Effect of microwave heating on the pressure leaching of vanadium from converter slag

Abstract

In this paper, a comparison is made between the leaching associated with microwave heating (MHL) and electric heating (EHL) of converter vanadium slag in an autoclave under an oxygen pressure of 0.4 MPa. The comparative study of the leaching processes showed that the vanadium leaching efficiency reached 46% in 20 min using EHL, whereas it reached 96% under the same condition when MHL was used. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses of MHL residue showed that decomposition of the spinel phase in the converter vanadium slag can be accelerated through this process. In addition, MHL can reduce the granularity and make the surface of the particles more porous. In general, using MHL is more effective than EHL, for the leaching of converter vanadium slag in pressure leaching process. Through kinetic studies of MHL and EHL, the activation energies of vanadium leaching were determined to be 14.8 and 40.5 kJ/mol, respectively. The reaction rate depends on acid concentration as well as oxygen partial pressure. The order of reaction with respect to H2SO4 concentration was found to be 0.99 for MHL and 2.21 for EHL. The order of reaction with respect to the oxygen partial pressure was found to be 0.51 and 0.65 for MHL and EHL, respectively. The kinetic equations are derived and reported for MHL and EHL processes.