A new approach for direct leaching of vanadium from LD converter slag

• Direct acid leaching was carried out in comparison to using alkaline roasting in other studies.
• Vanadium extraction from slag is important from environmental point of view.
• Optimization of parameters was done by RSM to maximize the vanadium recovery.
• Box–Cox power transformation was applied to normal the data and derive the best model.
• RSM data and shrinking core model was used to describe the kinetics of the process.

Direct acid leaching process was used to recover vanadium from Linz Donawitz (LD) converter slag. The leaching parameters were studied to obtain conditions that vanadium can be leached without using a pyro metallurgical step since the roasting process requires high energy consumption. The independent leaching factors investigated were liquid to solid ratio (L/S) (10–20 mL/g), temperature (40–70 °C), acid concentration (1.5–3.0 M), stirring rate (500–700 rpm) and time (60–120 min). Response surface methodology (RSM) was used to optimize the process parameters. The most influencing parameter was found to be temperature and the less effective was acid concentration. It was shown that the optimum condition for recovery of ca. 98% can be obtained at L/S ratio of 17.52, temperature of 70 °C, acid concentration of 2.82 M and leaching time of 120 min. The shrinking core model (SCM) was used to describe the kinetics of the slag acid leaching. A constrained multi-linear regression analysis using the least square technique was used to determine the rate controlling mechanism. This technique takes into account all three possible rate controlling mechanisms for leaching processes (i.e., chemical reaction, diffusion through product layer and liquid film mass transfer) simultaneously. Results of kinetic study by this method shown that the rate of the leaching is controlled by chemical reaction at low temperature whereas it is controlled by diffusion through the solid product layer in a long time, i.e., after 60 min from the start of the leaching process, at high temperature.