Recovery of Manganese Ferrite in Nanoform from the Metallurgical Slags
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pinel-type, transition-metal ferrites have obtained increasing interest because of their wide area of technological applications in magnetic recording,[1] energy conversion and storage,[2] gas sensing,[3] and biotechnology.[4–6] To produce the ferrite nanoparticles, different methods have been used (e.g., thermal decomposition of organometallic precursors or reduction of metal salts,[7] coprecipitation method, and the sol-gel route[8]). All these methods require pure reagents and energy consumption. The present work, however, shows the feasibility of the nanomanganese ferrite precipitation from the metallurgical wastes (metallurgical slags). Metallurgical plants produce millions of tons of slags every year. The main constituents of the slags are CaO, SiO2, Al2O3, MnO, FeO, and MgO. In Swedish and Ukrainian steelmaking practice, FeO content in the slag may reach up to 30 pct in some cases. These slags are only partially used in civil engineering, and the rest remains in dumps, increasing environmental burdens. The current authors proposed a way to recover iron from the liquid slags in the form of magnetite.[9] The concept was based on transformation of nonmagnetic ANNA SEMYKINA, 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] SESHADRI SEETHARAMAN, Professor, is with the Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm, Sweden, and Head of the Materials Process Science Division, Royal Institute of Technology, Stockholm, Sweden. Manuscript submitted September 2, 2010. Article published online December 7, 2010. 2—VOLUME 42B, FEBRUARY 2011
wu¨stite (FeO) to magnetic magnetite (Fe3O4) using an oxidizing atmosphere. Experiments on the ternary CaOFeO-SiO2 and quaternary CaO-FeO-SiO2-MnO systems, followed by thermodynamic and kinetic modeling, were performed.[10,11] The crystal precipitation during synthetic slag oxidation was observed using confocal scanning laser microscopy.[12] Precipitated phases were magnetite and manganese ferrite in the spinel form. From the technological point of view, the slag can be subjected to oxidation or cooling. The solid slag may be crushed and the magnetic part, consisting of magnetite/ manganese ferrite, can be separated by the magnetic method and can be used again. The rest of the slag (nonmagnetic) effectively will be used in the production of a cement binder or in other applications. Alternatively, magnetite/manganese ferrite can be extracted from molten slags using crossed electric and magnetic fields. The cold model simulation of the particle movement in a conducting liquid under electromagnetic buoyancy force was investigated by the present authors earlier.[13] Theoretical application of the obtained data on the real magnetite particle–liquid slag system showed that magnetite will move with an approximate velocity of 0.1 to 2.5 mm/min. The current work focuses on investigating the processin
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