Kinetics of manganese ore reduction by carbon monoxide
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I. INTRODUCTION
DURING industrial production of ferro- or silicomanganese, an important part of the reduction process takes place in the upper parts of the furnace, where carbon monoxide generated in the melting zone ascends and reacts with solid ore particles. Higher manganese oxides of the ore are reduced to the divalent oxide; further reduction is not thermodynamically feasible. Among other important gas-solid reactions taking place are the reduction of iron oxides, the Boudouard reaction, the decomposition of carbonates, and the cyclic reactions of alkalis. Together, these reactions have a big impact on the carbon and energy consumption of the process.[1] The mechanical strength of the solid reaction products is another important factor for the running of the furnace. Under certain circumstances, some solids may disintegrate, causing close packing of the charge and an uneven distribution of gas flow. In order to investigate the behavior of a furnace charge mixture, a natural first step is to provide knowledge about how each type of solid reacts under relevant conditions. In the literature, information may be collected about the Boudouard reaction[2] and the decomposition of carbonates.[3] Gaseous manganese oxide reduction is also described to some extent,[4,5,6] but the results of different investigators vary considerably and no convincing conclusions have been made on the reduction above 500 8C. Therefore, the present project was aimed at obtaining an extensive knowledge about how different ores react with carbon monoxide. Such information may subsequently be put into a packed bed model of the charge mixture, as outlined by Szekely et al.[7] The most significant ore-producing countries today are South Africa, China, Ukraine, Brazil, Australia, India, and Gabon. The largest landbased reserves (78 pct) are found in South Africa (the Kalahari field). South African ores and Australian ores (Groote Eylandt) are the most common ores used by the Norwegian ferroalloy industry, and these are K.L. BERG, formerly Ph.D. Student with the Department of Materials Technology and Electrochemistry, Norwegian University of Science and Technology, is currently studying Pedagogics. S.E. OLSEN, Professor, is with the Department of Materials Technology and Electrochemistry, Norwegian University of Science and Technology, 7491 Trondheim, Norway. Manuscript submitted January 19, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS B
the ones that were chosen for the present investigations. The mineralogy of the South African ores is dominated by manganese silicates, i.e., the braunite group.[8] The most commonly known forms are regular braunite and braunite II, whose chemical formulas are shown in Table I. In addition, there is a form similar to braunite II containing less calcium and silicon, called “braunite (new).” Other important manganese minerals of the Kalahari field are bixbyite and hausmannite. The Groote Eylandt ores are quite different from the Kalahari ores. The minerals found here are predominantly pyrolusite and cryptomelane
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