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Mechanical properties of natural and synthetic mineral phases in sinters having varying reduction degradation indices
Abstract
Efforts at understanding the important factors that determine the low temperature reduction degradation of sinters have concentrated on sinter chemical composition and on observations to determine the location and severity of cracks formed in the samples after reduction. A more definitive approach would include determining the physical properties of the mineral phases and some attempts have been made in this area using indentation techniques. In this study two commercially available indenters were used to determine the mechanical properties of the major phases in eight sinters from the Port Kembla Steelworks of BHP Co. Ltd. Results indicated that the fracture toughness of some phases decreased as the degradation tendency of the sinters increased. Based on fundamental theoretical considerations, a composite toughness has been defined and a linear decreasing trend is observed between this value and the reduction degradation index. This suggests that degradation is dependent on the propagation of cracks through the sinter rather than on the formation of cracks caused by the reduction of hematite.
... These phases are formed during the sintering process at temperatures above about 1000-1100°C and contain a large variety of minerals, mainly complex calcium ferrites (ie SFCA phases) in association with iron oxides and a limited amount of silicates. Sinter bonding phases such as SFCA have been studied extensively because of their important role in determining key sinter quality parameters such as reducibility (Kitamura, 1985;Bristow and Waters, 1991) and reduction degradation (Shigaki, Sawada and Gennai, 1986;Loo, Wan and Howes, 1988). More recently, Pownceby et al (2015) have shown that the sinter matrix, which includes the solid SFCA phases and pores, directly influences other sinter quality parameters such as strength before and after reduction. ...
... As indicated above, sinter bonding phases such as SFCA have been studied extensively because of their important role in determining key sinter quality parameters such as reducibility (Kitamura, 1985;Bristow and Waters, 1991) and reduction degradation (Shigaki, Sawada and Gennai, 1986;Loo, Wan and Howes, 1988). Pownceby et al (2015) have shown that the sinter matrix, which includes solid SFCA phases and pores, directly influences sinter quality parameters such as strength before and after reduction. ...
Characterisation of SFCA in IRON ORE SINTER.
... An uncommonly used parameter 'Fracture toughness' of individual phases was also determined and was correlated with the quality parameters of sinter. Previously it has been tried by many authors [8][9][10][11] to correlate between the strength of phases and the sinter quality. However, all the inputs for the calculation were not measured. ...
... Thus, cracks are observed to run indiscriminately across all the sinter phases. 9 Hence it is more relevant to define average fracture toughness values of sinter. A composite toughness value based on the fracture toughness of the individual phases and the volumetric composition of the phases present was defined. ...
In this study, pot sinter tests were carried out to study the sintering properties of iron ores of different alumina (2–4–6%) level. It was observed that the 6% alumina level ores have a higher RDI values and decreased tumbler index (TI) compared to its other two counterparts. It was observed that an increase in composite fracture toughness (CFT) of sinter improves the Tumbler as well as RDI of the sinter. Beyond 4 CFT there is remarkable improvement in TI, RDI and RI values. The mechanical strength parameters of sinter phases were further correlated and analysed with respect to the chemistry of sinter and mineralogy of sinter phases. There is strong evidence which suggests that the Al2O3 deteriorates the strength of the phases by making them hard and thus generating cracks in them. Unlike alumina, CaO and SiO2 tend to stabilise and improve the strength of the phase.
... Varios investigadores realizan estudios orientados a determinar los factores que influyen en la degradación a baja temperatura del sinter e incluyen estudios acerca de la correlación de propiedades físicas, generación de grietas durante al proceso de reducción y su relación con las fases mineralógicas presentes en el sinter. [1] En este trabajo se presenta un estudio comparativo entre dos muestras de sinter que contempla la determinación de la composición química, la identificación de las fases cristalinas mediante difracción de rayos X, la degradación física en frío y posterior a su reducción a 550 ºC, con el objetivo de correlacionar los resultados obtenidos en los diferentes ensayos con la microestructura observada en el análisis microscópico de las mismas. ...
... However, for successful briquette production, certain properties are essential, including reducible raw materials, high cold strength, consistent chemical composition, homogeneous particle size, Previous research has demonstrated the direct utilization of BFS as an iron source in blast furnaces through the process of briquetting with a suitable binder [22]. However, for successful briquette production, certain properties are essential, including reducible raw materials, high cold strength, consistent chemical composition, homogeneous particle size, low reduction disintegration index, and adequate cold strength [30][31][32]. In an effort to meet these criteria, researchers conducted a series of steps. ...
Steelmaking and ferrous metal processing companies are suppliers of great importance to a wide array of industries, thus being quintessential for the social and financial growth of regions and countries. Most used processes (i.e., blast furnace, basic oxygen furnace, and electric arc furnace-based) are, however, highly pollutant, generating hazardous wastes that were usually landfilled. Generated wastes are important sources of secondary raw materials such as zinc and iron, presenting interesting market value. Hence, aiming to develop green procedures, industries have been using diverse approaches to treat and detoxify hazardous wastes, extract and reuse added value components, or even use their existing infrastructures to convert the wastes generated by other industries into secondary raw materials for steel manufacturing. This paper reviews the main industrial processes, focusing on the waste-generating steps, and discloses the most recent and relevant industrial synergies toward a circular economy. The final contribution of this study consists of the compilation of industrial synergies and recovery technologies for the steelmaking and metal processes.
... Cracks were easily propagated in this phase, leading to a higher degradation of sinter. Previous studies by Loo et al. [16] and Peterson [17] show that in general higher degradation was obtained with a lower composite fracture toughness value. ...
The increase of H2 usage in a blast furnace (BF) affects the reduction degradation of ferrous burden materials, which has a strong influence on gas permeability inside the furnace. Previous studies on the degradation of sinter and lump show a disagreement about the effect of H2 on the degradation and it seems that the extent of degradation depends on the H2 content and type of ferrous burden materials. In this study, the reduction degradation test of sinter and Newman Blend Lump (NBLL) was performed with different gas mixtures containing CO and H2, including the gas composition of current BF and BF with maximum H2. Sinter shows a higher degradation than lump at all gas mixtures and the highest degradation was obtained with the mixture of CO and H2 as reducing gas. Lower degradation was obtained for BF with maximum H2 than the current BF, indicating the benefit of increasing H2 usage in BF operation.
... Microindentation testing is one means of determining a mineral's microhardness and fracture toughness (e.g. Loo et al. 1988;Peterson et al. 2017). If information is available about the area/ volume percentage of the mineral constituents of an individual ore particle (e.g. via optical image analysis -OIAor scanning electron microscopy), then it is possible to calculate a composite microhardness or fracture toughness for an ore particle. ...
This study utilised Vickers and Knoop microindentation testing to characterise the physical and chemical properties of a range of iron ore material types and lump ore samples. Lump ore composite microhardness (CH) and fracture toughness (CFT) correlated best with Tumble and Abrasion Indices and with Fe-total, Al2O3 and LOI contents. General trends were evident between CH/CFT and other common metallurgical indices, e.g. higher Reduction Degradation Index with lower CH. Correlations between ore group CH/CFT and the metallurgical data were generally similar, but relatively stronger, than those for the lump ores. The chemistry of mineralogical-textural sub-sets of ore groups correlated with lump ore CH/CFT. Calculating ore group CH/CFT using a textural method is therefore capable of capturing differences in ore group chemistry that relate in part to texture. A textural database of microhardness and fracture toughness can be utilised with automated optical image analysis to provide geometallurgical characterisation of iron ores.
... The mineral composition and structure formed during the crystallization of the sinter-binding glass phase are important factors affecting sinter quality [2], including its strength and reducibility. Previous studies [3][4][5][6][7] revealed that magnetite, hematite, and calcium ferrite followed by glass phase in the strength order from big to small. As the bonding phase of sinter, the compressive strength of the calcium ferrite is far greater than that of the glass phase. ...
The glass phase is one of the binding phases in high-basicity sinter, which is mainly formed during a high-temperature cooling process while cannot crystallize in time. The phase still involves the “structure” information of the binding phase’s liquid phase in the sinter. In addition, the generation of glassy phases can seriously deteriorate the metallurgical properties of sintered ore. However, the formation mechanism and crystallization process of glass phases are still unclear. In this work, the glass phase and the crystallized samples of the CaO-SiO2-Al2O3 system were characterized using X-ray diffraction, optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy and Raman spectroscopy. The effect of alkalinity (R) and Al2O3 on crystallization and the relationship between crystallization and structure are discussed. The results showed that the chemical composition significantly influences the crystallization of the CaO-SiO2-Al2O3 glass. Decreasing basicity (R = 0.8–1.2, the mass ratio of CaO and SiO2) favors the crystallization of the glass phase, while increasing the content of Al2O3 (9–12%) can inhibit the crystallization of the glass phase. In addition, the crystallization order of the 45mass%CaO-45mass%SiO2-10mass%Al2O3 sample is CaSiO3 → CaAl2O4. Raman spectroscopic analysis showed that increase of slag basicity promoted the aggregation degree (Q3/Q2), resulting in deterioration of the glass phase crystallization. and that the glass phase crystallization deteriorated as the aggregation degree increased. However, increasing the Al2O3 content has little effect on the agglomeration degree but does promote the formation of SiO4 tetrahedra (Q0), which results in the deterioration of glass-phase crystallization.
... [3,4] The quality of the iron ore sinter is largely determined by the phase proportion of silico-ferrites of calcium and alumina (SFCA), which is the main bonding phases in the iron ore sinter. SFCA phases are recognized as the most desirable adhesive phases in the iron ore sinter because they have high mechanical strength, [5,6] low reduction degradation index, and high reducibility, [7] all of which are significant factors for the BF process. The formation process and microstructure of the SFCA have been confirmed in multiple studies. ...
The solid-state reaction and diffusion behaviors of CaFe2O4 and TiO2 were investigated using a diffusion couple method at 1373 K to 1473 K under air atmosphere, and an in situ XRD method was used to analyze the solid-state reaction process. The reactions between calcium ferrite and TiO2 in the solid state are displacement reactions that produce perovskite and Fe2O3. The diffusion interface was divided into three layers based on phase analysis: layer I was composed of CaTiO3; layer II was composed of Fe2O3, CaTiO3, CaFe2O4, and Ca2Fe2O5; and layer III was composed of CaTiO3, Fe2O3, CaFe2O3, and CaFe4O7. The interface was formed in three stages. In stage I, CaTiO3 formed at the interface. In stage II, the gradual thickening of layers I and II was accompanied by the growth of the amount of CaTiO3 phase. In stage III, CF decomposed into CF2, and layer III formed. Micropores were formed in layer II due to the Kirkendall effect, and the diffusion rate of Ca2+ in CaFe2O4 was greater than that in CaTiO3. The squared thickness of layer I was found to depend linearly on time, and the expression for predicting the thickness of layer I was proposed: $$ \Delta x = ( 1. 1 7 3 1\times 10^{ - 18} T^{2} - 3.0206 \times 10^{ - 15} T + 1.9652 \times 10^{ - 12} )^{{\frac{1}{2}}} \cdot t^{{\frac{1}{2}}}
... Indentation on the surface of minerals, metals or other materials using a diamond indenter is a common technique to measure the microhardness of particular phases (e.g., Loo et al., 1988;Dukino and Swain, 1992;Dukino et al., 1995). The microhardness values obtained from such tests on a given phase are naturally variable (within a certain range) and the mean of several tests is usually given along with this range in values. ...
Manganese oxide, silicate and carbonate ores are mostly mined as feedstock for steelmaking where Mn is largely added as ferroalloy, but they are also used for battery and to a lesser extent fertiliser and pigment production. The physical, mineralogical and textural properties of manganese ore minerals are known to influence their thermal properties and thus their high temperature behaviour during sintering or alloy production.
Microhardness testing using the Vickers indenter is a potentially valuable characterisation technique to correlate the physical and optical properties of Mn ore minerals with their mineral chemistry and texture when used in conjunction with electron probe microanalysis (EPMA) and helium pycnometry. Microhardness values can also inform potential beneficiation pathways for lower grade Mn ores and/or assist in the prediction of lump: fines ratios during mine planning.
This study provides the results of microhardness testing of Mn ore minerals from several different Mn ore types with variable mineralogy and texture. The data indicates that there is a clear link between mineral microhardness and micro- to nano-scale porosity and microcrystallinity, leading to potentially large variations in microhardness for some common Mn ore minerals. For example, cryptomelane with lower reflectivity, interpreted as having higher nano- to micro-porosity and/or differences in microcrystallinity, has significantly lower microhardness (mean 267 kg/mm²) than cryptomelane with higher qualitative reflectivity (mean 629 kg/mm²).
EPMA conducted on mineral grains subjected to microhardness testing showed microhardness values did not vary systematically with changes in mineral chemistry but did vary with total element content as determined by EPMA. Low analytical totals were a de facto semi-quantitative measurement of mineral nano- to micro-porosity due to likely beam splitting/dispersion on more microporous samples identified during optical microscopy. Although there was no systematic link seen between microhardness and tetravalent Mn mineral element chemistry in this instance (e.g., K in cryptomelane), cryptomelane with lower reflectivity has lower Mn contents and higher contents of minor elements such as Fe, Al and Si.
... It was suggested [3] and later confirmed, [4][5][6] that the phases present and microstructures in sinter influence their strength and reducibility, and in turn the efficiency and productivity of the iron blast furnace. For this reason, there are ongoing efforts to identify optimal sinter microstructures and how they are produced. ...
The principal chemical components in iron ore sintering are Fe2O3, CaO, and SiO2. This sintering process consists of three key steps: heating, holding at peak temperature, and cooling. During the cooling stage, a liquid oxide solidifies to form the final sinter microstructures. To investigate the fundamental processes taking place during the cooling of sinters, a new experimental technique has been developed that allows the stages of solidification to be determined in isolation, rather than inferred from the final microstructures. Fe2O3-CaO-SiO2 oxide samples of a bulk composition having a CaO/SiO2 mass ratio of 3.46 and 73.2 wt pct Fe2O3 were cooled in air from 1623 K (1350 °C) at 2 K/s, quenched at 5 K temperature intervals from 1533 K to 1453 K (1260 °C to 1180 °C), and analyzed using Electron Probe Micro X-Ray Analysis (EPMA). During cooling, four distinct stages were observed, consisting of the phase assemblages Liquid + Hematite (I), Liquid + Hematite + C2S(II), Liquid + C2S + CF2(III), and C2S + CF2 + CF (IV). This solidification sequence differs from that predicted under equilibrium and Scheil–Gulliver Cooling. Importantly, no Silico-Ferrite of Calcium (SFC) phase was observed to form on solidification of the liquid. Based on the microstructures formed and liquid compositions, measured by EPMA, it was demonstrated that kinetic factors play a major role in determining the phases and microstructures formed under the conditions investigated.
... As shown in Figure 16, needle-like SFCA showed the highest compression strength of 1809 N, which was considerably higher than that of sheet-like SFCA, which reached 1186 N, and that of the calcium silicate, which showed the lowest compression strength of 1035 N. These results agree well with those of Loo et al. and Ying et al. [18,19]. Moreover, the fracture toughness and Vickers hardness of different kinds of minerals were also measured, and the results are shown in Figure 17. ...
SiO2 and Al2O3 are two important minerals that can affect the mechanical and metallurgical properties of sinter. This investigation systematically studied the influences of these minerals and revealed their functional mechanisms on sinter quality. Results showed that with an increasing Al2O3 content in sinter, the sintering indexes presented an improvement before the content exceeded 1.80%, while the quality decreased obviously after the content exceeded 1.80%. With an increasing SiO2 content, the sinter quality presented a decreasing tendency, especially when the content exceeded 4.80%. Consequently, the optimal content of Al2O3 was ≤1.80% and that of SiO2 was ≤4.80%. The evolution of the microstructure and minerals in sinter showed that enhancing the Al2O3 content increased the proportion of SFCA generated, which improved the sinter’s mechanical strength, while excessive Al2O3 led to the formation of sheet-like SFCA with weak mechanical strength. Increasing the content of SiO2 strained the formation of SFCA and promoted the formation of calcium silicate, the mechanical strength of which is lower than that of SFCA. The research findings will be useful in guiding practical sintering processes.
... The SFCA phase (SiO2-Fe2O3-CaO-Al2O3) is regarded as a desirable bonding phase for fluxed sinter [1,2]. Silica content influences the phase composition and bonding phase mass of SFCA because of their low melting point [3,4], high mechanical strength [5][6][7][8], and SFCA is an important part of the point of view of saving cost and energy from low temperature sinter. SiO2-Fe2O3-CaO (SFC) is believed to be the transition phase during the SFCA formation process and has been widely investigated [9][10][11]. ...
SiO2-Fe2O3-CaO (SFC) is believed to be the transition phase during the SiO2-Fe2O3-CaO-Al2O3 (SFCA) formation process. The effect of SiO2 on the mechanical property and reduction of the CaO-Fe2O3-SiO2 system was inspected in this study. Experiments were carried out under air at 1200 °C with different amounts of SiO2 mixed with Fe2O3 and CaO. The mechanical properties and reduction of samples were studied. Results indicate that the hardness of samples gradually increases with the increase of SFC content. That may be caused by SiO2 solid solution in calcium ferrite. The larger the amount and smaller size of acicular calcium ferrites in samples, the greater the fracture toughness. The solid solution of SiO2 in calcium ferrite is beneficial to decrease the initial reduction temperature. The apparent activation energy values of the samples with the different content of SiO2 from 0% to 5% are 167.23, 84.36, 87.90, 96.02, 92.44 and 107.83 kJ·mol−1, respectively. The microstructure of lump samples after reduction consists of four phases, i.e., CF (CaFe2O4), SFC, calcio-wüstite (CW) and Fe. It was not difficult to find the Fe in the samples reduced from CW. Scanning electron micrograph images have revealed that the acicular-like calcium ferrites are more easily reduced than the platy-like ones.
... Furthermore, the sinter mineralogy has a complicated nature, and its behaviors vary significantly and depend on various factors. [1][2][3][4][5][6] Numerous investigations [7][8][9][10] have aimed to determine the formation mechanisms of the sinter bonding phases of SFCA. SFCA phases influence the strength, reducibility, and reduction degradation index. ...
... The quality of high-basicity sinters is largely determined by the phase proportion of silico-ferrite of calcium and alumina (SFCA) as adhesive phases, because of their high mechanical strength, high reducibility, and slow degradation. [1][2][3][4][5][6] The usage of low-grade ores also influences the liquid phase formation, assimilation, and solidification of SFCA during the sintering process. ...
Calcium ferrite (CF) is a significant intermediate adhesive phase in high-basicity sinters. The wettability between calcium ferrite (CF) and gangue plays an important role in the assimilation process. The wettability of CF-based slags, in which a constant amount (2 mass pct.) of Al2O3, MgO, SiO2, and TiO2 was added, on solid SiO2 (cristobalite) substrates at 1523 K (1250 °C) was investigated. The interfacial microstructure and spreading mechanisms were discussed for each sample. All the tested slag samples exhibited good wettability on the SiO2 substrate. The initial apparent contact angles were in the range of 20 to 50 deg, while the final apparent contact angles were ~ 5 deg. The wetting process could be divided into three stages on the basis of the change in diameter, namely the “linear spreading” stage, “spreading rate reduction” stage, and “wetting equilibrium” stage. It was found that the CF-SiO2 wetting system exhibits dissolutive wetting and the dissolution of SiO2 into slag influences its spreading process. The spreading rate increases with a decrease in the ratio of viscosity to interfacial tension, which is a result of the addition of Al2O3, MgO, SiO2, and TiO2. After cooling, a deep corrosion pit was formed in the substrate and a diffusion layer was generated in front of the residual slag zone; further, some SiO2 and Fe2O3 solid solutions precipitated in the slag.
... The fundamental points of low temperature reduction disintegration occurred when the reduction in the regeneration of hematite ranged from 723 to 773 K. The phase transformation occurred from α-Fe2O3 to Fe3O4, when disintegration was caused by volume expansion [28][29][30]. The reduction disintegration improved and the hematite decreased when the hard-reduced magnetite formed a solid solution with the MgO. ...
Chengde chromium-bearing vanadium–titanium magnetite (CCVTM) has been used as an important mineral resource in sinter making. The MgO content of this sinter can be enhanced by adding dolomite, which improved operation of the blast furnace. The effects of MgO in the form of dolomite on metallurgical properties, microstructure and mineral compositions of CCVTM sinter were studied by a sinter pot test, X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), and mineral phase microanalysis. The results were as follows: The flame front speed and sinter coefficient decreased with an increase in MgO content from 2.66 to 3.86% by adding dolomite. With an increase in MgO content from 2.66 to 3.86%, the flame front speed, sintering utilization factor, and the value of RI decreased, while RDI and the softening–melting properties improved. In addition, the value of sinter strength (TI) reached a maximum value at MgO = 3.56%. In addition, an increase in the abundance of magnetite, magnesium ferrite, and silicate phase, as well as a decrease in hematite, was found with an increase in MgO content. We concluded that the most appropriate MgO content in the sinter is 3.56%.
... Since coke is the main fuel in the sintering process, the change of the coke ratio can vary the atmospheric nature and temperature level of the sintered material. Additionally, the coke ratio can affect the mineral composition and structure of sintered ore, which also has a great influence on the quality of the sintered ore [11][12][13][14][15][16][17][18]. Therefore, the study of the effect of the coke ratio in the sintering behavior of HCVTM is critical to improving the sinter quality and energy efficiency. ...
High-chromium vanadium and titanium magnetite (HCVTM) sinter has poor properties. The coke ratio has an important effect on the behavior of HCVTM sintering as it affects the mineral phases in the high-chromium vanadium and titanium sinter (HCVTS) via changing the sintering temperature and atmosphere. In this work, the sintering behavior of HCVTM mixed with varying coke ratios was investigated through sintering pot tests, X-ray diffraction (XRD), gas chromatographic analysis, and mineral phase analysis. The results show that, with the increase of the coke ratio from 4.0% to 6.0%, leading to the increase of the combustion ratio of the flue gas, the vertical sintering rate and sinter productivity decrease. Meanwhile, with the change of the coke ratio, the content of magnetite, silicate, and perovskite increase, while the hematite and calcium ferrite decrease. In addition, the tumble strength and reduction ability of HCVTS decrease, and its degradation strength increase. It was found that the appropriate coke ratio for the sintering process was 5.0 wt %.
... Sinter bonding phases such as SFCA have been studied extensively because of their important role in determining key sinter quality parameters such as reducibility (Kitamura 1985;Bristow and Waters 1991) and reduction degradation (Shigaki, Sawada and Gennai 1986;Loo, Wan and Howes 1988;Loo, Williams and Matthews 1992). Pownceby, Webster, Manuel and Ware 2015 have shown that the sinter matrix, which includes solid SFCA phases and pores, directly influences sinter quality parameters such as strength before and after reduction. ...
The mineralogy and microstructure of sinter play an important role in determining the physical and metallurgical properties of iron ore sinter. Characterisation of sinter phases is, therefore, a cost-effective and complementary tool to conventional physical and metallurgical testing of iron ore sinter in evaluating and predicting sinter quality. Over the years, CSIRO (Commonwealth Scientific and Industrial Research Organisation) has developed a scheme for characterising iron ore sinter which classifies primary sinter phases, such as un-reacted and partially reacted haematite, magnetite and remnant fluxes, and secondary phases including silico-ferrite of calcium and aluminium (SFCA), secondary haematite and magnetite, glass and larnite. Quantification of these phases has traditionally been carried out by manual point counting under a petrographic microscope. However, new technologies based on automated optical image analysis, quantitative X-ray diffraction and scanning electron microscopy are now available for evaluation. In this study, two sinter samples of varying chemistry were prepared and characterised using both point counting and automated optical image analysis. Quantification of sinter phases is a complementary tool for comparing the physical properties of sinter obtained from various sinter blends, and sinter phase quantification results can be used for comparing pot-grate sinter with different metallurgical properties.
... The SFC ss described by Pownceby et al. (1998) was in fact identical to the SFC phase first identified by Hamilton et al. (1989), who recognized it to be an alumina-free equivalent of SFCA (silico-ferrite of calcium and aluminium), the complex binder phase formed in lime-fluxed iron ore sinter systems (Hancart et al., 1967;Inoue & Ikeda, 1982;Ahsan et al., 1983;Dawson et al., 1983). Sinter bonding phases, as exemplified by SFCA, have been extensively studied on account of their important role in determining sinter quality parameters, such as reducibility (Bristow & Waters, 1991) and reduction degradation (Shigaki et al., 1986;Loo et al., 1988;Bristow & Waters, 1991). Hamilton et al. (1989) demonstrated that SFC had a very narrow compositional range at 1200°C (in air) extending between about 3.0 and 5.0 wt% SiO 2 , or approximately 7.0-11.5 wt% C 4 S 3 component, along the CF 3 -C 4 S 3 pseudobinary. ...
Quenching experiments have been performed to investigate the thermal stability, solid solution limits, and selected phase relationships of SFC (silico-ferrite of calcium) within the Fe2O3-CaO-SiO2 (FCS) system. Experiments were performed in air over the temperature interval 1050-1260°C using a combination of synthetic oxide mixtures and SFC compositions which had been pre-synthesized at 1200°C. SFC forms a solid solution along a trend line between the theoretical end-members CF3 and C4S3. The maximum solid solution range occurs between compositions containing approximately 7.0 through to 11.7 wt% C4S3 component. The solution range is valid between 1060°C and 1240°C. Above 1240°C the compositional range narrows until the liquidus is reached. The maximum liquidus temperature for SFC is composition dependent with the highest melting point (T = 1252°C) recorded from a sample containing 9.0 wt% C4S3. Determination of ferrous iron content in SFC shows a range between 0.24-0.37 wt% at 1200°C compared to 0.40-0.64 wt% at 1250°C. The absolute Fe2+ content is both temperature and composition dependent, with higher ferrous iron values measured at high temperature and high C4S3 contents. EPMA data, combined with the ferrous iron measurements, indicate a coupled substitution mechanism in SFC represented by the reaction 2(Fe3+) = (Ca2+, Fe2+) + Si4+. Data obtained in the present investigation combined with those available in the literature enable the construction of a series of isothermal sections showing phase relationships within the broader FCS system. These diagrams may be used as a guide to improving the understanding of fundamental sintering phase relations in the high iron corner of the FCS ternary system, as well as providing some insight into the compositional and thermal conditions required to maximize the stability of SFC phase in iron ore sinter.
... In the upper regions of the blast furnace, physical degradation in the ferriferous burden occurs between 300 • C and 700 • C because of the reduction of hematite to porous magnetite. During this process, volume expansion and stress relief occur because of the formation and propagation of cracks [1][2][3]. This expansion is associated with the crystallographic orientation The cold agglomeration process has been used in some steel plants with up to 5% of ferriferous burden, as a source of iron and carbon for the blast furnace. ...
It is important to understand the reduction disintegration mechanism in ferriferous burden that is used in blast furnaces. The behavior of this burden in the granular zone of this metallurgical reactor is important for smooth operation. The objective of this work was to prepare cold self-reducing briquettes using blast furnace dust and sludge and binders and compare the reduction disintegration index (RDI) of these agglomerates with conventional ferriferous burdens such as pellets, sinter and iron ore. In the present work, 25 different mixtures were prepared to produce briquettes in two geometries: pillow and cylindrical. The RDI value was determined for the briquettes that passed the tumbling test.
... Diffusion bonds resulting from the recrystallization of hematite (or magnetite grains) are less common as the formation of silicate bonding phases occurs before diffusion begins to operate effectively and are observed for iron rich fines (Ball et al. 1976;Inoue and Ikeda 1982;Hsieh and Whiteman 1989); although a study by Clout and Manuel (2003) suggests the formation of magnetite-magnetite diffusion bonds. Minimum strength of sinter has been ascribed to the formation of the most multi-phase composition because of the varied thermal coefficients of expansion, melting points, and crystalizability of individual phases as well as the variety of bonding phases (Loo, Wan, and Howes 1988). ...
Parallel experimentation allowing comparison of magnetite–hematite–goethite inland and hematite–goethite coastal mill blends in terms of sintering performance is reported. Magnetite–hematite–goethite blend affords slightly lower productivity, tumble index, and yield than hematite–goethite blend. However, magnetite–hematite–goethite blend required 9.2 kg · t−1 lower solid fuel rate than the hematite–goethite blend. The lower sintering temperature of the magnetite–hematite–goethite blend than that of the hematite–goethite blend contributed to higher reducibility and lower low temperature degradation under reduction. Its sinter product also contained lower proportions of columnar silico-ferrite of calcium and alumina, magnetite, and fayalite.
Calcium ferrite is the most basic bonding phase in sinter and the matrix of Silico-ferrites of calcium and aluminium (SFCA). In order to better understand the fundamentals of the reduction of CaO·Fe2O3, CaO·Fe2O3 samples were prepared by solid-state sintering and reduced by CO/CO2 mixture gas at 1000°C. Then, the equilibrium phase and morphology were tested by XRD and SEM-EDS. The experimental results indicated that (1) As CO/(CO + CO2) = 20%, CaO·Fe2O3 was reduced to CaO·FeO·Fe2O3 and 2CaO·Fe2O3. (2) As CO/(CO + CO2) = 40%, CaO·FeO·Fe2O3 was reduced to CaO·3FeO·Fe2O3 and 2CaO·Fe2O3, the equilibrium phases were CaO·3FeO·Fe2O3 and 2CaO·Fe2O3. (3) As CO/(CO + CO2) = 60%, CaO·3FeO·Fe2O3 was reduced to FeO and 2CaO·Fe2O3, and 2CaO·Fe2O3 was still the stable phase. (4) As CO/(CO + CO2) = 80%, FeO was reduced to metallic Fe, and 2CaO·Fe2O3 was reduced to metallic Fe and CaO. The finding from this work may be used as a theoretical foundation for the research of the reduction of SFCA.
Fe-Mn spinels are common bonding phases in ferromanganese sinter and play an important role in determining sinter strength. This study analysed spinel phases from ferromanganese sinter to determine the range of compositions present and examine the relationship between phase composition and microhardness. Spinels with α-vredenburgite and jacobsite compositions had notably increased mean Al content compared to that of end-member Fe- or Mn-spinels. There was a strong negative correlation between the Fe+Al content and the Mn/Fe ratio of sinter jacobsite and of α-vredenburgite, indicating the likely substitution of Al³⁺ for Mn³⁺ in the vredenburgite structure. Mixed Fe-Mn spinels had higher Vickers and Knoop microhardness and fracture toughness than end-member Fe- or Mn-spinels. It is likely that the presence of Al in the octahedral site in the α-vredenburgite structure is related to the increased microhardness and, therefore, should have a positive effect on sinter strength if vredenburgite is present in sufficient quantities.
The composite microhardness (SCH) and composite fracture toughness (SCFT) of seven sinter samples were calculated utilising the modal proportion of distinct particle textural types, ‘sinter microtypes’ (SM). Ten SM were defined based on phase association, phase texture and particle texture. The SCH/SCFT of each microtype was calculated by defining an idealised composition and utilising the mean microhardness/fracture toughness of different textural forms of common sinter phases. Comparison of SCH and SCFT with sinter metallurgical indices and major element chemistry showed relatively stronger linear correlations with the latter. Modifying the idealised compositions of SM to calculate SCH/SCFT did not notably change correlations with sinter RDI, RI, TI. Calculating SCH/SCFT by weighting the input of SM variably improved correlations with sinter RDI, RI, TI. Providing additional weighting to nuclei/primary phase-bearing SM provided the best correlation with RDI and RI, whereas additional weighting to bonding phase-bearing SM provided the best correlation with TI.
With the objectives of reducing CO2 emissions and applying hydrogen-enriched gas in the iron ore sintering process, a mathematical model was developed to simulate the natural gas (NG) injection in the sintering process. The accuracy of the model was verified via sinter pot tests. Additionally, an environmental assessment of CO2 mitigation was performed. Moreover, the effects of the injection quantity, location, and intensity on the sintering process were examined. Sintering process parameters were adopted to quantitatively assess the NG injection technology. The results indicated that this technology can reduce the CO2 emissions. The CO2 mitigation dosage is 11.75 kg/ton sinters when 15% solid fuel is replaced with NG. The melting zone thickness (MZT) and binding liquid phase amount in the upper sintering bed are gradually improved with NG injection quantity increased gradually, which indicates that the holding time of the high temperature zone in the upper bed is prolonged. Furthermore, the injection locations and intensities affect the sintering process. Earlier injection allows more heat storage and forms more binding liquid phase in the upper bed. Low intensity injection reduces the MZT of the sintering bed and negatively affects the sintering process.
In order to provide a reliable reference for utilizing Indonesia vanadium titano-magnetite (VTM) in blast furnace (BF) economically, metallurgical properties of iron ore sinter with addition of Indonesia VTM in mixed sintering materials were investigated, including low-temperature reduction degradation index (RDI), reducibility index (RI), and softening/melting properties. Additionally, influenced mechanism of Indonesia VTM on metallurgical properties of sinter was studied. It is found that adding Indonesia VTM in sintering process quickly increases the RDI of sinters, and decreases the RI from 78.02% to 68.43%. Moreover, both beginning temperature (T4) and final temperature (TD) of softening/melting increase gradually, and cohesive zone temperature range (TD–T4) enlarges from 219 ºC to 315 ºC. As a result, the permeability of cohesive zone gets worse, which is proven by the higher maximum pressure drop (δPmax) in softening/melting experiments. It is concluded that, after comprehensively considering all metallurgical properties mentioned above, the proper proportion of Indonesia VTM in sintering process is proposed in the new raw materials conditions.
The low silicon sintered ores are prepared, where C content is 3.3%, 3.5%, 3.7%, 3.9% and 4.1%, respectively. Their metallurgical properties are also measured. The results state that the low temperature reduction degradation property in low silicon sintered ore is to achieve the best when the carbon content was 3.7%. With increasing carbon content, it has a trend that the low silicon sintered reducing gradually become variation. In this range of carbon content, softening initial temperature exceed 1230 °C, the softening interval is less than 120 °C, so suitable C content are helpful to improve metallurgical properties for low silicon sintered ore.
The fitness for granulation of a ore mixture used to make a series of sintering in a pilot plant is studied. The quality indexes and the phases composition of sinterings is determined. The best sintering structure is checked. A serie of iron ores is classified as the granulation index (G index). The G index evolution of the ore mixtures used by ACERALIA for the last years is shown. An increase in productivity and a decrease in coke consumption in the sinter strand is observed as the G index improves.
Separated granulating sintering is a kind of new sintering process, which makes separately the concentrate ore into high basicity materials and acidic balls, then mix with fuels and returned mine to sinter. Sintering test was made in laboratory to study the effect of basicity and to define the new processing parameter. The results showed that when the basicity is low, the binder phase is based on C2S with viteic and the quality of sinter is good. With the increase of basicity, the content of CaO·TiO2 increases, which has badly destructive effect. When TiO2 is fully created into CaO·TiO2 and the basicity is 2.02, the content of SCFA is high, the liquid phase of sinter covers the pellet, the quantity of sinter is better and its metallurgical properties are improved.
Influence of different carbon content on the quality of chrome-bearing vanadium-titanium sinter was investigated through sinter pot test. The results show that with the increasing of the carbon content (mass fraction, 2.8%-4.0%), the production of liquid phase of the chrome-bearing vanadium-titanium sinter increases, the vertical sintering speed and the sintering rate are reduced, the production rate first increases and then decreases. The mineral components of the chrome-bearing vanadium-titanium sinter with different carbon content are almost the same, the iron-bearing mineral mainly consists of magnetite and hematite, and the binding phases are calcium ferrite, silicate and glassiness. With the increasing of carbon content, the content of magnetite, silicate and perovskite also increases, but the content of hematite and calcium ferrite decreases. However, the tumbler strength of the chrome-bearing vanadium-titanium magnetite first increases and then decreases, the reduction disintegration index increases and the reduction index decreases with the increasing of carbon content. The optimum carbon content for the sinter is 3.6%. ©, 2015, Editorial Office of Transactions of Materials and Heat Treatment. All right reserved.
Bed permeability, rate of reductant and productivity of blast furnace (BF) performance mainly depends on both iron bearing material but also carbonaceous material. Most of the BFs have the sinter being a major burden; hence, in JSW Steel Ltd, four sinter plants are operating to fulfill the four BF's requirement. For efficient BF operations, sinter plants are key units whose proper performance is vital to produce desired sinter strength. The tumbler index of the sinter is an important property of the sinter, and sinter strength depends on the raw material composition and machine parameters. For smooth sinter plants operation, changes to the operating conditions should be few and precise. To achieve this, a much better understanding of the mechanisms relating control inputs to a sinter production rate and quality needs to be established. In the present work, a neural network based model has been developed and trained relating sinter strength with a set of nine process variables, namely, basicity, Fe2O3/SiO2, MgO, MnO, FeO, moisture, coke breeze, burnthrough temperature and machine speed, to predict the tumbler index (-6.3 mm) of the sinter. The variables to which strength of the sinter was most sensitive were Fe2O3/SiO2, basicty, machine speed, and MgO, MnO and FeO. Tumbler index of the sinter was influenced by sinter porosity, which was itself determined by the firing temperature and green sinter mix carbon content. The predicted results were in good agreement with the actual data with <3.5% error. © 2016 Institute of Materials, Minerals and Mining and The AusIMM.
Permeability in the blast furnace shaft is adversely affected by low-temperature reduction degradation of sinters. The fundamental cause of this is the expansion of the iron oxide phase resulting from the reduction of hematite to magnetite. The present study shows that expansion behavior during the hematite/magnetite reduction step and the resulting microstructure are strongly influenced by the reduction temperature (partial oxygen pressure), the reducing agent and the nature of the hematite. The reduction rate is of minor importance. A reduction mechanism is proposed that can explain the dilation behavior and the magnetite microstructure. The results provide better insight into the reduction degradation behavior.
A review of currently used standard tests to characterise the behaviour of iron bearing materials in a blast furnace shaft is carried out. In particular, the relevance of standard test low temperature reduction degradation and reducibility results to blast furnace operation is discussed. Following a review of more sophisticated tests, designed to obtain a closer simulation of blast furnace conditions, a laboratory scale furnace built at the BHP Research Newcastle Laboratories is described. The furnace is capable of testing around 500 g of ferrous material with simulated vertical blast furnace profiles of temperature and gas composition. The maximum sample temperature used in the furnace was 900°C, and a gas mixture composed of N2, H2, CO2, and CO was used for reduction. Three BHP blast furnaces were considered, and temperature-gas composition profiles were calculated using a numerical two-dimensional flow, heat transfer, and reaction model of the blast furnace shaft. The wall and centre profiles of each of the furnaces were simulated. Finally, the properties of the iron bearing materials selected for the study, including sinters, pellets, and lump ores, were characterised under standard test conditions.
As a main charging form of BF (blast furnace), pellets play an important role in blast furnace process. However, comparing with sinters, pellets have many disadvantages, such as reduction swelling, low softening and melting temperature and so on. Therefore, the flux pellets have been applied in blast furnace widely, especially MgO containing pellets. The light burned magnesite is applied as MgO containing additive in pellet production. The characters of light burned magnesite are explored. Meanwhile, the effects of it on low-temperature metallurgical properties are investigated such as low-temperature reduction degradation index (RDI), compressive strength (CS) and the reduction swelling index (RSI). The light burned magnesite calcined at 850 °C manifests better grindability, larger specific surface area, and higher hydration activity. It is found that the addition of light burned magnesite can improve low-temperature metallurgical properties (RDI, RSI) of the pellets. With the increase of light burned magnesite in pellets, the RSI and RDI decrease gradually; when the proportion of light burned magnesite does not exceed 2.0% in pellets, the CS decreases slightly, but it still surpasses 2 689 N, which can still meet the demand of BF.
The effect of TiO2 content on the phase compositions of sinter was conducted under reaction equilibrium at oxygen partial pressure of 5 × 10-3 atm. The results showed that TiO2 mainly existed in the phase of perovskite. With the increase in TiO2 content, the content of secondary hematite phase increased and the ratio of hematite and magnetite in the sinter phase decreased. Meanwhile, the ratio of perovskite and Ca2SiO4 increased and the increased level of perovskite was larger than that of the Ca2SiO4 phase. The volume fraction of the phase silico-ferrite of calcia and alumina decreased from 44·9 to 41·5%, and the chemical formula of silico-ferrite of calcia and alumina changed from 4·7CaO.9·2Fe2O 3.Al2O3.2·3SiO2 to 1·6CaO.4·9Fe2O3.Al2O 3.1·8SiO2 when the percentage of TiO2 was from 0 to 12 mass-% in the sinter.
The phase compositions of high Ti bearing titanomagnetite sinter with different contents of B2O3 were studied at 1623 K under an oxygen partial pressure of 5×10−3 atm. The results showed that B2O3 mainly gathered in Ca2SiO4 phase and formed 2CaO.xSiO2.2/3(1−x)(B2O3) phase. The appearance of B2O3 can restrain the precipitation of CaTiO3 and 2CaO.xSiO2.2/3(1−x)(B2O3) and promote the amount of Fe bearing mineral phase in the current experimental condition. In addition, the shape of CaTiO3 changed from bulk to strip type with the increase in B2O3 content. The formula of silicoferrite of calcium and aluminium changed from 1·6CaO.4·9Fe2O3.Al2O3.1·8SiO2 to 2·5CaO.5·9Fe2O3.Al2O3.2·6SiO2, and the formula of dicalcium (boron) silicate changed from 2CaO.SiO2 to 2CaO.0·33SiO4.0·45B2O3 when B2O3 content was from 0 to 2·0 mass-% in the sinter. The change of phase compositions with the addition of B2O3 in the sinter will be beneficial for improving its metallurgical properties.
The calcined magnesite was utilized as a kind of MgO bearing additive to produce MgO bearing pellets. The effects of MgO on densification and consolidation of pellets were investigated. The experimental results show that, at the same process parameters, the porosity and pore size distribution of green pellets have no evident relation with the MgO bearing additive, pore size of green pellets is between 15 μm and 35 μm and the porosity of green pellets is about 34%. There is a densification and consolidation phenomenon during the induration process; the pore size and porosity of product pellets decrease gradually; and the structure of product pellets becomes dense. MgO makes a negative effect on the densification and consolidation of product pellets, the densification ratio of pellets decreases from 46.3% to 28.6% with the addition of MgO bearing additive from 0 to 2.0 %. The porosity and the pore size of product pellets increase gradually with the increase of MgO content; When the mass fraction of MgO bearing additive increases from 0 to 2.0%, the pore size of product pellet increases and the pore size distributes in a large range. Also, the porosity increases from 18.61% to 24.06%.
As a raw material, Indonesia vanadium-titanium sinters are being applied to the blast furnace process for iron making in the typical iron and steel plant. In order to keep the health running of blast furnace process, in this work we have investigated the softening and melting properties of Indonesia vanadium-titanium sinters. We found that the content of vanadium-titanium magnetite in sinter is correlated with the softening and melting ranges for those sinters considered here. With the increasing of the vanadium-titanium magnetite in sinter, the starting softening temperature increases gradually and the final softening temperature increases as well, thereby the softening range becomes narrow. Both starting and final melting temperatures begin to ascent, and the variation of melting range is not obvious. In addition, we also found that the coke is wetted by the molten slag and iron. From the viewpoint of blast furnace process, the softening and melting zone has to move downward. In this zone of blast furnace the contact area of solid-liquid phase will get larger because of the close contract among the molten slag, iron and coke. On one hand, this kind of behavior can definitely speed up the reduction of iron oxide. On the other hand, it simultaneously worse the ventilation properties and affect the normal running of air flow, because a lot of iron and slag can not be got smoothly into the hearth through coke layer.
During the iron ore sintering process, iron ore fines (<6.3mm) are mixed with limestone flux and coke breeze and heated to ~1300ºC. This results in partial melting of the mixture, converting the loose raw materials into a porous but physically strong composite material in which the iron-bearing minerals are bonded together by a range of complex ferrite-like phases known collectively as ‘SFCA’ (Silico-Ferrite of Calcium and Aluminium). These ‘SFCA’ phases can be divided on the basis of composition and morphology into two main types: a low-Fe form that is simply referred to as SFCA, and a second high-Fe, low-Si form called SFCA-I. SFCA and SFCA-I are believed to be the most desirable bonding phases in iron ore sinter because of their high reducibility, high mechanical strength and low reduction degradation, all of which are significant factors in determining the efficiency of the blast furnace.
Despite their importance in controlling the quality of iron ore sinter, the stability range and mechanisms of ‘SFCA’ formation from precursor phases are not well understood. CSIRO has attempted to improve understanding of phase relations within iron ore sinter by; a) conducting experimental phase equilibria studies within the Fe2O3-CaO-SiO2 (FCS) and Fe2O3-Al2O3-CaO-SiO2 (FACS) model sinter systems to establish the key thermal and compositional parameters that influence the bonding phase chemistry and stability and, b) conducting in situ X-ray diffraction experiments to determine the formation mechanisms of SFCA and SFCA-I under simulated sintering conditions. The combination of techniques will provide insights into sinter formation mechanisms which are important in designing strategies to counter some of the key problems facing the Australian iron ore industry.
The formation mechanisms of the complex Ca-rich ferrite iron ore sinter bonding phases SFCA and SFCA-I, during heating of a synthetic sinter mixture in the range 298-1623 K and at pO(2) = 0.21, 5 x 10(-3) and 1 x 10(-4) atm, were determined using in situ X-ray diffraction. SFCA and, in particular, SFCA-I are desirable bonding phases in iron ore sinter, and improved understanding of the effect of parameters such as pO(2) on their formation may lead to improved ability to maximise their formation. in industrial sintering processes. SFCA-I and SFCA were both observed to form at pO(2) = 0.21 and 5 x 10-3 atm, with the formation of SFCA-I preceding SFCA formation in each case, but via distinctly different mechanisms at each pO(2). No SFCA-I was observed at pO(2) = 1 x 10-4 atm; instead, a Ca-rich phase designated CFAlSi, formed at 1 420 K. By 1 456 K, CFAlsi had decomposed to form melt and a small amount of SFCA. Such a low pO(2) during heating of industrial sinter mixtures is, therefore, undesirable, since it would not result in the formation of an abundance of SFCA and SFCA-I bonding phases. In addition, CFA phase, which was determined by Webster et al. (Metall. Mater. Trans. B, 43(2012), 1344) to be a key precursor phase in the formation of SFCA at pO(2) = 5 x 10(-3) atm, was also observed to form at pO(2) = 0.21 and 1 x 10(-4) atm, with the amount decreasing with increasing pO(2).
The reaction sequences involved in the formation of iron ore sinter phases were determined using in situ synchrotron-based X-ray diffraction. Experiments were carried out using a synthetic sinter mixture containing 77.36 per cent Fe2O3, 14.08 per cent CaO, 3.56 per cent SiO2 and 5.00 per cent Al2O3 corresponding to a basicity of ~4. The alumina content represents the upper level of alumina concentrations measured in phases formed in industrially produced plant sinter. Data were collected during heating of the sample to 1350°C under an atmosphere of 0.5 per cent O2 in N2, equivalent to an oxygen partial pressure of 5 10-3 atm. This temperature was suffi cient to ensure melting. Data were also collected on cooling of the sample back to room temperature to examine recrystallisation of phases from the melt. Results showed the sequence of reactions initially involved the formation of calcium ferrite phases C2F and CF. These subsequently reacted with the silica and haematite leading to the solid state formation of SFCA and SFCA-1. SFCA and SFCA-1 were the last phases to form in the system and were both stable up to ~1260°C. Above ~1260°C, melting of the SFCA phases and reduction of the remaining haematite occurred producing the assemblage magnetite + melt. During cooling, both SFCA phase types recrystallised from the melt initially coexisting with magnetite until secondary haematite formed. This is the fi rst study to demonstrate that both SFCA and SFCA-1 are precipitated from the melt during cooling of iron ore sinter. Future work will extend the range of compositions studied to examine the effect of basicity and alumina concentration on the phase assemblages as a function of temperature and oxygen partial pressure.
The reduction of iron oxides, from hematite to iron, is a complex series of interrelated steps, with many new observations and still some unexplained questions. The present review describes a few remarkable features, observed and analyzed recently in the author's laboratory, mainly based upon the prominent role of the reaction product texture, and concerning the hematite-magnetite and the wustite-iron steps. Emphasis is put on two very different and uncommon features observed in the reduction of hematite into magnetite: cracking of the matrix and growth of lamellae which are tentatively considered as inner whiskers. In each case the mechanism is discussed, and a semi-quantitative treatment is proposed. In the wustite-iron step, the existence of a rate minimum in the temperature range, and the catalytic role of potassium are described and briefly discussed.
The crystal structures of Mg-rich SFCA (SFCAM); Ca-2(Ca0.10Mg1.20Fe5.55Si1.50Al3.65)O-20 (triclinic P (1) over bar, a = 8.848(1) angstrom, b = 9.812(1) angstrom, c = 10.403(1) angstrom, alpha = 64.35(1)degrees, beta = 84.19(1)degrees, gamma = 66.27(1)degrees, V = 742.4(1) angstrom(3), Z = 2) and Ca-2(Mg2.00Fe4.45Si2.15Al3.40)O-20 (triclinic P (1) over bar, a = 8.928(2) angstrom, b = 9.823(2) angstrom, c = 10.389(1) angstrom, alpha = 64.41 (1)degrees, beta = 83.90 (1)degrees, gamma = 65.69 (1)degrees, V = 746.0 (2) angstrom(3), Z = 2) were determined by the single crystal X-ray diffraction. The structure of SFCAM is iso-structural with aenigmatite and well demonstrated by an alternating stacking of the tetrahedral and octahedral layers. The tetrahedral sites of oxygen are occupied either by Fe, Al and Si. The octahedral sites of oxygen are occupied either by Fe, Mg and Al and this feature contrasts with that of the Mg-free SFCA phase where Al prefers tetrahedral sites, only. In particular, Si4+ and Mg2+ prefer the tetrahedral T1, T2 and T4 sites and octahedral M5 and M6 sites, respectively, by producing a structural slab similar to that of aluminous diopside. Such local concentration of divalent Mg2+ and tetravalent Si4+ in the structure of SFCAM is strongly favored in order to compensate the local charge valance. The SFCAM phase indicates the superior structural flexibility for a variety of cations and this feature is promising for the chemical design of the bonding phase in the sinter ore.
The main purpose of iron ore sintering is to produce a strong agglomerate for the blast furnace. This is achieved by partially melting a sinter mix at high temperature and then allowing the melt to solidify into a bonding phase for the unreacted material. The melt formation and subsequent solidification processes are highly dependent on the composition of the blended mix. This paper summarises the differences in sintering behaviour between hematite ores and goethitic ores based on past research programs carried out at BHP Billiton. From a fundamental evaluation of the sintering process, it is clear that productivity can be an issue with goethitic ores because of their low bulk density and high porosity. This paper recommends steps towards overcoming losses in productivity. The effect of goethitic ores on coke rates is also a matter of general concern and this study shows that the addition energy required to dehydrate goethites and remove the additional water introduced into the system is comparatively small. The properties of melts have been shown to be particularly important in determining yield from a sinter machine and it is evident that the easy-melting properties of goethitic ores will also have an impact on this area. This paper also reviews our current understanding of how goethitic ores can influence sinter quality. The implication of fundamental knowledge on practical sinter plant operation is discussed throughout and collated at the end of the paper.
Domestic iron ores and sinters from six mills in PRC have been evaluated. A large number of the ores consist of dense magnetite and hematite, and complex iron ores containing minerals including pyrite, pyrrhotite, biotite and siderite. One particular ore was extremely complex containing a high level of fluorite. Based on the sinter samples received, one sinter was obviously produced from predominantly magnetite blends as silicate grass and SFCA of high temperature morphology were the major bonding phases present and the major iron oxide mineral was magnetite. For the plants using predominantly hematite ore in their blends, SFCA is relatively well developed and the sinters also have a very high level of relict hematite. Sinters with this are characterised by high reducibility and a good strength. However, such a sinter structure is not formed automatically when a high level of hematite is present in the blend. The structure of three sinters indicated that when coke rate is high such a structure is not achievable although high temperature morphology SFCA is developed. The sinter produced from ore containing high fluorite is the most reducible but is also extremely weak. The strength of the different mineral phases in the sinters were characterised using indentation techniques. Good correlations were obtained between tumble indices of the sinters and a composite fracture toughness of the major phases. The study also showed that some of the more typical structures found in these plant sinters could be reproduced using a bench-scale furnace under controlled conditions.
Vickers indentation test was used to study the effects of mineral composition and microstructure on crack resistance of sintered ore, and the initiation and propagation of cracks in different minerals contained in sintered ore were examined. The results indicate that the microstructure of calcium ferrites is a major factor influencing crack resistance of sintered ore. Finer grain size of calcium ferrite will lead to higher cracking threshold and better crack resistance of sintered ore. The formation of calcium ferrite with fine grain size during sintering process is favorable for crack resistance of sintered ore.
Although dicalcium silicates can constitute up to 10 vol% of many modern hematite/goethite iron ore sinters, traditional mineralogical investigations of such sinters have largely overlooked this phase and focused on the more abundant iron oxides and ferrites. However, dicalcium silicates have a range of properties that make them unique in sinter parageneses. These properties may contribute significantly to bulk sinter properties and also make dicalcium silicates potentially exploitable in novel upgrading processes. Analyses on a pot grate test sinter have shown that phosphorous (and possibly other elements including potassium and chromium) was heavily concentrated in the dicalcium silicates. A series of etch tests have demonstrated that dicalcium silicates can be selectively removed from the surface of polished sinter samples using weak acids. In addition, bulk leaching trials showed that the phase can also be removed from powdered and coarser (-5mm) sinter in mild acids. These leaches resulted in a >90% reduction in phosphorous with a 7% improvement in iron grade for the powdered material and a 70% reduction in phosphorous with a 5% improvement in iron grade for the coarser material. Two novel processes are proposed to exploit the leachability of contaminated dicalcium silicates from sinter: one being a potential route to a high-grade iron product, the other being a return fines washing circuit.
Owing to the depletion of world lump iron ore stocks, pre-treated agglomerates of fine ores are making up a growing proportion of blast-furnace feedstock (∼80%). These agglomerations, or `sinters', are generally composed of iron oxides, ferrites (most of which are silicoferrites of calcium and aluminium, SFCAs), glasses and dicalcium silicates (C2S). SFCA is the most important bonding phase in iron ore sinter, and its composition, structural type and texture greatly affect its physical properties. Despite its prevalence and importance, the mechanism of SFCA formation is not fully understood. In situ powder X-ray diffraction investigations have been conducted into the formation of SFCA, allowing the study of the mechanism of its formation and the observation of intermediate phases with respect to time and temperature. Studies have been carried out to investigate the effects of changing the substitution levels of aluminium for iron. The use of the Rietveld method for phase quantification gives an indication of the order and comparative rates of phase formation throughout the experiments.
In the iron ore industry significant emphasis is placed throughout the mining process on meeting chemical composition specifications for the export of fine ores. However, little has been published on the implications of ore chemical composition for iron ore sinter and pellet product quality. The ore bulk composition and the nature of the minerals in the fine ore both play a critical role in determining the type of high temperature bonding phases that form during sintering and pelletising. This paper uses the experimental determination of phase relations in model sinter and pellet systems such as Fe2O3-CaO-SiO2 (FCS) and Fe2O3-Al2O3-CaO-SiO2 (FACS) to examine the links between iron ore chemical composition and the temperatures used during sintering and pellet firing. The phase relations help to establish the critical thermal and compositional parameters that control the bonding phase chemistry, which in turn influences the physical characteristics of the sinter or pellet matrix. Results show that lower Fe grade (
Complex silico-ferrites of calcium and aluminium (low-Fe form, denoted as SFCA; and high-Fe, low-Si form, denoted as SFCA-I)
constitute up to 50 vol pct of the mineral composition of fluxed iron ore sinter. The reaction sequences involved in the formation
of these two phases have been determined using an in-situ X-ray diffraction (XRD) technique. Experiments were carried out under partial vacuum over the temperature range of T=22 °C to 1215 °C (alumina-free compositions) and T=22 °C to 1260 °C (compositions containing 1 and 5 wt pct Al2O3) using synthetic mixtures of hematite (Fe2O3), calcite (CaCO3), quartz (SiO2), and gibbsite (Al(OH)3). The formation of SFCA and SFCA-I is dominated by solid-state reactions, mainly in the system CaO-Fe2O3. Initially, hematite reacts with lime (CaO) at low temperatures (T ∼ 750 °C to 780 °C) to form the calcium ferrite phase 2CaO·Fe2O3 (C2F). The C2F phase then reacts with hematite to produce CaO·Fe2O3 (CF). The breakdown temperature of C2F to produce the higher-Fe2O3 CF ferrite increases proportionately with the amount of alumina in the bulk sample. Quartz does not react with CaO and hematite,
remaining essentially inert until SFCA and SFCA-I began to form at around T=1050 °C. In contrast to previous studies of SFCA formation, the current results show that both SFCA types form initially
via a low-temperature solid-state reaction mechanism. The presence of alumina increases the stability range of both SFCA phase
types, lowering the temperature at which they begin to form. Crystallization proceeds more rapidly after the calcium ferrites
have melted at temperatures close to T=1200 °C and is also faster in the higher-alumina-containing systems.
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