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As a fundamental study of slags in metallurgical processes, liquidus lines in the FeO(wüstite)-CaO-SiO 2 and Fe 3 O 4 (spinel)-CaO-SiO 2 systems were determined at temperatures between 1573 and 1673 K and partial pressures of oxygen between 10 À4 and 36 Pa using a quenching method with a crucible of platinum foil. It was found that the two phases (solid wüstite and liquid) region in the FeO-CaO-SiO 2 system (1573 K) increased remarkably by changing the partial pressure of oxygen from 10 À4 to 10 À3 Pa. It was also found that the two phases (solid spinel and liquid) region in the Fe 3 O 4 -CaO-SiO 2 system (1573 K) at PO 2 of 10 À2 Pa was a little larger than that in the FeO-CaO-SiO 2 system at PO 2 of 10 À3 Pa but it was extended considerably when the oxygen pressure was increased to 10 À1 Pa. However, the two liquids region did no change too much in the range of oxygen pressure above 10 À1 Pa even though the liquidus line became almost parallel to the Fe 3 O 4 -CaO axis in the ternary diagram when the oxygen pressure was increased. Furthermore, it was found that the two phase region in the Fe 3 O 4 -CaO-SiO 2 system at PO 2 of 10 À1 Pa decreased remarkably with increasing temperature. On the basis of the obtained and reported data, the homogeneous liquid regions in the FeO X -CaO-SiO 2 systems (1573 K) at PO 2 of 10 À3 Pa, 10 À1 Pa and in air were compared.

As part of a fundamental study of copper smelting processes using oxygen or oxygen-enriched air as a blowing gas, phase equilibrium and distribution of minor elements between copper matte and SiO 2 -saturated FeO X -SiO 2 -MgO-based slag containing 5 to 10 wt pct MgO have been investigated at 1573 K under the SO 2 partial pressures of 10.1, 50.7, and 101.3 kPa. The copper and sulfur solubilities in the slag were found to be independent of p SO 2 when the matte grade was specified, and this behavior was ascribed to the constancy of ( p O 2 /p S 2 ) against p SO 2 at a given matte grade. When the distribution ratio of a minor element (X) between the slag and matte phases was defined as L s/m x ϭ (wt pct X in slag)/{wt pct X in matter}, L s/m x for arsenic, antimony, and bismuth at a given matte grade increased with increasing p SO 2 . On the other hand, the distribution ratio of silver at a given matte grade was almost constant against p SO 2 .