The reaction between iron oxides and carbon was experimentally studied at temperatures higher than 1473 K employing solid carbon or carbon dissolved in liquid iron as a reducing agent. Iron oxides–carbon composite pellets were submitted to thermogravimetric analysis under inert gas in the range 1473–1623 K; the carbon was in the form of graphite, coke fines and charcoal. It has been determined that the type of carbonaceous material has little effect in the reaction rate at high temperatures. The activation energies obtained varied from 46 to 120 kJ/mol, well below the ones obtained at lower temperature ranges, and it is proposed that at high temperatures the controlling mechanism of the reaction is heat transfer. Composite pellets and fired or cold bonded iron oxide pellets were also added to iron–carbon baths in the temperature range 1573–1912 K. It has been found that up to 1711 K the composite pellets present reaction times significantly shorter than the pure oxide pellets, whereas at higher temperatures the reaction times of both pellets are similar.
During stainless steel production in an electric arc furnace, the dust generated amounts to around 1% of the charge weight. This dust contains chromium, zinc and other heavy metal oxides; therefore, its final disposal in special landfill sites is expensive. On the other hand, the content of chromium oxide (~9 wt%), nickel oxide (~2•5 wt%) and iron oxides (~47 wt%) can be recovered by reduction with carbon or Fe-Si. In this paper, the dust was physically and chemically characterised, and used in the manufacture of composite pellets with carbon and Fe-Si. These pellets were added to iron-carbon melts at a temperature around 1600°C. After smelting-reduction, the recovery yields of Cr, Ni, and Fe were determined. These yields were: (i) with Fe-75%Si as reductant -Ni ~90%, Cr ~90%, Fe ~90%; and (ii) with coal as reductant -Ni ~12%, Cr ~35%, Fe ~90%). A preliminary economic evaluation for Brazilian conditions showed that the process is sustainable depending on the landfill cost for dusts and the availability of inexpensive Fe-Si. When coal is used as reductant, the electric energy becomes the main cost component and the above recycling process becomes economically feasible with landfill costs higher than US$ 150 t -1 .
Iron-carbon nuggets can be obtained by high temperature reduction of iron ore by carbonaceous material when both are agglomerated together as a carbon composite pellet. During this process, the stable oxides contained in the materials will form a slag. This work investigates the effect of this slag composition on iron nugget formation. Pellets were prepared with iron ore and two different carbonaceous materials. Through the addition of Portland ® cement, silica and alumina the slag composition was varied to adjust the expected liquidus temperature to 1573 and 2273 K. It has been shown that the formation of iron nuggets is favored for slags presenting low liquidus temperature. In order to further investigate this phenomenon, pellets containing iron powder and carbonaceous material, together with previously prepared slags, were also submitted to high temperature, and it has been shown that iron carburization depends on slag composition.
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