Abstract: The Bayan Obo ore is a typical low-grade polymetallic symbiotic deposit in China, with abundant reserves of key metal resources such as iron, niobium, titanium, and rare earth elements. The ore exhibits a complex mineralogical structure and hosts approximately 20 niobium-bearing minerals, which are characterized by intergrowth, mutual encapsulation, and intricate associations. During the beneficiation process, co-separation of iron-bearing gangue minerals and niobium minerals commonly occurs, resulting in difficulties in upgrading the niobium concentrate grade-a major constraint on the efficient utilization of niobium resources in China. Given the similar physicochemical properties and complex dissemination relationships between iron-bearing gangue and niobium minerals, this study proposed a mineral phase reconstruction strategy for niobium minerals. By modifying their surface properties and competitive adsorption behaviors, effective separation from iron-bearing minerals could be achieved, ultimately forming niobium-rich slag. To investigate the evolution of niobium mineral phases during the oxidation roasting of Bayan Obo ore pellets, the influence of varying Nb₂O₅ additions on phase transformation was systematically examined.Results indicate that at a calcination temperature of 1 200 ℃, increasing the Nb₂O₅ content reduces pellet porosity, decreases interconnected pores, lowers coordination number, deteriorates pore connectivity, and gradually enhances compressive strength. During roasting, a new crystalline phase-Ca₂Nb₂O₆F-forms within the oxidized pellets. This phase aggregates and distributes tightly with hematite, and the majority of niobium migrates into Ca₂Nb₂O₆F. The phase transformation pathway of niobium during roasting follows FeNb₂O₆→Ca₂Nb₂O₆F. This study clarifies the mineralogical transformation mechanisms of niobium, calcium, and fluorine in Bayan Obo ore, providing a novel approach for the targeted reconstruction of complex niobium minerals into a simplified, single niobium phase.