XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1921
N2 was continuously introduced. Finally, the reduction
product was cooled to temperature of 25 °C in N2. Then
the reduction product was taken out. A rod mill (XMB-70)
was grinded the reduction product to the particle size (the
grinding fineness of 95% passing 38 μm). After that, mag-
netic separation with a magnetic tube (XCSG-120) were
performed.
The iron grade of the samples was measured by potas-
sium dichromate titration, using titanium trichloride solu-
tion to reduce Fe(III) to Fe(II), which was completed in
the Analytical Testing Center of Northeastern University,
China. The mineral phase composition of the samples was
analyzed by XRD (SmartLab9, Rigaku, Japan). The VSM
(JDAW-200D) was utilized to investigate magnetic proper-
ties of the samples before and after minerals phase trans-
formation. The chemical state of iron on the surface of
the raw ores and reduction products were characterized by
XPS (Nexsa G2, Thermo Fisher Scientific) with an Al (Kα)
source (Yue, C., et al., 2021). The microstructure evolution
was performed by SEM (Quanta FEG 250, FEI, USA).
RESULTS AND DISCUSSION
Effect of the Minerals Phase Transformation
Effect of Reduction Temperature
The reduction temperature is an important factor to affect
the reductive degree of the reduction product. The effect of
the reduction temperature was investigated in the range of
500 °C to 600 °C, with a reduction time of 20 min, a total
gas flow of 600 mL/min, and a reductant concentration of
40% (CO:H2=1:3), the results were illustrated in Figure 3.
Figure 3 indicates that the iron grade in concentrate
fluctuated in the range of 56.52% to 56.95%, while the iron
recovery gradually increased from 91.70% to 93.36% with
the increase of reduction temperature was from 500 °C to
560 °C. This indicated that iron minerals were transformed
from hematite to magnetite with the increasing reduction
temperature (Xiaolong, Z., et al., 2023). As the reduction
temperature further increased to 600°C, the iron recovery
decreased at first and then steadily increased, reaching an
iron grade in concentrate of 57.42%. Since appropriately
elevating the reduction temperature can shorten the reduc-
tion time and reduce energy consumption (Qiang, Z., et
al., 2021), the optimum reduction temperature was deter-
mined at 540 °C, and the corresponding iron grade and
recovery in concentrate were 56.70% and 92.66%.
Effect of Reduction Time
To achieve an excellent separation index, the effect of
reduction time was determined, the results are illustrated in
Figure 4. The effect of reduction time was conducted in the
range of 15 min to 90 min at a reduction temperature of
540 °C, with a total gas flow of 600 mL/min and a reduc-
tant concentration of 40% (CO:H2=1:3).
As shown in Figure 4, when the reduction time increased
to 25 min, the iron recovery in concentrate gradually
increased from 89.16% to 94.03%, while the iron grade in
Figure 3. Effect of reduction temperature on separation indexes
N2 was continuously introduced. Finally, the reduction
product was cooled to temperature of 25 °C in N2. Then
the reduction product was taken out. A rod mill (XMB-70)
was grinded the reduction product to the particle size (the
grinding fineness of 95% passing 38 μm). After that, mag-
netic separation with a magnetic tube (XCSG-120) were
performed.
The iron grade of the samples was measured by potas-
sium dichromate titration, using titanium trichloride solu-
tion to reduce Fe(III) to Fe(II), which was completed in
the Analytical Testing Center of Northeastern University,
China. The mineral phase composition of the samples was
analyzed by XRD (SmartLab9, Rigaku, Japan). The VSM
(JDAW-200D) was utilized to investigate magnetic proper-
ties of the samples before and after minerals phase trans-
formation. The chemical state of iron on the surface of
the raw ores and reduction products were characterized by
XPS (Nexsa G2, Thermo Fisher Scientific) with an Al (Kα)
source (Yue, C., et al., 2021). The microstructure evolution
was performed by SEM (Quanta FEG 250, FEI, USA).
RESULTS AND DISCUSSION
Effect of the Minerals Phase Transformation
Effect of Reduction Temperature
The reduction temperature is an important factor to affect
the reductive degree of the reduction product. The effect of
the reduction temperature was investigated in the range of
500 °C to 600 °C, with a reduction time of 20 min, a total
gas flow of 600 mL/min, and a reductant concentration of
40% (CO:H2=1:3), the results were illustrated in Figure 3.
Figure 3 indicates that the iron grade in concentrate
fluctuated in the range of 56.52% to 56.95%, while the iron
recovery gradually increased from 91.70% to 93.36% with
the increase of reduction temperature was from 500 °C to
560 °C. This indicated that iron minerals were transformed
from hematite to magnetite with the increasing reduction
temperature (Xiaolong, Z., et al., 2023). As the reduction
temperature further increased to 600°C, the iron recovery
decreased at first and then steadily increased, reaching an
iron grade in concentrate of 57.42%. Since appropriately
elevating the reduction temperature can shorten the reduc-
tion time and reduce energy consumption (Qiang, Z., et
al., 2021), the optimum reduction temperature was deter-
mined at 540 °C, and the corresponding iron grade and
recovery in concentrate were 56.70% and 92.66%.
Effect of Reduction Time
To achieve an excellent separation index, the effect of
reduction time was determined, the results are illustrated in
Figure 4. The effect of reduction time was conducted in the
range of 15 min to 90 min at a reduction temperature of
540 °C, with a total gas flow of 600 mL/min and a reduc-
tant concentration of 40% (CO:H2=1:3).
As shown in Figure 4, when the reduction time increased
to 25 min, the iron recovery in concentrate gradually
increased from 89.16% to 94.03%, while the iron grade in
Figure 3. Effect of reduction temperature on separation indexes