Settling of copper drops in molten slags
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I.
INTRODUCTION
THE migration of sulfide drops in slags exposed to an electric field was first reported by Chlynov and Jesint~.2~ in 1958. They explained this on the basis of the electrocapillary motion phenomenon. Christiansenm was the first to report this migration phenomenon. He explained the migration of mercury drops to changes in the interracial tension caused by an electric field. The theory of electrocapillary motion was further developed by Levichtaj and Levich and Frumkin~4,51and confirmed experimentally by Bagockaja et a/. [6,71 Further experimental workt8 19] has been carried out to determine the effects of slag composition on the direction and rate of drop migration. The experimental techniques include (1) observation of a drop moving on the surface of a liquid slag and (2) quenching and inspection of a slag sample to determine the movement of a drop during short electric impulses. The possibility of using the electrocapillary motion for the recovery of pay metals from slags has been mentioned in a number of investigations.[1~176 When slag losses are dominated by mechanically entrained droplets, slag settling under an electric field may help to increase metal recoveries. Industrial scale experiments t22j have shown reduction in copper losses at low unitary energy consumption, and Kviatkovskij et al51~ demonstrated effective lead removal from slags using a constant electric field. In the slag cleaning work by Warczok and Utigard, t231the cathodic products were identified as copper matte with a composition close to that of the product matte. A summary of the experimental results of metallic or sulfide droplets migration in different slag systems is presented in Table I. This review shows that the effect of an electric field on the migration rate varies greatly and even differences in the migration direction are observed. In a majority of cases, the migration rate is proportional to the potential gradient and the drop size. The aim of this work was to determine the settling rate of copper drops in liquid slags as a function of (1) electric A. WARCZOK, Associate Researcher, and T.A. UTIGARD, Associate Professor, are with the Department of Metallurgy and Materials Science, University of Toronto, Toronto, ON, Canada M5S 1A4. Manuscript submitted August 6, 1993.
METALLURGICAL AND MATERIALS TRANSACTIONS B
field strength, (2) size of copper drop, and (3) slag composition. II.
E L E C T R O C A P I L L A R Y MOTION PHENOMENA
When a liquid metallic drop is placed in an electrolyte, an electric double layer forms at the metal-electrolyte interface. The charge of this double layer can be affected by external electric fields. Regrouping of ions in the diffusion layer takes place, creating a gradient in the electric charge density along the drop surface. Because the interfacial tension depends on the electric charge density, an interfacial tension gradient develops. To minimize the Gibbs energy of the system, fluid will flow from regions of low interfacial tension toward regions of high interfacial tension. The
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