Solubility of oxygen and sulfur in copper-iron mattes
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INTRODUCTION
M A G N E T I T E , a major constituent of copper smelting, is formed by oxidation of ore and slag in oxygen-enriched processes ~,2 and is introduced into reverberatory smelters as a component of converter slag and calcined ore charges. 3 There is a limited amount of information available in the literature on the conditions for the saturation of copper-iron mattes with solid magnetite. 4-s In the majority of the reported studies of magnetite saturation, mattes were simultaneously saturated with one or two phases in addition to Fe304(s), these being gas (Ps02 + Ps2 = 1 atm*), 4'5 Cu(1), 6"7 and "FeO"(s). 6 *1 atm = 1.013 x 105 Pa.
Considerable experimental effort has been directed to characterization of the thermodynamic behavior of oxygen and sulfur in copper-iron mattes in equilibrium with gas. 8'9'~~ A comprehensive study by Luraschi and Elliott 9 provides a coherent picture of the thermodynamics of unsaturated mattes at relatively low sulfur ( 1 0 -4 ---~ Ps, --< 10-2 atm) and oxygen (10 -1~ --< Po~ ~- 10-9 atm) pressures. The solubility of oxygen and sulfur in mattes in contact with silicate slags has been investigated extensively. 6' ,-is However, because of contradicting reports on silica solubility in matte and the limited precision by which the oxygen and sulfur pressures were controlled in the experiments, the results of these studies cannot be applied to establish the behavior of oxygen and sulfur in copper-iron mattes. The primary objective of the present investigation was to define the conditions for the saturation of mattes with Fe304(s), including matte and gas compositions. The secondary objective was to study the effects of oxygen and sulfur pressures on the oxygen and sulfur contents of mattes close to saturation with magnetite. A flowing gas equilibration system was employed in the experiments. Mixtures of CO, CO2, and SO2 gases were used to establish the desired oxygen and sulfur pressures in the gas phase. Application of the phase rule to the two-phase matte-gas equilibrium shows that there are five independent variables or degrees of freedom for the system. The variables selected were temperature (1468 K), total pressure ( - 1 atm), oxyD. L. KAISER is Postdoctoral Fellow, International Business Machines, Thomas J. Watson Research Center, Yorktown Heights, NY 10598. J. E ELLIOTT is AISI Distinguished Professor and Professor of Metallurgy, Massachusetts Institute of Technology, Room 4-140, Cambridge, MA 02139. Manuscript submitted June 20, 1985. METALLURGICAL TRANSACTIONS B
gen pressure (2.51 • 10 -~~ --< Po2 -< 7.94 • 10 -9 atm), sulfur pressure (0.001 --< Ps2 -< 0.025 atm), and iron metal weight fraction of the matte (WFc = wt Fe/(wt Fe + wt Cu) = 0.10 to 0.52). For the three-phase matte-magnetite-gas equilibrium, WFe was a dependent variable. A novel experimental technique was developed in which both unsaturated and magnetite-saturated mattes were equilibrated with a gas phase in a single run consisting of a series of experiments. Each run was carried out at a constant sulf
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