Effect of calcification roasting process on vanadium oxidation and extraction from vanadium titanomagnetite pellets via sulfuric acid Leaching: Mechanism and enhancement

[Display omitted] •The vanadium leaching characteristic of different roasted pellets in sulfuric acid leaching process was studied.•The low vanadium leaching rate attributes to dense pellet structure and insufficient vanadium oxidation.•The mechanism of core–shell structure formation and vanadium oxidation in preheating stage were revealed.•An optimized regime to produce roasted pellets with high vanadium leaching rate was proposed. Calcification roasting-sulfuric acid leaching is widely regarded as a clean and efficient alternative to sodium roasting-water leaching for directly vanadium extraction, and has been used industrially for vanadium extraction from vanadium slag. Nevertheless, limited research has been conducted on vanadium extraction from vanadium titanomagnetite (VTM). This knowledge gap contributes to suboptimal vanadium leaching rate and elevated iron leaching rate in the extraction process. This article systematically studied the effect of calcification roasting on vanadium oxidation and sulfuric acid leaching extraction vanadium from VTM pellets. The results reveal that the diminished vanadium leaching rate primarily stems from the dense pore structure of the roasted pellets and inadequate vanadium oxidation during calcification roasting process. Additionally, the formation of the core–shell structure during the preheating stage directly contributes to insufficient vanadium oxidation. Lastly, a thorough analysis of the core–shell structure formation mechanism was conducted, leading to the identification of the optimal calcification roasting regime. With the conditions of preheating at 900 °C for 25 min followed by roasting at 1150 °C for 15 min, the complete elimination of the core–shell structure was achieved, and the average valence of vanadium was 4.77 in roasted pellets. Finally, the vanadium leaching rate reached 72.78 % by sulfuric acid leaching.