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K. He et al.
reduction and smelting reduction [4]. Several smelting reduction processes such as
COREX, FINEX, and ITmk3 have been commercially proven. However, some of the
limitations of these processes are still existence for their commercialization [5]. For
these processes, Schenk et al. [6, 7] thought that fluidized bed direct reduction or prereduction processes have the possibility of using only H 2 as a reducing agent so that
an ironmaking process without carbon emissions is possible [7]. Consequently, the
reduction behaviors of hematite by H 2 needs to be understood and mastered, which is
very important in further promotion and application of corresponding technologies.
As a reducing agent, H 2 has been studied for many years and has been utilized
in a wide range of applications [8–13]. For example, D ˙ Ilmaç et al. [9] investigated
the reduction kinetics of Attepe iron ore by H 2 during the temperature range from
600 to 800 °C in a batch fluidized bed and reported that the most suitable model for
predicting the transforming process of iron ore is the “ad-hoc” model. Spreitzer et al.
[7, 14] studied the reduction of fine ore by H 2 –N 2 mixtures under 600–800 °C in
a laboratory scale fluidized bed and analyzed the difference in the reduction of the
ore with different composition [7]. These studies were practiced on the three-step
reaction process, i.e., Fe 2 O 3 → Fe 3 O 4 → FeO → Fe, with the reaction temperature
higher than 570 °C. But for FINEX® process, in general, the operating temperature is in the range from 400 to 800 °C. Hence, the reduction behaviors of hematite
in the temperature range 400–570 °C also need to be further understood. Jozwiak
et al. [15] studied the reduction of various iron oxides in H 2 and CO by temperatureprogrammed reduction systematically and reported that the lowest border limit of the
thermodynamic stability of FeO is the temperature 570 °C. Some other researchers,
i.e., Hou et al. [16], Gavira et al. [17], Pineau et al. [18], and so on, had investigated
the kinetics of reduction of iron oxides by H 2 at low temperatures (220–680 °C).
Nevertheless, the morphological and internal structure during the reduction of ore
fines, which is very important for a complete understanding of the reaction mechanism, were ignored in these researches. For this reason, investigation of the reduction
behaviors, i.e., morphological, internal structure, and reaction kinetics, is necessary.
The objective of this study is to investigate the reduction behaviors of hematite
to metallic iron by H 2 (20%H 2 + 80%Ar) under low temperature (400–570 °C) in a
micro-fluidized bed reaction analyzer (MFBRA). A gas flow rate that attenuated the
effect of gas external diffusion on the reduction process is determined in the microfluidized bed (MFB). The crystalline phases, morphological, and internal structures
of products during the reduction process are analyzed under 500 °C. Moreover,
the kinetics of two-step reactions, i.e., Fe 2 O 3 → Fe 3 O 4 and Fe 3 O 4 → Fe, are also
discussed.
K. He et al.
reduction and smelting reduction [4]. Several smelting reduction processes such as
COREX, FINEX, and ITmk3 have been commercially proven. However, some of the
limitations of these processes are still existence for their commercialization [5]. For
these processes, Schenk et al. [6, 7] thought that fluidized bed direct reduction or prereduction processes have the possibility of using only H 2 as a reducing agent so that
an ironmaking process without carbon emissions is possible [7]. Consequently, the
reduction behaviors of hematite by H 2 needs to be understood and mastered, which is
very important in further promotion and application of corresponding technologies.
As a reducing agent, H 2 has been studied for many years and has been utilized
in a wide range of applications [8–13]. For example, D ˙ Ilmaç et al. [9] investigated
the reduction kinetics of Attepe iron ore by H 2 during the temperature range from
600 to 800 °C in a batch fluidized bed and reported that the most suitable model for
predicting the transforming process of iron ore is the “ad-hoc” model. Spreitzer et al.
[7, 14] studied the reduction of fine ore by H 2 –N 2 mixtures under 600–800 °C in
a laboratory scale fluidized bed and analyzed the difference in the reduction of the
ore with different composition [7]. These studies were practiced on the three-step
reaction process, i.e., Fe 2 O 3 → Fe 3 O 4 → FeO → Fe, with the reaction temperature
higher than 570 °C. But for FINEX® process, in general, the operating temperature is in the range from 400 to 800 °C. Hence, the reduction behaviors of hematite
in the temperature range 400–570 °C also need to be further understood. Jozwiak
et al. [15] studied the reduction of various iron oxides in H 2 and CO by temperatureprogrammed reduction systematically and reported that the lowest border limit of the
thermodynamic stability of FeO is the temperature 570 °C. Some other researchers,
i.e., Hou et al. [16], Gavira et al. [17], Pineau et al. [18], and so on, had investigated
the kinetics of reduction of iron oxides by H 2 at low temperatures (220–680 °C).
Nevertheless, the morphological and internal structure during the reduction of ore
fines, which is very important for a complete understanding of the reaction mechanism, were ignored in these researches. For this reason, investigation of the reduction
behaviors, i.e., morphological, internal structure, and reaction kinetics, is necessary.
The objective of this study is to investigate the reduction behaviors of hematite
to metallic iron by H 2 (20%H 2 + 80%Ar) under low temperature (400–570 °C) in a
micro-fluidized bed reaction analyzer (MFBRA). A gas flow rate that attenuated the
effect of gas external diffusion on the reduction process is determined in the microfluidized bed (MFB). The crystalline phases, morphological, and internal structures
of products during the reduction process are analyzed under 500 °C. Moreover,
the kinetics of two-step reactions, i.e., Fe 2 O 3 → Fe 3 O 4 and Fe 3 O 4 → Fe, are also
discussed.