Hydrogen reduction and melting separation of Bayan Obo niobium–iron comprex ore

The Bayan Obo deposit is a complex iron ore rich in niobium, titanium, and rare earths. Hydrogen reduction provides a low-carbon, selective method for extracting iron and inhibits the formation of Nb- and Ti-carbides. This study presents a hydrogen-reduction and melting separation method that efficiently separates slag from iron in Bayan Obo ores, favoring the crystallization of single-phase niobium minerals. The FeO content in reduced briquettes was controlled by adjusting the reduction level, and slag basicity (CaO/SiO 2 ) was tuned during melting separation. The combined impact of FeO content and basicity on slag fluidity, separation efficiency, and slag phase crystallization was thoroughly examined. Measurements of flow temperature and viscosity in the simulated slag system indicate that the slag-iron separation temperature decreases from 1650 °C to 1450–1550 °C. Under optimal conditions (FeO = 2.43 wt% and basicity = 2.0), an iron ingot with 99.6% Fe and 96.31% recovery was obtained from the Nb–Fe ore. Moreover, 99.74% Nb, 99.97% Ti, and 99.78% rare earths were retained in the slag. XRD and SEM-EDS analyses of the slag phase revealed that the complex niobium-bearing phases in the Nb–Fe ore were converted into a single loparite-(Ce) phase, with particle sizes reaching 62.94 μm, which establishes favorable conditions for subsequent flotation. Under basicity of 1.2, the particle size of slowly cooled slag can reach 74.49 μm at 1350–1300 °C. This study demonstrates an efficient and environmentally friendly route for the simultaneous recovery of iron and critical metals from Nb–Fe ore.