Guiqin Fu

Oxidation induration process and kinetics of Hongge vanadium titanium-bearing magnetite pellets

The induration process and oxidation kinetics of Hongge vanadium titanium-bearing magnetite (HVTM) pellets have been investigated by employing X-ray diffraction, scanning electron microscope, energy-dispersive spectroscopy, thermogravimetric and differential thermal analysis and thermogravimetric and differential scanning calorimetry. The results indicated that HVTM was a high-chromium vanadium-bearing titanomagnetite containing 1.48 wt-% Cr2O3, and the crystal stock strength was 625 N. The compressive strength of HVTM pellets could be improved by increasing the roasting temperature and roasting time. Under the optimum conditions of oxidation roasting at 1200°C for 15 min, the compressive strength was found to be 2893 N. The phase transformations of the valuable elements could be described as follows: Fe3O4→Fe2O3; Fe2VO4→(Cr0.15V0.85)2O3; Fe2.75Ti0.25O4→FeTiO3→Fe9TiO15; FeCr2O4→(Fe0.6Cr0.4)2O4, Fe0.7Cr1.3O3, (Cr0.15V0.85)2O3. Three stages were identified during the induration process: initial oxidation, later oxidation, and haematite re-crystallisation, poly-crystallisation and induration. The development of strength mainly occurred in the last stage. Kinetic parameters of the oxidation process were determined from heating experiments. The results showed that the average value of activation energy was calculated to be 69.33 kJ mol−1 by the Flynn–Wall–Ozawa methods. This study aims to provide theoretical and technical bases for the effective utilisation of HVTM ore for use in either blast furnaces or shaft furnaces.

Reduction behavior and mechanism of Hongge vanadium titanomagnetite pellets by gas mixture of H2 and CO

Hongge vanadium titanomagnetite (HVTM) pellets were reduced by H2-CO gas mixture for simulating the reduction processes of Midrex and HYL-III shaft furnaces. The influences of reduction temperature, ratio of φ(H2) to φ(CO), and pellet size on the reduction of HVTM pellets were evaluated in detail and the reduction reaction kinetics was investigated. The results show that both the reduction degree and reduction rate can be improved with increasing the reduction temperature and the H2 content as well as decreasing the pellet size. The rational reduction parameters are reduction temperature of 1050 °C, ratio of φ(H2) to φ(CO) of 2.5, and pellet diameter in the range of 8–11 mm. Under these conditions (pellet diameter of 11 mm), final reduction degree of 95.51% is achieved. The X-ray diffraction (XRD) pattern shows that the main phases of final reduced pellets under these conditions (pellet diameter of 11 mm) are reduced iron and rutile. The peak intensity of reduced iron increases obviously with the increase in the reduction temperature. Besides, relatively high reduction temperature promotes the migration and coarsening of metallic iron particles and improves the distribution of vanadium and chromium in the reduced iron, which is conducive to subsequent melting separation. At the early stage, the reduction process is controlled by interfacial chemical reaction and the apparent activation energy is 60.78 kJ/mol. The reduction process is controlled by both interfacial chemical reaction and internal diffusion at the final stage, and the apparent activation energy is 30.54 kJ/mol.

Effect of Ni on the corrosion resistance of bridge steel in a simulated hot and humid coastal-industrial atmosphere

The corrosion resistance of weathering bridge steels containing conventional contents of Ni (0.20wt%, 0.42wt%, 1.50wt%) and a higher content of Ni (3.55wt%) in a simulated hot and humid coastal-industrial atmosphere was investigated by corrosion depth loss, scanning electron microscopy–energy-dispersive X-ray spectroscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical methods. The results showed that, with increasing Ni content, the mechanical properties of the bridge steel were markedly improved, the welding parameters were satisfactory at room temperature, and the corrosion resistance was enhanced. When the Ni content was low (≤0.42wt%), the crystallization process of the corrosion products was substantially promoted, enhancing the stability of the rust layer. When the Ni content was higher (~3.55wt%), the corrosion reaction of the steel quickly reached a balance, because the initial rapid corrosion induced the formation of a protective rust layer in the early stage. Simultaneously, NiO and NiFe2O2 were generated in large quantities; they not only formed a stable, compact, and continuous oxide protective layer, but also strongly inhibited the transformation process of the corrosion products. This inhibition reduced the structural changes in the rust layer, thereby enhancing the protection. However, when the Ni content ranged from 0.42wt% to 1.50wt%, the corrosion resistance of the bridge steel increased only slightly.

Effect of Cr 2 O 3 addition on the oxidation induration mechanism of Hongge vanadium titanomagnetite pellets

As part of a research project to develop a novel clean smelting process for the comprehensive utilization of Hongge vanadium titanomagnetite (HVTM), in this study, the effect of Cr2O3 addition on the oxidation induration mechanism of HVTM pellets (HVTMPs) was investigated in detail. The results showed that the compressive strength of the HVTMPs was greatly weakened by the Cr2O3 addition, mainly because of a substantial increase in the porosity of the HVTMPs. The Cr2O3 addition marginally affected the phase composition but greatly affected the microstructural changes of the HVTMPs. Increased amounts of Cr2O3 resulted in a decrease in the uniform distribution of the hematite grains and in an increase in the Fe–Cr solid solutions (Fe1.2Cr0.8O3 and Fe0.7Cr1.3O3) embedded in the hematite grains. Moreover, the compact hematite was destroyed by forming a dispersed structure and the hematite recrystallization was hindered during the oxidation induration, which adversely affected the compressive strength. On the basis of these results, a schematic was formulated to describe the oxidation induration mechanism with different amounts of added Cr2O3. This study provides theoretical and technical foundations for the effective production of HVTMPs and a reference for chromium-bearing minerals.

Effect of V2O5 addition on the oxidation induration process of Hongge vanadium titanomagnetite pellet

ABSTRACT In the present work, the effect of V2O5 addition on the oxidation induration process of Hongge vanadium titanomagnetite pellet (HVTMP) was investigated by various characterisation methods. Experimental results showed that with the increase of V2O5 addition, the compressive strength of HVTMP decreased and the porosity increased. The V2O5 addition had marginal effect on the phase composition, but greatly affected the microstructure during oxidation induration process of HVTMP. The addition of V2O5 destroyed the compact structure, located in grain boundary and hindered the haematite recrystallisation, eventually had detrimental effect on the oxidation induration of HVTMP. Besides, a schematic diagram was formulated to describe the oxidation induration mechanism of HVTMP with various V2O5 additions. The current study will not only provide experimental evidence to establish a correlation between the V2O5 addition and oxidation induration of HVTMP, but also provide both theoretical and technical bases for its effective utilisation in either blast furnace or shaft furnace.