Recrystallization Of Hematite Research Articles

Research on the ring formation mechanism of magnesian flux pellets in rotary kiln

The forming of rings was a key problem of magnesian flux pellets in rotary kiln, which seriously limited production efficiency. Pellet powder and flux were the raw materials of the ring. Based on this, the bonding strength, melting behavior and microstructure of pellet powder and its mixed powder with flux were investigated. The influence of basicity (R = CaO/SiO2) on ring behavior of pellet powder was analyzed, and ring formation mechanism of magnesian flux pellets was clarified. The results showed that acid pellet powder was not easy to form rings due to lower bonding strength of briquettes. Due to changes in bonding process after mixing of flux, magnesian flux pellet powder produced ferrite and silicate liquid phase with lower melting point, which promoted diffusion and recrystallization of hematite and enhanced compressive strength of briquettes, then finally caused rings to form. Moreover, it is required to control roasting temperature below 1200 °C, which is a necessary condition for magnesian flux pellet powder to form an initial ring which was easy to be destroyed.

From Fresh Itabirites and Carbonates to Weathered Iron Ore: Mineral Composition, Density and Porosity of Different Fresh and Altered Rocks from the Quadrilátero Ferrífero, Brazil

The weathering of Paleoproterozoic itabirites (metamorphic-banded iron formations) and dolomites from the Cauê and Gandarela Formations in the Quadrilátero Ferrífero (QF), Brazil, produces supergene iron ore with different mineralogical, chemical, and physical properties. In this work, we present a methodology to assess the changes in chemical and physical features of those rocks during weathering, via quantitative analyses of mineral assemblages. These mineral assemblages were calculated from chemical analyses of fresh and weathered samples collected from drill holes drilled in different iron ore deposits in the QF. In general, the number of mineral species found in fresh or/and weathered itabirite is restricted, which helps the quantification of the mass and volumes of minerals by normative calculation in a large dataset of drilling and channel samples. The calculation of the bulk density takes into consideration, besides the mineral phases, the voids and free water in the altered rock matrix. This study shows that the estimated porosity in supergene ore varies from 0% to 20%, for compact materials, and from 15% to 55% for friable rocks, indicating an important process of rock matrix dissolution during the weathering of itabirites. In this process, MgO, CaO, and FeO are leached out from carbonates, talc, and amphiboles. Magnetite is oxidized to hematite, releasing Fe2+, which is oxidized and precipitates as Fe-hydroxide. There is a concentration of Fe2O3, MnO, Al2O3, and SiO2 in the supergene ore (saprolite) by residual enrichment or recrystallization of hematite, goethite, quartz, manganese oxides, and kaolinite. A calculation of weathering effects on the original protoliths allowed for the establishment of a correlation between different types of fresh itabirites and their corresponding weathered materials. The calculation was carried out in several steps, to account for changes in porosity and masses and has taken into consideration differences in the mineralogical composition of the protolith. Within the weathered zones, a strong link is observed between the existence of collapse on the topographic surface and the presence of supergene ore underneath. The partial to total dissolution of quartz and carbonates from the protolith itabirite results in very porous materials and leads to gravitational collapses.

Induration aspects of low-grade ilmenite pellets: Optimization of oxidation parameters and characterization for direct reduction application

Induration of ilmenite pellets by oxidation is an essential step in the pelletization process since it decides the physical and metallurgical properties of the pellets. In this regard, the induration parameters such as temperature and roasting time have been optimized to obtain good quality ilmenite pellets made of concentrates obtained from low-grade ilmenite ores of Odisha, India. The oxidation temperature of 900 °C at a short roasting time of 15 min has been found suitable to achieve recommended requirements of various pellet properties such as cold compressive strength, porosity, metallization, tumble, and abrasion indices. X-ray diffraction and microstructural analysis indicate that the recrystallization of hematite in the oxidation process improves the mechanical strength of the pellets. In contrast, the formation of ferric pseudobrookite phase at 1000 °C and 1100 °C oxidation temperatures impairs the pellet strength.

Insight into the Consolidation Mechanism of Oxidized Pellets Made from the Mixture of Magnetite and Chromite Concentrates

To produce more competitive stainless steel products, the utilization of low-cost chromite concentrate is of great importance. In a previous study, a high-quality product pellet (CMP) for blast furnace smelting process made from a mixture of 40 wt pct chromite and 60 wt pct magnetite concentrates was manufactured by a high-pressure grinding rollers pretreatment. In this work, an insight into the consolidation mechanism of CMP is taken in comparison with the oxidized pellets (MP) made from 100 pct magnetite concentrate by adopting the scanning electron microscopy, energy-dispersive spectrometer, and X-ray diffractometer. The mineralogy of the pellets and the morphology of the preheated and roasted mineral particles are demonstrated. To gain better understanding of the consolidation mechanism of CMP, the thermodynamics of chromite–magnetite spinel system and hematite–sesquioxide corundum system in air are considered by using FactSage software. It can be found that the solid-state bonding is the dominant form in the consolidation of CMP, which mainly depends on the recrystallization of hematite, the solid solution bonding in adjacent areas of both magnetite–chromite particles and chromite–chromite particles. The latter two bonds rely on the formation of the miscible sesquioxide and spinel solid solution at the contact areas of particles, which is largely affected by the oxidizability of magnetite and chromite spinels. When more chromite concentrate is blended, the weak bonding among the chromite particles gradually becomes the dominant factor, which will lead to the decrease of the mechanical strength of fired pellets. The presence of a small quantity of siliceous liquid phase in CMP is believed to be beneficial to the hardening by accelerating the ion diffusion rate and forming slag bonds.

Micro‐Raman investigation of terra sigillata slips: a comparative study of central Italian and southern Gaul productions

AbstractTerra sigillata is certainly the most famous fine ware of the Roman period, and for this reason it has been a subject of interest for both the archeology and archeometry communities. X‐ray diffraction studies showed systematic differences in the mineral compositions between central Italian and south Gaul productions. All the slips contain hematite; the Gallic ones embody also a significant content of corundum, while the Italian productions contain a great proportion of spinel. Raman investigation fails to reveal directly these differences because the spectra are dominated by the hematite peaks. However, we originally demonstrate that, due to the occurrence of an upshift of bands, the Raman spectrum of these sigillata slips can be associated with a substituted hematite. This premise has been confirmed by comparing the crystallization of hematite in four annealed clays to that of the ancient slips. The results suggested that the presence of the strong additional Raman band at around 680 cm−1 present in both clays and ancient slips could be associated with the recrystallization of hematite, occurring above 750 °C. It could also be due to the magnetite content, but this hypothesis is not supported by X‐ray diffraction data. In addition, the reduction seems to take place only above 1050 °C, as suggested by the unveiling of hercynite as well as the darkening of the clay samples. Raman scattering is shown to be very sensitive to small variations in clays composition and to firing temperature, and it has been successfully used as an in situ sensitive probe for discriminating between Italian and south Gallic productions. Copyright © 2010 John Wiley & Sons, Ltd.

Hydrothermal syntheses of epidote and piemontites on the join Ca2Al2Fe3+Si3O12(OH)-Ca2Al2Mn3+Si3O12(OH) at relatively low pressures of 200-400 MPa

Syntheses of epidote minerals on the join Ca2Al2Fe3+Si3O12(OH)-Ca2Al2Mn3+Si3O12(OH) were conducted using standard cold-seal pressure vessels and solid oxygen buffering techniques at 200-400 MPa and 500 °C. Two types of starting materials were used: (1) oxide mixtures (type 1) + excess H2O, and (2) mixtures of synthetic CaFe3+AlSiO6-pyroxene and oxides (type 2) + excess H2O. The compositions of Ca2Al2Fe3+qMn3+1-qSi3O12.5 starting materials were q = 1.0, 0.9, 0.5 and 0.25 for the type 1, and q = 1.0, 0.75, 0.5 and 0.25 for the type 2. Mn3+-free epidote was not crystallized from the type 1 starting materials, even at 400 MPa, whereas Mn3+-Fe3+-Al piemontites were produced at 300 MPa, but they were along with some associated minerals. Recrystallization of hematite during runs is a major problem when using oxide mixture starting materials. However, recrystallization of hematite was suppressed by using the type 2 starting materials, and Mn-free epidote and Mn3+-Fe3+-Al piemontite were synthesized as almost single phases at 380 MPa and at 200-370 MPa, respectively. The chemical compositions of the synthetic Mn3+-free epidote and Mn3+-Fe3+-Al piemontites formed were generally close to those of the starting materials, except that Fe3+ contents tended to be slightly lower. Pressure, temperature and oxygen fugacity have been considered to be the main factors controlling the occurrence of epidote minerals. However, this study demonstrates the importance of Fe3+-source material. Although the results of previous synthesis experiments of epidote minerals have not necessarily been compatible with those of stability experiments and the natural occurrences of epidote minerals, the syntheses here succeeded in producing nearly single phase epidotes with Ca2Al2(Fe3+,Mn3+)Si3O12(OH) at relatively low pressures less than 400 MPa. This aids the understanding of the varied occurrence of natural epidote minerals.

Effects of reduction parameters on the amount of Pb, Zn, Cu and Cd in reduced pellets. a case study of Nizna Slana Iron ore pellets

A study of reduction of Nizna Slana Iron ore pellets using Hydrogen has been conducted. The structural and phase changes that occur in iron ore pellets at various temperatures have been investigated by scanning electron microscopy. The pellets were made from concentrates of Nizna Slana iron ore obtained from Slovakia, and were reduced at various temperatures in the range 600oC to 1200oC. It was found that recrystallization of hematite and melting of the gangue minerals present started at about 1100oC. At about 1150oC, the amount of Pb, Zn, Cd and Cu in the pellets were significantly reduced. Compressive strength measurements also showed that the strength of pellets reduced at 900oC or less were low compared to those of pellets reduced at 1150oC. At 1150oC, the observed fracture mode was transcrystalline. Keywords: Pellets, Temperature, Recrystallization. [Global Jnl Engineering Res. Vol.2(1&2) 2003: 85-94]

Microstructures, textures and deformation mechanisms in hematite

Deformation and recrystallization of hematite in iron formations and high-grade ore bodies of the Cauê Formation from the Quadrilátero Ferrı́fero District, Minas Gerais, Brazil, resulted in several types of fabrics, depending on the tectonic and metamorphic imprint. The fabrics vary from randomly oriented granoblastic to strongly oriented lepidoblastic/mylonitic with local development of cataclastic features.Complete pole figures of the crystallographic planes (003)-basal plane; {110}-prism and {104}-rhombohedron were measured on several samples from different areas by means of neutron diffraction revealing a typical crystallographic preferred orientation for the different fabric types. The configuration and intensity of the maxima are directly related to the magnitude of the deformation and the type of response of the ore.The analysis of the textures and microstructures of the iron ores and comparison with experimental deformation data lead us to the conclusion that three main mechanisms are active: basal slip, diffusion processes and anisotropic grain growth. Post-tectonic recrystallization and secondary grain growth did not affect the textures developed during deformation.

Controlled Recrystallization of Hematite from Two Highly Different Phases of Ferric Trihydroxide

ABSTRACTHematite Fe2O3, is a semiconductor, and its electrical properties are highly sensitive to the preparation methods and purity. Its precursors can be hydrated ferric oxides; however, these are usually obtained from poorly defined ferric gels, which are obtained by hydrolysis of an aqueous solution of a ferric salt by a base. We have designed a novel synthetic route to ferric hydroxide, by reaction of a peroxo-compound with an aqueous solution of a ferrous salt, which involves simultaneous oxidation of Fe(ll) to Fe(lll), and hydrolysis, in the same reaction process. The two kinds of ferric hydroxide are highly different, however, both give hematite by dehydration/recrystallization, however, the way this occurs for each is different.