Silico-ferrite Of Calcium And Aluminum Research Articles

Understanding Chromium Slag Recycling with Sintering-Ironmaking Processes: Influence of Cr2O3 on the Sinter Microstructure and Mechanical Properties of the Silico-Ferrite of Calcium and Aluminum (SFCA).

Chromium slag is a solid waste of chromium salt production, which contains highly toxic Cr(VI) and significant amounts of valuable metals, such as Fe and Cr. Recycling chromium slag as a raw sintering material in sintering-ironmaking processes can simultaneously reduce toxic Cr(VI) and recover valuable metals. A micro-sintering experiment, compressive strength test, microhardness test, and first-principles calculation are performed to investigate the influence of Cr2O3 on the sintering microstructure and mechanical properties of the silico-ferrite of calcium and aluminum (SFCA) in order to understand the basis of the sintering process with chromium slag addition. The results show that the microstructure of SFCA changes from blocky to interwoven, with further increasing Cr2O3 content from 0 wt% to 3 wt%, and transforms to blocky with Cr2O3 content increasing to 5 wt%. Cr2O3 reacts with Fe2O3 to form (Fe1-xCrx)2O3 (0 ≤ x ≤ 1), which participates in forming SFCA. With the increase in Cr doping concentrations, the hardness of SFCA first decreases and then increases, and the toughness increases. When Cr2O3 content increases from 0 wt% to 3 wt%, the SFCA microhardness decreases and the compressive strength of the sintered sample increases. Further increasing Cr2O3 contents to 5 wt%, the SFCA microhardness increases, and the compressive strength of sintered sample decreases.

Competitive Formation Behavior of Calcium Silicate and Calcium Ferrite in Sintering of Iron Ore Fines

Calcium silicate is the undesirable bonding phase in sinter with relatively high melting point and poor reducibility, while the formation mechanism in sinter is ambiguous. Herein, the phase transformation, phase quantification, and morphology evolution of calcium silicate and calcium ferrite in CaO‐SiO2‐Fe2O3‐Al2O3 systems under different n(Fe2O3)/n(CaO) and Al2O3 content are investigated. It is found that with the increase of n(Fe2O3)/n(CaO), the calcium ferrite phases transform from Ca2Fe2O5 (C2F) to complex calcium ferrite, and calcium silicate phases including β‐Ca2SiO4 (β‐C2S) and γ‐Ca2SiO4 (γ‐C2S) are promoted. Moreover, small amount (2%) of Al2O3 can effectively promote the content of silico‐ferrite of calcium and aluminum (SFCA) increasing from 20.95% to 46.69%, whereas inhibiting the β‐C2S from 51.79% to 42.34%. When the content of Al2O3 is over 4%, the Ca2Al(AlSiO7) phase is formed, where both the SFCA and calcium silicate are inhibited. On this base, the competitive mechanism for the formation of calcium silicate and calcium ferrite is revealed, where the Ca2+ and Si4+ are preferred to react with Fe3+ and Al3+ to form liquid phase SFCA, while the amount for β‐C2S or γ‐C2S can be decreased due to the deprivation of Ca2+ and Si4+.

Mineralization Characteristics of Iron Ore Sinter and the Effects of Cooling Rate on Mineral Phase Structure

The mineral phase composition and structure of sintered ore are closely related to its quality. Analyzing the characteristics of the phase structure of sintered ores and studying the influence of sintering conditions are important to optimize their quality. In this study, the mineralization characteristics of ore during the sintering process were studied through interrupted quenching experiments. The results clarified the evolution of the structure of the sintered ore phases during the heating and cooling and its mechanism. In this study, the effects of the cooling rate on the mineral composition and structure of sintered ore were also studied. The results showed that the structure of the mineral phase changed during the iron ore sintering process as follows: granular → molten → dissolution texture. During the cooling process, as the temperature decreased, the magnetite and liquid phase contents gradually decreased, and the silico-ferrite of calcium and aluminum (SFCA) and hematite contents increased; however, the porosity did not change to a great extent. The formation of SFCA during the cooling stage consumed hematite and magnetite, and SFCA preferentially formed and grew on magnetite. As the cooling rate of the sinter was increased, the magnetite and silicate contents increased, and the hematite and SFCA contents decreased. Meanwhile, the structure of SFCA changed from block-like to columnar and acicular, and the aspect ratio increased.

Effects of Basicity and Al<sub>2</sub>O<sub>3</sub> Content on the Crystal Structure of Silico-ferrite of Calcium and Aluminum

Silico-ferrite of calcium and aluminum (SFCA) is the primary bonding phase of iron ore sinter, the world’s most popular artificial feed material for ironmaking. However, fundamental questions about its crystal structure and the atomic occupancy at each site remain unanswered. To date, the quantitative phase analysis (QPA) of SFCA has mostly been conducted using two-dimensional information and only provided information regarding phase fractions. In contrast, Rietveld analysis uses bulk data and provides lattice information in addition to phase fraction information. This study investigates the effects of basicity and Al2O3 concentration on the crystal structure and atomic site occupancy of SFCA through Rietveld analysis of the X-ray diffraction patterns. Raman spectroscopy and micro-Vickers hardness tests are used to verify the analytical results. Changes in the chemical composition affect the atomic occupancies at sites Si1 (Si–Al), Ca2 (Ca–Fe), Ca3 (Ca–Fe), Fe4 (Fe–Al), Fe5 (Fe–Al), and Fe7 (Fe–Al). With increasing basicity or Al2O3 content, the microhardness increases linearly, which can be attributed to the modification of atomic site occupancies. The crystalline structure obtained in this study is essential for developing a thermodynamic model of SFCA that can be used to predict its phase stability. This information can then be used to design a novel high-performance iron ore sinter.

Utilization of micro-fines in sinter making and its implications on bed permeability and sinter quality

ABSTRACT Exploiting low-grade resources and raw material fines is a challenge for metallurgists developing new technologies. Iron-bearing and carbonaceous by-products are generated by ironmaking and steelmaking units and fed into the sinter plant. These by-products, which have varying proportions of ultra-fines, balling properties, moisture retention capacities, and so on, have a significant impact on sinter quality when used in sinter green mixtures. This study investigates the use of micro-fines and how it affects sinter quality while keeping operational factors such as moisture addition, balling index, and bed permeability in mind. In addition, the ideal moisture addition is investigated using higher micro-fines bearing dusts/sludges of various iron-bearing materials. The presence of columnar SFCA (Silico-ferrite of Calcium and Aluminium) is revealed by microscopic examination of the sinter produced with higher micro fines and good permeability, which improves the Reduction Degradation Index. It was also demonstrated that using more micro-fines in the blend and maintaining consistent moisture addition reduced the amount of return sinter produced.

Porosity, Mineralogy, Strength, and Reducibility of Sinter Analogues from the Fe2O3 (Fe3O4)-CaO-SiO2 (FCS) Ternary System

The presence of Ca-ferrite and silico-ferrite-of-calcium-and-aluminium (SFCA) bonding phases is thought to be crucial to maintain sinter quality due to their high reducibility and strength levels. However, new evidence suggests that porosity might be an equally important factor controlling reducibility, in addition to mineralogy. This work aims to fundamentally understand the development of porosity in simple sinter analogues from the Fe2O3-(Fe3O4)-CaO-SiO2 (FCS) ternary system (with no SFCA), and to connect results back to overall sinter mineralogy, strength, and reducibility properties. Laboratory-scale experiments were conducted to simulate the sintering process by firing tablets of magnetite, hematite, lime and silica mixtures under tightly controlled temperature, holding time and atmosphere conditions. Mineralogy of the fired samples was observed using microscopy techniques, porosity was measured by Mercury Intrusion Porosimetry (MIP), strength was determined using laboratory-scale tumble index equipment and reducibility was measured by the weight loss obtained after reaction of the tablets in a reducing atmosphere of CO/N2. The results confirmed that reducibility is strongly influenced by porosity, and highly reducible sinters can be produced without forming SFCA-like phases. Magnetite-containing samples had similar reducibility to hematite-containing samples, suggesting that magnetite-based sinters could potentially be used in the blast furnace.

Study of SFCA and SFCA-I Phase in the Ternary Phase System of Iron Ore Pellets

To get an effective makeover of available low-grade iron ore, the selection of additive with fixed composition is the key variable. Pellets thermal stability and effective reduction depend upon mineralogy, physio chemical characteristics which are governed by the basicity of pellets up to a certain extent. Basicity varies with gangue content present in the iron ore. Therefore to ascertain physio chemical characteristics, a deeper insight analysis is done, microstructure phase study within silico-ferrite of calcium and aluminium (SFCA) system was done. Phase relation of the intermediate phase is calcium ferrite formation which reacts further to form SFCA and SFCA-I. The Physio-chemical and physical properties especially strength is supported by SFCA-I. The grade of ore is also being the base of SFCA or SFCA-I. The ternary phase study gives an overview of the phase relation and thermal and compositional conditions for the formation of SFC phases. In the present study, SFCA/SFCA-I formation during firing at 12500C with pellets of varying basicity, 0.2-1.2 has been observed. The influence of the formation of SFCA/SFCA-I over physical properties is also considered and 0.6 basicity exhibits good pellet quality

Iron Ore Sinter Macro- and Micro-Structures, and Their Relationships to Breakage Characteristics

A systematic analysis of industrial iron ore sinter product and associated sinter returns was undertaken. The samples were characterised through identification of the major macro- and micro-structural types present in these materials. Examination of the breakage surfaces of the particles indicates a strong correlation between mechanical sinter strength and sinter microstructure. Preferential breakage was observed to occur in sinter materials having high porosity and those microstructures consisting of isolated hematite grains in a glass matrix. The bulk of the sinter product consisted of material with a microstructure of magnetite and silico-ferrite of calcium and aluminium (SFCA). The phases formed and the reaction sequences responsible for the formation of the principal microstructure types are explained by the non-equilibrium solidification of melts in the “Fe2O3”-Al2O3-CaO-SiO2 system.

Fundamentals of Silico-Ferrite of Calcium and Aluminium (SFCA) and SFCA-I Iron Ore Sinter Bonding Phase Formation: Effects of MgO Source on Phase Formation during Heating

Fundamentals of Silico-Ferrite of Calcium and Aluminium (SFCA) and SFCA-I Iron Ore Sinter Bonding Phase Formation: Effects of MgO Source on Phase Formation during Heating

A Short Review of the Effect of Iron Ore Selection on Mineral Phases of Iron Ore Sinter

The sintering process is a thermal agglomeration process, and it is accompanied by chemical reactions. In this process, a mixture of iron ore fines, flux, and coal particles is heated to about 1300 °C–1480 °C in a sinter bed. The strength and reducibility properties of iron ore sinter are obtained by liquid phase sintering. The silico-ferrite of calcium and aluminum (SFCA) is the main bonding phase found in modern iron ore sinters. Since the physicochemical and crystallographic properties of the SFCA are affected by the chemical composition and mineral phases of iron ores, a crystallographic understanding of iron ores and sintered ore is important to enhance the quality of iron ore sinter. Scrap and by-products from steel mills are expected to be used in the iron ore sintering process as recyclable resources, and in such a case, the crystallographic properties of iron ore sinter will be affected using these materials. The objective of this paper is to present a short review on research related to mineral phases and structural properties of iron ore and sintered ore.

A Study on Analysis of Sinter Microstructure and Phase Morphology

Sinter is a blast furnace input material obtained by heating to 900-1200 oC without full melting and adhering to each other with superficial melting. It is considered as a multi-phase material with its sinter heterogeneous microstructure. In general, the main mineral phases are hematite, magnetite, silicoferrite of calcium and aluminium (SFCA) and silicates. By determining the SFCA structure in the sinter material, the sintering process will be made more stable and important parameters affecting the quality in the sintering process will be examined. Sinter material obtained from iron ore, iron and steel industry by products and auxiliary materials. The scope of this project is the determination of the amount of SFCA formed by bonding SiO2, CaO, Fe2O3, Al2O3 and MgO compounds and monitoring this value as a parameter by the enterprise. Sinter samples having different characteristic features will be made ready for X-ray diffraction (XRD) and optical microscopy inspections by polishing, etching and freezing in epoxy for mineralogical researches. Before raw data obtained from the analysis is evaluated at Autoquan, they will be converted into Autoquan format and then, they will be read in XRD device and mineralogical composition of the sinter will be revealed by XRD analyses. Detailed view of mineralogical compounds will be investigated so as to complete scanning electron microscope (SEM) analyses and XRD analyses; elemental composition of the compounds and valence conditions of the elements will be researched by energy dispersive spectroscopy (EDS) method. Hematite, magnetite, calcium ferrite phase structures in different formations will be studied subject to melting and temperature during optical microscopy studies conducted on sinter samples. Furthermore, it will be researched variations of SFCA, SFCA-I and SFCA-II phase structures within the sinter matrix subject to different raw material input and process parameters. It will be ensured to interpret the results through rietveld method.

Automated Optical Image Analysis of Iron Ore Sinter

Sinter quality is a key element for stable blast furnace operation. Sinter strength and reducibility depend considerably on the mineral composition and associated textural features. During sinter optical image analysis (OIA), it is important to distinguish different morphologies of the same mineral such as primary/secondary hematite, and types of silico-ferrite of calcium and aluminum (SFCA). Standard red, green and blue (RGB) thresholding cannot effectively segment such morphologies one from another. The Commonwealth Scientific Industrial Research Organization’s (CSIRO) OIA software Mineral4/Recognition4 incorporates a unique textural identification module allowing various textures/morphologies of the same mineral to be discriminated. Together with other capabilities of the software, this feature was used for the examination of iron ore sinters where the ability to segment different types of hematite (primary versus secondary), different morphological sub-types of SFCA (platy and prismatic), and other common sinter phases such as magnetite, larnite, glass and remnant aluminosilicates is crucial for quantifying sinter petrology. Three different sinter samples were examined. Visual comparison showed very high correlation between manual and automated phase identification. The OIA results also gave high correlations with manual point counting, X-ray Diffraction (XRD) and X-ray Fluorescence (XRF) analysis results. Sinter textural classification performed by Recognition4 showed a high potential for deep understanding of sinter properties and the changes of such properties under different sintering conditions.

Study on Sintering Characteristics of Ultra-Poor Vanadium-Titanium Magnetite

Artificial rich ore for blast furnace use can be produced by sintering ultra-poor vanadium-titanium magnetite (PVTM) with a high-grade iron concentrate. Here, acid (R = 0.33, 0.50), self-fluxing (R = 1.10), and high-basicity (R = 2.60) PVTM sinters were produced in a sinter pot. Their performances were determined using the comprehensive index. The microstructures of the PVTM sinter were observed by metallographic microscope and scanning electron microscopy equipped with an energy dispersion spectrum (SEM-EDS). The results suggest that the acid PVTM sinter had a low flame front speed, low productivity, an uneven size distribution, and poor softening properties. It did have a high tumble index (TI) and low-temperature reduction disintegration index (RDI). The self-fluxing PVTM sinter had the worst performance (TI, RDI, reducibility index (RI)), while the high-basicity PVTM sinter had the highest flame front speed, highest productivity, a reasonable size distribution, excellent softening properties, and satisfactory TI and RDI values. The main consolidation form of the acid sinter was crystal stock, the main bonding phase of the self-fluxing sinter was silicate, and the main bonding phase of the high-basicity sinter was silico-ferrite of calcium and aluminum (SFCA). The comprehensive index values (from high to low) were the high-basicity (R = 2.60), acid (R = 0.50), natural acid (R = 0.33), and self-fluxing (R = 1.10) PVTM sinters. When the production capacity of the acid pellet was in shortage, the acid PVTM sinter (R = 0.50) could be produced by the surplus from the sinter plant. This replaced a part of the acid pellet and the burden structural model of the blast furnace smelting vanadium so the titanium burden could adopt a ‘high-basicity PVTM sinter + acid V-Ti pellet + acid (R = 0.50) PVTM sinter’.

Thermodynamic and Mineralogical Aspects of Injecting LPG, Coke Oven Gas, and Oxygen into Goethitic Iron Ore Sintering Process

The effect of substituting the fossil fuel partly with gaseous fuels on CO2 emission in sinter plants was assessed. Fuel gases such as coke oven gas (COG) and liquefied petroleum gas (LPG) were injected into the sinter pot, to see the effect on sintering speed and quality parameters. Densification was predominant in the case of COG and LPG, leading to an increase in both cold and hot strength. Acceleration of the sintering process was noticed when oxygen was injected. The various phases formed as a result of injecting COG, LPG, and oxygen were identified with the help of X-ray diffractometer (XRD). Dicalcium silicate, a detrimental phase, was found in the range of 16–25% when COG and LPG were injected and was absent when oxygen was injected. Magnetite (Fe3O4) and silico ferrite of calcium and aluminum (SFCA) formation got enhanced with oxygen injection. Injection of oxygen along with COG and LPG reduced dicalcium silicate and resulted in acceleration of the sintering process as well as superior quality parameters. The presence of manganese in the iron ore up to 2% resulted in MnFe2O4, a spinel phase that enriched the magnetite. No adverse effect of goethite was noticed due to gas injection. A reduction of 0.65 million tons in CO2 emissions per annum was envisaged by substituting 10 kg solid fuel with gaseous fuel per ton of sinter. After successful pot tests and encouraging results therein, a COG injection system was designed and installed in an industrial-scale sinter plant.

Effect of Temperature, Time, and Cooling Rate on the Mineralogy, Morphology, and Reducibility of Iron Ore Sinter Analogues

Analogue sinter tablets were produced at temperatures between 1250°C and 1320°C, with a range of hold times and cooling rates. Platy silico-ferrite of calcium and aluminum (SFCA) morphology was identified in samples produced at 1250°C using reflected light microscopy; however, quantitative x-ray diffraction (XRD) identified the presence of the SFCA phase, with no SFCA-I detected. This proves that the platy SFCA morphology common in analysis by reflected light microscopy cannot be attributed to the SFCA-I mineral without further analysis. Micro-XRD and electron probe micro-analysis (EPMA) were carried out on an area of platy SFCA confirming this result. The sinter analogue tablets were reduced in a 30% CO, 70% N2 gas mixture at 900°C in a tube furnace thermo-gravimetric analyzer. The degree of reduction of the tablets in this study was found to be controlled by the porosity of the samples, rather than by the morphology or mineralogy of the bonding phase.

Fundamentals of Silico-Ferrite of Calcium and Aluminum (SFCA) and SFCA-I Iron Ore Sinter Bonding Phase Formation: Effects of MgO on Phase Formation During Heating

The effect of MgO on the stability, concentrations and formation mechanisms of silico-ferrite of calcium and aluminum (SFCA and SFCA-I) iron ore sinter bonding phases during heating in synthetic mixtures was investigated using in situ x-ray diffraction. The novelty of this study is in the intricate detail in which the formation mechanisms of the SFCA-I and SFCA phases are characterized, and the observation of the effects of MgO addition on intermediate phases. For example, the significant mechanistic effect of increasing MgO content is the lack of additional SFCA formed after SFCA-I decomposition, with additional magnesioferrite spinel being formed instead. In MgO-free mixtures, the decomposition of SFCA-I typically results in a significant increase in SFCA concentration. Through the results of phase equilibria experiments, this study also provides evidence that the SFCA-I structure accommodates more Mg2+ than the SFCA structure, which is consistent with evidence that the SFCA-I structure contains a higher amount of Fe2+ than SFCA.

Effects of Basicity and Al2O3 Content on the Chemistry of Phases in Iron Ore Sinter Containing ZnO

The effects of basicity and Al2O3 content on the chemistry of phases in iron ore sinter containing ZnO were investigated by Rietveld analysis of the X-ray diffraction (XRD) patterns. Bulk composition analysis was carried out using inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and wet-chemical analysis. The composition of each phase was investigated using a scanning electron microscope-energy dispersive X-ray analyzer (SEM-EDX). It was found that ZnO exists in the franklinite and the silicoferrite of calcium and aluminum (SFCA) phases. With increasing ZnO content, the phase fraction of the franklinite increased, while the fraction of SFCA slightly increased. When ZnO content was fixed at 1 wt pct and basicity increased, the fraction of franklinite decreased and that of SFCA increased. Here, the solubility of ZnO in the SFCA increased. As the Al2O3 content increased, the fraction of franklinite decreased and that of SFCA increased, while ZnO content in the SFCA did not change significantly.

A STUDY ON THE EXAMINATION OF THE SINTER METALOGRAPHIC STRUCTURE

Sintering process is carried out domestic and imported iron ore powders, fluxes (limestone, dolomite etc.), coke dust, metallurgical recycling powders and slag forming agents. The purpose of the sintering process is to produce a charging material with suitable thermal, mechanical, physical and chemical properties that can be fed into the blast furnace. Nowadays, in order to obtain process and operating parameters that will work with the best sinter quality, extensive researches have been made by iron and steel industry. The sinter quality parameters followed by the sinter blend loaded on the sinter strand and then granulated were examined. In the sintering process, the temperature rises to 1450 oC, partially melting between the sinter grains and a series of reactions take place in the sinter matrix to be charged into the blast furnace to produce liquid crude iron. Many different approaches have been used to estimate sinter quality, to explain the effects of iron ore properties and process variables on sintering mechanisms, and to characterize sinter mineralogy of iron ore. We can obtain chemical analysis of the phases by scanning electron microscopy (SEM) technique, but full consistency with images is not always possible and especially SFCA (silico-ferrite of calcium and aluminium) and SFCA-I phases are difficult to distinguish from each other and future studies are required in this field. The mineralogy and microstructure of the sinter plays an important role in determining the physical and metallurgical properties of the iron ore sinter. Mineralogical characterization of sinter phases; it is a complementary tool to conventional physical and metallurgical tests applied to iron ore sinter to evaluate and estimate sinter quality. Measurement techniques used in this study; optical image analysis and X-ray diffraction (XRD), scanning electron microscopy (SEM), energy distribution spectroscopy (EDS), the results from raw data converted to autoquan format will be explained on the new studies on the interpretation of the Rietveld system. Depending on the measurement objectives of each technique, the quantification of the crystal phases, the relationship between the measurement results, the chemical composition of the phases and the relations between the minerals, as well as their advantages and disadvantages will be explained.

Effect of Basicity on Sintering Behavior and Metallurgical Properties of High-Chromium Vanadium-Titanium Magnetite

Basicity has an important effect on the behavior of high-chromium vanadium-titanium magnetite (HCVTM) sinter. The effect of basicity on sintering, reduction, and softening-melting properties was investigated in an experiment-scale sinter pot. The results showed that with the basicity increasing from 1.7 to 2.5, the vertical sinter speed, the productivity, the particle size, the reduction disintegration index (RDI), and the reducibility index (RI) increased. The yield increased first and then decreased, while the tumble index (TI) had the opposite trend. The perovskite content increased first and then stabilized, and the silico-ferrite of calcium and aluminum (SFCA) increased from the basicity of 2.3. The HCVTM sinter had a better tendency of the softening behavior with the basicity increase. In addition, the melt droplet comprehensive index S increased, which indicated that the increase in basicity negatively affected the droplet performance. As the basicity increased, the comprehensive index value increased. Considering the adverse effect of basicity on softening-melting properties, the best recommended value is 2.3.

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.