Magnesioferrite Formation Research Articles

Агломераттың физика-химиялық қасиеттеріне флюстерді қолданудың әсері

The results of a research of the fluxes usage effect on the physicochemical properties of sinter from mill scale are presented. The conducted studies have shown the expediency of introducing fluxes into the composition of the sintering charge. However, each flux in the form of quartzite or limestone (dolomitic) has its own advantage. When quartzite is used as a flux, X-ray phase analysis and microsection of the agglomerate confirm the presence of metallic iron. The introduction of limestone (dolomitic) into the sinter charge allows to produce a fluxed sinter. When using sinter for metal smelting, the fluxed sinter will allow limestone to be removed from the furnaces. The conclusion of which leads to the saving of a significant amount of heat spent on dissociation СаСО3 and MgСO3, thus saving fuel. Magnesio-ferrite formation (MgFe2O4), periclase (MgO), alumina in fluxed sinter is primarily due to the use of limestone (dolomitic). Magnesium contained in limestone dissociated with magnetite to form MgFe2O4 and MgO. To confirm the reliability of X-ray phase analysis, samples of the fluxed agglomerate were examined by scanning electron microscopy with the INCA Energy microanalysis system. Also, the average elemental composition of the sinter according to EDS analysis is shown in the figures and tables.

Reaction Characteristics Between Sinter and Serpentine

In recent years, adding an appropriate amount of serpentine into a blast furnace (BF) is considered to be a popular countermeasure to cope with the usage of iron ores with high Al2O3 content; this is because MgO in serpentine can improve the fluidity and desulphurization ability of BF slag with high Al2O3. Aimed to better understand the reaction characteristics between sinter and serpentine, a series of experiments were carried out between 1100 °C and 1300 °C under air atmosphere with a sinter to serpentine ratio between 100:1 and 100:6. The results indicated that higher temperatures and greater serpentine additions led to increased magnesioferrite formation. Samples with a sinter-to-serpentine ratio of 100:1 exposed to temperatures below 1300 °C did not have sufficient activation energy for diffusion to occur between the sinter and serpentine under the conditions to form magnesioferrite. But at 1300 °C, large amounts of magnesioferrite and silicate phases could be observed, and the major phases are magnesioferrite phase. At higher serpentine additions, where the sinter-to-serpentine ratio exceeded 100:3, the magnesioferrite reaction could be completed after reaching 1200 °C. Also, the serpentine first reacted with hematite followed by the reaction with SFCA (Silico-Ferrite of Calcium and Aluminum). The SiO2 in the serpentine formed silicate phases with CaO/Fe2O3 in the sinter. The findings from this work may provide guidelines for adding serpentine into BF and improve the operational performances of BF.

Experimental exploration of volcanic rocks-atmosphere interaction under Venus surface conditions

This study presents an inventory of possible chemical reactions affecting, or having affected, the Venus surface. Fluid rock reactions are simulated using experiments under conditions close to the present surface. Slabs or powder of several natural and synthetic silicate material (crystalline fresh basalt, altered basalt, obsidian, pumice and basalt glass) were reacted at 475 °C in CO2-H2O-H2S-SO2-CO gas mixture. Most of the runs were carried out at roughly 90 bars with a duration of one week, some experiments having longer (one month) or shorter (one day) durations. The role of H2O content was explored through a wide range of water pressure: from dry gas for the current Venus conditions up to 590 bars (86%H2O) for early Venus (or other early terrestrial planets). The gas phase was sampled before the completion of the runs for chemical analysis of major gas components (CO, H2S, SO2) as well as trace elements possibly released by the rocks. The altered samples were examined by a suite of mineralogical and chemical techniques (scanning and transmission electron microscopy, X-ray diffraction and spectroscopy).In dry atmosphere, the redox potential of the gas was close to the Ni/NiO buffer (−21.3 to −27.3 log fO2), thus close to the current Venus conditions. The sample alteration is tenuous and limited to surface oxidation of glasses and coating of olivine by iron oxides, as well as the general deposition of (Ca,Na)SO4 at the sample surface. The oxidation of glass is reflected in the formation of magnesioferrite under the surface and is accompanied by the release of Ca, Mg and Na into the gas phase or mineralized as sulfate at the surface. In wet atmosphere, obsidian recrystallizes into a mixture of plagioclase and amphibole while basaltic glass produced non-expandable clays minerals: chlorite-type (2:1:1) at the surface and likely celadonite (2:1) below the surface. Olivine is preserved. Using obsidian (the most alterable material) as a proxy of aluminosilicates, we discuss the surface reactions operating under supercritical conditions, and we used a shrinking-core equation for modeling the long-term reactions.These parametric exploration offer new insights into processes having affected the surface of Venus and contribute to the discussion of open questions such as the fate of water or the lifetime of vitreous dust or fine grain material if present in the current or past Venusian environment. Longer duration experiments will provide more kinetic parameters that can be extrapolated to the geologic history of Venus.

Effect of MgO addition on the metallurgical properties of the vanadium-titanium pellet with simulating blast furnace conditions

ABSTRACTMgO addition plays a vital role in improving the quality of pellets. In this study, the effects of MgO addition on the compressive strength, reducibility, reduction swelling characteristics and softening-melting performance of V-Ti pellets were explored systematically with simulating BF conditions. From the results, it can be observed that the compressive strength decreased with increasing MgO due to the formation of magnesioferrite, the restriction of recrystallization-agglomeration of haematite and the decreasing of molten slag. The reducibility of V-Ti pellets improved substantially due to the increase of the porosity. The decreasing of RSI is mainly caused by the decreasing of lattice volume swelling during the transition from MgO·Fe2O3 to (Mg,Fe)O. In addition, the softening-melting behavior and permeability of V-Ti pellets packed bed was found to be improved with increasing MgO content. In sum, the V-Ti pellets with a MgO content higher than 2.4% exhibits optimum metallurgical properties.

Effect of fluxing agents on reduction degradation behaviour of hematite pellets

During induration at a high temperature, a considerable amount of slag/melt phase forms inside the iron ore pellets, comprising SiO2, Al2O3, CaO, MgO and FeO. After cooling, the slag phase solidifies and acts as an important bonding phase in the finished pellets and influences their room temperature as well as high temperature properties, especially reduction degradation. Fluxing agents play an important role in forming these bonding phases depending on the type and amount of flux. In the present study, the effect of different fluxing agents, namely, limestone, dolomite, magnesite and pyroxenite, on melt formation and microstructure during induration and on reduction degradation behaviour during reduction was examined. From the results, it was understood that to reduce the disintegration during reduction it is essential to increase the amount and distribution of bonding phases like silicates, which are more stable as compared to oxide phases like hematite. Acid pellets exhibited highest reduction degradation due to the presence of more hematite bonds and less silicate bonds. In limestone fluxed pellets, reduction degradation index dropped considerably with increasing CaO content due to the formation of more amount of bonding phase. Dolomite–pyroxenite pellets, on the other hand, showed lower reduction degradation index up to 0.4 basicity, and beyond that, higher degradation was observed due to the increased pore size, which resulted in poor strength of the reduced pellet matrix and hence more degradation. Low reduction degradation observed in pyroxenite and magnesite fluxed pellets could be due to the formation of magnesioferrite and silicate melt, which are more stable phases compared to hematite.

Spectroscopic speciation and thermodynamic modeling to explain the degradation of weathering steel surfaces in SO2 rich urban atmospheres

The characteristic protection ability of weathering steel can be affected by the environment in SO2 rich urban atmospheres. Although sulphur dioxide can partially be oxidised to sulphur trioxide, both acid gases can be dissolved either in the atmosphere or in the moisture film present on the steel surface, forming sulphurous and/or sulphuric acid, and accelerating the corrosion of the material. Thermodynamic simulations, based on experimental data obtained by Raman and SEM–EDS techniques on different weathering steel sculptures located outside in Bilbao (Basque Country), were done to probe the role of SO2 in the formation of several soluble sulphates, such as, rozenite (FeSO4·4H2O) and retgersite (NiSO4·6H2O). According to the results, it was confirmed that the presence of atmospheric particles of calcium carbonate does not have an outstanding negative role in the metal decaying process. However, the presence of high magnesium calcite (HMC) plays an important role in the formation of magnesioferrite, another decaying product present in the surface of the weathering steel. As all these sulphates are soluble, rain water can dissolve them leading into a continuous decaying and material loss process.

Characterization of a calcium phospho-silicated apatite with iron oxide inclusions

An iron oxide containing calcium phosphate–silicate hydroxyapatite was synthesized by calcination at 900 °C of a sample obtained by precipitation in basic aqueous solution of Ca, P, Si, Fe and Mg containing acidic solution made from dissolution of natural minerals. XRD and FTIR were used for crystallographic characterization of the main apatitic phase. Its composition was determined using ICP-AES. EDX coupled with SEM and TEM evidenced the heterogeneity of this compound and the existence of iron–magnesium oxide. Magnetic analyses highlighted that this phase was non-stoichiometric magnesioferrite (Mg 1.2Fe 1.8O 3.9) spherical nanoparticles. Those analyses also put into evidence the role of calcination in synthesis. Carbonates detected by FTIR and estimated by SEM-EDX in non-calcinated sample were removed from apatitic structure, and crystallization of apatite was enhanced during heating. Moreover, there was phase segregation that led to magnesioferrite formation.

Effect of pyroxenite flux on the quality and microstructure of hematite pellets

Pellet properties are largely governed by the type and amount of oxide and bonding phases formed during induration and their stability during the reduction. In the present study, effect of MgO in the form of pyroxenite on melt formation and microstructure during the induration of hematite pellets was examined. Optical and electron microscope studies with EDS and X-ray mapping were carried to understand the amount and chemistry of different phases formed at different levels of MgO by varying the pyroxenite addition. These pellets were characterized for their strength and swelling index under blast furnace reduction conditions. Based on silicate slag chemistry formed in the fired pellets, microstructure and pellet quality, 5% pyroxenite addition to get 1.5% MgO in pellets found to be optimum flux dosage. Pellets with this optimized chemistry were also found superior to acid pellets in terms of reduction degradation index, reducibility and softening melting characteristics. Formation of magnesioferrite and high melting point slag with low FeO content in the fired pellets could be attributed to the improved performance of pyroxenite pellets.

Effect of application of a high magnetic field on the microstructure of Fe substituted layered double hydroxide clay for a magnetic application

In this study, the synthesis of Fe substituted layered double hydroxide (LDH) clays with unique layered structures, Mg∕Fe-LDH, was attempted by a coprecipitation method, and subsequent decomposition behaviors on in situ heat treatments under a high magnetic field were investigated for these LDH clays. Specifically, the evaluations of microstructure of Mg∕Fe-LDH were in detail carried out after in situ heat treatments with a high magnetic field of 10T. As a result, it was found that the thermal decomposition behaviors of Mg∕Fe-LDH on in situ heat treatments under the exposure of 10T were significantly different from the ones under 0T and the formation of magnesioferrite (MgFe2O4) with a spinel-type structure was enhanced by the application of a high magnetic field. Furthermore, there were some distinct differences between the morphologies of MgFe2O4 prepared between under 0 and 10T that were caused by the anisotropic magnetic susceptibility of MgFe2O4. Applying in situ heat treatment under 10T to the decomposition of Mg∕Fe-LDH led to the successful synthesis of nanosized MgFe2O4 at lower temperatures.

Influence of the olivine additive fineness on the oxidation of magnetite pellets

Olivine is used as an additive in Luossavaara–Kiirunavaara AB (LKAB) blast furnace pellets. The LKAB iron ore is magnetite which oxidizes to hematite during the sintering process. Olivine retards the oxidation of magnetite pellets if the threshold temperature of magnesioferrite formation is exceeded. In this study, we have developed a thermogravimetric measuring method to study the relationship between the olivine reactivity in green pellets and the olivine fineness. A less reactive olivine makes the pelletizing process more tolerant of excessively high temperatures in the green pellets during oxidation. The reactivity of olivine decreases when the amount of fine tail in olivine is decreased. The top size is limited by balling. Grinding tests in pilot scale show that if the olivine additive is ground in closed circuit with a ball mill keeping good control over the top size, the olivine fineness can be appreciably decreased without disturbing balling. The olivine reactivity can be decreased by 40% compared to the reference olivine in the production plant. Also, savings can be made on both the grinding energy and grinding media consumption. The results in both pilot scale and full production scale show that better oxidation in the grate due to a coarser olivine additive improves the low temperature reduction strength (LTD, ISO 13930) in pellets. The measuring method developed for the olivine reactivity enabled evaluation of different particle-sizing methods for olivine characterisation. The screening size fraction %−45 μm showed a good correlation to olivine reactivity in green pellets within a very large measuring range. The correlation of laser diffraction analysis to the olivine reactivity showed, however, that the laser diffraction measuring method is affected too much by variations in the large particles.

Formation of ferriolivine and magnesioferrite from Mg ? Fe-olivine: Reactions and kinetics of oxidation

Olivine samples (Fa 11) have been oxidized in air (f O2 = 0.2 atm) at temperatures ranging from 350–700 °C and examined by Mossbauer spectroscopy, transmission electron microscopy, X-ray powder diffraction and thermomagnetic analysis. Oxidation of olivine was found to result in ferriolivine, magnesioferrite (major oxide phase) and magnetite (minor oxide phase) formation. Ferriolivine forms planar (001) precipitates, 0.6 nm in thickness, in the olivine host; the composition is likely to be Mg0.5 v 0.5(Fe3+)1.0SiO4. Magnesioferrite MgFe2O4 exsolves as fine-grained precipitates (5–6 nm in size) filling interstices between the ferriolivine planar precipitates. Oxidation kinetic data at 700 °C show two stages of oxidation corresponding to formation of ferriolivine in the first stage and magnesioferrite in the second stage. The linear rate law with a rate constant k Fol = 1.23 · 10-3 s-1 was found for the first stage whereas a parabolic rate-law with a constant of k oxi = 3.28 · 10-3 s-1 was determined for the second stage of oxidation. It was found that ferriolivine is not an intermediate metastable phase in the oxidation process, terminated by magnesioferrite formation. The ferriolivine and magnesioferrite are considered to have formed by independent reactions which do not necessarily proceed simultaneously.

Magnesioferrite formation in low-concentration Fe/MgO single crystals

Single crystals of MgO containing iron in concentrations from 310 to 12900 ppm have been examined by magnetic resonance and reflection electron diffraction before and after ageing in oxygen in the temperature range 600–800° C. Before ageing, only the e.s.r. spectrum of isolated Fe3+ ions in cubic sites was seen and the diffraction patterns revealed MgO alone. After ageing, a strong anisotropic line, centered near g=2.00 and exhibiting the characteristics of ferrimagnetic resonance, was found and its presence was coupled with the appearance of a spinel pattern superimposed on that of the MgO. Analysis of the variation of anisotropy field with ageing time gave estimates of the room-temperature magnetization, first anisotropy constant and Curie temperature of 258 emu cm−3, −2.7× 10−3 J cm−3 and 500±10 K, respectively, which, in view of the close agreement with published data, suggested magnesioferrite formation even at very low iron concentrations. In the initial stages of ageing a strong isotropic resonance line was observed which appeared to be a precursor of the anisotropic ferrimagnetic line.