Effect of microwave irradiation and conventional calcification roasting with calcium hydroxide on the extraction of vanadium and chromium from high-chromium vanadium slag

A novel high-efficiency method based on microwave irradiation roasting has been proposed to extract valuable metals from minerals. In this study, we employed microwave irradiation and conventional roasting for extracting vanadium and chromium from high-chromium vanadium slag (HCVS) with the additive calcium hydroxide. Differential thermal-thermogravimetry analysis (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy analysis (SEM-EDS), particle size distribution analysis and chemical analyses were used for the characterization and analysis to explain the mechanism of the roasting process. The results shown that roasting temperature, the m(CaO)/m(V2O5) ratio, and roasting time roasted by microwave irradiation and muffle furnace had significantly effect on extraction ratio of vanadium while the effect on the extraction ratio of chromium was relatively small. For the same roasting temperature, the degree of oxidation of HCVS roasted by microwave irradiation was higher than that roasted by muffle furnace. When the m(CaO)/m (V2O5) ratio is low, Mn4V2O9 and CaV2O6 are formed; with the m(CaO)/m(V2O5) ratio increased, Mn4V2O9 and CaV2O6 gradually converted to CaV2O2, and CaCrO3 is formed. Microwave irradiation decreased the particles size and shortened the roasting time. The optimal roasting conditions was determined to be: roasting temperature of 850 degrees C, m(CaO)/(V2O5) ratio of 0.95, and roasting time of 1.5 h. The maximum extraction ratio of vanadium and chromium roasted by microwave irradiation and muffle furnace were 98.29%, 4.32% and 85.36%, 2.48%, respectively.