The Influence of Ash Impurities on Interfacial Reactions between Carbonaceous Materials and EAF Slag at 1550°C

Rahman, M.F.; Khanna, Rita; Sahajwalla, Veena; O'Kane, Paul

doi:10.2355/isijinternational.49.329

Cited by 31 publications

(28 citation statements)

References 23 publications

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“…After 15 min of heat treatment, iron oxide had reduced completely to iron as no XRD peak could be identified with this phase. This result is consistent with the published literature; the reduction of iron oxide is quite rapid at this temperature, and is expected to reach completion within few minutes [22]. While there was still some unreduced silica and unconsumed carbon, there was clear evidence of the formation of SiC and FeSi phases.…”

Section: X-ray Diffractionsupporting

confidence: 82%

Formation of Light-Weight Ferroalloys in the Fe2O3-Al2O3-C System at 1550 °C: Influence of Silica Impurities

Ikram-Ul-Haq

Mukherjee

Khanna

2017

Metals

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Light-weight ferro-aluminium alloys are finding increasing application in the transport sector to reduce overall weights, energy costs and CO 2 emissions. As the primary production processes of both Fe and Al are among the most energy-intensive industrial processes in the world, there is an urgent need to develop alternate routes for producing Fe-Al alloys. Our group has successfully produced these alloys in the Fe 2 O 3 -Al 2 O 3 -C system by producing molten iron in situ, followed by the reduction of alumina at 1550 • C and pick-up of Al by Fe. In this article, we report on the influence of silica, a typical impurity present in iron oxide and reductant carbon, on the reduction reactions in this system, and on the formation of ferroalloys. In-depth investigations were carried out on the Fe 2 O 3 -SiO 2 -C and Fe 2 O 3 -Al 2 O 3 -SiO 2 -C systems at 1550 • C for times of up to 60 min. Detailed HRSEM/EDS and XRD analysis was carried on the quenched reaction products recovered after various heat treatments. A complete reduction of silica and alumina was observed in the Fe 2 O 3 -SiO 2 -C system, along with the formation of FeSi and SiC. The reduction reactions were relatively slow in the Fe 2 O 3 -Al 2 O 3 -SiO 2 -C system. While the formation of SiC, FeSi and mullite (Al 6 Si 2 O 13 ) was observed, even small amounts of Fe-Al alloys could not be detected. The presence of silica impurities reduced the formation of Fe-Al to negligible levels by depleting molten iron from the reaction zone, a key ingredient for the low-temperature carbothermic reduction of alumina. This study shows that some impurities can be highly detrimental to the reaction kinetics and the formation of ferroalloys, and great care needs to be exercised during the choice of reaction constituents.

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Section: X-ray Diffractionsupporting

confidence: 82%

Formation of Light-Weight Ferroalloys in the Fe2O3-Al2O3-C System at 1550 °C: Influence of Silica Impurities

Ikram-Ul-Haq

Mukherjee

Khanna

2017

Metals

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“…26) With ash present in metallurgical coke as well as in the combusted rubber blends a 2-D interconnected network along the surface can form. The CO bubbles, formed originally along the carbon/slag interface, will prefer to grow vertically due to high contact angle with ash particles 20) leading to their separation with a relatively small volume. The surface then gets ready for further reactions and further bubble formation.…”

Section: Discussionmentioning

confidence: 99%

“…20) This technique is being used to determine carbon/slag interactions and associated nature of the slag foam by continuously monitoring the changes in droplet volume (a measure of gas entrapment) as a function of time. A schematic representation of the experimental setup is shown in Fig.…”

Section: Carbon/slag Interactionsmentioning

confidence: 99%

“…The continuous formation of gases and associated slag foaming changes significantly as a function of time depending on slag chemistry and operating conditions, thus the fluctuating behaviour needs to be considered. The method and experimental setup used here has been published recently in ISIJ International by Rahman, Sahajwalla et al 20) and has been successfully applied to compare conventional materials. The publication in Steel Research Int.…”

Section: Carbon/slag Interactionsmentioning

confidence: 99%

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Carbon/Slag Interactions between Coke/Rubber Blends and EAF Slag at 1 550°C

et al. 2009

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Using the sessile drop approach, interfacial reactions taking place in the slag/carbon region were investigated at 1 550°C in a horizontal tube furnace under inert atmosphere (1 L/min Ar). In this study, waste rubber tyres were blended with metallurgical coke, already used as injectant in electric arc furnace (EAF) steelmaking, in different proportions. Off gas analyses and physicochemical properties of the slag have been evaluated and correlated with the carbon/slag interactions. The gaseous emissions from metallurgical coke showed lower concentrations in comparison to the emissions from the coke-rubber blends. With an increase of rubber in the blend, gaseous emissions were enhanced. Significant carbon/slag interactions occurred when coke/rubber blends were used, with associated iron oxide reductions within the slag phase. Higher gas entrapment in the slag was also observed when the rubber partially replaced the coke.High levels of gas generation leads to increased likelihood of convective transport of reactants and products from the carbonaceous material surface due to evolution of gases as a result of slag/carbon interactions. The oxides present in the ash partially dissolve the molten slag, modifying the slag composition. The results have been discussed and correlated with the hydrogen, ash and sulphur contents of the carbonaceous residues as well as with the dynamic changes in slag composition.This study highlights significant differences in the carbon/slag interactions of coke/rubber blends with EAF slag, compared to interaction of coke with the same slag.KEY WORDS: rubber; EAF steelmaking; carbon/slag interactions; volume ratio; microscopic investigations. 1513© 2009 ISIJ factor is dependent on the bubble size and lamellae stability. 8) On the other hand, viscosity and surface tension influences the movement of the bubbles in the gas dispersed liquid. Foaming was described by Kozakevitch 9) and more recently by Hara et al. 8) in terms of surface chemistry. They measured the foam life and foam height for binary and ternary systems composed of CaO-SiO 2 -FeO and correlated the foam height with the physicochemical properties of metallurgical slags.Foaming is a dynamic phenomenon involving one dimensional two-phase flow.10) With time foaming shows fluctuating behavior due to the changes occurring in the slag composition.11) To account for these dynamic conditions Morales et al. 12) attempted to quantify the foaming behavior by introducing a foaming index which is correlated to the changes in the slag volume and the rate of generated gas. Bikerman et al.13) first described a foaming index which had been empirically related to physical properties of the slag such as the surface tension (s), viscosity (h), and density (r) of the liquid slag and the size of the bubbles (d b ). This index has a unit of time and can be considered as the residence time of the bubbles in the foam. Foaming has been shown to improve with decreasing surface tension and increasing viscosity of slag, 14) although the magnitude of the ...

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“…18,19) The carburizing reaction begins with the appearance of metal iron, it is known from iron-carbon phase diagram that the saturated carbon content in molten iron is related to the temperature, the amount of carbon to reach the saturation of molten iron is high owing to the molten iron temperature of large BF is high.…”

Section: The Carbon Undersaturation Degree Of Moltenmentioning

confidence: 99%