Effect of CaF 2 Addition on the Silicothermic Reduction of MnO in Ferromanganese Slag
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HIGH carbon ferromanganese (HCFeMn) slag generally contains about 40 mass pct MnO, which is used as a raw material in the molten state to produce ultra-low phosphorus FeMn (ULPFeMn) alloys by the reaction between the HCFeMn slag and silicomanganese (SiMn) alloy melt.[1] Understanding the silicothermic reaction kinetics is very important in the production of ULPFeMn not only to increase the process efficiency but also to lower the operating cost. For the present system, viz. for the silicothermic reduction of MnO in HCFeMn slag (the so-called the MnMSi exchange reaction), the rate of SiO2 formation and transportation (from slag-metal interface to bulk slag) is linked to that of MnO reduction and transportation (from bulk to slag-metal interface) in the slag phase. In previous articles,[2–8] because Si is a deoxidizer or impurity, the oxidation kinetics of Si in liquid metals, e.g., deoxidation and desiliconization (de-Si) behavior, have frequently been studied. Furthermore, several authors have investigated the reduction behavior of specific oxides in molten slag by Si in liquid metals.[8–14] However, the kinetics of the formation and transportation behavior of SiO2 in the slag phase has not been systematically investigated since SiO2 is only a reaction JUNG HO HEO, Graduate Student, and JOO HYUN PARK, Professor, are with the Department of Materials Engineering, Hanyang University, Ansan 426-791, Korea. Contact e-mail: basicity@hanyang. ac.kr YONGSUG CHUNG, Professor, is with the Department of Advanced Materials Engineering, Korea Polytechnic University, Siheung 429-793, Korea. Contact e-mail: [email protected] Manuscript submitted December 27, 2013. Article published online April 7, 2015. 1154—VOLUME 46B, JUNE 2015
product so that it was not considered as a critical factor affecting the reaction kinetics. Hence, we examined the oxidation behavior of Si herein. Fundamental studies on the de-Si and oxidation kinetics of Si in liquid metal have been performed previously.[2–8] The de-Si reaction was studied at different temperature ranges using a mathematical model with variation in the initial content of Si, slag composition, and amount of slag.[5] The rate controlling step of the de-Si process was the mass transfer of Si in the metal phase when FeO content in the slag was greater than 35 to 40 mass pct,[2,7] whereas the reaction was controlled by both mass transfer of Si in the metal phase and that of FeO in the slag phase when FeO content was lower than 40 mass pct.[2–4] Similar results were obtained in a subsequent study.[6] Also, the activation energy of the de-Si reaction was estimated to be approximately 197 kJ/mol,[8] from which the mass transfer of SiO2 and/or ZnO in the slag phase was proposed as a rate controlling step. The important findings of the previous studies of the oxidation of Si are summarized in Table I. We also thoroughly reviewed the literature on the reduction behavior of MnO in multi-component slag systems.[9–19] These studies provide important information including the rate controlling step and the
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