Production and in situ transformation of hematite into magnetite from the thermal decomposition of iron nitrate or goethite mixed with biomass

Effect of limestone and dolomite flux on the quality of pellets using high LOI iron ore

Study of thermal evolution of porous hematite by emanation thermal analysis

Constant rate thermal analysis (CRTA) has been used for studying the decomposition of three synthetic needle-shaped goethite samples. This method controls the reaction temperature such that the reaction rate and partial pressure of water vapour are kept constant at a selected value. The effects of the pressure of water vapour generated during the dehydration of goethite and of the decomposition rate on the porosity of the resulting hematite have been studied. The effect of the particle size of the precursors on the texture of the final products has also been analysed. By this method, acicular particles of α-Fe 2 O 3 with controlled porosity oriented along the c-lattice axis (the long axis of the particle) have been prepared.

The lepidocrocite (γ-FeOOH) to maghemite (γ-Fe2O3), and the maghemite to hematite (α-Fe2O3) transition temperatures have been monitored by TGA and DSC measurements for four initial γ-FeOOH samples with different particle sizes. The transition temperature of γ-FeOOH to γ-Fe2O3 and the size of the resulting particles were not affected by the particle size of the parent lepidocrocite. In contrast, the γ-Fe2O3 to γ-Fe2O3 transition temperature seems to depend on the amount of excess water molecules present in the parent lepidocrocite. Thirteen products obtained by heating for one hour at selected temperatures, were considered. Powder X-ray diffraction was used to qualify their composition and to determine their mean crystallite diameters. Transmission electron micrographs revealed the particle morphology. The Mossbauer spectra at 80 K and room temperature of the mixed and pure decomposition products generally had to be analyzed with a distribution of hyperfine fields and, where appropriate, with an additional quadrupole-splitting distribution. The Mossbauer spectra at variable temperature between 4.2 and 400 K of two single-phase γ-Fe2O3 samples with extremely small particles show the effect of superparamagnetism over a very broad temperature range. Only at the lowest temperatures (T⩽55 K), two distributed components were resolved from the magnetically split spectra. In the external-field spectra the ΔmI=0 transitions have not vanished. This effect is an intrinsic property of the maghemite particles, indicating a strong spin canting with respect to the applied-field direction. The spectra are successfully reproduced using a bidimensional-distribution approach in which both the canting angle and the magnetic hyperfine field vary within certain intervals. The observed distributions are ascribed to the defect structure of the maghemites (unordered vacancy distribution on B-sites, large surface-to-bulk ratio, presence of OH- groups). An important new finding is the correlation between the magnitude of the hyperfine field and the average canting angle for A-site ferric ions, whereas the B-site spins show a more uniform canting. The Mossbauer parameters of the two hematite samples with MCD104 values of respectively 61.0 and 26.5 nm display a temperature variation which is very similar to that of small-particle hematites obtained from thermal decomposition of goethite. However, for a given MCD the Morin transition temperature for the latter samples is about 30 K lower. This has tentatively been ascribed to the different mechanisms of formation, presumably resulting in slightly larger lattice parameters for the hematite particles formed from goethite, thus shifting the Morin transition to lower temperatures.

This study aims to assess the thermal properties of mixtures of sugarcane bagasse and iron(III) nitrate in the following proportions (mass/mass): 1/2, 1/1, and 2/1, using thermogravimetry/differential thermogravimetry and differential thermal analysis. These thermoanalytic techniques were performed to assess the best temperatures for the heat treatment of the mixtures for the subsequent production of the carbonaceous material/iron oxide composites and their behavior at different temperatures. According to thermal analysis, the decomposition profile of the mixture depends on the ratio of sugarcane bagasse to iron nitrate (BC/NF). The synthesized composites were characterized by X-ray diffraction, proving the formation of phases established from thermal analyses performed at 400, 500, and 600 °C. It was concluded that composites of the precursor mixtures may be produced to have different and interesting properties according to their application in sewage treatment processes such as adsorption.

Magnetite formation during the reduction of nanoparticulate hematite by Shewanella putrefaciens 200R is investigated in media of variable composition, at circumneutral pH and with lactate as electron donor. The relative rates of production of dissolved Fe(II) and Fe(III), aqueous speciation, plus chemical gradients control whether or not magnetite forms in the experiments. High bicarbonate concentrations result in the precipitation of magnetite, presumably by enhancing the non-reductive dissolution of hematite, hence causing the simultaneous production of soluble Fe(III) and Fe(II) in the incubations. Magnetite formation is inhibited when hematite dissolution is slowed down by adsorption of oxyanions (phosphate and sulfate) at the mineral surface, when the reduction of soluble Fe(III) is enhanced by increasing the cell density or adding an electron shuttle (AQS), or when aqueous Fe(II) is complexed by ferrozine. In experiments where hematite suspensions with and without bacteria are separated by a dialysis membrane, magnetite formation occurs mainly in the cell-free portion of the reaction system. Most likely, precipitation of magnetite is favored in the cell-free suspension because of a higher soluble Fe(III) to Fe(II) ratio. The formation of magnetite in the absence of cells further implies that its nucleation is not catalyzed by the bacterial surfaces.

Pervoskite lanthanum ferrite and related compounds have attracted considerably due to their wide applications in fuel cells, catalysts, sensors, and environmental monitoring systems. In this work, lanthanum ferrite and substituted compounds have been prepared by combustion synthesis process using lanthanum nitrate, ferric nitrate, and urea. The parent compound has been substituted with alkaline earth metals like Mg and Ca. The synthesized compounds are characterized using thermal analysis, X-ray diffraction (XRD), UV-visible, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM). From thermal analysis, it is seen that Mg2+ and Ca2+ ions have pronounced effect on the phase formation process. From XRD spectrum, it is seen that the crystalline lanthanum ferrite possesses an orthorhombic disorder perovskite structure with space group Pbnm with four formula units per unit cell, where La ion is tetragonally coordinated. The UV-visible reflectance spectra of lanthanum ferrite and substituted compounds shows two prominent absorption bands, which are shifted towards the lower wavelength side on substitution. The FTIR spectra of the parent substituted compounds recorded between 400 to 4000 cm−1. The existence of the prominent bands shows the formation of the single-phase crystalline lanthanum ferrite. From the SEM figure, if we compare the morphological features of the electrodes before and after substitution, it could be seen that the surface of the materials are disintegrated on oxygen evolution and weaken the intergrain spots.

Glass–crystalline materials with high iron oxide concentration: Phase composition, redox ratio and magnetic properties

Nanocrystalline of Barium Hexaferrite (BaFe12O19) powders have been synthesized using the sol gel auto combustion method. The ferrite precursors were obtained from aqueous mixtures of Barium nitrate and Ferric nitrate by auto combustion reaction from gel point. These precursors were sintered at different temperatures ranging from 700 to 1000oC for constant calcinations time 2,5 h in a static air atmosphere. Effects of Fe3+/Ba2+ mol ratios and sintering temperatures on the microstructure and magnetic properties were systematically studied. The powders formed were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM) and VSM. The results obtained showed that the phase BaFe12O19 powders were achieved by the Fe3+/Ba2+ mole ratio from the stoichiometric value 11, 11.5 and 12 at temperature 950OC. With increasing of temperature sintering, coercivity and magnetization value tends to rising. The maximum saturation magnetization (66.16 emu/g) was achieved at the Fe3+/Ba2+ mole ratio to 11.5 and the sintering temperature 950OC. The maximum coercivity value 3542 Oe achieved at mole ratio sample 12 with sintering temperature 950OC. Maximum saturation 6616 emu/g achieved at mole ratio sample 115 with the same temperature.

M-type barium ferrite (BaFe12O19) particles, from a mixture of barium nitrate, ferric nitrate, cetyltrimethylammonium bromide (CTAB), and ammonium carbonate, have been successfully prepared through simple grinding and calcination in the absence of any solvent. The products are characterized by X-ray diffraction, scanning electron microscope, and vibrating sample magnetometer, whose results indicate that they have well crystalline phase of BaFe12O19, typically hexagonal platelet-like structure, large saturation magnetization, even submicrometer particle size under the optimum condition. Meanwhile, the effects of Fe/Ba ratio, CTAB, and ammonium carbonate are also investigated. It has been found that the proper Fe/Ba ratio could suppress the intermediate phase such as α-Fe2O3 and BaFe2O4, CTAB could promote the crystallinity of BaFe12O19 and produce hexagonal crystal structure, and ammonium carbonate was the key for forming BaFe12O19 phase. This facile method may be helpful for the preparation of other multicomponent functional materials.

Pure perovskite compound SrFeO3 nanocrystals were successfully synthesized in molten NaNO3–KNO3 eutectic with Na2O2 from a mixture of strontium nitrate and ferric nitrate. The effect of metal precursors, salt medium, annealing temperature (mainly 400–800°C), and oxidizing properties of the melt on the phase composition, crystallite size and morphology of the resulting metal oxides were systematically studied by simultaneous TG/DSC, X-ray diffraction (XRD), scanning electron microscopy (SEM) methods. The results showed that the formation of the SrFeO3 phase mainly depended on the nature of the metal precursor and salt medium. It was found that metal nitrates are the suitable precursors and NaNO3–KNO3 eutectic with Na2O2 is the suitable salt medium, which results in the formation of pure SrFeO3 nanocrystals at a much lower temperature of 400°C.

The Fe3O4 magnetite nanoparticles are the most promising materials in the medical applications because of their biocompatibility, stability and ease in synthesis. In the present study PVP capped iron oxide (Fe3O4) nanoparticles with a size range of 5-9nm were synthesised by the chemical co-precipitation method in an inert environment created by nitrogen gas flow. The PVP coating serves as the stabiliser and controls the crystal growth thereby the particle size. The diameter range of synthesised nanoparticles is preferred in the medical applications such as drug delivery system, MRI contrast agent and hyperthermia is in vicinity of 10nm. The Fe3O4 magnetic nanoparticles were prepared by the aqueous co-precipitation of FeCl3·6H2O and FeC12·4H2O with addition of sodium hydroxide and PVP at room temperature. The nanoparticles of different diameters were obtained by varying the concentration of the precursors and keeping the other experimental parameters same. The formation of magnetite is confirmed by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The particle size and the morphology are characterized by scanning electron microscopy (SEM) and XRD. The hysteresis loop and the saturation magnetisation were measured by vibrating sample magnetometer (VSM). The results revealed that the magnetic nanoparticles are spherical in shape and with narrow size distribution with high magnetic saturation. With the increase in the concentration of precursors not only the diameter but also the crystallinity and saturation magnetisation increases. The synthesised nanoparticles are ideal candidate for the hyperthermia owing to the size, superparamagnetic nature and saturation magnetisation.

The drying and gas reduction of the iron oxides in the red mud of bauxite processing are studied. It is shown that at most 25% of aluminum oxide are fixed by iron oxides in this red mud, and the other 75% are fixed by sodium aluminosilicates. A software package is developed to calculate the gas reduction of iron oxides, including those in mud. Small hematite samples fully transform into magnetite in hydrogen at a temperature below 300°C and a heating rate of 500 K/h, and complete reduction of magnetite to metallic iron takes place below 420°C. The densification of a thin red mud layer weakly affects the character and temperature range of magnetizing calcination, and the rate of reduction to iron decreases approximately twofold and reduction covers a high-temperature range (above 900°C). The substitution of a converted natural gas for hydrogen results in a certain delay in magnetite formation and an increase in the temperature of the end of reaction to 375°C. In the temperature range 450–550°C, the transformation of hematite into magnetite in red mud pellets 1 cm in diameter in a converted natural gas is 30–90 faster than the reduction of hematite to iron in hydrogen. The hematite-magnetite transformation rate in pellets is almost constant in the temperature range under study, and reduction occurs in a diffusion mode. At a temperature of ∼500°C, the reaction layer thickness of pellets in a shaft process is calculated to be ∼1 m at a converted-gas flow rate of 0.1 m3/(m2 s) and ∼2.5 m at a flow rate of 0.25 m3/(m2 s). The specific capacity of 1 m2 of the shaft cross section under these conditions is 240 and 600 t/day, respectively. The use of low-temperature gas reduction processes is promising for the development of an in situ optimum red mud utilization technology.

Purpose: The interest in sustainability has increased the demand for materials from renewable sources or that are potentially reusable; recyclable or biodegradable. In order to make possible the application of these materials, the technical and scientific knowledge are applied in the development of blends with biodegradable constituents. In this study, polymer blends of poly(lactic acid) and polypropylene were prepared by twin screw extruder. Methods: The addition of polypropylene-graft-maleic anhydride (PP-g-MAH) or ethylene/methyl acrylate/glycidyl methacrylate (EMA-GMA) terpolymer as compatibilizer was studied. The polymer blends were comprised of PLA:PP ratios 70:30 with addition of 3 wt% of compatibilizer. The samples were processed by injection molding process and the products were subjected to thermal, mechanical properties and morphology analysis with a scanning electron microscope (SEM), thermal analyses (TGA/DSC) and X-ray diffraction (XRD). Results: The thermal analyses confirmed that addition of the compatibilizer has effect on crystalline melting temperature of the polymer components as well as on the mechanical properties. The SEM results showed the textural characteristics and the particles size of the polymers were modified after the synthesis of blends. The XRD results and TGA/DSC showed that the composites preserved the crystallization of polymers. The tensile strength of polymer blends increased with the presence of the compatibilizers and the morphology study of the polymer blends confirmed the better compatibily of PLA and PP by assistance of PP-g-MAH or EMA-GMA. Conclusion : The research results confirmed the application of polymer blend system to injection molding process.

Porous magnetite (Fe3O4) and hematite (α-Fe2O3) nanoparticles were prepared via the sol-gel auto-combustion method. The gels were prepared by reacting ferric nitrates (as oxidants) with starch (as fuel) at an elevated temperature of 200 °C. Different ratios (Φ) of ferric nitrates to starch were used for the synthesis (Φ = fuel/oxidant). The synthesized iron oxides were characterized by Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmet-Teller (BET) and vibrating sample magnetometer (VSM) analysis techniques. The crystal structure, morphology, and specific surface area of the iron oxide nanoparticles (Fe3O4 and α-Fe2O3) were found to be dependent on the starch content. The FT-IR, XRD and VSM analysis of the iron oxides for Φ = 0.3 and 0.7 confirmed the formation of the α-Fe2O3 core, whereas at Φ = 1, 1.7, and 2 showed that Fe3O4 cores were formed with the highest saturation magnetization of 60.36 emu/g at Φ = 1. The morphology of the Fe3O4 nanoparticles exhibited a quasi-spherical shape, while α-Fe2O3 nanoparticles appeared polygonal and formed clusters. The highest specific surface area was found to be 48 m2 g-1 for Φ = 1.7 owing to the rapid thermal decomposition process. Type II and type III isotherms indicated mesoporous structures.