Phase Transformation and Dissolution Behavior of Pyrite in the Roasting-Sulfuric Acid Leaching Process of Vanadium-Bearing Stone Coal

The selective leaching of vanadium and iron has been one of the main concerns in the field of vanadium recovery from stone coal, but the source of iron ions and their release characteristics were still unclear. In this work, the dissolution of pyrite and its roasted product, under conditions in accordance with the vanadium leaching process from stone coal by blank roasting-acid leaching, were studied. The results indicated that the leaching performances of V and Fe in stone coal were significantly correlated, with both depending on the leaching parameters of the H2SO4 concentration, the leaching temperature, the leaching time and the solid to liquid ratio. Under air conditions, with a roasting temperature of 700 °C, the roasted product of pyrite was hematite. Approximately 45% of the roasted product dissolved at its optimal leaching condition—35% higher than that of the raw pyrite. However, any further improvement was difficult, due to the difference in texture between its outer sphere and inner core. The results demonstrated that the roasting treatment led to a significant increase in the release of iron ions during the vanadium leaching process. The pre-removal of pyrite from the raw ore was necessary to reduce the concentration of iron ions in the leachate.