why is magnatite used for coal washing

magnetite - oham industries

magnetite - oham industries

Magnetite is a natural aggregate manufactured from the iron oxide Magnetite. With its high specific gravity Magnetite is used as a coarse material to produce heavyweight concrete.When used as the aggregate portion of a concrete mix, magnetite increases the density of the concrete to twice that of standard concrete. This heavy concrete is as common building material in radiation shielding (medical or nuclear plants). Beyond that, however, heavy concrete is used to make counter weights and as thermal mass in heat storage situations.

Magnetite acts as a heat sink by absorbing heat from its surroundings, storing it and releasing it slowly over a period of time. With Magnetite used as an aggregate in concrete, this effect will mean that the heat of hydration produced during curing will be absorbed and the maximum temperature attained within the concrete will be lower than with normal aggregates. The risk of thermal cracking, which is often associated with thick sections, is therefore reduced by incorporating Magnetite.

Heavy media gravity separation means separating products with different densities.Magnetite and water are used to make a slurry on which one product will float (the product with a lower density than the slurry) and in which the other product will sink (the product with a higher density than the slurry). Hence the term sink-and-float separation is often used. Depending on the densities of the products that need separating, the ratio of magnetite and water in the slurry can be varied to achieve the required intermediate density.

Using magnets, magnetite can be easily recovered from the waste and coal streams and then re-used in the coal separation circuit. Recyling the magnetite provides a cost saving to the operator, and is an environmentally conscious method of utilizing this valuable resource. About 90% of the magnetite can be recovered for reuse from the process, but the remaining 10% must be must be replaced.

In order to feed the more than 7 billion people on the planet, the markets rely on industrial agriculture to crank out acre after acre of high-yield, high-value crops. In order to accomplish this feat, agricultural operations require vast quantities of fertilizers and nutrients in order to maximize crop outputs.

Magnetite serves a vital role in the worlds food chain. Whether its as a catalyst for the production of fertilizer or as a micronutrient added to the soil to provide just a little boost of iron to young crops, magnetites role in agri-business is continually growing and evolving.

A core component of many industrial fertilizers is Chelated Iron and Iron Sucrate. Magnetite is a key component in the production of these two products. Chemical engineers can also introduce quantities of magnetite to the reactions that release ammonia, and magnetite again acts as a catalyst for the capture of ammonia. Without ammonia, many fertilizers would be useless. And without magnetite to act as a catalyst, the production of ammonia would be a far more expensive and potentially more dangerous occupation.

Yet, with magnetite, the production of ammonia is rendered safer and faster, improving output and the quality of fertilizers in the field. Without magnetite, many fertilizers in use today would never have seen the marketplace.

In addition to its role as a valuable catalyst in a host of reactions, magnetite also makes an effective and efficient micronutrient that, when added to the soil, provides young plants an added boost of iron and oxygen.

Many plants rely on a steady supply of iron to grow healthily, to produce fruit, or to improve uptake of the fertilizers that improve crop yields. When magnetite is added to soil, it can produce more robust crops with stronger, nutrient-rich soil.

Researchers are continuing to find new and powerful uses for magnetite-infused aggregates and concretes Since ancient Rome, concrete has been a wonder product, enabling the construction of both extensive, durable roads and massive structures that soar above our heads. Concrete has also proven to be a valuable material in the manufacturing field, where engineers have designed everything from small refractories to massive chambers out of concrete.

Recent research shows that magnetite aggregate in concrete allows the material to perform well at much higher temperatures than non-magnetite infused concrete. This discovery marks an important milestone for concrete, which previously was susceptible to cracking and degrading when subjected to extreme temperatures.

Magnetite aggregate is also a key component to protecting personnel and equipment from the harmful effects of gamma radiation. Long the go-to choice for reactor shielding, magnetite aggregate is added to concrete to increase density, which improves the performance of concrete shielding, blocking harmful radiation and preventing heat buildup, which can degrade concretes performance over time.

magnetite ore, magnetite iron ore, iron ore mining process

magnetite ore, magnetite iron ore, iron ore mining process

Coal washing using magnetite is used to remove contamination from run-of-mine (ROM) coal, which usually contains rocks, middlings, used consumables and other contamination introduced by the mining process.

Magnetite ore is a ferromagnetic material, with the chemical formula Fe3O4, and is one of several types of iron oxide. It is a ubiquitous mineral in many parts of the world, including Australia, the USA, Canada, South Africa, Mozambique and many other countries across most of the world's continents.

Magnetite ore often occurs in metamorphic rocks, which formed from ferruginous sediments in both regional and contact metamorphic settings. It is commonly formed by the reduction of hematite and ferric hydroxide minerals in these rocks. Banded Precambrian iron formations commonly contain magnetite ore.

Magnetite is characteristically recognised by its strong magnetism, colour and streak. It is commonly used in magnetic separation and coal washing. However, it is not limited to these purposes, as its abundance and magnetic properties means has been used in the production of audio tape, and now more commonly in computer information storage media.

coal washing, magnetic separation & processing

coal washing, magnetic separation & processing

Most traditional iron ore projects mine ore deposits that are enriched naturally and contain high levels of iron known as hematite or direct shipping ore (DSO). DSO passes through a simple crushing, screening and blending process (beneficiation) before it is shipped overseas, mainly for steel production.

In comparison magnetite ore has lower iron content when mined of between 25% and 40% Fe and requires processing, or magnetic separation, to separate magnetic minerals from other minerals in the ore.

The main iron mineral in magnetite ore is the ferrous iron oxide magnetite (Fe3O4) which when processed produces a magnetite concentrate with a magnetic content in excess of 96% magnetics. Further magnetic separation and milling produces even higher iron levels in the magnetite concentrate.

what are the uses of magnetite?

what are the uses of magnetite?

Magnetite increases the density of most mixtures in which it is present. This property allows magnetite to be used in the manufacture of heavy concrete, water filtration, coal mining, landscaping and production of certain iron-based chemicals.

Magnetite increases the density of most mixtures in which it is present. This property allows magnetite to be used in the manufacture of heavy concrete, water filtration, coal mining, landscaping and production of certain iron-based chemicals.

When magnetite is added to a concrete mix, it produces heavy concrete, which is twice as dense as standard concrete. Heavy concrete is widely used in buildings that require protection from radiation, such as nuclear power plants, X-ray facilities and uranium mining sites. Heavy concrete retains heat more efficiently than standard concrete and can be used in building houses to retain solar heat.

When magnetite is added to a concrete mix, it produces heavy concrete, which is twice as dense as standard concrete. Heavy concrete is widely used in buildings that require protection from radiation, such as nuclear power plants, X-ray facilities and uranium mining sites. Heavy concrete retains heat more efficiently than standard concrete and can be used in building houses to retain solar heat.

Magnetite can also be used in water filtration systems. A water filtration system with magnetite has a more aggressive backwash in the cleaning phase, as well as the ability to recover the magnetite by using a magnet.It is also used in coal mining operations as a slurry with water to remove the heavier impurities by allowing the less dense coal to float to the surface. The magnetite can be reused in this process 90 percent of the time.Magnetite is also used as a source of iron to manufacture iron-based chemicals and fertilizers. Ferric chloride and ferric sulphate are manufactured with magnetite as one of the starting materials. These chemicals are effective in clarifying raw water in water purification plants. The dark, glossy nature of magnetite ore has led to its use in landscaping as accent rocks.

Magnetite can also be used in water filtration systems. A water filtration system with magnetite has a more aggressive backwash in the cleaning phase, as well as the ability to recover the magnetite by using a magnet.

It is also used in coal mining operations as a slurry with water to remove the heavier impurities by allowing the less dense coal to float to the surface. The magnetite can be reused in this process 90 percent of the time.

Magnetite is also used as a source of iron to manufacture iron-based chemicals and fertilizers. Ferric chloride and ferric sulphate are manufactured with magnetite as one of the starting materials. These chemicals are effective in clarifying raw water in water purification plants. The dark, glossy nature of magnetite ore has led to its use in landscaping as accent rocks.

what are the uses of magnetite? (with picture)

what are the uses of magnetite? (with picture)

Magnetite is an iron oxide mineral belonging to the group known as spinels. It is a very common and is a valuable iron ore. Magnetite has been known to mankind since early history and led to the earliest discovery and understanding of magnetism. It is the most highly magnetic naturally occurring mineral, and the variety known as lodestone was the basis for the first crude magnetic compasses. Today, there are many uses of magnetite, such as for abrasives and coatings.

Several minerals serve as sources of iron ore, and magnetite is one of the most important. Large quantities of magnetite are mined and processed into iron for use in the production of steel. Most of the magnetite mined annually is used for this purpose.

Much smaller amounts of magnetite are used in other but no less important ways. Abrasives are one such use, and magnetite is used to make the common abrasive known as emery, which is affixed to stiff pieces of wood or cardboard and impregnated into cloth, both of which are used in much the same way as sandpaper. Emery boards are a popular cosmetic tool for filing and sanding fingernails for example. Granulated magnetite is sometimes added to water jet devices that are used for cutting and and to sandblasting material as an abrasive.

Water treatment may be one of the most important uses of magnetite as the mineral attracts and binds dissolved arsenic. Extremely small particles of magnetite are highly effective in removing arsenic, which is a major and dangerous contaminant of water sources around the world.

The production of ammonia and manmade hydrocarbons are two more uses of magnetite. It is not directly involved in the chemical reactions that produce these compounds, but it does act as a catalyst for them, increasing output and improving efficiency. Ammonia production is a key step in the production of fertilizers that are used to produce crops that feed the world's population. Magnetite is sometimes used as an additive to fertilizer, providing iron as a micronutrient.

Providing the pigment in some paints and toners is another of the uses of magnetite. It is especially common in the toner used in the photocopying process. Magnetite is also used to coat the inside of some types of boilers and other containers that are intended to hold liquid at high temperatures. High-density concrete often has ground magnetite as an additive.

Very informative post and one that reassures me that magnetite is perhaps not toxic to humans. I read on a blog somewhere about making magnetic blackboard by mixing magnetite with PVA glue and painting over a piece of board; then painting over with chalkboard paint. I am attempting to make one for my kids and wanted to make sure this is a safe medium to work with. Thanks.

@Terrificli -- That is exactly right. I live in one of those neighborhoods with a lot of magnetite in the bedrock. We had to have a couple of pine trees cut down because they had been struck by lightning several times and were dying. The problem was the trees were huge and over 100 years old. Had they died and started to decay, our home could have been crushed by huge, falling limbs or (perhaps) a giant tree falling over on it. Scary stuff, but I'm told it is not uncommon to have trees get in that bad a shape due to lightning strikes.

The problem was the trees were huge and over 100 years old. Had they died and started to decay, our home could have been crushed by huge, falling limbs or (perhaps) a giant tree falling over on it. Scary stuff, but I'm told it is not uncommon to have trees get in that bad a shape due to lightning strikes.

The problem was the trees were huge and over 100 years old. Had they died and started to decay, our home could have been crushed by huge, falling limbs or (perhaps) a giant tree falling over on it. Scary stuff, but I'm told it is not uncommon to have trees get in that bad a shape due to lightning strikes.

Darn right this stuff is common, and what a lot of people don't know is that it is not unusual to find a bunch of magnetite in the bedrock under certain neighborhoods. Under certain conditions, that stuff can attract lightning like crazy. Houses typically aren't in danger as long as there are tall trees around, but the taller trees can get struck by lightning several times and that can lead to dead trees.

Under certain conditions, that stuff can attract lightning like crazy. Houses typically aren't in danger as long as there are tall trees around, but the taller trees can get struck by lightning several times and that can lead to dead trees.

Under certain conditions, that stuff can attract lightning like crazy. Houses typically aren't in danger as long as there are tall trees around, but the taller trees can get struck by lightning several times and that can lead to dead trees.

magnetite - an overview | sciencedirect topics

magnetite - an overview | sciencedirect topics

In the VNIR, magnetite and maghemite display low reflectance, around 2% for the former and 11% for the latter (Figure 6.6). In the 600014,000nm wavelength region, magnetite reflects poorly, but its reflectance baseline shows an increase toward longer wavelengths with such a low degree that magnetite can only be indirectly indicated by a significant vertical offset in the spectrum (Schodlok and Ramanaidou, 2011). Work on vibrational spectroscopy of magnetite has been carried out, for example, by numerous studies (e.g., Gasparov et al., 2000; Lane et al., 2002; Liese, 1967; Chamritski and Burns, 2005; Ebad-Allah et al., 2009).

Magnetite is simply iron corrosion products in the presence of a reducing environment [65]. Numerous researchers have been worked out to investigate the magnetite adsorption capability for the sorption of few radionuclides [66]. Magnetic iron oxides like magnetite (Fe3O4) and maghemite (Fe2O3) can be tailored to get improved magnetic properties, lower toxicity, and lower cost. Very less work was found in the synthesis of chitosan/magnetite composites for the elimination of heavy metals in contaminated water [67]. Tran et al. [67] observed that hydrogel (2-acrylamido-2-methyl-1-propanesulfonic acid) showed higher attraction for the elimination of impurities, while Yang and Chen [68] synthesized cross-linked chitosan-magnetite composites with the help of epichlorohydrin as the cross-linking agent. It was observed that alteration by cross-linking did not always decrease adsorption capacity.

Hematite and magnetite, the two predominant iron ores, require different processing routes. High-grade hematite direct shipping ores (DSOs) generally only require crushing and screening to meet the size requirements of lump (typically between 6 and 30mm) and fines (typically less than 6mm) products. Low-grade hematite ores require additional beneficiation to achieve the desired iron content, but the comminution of these ores still generally only involves crushing and screening, which is not particularly energy-intensive. Conversely, fine-grained magnetite ores require fine grinding, often to below 30m, to liberate the magnetite from the silica matrix, incurring greater costs and energy consumption. The comminution energy consumption could be over 30kWh/t, an order of magnitude higher than for hematite ores. However, with the depletion of high-grade deposits and strong demand for steel, a greater number of low-grade deposits are being developed.

To operate viably and sustainably, there is a need to reduce costs and energy consumption, particularly of the energy-intensive grinding required for low-grade magnetite deposits. This chapter reviews current iron ore comminution and classification technologies and presents some examples of flowsheets from existing operations. New trends and advances in comminution technologies are presented and discussed, particularly with regard to the impact on energy, operating, and capital costs.

Magnetite appears to be the main deposit on oil and gas production systems under high temperature conditions >150C (302F) and anoxic conditions, especially on carbon steels [31,32]. Even though various models have been developed to predict Fe3O4 solubility, predictions made from these models are only applicable below 100C (212F) at low pressure and in low TDS brine [33]. Limited research on the effect of high pressure and salinity on solubility of magnetite has been conducted.

Measuring the magnetite solubility has proven to be more difficult than that of other oxides, such as NiO, due to the reductive dissolution of magnetite from Fe(III) to Fe(II) [32]. Thus the reduction potential of the entire system plays an important role in magnetite solubility. In more complicated synthetic brines with high ionic strength, the reductionoxidation (redox) potential, which controls the dissolved iron concentration in the produced saltwater may cause large differences in the observed solubility.

Magnetite solubility experiments were conducted to determine the Ksp value at different temperatures and pressures. The results vary from the ones reported in the literature. For example, at room temperature and 345bar (5000psig) the total dissolved iron concentration is 0.068mg/L, which is about six times lower than the literature reported total Fe concentration (0.44mg/L). The effects of various reaction parameters on magnetite solubility were also studied and detailed results can be found in Yan etal. [34]. A change in pH or Eh has a much greater effect on magnetite solubility than pressure and temperature in this preliminary investigation.

Magnetite is often contaminated with titanium, forming minerals like ilmenite. The contaminated mineral shows an appreciable degree of magnetism. This property is made use of in the separation of ilmenite from other economical minerals such as rutile, monazite, zircon, leucoxene in Western Australia, Weipa in Queensland, Kerala in South India and other places where heavy minerals are present in beach sands.

The ionic model of magnetite is considered as Fe3+ [Fe3+ Fe2+] O42. The crystals are cubic with an inverse spinel structure. The cations [Fe3+, Fe2+] are in the octahedral sites. The Fe3+ is half in tetrahedral and half in the octahedral sites. The spontaneous magnetism exhibited by magnetite is therefore entirely due to Fe2+ per Fe3O4. The electronic configuration of Fe3+ is (3d)5 and that of Fe2+ is (3d)6. Quantum mechanics has helped establish discrete changes in magnetic moments that can occur. The orientations of magnetic moments in the crystals are either parallel or anti-parallel to the applied magnet field.

Magnetite is a ferromagnetic iron oxide of inverse spinel structure with the cubic packing of oxygen anions and iron cations located at tetrahedral and octahedral sites. In stoichiometric magnetite Fe2+ occupies half of the octahedral lattice sites because of the greater ferrous crystal field stabilization energy, while Fe3+ species occupy the other octahedral lattice sites and all tetrahedral sites (Cornell and Schwertmann, 1996). Electron transition between the Fe3+ and Fe2+ ions provides the half metallic properties of magnetite.

Figure 15.2 shows the representative X-ray diffraction diagram of Fe3O4 NPs. The peak intensity can give information about the proportion of iron oxide in a mixture by comparing it with the reference peak intensities. The line bordering parameter includes information about the crystal size that can be obtained using the Scherrer equation (Calvin et al., 2003). At the presented data (Figure 15.2) the patterns are close to those of maghemite -Fe2O3 and additional examination is needed to reveal the magnetite phase. Fourier transform infrared spectroscopy and Mssbauer spectroscopy can indicate the superstructure parameters of analyzed materials (Goti et al., 2009). As Fe2+ cations of magnetite are susceptible to oxidation the traces of impurities are always detected.

Without a special coating magnetite is susceptible to oxidation that deteriorates its magnetic properties. Oxidation and agglomeration of NPs can be considerably decreased by modification with different agents. Figure 15.3 shows the transmission electron microscopy (TEM) images obtained for 0.5% starch-stabilized magnetite NPs. The electronic diffraction pattern is inserted. Size, distribution, and shape of the particles can be analyzed. The average size of observed NPs is 105nm. For nonmodified control the tendency to form agglomerates is pronounced. The addition of starch as a stabilizer decreases the amount of agglomerated NPs (Soshnikova et al., 2013). However, the presented example is likely an exception model of massive agglomeration of nonmodified particles because TEM analysis usually does not reflect the real agglomeration tendency of the material for the specificity of sample preparation and additional examination by means of other methods is needed. Sometimes TEM may help to distinguish the crystalline part of the particles from the amorphous core. The atomic level of the NPs (lattice defects, vacancies, surface arrangement, self-assemblies, etc.) may be analyzed by means of high-resolution transmission electron microscopy (Wang, 2000).

Time-dependent changes in the dispersed material can be studied by scanning microscopic observations. Atomic force microscopy (AFM) allows to obtain the height profiles and estimate the lateral sizes of micro- and nanoobjects. In comparison to TEM the sample preparation is simplified and it is possible to study the nonconductive materials that can help to analyze the real sizes of organic modified NPs. The glycerin-coated NPs obtained 24 and 75h after the synthesis from AFM are presented in Figure 15.4. One can see that the highly dispersed NPs of 1012nm in size for approximately 50h storage in water at room temperature form agglomerates with the size up to 200nm.

The properties of dispersed NPs can appreciably differ from those obtained after drying and preparing the microscopic samples. That is why the liquids containing NPs for use in biomedical testing should be analyzed excluding the stage of particle extraction. Dynamic light scattering (DLS), also known as proton correlation spectroscopy, is a powerful method to determine the size distribution of dispersed material in a broad range of concentrations. It is based on the correlation between the size of the particle and its Brownian motion. Particles in aqueous medium are illuminated by laser and the intensity fluctuations of scattered light are analyzed. DLS provides the size evaluation of dispersed magnetite NPs by measuring the translational diffusion coefficient (D) distribution. The hydrodynamic radii Rh of spherically shaped particles can be calculated from the diffusion coefficients by the StokesEinstein equation: D=kBT/6gRh, where kB is the Boltzmann constant, T is the absolute temperature, and g is the viscosity of the analyzed medium. The calculation is correct for spherical and homogeneous particles and gives only an estimate of hydrodynamic radii in other cases.

Figure 15.5 presents the DLS data for starch-modified magnetite NPs for three different concentrations of starch. The optimum starch concentration was determined according to the investigation (Soshnikova et al., 2013). From the data it can be seen that there is a concentration value of 0.5% (mass) that allows to obtain a stable dispersion of NPs with an average hydrodynamic radius of 45nm. A 0.1% concentration is not so effective and led to an increase in the average radius value up to 100nm, while the use of 1% starch concentration caused the growth of the system viscosity and appearance of concentration effects.

Time- and temperature-dependent changes can be revealed by DLS. Figure 15.6 presents the distribution of 0.5% starch-stabilized magnetite NP dispersion as the temperature increases up to 70C. According to the data the dispersions demonstrate chemical stability within the studied temperature range.

DLS is more sensitive for larger particles (10nm), whereas the analytical ultracentrifuge (AUC) provides a more sensitive probe for smaller particles (Brown and Schuck, 2006). The method is based on measuring light absorption or interference optical refractive index of the analyzed material with the applied centrifugal field. Sedimentation velocity experiments monitor the entire time-course sedimentation and provide the sedimentation coefficient distribution c(s) of Lamm equation solutions:

where C is particle concentration, r is length that the particle passes under the centrifugal force in radial direction at the centrifuge cell, t is experimental time, w is angular velocity of the rotor, D is diffusion coefficient, and s is sedimentation coefficient. Based on the known c(s) distribution, the average Stokes radii of analyzed particles can be determined. The method is widely used in research of protein macromolecules, while its applications for dissimilar systems, such as crystalline NPs and organic stabilizers, are limited. However, some efforts were made to analyze the very small fractions of stabilized magnetite NPs where the small particles (<10nm) were preliminarily separated from agglomerates. Figure 15.7 shows the c(s) distribution for the 0.5% starch-modified magnetite NPs (Soshnikova et al., 2013). The corresponding average Stokes radius value is 4.8nm.

Magnetic properties of magnetite strongly depend on such factors as the NP size, shape, and chemical phase. Bulk magnetite can be described as ferrimagnetic as a result of the parallel alignment of magnetic moments of the tetrahedral site and antiparallel alignment of the Fe2+ and Fe3+ spins of octahedral sites. However, when the particle size is decreasing the tendency to spontaneous magnetization becomes weaker and magnetite NPs tend to demonstrate paramagnetic or superparamagnetic properties. To study magnetic characteristics several techniques were developed. Magnetic particles can be characterized by measuring their magnetic transition temperature, saturation magnetization, or magnetic susceptibility. Magnetic transition temperature (Curie temperature) corresponds to a point where the intrinsic magnetic moment changes its direction and the temperature values can be obtained by means of differential thermal analysis (Thapa et al., 2004). Saturation magnetization reflects the value of magnetization when an increase in the applied external magnetic field cannot further increase the magnetization of the material. It can be measured using a magnetometer. For the particles <100nm, the size effects are observed. Thapa et al. presented the decrease in magnetic transition temperature and saturation magnetization as the size of NPs decreases from 90 to 6nm (Thapa et al., 2004). The oxygen content in small NPs is reduced, which leads to the lowering of the cation valance and increase of Fe2+ species content that possesses a higher ionic radius than Fe3+. It consequently results in an increase in the unit cell volume of small NPs (Thapa et al., 2004). The authors also observed a drop in magnetization for the NPs <10nm, which can be explained by the pronounced surface effect. Magnetization of the core atoms is higher than that of the surface ones and as the size decreases the surface contribution becomes prominent. Small monodomain magnetite NPs demonstrate superparamagnetic behavior (SPIONs) and exhibit magnetization only in the presence of an external magnetic field that attracts a great deal of interest in their potential applications in biomedicine (Lin et al., 2009). Sometimes, to characterize magnetic materials, it is enough to measure their magnetic susceptibility. This indicates the dimensionless proportionality constant of the material magnetization degree in response to an applied magnetic field. It was already mentioned that NPs magnetic properties can be significantly different from those of the bulk material. The principal mechanism of the magnetic susceptibility dependence on the particle size is the transition from multidomain to monodomain particles. Magnetic susceptibilities of magnetite NPs obtained by laser ablation and chemical synthesis are presented in Table 15.1.

The samples were obtained by drying the dispersion droplets at the coverslips. For the specified cylindrical volume, the NPs, mass and density were determined accurately (within 1mg). Magnetic susceptibility was measured by gravimetric analysis similar to the Faraday method. The conventionally used enormous solenoid was replaced by a cylindrical permanent magnet that maintained the constant gradient of magnetic induction at the sample placement. Magnetic induction distribution measurement along the magnet axis was carried out by the micrometrical sensor and inductometer with an accuracy of 5mT. From the presented data it can be seen that the magnetization of the NPs derived from laser ablation is more pronounced than that for the chemically synthesized.

Magnetite possesses an inverse spinel structure AB2O4 (space group Fd3m; a=8.39) (Fig.5.1A), wherein oxygen anions form a cubic face-centered (fcc) lattice and large interstices between O2 are partially occupied by iron cations. Tetrahedral A positions are occupied by Fe3+ cations, while octahedral B positions are equally occupied by Fe3+ and Fe2+ cations (FeA3+[Fe2+Fe3+]BO4). Fig.5.1B shows magnetite electronic structure [2,3]. The density of states (DOS) occupied by the electrons of the octahedral B sites can be thought of in terms of a spin-up () band and a spin-down () band which are split by an exchange energy. The five degenerate d-electron levels of Fe ions are further split by the crystal field, into three degenerate t2g and two degenerate eg levels. For both Fe2+ and Fe3+ ions, five electrons occupy the majority t2g and eg levels. The extra electron of the Fe2+ ion occupies the minority t2g band, which is the only band located at Fermi level EF, giving rise to half-metallicity (100% spin polarization). The high room temperature conductivity (1041051m1; which is 0.1% of Cu metal at 300K) of magnetite is attributed to the hopping of this electron between octahedral (Fe2+Fe3++e) B sites which dominate the DOS around Ef.

Figure5.1. Illustration of tetrahedral and octahedral sites in inverse spinel structure of Fe3O4 (A).Density of states occupied by electrons of the ions at the two sites (B). Essential spin conservation and ferromagnetic ordering in Zener double exchange mechanism (C).

Zener double exchange best explains this hopping mechanism (Fig.5.1C) [4]. The term double indicates here that an extra electron of Fe2+ ions is transferred to the empty orbitals of Fe3+ by displacing electrons from the intervening O2 ions in a double-exchange process: Fe2+ to O2 and O2 to Fe3+. An antiparallel coupling is present between the spin-down () electron coming to Fe3+ from neighboring 2p O2 orbital, at the same time the empty 2p O2 orbital accepts the extra hopping electron from Fe2+ creating a parallel coupling. This overall energy saving mechanism leads to a FM ordering with conservation of spin. The probability for exchange is a sensitive function of both the metaloxygen distance and of the Fe3+O2Fe2+ angle, being greatest when theangle is 180 and smallest when it is 90. The Fe3+O2Fe2+ bond angle for the ions is 90 for BOB sites, the AOA site's angle is 80, and the AOB site's angle is 125. Therefore, AB interaction is the strongest and favors antiparallel alignment to save energy. Thereby, all the A spins align parallel to each other and the B spins do the same (Fig.5.1A). At B sites, double exchange creates FM alignment in BOB, resulting in a magnetic moment of (5+4) B. To decrease the energy the five unpaired electrons of the A site align antiferromagnetically with the nine parallel on B site, lowering the magnetic moment to (95=4)B. An additional unquenched angular moment (L)of Fe2+ ions gives total moment J=L(0.2)+S (4)=4.2B.

Upon cooling of magnetite below 120K, the electron hopping between Fe2+ and Fe3+ ions freezes and a combination of 2+and 3+species then arrange themselves in a regular pattern without moving (charge ordering). In this nonconducting state the stagnant Fe2+ ions are JahnTeller (J-T) active [2], this means, the extra electron in Fe2+ has a choice between occupying anyone of the three available half-filled orbitalsdxy or the two dxz/yz, as they all have the same energy (depicted by arrows in Fig.5.2A). Electrons prefer to occupy the orbit with the least energy. Therefore, to break this choice, an effective energy separation between dxy and dyz/dzx is created if the four FeO bonds (depicted by arrows in Fig.5.2A) in the xy plane are elongated or contracted. The negative value of t2g signifies that the energy of dxy is lower than that of dyz/dzx, that is, tetragonal distorted Fe2+O6 octahedra with elongated FeO bonds in the xy plane. On top of this, an additional structural distortion in which B site FeFe distances within linear Fe3+Fe2+Fe3+ units (depicted by the green ellipsoid) are anomalously shortened showing that electrons are not fully localized as Fe2+ states but are instead spread over the three sites resulting in highly structured three-site polarons defined as a single trimeron [2]. The JT distortion in Fe2+O6 octahedra mentioned earlier directly couples to the neighboring Fe3+O6 octahedra constituting the trimerons, although they are JT inactive in the first approximation. Due to trimeron formation, distances from Fe2+ states to their two B site neighbors in the local orbital ordering plane are anomalously shortened (Fig.5.2A). The cumulative effect of this trimeron shortening penetrates throughout the crystal in the various trimeron locations to significantly perturb the cubic magnetite structure to the complex overall distortion (Fig.5.2B). The cubic spinel [a=b=c] type structure of magnetite distorts to a monoclinic superstructure with Cc space group symmetry [a=b c] [2,2,2]. This structural transformation was first found by Verwey in 1939 and was named after him. The charge, orbital, and trimeron orders of magnetite stand out as perhaps the most complex electron ordered ground state known.

Figure5.2. Energy separation due to JahnTeller distortion (down), depiction of trimeron concept in single (top) Fe+2O6 octahedra (A) [2]. Trimerons distributed over the lattice points [2] (B). Changes in magnetization, resistivity, and specific heat at Verwey temperature, Tv (C) [5].

Because of this structural transformation in Fe3O4, many physical properties (specific heat, magnetization, and resistivity) show abrupt change around VT [5] (Fig.5.2C). Even after intense research there still exist two major schools of interpretation: the first one interprets the Verwey transition as a transition driven by charge/orbital ordering and the second one exploits the mechanism of a lattice distortion-driven charge-ordering leading to a metal-insulator behavior.

Magnetite NPs are commonly used as T2 contrast agents because they accelerate spin-spin relaxation. Superparamagnetic iron oxide particles form strong local magnetic field gradients that affect the protons surrounding these particles. This interaction depends on the distance between superparamagnetic particles and protons. First of all, two physico-chemical characteristics of the contrast agentthe mobility of the NPs and their magnetizationhave an effect on the time of transverse relaxation. Thus, the size, degree of aggregation, and magnetization, as well as the state of NPs due to phase transitions, influence the contrasting properties of superparamagnetic particles (Hingorani et al., 2015).

The presence of contrast agents changing the longitudinal relaxation in the object of research causes an increase of the Mr signal intensity. Such substances are often called positive contrast agents. On the contrary, the substances that predominantly modify transverse relaxation are called negative contrast agents, since they cause the appearance of regions with a low signal intensity in Mr images.

Currently, a number of preparations containing superparamagnetic particles based on iron oxideSinerem, Resovist, Feridex, Ferumoxtranare produced. Usually in a clinical MRI, superparamagnetic iron oxide NPs are used to determine liver diseases because they are selectively absorbed by Kupffer cells in the liver, spleen, and bone marrow (Na et al., 2009). As a result of the disease normal structure of liver tissue is broken, then this area will have a deficiency of Kupffer cells. Because of the small absorption of NPs by atypical liver tissue, the Mr tomograms show a strong contrast between normal and atypical tissue.

Nevertheless, high absorption of NPs in the liver leads to their rapid excretion from the blood plasma, which greatly reduces the time of their circulation in the bloodstream. It is important to note that the circulation time of NPs in the blood strongly depends on their size. In clinical MRI, iron oxide NPs having the size <50nm are also used to visualize lymph nodes (Harisinghani et al., 2003). Since the NPs are very small, their extravasation from the blood vessels to the interstitial space can occur. Thus, the NPs can be transported to the lymph nodes through the lymphatic vessels. Also, the stem and immune cells are preloaded with superparamagnetic iron oxide particles coated with carbon and dextran as a T2-contrasting agent and then transplanted into the body, which allows one to monitor them in vivo (Lepore et al., 2006; Qiu et al., 2007).

Superparamagnetic iron oxide NPs coated with ascorbic acid can be considered as a potential Mr contrast agent, which simultaneously possesses antioxidant and therapeutic properties (Sreeja et al., 2015). It is shown that antioxidant properties of ascorbic acid persist after its adsorption on the surface of iron oxide NPs. The values of relaxation time of such particles are comparable with the values of relaxation time of the currently used clinical preparations, for example, ferumoxtran.

To obtain NPs suitable for use as an MP contrast agent, block copolymers are used during the synthesis of NPs by the co-precipitation of iron salts in the presence of a base (Basuki et al., 2014). The properties of NPs, including colloidal stability and relaxation, can be varied by changing the concentration of the copolymer and carefully selecting the anchor groups. The value of r2 for a colloid of such NPs is 370mM1s1, which is similar to the characteristics of the commercial drug Resovist.

It is shown that the contrast enhancement in T2 depends mainly on the degree of aggregation of NPs having a polymer coating using NPs, while the effect of the polymer itself on the Mr signal is relatively small (Carroll et al., 2011). The authors (Carroll et al., 2011) suggest the hypothesis that the control for the aggregate formation can serve as a means for achieving high contrast while maintaining colloidal stability. However, it should be noted that strong aggregation of magnetite NPs leads to artifact arising on Mr tomograms because the magnetic moment of the aggregates becomes very large. This is due to the fact that the magnetic field gradients are used in MRI for spatial encoding of information, and their strong local heterogeneity, as well as an increase in the magnetic permeability of the region of interest, breaks this process, resulting in the formation of spatial distortions on the tomograms. The proton relaxation rate also strongly depends on the particle size of iron oxides, in a less degreeon the composition of their coatings and the hydrophilicity of their surface (Duan et al., 2008).

The authors of this research (Zhao et al., 2013) describe the synthesis of iron oxide NPs in the form of an octapod and show the possibility of their application as a T2 contrast agent for MRI. It is shown that such particles more efficiently accelerate spin-spin relaxation in comparison with spherical particles. This fact solves the problem of achieving the necessary contrast at a relatively low concentration of NPs. For example, sufficient MRI contrast in vitro is obtained by the authors at the concentration of 0.2mM of these NPs, which is better in comparison with the spherical iron oxide particles described in the same work (> 0.4mM).

However, it should be noted that the synthesis of such particles by the method of thermal decomposition is quite complex and the problem of its adaptation for mass production remains actual. In addition, it is difficult to predict colloidal and chemical composition stability of the NPs with a similar surface to volume ratio.

To increase the accuracy of diagnosis with MRI, contrast agents changing both longitudinal proton relaxation and transverse relaxation are developed. For example, a core-shell structure is proposed for changing T1 and T2 relaxation (Shin et al., 2014) where superparamagnetic NPs of iron oxide are used as a core. The NPs are coated with silicone dioxide shell and then a layer of a paramagnetic compound that alters predominantly longitudinal relaxation is adsorbed onto the silicon dioxide.

There is a problem to differ the effect of contrast agents and artifacts on Mr images. MRI artifacts are caused by certain endogenous conditions, such as calcification, the presence of fat, hemorrhage, blood clots, or air bubbles. Obviously, these artifacts are problematic because they mimic signals coming from the Mr contrast agents. Thanks to the use of the contrast agents changing T1 and T2 relaxation the possibility of false diagnosis due to the influence of such artifacts is eliminated.

A number of works describe the concept of multifunctional nanoobjects, which can be visualized by various methods. It demonstrates the possibility of obtaining contrast agents based on superparamagnetic NPs accelerating transverse relaxation (T2) in MRI and having luminescence (Lee et al., 2006). The concept of multifunctional hybrid NPs can serve as a technological platform for a new generation of biological sensors.

The commercial particles coated with dextran of bacterial origin have a number of drawbacks, such as increased allergenicity (Mornet et al., 2005), low penetration efficiency in the cell by endocytosis of the liquid phase (Wilhelm and Gazeau, 2008). Dextran is also inconvenient to attach additional functional groups that could improve the internalization of particles into cells. In addition, a dextran shell is rapidly destroyed by lysosomes, resulting in the unwanted release of iron oxide into the cytoplasm (Arbab et al., 2003). Due to high biocompatibility of phospholipids, the phospholipid bilayer shell has a number of significant advantages in comparison with polymer NP stabilizers (Lacava et al., 2004). In addition, the phospholipids adhere to the surface of the particles well (De Cuyper and Joniau, 1988) and degrade in the cytoplasm much slower (Al-Jamal and Kostarelos, 2007), which allows one to reach large particle concentrations in the cells that require for NMR imaging. It is noted that the application of large monolamellar magnetoliposomes makes it possible to obtain a very good contrast in angiographic studies on animals (Martina et al., 2005).

At present, a lot of works are devoted to obtaining and studying magnetoliposomes containing MNPs both in the internal volume and inside the lipid bilayer. For example, the magnetoliposomes are produced by enclosing maghemite NPs in the internal volume of the vesicles (Martina et al., 2005). The resulting magnetoliposomes were used to increase the contrast in magnetic resonance angiography. In the study (Chen et al., 2014), the authors subsequently incorporate hydrophobic maghemite NPs in a lipid bilayer. The presence of maghemite NPs in the liposome envelope makes it possible to provide the remote release of encapsulated cytostatic (doxorubicin) by an alternating magnetic field (Chen et al., 2014).

The delivery and in vivo monitoring by MRI of polyelectrolyte microcapsules containing superparamagnetic NPs are shown in (Yi et al., 2014). The authors present that magnetic microcapsules do not exhibit obvious acute toxicity after the injection in the tail vein. Magnetic microcapsules enhance T2 Mr contrast in liver over 6h after administration. This study shows relatively faster clearance of Parg/DS magnetic capsules than the PAH/PSS ones in liver.

Superparamagnetic iron oxide NPs incorporated into the shells of polyelectrolyte multilayer capsules have different magnetic and NMR relaxivity properties than NPs freely dispersed in a sodium borate buffer solution (Abbasi et al., 2011). As shown superparamagnetic NPs in the polyelectrolyte shell have a smaller r2 relaxivity value compared with an uniformly distributed ensemble of NPs. In addition, the blocking temperature TB for the ensemble of MNPs decreases as a function of packing fraction.

Composite microcapsules are able to change the MRI contrast in T1 and T2 regime by varying the concentration of magnetite NPs and due to enzymatic degradation of the capsule shell in vitro and in vivo (German et al., 2016). Both relaxivity values depend on the average distance between the NPs in the microcapsule shell that can be easily varied for LbL approach by the changing magnetite NP layers, magnetite NP concentration in the colloid that are used for layer deposition (Fig. 6.3). The microcapsules with an average distance between the magnetite NPs equal to 54nm exhibit the maximum of Mr signal intensity change for the T1- and T2-weighted images. It is also shown that enzymatically destruction of microcapsules with high concentration of magnetite NPs in the shell leads to significantly increasing of Mr contrast. This effect can be used for the evaluation of degradation time of microcapsules in vivo.

This section describes the composition of the EPRI/SGOG magnetite solvent, the crevice solvent, the copper solvent, and the passivation solvent. The magnetite solvent is for the dissolution of the bulk deposit. The crevice solution attacks the deposit that is located in the crevice between the tube and the tube support plate. The crevice solution needs some mechanical help in order to replenish the solvent in the crevice area. The copper step dissolves and removes the copper deposits while the passivation step, which is applied after the copper step, puts a small oxide coating on all of the bare carbon steel surfaces in order to reduce the corrosion of the carbon steel during the following startup and operation.

These parameters were only finalized after many beaker tests followed by potboiler tests. The pH was selected after the testing of several more acidic solutions. The resultant pH was a compromise of dissolution rate vs the carbon steel corrosion in the SG. Most processes that employ chelates (EDTA) typically require temperatures approaching boiling in order to achieve an acceptable rate of dissolution. How the temperature is achieved will be discussed in a later section.

High temperature is required to allow venting of the SG through the SG pressure relief valve. The boiling results in the expulsion of the depleted solvent in the crevice so that the crevice can be replenished with fresh crevice solvent that has dissolution capability remaining. The venting process will be discussed later on a section on heating and venting SGs.

As stated earlier the passivation step is utilized to leave the exposed carbon steel in the SG with a protective coating on the surface to reduce the corrosion of the carbon steel during startup and initial operation prior to the buildup of the normal operational corrosion film layer. The passivation step is composed of the following:

The generic EPRI/SGOG process was developed and qualified for a well-defined range of application conditions. Any major deviation from these conditions should be specifically qualified in a major test vehicle similar to those used in this qualification program. Plant-specific testing should be done before cleaning to verify process effectiveness and to confirm acceptable corrosion with plant materials of construction. It is recommended that actual plant sludges be used for this testing whenever possible.

3-Aminopropyltriethoxysilane coupling agent has been used to increase higher saturation magnetization, storage modulus, and glass transition temperature of epoxy composite.3 Figure 2.73 shows results of modification of magnetite by silane.3 Thickness of silane coating clearly depends on silane concentration.3 Too thick coating reduces magnetic properties of composite.3

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