Enhancing Magnetic Contrast through Mineral Phase Transformation: Flotation Performance of Bastnaesite-Transformed Products

With resource depletion, the integrated utilization of low-grade rare-earth ores has garnered widespread focus. However, conventional beneficiation processes are unable to efficiently recover valuable components. This study provides a mineral phase transformation (MPT) strategy to enhance separation by amplifying the magnetic contrast between bastnaesite and iron minerals. Roasting was conducted on single bastnaesite, bastnaesite-hematite mixed minerals, and Bayan Obo low-grade polymetallic ore (BOLPO). The effect of MPT on magnetic separation and subsequent flotation was explored. Relevant analytical tests were employed to examine the phase and surface property changes of bastnaesite during MPT, elucidating the flotation behavior of bastnaesite MPT products. The results showed that MPT improved the magnetic contrast, yielding favorable magnetic separation indices for iron. Furthermore, bastnaesite MPT products were efficiently recovered using benzohydroxamic acid (BHA). For BOLPO, magnetic separation produced a concentrate with 61.69% iron grade and 84.24% iron recovery, while open-circuit flotation yielded a rare-earth concentrate with 60.46% REO grade and 50.78% recovery. During MPT, bastnaesite experienced oxidation decomposition, cerium reduction, and reoxidation, forming roasting products of Ce₇O₁₂ and CeF₃. During reduction, Ce(IV) was partially reduced to Ce(III), with the flotation performance of the reduction products affected by oxygen vacancies and the specific surface area. Oxygen vacancies increased the hydrophilicity and BHA consumption. Conversely, the decreased specific surface area enhanced hydrophobicity, lowering BHA depletion. In reoxidation, oxygen adsorption filled the oxygen vacancies, further declining BHA consumption. This study provides insights into the comprehensive utilization of low-grade rare-earth ores.