of solid-to-liquid ratio, concentration of acid solution, reaction temperature, reaction time and particle size on leaching efficiency of vanadium were examined. A new defined parameter, encapsulation efficiency, was applied to describe the leachate loss in the filtration process. Results showed that the leaching efficiency of vanadium and encapsulation efficiency had opposite change trends. Under the optimal conditions (solid-to-liquid ratio of 50 g slag/200 mL acid solution, concentration of 0.25 mol/L H2SO4, reaction temperature of 323 K, reaction time of 60 min, particle size under 75 pm and stirring rate of 500 rpm), the leaching efficiency and encapsulation were 91% and 6%, respectively. The calcium sulphate formed during the leaching process would absorb on the surface of slag and block the pore channel between the particles, and it had negative effect on filtration process. The shrinking core model expressed by [(1-eta)-1/3 - 1] + 1/3ln (1-eta) = kt was used to describe the leaching kinetics of vanadium in sulphur acid solutions. And the apparent activation energy of vanadium extraction was determined to be 12.45 kJ/mol, which indicated that the leaching process was controlled mainly diffusion of solution through surface layer.