Enhancing vanadium extraction from shale by microwave irradiation for VBS grindability improvement: Hot spots and thermal stress

Abstract

The effect of microwave pretreatment in improving the grindability of vanadium shale was investigated by experimental and COMSOL simulation methods. The microwave pretreatment led to shortening of the grinding time by 33.33 %, an increase in the vanadium recovery by 16.42 %, and a reduction in the grinding power consumption by 31.06 %. COMSOL simulation results demonstrated that when vanadium shale particles contact each other, electric field polarization occurred, producing a high-temperature hot spot of 2000–5000 °C and a temperature difference of 500–1500 °C between the hot spot and other areas of the vanadium shale particles. The large temperature difference generated a thermal stress of 0.98–1.86 GPa on the particles, thus damaging the mineral structure and increasing their grindability. Simultaneously, owing to variation in the dielectric properties, the heating rates of different mineral components in a single particle were different, leading to a temperature difference of 800–2000 °C and a thermal stress of 4.87–78.5 GPa, which cracked the mineral components. These results set the stage for the practical application of microwave-assisted grinding for the extraction of vanadium from shale.