This study investigated the solid-state reduction characteristics of natural chromite ore and the effect of iron powder on the solid-state reduction characteristics of natural chromite ore under isothermal conditions below 1200 °C. The enhancement mechanism of iron powder on the solid-state reduction of natural chromite ore was revealed using optical microscopy, X-ray diffraction (XRD), and scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS). The iron metallization rate of chromite ore exhibited a trend of increasing first and then decreasing with the addition of iron powder, and the optimal iron powder addition was determined to be 30%. The multi-step reaction gradually transforms into a single-step reaction with the increase in the dosage of iron powder. Iron powder facilitates the generation of a low-melting Fe-C alloy liquid phase and accelerates the speed of the solid-state reduction reaction of chromite ore and the disintegration of chromite spinel particles. When the iron powder dosage exceeds 30%, most of the multi-step reduction reaction of chromite ore is transformed into the single-step reduction reaction, which reduces the disintegration of chromite spinel particles and weakens the enhancement effect of iron powder on the solid-state reduction of chromite ore.

Pelletizing is an effective way of converting abundant phosphate ore fines into usable feedstocks for yellow-phosphorus production. In this work, the oxidation-roasting behavior of siliceous–calcareous phosphate ore pellets and siliceous phosphate ore pellets was evaluated in a laboratory tube furnace. The consolidation mechanisms were revealed using optical microscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The results indicate that siliceous phosphate ore pellets exhibit superior oxidation-roasting performance relative to siliceous–calcareous phosphate ore pellets. After roasting, oxidized siliceous–calcareous phosphate ore pellets show a loose and porous framework with large pores, thin walls, and occasional surface cracking. The consolidation of siliceous–calcareous phosphate ore pellets is mainly governed by the recrystallization bonding of silicon–magnesium-bearing fluorapatite. In contrast, oxidized siliceous phosphate ore pellets display a denser microstructure and stronger intergranular bonding. The dominant bonding forms are the recrystallization bonding of silicon-bearing fluorapatite and solid-state bonding between silicon-bearing fluorapatite particles and quartz particles. Furthermore, carbonate gangue minerals are detrimental to strength development because CO₂ release during roasting promotes the development of interconnected porosity and defects, thereby reducing the compressive strength of oxidized phosphate ore pellets.

This study investigated the solid-state reduction characteristics of natural chromite ore and the effect of iron powder on the solid-state reduction characteristics of natural chromite ore under isothermal conditions below 1200°C. The enhancement mechanism of iron powder on the solid-state reduction of natural chromite ore was elucidated using optical microscopy, X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The optimal reduction performance was achieved with a carbon dosage of 20% and an isothermal reduction at 1175°C for 2 hours, resulting in an iron metallization rate of 97.15%. The iron metallization rate of chromite ore exhibited a trend of initially increasing and subsequently decreasing with the addition of iron powder and the optimal iron powder addition determined to be 30%. The iron metallization rate increased from 91.31% (without iron powder) to 96.33% (with 30% iron powder, calcined at 1175°C for 1.5 hours with 20% carbon dosage). Increasing iron podwer dosage from 0 to 30% facilitates the generation of a low-melting Fe-C alloy liquid phase, the in-situ fusion of newly generated iron and the disintegration of chromite spinel particles, enhancing the solid-state reduction of chromite ore. When the iron powder dosage exceeds 30%, the reduction reaction mechanism transitions from multi step reaction to single step reaction, which reduces the disintegration of chromite spinel particles and the enhancement effect of iron powder on the solid-state reduction of chromite ore.