Equilibria between silica-saturated iron silicate slags and molten Cu-As, Cu-Sb, and Cu-Bi Alloys
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I.
INTRODUCTION
D U R I N G the smelting of copper concentrates, it is important to eliminate deleterious minor elements. They deteriorate not only the electrical conductivity of copper but its workability in hot working. The former is caused by such elements as phosphorous, iron, tin, aluminum, arsenic, and antimony, and the latter is brought about by lead, bismuth, etc. Among these impurities, arsenic, antimony, and bismuth are all Group Va elements, so they have similar properties and usually coexist together in copper concentrates. Minor elements are eliminated in the copper smelting process by slagging and volatilization. In relation to these mechanisms, it is essential to understand the distribution of these elements among molten copper, slag, and gas phases. It is also essential to comprehend their thermodynamic properties in liquid copper and molten slags. Activity data for minor elements in metallic copper phase have been measured by Azakami et al. ~'2 On the other hand, studies on distribution of minor elements in slags are relatively incomplete. While Nagamori et al. 3 showed that dissolution of bismuth, antimony, and arsenic in silica-unsaturated fayalite slags was independent of the oxygen potential, suggesting atomic dissolution, Schmiedle e t al. 4 considered antimony in slags as oxidic antimony, and Doi et al. 5 assumed the form of arsenic in slags as AsO~.5 or A s O z s . In addition, Kashima e t al. 6 suggested that arsenic and antimony in slags were oxides; Kozuka et al. 7 regarded antimony as SbO~s; and Fukatsu e t al. 8 considered bismuth as BiO~5. Solubility measurements and dissolution studies of arsenic, antimony, and bismuth, which are typical elements in copper smelting, have, however, been incomplete due to the difficulties of equilibrium experiments and inaccuracies in chemical analyses. The aim of this study is to investigate the distribution behavior of these elements, especially to find out their dissolution in slags. For this purpose, equilibria between CuAs, Cu-Sb, Cu-Bi alloys and silica-saturated iron silicate ITARU JIMBO, Graduate Student, SAKICHI GOTO, Professor, and OSAMU OGAWA, Associate Professor, are all with The University of Tokyo, Tokyo, Japan. Manuscript submitted October 3, 1983.
METALLURGICALTRANSACTIONS B
slags were achieved at 1473 and 1523 K under controlled CO2-CO atmospheres.
II.
EXPERIMENTAL
The stock of iron silicate slag was prepared by the following procedure. Chemical FeO (containing a few percent Fe203) and reagent grade silica were mixed together in the proportion 3:2, by weight. The mixture was heated in a pure iron crucible to a temperature of s o m e 1623 K under a stream of nitrogen gas. It was granulated in water and crushed to -100 mesh after drying. By this procedure, Fe:O3 content in the slag was found to be 3 to 4 pct. As will be described, it takes too long a time for an equilibrium to be attained by reducing the slag with C 0 2 - C 0 gas mixture, and therefore another stock with low Fe203 content was prepared. In this case, the former stoc
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