Carbothermic Reduction of Chromite Ore Under Different Flow Rates of Inert Gas
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ERROCHROME and charge chrome are produced in the submerged-arc furnace (SAF). Carbon is the reducing agent employed to reduce the oxides of chromium and iron. The heat required for the reduction reaction is supplied through electrical energy. The increasing cost of electrical power has led to efforts to reduce the oxide outside the SAF using cheaper sources of heat such as fossil fuels. Carbon is still used as the reducing agent. The ‘‘prereduced’’ ore is charged into the SAF to produce ferrochrome. These processes of prereduction usually operate at about 1673 K to 1773 K. A process that operates at low temperatures will have several advantages, such as less operational cost, less capital cost, and increased life of refractory used in the ‘‘prereduction’’ furnace. Parameters such as particle size, ore/coke ratio, use of catalysts, etc. can be controlled to enhance the reducibility of the ore and make the process viable at low temperatures. One parameter that can have a significant influence on the rate of reduction of the ore is the flow rate of inert gas over the reaction zone. However, no information is available in literature on the influence of the flow rate of inert gas on the rate of reduction of chromite ore. Experiments were carried out to explore the influence of the flow rate of inert gas on the reducibility of chromite ore. DOLLY CHAKRABORTY, formerly Research Fellow with the National Metallurgical Laboratory, Jamshedpur 831 007, India, is now Lecturer with the Department of Engineering Chemistry, B.A. College of Engineering and Technology, Jamshedpur 832 304, India. S. RANGANATHAN, Deputy Director, is with the National Metallurgical Laboratory, Jamshedpur 831 007, India. Contact e-mail: [email protected]. S. N. SINHA, Head, is with the Department of Metallurgical Engineering and Materials Science, National Institute of Technology, Jamshedpur 831 014, India. Manuscript submitted December 25, 2008. Article published online September 15, 2009. 10—VOLUME 41B, FEBRUARY 2010
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REDUCTION OF CHROMITE ORES
The solid-state reduction of chromite ores under different conditions has been studied by several investigators.[1–24] The chromite ores have a spinel structure that can be represented by the general formula (Fe,X)OÆ(Cr,Y)2O3. Here, X and Y are elements that dissolve in the two different cationic sublattices. The two lattices are the octahedral and tetrahedral sites in the structure, respectively. Divalent cations such as Mg2+ occupy the tetrahedral sites, and trivalent cations, such as Al3+, Fe3+ etc., occupy the octahedral sites. Iron can be present in either of the two sublattices. Iron gets reduced early, ahead of chromium. Iron forms the carbide Fe3C, which acts as a reducing agent to enhance the rate of reduction of chromium. In the later stages of reduction, the complex carbides of iron and chromium are formed. It is observed that the higher the (Fe/Cr) ratio of the ore, the higher is its reducibility.[5,8] This is attributed to the formation of Fe3C, which acts as a reducing agent. It has been obse
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