The kinetics of S 35 exchange between SO 2 /CO/CO 2 gas mixtures and copper sulfide melts at 1523 K
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INTRODUCTION
THE reaction of oxygen with
metal sulfide melts is the basis of production of a number of base metals from their sulfides. While much is known of the equilibrium thermodynamics of these systems, the kinetics of the chemical reactions involved have yet to be characterized. The high utilization of oxygen in industrial copper converters indicates that these reactions are fast compared with transport processes in the gas or melt. This view has been confLrmed in laboratory studies in which melts are suspended in flowing gas streams, tl-6] gas jets are directed at the surfaces of the melts, t71 and sulfides are mixed with molten oxides, t81 The above techniques are dynamic experiments in that they involve the net removal of sulfur from the system, for example, through the overall reaction Cu2S (1) + 02 (g) ~ 2Cu (1) + SO2 (g)
[1]
The approach taken in the present study is significantly different from those quoted above in that the melt and the gas phase are in chemical equilibrium. Under these conditions, there is no net sulfur removal from the system but, rather, the transfer of labeled sulfur species, in the form of S 3s radioisotope, from the melt to the gas phase. The kinetics of the reaction are followed by measuring the rate of transfer of labeled species to the gas phase. Sulfur-35 is a 100 pct/3 emitter, t9] having a halflife of 87.4 days. The change in concentration of S 3s atoms in the gas phase can therefore be followed using a suitable radiation detector device, in this case, a GeigerMiiller (G-M) tube. The oxygen potentials of the gas mixtures were controlled by using mixtures of CO and C02.
P.T. MORLAND, formerly Research Assistant, University of Queensland, is a Graduate Student, Domaine University, Grenoble, France. S.P. MA'ITHEW, formerly Postdoctoral Fellow, University of Queensland, is a Research Metallurgist with Mt. Isa Mines Ltd., Mt. Isa, Queensland 4825, Australia. P.C. HAYES, Associate Professor in Extractive Metallurgy, is with the Department of Mining and Metallurgical Engineering, University of Queensland, St. Lucia, Brisbane, Queensland 4067, Australia. Manuscript submitted August 7, 1989. METALLURGICAL TRANSACTIONS B
EXPERIMENTAL
A. Materials The high-purity nitrogen, sulfur dioxide, and carbon dioxide gases used in these experiments were passed through packed columns of silica gel, DRIERITE,* and magnesium perchlorate to remove water vapor. Carbon monoxide gas was produced in the laboratory by passing dry carbon dioxide through a bed of packed carbon held at 1523 K. Residual carbon dioxide in the carbon monoxide was removed by passing the gas through ASCARITE.** Sulfur-35 was obtained from Amersham *DRIERITE is a trademark of Drierite Company, Xenia, OH. **ASCARITE is a trademark of Thomas Scientific, Swedesboro, NJ.
International Ltd. (Amersham, United Kingdom) as rhombic crystalline sulfur at an initial activity of 200 M Bq. Copper sulfide, Cu2S, was prepared by placing stoichiometric quantities of high-purity copper (Leico, 99.999 pct) and sulfur (Aldrich, 9
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