The Kinetics of Oxidation of Liquid FeO-MnO-CaO-SiO 2 Slags in Air
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NTRODUCTION
SLAG from the first stage of electric arc furnace (EAF) contains a significant amount of FeO, up to 30 mass pct in the Swedish and Ukrainian steelmaking industries. It is important to maximize the amount of iron that is recovered from this slag so that the remaining portion can be used for civil engineering purposes. To find a practical solution, joint efforts were made at the Royal Institute of Technology, Sweden and National Metallurgical Academy of Ukraine as a part of the eco-steelmaking national project in Sweden. The phase equilibria for the slag systems containing iron oxides were studied by Turkdogan,[1] Bodsworth and Bell,[2] and Kongoli and Yazawa.[3] Muan and Osborn[4] reported the phase diagrams for the FeOMnO system in a low oxygen pressure as well as FeOMnO-SiO2 system in CO2/H2 and air atmospheres. A structural model for binary silicate systems including MnO-SiO2 and CaO-SiO2, as well as thermodynamics of Fe3O4–Mn3O4 spinels are presented in work of Pelton et al.[5,6] Pownceby et al.[7] analyzed the effects of basicity on the phase equilibria of Fe2O3-CaO-SiO2 in air at 1513 K to 1573 K (1240 °C to 1300 °C). Zhang et al.[8] presented an oxidation mechanism of CaOFeOx-SiO2 slag with high iron content in pure oxygen atmosphere. Sun and Jahanshahi[9] summarized measurements of redox equilibria in the slags involving Fe, Mn, Ti, and V transition metals, as well as the kinetics of CO-CO2 reactions with slags. ANNA SEMYKINA, PhD and Senior Researcher, is with the Royal Institute of Technology, SE-100 44 Stockholm, Sweden, and with the National Metallurgical Academy of Ukraine, Dnipropetrovsk 49600, Ukraine. Contact e-mail: [email protected]; asemykina@gmail. com Manuscript submitted July 22, 2010. Article published online September 15, 2011. 56—VOLUME 43B, FEBRUARY 2012
The previous work by the author focused on the oxidation of FeO in the slag toward the recoverable magnetic form.[10] A thermogravimetric analysis (TGA) and confocal scanning laser microscopy (CSLM)[11,12] were used to investigate the oxidation kinetics and formation of the magnetite particles. As a continuation of the previous work,[10–12] the kinetics of the crystal precipitation from the liquid FeOMnO-CaO-SiO2 slags was investigated by the CSLM.[13] Successive CSLM video images showed that crystals grew and agglomerated, reaching 50 lm in length in some cases. Different shapes of crystals were observed at different temperatures. The results from a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS) showed the presence of calcium silicate and spinel containing manganese ferrite and magnetite. The current work focused on kinetic studies of the FeOMnO-CaO-SiO2 slag systems under oxidizing conditions using a TGA. The experimental temperature range was 1500 K to 1600 K (1227 °C to 1327 °C). Air was used to produce an oxidizing atmosphere.
II.
THERMODYNAMIC ANALYSIS
The current work investigated the oxidation of liquid FeO-MnO-CaO-SiO2 slags in air. The slag compositions studied are presented in Table I
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