Metastable phase reconstruction for enhanced vanadium extraction via cerium oxide-catalyzed low-sodium roasting

Abstract

Excessive Na₂CO₃ usage in current vanadium extraction processes from vanadium slags leads to substantial CO₂ emissions and the accumulation of toxic residues and wastewater, posing serious environmental hazards. In response to the Paris Agreement and national “dual carbon” goals, this study explores a sustainable, low-carbon vanadium extraction process by introducing a novel cerium oxide (CeO₂)-catalyzed sodium roasting method. To address the challenge of limited knowledge on phase transitions in vanadium slag roasting, this study employs transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) to confirm the presence of metastable phases in the slag and to analyze CeO₂'s catalytic effects on phase transformation. The results reveal that CeO₂ effectively promotes the transformation of metastable phases and the oxidation of low-valence vanadium, forming stable, soluble vanadates (Na₄(V₂O₇)). Data indicate that adding CeO₂ enables a 5 wt% reduction in Na₂CO₃ usage while maintaining a vanadium extraction rate of over 90 %. Mechanistic studies further demonstrate that CeO₂ produces oxygen vacancies during roasting, activating a Ce³⁺/Ce⁴⁺ redox cycle that enhances oxygen utilization and accelerates vanadium oxidation. Furthermore, the regenerated CeO₂ catalyst retains catalytic activity after multiple cycles, achieving a vanadium extraction rate of 95 % upon reuse. This CeO₂-catalyzed roasting method significantly reduces Na₂CO₃ requirements, minimizing CO₂ emissions and hazardous residue production, thereby presenting an efficient, low-impact approach to sustainable vanadium extraction and contributing valuable insights for advancing green metallurgical processes.