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I.

INTRODUCTION

ALTHOUGHextensive studies have been carried out concerning the reduction of iron oxide, manganese oxide, and silica in liquid slag by carbon or carbon dissolved in iron, which are of industrial importance, little information is available in the literature concerning the corresponding reduction behavior of lead oxide and nickel oxide. Therefore, it was decided to carry out a systematic study of the reduction of iron oxide, manganese oxide, nickel oxide, and lead oxide in liquid slag by carbon dissolved in iron. Almost all previous studies on the reduction of metallic oxides from slag have been carried out with graphite present in the system, either as the containing crucible or as a rod suspended in the slag layer. In some cases the presence of metal was avoided, so that graphite was the sole reductant. In other cases, carbon-saturated metal was present so that reduction was accomplished by two reductants, and the contributions of each to the total reaction rate had to be separated. Furthermore, since the slag was buoyed up by the carbon monoxide evolved during the reaction, the total slag/reductant interfacial area varied during the course of reaction in all these investigations. In view of these factors, it was decided to conduct the present study on the reduction of PbO in such a way as to exclude as many of these complications as possible. Thus, in this paper the kinetics and mechanism(s) of reduction of lead oxide in liquid slag by carbon dissolved in iron will be discussed; i.e., the reaction under scrutiny is: (PbO) + [C] = Pb0)+ CO(g)

through the bottom of the mullite tube, and with its top touching the bottom of the reaction crucible. The furnace arrangements are shown schematically in Figure 1. The nature of the reacting materials requires a composite cont a i n e r - - a refractory crucible to contain the high-carbon iron and prevent its contact with the outer mild steel crucible which is required to withstand slag attack. A mild steel outer crucible was chosen because of the ease of sealing this

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II. E X P E R I M E N T A L PROCEDURES AND MATERIALS

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In the furnace used for this experimental work, the 5 cm I.D. mullite tube was heated by radiation from four silicon carbide resistance elements. With this kind of arrangement a temperature of over 1400 ~ could be obtained within five hours. The temperature in the reaction zone inside the tube was measured by a Pt/Pt-13Rh thermocouple, introduced

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INLET K. UPADHYA is Assistant Professor of Metallurgical Engineering, Department of CEMM, University of Illinois at Chicago, Chicago, IL 60680. Manuscript submitted October 18, 1984. METALLURGICALTRANSACTIONS B

IIEASURING THERMOCOUPLE Fig. 1 --A schem~ic of the ~mace arrangements. VOLUME 17B, JUNE 1986--271

crucible by welding, while alumina was chosen for the inner crucib