Thermal Decomposition Of Goethite Research Articles

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

Owing to the depletion of high-grade iron ore quality, many steel plants over the world are now using pellets after beneficiation of low grade ores as blast furnace feed. For the effective utilization of low-grade iron ore resources (59–62% Fe) with high loss of ignition (LOI), mineralogical characteristics play the vital role to improve the process efficiency. The present work illustrates the effect of limestone and dolomite as flux material in pelletization of an Indian goethetic-hematite iron ore with 59.75% Fe, 4.52% SiO2, 3.84% Al2O3, and 4.85% LOI. As per mineralogical analysis, this ore contains 30.11% goethite and 9.71% kaolinite, which contribute major LOI of the sample. The self-binding properties of the ore ensured the complete elimination of an external binder due to the presence of kaolinite. LOI of the ore indeed affected the quality of indurated pellets by cracking, which might be the reason for the degradation of pellet quality. Concurrently, the same LOI enhanced the pellet quality when suitable fluxes were added. Limestone, dolomite, and their combinations were used as fluxing agent. The effects of CaO and MgO for the improvement of inherent pellet properties were evaluated through the physical, mineralogical, thermal, chemical, and metallurgical properties of the fluxed pellet using different analytical techniques, i.e., Thermogravimetric Analysis (TGA), X-ray diffraction, Stereomicroscopy, Optical Microscopy, Field Emission Scanning Electron Microscopy, and Wavelength Dispersive Microscopy with Electron Microprobe. TGA results indicated the thermal decomposition of goethite, kaolinite, and fluxes at different temperatures. With the addition of dolomite and limestone in the pellet feed material, CCS (Cold Compressive Strength/kg.pellet−1), RI (Reducibility Index/%), RDI (Reduction Degradation Index/%), SI (Swelling Index/%) and porosity could be improved. Due to the loss of mass in flux materials, by increasing the MgO content, it is possible to reduce swelling index and increase the pellet porosity. Simultaneously, the strength of the pellet increases because of slag formation in the form of calcium/magnesium aluminum silicate. The physical and metallurgical properties, i.e., CCS, porosity, SI, RDI, and RI of the fluxed pellets were optimized. At particular ratio of limestone and dolomite, synergistic effect was observed with respect to pellet characteristics.

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

Among the methods of obtaining hematite (α-Fe2O3), the thermal decomposition of goethite (α-FeOOH) or iron (III) nitrate (Fe(NO3)3·9H2O) is of special importance. These solids can be combined with other materials, thus altering the properties of the oxide obtained. The decomposition of goethite or nitrate mixture with biomass in an inert atmosphere yields hematite/carbonaceous material or magnetite/carbonaceous composites with different morphologies and crystallinities, as observed by scanning electron microscopy and X-ray diffraction, respectively. The transformation of hematite to magnetite occurs at 623 K (for biomass/nitrate mixture) and 723 K (for biomass/goethite mixture). The formation of magnetite is a consequence of the pyrolysis of biomass, which produces a reducing mixture, and the difference in the temperature for obtaining Fe3O4 for the two precursors was investigated by thermal analysis by observing the mass and energy variations at each stage.

Adsorption of As(V) inside the pores of porous hematite in water

As(V) adsorption inside the pores of porous hematite in water has been studied in this work. This study was performed on nonporous hematite and porous hematite prepared from the thermal decomposition of goethite and siderite through the measurements of adsorption isotherm, SEM–EDX, XRD and BET. The results demonstrated that the As(V) adsorption was difficult to be realized inside pores if they were too small. This observation might be due to that the pore entrances were blocked by the adsorbed ions and thus the inside surfaces became invalid for the adsorption. Only if the pore size is large enough, the effective surface area inside pores would be close to that on non-porous hematite for As(V) adsorption. In addition, it was found that siderite is better than goethite for preparing porous hematite with thermal decomposition as adsorbent for arsenic removal.

Synthesis, characterization, and cytotoxicity of the plasmid EGFP-p53 loaded on pullulan–spermine magnetic nanoparticles

Magnetic nanoparticles have been used as effective vehicles for the targeted delivery of therapeutic agents that can be controlled in their concentration and distribution to a desired part of the body by using externally driven magnets. This study focuses on the synthesis, characterization, and functionalization of pullulan–spermine (PS) magnetic nanoparticles for medical applications. Magnetite nanopowder was produced by thermal decomposition of goethite (FeOOH) in oleic acid and 1-octadecene; pullulan–spermine was deposited on the magnetite nanoparticles in the form of pullulan–spermine clusters. EGFP-p53 plasmid was loaded on functionalized iron oleate to transfer into cells. Synthesized nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), vibrating sample magnetometry (VSM), and transmission electron microscopy (TEM). The encapsulation efficiency and drug loading efficiency of the nanocomplexes were tested. FTIR studies showed the presence of oleic acid and 1-octadecene in the iron oleate nanopowder and verified the interaction between spermine and pullulan. The characteristic bands of PS in the spectrum of the pullulan–spermine-coated iron oleate (PSCFO) confirmed that PS covered the surface of the iron oleate particles. TEM studies showed the average size of the iron oleate nanopowder, the PSCFO, and the plasmid-carrying PSCFO (PSCFO/pEGFP-p53) to be 34±12nm, 100±50nm and 172±3nm, respectively. Magnetic measurements revealed that magnetic saturation of the PSCFO was lower in comparison with the iron oleate nanopowder due to the presence of organic compounds in the former. In cytotoxicity tests performed using U87 cells as glioblastoma cells, a 92% survival rate was observed at 50µg/µl of the plasmid-carrying PSCFO, with an IC50 value of 189µg/µl.

Study of thermal evolution of porous hematite by emanation thermal analysis

Abstract Emanation thermal analysis (ETA) was used for the characterization of surface and porosity annealing of acicular porous hematite samples in the temperature range from 20 to 600 °C under in situ conditions of heating in air flow. Two hematite samples with different surface areas (85 and 44 m 2 g −1 , respectively) were prepared by thermal decomposition of goethite using constant rate thermal analysis (CRTA) equipment. ETA results characterizing the thermal evolution of the porous hematite samples were compared with surface area determined by B.E.T. method, transmission electron micrographs and crystallite size determined by XRD.

The use of constant rate thermal analysis (CRTA) for controlling the texture of hematite obtained from the thermal decomposition of goethite

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.

Mössbauer study of the thermal decomposition of lepidocrocite and characterization of the decomposition products

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.

Evolution of the surface of haematite prepared by thermal decomposition of goethite: A microcalorimetric study

α-Fe 2O 3 samples have been prepared by thermal decomposition of crystalline α-FeOOH in air, and have been characterized by XRD and SEM analyses and surface area measurements. Three samples, decomposed at 673, 973 and 1373 K, respectively, have also been characterized by microcalorimetry following the adsorption at room temperature of water, n-butylamine and hexafluoroisopropanol. It has been concluded that the nature of the active surface sites of the haematite samples is not modified by thermal treatment; both rather strong acidic sites and moderately basic sites are retained. However, the local density is markedly changed, due to the poisoning effect of chemisorbed water present only on samples obtained by decomposition at the lower temperatures.

IR characterization of surface hydroxy groups on haematite

The OH stretching absorptions (3670, 3640 and 3460 cm−1) detected on haematite samples obtained by thermal decomposition of goethite, are assigned to monocoordinated and bridged free surface OH's and to hydrogen bonded OH's in surface micropores, respectively, on the basis of their behavior to successive adsorption of methanol, pyridine and D2O and surface structural models.