Reduction Of Fe2O3 Research Articles

Obtaining Electroheating Elements Based on Products of Carbothermal Reduction of Fe2O3 by Waste Activated Sludge (WAS)

In this work, the prospects of fabrication of heating elements from heat-treated (sintered) mixtures of waste-activated sludge (WAS) and Fe2O3 under oxygen deficiency conditions are considered. During heat treatment of mixtures in the 800–900 °C temperature interval, Fe2O3 reduces to Fe3O4, Fe0.94O, and Fe. A heat treatment at 1000 °C leads mainly to the formation of amorphous iron doped with carbon, silicon, and aluminum. Based on these compacted mixtures, having different electrical resistivity (from ~ 10–4 up to 10–1 Ω·m), it is possible to fabricate heating elements, whose working temperature ranges from ~ 100 °C up to 600 °C.Graphical

Analysis of wide diffuse halo formation in the x-ray diffraction spectrum during the reduction of Fe2O3 by waste-activated sludge (WAS)

A simulation of the diffuse experimental x-ray halo obtained when waste-activated sludge (WAS) was used as the Fe2O3 reducing agent made it possible to explain the large width of the experimental halo and the change in its shape as a result of the change in the amorphous phase content. The halo consists of different sets of amorphous phase convolutions. The synthesized product was a composite consisting of amorphous iron with inclusions of amorphous oxides of aluminum and silicon, amorphous carbon, and amorphous Si, Al, and C alloys on the surface of the Fe particles. The shift in the halo makes it possible to qualitatively estimate the contributions of oxide and carbon components or alloys to the halo of amorphous iron.

Preparation and characterization of ultra-lightweight ceramsite using non-expanded clay and waste sawdust

Expanded clay as a high-quality raw material to produce ceramsite is rapidly consumed in the past decades. A novel and green process to prepare the ultra-lightweight ceramsite using non-expanded clay and waste sawdust as raw materials was proposed in the present study, and the physical properties and phase transition mechanism of the ultra-lightweight ceramsite under different raw material formulas and sintering parameters were investigated. The synergistic effects of sawdust and Fe2O3 have a great influence on the expansion properties of ceramsite. The bulk density of ceramsite decreases with the increasing Fe2O3 content and sintering temperature, and it decreases first and then increases with the increase of sawdust content. The generation of gas and vitreous phase by sawdust burning and Fe2O3 reduction can promote the expansion of ceramsite. The typical core-cortex structure of ceramsite is formed, and the compact structure of the external layer significantly reduces the water absorption of ceramsite. The ultra-lightweight ceramsite was obtained with a bloating index of 321%, water absorption of 12.5%, bulk density of 280 kg/m3, and compressive strength of 1.0 MPa under the optimum conditions.

Reduction of FeO in Molten Slag by Solid Carbonaceous Materials for HIsarna Alternative Ironmaking Process

To investigate the use of biomass in the novel HIsarna technology, the reduction of FeO in the slag by chars produced from thermal coal (TC), charcoal (CC), and Bana grass char (BGC) was studied. A drop tube furnace coupled with a quadrupole mass spectrometer (DTF-QMS) was employed to study the injection of chars into pre-melted slag in the temperature range between 1450 °C and 1525 °C. The reduction rate was calculated from evolved gases and the extent of FeO reduction was confirmed by wavelength-dispersive X-ray fluorescence (WDXRF). The FeO reduction proceeds through two stages, starting with a rapid reduction, which is dependent on the carbon type, and followed by gradual leveling off. The reduction rate with the charcoal char (CC) was the highest, over 60 pct reduction was achieved in the first 500 seconds at 1500 °C, while ~ 50 and 40 pct achieved with TC and BGC chars, respectively, for the same reaction time. The kinetic analysis suggests that the first and second stages of the reaction can be described by the second-order (F2) and three-dimensional diffusion (D3) models, respectively. The apparent activation energy values for the first stage were 290, 229 and 267 kJ/mol for reactions with TC, CC and BGC chars, while 265, 369, and 282 kJ/mol were obtained for the second stage. Based on the experimental data and kinetic results, it can be concluded that the first stage is controlled by chemical reactions on the carbon surface, and the second stage is influenced by a mixed-controlling mechanism.

Viscosity and structure evolution of molten vanadium slag during carbothermic reduction process

In this study, the viscosity and structure evolution of molten vanadium slag at different stages during carbothermic reduction process were investigated through employing the rotating cylinder technique, Fourier transformation infrared (FTIR) and Raman spectroscopy. The results showed that both the viscosity and apparent activation energy of the slag continuously increased with the decrease of FeO and MnO contents, while decreased with the decrement of Cr2O3 and V2O3 contents. The mole fractions of Q2 and Q3 units in the silicate melt increased significantly due to the decrease in the concentration of free oxygen with the reduction of FeO and MnO, and the structural units transformed from prevalent Q0 and Q1 to Q2 and Q3 dominant, resulting in the fact that the trough depth of the [SiO4]-tetrahedral band was obviously enhanced and its center shifted to a higher wavenumber region in the FTIR spectroscopy. On the contrary, the reduction of Cr2O3 and V2O3 brought a gradual increasing Q0 and Q1 concentration and lower polymerization degree of molten slag, while the trough depth of the [SiO4]-tetrahedral band was weakened and its center shifted to a lower wavenumber region, which responded well to the viscosity variation of the slag.

Analyzing the formation mechanism of ‘Huoshihong’ characteristics in the blue-and-white porcelain of the Yuan Dynasty from Jingdezhen

Energy Dispersive X-Ray Fluorescence, field emission scanning electron microscopy and X-ray Absorption Fine Structure analysis were used to study the formation mechanism of the ‘Huoshihong’ (火石红) on the blue-and-white porcelain body of the Yuan Dynasty. The color rendering component for ‘Huoshihong’ is mainly α-Fe2O3. Liquid phase forms in high temperatures due to the invasion of external flux is the primary condition of the formation of ‘Huoshihong’. Fe enrichment also occurs at the places, but the Fe2+/Fe3+ ratio where ‘Huoshihong’ occurs is similar to other areas. The formation of ‘Huoshihong’ can be divided into three stages: oxidation of the body and reduction of Fe2O3, blending of Fe2+ into the liquid phase and enriched on body surface, re-oxidation of Fe2+ and crystallization stage of nanometer-scale α-Fe2O3. Experimental archaeological results corroborate theoretical analysis showing that the appearance and re-oxidation of Fe2+ are necessary conditions for ‘Huoshihong’ formation.

Influence of temperature during pyrolysis of Fe-alginate: Unraveling the pathway towards highly active Fe/C catalysts

Transition metals supported on carbons play an important role in catalysis and energy storage. By pyrolysis of metal alginate, highly active catalysts for the Fischer-Tropsch synthesis (FTS) can be produced. However, the evolution of the carbon (alginate) and transition metal (Fe3+) during pyrolysis remains largely unknown and was herein corroborated with several advanced in situ techniques. Initially, Fe3+ was reduced to Fe2+, while bound to alginate. FeO nucleated above 300 °C, destabilizing the alginate functional groups. Increasing temperatures improved carbonization of the carbon support, which facilitated reduction of FeO to α-Fe at 630 °C. Catalysts were produced by pyrolysis between 400 and 700 °C, where the highest FTS activity (612 µmolCO gFe−1 s−1) was achieved for the sample pyrolyzed at low temperature. Lower metal loading, due to less decomposition of alginate, moderated sintering and yielded larger catalytic surface areas. The results provide valuable knowledge for rational design of metal-alginate-based materials.

A DFT-based microkinetic theory for Fe2O3 reduction by CO in chemical looping

Redox kinetics of oxygen carrier in chemical looping is an important component for material preparation, reactor design and process demonstration. How to bridge the gap between the microscale density functional theory (DFT) and the macroscale redox kinetics and develop a first-principle-based theoretical model is still a challenge in the field of chemical looping. This study addresses this challenge and proposes a DFT-based microkinetic rate equation theory to calculate the heterogeneous kinetics of Fe2O3 reduction by CO in chemical looping. Firstly, the DFT calculation is adopted to search the reaction pathways and to obtain the energy barriers of elementary reactions. Secondly, the DFT results are introduced into the transition state theory (TST) to calculate the reaction rate constants and build the rate equations of elementary surface reactions. Finally, by considering the bulk diffusion, a rate equation is developed to bridge the gap between the elementary surface reactions and the grain conversion. In the theory, the reaction mechanism obtained from DFT and kinetic rate constants obtained from TST are directly implemented into the rate equation to predict the reduction kinetics of oxygen carriers without fitting experimental data. The accuracy of the developed theory is validated by experimental data of two Fe2O3 oxygen carriers obtained from the thermogravimetric analyzer (TGA). The microkinetic rate equation theory is based on the first principles calculation and can predict directly the redox kinetics of oxygen carriers without depending on the experimental kinetic data, therefore, it provides a powerful theoretical tool to screen the oxygen carrier materials and optimize the microstructure of oxygen carriers.

Novel Hybrid Nanomaterials Based on Poly-N-Phenylanthranilic Acid and Magnetic Nanoparticles with Enhanced Saturation Magnetization.

A one-step preparation method for cobalt- and iron-containing nanomaterials based on poly-N-phenylanthranilic acid (P-N-PAA) and magnetic nanoparticles (MNP) was developed for the first time. To synthesize the MNP/P-N-PAA nanocomposites, the precursor is obtained by dissolving a Co (II) salt in a magnetic fluid based on Fe3O4/P-N-PAA with a core-shell structure. During IR heating of the precursor in an inert atmosphere at T = 700–800 °C, cobalt interacts with Fe3O4 reduction products, which results in the formation of a mixture of spherical Co-Fe, γ-Fe, β-Co and Fe3C nanoparticles of various sizes in the ranges of 20 < d < 50 nm and 120 < d < 400 nm. The phase composition of the MNP/P-N-PAA nanocomposites depends significantly on the cobalt concentration. The reduction of metals occurs due to the hydrogen released during the dehydrogenation of phenylenamine units of the polymer chain. The introduction of 10–30 wt% cobalt in the composition of nanocomposites leads to a significant increase in the saturation magnetization of MNP/P-N-PAA (MS = 81.58–149.67 emu/g) compared to neat Fe3O4/P-N-PAA (MS = 18.41–27.58 emu/g). The squareness constant of the hysteresis loop is κS = MR/MS = 0.040–0.209. The electrical conductivity of the MNP/P-N-PAA nanomaterials does not depend much on frequency and reaches 1.2 × 10−1 S/cm. In the argon flow at 1000 °C, the residue is 77–88%.

Separate H2 and CO production from CH4‐CO2 cycling of Fe‐Ni

AbstractCH4‐CO2 chemical looping is proposed for separate H2 and CO production using nanostructured Fe‐Ni looping materials. The product streams are obtained by first feeding CH4, which decomposes to H2 and carbon. The latter acts as reductant for the subsequent CO2 feed, which together with Fe re‐oxidation yields CO. After 25 CH4‐CO2 cycles, 10Fe5Ni@Zr has a higher H2 space–time yield than 10Fe0Ni@Zr ( vs. ), a 2.6 times higher CO yield () and lower deactivation. This improvement has two reasons: (i) CH4 activation over Ni leading to cracking, (ii) product hydrogen causing deeper FeO reduction. Deactivation follows from accumulated carbon, non‐reactive for CO2. On Ni and Fe sites, carbon can be removed by lattice oxygen or CO2, yielding more CO compared to the theoretical value for Fe oxidation. However, carbon that migrates away from the metals requires oxygen for removal, which restores the activity of the Ni‐containing samples.

Synergistic effect of volatile inherent minerals on catalytic pyrolysis of wheat straw over a Fe–Ca–Ni catalyst

This work aimed to investigate effects of volatile inherent minerals on catalytic pyrolysis of wheat straw over a Fe–Ca–Ni catalyst. The wheat straw was pretreated by HNO3 (0.2 mol/L), And the internal structure of biomass does not change. Pickling mainly removes the metal species inherent in biomass. The experiment results indicated that inherent minerals and the Fe–Ca–Ni catalyst have a synergistic catalytic effect. The gas yields of gas and H2 under the 5 Fe 1.5 Ca-HC catalyst were 55.97% and 250.61 mL/g, respectively. Meanwhile, the gas production content is 42.32%, H2 yield reached 312.79 mL/g in the presence of 5 Fe 1.5 Ca 0.8 Ni-HC catalyst. Characterization results revealed that the inherent mineral promotes the reduction of Fe2O3 and NiO species also the dispersion of Fe2O3 phase. The metallic form of iron and nickel instead of oxide is considered to be active sites for volatiles reforming during biomass pyrolysis. The volatile minerals play a synergistic catalytic and dispersant role during the catalytic pyrolysis reaction with Fe–Ca–Ni-char catalyst.

Slag Modification in Reduction of Kiviniemi Ferrous Scandium Concentrates

Several research projects are currently focused on the search for new sources of scandium due to its expected increasing demand in advanced technology applications. The Kiviniemi Fe-Sc-enriched mafic intrusion is a potential primary source for Sc. According to the recent investigations on the FeO component reduction in the Kiviniemi magnetic Sc concentrate at various end temperatures, complete FeO reduction is achieved at the highest experimental temperature (1500 °C). However, efficient separation of metal from the Sc2O3-enriched slag is hindered by the high viscosity of the slag. In this study, investigations of the Kiviniemi-type concentrate reduction characteristics are complemented from three perspectives: (1) slag modification with CaF2 and/or CaO to promote the reduction of the FeO component and metal separation, (2) reduction characteristics of the concentrates with a slightly different modal mineralogy and chemical composition, and (3) description of the main features of the progression of reduction at selected temperatures (950, 1050, 1150, 1250, and 1350 °C) with CaO addition. Both CaF2 and CaO increase conversion rates at a lower temperature region and promote the separation of metal from the slag. High-temperature behavior of the concentrates used in this study is essentially similar, although the main reduction stage is initiated at a slightly higher temperature for concentrates with less amphibole and a higher amount of nonferrous gangue minerals. Only after the complete decomposition and melting of clinopyroxene and nonferrous minerals of the concentrate, the final reduction of the FeO component from the slag can take place.

Simultaneous Reduction of P2O5 and FeO from CaO–SiO2–FeO–P2O5 Synthesized Slag by Carbothermic Reduction

Simultaneous Reduction of P2O5 and FeO from CaO–SiO2–FeO–P2O5 Synthesized Slag by Carbothermic Reduction

A Numerical Study on the State of the Blast Furnace Thermal Reserve Zone under Different Starting Temperatures of Coke Solution Loss Reaction

As a measure to improve the blast furnace gas utilization efficiency during the iron making, decreasing the temperature of blast furnace thermal reserve zone (here called TRZ for short) by increasing the coke reactivity and therefore lowering the starting temperature of coke solution loss reaction (CSLR) has received much attention. However, this measure is proposed merely from a thermodynamic point of view by considering that the FeO reduction with CO is slightly exothermic. The effect of the CSLR starting temperature on the state of TRZ that also determines the kinetic conditions for indirect reduction has yet to be clarified. For this, a 1D kinetic model built previously is adopted in this paper to investigate how the TRZ state and gas utilization efficiency respond to the changes in the starting temperature of CSLR. The results show that with a decrease in the starting temperature, the height and average temperature of TRZ decrease, and the lower edge of TRZ shifts upwards. The gas utilization efficiency increases first and then decreases, thus leading to a critical starting temperature. Moreover, a lower critical temperature corresponds to a higher gas utilization efficiency. An increase in iron ore reducibility or top pressure can lower the critical temperature.

Utilization of Hematite Particles for Economical Removal of o-xylene in a High-Temperature Gas-Solid Reactor.

To establish a novel approach for VOCs resource utilization, coupled o-xylene oxidation and hematite reduction was investigated in this study in a high-temperature gas-solid reactor in the temperature range 300–700 °C. As the o-xylene-containing inert gas (N2) stream traveled through the hematite particle bed, its reaction behavior was determined in programmed heating and constant temperature modes. Consequently, the effect of bed temperature, flow rate and o-xylene inlet concentration on both o-xylene removal performance and degree of hematite reduction was studied. The raw hematite and solid products were analyzed by TGA, XRF, XRD and SEM-EDS. The results showed that a temperature above 300 °C was required to completely eliminate o-xylene by hematite, and both o-xylene removal capacity and degree of hematite reduction at 5% breakthrough points enhanced on increasing the temperature and decreasing the flow rate. The increment in temperature from 300 °C to 700 °C led to a gradual reduction of Fe2O3 to Fe3O4, FeO and metallic iron. Thus, this study provides a novel, economic and promising technology for treating the VOC pollutants.

Reduction characteristics of Kiviniemi ferrous scandium concentrate

• The main reduction stage of ferrous Kiviniemi concentrate is initiated at ∼ 950 °C. • Derivative conversion rates increase sharply from 1050 °C with high rates until ∼ 1250 °C. • Complete reduction of FeO is achieved at 1500 °C. • The properties of the resulting slag will need to be modified to promote metal separation. Scandium provides technological advantages particularly in solid oxide fuel cells and aluminum alloys. Potential new sources are investigated to respond to the expected increasing demand of this rare earth metal, which is currently classified as a critical raw material for the European Union. The recently discovered Kiviniemi mafic intrusion in Finland has been estimated to contain a total resource of 13.4 Mt of Sc with an average grade of 163 g/t. At Kiviniemi, Sc is incorporated within the lattices of ferrous silicates. Magnetic separation has been proposed as the first processing step to lower the amount of alkali-bearing diamagnetic minerals in Kiviniemi concentrates. Pyrometallurgical processing is suggested as the second step to decrease the amount of the ferrous oxide component from the concentrate prior hydrometallurgical processing. This study presents the first results of thermogravimetric experiments on pyrometallurgical reduction of the Kiviniemi concentrate up to temperatures of 1350–1500 °C. The aim of the study was to investigate the progression and extent of ferrous oxide reduction in the concentrate and to characterize the properties of resulting Sc-enriched slag and metal. The main reduction stage is initiated at ∼ 950 °C with a sharp increase in the derivative conversion rates between 1050 and 1170 °C and high rates until ∼ 1250 °C. Although complete reduction of FeO is achieved, the segregation of metal from the highly viscous slag will need to be promoted by adjusting the viscosity of the slag prior hydrometallurgical experiments.

Kinetics of the Isothermal Reduction of Fe2O3 with Hydrogen in a Magnetic Field

Kinetics of the Isothermal Reduction of Fe2O3 with Hydrogen in a Magnetic Field

Determining the kinetic rate constants of Fe3O4-to-Fe and FeO-to-Fe reduction by H2

Steel production using coal accounts for ∼ 8% of global carbon emissions. “Green Steel” is a new grand concept proposed recently to make steel from iron ores using renewable derived “Green Hydrogen” to achieve zero carbon emission. The kinetics and rate-limiting steps of iron ore reduction into iron with H2 as a reducing agent is critically important to the success of this new technology. While reduction of Fe2O3 into Fe by H2 follows multiple steps, the past research on this topic mainly deals with the overall averaged kinetics, giving little information on the elemental and rate-limiting steps. Here we report a kinetic study specifically design to attain kinetic rate constants of one-step reduction of Fe3O4-to-Fe and FeO-to-Fe. Guided by thermodynamics, we show first how to create in situ the desirable starting oxide phases, i.e., Fe3O4 and FeO, with precisely controlled the ratio of partial pressures of H2O and H2. We then show time-dependent raw H2O content data collected by a mass spectrometer and the processed reduction data to extract kinetic rate constants. We found that the kinetics of the two one-step reduction reactions follows nicely the Johnson-Mehl-Avrami (JMA) phase transformation model. The one-step reduction mechanisms and activation energy are also discussed.

Effects of Si and Al elements in coal on Fe-catalyzed brown coal pyrolysis

In our previous work, the experiments mainly investigated the effects of inherent minerals (K, Na, Ca and Mg) on Fe catalyst (5 wt%), respectively. Currently, the effects of Si and Al on Fe catalyst were further explored, and the aim is to improve the catalytic activity of Fe-catalyzed coal pyrolysis. The results indicate that the activity of Fe catalyst is improved with the increase of Si or Al content (0.1–1.0 wt%), and the promotion is affected by the ash content of coals. Simultaneously, Si or Al inhibits the activity of Fe catalyst with the increase of content (>1.0 wt%). The reasons were that Si surface substituted the hydroxyl of FeOOH in Fe catalyst to form Fe-O-Si which hindered the reduction of FeO to Fe, and Al2O3 inhibited the FeO reduction through the generation of FeO•Al2O3. The activity of promoters (K, Na, Ca and Mg) on Fe catalyst was investigated. The results reveal that Ca-Fe compounds in raw coal facilitate the formation of H2, and Mg-Fe compounds promote the generation of liquid. The work was beneficial to further understand the promotion/inhibition of Si and Al for Fe-catalyzed coal pyrolysis.

Discussion on Criterion of Determination of the Kinetic Parameters of the Linear Heating Reactions

Generally, the linear correlation coefficient is one of the most significant criteria to appraise the kinetic parameters computed from different reaction models. Actually, the optimal kinetic triplet should meet the following two requirements: first, it can be used to reproduce the original kinetic process; second, it can be applied to predict the other kinetic process. The aim of this paper is to attempt to prove that the common criteria are insufficient for meeting the above two purposes simultaneously. In this paper, the explicit Euler method and Taylor expansion are presented to numerically predict the kinetic process of linear heating reactions. The mean square error is introduced to assess the prediction results. The kinetic processes of hematite reduced to iron at different heating rates (8, 10 and 18 K/min) are utilized for validation and evaluation. The predicted results of the reduction of Fe2O3 → Fe3O4 indicated that the inferior linear correlation coefficient did provide better kinetic predicted curves. In conclusion, to satisfy the above two requirements of reproduction and prediction, the correlation coefficient is an insufficient criterion. In order to overcome this drawback, two kinds of numerical prediction methods are introduced, and the mean square error of the prediction is suggested as a superior criterion for evaluation.