XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1863
indicating that there were few pores. After reduction at
500–550 °C, the porous structure of the samples led to a
significant increase in the saturated adsorption capacity,
which corresponded to the porous metallic iron structure in
Figures 10 (a)–(e). However, at temperatures above 600 °C,
the saturated adsorption capacity decreased significantly,
which may be attributed to the formation of a structurally
dense metallic iron.
Quantitative data on the pore parameters of samples
were calculated according to the Brunauer-Emmett-Teller
(BET) and BJH methods (Brunauer et al., 1938 Han et
al., 2020). As shown in Table 2, the results of pore param-
eters further confirmed the structural differences of reduced
products in SEM analysis. At a reduction temperature of
550 °C, the specific surface area and total pore volume
were sharply increased by 4.0961 m2/g and 0.0298 cm3/g,
respectively, compared to the raw material, which con-
firmed the porous structure of metallic iron. Above 600
°C, the metallic iron reduced by wüstite presented a dense
structure, with a significant decrease in specific surface area
and total pore volume.
Hydrogen Reduction Mechanism of Boron-bearing
Iron Concentrate
Based on the above analysis, Figure 13 provides the hydro-
gen reduction mechanism of boron-bearing iron concen-
trate in a fluidized bed.
The magnetite was reduced to metallic iron in a single
step by hydrogen at 500–550 °C, and the metallic iron
was characterized by a porous structure and high porosity.
However, the stable existence of ludwigite limited the
increase of the metallization degree. After increasing the
temperature, suanite and forsterite were formed by the
decomposition of szaibelyite and chrysotile, respectively.
Magnetite was first reduced to wüstite, and then to dense
metallic iron, which increased the mass transfer resistance
between the wüstite and metallic iron phase, resulting in a
rapid drop in metallization degree at 600–650 °C. When
the reduction temperature was ≥ 700 °C, ludwigite started
to be reduced by hydrogen. Above 750 °C, since water
vapor was accumulated in some defects (e.g., vacancies, dis-
locations, or micropores) in the iron layer, and the volume
variation after the loss of oxygen, the iron layer ruptured
and formed cracks and pores under internal stress. Thus,
the reduction proceeds along the cracks to the interior
Figure 12. N
2 adsorption-desorption hysteresis loops patterns and pore diameter distribution: (a) raw material (b) 500 °C
(c) 550 °C (d) 600 °C (e) 650 °C (f) 700 °C (g) 750 °C (h) 800 °C
Table 2. Pore parameters of the raw material and reduced
products
Sample
Conditions
BET surface
Area (m2/g)
Total Pore
Volume (cm3/g)
Average Pore
Diameter
(nm)
Raw material 0.4754 0.0024 26.2523
500 °C 3.5730 0.0252 27.8399
550 °C 4.5717 0.0322 28.1359
600 °C 3.4136 0.0216 23.6536
650 °C 3.0438 0.0176 21.2737
700 °C 2.8054 0.0161 23.2717
750 °C 2.4867 0.0157 28.5621
800 °C 1.8567 0.0139 34.9188
indicating that there were few pores. After reduction at
500–550 °C, the porous structure of the samples led to a
significant increase in the saturated adsorption capacity,
which corresponded to the porous metallic iron structure in
Figures 10 (a)–(e). However, at temperatures above 600 °C,
the saturated adsorption capacity decreased significantly,
which may be attributed to the formation of a structurally
dense metallic iron.
Quantitative data on the pore parameters of samples
were calculated according to the Brunauer-Emmett-Teller
(BET) and BJH methods (Brunauer et al., 1938 Han et
al., 2020). As shown in Table 2, the results of pore param-
eters further confirmed the structural differences of reduced
products in SEM analysis. At a reduction temperature of
550 °C, the specific surface area and total pore volume
were sharply increased by 4.0961 m2/g and 0.0298 cm3/g,
respectively, compared to the raw material, which con-
firmed the porous structure of metallic iron. Above 600
°C, the metallic iron reduced by wüstite presented a dense
structure, with a significant decrease in specific surface area
and total pore volume.
Hydrogen Reduction Mechanism of Boron-bearing
Iron Concentrate
Based on the above analysis, Figure 13 provides the hydro-
gen reduction mechanism of boron-bearing iron concen-
trate in a fluidized bed.
The magnetite was reduced to metallic iron in a single
step by hydrogen at 500–550 °C, and the metallic iron
was characterized by a porous structure and high porosity.
However, the stable existence of ludwigite limited the
increase of the metallization degree. After increasing the
temperature, suanite and forsterite were formed by the
decomposition of szaibelyite and chrysotile, respectively.
Magnetite was first reduced to wüstite, and then to dense
metallic iron, which increased the mass transfer resistance
between the wüstite and metallic iron phase, resulting in a
rapid drop in metallization degree at 600–650 °C. When
the reduction temperature was ≥ 700 °C, ludwigite started
to be reduced by hydrogen. Above 750 °C, since water
vapor was accumulated in some defects (e.g., vacancies, dis-
locations, or micropores) in the iron layer, and the volume
variation after the loss of oxygen, the iron layer ruptured
and formed cracks and pores under internal stress. Thus,
the reduction proceeds along the cracks to the interior
Figure 12. N
2 adsorption-desorption hysteresis loops patterns and pore diameter distribution: (a) raw material (b) 500 °C
(c) 550 °C (d) 600 °C (e) 650 °C (f) 700 °C (g) 750 °C (h) 800 °C
Table 2. Pore parameters of the raw material and reduced
products
Sample
Conditions
BET surface
Area (m2/g)
Total Pore
Volume (cm3/g)
Average Pore
Diameter
(nm)
Raw material 0.4754 0.0024 26.2523
500 °C 3.5730 0.0252 27.8399
550 °C 4.5717 0.0322 28.1359
600 °C 3.4136 0.0216 23.6536
650 °C 3.0438 0.0176 21.2737
700 °C 2.8054 0.0161 23.2717
750 °C 2.4867 0.0157 28.5621
800 °C 1.8567 0.0139 34.9188
