Thermodynamic–Diagram Analysis of the Fe–Mn–C–O System: Geometrical Construction and Mössbauer Characterization of Magnetizing-Roasting Products

The selective transformation of iron-bearing phases in ferruginous manganese ores requires control of temperature and local reducing conditions. This study examines temperature-dependent relationships in the Fe–Mn–C–O system through thermodynamically guided geometrical constructions using a stoichiometric approximation. Boundary ternary systems were triangulated, followed by tetrahedral subdivision of the quaternary composition space at 550, 750, 950, and 1150 °C. A key temperature-dependent feature is the direct adjacency of Fe3O4-containing and metallic-Fe-containing subdivisions at 550 °C, whereas FeO-containing subdivisions form an intermediate zone at 750–1150 °C. These relationships were qualitatively compared with room-temperature Mössbauer spectra of three roasted ferruginous manganese ore samples. At 500–550 °C with 30% coal, magnetite/spinel-like components accounted for 72.4% of the spectral area, compared with 20.7% at 500–650 °C with 10% coal. Hematite-like components predominated at 500–550 °C with 10% coal, accounting for 92.7%. No independently resolved FeO-type component was identified in the cooled products. The comparison demonstrates a pronounced redistribution of iron-bearing environments between the investigated roasting regimes, with the largest magnetite/spinel-like contribution obtained at the higher coal addition. The combined analysis links temperature-dependent end-member relationships with spectroscopic evidence of iron transformation and provides a framework for interpreting magnetizing-roasting behavior.