Upgrading of Low-Grade Manganese Ore by Selective Reduction of Iron Oxide and Magnetic Separation
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MANGANESE is an element of considerable importance for the steelmaking industry. During the steelmaking process, it is added as a desulfurizer, a deoxidizer, or an alloy additive in such forms as ferromangese, silicomanganese, and manganese metal, all of which are produced from manganese ores. Manganese ores are classified by their Mn contents, as shown in Table I.[1] The intensive mining of high-grade manganese ores has brought about the unavoidable problem of utilizing the low-grade ores. There are several physicochemical differences among the components in manganese ores, which can be used for the enrichment of manganese. In particular, for the abundant manganese ores containing iron oxide, it is not thermodynamically possible to reduce manganese oxides beyond MnO by carbon or carbon monoxide at temperatures from 673 K to 1273 K (400 C to 1000 C), while the iron oxide can be reduced to magnetite (Fe3O4) or metallic iron. The latter two are strongly magnetic, while the manganese
YUBO GAO and M. OLIVAS-MARTINEZ, Graduate Students, and H.Y. SOHN, Professor, are with the Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112. Contact e-mail: [email protected] HANG GOO KIM, formerly Research Associate Professor with the Department of Metallurgical Engineering, University of Utah, is now Director of Technology Research Institute, POSCO MTech, Pohang, South Korea. CHAN WOOK KIM, Research Manager, is with the New Materials Research Department, Research Institute of Industrial Science and Technology, Pohang, South Korea. Manuscript submitted March 14, 2012. Article published online September 26, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS B
oxides are weakly magnetic or non-magnetic. Therefore, the ferruginous low-grade manganese ore may be upgraded by selective reduction and magnetic separation. For the upgrading of ferruginous low-grade manganese ore by magnetic separation, several studies[2–4] on selective reduction using solid carbon have been reported. In comparison with solid carbon, reduction by CO may result in a faster rate even at a lower temperature, owing to the advantages of gaseous reduction over carbothermal reduction.[5] Up to now, little research has been carried out on the gaseous reduction of manganese ore by CO, and a further study on selective reduction by CO is essential to develop effective and suitable techniques for the beneficiation of ferruginous low-grade manganese ores. If manganese enrichment by such an upgrading process is performed, there is an additional benefit that the resulting lower oxides Fe3O4 and MnO require less reducing agent and fuel than Fe2O3 and MnO2 in the subsequent smelting process for the production of manganese alloy. The pre-reduction for upgrading can also utilize the off-gas from the smelting furnace itself. The objective of this work was twofold: (a) to test the feasibility of upgrading ferruginous low-grade manganese ore by selective reduction by CO followed by magnetic separation and (b) to determine the main operating paramete
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