Large amounts of silicomanganese slag are generated and discarded from the silicomanganese alloy smelting furnaces that treat ferromanganese slag to produce silicomanganese alloy, which contain 10-14 mass% Mn. It is thus important to find a possibility for recovering manganese from silicomanganese slag in terms of environmental and economic points of view. Upgrading of manganese from the silicomanganese slag for recycling the slag back to the silicomanganese furnaces must be necessary to decrease the slag volume which causes irregularities in their operation. In this study, a physical separation process for the upgrading of manganese from silicomanganese slag discarded has been suggested. The process first grinds silicomanganese slag between À500 mm and +75 mm, followed by the dry magnetic separation process to separate and concentrate manganese from the ground slag. Based on the results obtained, a manganese rich slag which contains over 20 mass% manganese was calculated to be separated and concentrated from silicomanganese slag under a magnetic field of about 6,000 Tesla using the proposed process. The manganese rich slag obtained should be used as a manganese resource for manufacturing silicomanganese alloy.

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Manganese dust which contains significant amounts of manganese, zinc and potassium is collected from the off-gas during manufacturing ferromanganese and silicomanganese alloys at Dongbu Metal Company in Korea. The removal of zinc and potassium from the manganese dust is very important in the process for recycling the dust back into the ferromanganese smelting furnace. This is because the potential accumulation of zinc and potassium in the smelting furnace can cause irregularities in the operation of the smelting furnace. In this study, the reductionvolatilization reaction of the zinc oxide contained in the manganese dust with carbon was examined at reaction temperatures between 923 and 1323 K in nitrogen atmosphere using a thermogravimetric method. The results of experiments on the kinetics of the reaction are presented in this paper. Experimentally, the rate of this reaction was demonstrated by the removal of 99% zinc in 20 min at 1198 K under a carbon addition amount of 9 mass%. The reduction-volatilization reaction started at above 973 K and proceeded very fast at above 1023 K. Furthermore, manganese and iron oxides in the dust was partially reduced during the reaction. The shrinking-core model for a surface chemical reaction control was found to be useful in describing the reduction-volatilization reaction rate, which had an activation energy of 173 kJ/mol (41.3 kcal/mol).

A new process for utilizing low grade zinc sulfide concentrate containing a large amount of iron as a zinc and iron resource has been developed in Korea. The process largely consists of oxidative roasting and reduction-volatilization processes. In this process, zinc is recovered as zinc oxide form in the gas phase and iron is concentrated as partially reduced iron oxide compounds in the residue phase. In the present work, a kinetic study on the oxidative roasting of low grade zinc sulfide concentrate rich in iron obtained after several mineral separation processes at Gagok mine in Korea was experimentally investigated. The experiments were carried out to understand the oxidative roasting process of the zinc concentrate over a temperature range of 998 to 1073 K under air using a thermogravimetric method. The oxidative roasting rate of the zinc concentrate was found to be relatively fast under the whole temperature range and almost 95% of sulfur contained in the concentrate was removed after the oxidative roasting at 1073 K for 20 min. Sulfur removal ratio as a function of time has been analyzed by using a spherical shrinking-core model.