Kinetics of the Carbothermic Reduction of Manganese Oxide from Slag
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INTRODUCTION
PAST studies[1,2] by the authors on the silicothermic reduction of MnO from slag were conducted to better understand the reduction mechanism and provide data to support direct or reductive alloying as a method for manganese addition to 3rd Generation Advanced High-Strength steels (3G AHSS). Should direct alloying processes prove feasible for material addition, an opportunity exists for significant economic improvements related to the production of the 3G AHSS.[3] Direct or reductive alloying is a proposed method of alloying element addition to steel; in the current case manganese ore can be added to slag in-situ and reduced with reductants such as silicon or carbon.[4–7] Such additions avoid (or offset) ferroalloy requirements saving producers the need to purchase finished product to add in the ladle. The current work addresses the fundamental reduction process of MnO by high-carbon iron. Previous work by two of the current authors[1] showed evidence that the reduction of (MnO) by [Si] was under mixed
B.J. JAMIESON is with McMaster University, Hamilton, ON L8S 4L8, Canada and also with the ArcelorMittal Global R&D Hamilton, Hamilton, ON L8H 3N8, Canada. M. BARATI is with the University of Toronto, Toronto, M5S 3H7, Canada. K.S. COLEY is with McMaster University and also with Western University, London, ON N6A 3K7, Canada. Contact e-mail: [email protected] Manuscript submitted February 19 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
mass transport control in the regime of study; the greatest contributor to transport resistance was MnO mass transport in the slag; however, this alone did not fully explain the rate controlling process for the system. It was proposed that [Si] transport in the metal also had an impact on the reduction rate. In contrast to the authors’ past work, the carbothermic reduction of MnO is a much more widely studied topic than that of silicothermic reduction. However, across a wide range of studies there is significant variation in the described mechanism for the reaction. Some authors have concluded that chemical reaction controls the rate.[8–11] Others provided evidence of control by mass transport of manganese ions in the slag.[12–14] Another group of authors analyzed the systems assuming mixed mass transport control of manganese in the metal and manganese ions or oxygen in the slag.[15–17] All authors ultimately provided evidence for their assumed controlling step. All studies were conducted using experiments where a layer of slag rests atop a layer of metal, and with a greater metal volume than slag volume. The goal of the present study is to document the rate of reduction of MnO by carbon dissolved in liquid iron droplets. Compared to past literature, where flat bath experiments are more representative of reactions occurring directly between the metal bath and slag layer of a reactor, the present study represents metal droplets ejected into bulk slag and slag foam. Further, findings here will be compared to past work by the authors on the silicothermic reduction of MnO from
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