Microwave roasting with size grading based on the influence of carbon on vanadium extraction from stone coal via microwave roasting-acid leaching

Abstract

Carbon in stone coal has a double-edged function in the microwave roasting-acid leaching of stone coal; it provides stone coal with good heating characteristics, but it hinders the oxidization of vanadium and causes the sintering phenomenon. Adjustment of the particle size and microwave input power is performed to use the advantages of carbon and avoid its disadvantages. Fine particles are not suitable for direct microwave roasting due to their low heating rate, low final temperature and serious sintering phenomenon. However, for coarse particles, a high microwave input power causes more carbon to be retained in the stone coal in the heating stage to obtain a high heating rate and final temperature. These carbon particles are removed in the temperature holding stage because of the unique cracks and pores of coarse particles under the high microwave input power condition. Comprehensively considering the heating characteristics and vanadium leaching efficiency of stone coal, a 1–3 mm particle size and 1200–1800 W microwave input power are suitable for the microwave roasting of stone coal. The vanadium leaching efficiency of the roasted sample in this condition is 14% higher than the roasted sample without size grading.