Microscopic Study of Carbon Surfaces Interacting with High Carbon Ferromanganese Slag
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RODUCTION
HIGH carbon ferromanganese (HCFeMn) is commonly produced in submerged arc furnace. In this process, manganese oxides in the form of lump ore, sinter, etc., are generally reduced to MnO directly by CO gas. In the coke bed area of the furnace, where the process heat is generated by graphite electrodes, manganese is mainly produced through the interaction of a high MnO-containing silicate slag with carbon: ðMnOÞ þ CðsÞ ¼ Mn ðlÞ þ COðgÞ DG½1573 K to 2073 K ð1300 C to 1800 CÞ ¼ 288 0:17T kJ
½1
The rate of chemical Reaction [1] is important in HCFeMn process, which is a process rate limiting step. It is worth mentioning that in the process a molten metal saturated of carbon is also in contact with the slag down in the furnace and the dissolved carbon in metal can also reduce the slag. The kinetics and mechanism of MnO reduction from slags by the dissolved carbon in liquid Fe and Fe-Mn melts has been studied in the past. It has been observed that the rate of MnO reduction is not affected by the melt stirring,[1] while it is affected by the slag chemical composition.[1–3] The rate of MnO reduction by the Fe-Mn-C melts containJAFAR SAFARIAN, Researcher, is with the SINTEF Materials and Chemistry, Alfred Getz Vei 2, 7465 Trondheim, Norway. Contact e-mail: [email protected] LEIV KOLBEINSEN, Professor, is with the Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), Alfred Getz Vei 2, 7491 Trondheim, Norway. Manuscript submitted April 25, 2014. Article published online September 12, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
ing lower Mn concentrations and higher C concentrations is higher as studied for the reduction of high MnO-slags.[4–6] The kinetics of MnO reduction is not affected by changing the ambient pressure,[3] while it is increased with increasing temperature.[1,2,4,5] An appropriate mechanism for MnO reduction by the dissolved carbon which can explain the effect of various process parameters was proposed by Pomfret and Grieveson.[3] According to this mechanism, MnO reduction by the dissolved carbon takes place through the following simultaneous sub-reactions: At slag=metal interface : ðMnOÞ þ Fe ¼ ðFeOÞ þ Mn ½2 At slag=gas interface : ðFeOÞ þ COðgÞ ¼ Fe þ CO2 ðgÞ ½3 At metal=gas interface : C þ CO2 ðgÞ ¼ 2COðgÞ
½4
A significant amount of gas is produced in the system and the gas bubbles that grow at the slag/metal interfacial area create the metal/gas and slag/gas interfaces. A kinetic model for MnO reduction by the dissolved carbon in iron was developed by the authors previously[7] and activation energy as 90 kJ/mol for MnO reduction was determined. The kinetic and mechanism of MnO reduction by solid carbon has been studied through several studies.[8–13] The effect of process parameters on the rate of MnO reduction from high MnO-containing slags is mostly similar to the studies on the reduction by the dissolved carbon in the metal phase. Solid carbon material is important in VOLUME 46B, FEBRUARY 2015—125
HCFeMn process and the
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