LI Li, LI Pengyu, LI Hongwu, LIU Yuejun, LIN Jianting, LI Xianchun
The thermodynamic characteristics, reaction mechanisms, and the impact of temperature and time on the reduction process of hematite （Fe2O3） by ammonia （NH3） were to be explored. The standard Gibbs free energy of the reduction reactions between Fe2O3 and Fe2SiO4 with NH3, H2, and CO was calculated using HSC Chemistry 6.0 software to assess the feasibility of NH3 as a reducing agent. The horizontal high-temperature furnace was used to heat and reduce hematite, with the reduction effects investigated under various temperature and time conditions with NH3. The results show that NH3 can effectively reduce Fe2O3 at 290 ℃, while H2 requires a higher temperature of 542 ℃, indicating that NH3 has a reduction advantage at lower temperatures. The thermodynamic reaction temperature for NH3 reduction of Fe2SiO4 is 480 ℃, in contrast, CO and H2 are not spontaneous at this temperature, demonstrating the thermodynamic advantage of NH3 in reducing Fe2SiO4. As the temperature increases, the weight loss and reduction rates of hematite increase, and hematite can be completely reduced by NH3 with the volume fraction of 30% at 900 ℃. The extension of reduction time also leads to an increase in weight loss and reduction rates, with 90% reduction rate achieved in 60 min and 100% reduction rate in 180 min. Characterization of the reduced samples by XRD, SEM, and OM reveals that Fe2O3 is first converted to Fe3O4, then rapidly to FeO, and finally FeO is converted to pure iron （Fe）. EDS spectral analysis shows that as the reaction proceeds, the content of O atoms decreases while the content of Fe atoms increases, ultimately achieving the complete reduction of Fe2O3 to pure Fe. During the NH3 reduction of Fe2O3, the number of N atoms first increases and then decreases, indicating that Fe is nitrided by NH3 to form Fe4N, which then decomposes at high temperatures to produce Fe and N2. NH3 shows a significant thermodynamic advantage in the reduction of hematite, and the reduction process can be divided into several stages, initial slow conversion, rapid reaction in the middle, and a decrease in reaction rate in the later stage due to product coverage. The entire process is completed within 30 min, ultimately achieving the complete conversion of Fe2O3 to pure Fe. Theoretical basis and experimental data support are provided for the industrial use of NH3 to reduce hematite.
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