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.
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 −500 μm and +75 μm, 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.
동정광으로 동을 제련하는 동제련소에서는 대략 35-45%정도 철을 함유한 폐동슬래그가 다량 배출되어 대부분 폐기처분되고 있다. 따라서 폐동슬래그로부터 철을 회수하여 철을 자원화하는 것은 자원의 효율적인 활용측면과 환경문제를 감소하는 측면에서 관심이 크게 증대되고 있다. 본 연구에서는 동제련소에서 발생되는 다량의 철 성분이 포함된 폐동슬래그로부터 철의 품위향상을 위한 physico-chemical 분리 공정이 개발되었다. 개발된 공정은 먼저 폐동슬래그를 1 mm이하로 파쇄하는 공정(1차 파쇄공정)과, 이어서 $1225^{\circ}C$에서 90분 동안 탄소 환원하는 공정(탄소 환원공정), 그리고 환원된 슬래그로부터 $104{\mu}m$ 이하로 2차 파 분쇄하는 공정(2차 파쇄공정)과, 이어서 철 농축물을 분리 회수하는 습식자력선별 공정(습식 자력선별공정)으로 구성된다. 개발된 공정을 이용하여 환원된 폐동슬래그를 0.2 T의 자력세기에서 습식자력선별 함으로써 철 품위가 66 wt.%인 철 농축물을 얻었고, 같은 조건에서 철 회수율은 72%이었다. 따라서 분리 회수된 철 농축물은 철 원료로 사용될 수 있을 것으로 판단된다. A large amount of waste copper slag containing about 35 ~ 45% iron has been generated and discarded every year from pyrometallurgical processes for producing copper from copper concentrate. Thus, recovery of iron from the waste copper slag is of great interest for comprehensive use of mineral resource and reduction of environment problems. In this study, a physico-chemical separation process for upgrading iron from the waste copper slag discharged as an industrial waste has been developed. The process first crushes the waste copper slag below 1 mm (first crushing step), followed by carbon reduction at $1225^{\circ}C$ for 90 min (carbon reduction step). And then, resulting material is again crushed to $-104{\mu}m$ (second crushing step), followed by wet magnetic separation (wet magnetic separation step). Using the developed process, a magnetic product containing more than 66 wt.% iron was obtained from the magnetic separation under a magnetic field strength of 0.2 T for the waste copper slag treated by the reduction reaction. At the same conditions, the percentage recovery of iron was over 72%. The iron rich magnetic product obtained should be used as a iron resource for making pig iron.
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 reduction-volatilization 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).
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