Characterization and Reduction Behavior of Mill Scale (original) (raw)
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Scale Recycling Through Self-Reducing Briquettes to Use in EAF
ISIJ International
This work is part of a project which aimed to provide a theoretical and experimental basis for recycling of mill scale from mini-mill plants. The focus of the present study was to evaluate the kinetics and the mechanisms of reduction in self-reducing briquettes composed of scale, charcoal and binders, aiming its use in EAF. Such briquettes were submitted to the following tests: thermogravimetry in micro-and macrothermobalances with analysis of the generated gas, evaluation of the temperature profile inside the briquette and the metallization degree obtained by tests carried out in muffle furnace at a high heating rate. Previous studies, concerning scale and charcoal taken together with the results of this work indicate that both, the kinetics of scale reduction and the heat transfer limit the overall reaction rate of the briquette. However, the relatively high metallization degree of 76% obtained in the high temperature tests indicates the interest in using such the briquettes for scale recycling in industrial plants. The risk of reoxidation is low due to the protective role of gas evolving from the briquette during self-reduction.
Structural changes occurring during reduction of hematite and magnetite pellets containing coal char
Transactions of the Iron and Steel Institute of Japan, 1983
The structural changes that occurred during the reduction of hematite and magnetite pellets containing coal char, in the temperature range between 900 °C and 1200 °C, were studied. The behavior of the pellets was complex. Significant temperature gradients within the pellet were attained during the process, and the reduction was accompanied by catastrophic swelling of the pellets between 900 °C and 1 000 °C, while shrinkage was observed at 1 100 and 1200 °C. Observed microstructural features such as intragranular porosity and cracking of oxide grains resulted from severe lattice disturbances occurring upon transformation of hematite to magnetite. The catastrophic swelling observed for hematite and magnetite pellets 900 and 1 000 °C was due to the filamentary or whisker growth of iron outward from the wustite surfaces. The whisker formation appears to be due to a changing reducing potential of the gas phase within the pellet coupled with the presence of calcium oxide on the wustite surface. The shrinkage reported at 1 100 and 1200 °C is accounted for in terms of sintering of iron filaments. The pellets strength was found to decrease between 900 °C and 1 000 °C, and increased at higher temperatures. The weakness at low temperatures was due to the absence of bonding between iron filaments or whiskers. The high strength obtained at higher temperatures (1100 and 1200 °C) was produced by sintering of iron filaments.
Journal of Materials Research and Technology, 2020
The objective of this study was to analyze the recycling possibility of the electric arc furnace dust (EAFD) in the form of a briquette. This paper studied the kinect behavior of the briquette's self-reduction and in contact with molten steel (steel-briquette system) and it was aimed at finding the optimal briquette composition used to recover elements such as Cr, V and W. Thermodynamic simulations with FactSage were carried out to validate the experimental results. The EAFD material as-received was magnetically separated to the form of a magnetic electric arc furnace dust (MEAFD) then characterized analytically and microstructurally. Analytical characterization demonstrated that the EAFD was rich in Cr, W and V. Microstructural analyses revealed the presence of oxides and spinel phases. Three different compositions of briquettes were prepared for the experiments: the first with 84% of MEAFD and 16% C; the second with 82% of MEAFD and 18% C; and the third with 80% of MEAFD and 20% C. Reduction experiments at the temperature of 1500 • C were carried out to study the reduction rate differences in the briquettes and the steel-briquettes systems. Reduction experiments showed that the fastest reaction occurred in the briquette with 20% C for both systems. Among the wide experimental dataset analyzed, the optimal measured recovery was 48.1% Cr, 72.7% W and 47.5% V (in wt%).
Journal of Sustainable Metallurgy
Jarosite sludge coming from the hydrometallurgical zinc production route is a hazardous material, which is currently neutralized and landfilled by the so-called Jarofix® process. The present study aims to assess the mechanical and metallurgical properties of briquettes made of jarosite powder with blast furnace sludges, acting as a reductant material, to recover the iron oxide in the form of pig iron and produce an inert slag, increasing the recovery of materials considered as wastes nowadays. Starch was used as a binder (0, 5, 10 wt%), and two different briquetting pressure levels were used (20 and 40 MPa). The results show that briquetting without a binder is not desirable, as the agglomerating forces provided by pressure only are not sufficient, as the briquettes are very fragile and not handy. The binder addition increased noticeably the briquettes resistance, however, only little distinction between the 5 and 10 wt% levels were seen. The briquetting pressure, on the other hand,...
Steel Research International, 2010
For optimization of iron ore fines reduction processes, fundamental knowledge of the reduction kinetics under industrial operating conditions is required. Reduction tests with coarse hematite iron ore were performed in H2-rich reduction gas atmospheres of H2, H2O, CO, CO2 and CH4 considering elevated pressures similar to industrial process conditions. The reaction kinetics of the reactions hematite to magnetite, magnetite to wüstite and hematite to wüstite were investigated in a laboratory-scale pressurized fluidized bed reactor. To facilitate kinetic measurements, the laboratory-scale fluidized bed reactor is equipped with a sampling system, which allows sampling of the bed material at operating conditions. Process conditions were chosen close to industrial plants in a temperature range from 400 to 700 °C. Significant influence of temperature on the rate of reduction was found in all tests. Variation of reduction gas composition showed no influence on the rate of reduction in the range of concentrations investigated. Results presented herein proved the feasibility of depicting industrial process conditions in laboratory scale. For the reduction of hematite to magnetite and magnetite to wüstite topochemical phase growth were observed. In the single step reduction of hematite to wüstite, magnetite appeared as intermediate product formed by topochemical reaction while progressive conversion of magnetite to wüstite was found.
Two wü stite samples were prepared from reagent grade hematite and Baharia iron ore sinter by a gaseous reduction with 50%CO–CO 2 gas mixture at 1273 K. Both wü stite samples were isothermally reduced at 1173–1373 K by different ratios of CO/CO 2 /N 2 which closely represent the coke gases in the blast furnace. The influences of temperature and gas composition on the reduction behaviour and the morphology were investigated. The reduction rate of both wü stite samples increased gradually with increasing reaction temperature and also by increasing the CO concentration in the reducing gas mixture. The apparent activation energy values were calculated and correlated with the gas–solid reaction formulations to elucidate the corresponding mechanism at both early and final reduction stages. The reduction rate of pure wü stite samples is most likely controlled by the combined effect of chemical reaction and gaseous diffusion mechanisms while the reduction rate of wü stite from iron ore sinter is most likely controlled by interfacial chemical reaction mechanism.
The demand of iron for the manufacture of different types of steel is increasing continuously and new solid reductant-based sponge iron plants are being commissioned. In the existing blast furnace, an increase in production by at least 25% to 35% can be achieved by using reduced iron ore. Also, the majority of fines which are generated during the course of handling, mining and transportation are exported at a through away price which needs to be utilized by making iron ore briquettes for sponge iron making. A lot of investigations have been carried out on direct reduction of iron oxides by using hydrogen gas. In the present work, an attempt has been made to study the reduction behavior and kinetics of fired mill scale added to iron ore pellets. The effect of different reduction parameters such as temperature and hydrogen flow rate also, the effect of drop damage resistance, applied pressure and compressive strength was studied. Reduction of briquetted fine mill scale added to iron ore by hydrogen is carried out in the temperature range 700 to 1000 o C. In the reduction kinetic study, the most satisfactory model is to take the slope of the initial linear region of fractional reduction vs. time curve as a measure of rate constant (k) and lnk vs. 1/T plots are straight line from which activation energy was calculated. In kinetic studies relating to reduction of ores, a mechanism is assumed that correlates time (t) to conversion (R): R=F (t) The most satisfactory model is that which gives the higher R 2 coefficient on plotting F (R) against (t).
Reduction of Iron Ore/Empty Fruit Bunch Char Briquette Composite
ISIJ International, 2013
Utilization of Malaysian low grade iron ore is an attractive option of domestic iron resource; however, extra energy consumption is required and thus contributes to greenhouse gases. In this study, incorporation of low grade iron ore deposits with oil palm waste as substitution of coke was studied. Briquette composites of iron ore and char derived from oil palm empty fruit bunch (EFB) pyrolysis were produced with minute amount of distilled water. Reduction processes were carried out at 873 K to 1 173 K under argon atmosphere in an electric furnace for briquette composites with different mass ratio of ore/char. For kinetic analysis, briquette with 8:2 ore/char ratio was used and reduction was carried out by varying the residence time. The percentage of reduction was estimated by oxygen removal and considering the weight loss. The structural and chemical changes of raw materials and briquettes were characterized using XRD, TG/DTA, and XRF. The results indicate that increasing in temperature, time and EFB char content in the briquette will increase the percentage of reduction. XRD and XRF results show that the original iron oxide hydrate has been transformed into partial wustite by several stages and the iron content increased up to 62.7 wt% for 6:4 ore/char ratio briquette. Kinetic results suggest that reduction of iron is controlled by gasification of carbon and the activation energy is 43.21 kJ. EFB char appears to be a promising energy source for replacing part of coal consumption in iron making, and reducing CO2 emission.
Steel Research International, 2022
Accepted Article This article is protected by copyright. All rights reserved The in-plant recycling routes of several side streams produced in Electric Arc Furnace (EAF) steelmaking remain under-explored. Briquetting is an attractive technique to enable recycling of inplant side streams. Briquettes introduced into EAF must possess certain mechanical and chemical properties. However, no standard is available to determine the suitability of briquettes used in the EAF process. In this work, eight side streams were characterized, and used to produce seven different briquettes to be used in EAF. Side streams were obtained from three different EAF steel plants as well as two other industrial sites. Briquettes tested consisted of four self-reducing briquettes and three slag-forming briquettes produced using different recipes. The briquettes were subjected to several mechanical and thermal tests which reflect their intended use in EAF. The mechanical tests included compression and drop tests, and the thermal tests included optical dilatometry, TGA-DTG-MS, and full-scale briquette reduction tests. Moreover, melting trials were performed to assess the melting behavior of selected briquettes and their interaction with slag. Suitability of briquettes characteristics were assessed based on values from literature and against reference ferroalloys and lime stones used in one of the steel plants. Two briquettes were deemed suitable for EAF use, while three briquettes were deemed unsuitable, and two briquettes were considered of limited use.
Effect of Nature Gas Injection on Reducibility of Wustite Prepared from Baharia Iron Ore Sinter
The main method for iron production is the blast furnace. It emits about 2 billion tons CO2 per year, which has the largest contribution in global warming. Using thermo-gravimetric technique, wustite samples prepared from Baharia iron ore sinter were isothermally reduced at 900-1100 oC by different ratios of H2/CO/CO2/N2 which is somewhat simulating the composition of the reducing gas in case of natural gas injection with low oxygen enrichment in the blast furnace. The reduction extent for wustite from iron ore sinter is clearly enhanced to be in the range of 54-69% comparatively with that reduced with coke gases (30-50%) as industrial data. Enhancement of wustite reducibility decreases the remaining quantity of unreduced wustite, which descends to high temperature region at which reduction depends mainly on solid carbon that will consequently lead to reduction of coke consumption and CO2 emission. The reduction rate of wustite samples is independent on either the reaction temperature or the H2 concentration in the reducing gas mixture due to the water gas shift reaction. The reduction rate of wustite samples at initial stages are most likely controlled by the combined effect of chemical reaction and gaseous diffusion mechanisms while at final stages are most likely controlled by interfacial chemical reaction mechanism.