Crystallization Behaviors of Spinel During Cooling Process of Modified EAF Slag
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TRODUCTION
THE iron and steel industry is extremely energy-intensive, accounting for the consumption of approximately 17 pct of the energy used by industries worldwide.[1] Although significant achievements have been made to reduce the energy intensity of steel production, there are still untapped energy conservation opportunities for today’s industry. For example, the waste heat of high temperature (1450 C to 1650 C) slag produced in a blast-furnace (BF), converter, and electric-furnace (BOF and EAF)[2,3] is equivalent to approximately 36 million tonnes of standard coal (TCE). In 2018, the world produced 1.18 billion tonnes of iron, and discharged approximately 375 million tonnes of BF slag with an energy equivalent to 22 million TCE. In addition, 100 million tonnes of steel slag, including basic oxygen furnace (BOF) and electric arc furnace (EAF) slag with a thermal energy of 6.8 million TCE, was produced in 2014, without any attempts to recover
YU LI, XINYANG MENG, and KUIYUAN CHEN are with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, P.R. China. Contact e-mail: [email protected] MANSOOR BARATI is with the Department of Materials Science and Engineering, University of Toronto, 140 e 184 College Street, Toronto, ON, Canada M5S 3E4. Contact e-mail: [email protected] Manuscript submitted August 18, 2019.
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such energy.[4] Slag has been reused in many applications in construction, agriculture, and environment, while the construction industry accounts for the largest utilization of slag as cement making material, aggregate, and insulation material.[5–9] The conventional methods applied or proposed for the recovery of the materials and energy of slag would treat the slag, as-is, without any modification to its chemistry. In these methods, slag is first cooled and then directed to various applications depending on its chemical composition, product size and shape, and structure. The heat may be partially recovered during the cooling process, if, for example, dry granulation methods are applied, but such practices are extremely limited in use as they require substantial capital investment for a relatively small return. A different method of slag handling, known as hot slag modification, aims at tailoring the slag chemistry, hence rendering the properties of the slag suitable for different value-added materials.[4] In such methods, the chemistry of the slag is adjusted for the end application by adding reagents (e.g. oxides), and then cooled in a controlled fashion to yield the required mineralogy and microstructure. Not only high-value products (such as stablized steel slag or glass ceramics) are produced by this method, but also the thermal energy of slag is partly utilized to melt and dissolve the additives. For example, it has been shown that up to 20 pct of a modifier can be dissolved in slag at high temperatures, without a need for external energy.[10]
EAF slag contains large amounts of Fe, Mg, and smalle
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