The activities of sulfide and oxide components and the solubility of oxygen in copper-iron-sulfur-oxygen mattes at 1300
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TRODUCTION
L I Q U I D mattes exist in the quaternary system Cu-FeS-O in a volume bounded by surfaces of saturation with TFe, liquid Cu, solid " F e O , " solid Fe304, and a sulfur-oxygen gas phase at 1 atm pressure, m The structures of molten mattes are complex. The electrical conductivities of melts in the binary system Fe-S are characteristic of a metal, the conductivities of melts in the system Cu-S are characteristic of a semiconductor, and the electrical conductivities of melts in the system Cu-Fe-S are orders of magnitude higher than those characteristic of ionic melts, t21 Nevertheless, the thermodynamic activities of the components CuzS and FeS in the pseudobinary Cu2S-FeS closely follow Ternkin's law, which assumes random mixing of cations and anions on their respective sublattices. [3,4] Change in the composition of a Cu-Fe-S-O matte within the phase volume is effected by changing the ratio of Fe to Cu, the oxygen pressure, and the sulfur pressure, and although the composition of a matte cannot be described in terms of the concentrations of its component stoichiometric oxides and sulfides, the interactions among the atoms in the melt give rise to thermodynamic activities of these components. For example, when magnetite is dissolved in a matte, it loses its identity as magnetite and the concentration of magnetite in the liquid
C. SOMSIRI is Head of the Department of Metallurgical Engineering, Chulalongkom University, Bangkok, 10330 Thailand. D.R. GASKELL, Professor, is with the School of Materials Engineering, Purdue University, West Lafayette, IN 47907-1289. Manuscript submitted June 30, 1992. METALLURGICALAND MATERIALSTRANSACTIONSB
matte cannot be specified. Saturation of a matte with magnetite occurs when the activity of the component Fe304 reaches unity, at which point crystalline magnetite is precipitated from the melt. In spite of this, attempts have been made to plot the solubility of magnetite in mattes as a function of matte grade and temperature.tS] Saturation of a matte with magnetite is primarily determined by the oxygen content of the matte, which, in ram, is determined by the oxygen pressure, and, consequently, several studies have been made of the oxygen contents of mattes saturated with magnetiteSWlo] In the present study, the activities of Cu and Fe and the solubilities of oxygen in Cu-Fe-S-O mattes have been determined by equilibrating mattes with gas mixtures of fixed partial pressures of oxygen and sulfur and equilibrating a small mass of platinum with the matte to form a Pt-Cu-Fe alloy in which the activities of Fe and Cu had the same values as in the matte. The activities of Cu and Fe in the matte were then determined from knowledge of the activities of Fe and Pt in the system Pt-Cu-Fe.
II.
EXPERIMENTAL PROCEDURES
Weighed mixtures of high-purity iron and copper powders, contained in alumina boats, were sulfidized by reaction with H2S at 360 ~ The sulfides produced were of WF~ = 0.1, 0.3, and 0.5, where WFo = wt pct Fe/(wt pct Fe + wt pct Cu). Duplicate specimens of mass 2 g were
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