The reduction of zinc from slags by an iron-carbon melt
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I.
INTRODUCTION
T H E R E is currently much interest in the process for smelting iron ores known as "reduction smelting," "direct smelting," or "bath smelting." In the process, iron is produced by adding ore or partially reduced ore directly to a molten bath of high-carbon iron. Process heat is generated in the bath by injecting a fuel (coal, oil, or natural gas) and air or oxygen through tuyeres or a lance. Several versions of the process have reached the large pilot-plant stage of development. ~-4] In one variant, [5] chromite ore is charged with iron ore to produce a highcarbon chromium alloy which is subsequently refined to stainless steel in the same reactor. In these reactors, the generation of heat within the bath by combustion ensures high heat-transfer rates to the bath, and the gases promote stirring which results in high masstransfer rates. The throughput per unit volume of such intense reactors, therefore, is potentially very high. The high carbon content of a bath of molten iron makes the bath a powerful reducing medium and, in principle, oxides other than those of iron could be reduced. Apart from producing ferrochromium and other ferroalloys, there is the largely unexplored possibility that an iron-carbon bath could be used for reducing oxides of nonferrous metals. In practice, however, the number of such applications is probably fairly limited. Most metals, including the common base metals copper, nickel, and tin, have substantial solubilities with iron and could not be produced in a pure form. Lead is effectively immiscible with iron and could be formed as a separate liquid phase or as gas, according to the process conditions. Zinc is miscible with iron, but at atmospheric pressure, it volatilizes. The present work was motivated by the possibility of reducing zinc and lead oxide materials commercially, W.J. RANKIN, Director, is with the G.K. Williams Centre for Extractive Metallurgy, Department of Chemical Engineering, University of Melbourne, Parkville, VIC, 3052, Australia. S. WRIGHT, Experimental Scientist, is with the Division of Mineral and Process Engineering, CSIRO, Clayton, VIC, 3168, Australia. Manuscript submitted September 12, 1988. METALLURGICAL TRANSACTIONS B
using an iron bath as t h e reducing medium. Potential feedstocks for such a process include zinc calcine, zinclead sinter, dusts and fume from iron and steelmaking plants, and high-zinc and/or lead slags from Sirosmelt, Kivcet, or QSL reactors. In the present investigation, the kinetics and mechanisms of reduction of zinc from slags having a high zinc concentration were examined in the laboratory. Reduction with solid carbon and reduction in the presence of an iron bath were both examined so that a comparison of the two could be made. The slag contained a small amount of lead and copper in addition to zinc, and some information on the reduction of these in the presence of an iron bath was also obtained. II.
EXPERIMENTAL
A. Raw Materials
Granulated lead blast furnace slag having the composition shown in Table I was used for
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