Mineralogical characterization and flotation properties of rare earths in refractory iron tailings subjected to hydrogen-based mineral phase transformation

Hydrogen-based mineral phase transformation (HMPT) technology has demonstrated its effectiveness in separating iron and enriching rare earths from Bayan Obo refractory ores. However, further research is needed to clarify the phase composition and floatability of rare earths obtained after HMPT owing to the associated phase transformations. This study explored the mineralogical characteristics and separation behavior of rare earths in HMPT-treated iron tailings. Process mineralogy studies conducted via BGRIMM process mineralogy analysis and X-ray diffraction revealed that the main valuable minerals in the tailings included rare-earth oxides (9.15 wt%), monazite (5.31 wt%), and fluorite (23.52 wt%). The study also examined the impact of mineral liberation and gangue mineral intergrowth on flotation performance. Flotation tests achieved a rare-earth oxide (REO) grade of 74.12 wt% with a recovery of 34.17% in open-circuit flotation, whereas closed-circuit flotation resulted in a REO grade of 60.27 wt% with a recovery of 73%. Transmission electron microscopy and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy revealed that monazite remained stable during the HMPT process, while bastnaesite was transformed into Ce₇O₁₂ and CeF₃, leading to increased collector consumption. Nonetheless, the HMPT process did not significantly affect the flotation performance of rare earths. The enrichment of fluorite in the tailings highlighted its further recovery potential. The integration of HMPT with magnetic separation and flotation presents an efficient strategy for recovering rare earths, iron, and fluorite from Bayan Obo ores.