Reduction Of Hematite Research Articles

α-Fe2O3 Nanoparticles as Oxygen Carriers for Chemical Looping Combustion: An Integrated Materials Characterization Approach to Understanding Oxygen Carrier Performance, Reduction Mechanism, and Particle Size Effects

Through continuous flow reactor experiments, materials characterization, and theoretical calculations, we provide new insights into the reduction of hematite (α-Fe2O3) nanoparticles by methane (CH4) during chemical looping combustion (CLC). Across CLC-relevant temperatures (500–800 °C) and gas flow rates (2.5–250 h–1), decreasing α-Fe2O3 particle size (from 350 to 3 nm) increased the duration over which CH4 was completely converted to CO2 (i.e., 100% yield). We attribute this size-dependent performance trend to the greater availability of lattice oxygen atoms in the near-surface region of smaller particles with higher surface area-to-volume ratios. All particle sizes then exhibited a relatively rapid rate of reactivity loss that was size- and temperature-independent, reflecting a greater role for magnetite (Fe3O4), the primary α-Fe2O3 reduction product, in CH4 oxidation. Bulk (X-ray diffraction, XRD) and surface (X-ray photoelectron spectroscopy, XPS) analysis revealed that oxygen carrier reduction procee...

Extraction of Alumina from Red Mud for Synthesis of Mesoporous Alumina by Adding CTABr as Mesoporous Directing Agent

Mines in Bintan were producing bauxite for many years. The production process of bauxite to alumina produced much red mud. From X-ray Fluorescence (XRF), alumina content on Bintan’s red mud was 28.87 wt.%. This research was studying on the extraction alumina from red mud with reduction of hematite (Fe2O3) and desilication processes. After extraction process alumina was collected about 52.89 wt.%. Synthesis of mesoporous alumina from red mud using sol-gel method at the room temperature for 72 h with cetyltrimethylammonium bromide (CTABr) as mesoporous directing agent. The CTABr/Al-salt ratio, i.e. 1.57; 4.71 and 7.85 with the sample code of AMC-1, AMC-3, AMC-5, respectively. The product was calcined at 550 °C for 6 h. The synthesized materials were characterized by X-ray Diffraction (XRD), scanning electron microscopy-energy dispersive X-ray (SEM-EDX), transmission electron microscopy (TEM), and N2 adsorption-desorption techniques. XRD pattern of AMC-1, AMC-3, and AMC-5 showed that all synthesized materials have amorphous phase. The morphology were wormhole aggregate that were showed by SEM and TEM characterization. N2 adsorption-desorption characterization showed the distribution of pore size of about 3.2 nm. The highest surface area and pore volume were obtained in solid-solid ratio CTABr/GM-AL by 1.57 (AMC-1) i.e. 241 m2/g and 0.107 cm3/g, respectively.

Direct electrochemical reduction of hematite decorated graphene oxide (α-Fe2O3@erGO) nanocomposite for selective detection of Parkinson's disease biomarker

An unusual approach is reported herein to fabricate magnetic hematite (α-Fe2O3) decorated electrochemically reduced graphene oxide (α-Fe2O3@erGO) nanocomposite. The method utilizes direct electrochemical reduction of self-assembled, ex-situ synthesized α-Fe2O3 anchored GO to erGO (α-Fe2O3@erGO) on glassy carbon electrode (GCE) for selective detection of dopamine (DA), an important biomarker of Parkinson's disease. The formation of α-Fe2O3@erGO/GCE has been confirmed by XPS and Raman spectroscopy. α-Fe2O3@erGO modified GCE exhibits synergistic catalytic activity nearly 2.2 and 5 fold higher than α-Fe2O3@GO and other modified electrodes, respectively towards oxidation of DA. The fabricated sensor exhibited linear dynamic ranges over 0.25 − 100 µM in response to DA with a LOD of 0.024 µM (S/N = 3), LOQ of 0.08 µM (S/N = 10), and a sensitivity of 12.56 µA µM–1 cm–2. Finally, the practical analytical application of the proposed α-Fe2O3@erGO/GCE was investigated for the determination of DA in commercially available pharmaceutical formulation and human serum samples, and showed satisfactory recovery results towards DA.

Growth Behavior and Size Characterization of Metallic Iron Particles in Coal-Based Reduction of Oolitic Hematite–Coal Composite Briquettes

To reveal the growth behavior and size characterization of iron particles in coal-based reduction, we reduced oolitic hematite–coal composite briquettes at various temperatures, durations and ore size fractions. The degree of metallization and microstructure of the reduced briquettes and the characteristic of iron particle size were investigated through chemical composition analysis, scanning electron microscopy, energy dispersive spectroscopy, and Bgrimm process mineralogy analysis. Results showed that iron oxides in the oolitic hematite ore were reduced to metallic iron from outer to inner layers; these oxides gradually grew into quasi-spherical iron particles with random distribution in the gangue. As reduction continued, iron grains agglomerated occurred, and iron particle clusters were formed in the form of quasi-spherical, chained, blocky, and clavate when they were viewed in the cross section. The boundaries among the iron grains of the iron particle cluster continuously faded and disappeared, and an iron particle with increased size and homogeneity was finally produced. The reduction temperature, time, and ore size fraction influenced the reduction of composite briquettes and iron particle size. The degree of metallization increased as reduction temperature was increased, reduction time was extended, or ore size fraction was decreased until the equilibrium of reaction was achieved. Moreover, the iron particle size gradually increased as reduction temperature was increased, reduction time was extended, or ore size fraction was decreased.

Sustainable development of selective iron carbide, silicon carbide and ferrosilicon (low temperature) phases during iron ore reduction using only polymers

Production of selective iron phases of iron carbide (nanoscale<2nm), silicon carbide or ferrosilicon using polymer resins and hematite is presented. Commercial epoxy resin, epiglue and silicones are used. Nonrenewable resources such as coke or high pure quartz are not used. A solid-liquid reaction provides for better intimate contact and reaction efficiency. Viscous epoxy and silicone resins can completely wet the reactants forming interfacial covalent bond between the metal oxide and the desired elements in the resins when cured at room temperature for 24h, while facilitating migration of desired elements into iron matrix during reduction of hematite. Secondary ion mass spectroscopy, X-ray diffraction, Scanning Electron Microscopy and off gas studies confirmed the formation of iron alloy phases. The study opens pathway for feedstock recycling of silicones maximizing resource recovery reducing the landfill/depolymerization of silicones. The valuable resources such as silicon, carbon and hydrogen in waste silicones, can replace metallurgical coke and quartzite as alloying elements in FeSi or SiC. Recyclable bioepoxy resin /bio renewable/recycled epoxy resin, which will otherwise be landfilled or incinerated, make this process sustainable, cleaner and cost-effective. FeSi formation at much lower temperature (~1500°C) as opposed to very high temperatures (>1800°C) spells energy savings and emission reductions. A potential replacement of nonrenewable coke by the composites of the resins and iron oxide as spacer provides for added benefit. The SiC, Fe3C and ferrosilicon find application in the economical production of high pure hydrogen and photovoltaic industry.

Reduction kinetics of hematite ore fines with H2 in a rotary drum reactor

Porous hematite ore was prepared by the dehydration of low-grade limonite ore with high moisture content. In this study, the mechanisms and kinetics of the isothermal reduction of hematite ore fines by hydrogen–nitrogen gas mixtures were investigated using a rotary drum reactor in the temperature range of 700–900 °C. The reduction rate and degree of reduction initially increased with H2 content and temperature, and subsequently, the reduction rate decreased with the increasing reduction reactions of iron oxide. Our results indicate that the dehydration significantly increases the specific surface area of the original limonite ore, creating nanopores. We found that the reduction of hematite (Fe2O3) to metallic iron (Fe) was controlled by a first-order reaction model (one-dimensional formation and growth of nuclei) below 850 °C. However, at 900 °C, the reaction initially followed the above model and then shifted to follow a diffusion-controlled reaction model in the final stages of reduction owing to the low diffusion rate of oxygen in the formed dense iron layer. The value of the apparent activation energy for the overall reduction process of hematite to metallic iron was ~51 kJ/mol.

Iron ore pellet drying assisted by microwave: A kinetic evaluation

ABSTRACTDrying is a critical process step to achieve excellent pellet quality in pelletizing process. The complexity and energy consumption toward moisture removing, especially for highly hydrated iron ore, increased the need for breakthrough enhancements to this process. The present study has evaluated kinetics parameters of the moisture release from iron ore green pellet using energy transmitted through microwave (frequency of 2.45 GHz). The influence of pellet size and output power on the moisture effective diffusivity (Deff) and the drying activation energy (Ea) were evaluated. The results make possible to compare the cutting-edge approach with traditional convective drying. Pellet physical quality was investigated through the green crushing strength (GCS), which shows smooth reduction in earlier stages, however not affecting the final dry GCS results. Bonded hematite reduction and calcination of goethite was identified at the microstructure through reflected light microscopy, SEM showed micro cracks formation in several grains.

Synthesis and magnetic properties of magnetite prepared by chemical reduction from hematite of various particle sizes

In the process of beneficiating iron ores by the magnetic separation, particles of hematite and quartz accumulate, forming tailings that occupy large areas of agricultural lands. Such man-made deposits are quite common and contain large quantities of iron oxides such as hematite. Therefore the tailings can be used as raw material for the production of magnetite. In this work, magnetite was synthesized by hematite reduction at a temperature of 500 °C in an atmosphere of carbon monoxide. The source hematite was separated initially into ten particle size categories ranging from 0.05 to 2.5 mm. The reduction was carried out with carbon monoxide, which was synthesized by reaction of air and activated carbon at 750 °C. It was determined by X-ray diffraction analysis and magnetometry that, after reduction, samples of each particle size consisted mainly of magnetite. In addition, the magnetic properties of the resulting magnetite were noted to be somewhat different from those of natural magnetite. In particular, remanence and coercivity are higher for synthetic magnetite than for natural magnetite. The saturation magnetization of transformed samples increases to 60–80 Am2/kg, while the source hematite does not have strong magnetic properties. Hematite with a particle size from 0.05 to 0.25 mm is completely converted into magnetite, but if the size of hematite particles increases to from 0.25 to 2.5 mm, incomplete conversion of hematite to magnetite is observed. The obtained results are important for the development of technology for converting hematite to magnetite, which can, in turn, be used to beneficiate iron ores.

Mediated Electrochemical Reduction of Iron (Oxyhydr-)Oxides under Defined Thermodynamic Boundary Conditions.

Iron (oxyhydr-)oxide reduction has been extensively studied because of its importance in pollutant redox dynamics and biogeochemical processes. Yet, experimental studies linking oxide reduction kinetics to thermodynamics remain scarce. Here, we used mediated electrochemical reduction (MER) to directly quantify the extents and rates of ferrihydrite, goethite, and hematite reduction over a range of negative reaction free energies, ΔrG, that were obtained by systematically varying pH (5.0 to 8.0), applied reduction potentials (-0.53 to -0.17 V vs SHE), and Fe2+ concentrations (up to 40 μM). Ferrihydrite reduction was complete and fast at all tested ΔrG values, consistent with its comparatively low thermodynamic stability. Reduction of the thermodynamically more stable goethite and hematite changed from complete and fast to incomplete and slow as ΔrG values became less negative. Reductions at intermediate ΔrG values showed negative linear correlations between the natural logarithm of the reduction rate constants and ΔrG. These correlations imply that thermodynamics controlled goethite and hematite reduction rates. Beyond allowing to study iron oxide reduction under defined thermodynamic conditions, MER can also be used to capture changes in iron oxide reducibility during phase transformations, as shown for Fe2+-facilitated transformation of ferrihydrite to goethite.

Mechanism and Kinetics of the Reduction of Hematite to Magnetite with CO–CO2 in a Micro-Fluidized Bed

The mechanism and kinetics of the reduction of hematite to magnetite in a laboratory-scale, micro-fluidized bed reactor were isothermally investigated. The procedure consisted of the isothermal heating in a flow of a 20%CO–80%CO2 mixture at temperatures from 500 °C to 600 °C. It was found that the Avrami–Erofe’ev model of nucleation and 1D growth (n = 1.58) successfully described the phase transition of hematite to magnetite, and the value of activation energy ΔEa of the reaction was estimated to be 48.70 kJ/mol. The microstructure properties for specimens with different conversion degrees were analyzed using the Brunauer, Emmett and Teller (BET) method and scanning electron microscopy (SEM). The results showed that the magnetite nuclei were needle-like, and the hematite specimens became thoroughly porous after complete reduction to magnetite. The physical and chemical processes of the reaction were also discussed.

Investigation into coal-based magnetizing roasting of an iron-rich rare earth ore and the associated mineralogical transformations

The factors influencing goethite to magnetite conversion during magnetizing roasting of an iron-rich rare earth ore using coal as the reductant were explored in the present paper. The effect of temperature, time and reductant addition on magnetite conversion; and the optimal conditions which resulted in complete conversion of goethite to magnetite were determined through the use of satmagan and quantitative X-ray diffraction. For this particular ore, optimal roasting conditions were determined to be a roasting temperature of 600–650°C with the addition of 10–20wt% coal in the mixture and a roasting time of 90min. The mineralogical changes occurring during magnetizing roasting were also investigated using X-ray diffraction. Magnetite formation was found to proceed by the reduction of hematite formed from the dehydroxylation of goethite. X-ray diffraction showed that further reaction of magnetite to form wüstite and fayalite had taken place under highly reducing conditions and temperatures exceeding 650°C. The primary rare earth mineral in this ore, monazite was stable at all roasting conditions whilst florencite underwent thermal decomposition resulting in an increase in the monazite content of the roasted ore.

Investigation on gasification performance of sewage sludge using chemical looping gasification with iron ore oxygen carrier

Chemical looping gasification (CLG), with inherent characteristic of low pollutant emissions can realize the treatment and disposal principle of sewage sludge of harmlessness, reduction, stabilization and reutilization. This work attempted to investigate the feasibility of CLG of sewage sludge with hematite oxygen carrier. The role of hematite in CLG was firstly determined and it was used as gasification agent to provide the required oxygen for sludge conversion. Subsequently, the effect of various operating parameters on sludge CLG was discussed. An optimal mass ratio of sludge to hematite oxygen carrier was determined at 0.33 to achieve the high-efficient conversion of sludge. The reaction temperature of sludge gasification was set at 900 °C to avoid the excessive reduction of hematite. Suitable steam content was assigned to at 19.52%, where the sludge conversion attained the maximum. Ash deposited caused the decrease of specific surface area of hematite, but the accumulated mineral elements in sludge ash can improve the reactivity of oxygen carrier. Additionally, the ash accumulation also can prolong the gas mean residence time. Hence, the sludge conversion showed a slight uptrend with the cycle numbers. The phosphorus element of sludge was formed of CaH2P2O7 and CaHPO4 during the CLG. Although some sludge ash deposited on the surface of hematite particles, the new compounds were not observed in the reacted oxygen carrier. Additionally, sludge ash has a relatively high resistance trend for bed agglomeration and deposit formation due to the high content of Ca/Al elements. Consequently, the accumulation of sludge ash only reveals physical effects rather than chemical effects on the hematite particles. Thus, it is easy to separate the sludge ash from hematite particles according to the differences in density and size.

Reduction of Hematite to Magnetite in CO/CO2 Gas Mixtures Under Carbon Looping Combustion Conditions

Iron oxides have been identified as promising materials for use as oxygen carriers in chemical looping combustion technologies as there are abundant resources available in the form of ore and in industrial wastes. The isothermal reduction of hematite (Fe2O3) in the fuel reactor and the subsequent oxidation of magnetite (Fe3O4) in air are the principal reactions of interest for these applications. Experimental investigations have been carried out to characterize the microstructural changes taking place as a result of the reduction reactions for a range of CO/CO2 gas compositions at temperatures between 1073 K and 1373 K (800 °C and 1100 °C). It has been shown that magnetite spinel is formed directly from hematite under these conditions and that porous magnetite or dense platelet or “lath” type morphologies can be formed depending on gas composition and reaction temperature. The conditions for the lath/pore transition are established. Dendritic gas pores are formed during the creation of the porous magnetite. This morphology allows continuous contact between the gas reactant and reaction interface and results in high reduction reaction rates.

Analysis of the Reduction Rate of Hematite Concentrate Particles in the Solid State by H2 or CO in a Drop-Tube Reactor Through CFD Modeling

The kinetic analysis of the reduction of hematite concentrate particles by individual reducing gas H2 or CO was performed using a computational fluid dynamics (CFD)-based approach in this paper. The particle residence time was calculated through the integration of the equation of particle motion. Non-uniform particle temperature profiles inside the reactor were obtained, and were taken into consideration for the kinetic analysis. The calculated reduction degrees based on this approach are in good agreement with the experimental values.

Powder reduction kinetics of dicalcium ferrite, calcium ferrite, and hematite: Measurement and modeling

Shrinking core model is widely applied to describe the reduction of iron ore pellets, but limited to the illustration on powder sample. The reduction of powder materials is commonly observed in blast furnace production but has been rarely investigated. In this study, thermal kinetics analysis was conducted to describe the powder reduction of dicalcium ferrite (2CaO⋅Fe2O3, C2F), calcium ferrite (CaO⋅Fe2O3, CF), and hematite (Fe2O3, H), with particle sizes below 70µm. Isothermal reduction experiments were performed through thermogravimetry analysis under CO atmosphere. The reduction degrees and reaction rate constants increased in the order of C2F, CF, and H at 1123, 1173, and 1223K. The reduction rate analysis illustrated that the reduction of C2F, CF, and H appeared as one-, two-, and three-stage reactions, respectively. Moreover, the reduction of C2F and CF proceeded as the 2D reaction mechanism described by Avrami–Erofeev (A-E) equation. The reduction of H was initially controlled by 2D, followed by the 3D A-E kinetics equation. Phase with superior reducibility could be reduced by CO in more dimensions of sample layers. The reduction degrees and rate change expressed by A-E equations were verified to be in accordance with the experimental data. A new kinetics model was proposed to elucidate the reduction of C2F, CF, and H in ultrafine powder compared with that in pellets. The reduction process in the powdered samples comprised independent reduction stages caused by uniform CO diffusion in powdered particles.

Effect of Na2CO3 and CaCO3 on coreduction roasting of blast furnace dust and high-phosphorus oolitic hematite

Iron was recovered from blast furnace dust and high-phosphorus oolitic hematite in the presence of Na2CO3 and CaCO3 additives. The functions of Na2CO3 and CaCO3 during the coreduction roasting process were investigated by XRD and SEM-EDS analyses. Results indicate that these additives not only hinder the reduction of fluorapatite, CaCO3 also decreases the P content of direct reduced iron (DRI) by increasing the reduction alkalinity. P remains as fluorapatite in the slag, which can be removed by grinding and magnetic separation under optimal conditions. The Na2CO3 promotes hematite reduction and improves the iron recovery (eFe) by replacing the FeO from fayalite, which results in quick growth and aggregation of metallic iron and improvement of eFe in DRI. A DRI with 91.88 mass% Fe, and 0.065 mass% P can be achieved at a recovery of 87.86 mass% under the optimal condition.

Hydrogen purification over lanthanum-doped iron oxides by WGSR

Hydrogen technology has been greatly increased in last decades as a promising solution to protect the environment. When carbon-based feedstocks are used, such as natural gas, biomass and biogas, the water gas shift reaction (WGSR) plays an important step in the production of high pure hydrogen for several purposes. By this reaction, the residual carbon monoxide in the gaseous stream (coming from steam reforming of carbon-based feedstocks) can be converted to carbon dioxide and then removed from the stream, avoiding the poisoning of industrial metallic catalysts as well as of electrocatalysts in fuel cells. Aiming to obtain no toxic catalysts that can replace the commercial chromium-doped hematite catalysts, lanthanum-doped hematite was studied in this work. Iron oxide-based samples with different amounts of lanthanum (La/Fe (molar)=0.02; 0.08 and 0.2) were obtained by sol-gel method and calcined at 600°C. The catalysts were characterized by X-ray diffraction, specific surface area measurements, temperature programmed reduction, Raman spectroscopy, Mössbauer spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. It was found that lanthanum affected the textural and reducing properties of hematite, depending on the amount. Moreover, lanthanum oxide increased the activity of hematite by decreasing the size of hematite crystals and then increasing the number of exposed active sites. In addition, lanthanum favored hematite reduction to produce magnetite (active phase). The activity increased with the amount of lanthanum in solids, the lanthanum-richest sample being the most active catalyst.

Reduction roasting of hematite to magnetite using carbohydrates

Thermomagnetic analysis was conducted on phase transformations performed for synthetic and natural hematite by reduction involving various carbohydrates (starch, glucose, fructose, sucrose, and ascorbic acid). Thermomagnetic measurements were carried out using a laboratory facility that allows the automatic registration of a sample's magnetization as the temperature changes (the rate of sample heating/cooling was 65°/min). The results were then analyzed. The reduction reaction of synthetic hematite for all carbohydrates starts at a temperature of ~350°C, while the reduction of natural hematite for all carbohydrates starts at a temperature of ~365°C. The magnetite formed by the reaction has a Curie temperature of 565°C. Both magnetite and hematite are present in all transformed samples. Saturation magnetization increases to ~50Am2/kg for the samples obtained from synthetic hematite and ~25Am2/kg for the sample obtained from natural hematite. The difference in the value of saturation magnetization is attributed to a lower magnetite content for the sample obtained from natural hematite. Synthetic hematite transforms more effective, suggesting the synthetic sample is characterized by a larger surface area compared to natural hematite.

Dynamics of carbide formation in iron-supported catalysts of the Fischer–Tropsch process promoted by copper and potassium

The kinetics of the formation of iron carbides during the activation of iron-coated catalyst for Fischer–Tropsch synthesis promoted by copper and potassium, and by carbon monoxide and syngas, is studied. It is established that the presence of copper lowers the initial temperature of hematite reduction to magnetite and leads to the formation of carbide in both CO and СО/Н2. Potassium slows the rate of magnetite formation, but it accelerates the formation of iron oxide. It is shown that the rate of carbide formation during magnetite reduction for catalysts is half that in the reaction of hematite reduction to magnetite in both CO and СО/Н2.

Designed porous microstructures for electrochemical reduction of bulk hematite ceramics

This work proposes a new approach for electrochemical reduction of hematite to magnetite and/or metallic iron, based on ceramic cathodes with designed microstructures. The processing method, involving emulsification of concentrated aqueous ceramic suspensions with melted paraffin, enables preparation of cellular hematite ceramics possessing open porosity and pore interconnectivity controlled by simple process parameters. The obtained porous hematite ceramics were successfully used as cathodes for in situ electrochemical reduction in aqueous alkaline electrolyte. Electrochemical reduction converts the designed ceramic microstructure to corresponding cellular Fe/Fe3O4/Fe2O3 composites with adjustable phase distributions and high prospects for applications in heterogeneous catalysis or other applications, based on unique combinations of active functionalities of metallic Fe, magnetite and hematite.