Kinetics of the dissolution of zinc sulfide in an oxidizing slag
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I.
INTRODUCTION
THE modern
methods of zinc production--electrolytic and Imperial s m e l t i n g - - a r e highly energy-intensive. Apart from this, the electrolytic process uses high-grade zinc concentrates and an expensive form of energy (electric power) and is facing the most difficult environmental problem for the disposal of large amounts of solid w a s t e - jarosite, goethite, or hematite. However, the Imperial Smelting Process (ISP) uses less energy than the electrolytic processm and is suited to the treatment of a wide range of relatively low-grade and complex materials. Its major drawback is that it utilizes a sinter plant from which it is difficult to prevent particulates and fume in the workplace atmosphere. The production of sinter requires strict control of composition of feed for good quality sinter and involves extra expenses. The ISP requires metallurgical coke as both fuel and reductant, which is also an expensive raw material. There is therefore an urgent need to develop a process for zinc production that uses less energy than existing processes and simplifies problems of environmental control without requiring excessive capital investment. Keeping these factors in mind, laboratory-scale trials have been carried out for developing a new pyrometallurgical process. This process can use a wide variety of zinc concentrates involving complex concentrates, solves the environmental problems, and requires a low capital investment as compared to the current processes. It is a two-stage process involving the oxidation of zinc sulfide to oxide and dissolution into slag and then fuming of zinc from the slag by injecting carbonaceous materials into it to produce zinc vapors. These vapors may be condensed in a similar type of leadsplash condenser such as in operation in the ISP or zincsplash condenser. The proposed process would avoid two liabilities of the I S P - - t h e need to agglomerate the feed and the need for very expensive lump coke. The gas resulting from the reactions in the second stage would be richer in zinc than I S P gas and could be condensed in a lead-splash condenser without reoxidation and with a much lower rate of lead circulation than currently used for lean ISP DR. SURESH K. G U P T A , is with the G.K. Williams Centre for Extractive Metallurgy, Department of Chemical Engineering, Melbourne University, Parkville, Victoria 3052, Australia. Manuscript submitted M a y 30, 1989. METALLURGICAL TRANSACTIONS B
gas (--7 pet Zn). The condenser off-gas would be a much richer fuel than the low calorific value gas ( - 2 1 pct CO) from the ISP and could be burned in a boiler to produce surplus steam or electric power. Therefore, this process has a very large energy advantage over the existing process. A number of experimental investigations on the different aspects of oxidation of zinc sulfide have been reported in the literature, t2-341 However, there is no study available as far as it is known on the kinetics of oxidation of zinc sulfide to zinc oxide and its dissolution into a slag. This stud
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