Copper removal from carbon-saturated molten iron with Al 2 S 3 -FeS flux
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I.
INTRODUCTION
COPPER dissolved in steel as an impurity tends to bring hot shortness in the hot-rolling operation of the steelmaking process. Once copper is brought into molten iron, it is difficult to remove it economically. While recycling of scrap iron must be promoted along with efforts to decrease CO2 generation from iron blast furnaces, the quantity of recycled iron that can be used is restricted because it can contain considerable quantities of copper. Numerous ideas have been proposed for the removal of copper from molten iron, i.e., extraction by metal bath, preferential melting, vacuum distillation, and sulfide slagging.[1–11] The characteristics of these processes were summarized in detail in an article by Jimbo et al.[9] The method of sulfide slagging implies the copper extraction by sulfide fluxes containing FeS. The principle of this method is that FeS in the fluxes reacts with copper in molten iron and Cu2S generated by the reaction transfers into the sulfide fluxes. This method has been mainly investigated on each sulfide system, which consists of iron sulfide and a sulfide of an alkali metal or alkaline-earth metal such as the Na2SFeS,[1–11] Li2S-FeS,[11] and BaS-FeS[11] systems, where the sulfides of the alkali metals or alkaline-earth metals may play a role in decreasing the value of the activity coefficient of Cu2S in the flux phase. The Al2S3-FeS system has, nevertheless, not been examined yet, although some investiRYOKICHI SHIMPO, Research Associate, and OSAMU OGAWA, Professor, are with the Graduate School of Engineering, The University of Tokyo, 113, Japan. YUICHI FUKAYA, formerly Graduate Student, Graduate School of Engineering, the University of Tokyo, is with Ishikawajima-Harima Heavy Industries Co., Ltd., Tokyo, 135, Japan. TAKEHIRO ISHIKAWA, formerly Graduate Student, the University of Tokyo, Nippon Steel Co., Kimitsu Works, Chiba, 299-11, Japan. Manuscript submitted October 7, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
gators[1,9] have reported on the effects of the addition of Al2S3 to the flux of the Na2S-FeS system. In this study, the distribution of copper between carbon-saturated molten iron and the Al2S3-FeS flux has been examined in the temperature range from 1473 to 1673 K. A technique for recovering copper from the flux after having extracted copper from molten iron is also proposed, in which Cu2S in the flux can be reduced to Cu-Al-Fe alloy by the addition of metallic aluminum to the flux. The technique enables the iterative use of the flux for copper extraction from molten iron, and it will make copper removal from the molten iron more effective than with the use of other sulfide fluxes. II.
EXPERIMENTAL
A. Equilibrium between Carbon-Saturated Ferrous Alloy and Al2S3-FeS Flux An alloy of carbon-saturated iron containing copper was prepared by heating the mixture of electrolytic iron chips and reagent copper with graphite powder in a graphite crucible at 1473 K for 1 hour in a vertical electric furnace under a purified argon atmosphere. After separation from the cr
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