Silico-ferrite Of Calcium Research Articles

Reaction Characteristics and Kinetics for the Interaction between Biomass and Silico-Ferrite of Calcium and Aluminum (SFCA)-Type Oxygen Carrier in Chemical Looping Gasification

Reaction Characteristics and Kinetics for the Interaction between Biomass and Silico-Ferrite of Calcium and Aluminum (SFCA)-Type Oxygen Carrier in Chemical Looping Gasification

Detoxication and recycling of chromium slag and C-bearing dust via composite agglomeration process (CAP)-blast furnace method

The utilization of virulent chromium slag has always been a worldwide problem, and lots of C-bearing dust produced in steel industry has not been utilized efficiently. Sintering is a potential method to treat these two kinds of solid wastes, but it is limited by small treatment capacity, incomplete detoxification of Cr(Ⅵ) when they were directly added into sintering process. In this study, an innovative technology of co-processing chromium slag and C-bearing dust via composite agglomeration process (CAP)-blast furnace method was put forward and systematically investigated. In the CAP, the chromium slag and C-bearing dust were first made into composite pellets and added into the matrix feed for co-sintering. The results showed that, 20% chromium slag and 5% C-bearing dust could be co-disposed by the CAP without destroying the quality of the sinters. Cr(VI) was completely reduced to Cr(III) or metal Cr. 12.83% Cr existed as metal Cr, and the rest of Cr existed in spinel as (Mg, Fe)(Cr, Al)2O4 or in silico-ferrite of calcium and alumina as Cr(Ⅲ). After blast furnace smelting, 90.22% Cr in sinters entered stainless mother liquor to be recycled.

A Review of Calcium Ferrite in Sintering of Iron Ore and The Effect of Gangue Composition on Its Formation

In this paper, published studies on the bonding phase of calcium ferrite are reviewed. As the main bonding phase of high-basicity sinter, calcium ferrite has the advantages of high strength, good reducibility and easy formation of liquid phase. In particular, we emphasize the formation process of calcium ferrite phases, especially Silico-Ferrite of Calcium and Aluminum(‘SFCA’), and the influence of common gangue components (Al2O3, SiO2, MgO) on its formation. Based on the critical analysis of the current data, some deficiencies in this field are put forward and the research directions we think will be key in this field in the future are attached, so as to improve the theories related to calcium ferrite in iron ore sintering. The relevant results provide theoretical basis for understanding the formation process of calcium ferrite and producing high quality sinter.

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.

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.

<i>In-Situ</i> X-ray Diffraction Analysis of Phase Formation during Heating of Silico-Ferrite of Calcium (SFC) Compositions

The phase evolution during heating of two Al2O3-free mixtures designed to form the SFC iron ore sinter bonding phase was investigated using in-situ X-ray diffraction over the temperature range 293–1623 K. Results showed that during heating at an oxygen partial pressure of 5 × 10−3 atm, SFC formation was preceded by the formation of γ-Ca4Fe14O25 and γ-CFF (nominal composition Ca3.0Fe14.82O25) intermediate phases. On further heating the SFC melted to form Fe3O4 in a Fe2O3–FeO–CaO–SiO2 melt. During heating of one of the mixtures in air, it was not possible to distinguish between SFCA-I and α-CFF (nominal composition Ca3.43Fe14.39O25) as intermediate phases in the formation of SFC. The improved signal-to-noise ratio and angular peak resolution afforded by synchrotron-based XRD experimentation would be required to possibly distinguish between these two phases. Regardless of whether SFCA-I or α-CFF formed as intermediate phases during heating in air, this work shows that the oxygen partial pressure has a significant effect on phase formation mechanisms in the Al2O3-free SFC system.

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.

Development and application of a novel fluxing compound for improving sintering performance of high alumina iron ore

ABSTRACT Blast furnaces (BF) ferrous burden consist of sinter (>50%) with rest being pellets and lump ore. Good sinter quality is necessary for efficient BF operation which depends on iron ore quality and its gangue. In gangue, alumina has a strong influence that adversely affects product quality and productivity. To address those effects this study presents a two-stage method. It involves the development of a novel low temperature melting synthetic flux i.e. Iron Rich Calcium Ferrite (IRCF) at Stage-1 and its addition in high alumina sinter feed at stage-II. Microstructural and dilatometry studies show that IRCF encourages the formation of silico-ferrite of calcium and aluminum (SFCA-1). The IRCF addition (6% max) in the high alumina (3.1%) sinter feed improves the Tumble index by 4.7 points, lowers the Abrasion index by 2.7 points, and decreases the return fines by 4.4%. Moreover, the Reduction degradation index (RDI) was also improved by 7.9 points.

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.

A Study on the Effect of Alumina on the Morphology and Reduction Behavior of Sinter by In Situ Observation

The effects of Al2O3 content on the morphology and reducibility of sinter were respectively investigated using confocal laser microscopy and thermogravimetric analysis at 1273 K under CO gas. To understand the effects of the sintering process, separate samples were prepared via the equilibrium and metastable reaction routes. In the equilibrium samples, the addition of Al2O3 led to the formation of the silico-ferrite of calcium and alumino phase and a decrease in the reduction rate due to the lowered reactivity of iron oxide. In contrast, in the metastable samples, the reduction rate increased after the addition of 2.5 mass% Al2O3. The addition of Al2O3 decreased the fraction of the liquid phase and increased the fraction of pores in the sample. As a result, the reduction rate is proportional to the Al2O3 content owing to the changes in the sinter morphology. In determining the reduction rate of the sinter, the influence of the microstructure on the diffusion of the reducing gas is more significant than that of the interfacial chemical reaction due to the formation of the SFCA phase. The microstructure changes of the sinter with the addition of Al2O3 and the corresponding reduction behaviors are further discussed.

Dominant Factor Affecting Reducibility of Calcio-wüstite Originating from Silico-ferrite of Calcium and Aluminum

Dominant Factor Affecting Reducibility of Calcio-wüstite Originating from Silico-ferrite of Calcium and Aluminum

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.

Efficient Preparation of Blast Furnace Burdens from Titanomagnetite Concentrate by Composite Agglomeration Process

Titanomagnetite concentrate is difficult to agglomerate by the traditional sintering process (TSP). In this study, the agglomeration properties of titanomagnetite concentrate were studied using the composite agglomeration process (CAP). It was shown that, by adding 40 wt.% pelletized feed, an excellent sinter with yield of 74.33%, a tumbler index of 58.93%, and productivity of 1.65 t (m2 h)−1 were achieved, which were increased by 11.72%, 12.03%, and 37.16% compared with TSP, respectively. Meanwhile, for CAP, the solid fuel consumption was only 43.87 kgcoke/tproduct and the reduction disintegration index of RDI+3.15 was 73.53%. They were decreased by 6.34 kgcoke/tproduct and increased by 24.31%, respectively. The better product quality was mainly attributed to a larger proportion of calcium ferrite and silicoferrite of calcium and aluminum group minerals formed in CAP, which restrained the negative effect of perovskite on agglomeration in association with the matrix feed with ultra-high basicity. The results showed that CAP is an efficient method for agglomeration of titanomagnetite concentrate.

Experimental study and thermodynamic optimization of the ZnO–FeO–Fe2O3–CaO–SiO2 system

Liquidus phase equilibrium experimental data from the present study for the ZnO-“Fe2O3”-CaO-SiO2 system in air, combined with phase equilibria and thermodynamic data from the literature on the ZnO-“Fe2O3”-CaO system in air and ZnO-“FeO”-CaO-SiO2 system in equilibrium with metallic Fe, have been used to obtain a self-consistent set of parameters of the thermodynamic models for all phases in the ZnO–FeO–Fe2O3–CaO–SiO2 system. The modified quasichemical model is used for the liquid slag phase; spinel (Fe,Zn,Ca)tetr (Fe,Zn,Ca,Va)oct2O4, melilite Ca2(Fe2+,Fe3+,Zn)(Fe3+,Si)2O7 and olivine (Fe,Zn,Ca)I(Fe,Zn,Ca)IISiO4 are described with compound energy formalism; lime and wustite (monoxide) (Ca,Fe,Zn)O, zincite (Zn,Fe,Ca)O1+x, calcium-zinc ferrites Ca2Fe2O5-“CaZnO2” and CaFe4O7-“ZnFe4O7”, α- and α′-dicalcium silicate (Ca,Fe,Zn)2SiO4 and tricalcium silicate (Ca,Fe,Zn)3SiO5 and silicoferrite of calcium (SFC) Ca9Fe46SiO80–Ca12Fe40Si4O80 are described within Bragg-Williams formalism; for other phases, previous assessments have been adopted. The phase diagrams are back calculated with the optimized model parameters. Present study is a part of research program on the characterization of the multicomponent PbO–ZnO–FeO–Fe2O3-“Cu2O”-CaO-SiO2 system.

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.

Effective Utilization of Limonitic Nickel Laterite via Pressurized Densification Process and Its Relevant Mechanism

Limonitic laterite contains low iron and nickel grades and much high smelting minerals and loss on ignition (LOI), identified as refractory iron ore for sintering. Thus, sinter pot tests of limonitic laterite via pressurized densification sintering and its intensification mechanism were conducted, and the industrial application prospect was explored. The results indicate that the sintering performance of the limonitic laterite of the new process is significantly improved with the tumble index and productivity increased by 19.2% and 18.6%, respectively, and solid fuel rate lowered by 10.3%. The external pressure field promotes the synchronization of heat front velocity and combustion front velocity for better sintering heat and mass transfer conditions, which also greatly improves the mineral compositions and microstructure of the product sinter. The microstructure is converted from large thin-wall pores into small thin-wall or large thick-wall pores with the sinter porosity decreased by 42.4%. Much close interlocking texture between hercynite and silico-ferrite of calcium and alumina (SFCA) is formed with hercynite grains aggregation and growth, and SFCA amount substantially increased. The better sintering performance will bring about a remarkable economic benefit of 282.78 million RMB/a if the industrial application is implemented. The pressurized densification sintering process is considered as one of the effective technologies for improving limonitic laterite sintering.

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.