Fine Iron Oxide Research Articles

CFD-DEM investigation on the agglomeration behavior of micron-sized combusted iron fines

The occurrence of agglomeration due to particle sintering is one of the most significant technical issues hindering the direct reduction process of iron oxide fines (DRI) in a high-temperature fluidized bed. To get a better understanding of the agglomeration mechanism, the (de-)fluidization behavior of micron-sized iron oxide particles in a 3-D fluidized bed is investigated using Computational Fluid Dynamics coupled with a coarse-grained Discrete Element Method (CFD-cgDEM). The inter-particle cohesive force is considered as a temperature-dependent solid bridge force. The coarse-grained method is first verified by comparing results for different scaling factors. Subsequently, the effects of temperature on the bed pressure drop, void fraction distribution, particle velocity distribution, and agglomerate size are investigated. In conclusion, the developed model shows the capacity for reliable prediction of particle agglomeration behavior, which can shed light on the design of the DRI process in high-temperature fluidized beds.

Probable causes of hardening of redoximorphic features in Plinthosols of the Araguaia River floodplain, Central region of Brazil

This study aimed to investigate the possible causes or conditions for the greater hardening or more hardened consistency of the plinthic feature, particularly in relation to forms and quantities of iron both in wet and dry conditions, taking into account that variations in the degree of consistency of these features are a phenomenon of great importance in the behavior of the soils of the Araguaia River floodplain, Brazil, due to its wide agricultural use. Soil features were collected at five positions in the profiles, where initial, central, and base plinthic horizons were detected. The separated samples of matrix, mottle, and plinthite were broken by the Instron apparatus and ground into powder. Then, chemical determinations were carried out by X-ray fluorescence (XRF), sulfuric acid attack (H2SO4), citrate-bicarbonate-dithionite (CBD), acid ammonium oxalate, and X-ray diffraction. The greater hardness of the plinthic features of the soils is directly related to the iron content in the oxidized form contained in its fine fraction and iron oxides are the elements responsible for promoting and maintaining the hardening of the features. The presence of the plinthic feature with the adequate hardness requirements was observed in the cases that presented a combination of the following factors: seasonality of the water regime; absolute Fed contents of at least 40.0 g kg−1 associated with a Fed/Fes ratio of at least 0.35; and Fes values equal to or >100 g kg−1 associated with a Fes/Fet ratio of at least 0.70. High Feo/Fed ratios, above 0.07, are indicative of more unstable features and, at the same time, with greater potential for hardening after drying.

Reduction kinetics of combusted iron powder using hydrogen

Despite extensive research on reduction of iron oxides in literature, there is no consensus on the most accurate reduction kinetics, especially for micron-sized iron oxide powders with high purity. Such data is particularly important for the application of metal fuels and chemical looping combustion, in which high purity iron powders function as dense energy carriers. Hence, in this work, hydrogen reduction of iron oxide fines, produced by iron combustion, were investigated using thermogravimetric analysis (TGA). The isothermal reduction experiments were conducted at the temperature range of 400–900 °C and at hydrogen partial pressures of 0.25–1.0 atm. Scanning electron microscopy (SEM) showed that the morphology of the reduction products depends on the reduction temperature but not on the hydrogen partial pressure. Reduction at higher temperatures leads to larger pore sizes. Based on an extended Hancock-Sharp “lnln”-method the appropriate gas-solid reaction models are determined, suggesting that the reduction can be described by a single-step phase boundary controlled reaction at temperatures below 600 °C, whereas a multistep mechanism is required for the description of reactions at higher temperatures.

Modelling of Defluidization of ZrO<sub>2</sub>/Fe Particles in High Temperature Gas Fluidization: Influence of Fe Contents

The contents of Fe on the surface of iron ore fines had a great influence on the fluidization behavior during high temperature fluidized bed reduction, which would cause defluidization when exceeding a critical value. In this paper, simplistically, ZrO2/Fe particles with different Fe contents on the surface were used as raw materials. Through modification of previous models, a quantitative relationship was established to predict the defluidization temperature of ZrO2/Fe particles with different Fe contents, and the calculation results corresponded well with the experimental data obtained from the defluidization test. The model in this paper firstly explained the dependence of defluidization behavior on the contents of Fe in high temperature gas fluidization, and it could well predict the metallization degree of commercial iron ore fines when defluidization occurred during fluidized bed reduction. Therefore, the model could be used as a reference to select suitable operating conditions for treating fine iron oxide particles in high temperature gas fluidization processes, such as direction reduction and chemical looping.

Arsenic sequestration by iron oxide coated geopolymer microspheres

A green, low-cost adsorbent based on geopolymer “microspheres” is reported for the first time for arsenic adsorption. A simple two-step process involves synthesizing geopolymer microspheres by inverse suspension polymerization and impregnating them with iron oxide. The low hydraulic conductivity of fine iron oxide powders demands the use of suitable support materials. Iron oxide modified geopolymer microparticles synthesized here, are small, spherical, porous, mechanically, and chemically stable, have high surface area of 270 m 2 /g and can be easily separated from water after adsorption is complete. A comprehensive adsorption study was conducted by employing environmentally critical arsenic species, viz. As(III), As(V), monomethyl arsenate and dimethyl arsenate. The role of contact time, initial arsenic concentration, temperature, adsorbent dosage, pH and competing ions was evaluated. Highest arsenic adsorption was observed at an iron content of 20 wt%. High percent removal of ∼86%, 100%, 95% and 96% for As(III), As(V), DMA and MMA respectively, were observed at initial arsenic concentration of 0.5 mg/L, an adsorbent dosage of 10 g/L and in just 60 min. Low pH favored adsorption of As(V), monomethyl arsenate and dimethyl arsenate while high pH favored adsorption of As(III). The applicability of the novel adsorbent in column mode, its high regeneration capacity and, facile, green, and cheap production are few of its advantages. Moreover, unmodified geopolymer microspheres, introduced here, can be employed as adsorbents for other toxic heavy metals such as Pb, Cd and Hg. • Inverse suspension polymerization was used to synthesize geopolymer microspheres. • Geopolymer microspheres were infused with iron oxide for arsenic adsorption. • Highest amounts of arsenic was removed by geopolymer containing 20 wt% iron. • Removal of As(III), As(V), monomethyl arsenate and dimethyl arsenate was evaluated. • New adsorbent showed excellent regeneration, hence making it economically viable.

Grain Refinement of Fe-X Alloys Fabricated by Laser Powder Bed Fusion

Grain refinement tendency of pure Fe and Fe-X (X=5~10at%Al, 2~10at%Ti) alloys produced by laser powder bed fusion (LPBF) process was investigated. Pure Fe, Al, and Ti powders were dry mixed and cubic samples were built from the mixtures. The microstructure analysis revealed that (1) the microstructure of pure Fe consisted of equiaxed grains having an average diameter of 1.7 μm with fine iron oxide particles. (2) Fe-5 and 10at%Al alloys showed coarse columnar grains. (3) Fe-2at%Ti shows a mixture of fine equiaxed and columnar shape grains. (4) the microstructures of Fe-5at%Ti and 10at%Ti alloys are fully equiaxed, and grain refinement tendency was confirmed with increasing Ti content. Ti(N,O) oxi-nitrides are efficient in reducing the grain size because of the low lattice misfit with the ferrite matrix. Additionally, the effectiveness of Ti(N,O) particles as grain refiners was confirmed by building samples using TiN powder mixed with Fe-10at%Al and Fe-2at%Ti. While these alloys alone are coarse grained, a dispersion of Ti(N,O) particles achieved a fine-grained microstructure.

Preparation of high-strength biochar composite briquette for blast furnace ironmaking

In this research, using iron-oxide fines (average size: 2.5 μm) and biochar fines (average size: 50.0 μm), the biochar composite briquette (BCB) for blast furnace (BF) application was prepared by cold briquetting followed by heat treatment. The preparing conditions were optimized regarding its cold crushing strength. Anti-pulverization capability, reaction development, and structure evolution of the optimally-designed BCB under simulated BF conditions were then examined. Results of optimizing BCB preparation conditions showed that a heating temperature of 1073 K was optimal for preparing the BCB. The optimally-designed BCB contained 11.10 wt.% carbon, 72.21 wt.% Fe3O4, 11.25 wt.% FeO, and 0.77 wt.% Fe, 6.44 wt.% gangue, and had a cold crushing strength of 1800 N/briquette. Results of BCB behavior under simulated BF conditions showed that the cold crushing strength after partial reaction of the BCB ranged from 1500 N/briquette to 5500 N/briquette and its maximum volume shrinkage degree was 0.45. The high anti-pulverization capability of the BCB was supported by the slag matrix or the iron network. Under the simulated BF conditions, the BCB underwent five stages of reduction by atmosphere, partial self-reduction and reduction by atmosphere, full self-reduction, partial self-reduction and gasification by atmosphere, and gasification by atmosphere. It is inferred from the experimental findings that, by charging the BCB in BF, an increase of top gas utilization efficiency could be realized, and a favorable influence on lowering the temperature level of the thermal reserve zone could be obtained.

Variable importance assessments of an innovative industrial-scale magnetic separator for processing of iron ore tailings

ABSTRACT Reprocessing of iron ore tailings (IOTs) and extracting recoverable valuable iron oxides will become increasingly financially attractive for mining companies and also may reduce environmental problems. Using databases built based on long term monitoring of units installed on plants to control the operational conditions to generate artificial intelligence models can decrease the cost of reprocessing operations Although some investigations have been focused on the reprocessing of IOTs, several challenges still remain which need to be addressed, especially for fine particles. SLon®, has developed a pulsating high gradient magnetic separator for the processing of fine iron oxides. However, there has been no systematic optimisation and variable assessments for SLon® operating variables to examine their effects on metallurgical responses (separation efficiency) on the industrial scale. This study addressed these drawbacks by linear (Pearson correlation) and non-linear (random forest) variable importance measurements (VIM) through an industrial SLon® installation.

Understanding the Self-Sintering Process of BOS Filter Cake for Improving Its Recyclability

Basic oxygen steelmaking (BOS) filter cake has been found to undergo a self-sintering process, improving its mechanical properties to allow easier recycling and utilization on plant. The aim of this study was to gain an understanding of the self-sintering of the BOS filter cake in terms of what reactions occurred, and how strength developed in the filter cake during self-sintering. The approach used was to characterize samples before reaction, and to measure the reactivity of the BOS filter cake during heating in air. Reacted samples were characterized and compared to self-sintered samples from the plant. The BOS filter cake consisted of very fine particles (200–500 nm) of metallic iron and wustite. Upon heating in air from 100 to 1000 °C, the BOS filter cake underwent a sequence of drying, oxidation, and calcination events. The primary reactions in self-sintering were found to be the oxidation of metallic iron and wustite to hematite and zinc ferrite, beginning at approximately 120 °C and were largely completed by 500–600 °C. These exothermic oxidation reactions at low temperatures were likely driven by the very fine particle size, and provided the energy required to heat the stockpiles and drive self-sintering. The strength required for recycling the BOS filter cake appeared to result from a network of particle–particle bonds that formed between the very fine iron oxide particles in the matrix during oxidation at elevated temperatures. Temperatures between 600 and 800 °C under oxidizing conditions are likely sufficient to form adequately strong material for transport and recycling in the BOS.

Morphology of Iron and Agglomeration Behaviour During Reduction of Iron Oxide Fines

The morphology of iron and agglomeration behaviour in the reduction progress of iron oxide fines were investigated in terms of isothermal reduction at 800 °C in an atmosphere of CO and H2. Agglomeration index was employed to evaluate the agglomeration behaviour during reduction. Sticking and agglomeration occurred regardless of the iron oxides and reducing atmosphere. Reduction by CO showed a higher tendency for sticking due to the formation of iron whiskers. The addition of CaO and MgO to Fe2O3 in sintering process could improve the reduction, and also decrease the sticking by forming calcio/magnesio-wustite on the surface. Iron whiskers were still formed with the addition of CaO and MgO, and the shape of whiskers were different from that of pure Fe2O3. Uniform coating layer on the surface of particles might be one of the important factors affecting the decrease in sticking between particles.

An iron oxide -copper bismuth oxide photoelectrochemical cell for spontaneous water splitting

Highly efficient water splitting reaction on hematite photoelectrode has been encumbered by its low photovoltage and photocurrent in a water splitting cell. In this work, a nanostructured hematite photoanode was prepared via a hydrothermal method, and its water oxidation activity was greatly enhanced by the synergetic application of uniform in-situ cobalt-doping and surface modification with fine cobalt iron oxide nanoparticles electrocatalyst. As a result, its remarkable low onset potential of 0.55 VRHE for water oxidation allows the construction of tandem cell with a novel metal oxide photocathode CuBi2O4, which has already proven reasonably robust photoactivity for water reduction reaction. The photocurrent and long-term stability of this metal oxides based device in alkaline electrolyte for unassisted overall water splitting reaction were investigated. A solar to hydrogen efficiency of 0.15% was measured accordingly on this spontaneous hydrogen production device, without the involvement of precious metal components.

Suction stress characteristics in granite red soils and their relationship with the collapsing gully in south China

The main goal of this research is to study the relationship between the soil suction stress and soil properties within four different soil profiles of collapsing gullies in the hilly granitic region of southern China. Large differences were found in the four soil layers between granite red soils, which are manifested in terms of soil bulk density, porosity, particle composition, clay minerals, micromorphology, organic matter, cation exchange capacity, permeability, oxide and hydraulics properties. The suction stress of the upper soils increases rapidly and almost linearly monotonously with the increase of matric suction, whereas C layers increases rapidly first, followed by a slow increase. The suction stress of the lower soils is significantly smaller than the upper soils under the same matric suction. These findings illustrate that the collapsing gully starts from the lower part of the granite red soil, and finally caused the gravity collapse in the upper soils, which is the main aspect that is different from the other types of soil erosion. Furthermore, suction stress has a very significant correlation with soil properties, with a positive correlation to the fine particle content, iron and aluminum oxide, and a negative correlation to coarse particles. In addition, suction stress can also be explained as being directly proportional to weathering degree. Our research provides a theoretical basis for the mass failures of the granite-derived red soil in southern China.

Effect of an acid mine spill on soils in Sonora River Basin: Micromorphological indicators

The role of soil could be decisive for the neutralization of the acid solution and immobilization of the metallic contaminants produced by mining industry. We studied micromorphological indicators of the interaction between the acid solution and soil material in the profile of Fluvisol at the Bacanuchi river (Sonora River Basin, Mexico) terrace affected by the catastrophic mine spill and in analyzing sample from a soil column treated with an acid liquid imitating the spill. Original unaffected soil is sandy with poorly developed pedogenetic features, however, frequent primary and secondary micritic and sparitic carbonates define high pH values. In the soil influenced by acid solutions under natural and laboratory conditions, carbonates were absent whereas neoformed gypsum crystals with radial intergrowth were observed together with accumulation of fine material enriched in ferruginous pigment. Micromorphometric quantification of the iron-rich fine material has shown its increase after interaction with the acid solution. We conclude that the interaction consisted of the neutralization reaction between the more reactive phases of the soil and the acid solution during which carbonates were consumed and gypsum was neoformed. Fine iron oxides precipitated after neutralization of acidity, the pH increased and the color changed. It is highly probable that other metallic contaminants co-precipitated with the ferruginous components.

Deposition of fine iron oxide particles in tap water using electrophoretic deposition (EPD) technique

An investigation of using the electrophoretic deposition (EPD) technique to deposit negatively charged fine iron oxide particles in tap water samples on a counter charge electrode (anode) was conducted. Characterizations of fine iron oxide particles in tap water from two different locations, i.e. commercial and residential areas, were identified. After centrifuging the tap water samples, a particle analyzer was used to analyze the particle sizes and zeta potential values. The average particle sizes for the supernatant region from the commercial and residential areas were 230±22.30 and 260±3.68nm, respectively. The zeta potential value from the residential area was higher than the commercial area, i.e. −42.27±0.12 and −34.83±0.23mV, respectively. X-ray diffraction (XRD) analysis indicated that the tap water samples consisted of iron oxide polymorphs, namely goethite (α-FeOOH), hematite (α-Fe2O3), magnetite (Fe3O4), and maghemite (γ-Fe2O3). During the removal of fine iron oxide particles using the EPD technique, the direct current (DC) voltage was varied from 5 to 25V at a constant electrode distance of 30mm. By increasing the surface area of the electrode from the carbon plate (64.87cm2/g) to the carbon fiber (679.35cm2/g), a higher percentage of fine iron oxide particles deposition was obtained from the carbon fiber than the carbon plate electrode. Thus, the removal of fine iron oxide particles at 5V was 96%±1.42 and 58%±2.17 for carbon fiber and carbon plate, respectively. EDX analysis confirmed that fine iron oxide particles were deposited on the anode electrode. The results proved that EPD was effective at removing fine iron oxide particles in tap water.

Removal of Iron Oxide With Superconducting Magnet High Gradient Magnetic Separation From Feed-Water in Thermal Plant

By the accident of Fukushima Daiichi Nuclear Plant, all the nuclear plants have stopped in Japan. As a result, the operation rate of thermal power plants has been increased. It caused growth in CO 2 emission, which requires some kind of countermeasure. We focused on the iron oxide scales deposited on the piping system and boiler which declines the heat exchange efficiency of thermal power plants. In this study we attempt to remove the iron scales from the piping system and the boiler to maintain the power generation efficiency. In the current thermal plant treated by All Volatile Treatment (AVT) the iron elutes to the feed water in the low-temperature part which changes into iron ion or the paramagnetic fine iron oxide particles. On the other hand at the high-temperature part the main component of the scales is large ferromagnetic particles of magnetite. Therefore the magnetic separation at the high-temperature part is the more effective to remove the scale than that at the low-temperature part. For the reason, the existing method using the electromagnetic filter placed in the low-temperature part is not effective to remove the scales. We studied the high gradient magnetic separation (HGMS) at high-temperature part to remove a large amount of the scale. In this study, we assumed to install the HGMS system using the superconducting magnet at the inlet of the boiler.

Flame propagation in hybrid “coal-methane-air” aerosuspensions

Results of laminar flame propagation experimental studies on hybrid aerosuspensions «methane-coal-air» are presented. Combustion of fine coal dust clouds (r0 = 8 microns, volume 4 · 10-3m3) and iron oxide clouds (r0 = 5 microns, volume 4 · 10-3m3) is investigated in isobaric conditions. Volumetric methane concentration was 6%. Comparison of visible and normal flame propagation velocities of mixtures "methane - air", "methane - coal - air" and "methane - inert component - air" testifies that fine coal particles increase flame propagation rate.

Development of fluxed micropellets for sintering utilising iron oxide waste fines

Ultrafine iron oxide wastes such as slime, blue dust and Linz–Donawitz (LD) converter sludge have very limited use in sintering of iron ore due to their excessive fineness (−50 μm). Pelletisation of these ultrafine materials for use in blast furnace involves high temperature curing, which is a highly energy intensive process. Briquetting of LD sludge requires costly binders and contains high moisture, which creates problem at high temperature of the downstream process. In order to alleviate these problems, the current study has developed a process for preparing micropellets of waste iron oxide fines (2–6 mm size) without using any binder. The strength of the micropellet has been increased by a novel CO2 treatment process at room temperature. Developed micropellets exhibit very suitable drop strength (125 Nos), tumbler properties and cold compressive strength (∼9 kg/pellet) to withstand cold handling. Low lime containing micropellets have the possibility of being used as a mixed material in usual sinter making, and high lime containing micropellets may be exploited for making super fluxed sinter that can be used as synthetic flux in the basic oxygen furnace process towards the formation of low melting oxidising slag at the early stage of blow.

Synthesis, Characterization and Functionalization of the Coated Iron Oxide Nanostructures

The iron oxides nanoparticles and iron oxide with other compounds are of importance in fields including biomedicine, clinical and bio-sensing applications, corrosion resistance, and magnetic properties of materials, catalyst, and geochemical processes etc. In this work we describe the preparation and investigation of the properties of coated magnetic nanoparticles consisting of the iron oxide core and organic modification of the residue. These fine iron oxide nanoparticles were prepared in air environment by the co-precipitation method using of Fe 2+ : Fe 3+ where chemical pre- cipitation was achieved by adding ammonia aqueous solution with vigorous stirring. During the synthesis of nanoparti- cles with a narrow size distribution, the techniques of separation and powdering of nanoparticles into rather monodisperse fractions are observed. This is done using controlled precipitation of particles from surfactant stabilized solutions in the form organic components. It is desirable to maintain the particle size within pH range, temperature, solution ratio wherein the particle growth is held at a minimum. The iron oxide nanoparticles can be well dispersed in an aqueous solution were prepared by the mentioned co-precipitation method. Besides the iron oxide nanowires were prepared by using similar method. These iron oxide nanoparticles and nanowires have controlled average size and the obtained products were investigated by X-ray diffraction, FESEM and other methods.

Development of Prefused Synthetic Flux for Basic Oxygen Steel Making through Micro-Pelletization and Sintering of Iron Oxide Fines

Calcined lump lime is used as flux material in basic oxygen furnace (BOF) steel making. Due to its high melting point and poor dissolution property, slag formation takes a long time. Since, Fe2O3–CaO has eutectic melting point of 1230°C at the composition of 22% CaO, material containing Fe2O3 and CaO can easily melt and form basic oxidizing slag at the very beginning of the blowing to make the refining process faster. A partially prefused synthetic flux in combination of mainly CaO and Fe2O3 has been prepared through micro-pelletization and sintering (MPS) of waste iron oxide fines generated in steel plant. The fines were converted to strong micropellets to make it suitable for sintering. Cold handling strength in micropellets was imperted by a novel CO2 treatment technique at room temperature and cold compressive strength up to 9 kg/pellet with a good abrasion resistance could be observed. The sintering of the developed micropellets was carried out without using coke breeze and produced sinter showed good handling strength, resistance to thermal shock and weathering, low softening temperature and thus qualifying it as a suitable alternate flux material for BOF towards fast formation of oxidizing and basic slag.

Granular iron oxide adsorbents to control natural organic matter and membrane fouling in ultrafiltration water treatment

Fine iron oxide particles (IOPs) are effective in removing natural organic matter (NOM) that causes membrane fouling in water treatment, but the separation of used IOPs is problematic. This study focused on the fabrication and use of granular iron oxide adsorbents, in combination with ultrafiltration (UF) membranes while investigating the NOM removal efficiency and fouling control. Sulfonated styrene-divinylbenzene copolymer beads were coated with two types of iron oxides (ferrihydrite and magnetite) and their performances were compared to that of fine IOPs. A significant amount of iron oxide coating (52–63 mg of Fe per g bead) was achieved by means of electrostatic binding and hydrolysis of iron ions. Iron oxide coated polymer (IOCP) beads were able to remove some amounts (∼20%) of dissolved organic carbon (DOC) comparable to that achieved by IOPs within a short period of time (<15 min). Regenerated IOCPs exhibited the same sorption capacity as the fresh ones. The integrated IOCP/UF system operation with a 15-min empty bed contact time and 10-h cyclic regeneration maintained the 20% DOC removal with no sign of significant membrane fouling. In contrast, a sharp transmembrane pressure buildup occurred in the UF system when no iron oxide pretreatment was applied, regardless of the types of membranes tested. Iron oxide adsorbed the NOM fraction with molecular weights of >1000 kDa which is believed to be responsible for severe UF fouling.