Magnetite Powder Research Articles

Evaluation of the separation performance of an air dense medium gas-solid fluidized bed for coal cleaning: Effect of the binary dense media

The binary dense media plays a significant role in the air dense medium gas–solid fluidized bed for coal separation. Magnetite powder with a narrow size fraction of −0.20 + 0.15 mm and −0.35 + 0.25 mm quartz sand were mixed in proportion to form a binary dense media. The separation performance of −13 + 6 mm coal was evaluated through the combination of various indicators of the yield and ash content of products, combustible material recovery, relative segregation degree, and probable error. Results suggested that the optimal separation performance was achieved by an adjustment of the appropriate operational gas velocities of the bed and use of the binary dense media with a suitable composition as the separating medium. The proportion of the quartz sand mixed in the binary dense media should be adjusted as 10% or 20% and the fluidization number could be varied from 1.6 to 1.8. The satisfactory ash content and yield of clean coal were 10.12% and 68.29%, respectively, with a combustible material recovery of 92.09%. The largest relative segregation degree was 0.95, and the minimum probable error was 0.085 g/cm3 with a standard deviation of 0.024 g/cm3. These findings indicated efficient coal cleaning.

Nanosized Magnetite Powder as a Material for Skimming Oil Products from Water Surface

Parameters of structure, dispersity, morphology, and magnetic properties of nanosized powder of magnetite obtained by mechanochemical synthesis from salt systems are reported. Results of using the magnetite nanopowder as a material for skimming mineral oil are discussed.

In-Situ High Resolution Dynamic X-ray Microtomographic Imaging of Olive Oil Removal in Kitchen Sponges by Squeezing and Rinsing.

Recent advances in high resolution X-ray tomography (μCT) technology have enabled in-situ dynamic μCT imaging (4D-μCT) of time-dependent processes inside 3D structures, non-destructively and non-invasively. This paper illustrates the application of 4D-μCT for visualizing the removal of fatty liquids from kitchen sponges made of polyurethane after rinsing (absorption), squeezing (desorption) and cleaning (adding detergents). For the first time, time-dependent imaging of this type of system was established with sufficiently large contrast gradient between water (with/without detergent) and olive oil (model fat) by the application of suitable fat-sensitive X-ray contrast agents. Thus, contrasted olive oil filled sponges were rinsed and squeezed in a unique laboratory loading device with a fluid flow channel designed to fit inside a rotating gantry-based X-ray μCT system. Results suggest the use of brominated vegetable oil as a preferred contrast agent over magnetite powder for enhancing the attenuation coefficient of olive oil in a multi fluid filled kitchen sponge. The contrast agent (brominated vegetable oil) and olive oil were mixed and subsequently added on to the sponge. There was no disintegration seen in the mixture of contrast agent and olive oil during the cleaning process by detergents. The application of contrast agents also helped in accurately tracking the movement and volume changes of soils in compressed open cell structures. With the in house-built cleaning device, it was quantified that almost 99% of cleaning was possible for contrasted olive oil (brominated vegetable oil with olive oil) dispersed in the sponge. This novel approach allowed for realistic mimicking of the cleaning process and provided closer evaluation of the effectiveness of cleaning by detergents to minimize bacterial growth.

The effect of pH and sintering treatment on magnetic nanoparticles ferrite based synthesized by coprecipitation method

Ferrite nanoparticles synthesized by coprecipitation method depend mostly on parameters synthesis such as reaction temperature, pH of the suspension, and initial molar concentration. Here, we reported the physical properties of nanoparticles magnetite (Fe3O4) synthesized by coprecipitation method with variation of pH in the range between 8 and 11, in order to investigated the effect of pH treatment to its optical properties, particles size, and phase changes after sintering treatment. The band gap parameters of magnetite nanoparticles and crystal structure of magnetite powder are determined. From UV-Vis measurement, it is found that the band gap of magnetite nanoparticles was in the range of 1.3 eV to 1.5 eV with the smallest size of nanoparticles was 9.69 nm obtained at condition of pH = 10. From XRD characterization, it was found that all samples sintered at 100°C for 4h have magnetite phase of Fe3O4 with cubic structure, while all samples sintered at 1100°C for 4 h have hematite phase of a-Fe2O3 with hexagonal structure.

Characterization of temporal and spatial distribution of bed density in vibrated gas-solid fluidized bed

This study uses a Φ 200 mm × 900 mm vibrated gas-solid fluidized bed (VGFB) with −0.3 + 0.074 mm magnetite powder was utilized to characterize the temporal and spatial distribution of bed density in VGFB and the influence of bubble movement on fluctuations in bed density. The results indicate that the bed density decreases with an increase in gas velocity (U) and the frequency (f) and amplitude (A) of vibration and that the bed density spatial distribution is lower in the central region but higher in the border regions. The standard deviation of the density first increases then decreases and finally tends to stabilize with an increase in apparent gas velocity. Moreover, when A = 2 mm, f = 25 Hz and U = 14 cm/s, the density distribution is 1.82–1.88 g/cm3 and the fluidization state is improved. The energy of the pressure signal increases with an increase in gas velocity and vibration amplitude. In particular, the low-frequency band of the pressure signal exhibits the highest amplitude and energy, which reveals that bubbles are the main cause of pressure fluctuation. Furthermore, the bed density decreases with an increase in bubble generation frequency, and the relationship between these follows the ExpDec 2 mathematical equation.

A stable novel nanostructure of ZnFe2O4 based nanocomposite for improved photoelectrocatalytic and photocatalytic activities

A nonagon ZnO–ZnFe2O4 nanocomposite was synthesized using high-energy ball milling followed by post-annealing with an initial mixture of high purity magnetite (Fe3O4) and zincite (ZnO) powders. The effects of the process parameters on the structural, optical, photocatalytic, and photoelectrocatalytic activities were investigated. X-ray diffraction analysis was used to confirm the presence cubic spinel ZnFe2O4 and hexagonal ZnO crystal phases. The lowest optical bandgap observed was 1.83 eV, which decreased due to post-annealing. The photocatalytic activity of the 800 °C post-annealed nanocomposite exhibited the highest degradation percentage of 96% over 180 min under visible light, with a degradation rate constant of 1.5 min−1. Furthermore, the optimized sample showed no substantial decrease in photocatalytic activity after five cycles of the repeated catalysis experiment. In electrochemical studies, when compared to the other post-annealed samples, the 800 °C post-annealed nanocomposite showed the highest water splitting activity with the lowest charge-transfer resistance of 75 Ω, photocurrent density of 4.3 × 10−5 Acm−2, exchange current density of 4.19 log JA−1 cm−2, and Tafel slopes of 74.1 mVdec−1. In dual activities, the performance of the 800 °C post-annealed nanocomposite was noticed to be enhanced. This nanocomposite has potential industrial applications as a cost-effective catalyst.

Structural Aspects of Fe3O4/CoFe2O4 Magnetic Nanoparticles According to X-Ray and Neutron Scattering

Structural aspects of powders containing magnetic nanoparticles Fe3O4/CoFe2O4 with the anticipated “core-shell” structure are considered by means of comparative analysis with individual particles of Fe3O4, CoFe2O4 in accordance of data obtained from X-ray powder diffraction and small-angle scattering of X-ray (synchrotron) radiation and neutrons. It is shown that magnetic particles in the powders under study have a strong polydispersity and form complex aggregates. Characteristic sizes of the crystallites, as well as a ratio of magnetite to cobalt-ferrite in the composition of the Fe3O4/CoFe2O4 particles were evaluated from the analysis of the diffraction peaks. Аnalyzing the data on small-angle scattering, the dimensional characteristics of particles and aggregates, as well as the volume fraction of the last ones in the powders, have been obtained. Fractal dimensions of aggregates are determined. A significant difference is observed in the scattering on Fe3O4/CoFe2O4 particles and the total scattering consisting of partial contributions to scattering on individual magnetite (Fe3O4) and cobalt-ferrite (CoFe2O4) powders, which does not exclude the formation of the “core-shell” structure.

Effect of particle size and apparent density on the initial stages of temperature increase during the microwave heating of Fe3O4

Effect of the particle size and apparent density on the time required for the initial temperature increase during the microwave heating of Fe3O4 was investigated to clarify the mechanism of interaction between the magnetite powder and microwave at temperatures lower than the Curie point of Fe3O4 (585 °C). Samples in the form of powders and briquettes (density, 3.3 g/cm3) with particle sizes of 75–150 μm, 45–75 μm, and < 45 μm were heated in multi-mode and maximum E- and H-field modes using a microwave generator at a frequency of 2.45 GHz. Results reveal that the microwave absorption capability of a sample with higher apparent density is lower because of its higher electrical conductivity, which causes a shallower penetration depth. Further, the effect of the particle size on the microwave heating of Fe3O4 at temperatures higher than the Curie point is different in the presence and absence of a strong electric field. This is attributed to a change in the heating mechanism from dielectric loss in the presence of the E-field to Joule loss in its absence. At temperatures lower than the Curie point, some of the small particles would be transparent owing to a greater penetration depth of the microwaves, which causes an early onset of temperature increase in the magnetite sample with a larger particle size. Moreover, the mechanism for the formation of spark and plasma during the microwave-induced heating is discussed by applying a novel approach to analyse the interactions between the powdery materials and microwaves.

Solution Combustion Synthesis of Fe3O4 Powders Using Mixture of CTAB and Citric Acid Fuels

Magnetite (Fe3O4) powders were synthesized by solution combustion method using a mixture of cetyltrimethylammonium bromide (CTAB) and citric acid fuels at various fuel to oxidant ratios (ϕ = 0.5, 1, 1.5, and 2). Phase evolution investigated by x-ray diffraction method showed single-phase Fe3O4 powders were only formed at ϕ = 1 using mixture of fuels, while impurity α-Fe2O3 phase together with magnetite phase was completely disappeared at ϕ = 2 for CTAB fuel alone. The specific surface area and porous structures of the as-combusted Fe3O4 powders were characterized by N2 adsorption-desorption isotherms and scanning electron microscopy techniques, respectively. The specific surface area using the mixture of fuels (37 m2/g) was higher than that of CTAB fuel alone (32 m2/g). Magnetic properties of the as-combusted powders were studied by vibration sample magnetometry method. The highest saturation magnetization of 83 emu/g was achieved by mixture of fuels at ϕ = 1, due to the high purity and large particle size.

Synthesis of magnetite powder from the mixture consisting of siderite and hematite iron ores

Phase transformation of weakly magnetic iron minerals into a strongly magnetic magnetite is a promising technique for iron ore beneficiation with the further magnetic separation. Thermal decomposition of siderite leads to both magnetite and carbon monoxide formation. Carbon monoxide, as a reductant, sequentially triggers the transformation of hematite into magnetite. Therefore, this method of magnetite formation does not require any additional reducing agent. In the present paper, the source materials were hematite and siderite ores, which were mixed in different mass ratios. Phase transformation of ores’ mixture was performed at various temperatures and for various time intervals. It was shown within the experiments that siderite and hematite transformed to magnetite. The starting temperature of magnetite formation was about 400 °C. X-ray diffraction analysis confirmed the formation of the spinel structure that corresponds to magnetite. The saturation magnetization of transformed samples increased immensely up to 70 Am2/kg for the sample in 1:1 ratio of hematite to siderite. Optimal conditions for the conversion included heating the mixture at 600 °C for 12 min. Under these conditions, siderite and hematite completely transformed to magnetite, since solely magnetite was detected in transformed samples. Simultaneous roasting of hematite and siderite ores is a simple and an economically efficient technique for magnetic powder preparation.

Anhysteretic remanent magnetization: model of grain size distribution of spherical magnetite grains

A phenomenological model based on a linear relationship between the magnetic coercivity field and the reciprocal of the grain diameter is applied to explain the anhysteretic remanent magnetization (ARM) imparted to artificial samples with different concentrations of a very well characterized magnetite powder. By analyses of scanning electron microscopy images, the spherically shaped single domain synthetic magnetite is found to follow a lognormal grain size distribution with ~86 nm of mean diameter. The proposed model, fitted to ARM measurements up to a peak alternating field of 100 mT, yields a very good agreement. The coercivity behaviour predicted by micromagnetism theory disagrees with the experimental results of this work. A likely explanation for the discrepancy is that the magnetite particles, which consist of a mixture of grains in coherent rotation and curling modes, produce similar observations as domain processes.

Effect of vibration energy on fluidization and 1–6 mm coal separation in a vibrated dense medium fluidized bed

ABSTRACTIn this study, a uniform and stable vibrated dense medium fluidized bed (VDMFB) with Geldart B magnetite powder was formed, where it was considered suitable for 1–6 mm coal separation. The formation mechanisms of the best separation environment including the fluidization phenomena under different vibration parameters, the transfer process of the vibration energy, the pressure drop fluctuation and particle oscillation velocity distribution at different bed heights, as well as the corresponding effect on the uniformity and stability of the bed density were investigated. Furthermore, the separation experiment was carried out, and the results exhibited an efficient dry separation performance in the VDMFB.

Enhancing electron transfer by magnetite during phenanthrene anaerobic methanogenic degradation

Recently, the potential of magnetite facilitating anaerobic methanogenic degradation of organic matters in natural or engineered microbial ecosystems has been reported. Here, we evaluated the effects of magnetite powder (<5 μm) and nanoFe3O4 powder (50–100 nm) on phenanthrene methanogenic degradation by a mixed consortium enriched from petroleum contaminated soil. The results showed that complete phenanthrene degradation in our enrichment cultures required a syntrophic cooperation between degrading bacteria and methanogens. The addition of magnetite and nanoFe3O4 did not increase the relative abundance of methanogens, but improved phenanthrene degradation rates by 25.92% and 25.99%, and enhanced methane production rates by 21.5% and 20.1%, respectively. Further studies showed that the addition of magnetite and nanoFe3O4 improved electron transporting system (ETS) activities in the enrichment cultures, possibly through serving as electron conduits to facilitate DIET between syntrophic bacteria and methanogens.

Characteristic gas velocity and fluidization quality evaluation of vibrated dense medium fluidized bed for fine coal separation

In order to remove incombustible impurity minerals, a vibrated dense medium fluidized bed (VDMFB) can be adopted for fine coal dry separation, while Geldart B magnetite powder can serve as the medium. The influence of vibration on characteristic gas velocity in flow pattern transition stage was experimentally investigated at a vibration amplitude range of 0.5–4 mm and frequency range of 5–35 Hz. The experimental results demonstrate that at a low frequency (f < 10 Hz), the vibration effect results in a denser bed and a slightly smaller initial fluidization gas velocity. As the vibration frequency increases to a level similar to the bed’s natural frequency, the minimum fluidization gas velocity reduces sharply. The minimum fluidization gas velocity correlation in the VDMFB is obtained by means of theoretical deduction and experimental data fitting. Furthermore, a method is proposed for evaluating the effects of vibration on improving fluidization quality. Based on that, using the coal separation probable error Ep⩽0.1 as the evaluation index, a suitable effective operating gas velocity range for coal separation under different vibration parameters is determined. The ratio of the boundary operating gas velocity to Umfc is 0.67–2.28. Thus, a uniform and stable fluidization environment is provided for dry fine coal separation.

Efecto de la concentración de magnetita en la estructura, propiedades eléctricas y magnéticas de un material compuesto a base de resina de poliéster

Se reporta el efecto de la concentración de polvos de magnetita (Fe3O4) sobre las propiedades eléctricas y magnéticas de un material compuesto a base de resina de poliéster termoestable. Las muestras se elaboraron mediante el método de colado manual en concentraciones de: 60-40, 70-30, 80-20, 90-10 y 100-0 (% en peso), donde la fase mayoritaria es la resina y la minoritaria los óxidos de Fe3O4. La estructura cristalina se estudió usando la técnica de difracción de rayos X y la caracterización superficial tuvo lugar a través de la técnica de microscopía electrónica de barrido. Se midió la respuesta eléctrica por medio de curvas de polarización eléctrica en función del campo eléctrico y de resistividad eléctrica volumétrica a través de un electrómetro. La respuesta magnética se determinó mediante curvas de magnetización en función de la intensidad de campo magnético aplicado y en función de la temperatura. El análisis estructural indica que el porcentaje de cristalinidad aumenta a medida que se adiciona la concentración de Fe3O4 a las muestras. La caracterización eléctrica del material evidencia que la resistividad volumétrica disminuye con el incremento de magnetita, mostrando una transición aislante-conductor, con valores de la constante dieléctrica cada vez mayores. La caracterización magnética evidencia un aumento lineal de la magnetización de saturación y del momento magnético en función de la cantidad de magnetita adicionada a la matriz polimérica, mientras que la coercitividad evidencia comportamientos de materiales magnéticos blandos tanto en T˃TV como en T&lt;TV, donde TV representa la temperatura de Verwey.

Flow pattern transition characteristics in vibrated gas-solid fluidized bed of Geldart B magnetite powder using pressure drop signals analysis

The vibrated gas-solid fluidized bed with the −0.3+0.074mm magnetite powder was utilized to study the flow pattern of bed and the effects of bubble motion on the fluidization characteristics. The results demonstrated that the standard deviation of the bed pressure fluctuation changed, as the gas velocity increased forming an inverted “U” shape plot. When the bed was in the bubbling fluidization mode, the bubbles were produced with a main frequency of 7.5Hz and the pressure drop signal energy was high. When the bed was in a quasi-turbulent state, the bed mainly produced relatively smaller bubbles between 7.5 and 20Hz in frequency and the pressure drop signal energy was low. As the vibration frequency increased, both the bed initiation bubbling velocity u1 and the onset velocity of turbulent fluidization u2, decreased. The values of Δu=u2−u1, firstly increased and then gradually decreased with the increase of vibration frequency. Under the condition of vibration frequency f=25Hz and three different vibration amplitudes A (i.e., 1, 2 and 3mm), the maximum values of Δu are 8.9cm/s, 7.67cm/s and 7.28cm/s, respectively.

Study of a magnetorheological fluid submitted to a uniform magnetic field

In this work, the rheological and hyperfine properties of a magnetorheological fluid (MRF) under the action of a uniform external magnetic field are analysed. Powders of native mineral magnetite of micrometric particle size, after a pulverization process, form the solute of these fluids. The sizes of these samples are selected by sieving in order to obtain sizes of around 20µm and 45µm. The powders are characterized by means of Mössbauer spectroscopy to analyse their stoichiometry giving rise to a non-stoichiometric magnetite Fe2.96O4 in addition to a hematite component. Result of viscosity and shear stress in the low-speed regime were analysed using the Hershel Buckley method. In particular, the case of surface tension it decreases with the application of a uniform magnetic flux density, which is understood in terms of a phase separation due to the formation of mesoscopic structures, thus decreasing the cohesion force and increasing the adhesion force.

Simultaneous removal of Fe3+ and nitrate in the autotrophic denitrification immobilized systems

Abstract In this study, strain CC76, identified as Enterobacter sp., was tested for the reduction of Fe3+ and denitrification using immobilized pellets with strain CC76 as experimental group (IP) and immobilized pellets with strain CC76 and magnetite powder as experimental group (IPM) in the autotrophic denitrification immobilized systems (ADIS). Compared with IP, a higher nitrate removal rate was obtained with IPM by using three levels of influent Fe3+ (0, 5, and 10 mg/L), four levels of pH (5.0, 6.0, 7.0, and 8.0), and three levels of hydraulic retention time (HRT) (12, 14, and 16 h), respectively. Furthermore, response surface methodology (RSM) analysis demonstrated that the optimum removal ratios of nitrate of 87.21% (IP) and 96.27% (IPM) were observed under the following conditions: HRT of 12 h, pH of 7.0 and influent Fe3+ concentration of 5 mg/L (IP) and 1 mg/L (IPM).

Intensification of the density stability in the air dense medium gas–solid fluidized bed based on a binary dense media

Intensification of the density stability in the air dense medium gas−solid fluidized bed is significantly important to the separation efficiency of this density-based separator. A binary dense media composed of the magnetite powder and quartz sand was used to achieve the intensification of the density stability. The fluctuation characteristics of the bed pressure gradients were investigated to seek for the optimum composition of binary dense media. The weight proportion of quartz sand in the binary dense media should not exceed 30%. The stability and uniformity of the bed density along the axial and radial directions of fluidized bed were experimentally investigated. The results indicated that the weight proportion of quartz sand should be controlled within 10%–20%, and the fluidization number should be adjusted from 1.5 to 1.6. A reliable mathematical model was established to predict the bed density. The calculation and measurement results agreed well, which validated the prediction accuracy. With a 10% weight proportion of quartz sand, the ash content of −13+6mm sized coal was decreased from 33.35% to 11.55% with a clean coal yield of 69.48% at a fluidization number of 1.6. A satisfactory probable error value of 0.095g/cm3 indicated notable separation performance.

Preliminary experiments to assess the effectiveness of magnetite powder as an erosion tracer on the Loess Plateau

Soil water erosion monitoring is essential for long-term soil conservation and ecological restoration on the Loess Plateau region of China. Traditional approaches, such as runoff plots and water weirs in a watershed, provide reliable spatially averaged soil erosion data but cannot validate process-based erosion prediction models for dynamic soil erosion evaluation. Erosion tracer techniques are capable of quantitatively determining spatial distribution of soil erosion. Ideal tracers are expected to provide highly contrasting values compared with background ones, and be analyzed efficiently and acquired cost-effectively. In this laboratory study, magnetite powder was selected as an erosion tracer to test. The tracer was implanted into loessial soils from the Loess Plateau using a wet soil-tracer mixing procedure. The effectiveness of magnetite powder as an erosion tracer was evaluated in aspects of basic magnetic features between the tracer and soils, distribution under different soil aggregate sizes, mobility along soil profiles, and detachment of tracer-labeled loessial soils by shallow surface flow along a slope. Results showed that magnetite powder was bound tightly to loessial soil aggregates, with no noticeable vertical mobility under long-term leaching conditions, and almost synchronous detachment with the eroded soils. Furthermore, the tracer is an inexpensive tracer (approximately 0.08 US$·kg−1), which has higher magnetic susceptibility over two or three orders of magnitude than ordinary soils and high sensitivity of analysis (<1% measuring error). It can also provide quick measurement (<15s) with equipment expenditure at relatively low price (approximately 5000 US$). The work demonstrates that magnetite powder as a promising erosion tracer will be great potential on the Loess Plateau region. Effectiveness of the magnetite powder tracer under simulated and natural rainfall conditions in this region still need to be testified in the future studies.