The sintering basic characteristics of iron ore play a key role in the process of sintering. In this study, the effects of B2O3 on the assimilation characteristics, softening temperature, fluidity of liquid phase, compressive strength of bonding phase, and microstructure of the mixed fine powder of hematite and vanadium-titanium magnetite (H-VTM) are studied. Results show that B2O3 content from 0%–5% (wt%) could improve the assimilation characteristics of the H-VTM and increase the amount of the liquid phase. The liquidity of the bonding phase index (LBPI) of the H-VTM increases from 3.7 to 24.2. When B2O3 content exceeds 2%, the diameter of the pore in the H-VTM sintered samples enlarges. However, the compressive strength gradually decreases. Boron and calcium-magnesium-aluminium elements are abundant in the bonding phase, which can reduce the formation of calcium silicate and perovskite in H-VTM sintered samples.
With the rapid development of the steel industry, the supply of high-quality iron ore is insufficient, so the vanadium-titanium magnetite (VTM) with sufficient reserves is highly needed. The extraction of iron, vanadium, titanium, and other elements in VTM has remarkably progressed, and its industrial-scale production is still dominated by the blast furnace ironmaking process. The primary raw materials for the blast furnace are vanadium-titanium sinter and vanadium-titanium pellets [
Vanadium-titanium sinter is the raw material for the blast furnace, and there are still many difficulties in the production of vanadium-titanium sinter. As increasing the proportion of VTM in sintering, the amount of the liquid phase and the liquid-phase bonding force both decrease. Resulting in a lower yield and drum strength of vanadium-titanium sinter, the production volume of small size sinter also increases. Low-temperature reduction pulverization index (RDI−3.15) of the vanadium-titanium sinter is significantly higher than the sinter without vanadium-titanium magnetite [
Zhou et al. [
Ren et al. [
In summary, we find that adding boron slime, boric acid, and boron-iron concentrate could improve the strength and the metallurgical performance of sinter and reduce the low-temperature pulverulent ratio, which is conducive to the blast furnace. It is not difficult to find that boron oxide plays a very important role in the sintering process. However, existing researches mainly focus on the effect of boron oxide on the macroperformance of vanadium-titanium sinter. Studies on the influence of B2O3 on the sintering basic characteristics of mixed ore powders using vanadium-titanium fine powder as the main raw material are rarely reported. Especially the researches on the influence mechanism of B2O3 on the sintering basic characteristics of mixed ore powder of vanadium-titanium magnetite and hematite have not been reported so far.
Hence, in this work, according to the actual production of mineral types and proportions in southwest China. Experimental samples are mixed with VTM concentrate and Australian hematite powder with a specific mass ratio (8 : 2), and this particular mixture powder is called H-VTM. The effects of B2O3 content on the assimilation characteristics, melting temperature, liquidity of liquid phase, compressive strength, and microstructure changes are studied. The influences of different B2O3 contents on the sintering basic characteristics of H-VTM sintering samples are obtained. The mechanism of B2O3 affecting the sintering process of vanadium-titanium magnetite and hematite is also clarified. Meanwhile, it is possible to find a new method for the recycling of B2O3 in boron-containing solid wastes.
The chemical composition of the sintered raw material is shown in Table
Chemical composition of ore powder (wt%).
Ore powder | TFe | SiO2 | CaO | Al2O3 | MgO | TiO2 | MnO | FeO | P | S |
---|---|---|---|---|---|---|---|---|---|---|
VTM | 55.78 | 4.33 | 0.69 | 3.86 | 2.78 | 9.08 | 0.36 | 30.50 | 0.09 | 0.54 |
Hematite | 59.76 | 4.32 | 0.73 | 3.16 | 0.14 | 0.12 | 0.16 | 0.80 | 0.07 | 0.09 |
H-VTM | 56.58 | 4.33 | 0.70 | 3.72 | 2.25 | 7.29 | 0.32 | 24.56 | 0.09 | 0.45 |
The assimilation characteristics experiment is shown in Figure
Diagrammatic chart of the assimilation characteristics experiment.
The experiment of melting temperature is shown in Figure
Diagrammatic chart of melting temperature experiment.
The experiment of the compressive strength of the bonding phase is shown in Figure
Diagrammatic chart of compressive strength of bonding phase.
The experiment of the fluidity is shown in Figure
Diagrammatic chart of the fluidity of liquid-phase experiment.
The chemical composition of the samples ensured the binary basicity
In Figure
Sintering basic characteristics of the H-VTM sintered sample with different B2O3 contents.
As is shown in Figure
The average compressive strength of H-VTM fluctuated significantly with the rise of B2O3. The compressive strength was 531 N/P without B2O3. The compressive strength grew significantly with the increase of B2O3 content, peaking at 857 N/P with B2O3 content at 2.00%. As the B2O3 ratio further increases, the compressive strength dropped sharply, reaching its lowest point at 356 N/P with B2O3 ratio at 5.00%.
In Figure
The volume of liquid phase with different B2O3 contents.
The X-ray diffraction (XRD) is used to investigate the phases changes of the sintered samples. As is shown in Figure
XRD patterns of H-VTM-sintered samples with different B2O3 contents. 1: Fe2O3; 2: Fe3O4; 3: CaO·Fe2O3; 4: 2CaO·SiO2.
The addition of B2O3 could inhibit the formation of 2CaO·SiO2 and promote the formation of CaO·Fe2O3. This scene is shown in Figure
2CaO·SiO2 contents in the samples with different B2O3 contents.
The microstructures of the samples with different content of B2O3 were observed using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscope (EDS). In Figure
SEM of H-VTM with different B2O3 contents.
The scanning results of the sintered sample with 5.00% B2O3 are shown in Figure
Surface scanning of the H-VTM sample with 5% B2O3.
SEM-EDS was carried out on the cooled sample with 5.00% B2O3, as is shown in Figure
SEM-EDS of the sample with 5% B2O3.
SEM-EDS analysis of the sample with 5.00% B2O3 (wt%).
Point | B | O | Fe | Si | Ca | Ti | Mg | Al |
---|---|---|---|---|---|---|---|---|
A | 1.01 | 24.29 | 67.29 | 0.12 | 0.45 | 1.98 | 1.00 | 0.37 |
B | 7.73 | 37.61 | 23.83 | 6.14 | 14.35 | 1.13 | 1.64 | 2.66 |
C | 6.25 | 36.41 | 28.71 | 5.77 | 13.34 | 1.23 | 1.82 | 2.56 |
The assimilation characteristics, melting temperature, fluidity of the liquid phase, compressive strength of the bonding phase, and microstructure of H-VTM with different B2O3 were studied through different methods: B2O3 reduces the assimilation temperature of H-VTM and enhances its assimilation characteristics. As the amount of B2O3 increases, the melting temperature of H-VTM decreases, as well as LBPI. The addition of B2O3 can increase the amount of liquid phase and enhance the fluidity of the liquid phase. B2O3 (<2.00%) improves the bonding phase strength of sintering samples, but the diameter of the pore in H-VTM enlarges when the amount of B2O3 is over 2.00% and the number of the pore increase. Thus, the H-VTM microstructure becomes more porous, and its compressive strength decreases. Boron and calcium-magnesium-aluminium concentrated in the bonding phase can reduce the formation of calcium silicate and perovskite in the mixed samples of vanadium-titanium and hematite.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare no conflicts of interest.
Hao Liu, Ke Zhang, Qingfeng Ling, and Xinlong Wu contributed to perform the experiments, material characterization, data analysis, and paper writing. Yuelin Qin revised the paper and refined the language. Hao Liu and Yuelin Qin contributed to the design of the experiment.
This work was supported by the National Natural Science Foundation of China (Grant no. 51974054), Youth Project of Science and Technology Research Program of Chongqing Education Commission of China (no. KJQN201901), and China Scholarship Council (no. 201802075005).