Mixture Of Magnetite Research Articles

Iron oxide mineralogy in Mollisols, Aridisols and Entisols from southwestern Pampean region (Argentina) by environmental magnetism approach

Ferromagnetic compounds of seven southwestern soils from Pampean region comprise iron oxides and oxyhydroxides that have an important role, because of their high surface reactivity, controlling soil adsorption and formation/conservation of soil structure among other properties. We detected minutes of iron oxides quantities by selective dissolution techniques: acid oxalate extraction (<12% of the total Fe) and dithionite-citrate-bicarbonate (<44% of the total Fe), moreover, we identified/quantified mixtures of magnetite, maghemite, goethite and hematite minerals by environmental magnetism approach. The magnetic particle size dependent parameters evidence a relationship with extractable Fe oxides, indicating that magnetic particle size distribution on these soils is a relevant property associated to poorly crystalline and free amorphous Fe oxides. In addition, the particle size and SP concentration of ferromagnetic iron oxides are associated with increments of cation exchange capacity and the specific surface area of soil samples. The estimated amounts of hematite are below 2.20 wt%, and lower contents of about 0.25 wt% correspond to magnetite components. Both magnetic iron oxides concentration, as well as the remanent coercivity, increase towards the western region, on the contrary, anhysteretic ratios decrease and hence relatively coarser magnetic particles are dominant in this western region. The present study provides valuable data to characterize Aridisols, Entisols and Mollisols in a region of high fertility that comprises ones of the world’s most productive agricultural soil region.

Characterization of the Oxidation of Magnetite Nanoparticles during Their Synthesis by Different Structural Analysis Techniques

Water colloidal solutions of iron oxide nanoparticles coated with tetramethylammonium hydroxide were synthesized by co-precipitation methods. Dimensional analyses were accomplished by transmission electron microscopy (TEM) and the crystalline features of nanoparticles were studied by means of X-ray diffraction (XRD). The iron oxide nanoparticle structure was characterized by the use of the attenuated total reflectance Fourier transform infrared (ATR-FTIR) and Raman spectroscopic techniques. For the nanoparticle samples prepared at higher temperatures during synthesis, the Raman spectra demonstrated that magnetic core of iron oxide nanoparticles is composed of a mixture of magnetite (Fe3O4) and maghemite (γ-Fe2O3) phases. We believe that the oxidation of magnetite to maghemite has been occurred during the preparation protocol of nanoparticles performed at higher temperature.

In Situ Biosynthesized Superparamagnetic Iron Oxide Nanoparticles (SPIONS) Induce Efficient Hyperthermia in Cancer Cells

Despite the promising role of magnetic hyperthermia in cancer therapy, its use in patients has been restricted by hurdles that include inefficient targeting of magnetic particles to the tumor site, limited bioavailability, and high toxicity, etc. Taking advantage of the unique metabolic property of cancer cells, we explored the potential of these cells to biosynthesize magnetic nanoparticles for potential hyperthermia applications. Treatment of cancer cells with a mixture of FeCl2 and zinc gluconate resulted in a significant increase in intracellular Fe and Zn content in these cells. Exposure of these cells to an alternating magnetic field (AMF) for 30 min resulted in a substantial temperature rise of 5-6 °C. The in situ formed particles were identified as iron oxide and ZnO nanoparticles. Based on the magnetic property and size, the iron oxide nanoparticles were classified as superparamagnetic iron oxide nanoparticles (SPIONS) comprising a mixture of magnetite (Fe3-δO4) and maghemite (γ-Fe2O3). The role of reactive oxygen species (H2O2) and the involvement of the glycolytic pathway in the biosynthesis of the nanoparticles were confirmed using appropriate in vitro studies. The simplicity of treatment, the specificity of cells capable of synthesis of SPIONS, and the hyperthermia response observed in cancer cells indicate a promising strategy to achieve effective magnetic hyperthermia for cancer therapy.

Preparation, characterization, and application of magnetic activated carbon for treatment of biologically treated papermaking wastewater

In view of the urgent need for tertiary treatment of papermaking wastewater and the difficulty in separating powdered activated carbon (PAC) from water, the magnetic activated carbon (33%-MPAC, 50%-MPAC and 67%-MPAC) were prepared by chemical coprecipitation method for adsorption of biologically treated papermaking wastewater (BTPW). A series of characterization of MPAC and PAC were carried out and show that the content of iron oxides is negatively related to the proportion of micropores in MPAC. The loaded iron oxides is mainly the mixture of magnetite and maghemite, and the maximum saturation magnetization of MPAC can reach 29.68 emu/g. Batch mode experiments were performed, and found that the adsorption effect of MPAC is slightly worse than that of PAC, the adsorption capacity of COD in MPAC can reach about 65 mg/g, and pH = 2 and 10 °C are more favorable for adsorption. The adsorption isotherms and kinetics were well fitted by the Freundlich model and pseudo-second-order kinetic model, respectively. The selective adsorption was studied by using the excitation emission matrix (EEM) fluorescence spectrum and high-performance size exclusion chromatography (HPSEC). It is concluded that all adsorbents are preferred to adsorb humic acid-like substances (HA). And all adsorbents are preferred to adsorb low apparent molecular weight substances (LAMW, AMW < 1500 Da), with the increase of iron oxides content, the phenomenon of MPAC preferentially adsorbed LAMW became less obvious.

Mössbauer and EPR study of ferrihydrite and siderite biotransformations by a syntrophic culture of alkaliphilic bacteria

Transformations of iron-containing minerals − synthesized ferrihydrite and natural siderite performed by a syntrophic co-culture of Candidatus “Contubernalis alkalaceticum” and Geoalkalibacter ferrihydriticus in presence of ethanol as the substrate for the obligate syntroph – were studied by 57Fe Mössbauer and EPR spectroscopic techniques. Mössbauer spectra of solid phase samples were collected in the range of temperatures 5.5–300 K. X-band EPR studies were carried out at room temperature. The formation of a mixture of magnetite and maghemite, siderite and iron oxyhydroxycarbonate was found as the result of biogenic transformations of synthesized ferrihydrite. In the case of siderite, the formation of a mixture of magnetite and maghemite and iron oxyhydroxycarbonate was observed.

Stabilization of CCA-contaminated soil with iron products - a field experiment

Chemical stabilization of metals is lately considered as a possible pretreatment for soilcontaminated with average levels of trace elements. The element mobility in soil can bealtered by adding soil amendments that can adsorb, complex, or co-precipitate trace elements.As a consequence, pollutant spreading from the contaminated soil and effect on the recipientcan be reduced. The different contaminants originating from wood impregnation chemicals,e.g. Cu, Cr, and As limit the choice of amendments because e.g. large pH fluctuations andconsequent mobilization of Cu or As should be avoided. The results show that the leaching ofarsenic is lowest in the lysimeter with 15% Fe3O4. In both lysimeters with untreated soil andwith 1 % Fe 0, the arsenic leaching seems to decrease with the sampling depth. The leaching ofcopper is generally low. Further the addition of iron seems to increase the leaching ofmanganese and nickel but to reduce the leaching of zinc. Results from the laboratoryexperiment show that the arsenic content in the leachate is lowest with the highest mixture ofmagnetite. Mixing is one of the key issues when discussing the treatment efficiency andpossible use of the treated soil. The results so far indicate that magnetite can be used fortreatment of CCA contaminated soil also at a large scale. Reduction of both arsenic andcopper using a single amendment is challenging as they behave opposite. Magnetite seems tobe a promising amendment even though a high amount of amendment needs to be added.Moreover, the potential establishment of reducing conditions at larger depths in the soil is ofconcern since this might lead to a rapid increase in arsenic leaching

Extreme geomagnetic reversal frequency during the Middle Cambrian as revealed by the magnetostratigraphy of the Khorbusuonka section (northeastern Siberia)

We present new magnetostratigraphic results obtained for the Drumian stage (504.5–500.5 Ma; Epoch 3/Middle Cambrian) from the Khorbusuonka sedimentary section in northeastern Siberia. They complement previous data that did not allow the determination of a reliable estimate of the geomagnetic reversal frequency during this time. Magnetization of the samples is carried by a mixture of magnetite and hematite in various proportions. Thermal demagnetization makes it possible to distinguish two magnetization components. The low unblocking temperature (<350°C) component has a steep inclination and likely originates from remagnetization in a recent field. At higher temperatures, the magnetization isolated possesses the two polarities. Its direction is usually well determined; however, for a noticeable set of samples, a strong overlap between the demagnetization spectra of the two components prevents the determination of reliable directions, although their polarities are well established. The directions from 437 samples define a sequence of 78 magnetic polarity intervals, 22 of which are observed in a single sample. Biostratigraphic data available from the Khorbusuonka section indicate that the duration of the studied section is ∼3 Myr. A geomagnetic reversal frequency of 26 reversals per Myr is therefore estimated for the Drumian, reduced to 15 reversals per Myr if only the polarity intervals defined by at least two consecutive samples are retained. This is an extreme reversal rate, similar to that reported for the Late Ediacaran (late Precambrian), ∼50 Myr earlier, and proposed to be potentially linked to a late nucleation of the inner core. The reversal frequency appears to have drastically dropped for ∼3–4 Myr from a value probably >20 reversals per Myr during the Drumian to ∼1.5 reversals per Myr during the Furongian/Upper Cambrian. Such a sharp decrease is consistent with a transition at a ∼1-Myr timescale, probably caused by threshold effects in core processes, between two geodynamo modes, one characterized by reversals occurring at frequencies ranging from 1 to 5 reversals per Myr, and the other marked by hyperactivity of the reversing process, with reversal rates >15 reversals per Myr.

Chemical Inhomogeneity in Iron Oxide@CoO Core-Shell Nanoparticles: A Local Probe Study Using Zero-Field and In-Field 57Fe Mössbauer Spectrometry.

Core-shell magnetic nanoparticles type Fe3-xO₄ (≈10 nm)@CoO (≈3 nm) prepared by forced hydrolysis in polyol medium have been investigated through the combined use of dc magnetization measurements by SQUID and local analysis by 57Fe Mössbauer spectrometry. A shift of the hysteresis loop along the field axis was observed, which highlights the presence of exchange bias coupling in these nanoparticles. This exchange bias coupling is accompanied by an unexpected high value of coercive field in hysteresis loop in mode ZFC. A local probe study using both zero-field and in-field Mössbauer spectrometry reveals complex hyperfine structures. Great attention is paid to the fitting procedure: it is concluded that Fe3-xO₄@CoO nanoparticles result from a mixture of magnetite and maghemite phases in addition to the formation of an interface-like layer close to a cobalt ferrite. Such a structure explains both the high coercive field value observed by SQUID and the presence of exchange bias coupling.

Review of recent developments in aeolian dust signals of sediments from the North Pacific Ocean based on magnetic minerals

AbstractThe North Pacific Ocean (NPO) has received abundant aeolian dust transported by westerlies from the Asian inland. The aeolian components preserved in NPO sediments record information on palaeoclimatic and palaeoenvironmental changes in Asian source areas at different timescales. Previous studies have systematically investigated the source–sink effect of aeolian dust using the sedimentology, geochemistry, isotope and magnetic methods. In this study, we focus more on recent developments of aeolian signals in NPO sediments obtained by magnetic approaches. Generally, aeolian components contain a mixture of magnetite, maghemite, hematite and goethite of different origins. Magnetic properties (mineral category, concentration and particle size) of these minerals are modulated primarily by climatic/environmental conditions in source areas and sorting effects during the transportation process. Compared with the other methods, magnetic measurements have the advantages of non-sample destruction, high sensitivity and high efficiency. Finally, future studies are also discussed to address the importance of magnetism for tracing the dynamic transportation processes of the aeolian dust.

Study on multi-component particle behaviour in a hydrocyclone classifier using experimental and computational fluid dynamics techniques

Feed to the hydrocyclone classifier in mineral comminution circuit is comprised of a mixture of different size and density particles having various degrees of liberation can be termed as multi-component particulate system. In this study, an artificial mixture of silica and magnetite with different proportions is used for multi-component classification experiments in a 75 mm hydrocyclone. The effect of magnetite fraction on the separation efficiency of silica is analyzed experimentally. An interaction is observed between the components during the classification leading to an increased component cut-size and reduced component mass recoveries in the mixture compared to when it is classified individually. Numerical simulations are also carried out using the modified mixture multiphase model with additional shear lift, hindered settling drag law and slurry viscosity by solids and fines content. The comparison of simulated and experimental performance data is found to be in close agreement. At similar particle sizes, the heavier density component influences the lighter component by placing it away from the wall region and thereby a shift in the locus of zero vertical velocity towards the forced vortex. This results a significant increment in the lighter particle cut-size. Separation characteristics of the silica and magnetite particles are analyzed fundamentally using the equilibrium radius concept.

Minimum fluidization velocity of binary mixtures of medium particles in the Air Dense medium fluidized bed

Minimum fluidization velocity of binary mixtures is one of the most important parameters when applying an Air Dense Medium Fluidized Bed for dry coal beneficiation. Measurements of minimum fluidization velocities were carried out for binary mixtures of magnetite and sand/gangue/coal particles. The experimental results showed that the minimum fluidization velocity of binary mixtures remained almost unchanged when the volume fraction of magnetite particles was above 50%, whereas it varied significantly when the volume fraction of magnetite particles was below 50%. A general correlation based on the Cheung equation has been developed for predicting the minimum fluidization velocity of binary mixtures in terms of particle size ratio, volumetric composition and incipient fluidization velocity of each component. The extended Cheung equation is in reasonable agreement with almost all the available experimental data in the present work and the literature, and it can be used to estimate accurately the minimum fluidization velocity of binary mixtures of medium particles for the ADMFB and other similar fluidized bed operations.

Kinetics and mechanism of selenate and selenite removal in solution by green rust-sulfate.

This work investigated the removal of selenite and selenate from water by green rust (GR) sulfate. Selenite was immobilized by simple adsorption onto GR at pH 8, and by adsorption–reduction at pH 9. Selenate was immobilized by adsorption–reduction to selenite and zero valent selenium (Se0) at both pH 8 and 9. In the process, GR oxidized to a mixture of goethite (FeOOH) and magnetite (Fe3O4). The kinetics of selenite and selenate sorption at the GR–water interface was described through a pseudo-second-order model. X-ray absorption spectroscopy data enabled to elucidate the concentration profiles of Se and Fe species in the solid phase and allowed to distinguish two removal mechanisms, namely adsorption and reduction. Selenite and selenate were reduced by GR through homogeneous solid-phase reaction upon adsorption and by heterogeneous reaction at the solid–liquid interface. The selenite reduced through heterogeneous reduction with GR was adsorbed onto GR but not reduced further. The redox reaction between GR and selenite/selenate was kinetically described through an irreversible second-order bimolecular reaction model based on XAFS concentration profiles. Although the redox reaction became faster at pH 9, simple adsorption was always the fastest removal mechanism.

Dry coal beneficiation by the semi-industrial Air Dense Medium Fluidized Bed with binary mixtures of magnetite and fine coal particles

Air Dense Medium Fluidized Bed (ADMFB) is deemed to be one of the most efficient methods for dry coal beneficiation. In the present work, a semi-industrial ADMFB system in continuous operation was utilized to study the effects of operating gas velocity, feed coal size, and mixture composition of medium particles on the coal beneficiation in industrial practice. Binary mixtures of magnetite and fine coal particles were used as the medium material, and four different feed coal samples with the size ranges of −50 + 25, −25 + 13, −13 − 6, and −6 + 2 mm were tested individually. The experimental results showed that the influence of excess gas velocity on the dry coal separation is relatively small in the lower flow rates. The separation density and probable error increase with the decreasing of feed coal size, regardless of the type of feed coal. The separation density can be continually reduced by further increasing the fraction of fine coal in the medium material, with the compromise of the increased probable error. Moreover, the ash content and calorific value of −50 + 6 mm coarse coal can be effectively upgraded, but the beneficiation of −6 + 2 mm fine coal was less efficient.

Numerical unmixing of weakly and strongly magnetic minerals: examples with synthetic mixtures of magnetite and hematite

Numerical unmixing of weakly and strongly magnetic minerals: examples with synthetic mixtures of magnetite and hematite

Core-shell magnetic particles obtained by seeded suspension polymerization of acrylic monomers

Abstract Core-shell magnetic polymer particles were synthesized by seeded suspension polymerization. The core was made of poly(methyl methacrylate-co-divinylbenzene) and a mixture of magnetite, maghemite and goethite (P(MMA-co-DVB)-M). The shell was composed of poly(glycidyl methacrylate-co-divinylbenzene) (P(GMA-co-DVB)). These particles were characterized by infrared spectrometry (FTIR), thermal analysis (TG), scanning electron microscopy (SEM), dynamic light scattering (DLS) and vibrating sample magnetometry (VSM). The results showed the formation of core-shells with good magnetic properties (≈7.1 emu/g) and good thermal resistance (≈300 oC). The light scattering experiments showed that the particle size of these materials changed from 5-90 microns (core) to 5-120 microns (core-shell). Scanning electron microscopic images were useful to show the formation of P(GMA-co-DVB) shells on P(MMA- co-DVB)-M cores. The materials synthesized in this work have potential to be modified and employed in magnetic separation processes in the biotech and environmental fields.

Minimum fluidization velocity growth due to bed inventory increase in an Air Dense Medium Fluidized Bed

Minimum fluidization velocity is one of the most important fluidization characteristics when applying an Air Dense Medium Fluidized Bed to dry coal beneficiation. Measurements were carried out for magnetite particles (150–300 μm) and the binary mixtures of magnetite mixed with sand/gangue/coal particles (300–425 μm) to determine the influence of bed inventory on the characteristics at incipient fluidization state. The experimental results demonstrate that the minimum fluidization velocities of both single and binary mixtures of solid particles increase with increasing bed mass, which has not properly accomplished by the existing equations. The correlation proposed by Wen and Yu has been modified to predict the minimum fluidization velocity as a function of bed inventory. It only requires the knowledge of Archimedes number and the pressure drop of fluidized bed. This correlation is in reasonable agreement with almost all available data in the literature and the present work.

Co-adsorption of arsenite and arsenate on mixed-valence Fe(II,III) (hydr)oxides under reducing conditions

The reduction of Fe(III) in iron hydroxides plays a significant role in the geochemical cycling of arsenic. However, the adsorption behavior of arsenic (As) at mixed-valence Fe(II,III) (hydr)oxides/water interface remains unclear. This work presents the kinetics, isotherms, and pH edge of arsenite (As(III)) and arsenate (As(V)) co-adsorption on the surface of Fe(II,III) (hydr)oxides as a function of Fe(II)/Fe(III) molar ratio and pH under anoxic environment. The XRD and Raman results indicated that by using Fe(II) and Fe(III) mixed solution as precursors, the coprecipitated products at pH 9 possibly were the mixture of ferrihydrite, goethite, magnetite and green rust, leading to a significantly smaller surface area than ferrihydrite. The adsorption of both As(III) and As(V) decreased significantly as the Fe(II)/Fe(III) molar ratio in the synthetic Fe(II,III) (hydr)oxides increased from 0 to 4. The adsorption of both As(III) and As(V) on the Fe(II,III) (hydr)oxides was strongly pH-dependent and showed completely opposite trends. As(V) was more easily adsorbed on the Fe(II,III) (hydr)oxides under acidic conditions, whereas an increasing amount of As (III) was adsorbed on Fe (hydr)oxides under alkaline conditions, possibly due to the competitive adsorption. Our findings may contribute to the understanding of the interfacial behavior of arsenic in the reducing environments.

Sulfurization of hematite Fe2O3 and anatase TiO2 by annealing in H2S

Abstract Spray-deposited hematite Fe2O3 and spin-coated anatase TiO2 thin films were annealed under H2S in order to investigate the effect of sulfurization by H2S. Sulfurized films were characterized using UV–vis spectrophotometry, X-ray diffractometry, Raman spectroscopy, field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Sulfurized Fe2O3 and TiO2 films are composed of multiple phases. The Fe2O3 film undergoes phase transformation from hematite into a mixture of magnetite (Fe3O4) and pyrrhotite (FeS) at annealing temperatures above 250 °C. At 450 °C α-Fe2O3 is fully transformed into pyrite (FeS2). The TiO2 film transforms into a mixture of TiO2 and TiS2. TiS2 formation begins at temperatures above 550 °C. At 700 °C, TiO2 is completely transformed into TiS2.

Synthesis and characterization of magnetic-montmorillonite and magnetic-organo-montmorillonite: Surface sites involved on cobalt sorption

Montmorillonite magnetic-clay nanoparticles (MtMag) and its exchanged product with hexadecyltrimethylammonium (O100MtMag) were synthetized by alkaline oxidation of ferrous sulfate, characterized by diverse techniques (XRD, Mössbauer spectroscopy, VSM, SEM, Zeta Potential, total specific surface area, TOC) and used as Co2+ sorbents. The magnetic characteristic of these materials allows them to be used in cases of decontamination of water polluted with dangerous materials, such as radioactive ones, reducing the risk to health due to indirect manipulation by means of external magnetic fields. For comparison, samples without magnetic material (O100Mt) and in absence of clay (Mag) were also synthetized. The synthesis of magnetic materials disclosed the presence of magnetite and goethite nanoparticles, while the saturation magnetization displayed by O100MtMag was higher than that obtained for MtMag, indicating the existence of a higher amount of magnetite particles in the first one. This suggests that O100MtMag could be manipulated easier than MtMag through external magnetic fields. Moreover, the surface electric charge of MtMag sample can be described as a mixture of Magnetite and montmorillonite, with ratios related to the surface of both components. Co2+ sorption percentages, using an initial Co2+ concentration of 85 mg/L, resulted similar for the different materials while the Co2+ sorption was ascribed to interactions with the montmorillonite interlayer and external surface. The current results indicate that O100MtMag is a more appropriate material than MtMag for Co2+ removal by external magnets.

Delineating Individual Ferromagnetic Minerals in Synthetic Mixtures of Magnetite and Hematite

Delineating Individual Ferromagnetic Minerals in Synthetic Mixtures of Magnetite and Hematite