Comparison of microwave and conventional blank roasting and of their effects on vanadium oxidation in stone coal

The oxidation behaviour of vanadium in stone coal and its mechanisms in conventional blank roasting (CBR) and microwave blank roasting (MBR) are investigated. In both roasting methods, vanadium oxidation rates are increased and the controlling step of vanadium oxidation reaction is changed from chemical control to internal diffusion control with increasing temperature. Compared to CBR, MBR was more efficient in vanadium oxidation under same roasting conditions. The change of controlling step occurred at the temperature range of 500–600 °C and 600–700 °C for MBR and CBR, respectively. This oxidation behaviour of vanadium was mainly dependent on the reducing materials in stone coal and their reaction characteristics. Due to efficient and the lower temperatures of mineral transformations (including reaction of reducing materials and deformation of muscovite structure), MBR had higher vanadium oxidation efficiency and lower temperature range of changing the controlling step than CBR.