Kinetic Investigations of SiMn Slags From Different Mn Sources
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The results show that the choice of raw materials in the charge considerably affected the reduction rate of MnO and SiO2. The highest reduction rate was found to be from charges using HC FeMn slag. The difference in the driving forces was insignificant among the SiMn slags, and the similar slag viscosities could not explain the different reduction rates. Instead, the difference is attributed to small amounts of sulfur and the amount of iron in the charge. In addition, the rate models were applicable to describe the reduction of MnO and SiO2 in SiMn slags. https://doi.org/10.1007/s11663-018-1238-3 The Minerals, Metals & Materials Society and ASM International 2018
I.
INTRODUCTION
THE production of ferromanganese (FeMn) and silicomanganese (SiMn) is an important process due to its contribution to the steel producing industries. It is well known that Mn as an alloying unit enhances the strength, toughness, and hardness of steel products, and that both Mn and Si are excellent deoxidizers which prevent porous structures.[1–8] Also, there is an increasing trend of more use for SiMn. SiMn is a more effective deoxidizer and adds less phosphorus, carbon, aluminum, and nitrogen to steel than FeMn.[2] The standard SiMn alloy typically contains approximately 70 wt pct Mn, 18 to 20 wt pct Si, and 10 wt pct Fe.[2] While manganese thermodynamics have been studied intensively over the past two decades,[2,9] kinetic information for the SiMn process is scarce.[10,11] The absence PYUNGHWA PEACE KIM and MERETE TANGSTAD are with the Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway. Contact e-mail: [email protected] Manuscript submitted December 5, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
of kinetic information increases the ambiguity of the reduction mechanisms, and it is not clear how different raw materials affect the reduction of MnO and SiO2 in the SiMn process. The metal-producing reactions in the SiMn process are described by the following reactions: MnOðlÞ þ C ¼ MnðlÞ þ COðgÞ
SiO2ðlÞ þ 2C ¼ SiðlÞ þ 2COðgÞ : Previous studies have shown that both MnO and SiO2 reduction becomes significant above 1773 K (1500 C).[12,13] The mass loss observed in a Thermogravimetric analysis (TGA) indicating MnO and SiO2 reduction was insignificant until 1773 K (1500 C), but increased drastically at higher temperatures. Therefore, the present study focuses on estimating the kinetic parameters, such as activation energies and rate constants, in different SiMn slags (MnO-SiO2-CaOMgO-Al2O3) between 1773 K and 1923 K (1500 C and 1650 C). The main goal is to describe the reduction rates of MnO and SiO2 in SiMn slags from raw material Mn sources such as Assmang ore and HC FeMn slag (High-Carbon Ferromanganese slag).
II.
THEORETICAL CONSIDERATIONS
Previous studies have shown that the reduction rate of MnO in ferromanganese (FeMn) slags can be described by Eq. [1], which implies that the chemical reaction is the rate-determining step.[2,9] SiMn slags
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