Effect of Initial FeO Content and CaO:SiO 2 Ratio on the Reduction Smelting Kinetics of the CaO-SiO 2 -MgO satd. -FeO Sl
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SINCE the first commercial electric arc furnace (EAF) in 1907, EAFs have been widely used to meet recycling demands and produce steel with a lower carbon footprint. Newly designed furnaces allow scrap pre-heating systems, single-bucket operation, and supersonic lances for gas injection. These innovations have not only minimized energy consumption, but also provided solutions to environmental problems using recyclable raw materials such as scrap and other Fe-rich by-products.[1–4] However, attempts to utilize partially reduced iron-containing by-products with a total Fe content below 50 pct and significant gangue content required additional carbon addition for reduction, which induced significant compositional changes to FeO and MgO in the EAF slags during operation, subsequently disturbing optimal slag foaming and lowering the operational stability. JONG BAE KIM and IL SOHN are with the Department of Materials Science and Engineering, Yonsei University, 262 Seongsanno, Seodaemun-gu, 120-749 Seoul, Korea. Contact e-mail: [email protected] Manuscript submitted December 1 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Several previous works have studied FeO reduction in slag and the subsequent foaming behavior. Ozawa et al.[5] described the carbothermic reduction of EAF slags containing a FeO content as high as 60 mass pct and concluded that reduction is controlled by the liquid-phase mass transfer of FeO to carbon and that a higher CaO:SiO2 ratio (CaO mass pct/SiO2 mass pct) increased the reduction rate due to increased slag foaming. Dankwah et al.[6] reduced FeO in EAF slags with coke and waste polymers, which showed significant CO generation, induced foaming, and promoted faster reduction kinetics within 6 minutes of the initial reduction. Qiu et al.[7] conducted a series of room-temperature experiments to identify the parameters that effect slag foaming during chemical reactions and found that a higher slag viscosity extended the foaming elimination time, but reduced the maximum foaming height. Higher surface tension was also found to suppress foaming, and the co-existence of solid particles in the solution significantly increased the viscosity. Busolic et al.[8] investigated the recovery of iron from copper flash smelting slags with coke, which indicated the possibility of reducing FeO in the slag, but did not distinguish between the reduced Fe droplet and subsequent iron recovery. Heo et al.[9] discussed in detail the promotion of FeO reduction with carbon in similar CaO-MgO-SiO2-
Al2O3-FeO copper smelting slags at FeO contents above 50 mass pct during slag foaming, but differentiated between iron recovery and FeO reduction and observed suppressed iron recovery due to excessive foaming. Past literature on the reduction rate of FeO in slag by carbon identified slag foaming to accelerate reduction through the generation of CO gas from the C-FeO reaction, which strongly agitates the melt, increasing the liquid-phase mass transfer and subsequently the FeO reduction rate.[9,10] Generally, the reduction of FeO with c
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