The activity coefficients of oxygen in Ni-S and Co-S melts
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I.
INTRODUCTION
N I C K E L - c o p p e r sulfide ores are smelted in a reverberatory furnace or a blast furnace. The resultant matte, which contains nickel, copper, iron, sulfur, and a minor amount of cobalt, is subjected to oxygen blowing in a converter to produce a final matte, i.e., white metal. Ill For a better understanding of the thermodynamic behavior of oxygen in this process, several investigators have determined the oxygen solubility in copper-sulfur, t2,31ironsulfur, t41 and copper-iron-sulfur melts t5,61 under Ar-SO2 or CO-CO2-SO2 gas mixtures. In the range of a relatively low oxygen concentration, two of the authors tT] have recently measured the activity coefficients of oxygen, 3'o, in copper-sulfur melts, utilizing a modified coulometric titration technique, t8~ The 3'o values measured at 1423 K depend strongly on the sulfur concentration; the 3'o in the Cu-S matte phase in equilibrium with the copper phase is one order smaller than that in the copper phase and rapidly increases with increasing the sulfur concentration. There are no reliable data on 3'0 in nickel-sulfur and cobalt-sulfur melts. It was therefore decided in the present study to measure the activity coefficients of oxygen, 3"o, in nickel-sulfur and cobalt-sulfur melts, utilizing the modified coulometric titration method. The comparison of the present results with the previous ones in a copper-sulfur-oxygen system may be of interest in view of the fact that the nickel-sulfur and cobalt-sulfur matte phases at 1423 K coexist with the solid metal phases with decreasing the sulfur content, unlike the coppersulfur system. II.
EXPERIMENTAL
The theoretical basis tS] and details of the experimental technique have been presented in earlier publications, t9,1~ A cylindrical electrochemical cell (O in Ni-S or Co-S melt/ZrO2(+CaO)/air, Pt) with an alumina stirSHINYA YAO (former name, SHINYA OTSUKA), Associate Professor, and ZENSAKU KOZUKA, Professor, are with the Department of Materials Science and Processing, Faculty of Engineering, Osaka University, Yamada-oka 2-1, Suita-city, Osaka 565, Japan. AKIHIKO AKATA and MOTOHISA TAGUCHI, formerly Graduate Students, Osaka University, are with the Sumitomo Metal Mining Co. Ltd., Niihama, and the Mitsubishi Electric Co. Ltd., Amagasaki, Japan, respectively. Manuscript submitted May 31, 1989. METALLURGICAL TRANSACTIONS B
ring rod was constructed. A schematic diagram of the cell is shown in Figure 1. A ZrOz(+5 wt pct CaO) solid electrolyte tube (8-mm OD, 5-mm ID, and 300-ram long), closed at one end, was supplied by Nippon Kagaku Togyo Co. Ltd., Sakai, Japan. The outside surface of the electrolyte was coated with platinum paste over a length of about 65 mm from its lower end. The platinum wires wound on it act as lead wires for the air/platinum reference electrode. Lanthanum chromite rods (1.5-mm OD, 15-mm long), connected to KANTHAL* wires, were used as leads with *KANTHAL is a trademark of Kanthal Corporation, Bethel, CT.
the rods immersed in the Ni-S and Co-S melts; the rod was supplied by Nippon Kag
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